Abteilung Oberflächengewässer

Climate warming threatens short-term environmental forecast skill, yet its effect on water quality predictability is largely unquantified. Here, we demonstrate a new approach for assessing climate change effects on lake forecasts. Random forest (RF) and gated recurrent unit network models were trained on data from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) Local Lakes Sector (five central-European lakes, four hydrodynamic models) and then used to forecast daily lake surface temperature 14 days ahead for 2060 - 2100 under four climate scenarios. We then varied (i) sensor-sampling interval (3, 7, 14 days) and (ii) training-set length (1 - 30 years). Under the strongest forcing (SSP585), the summer mean absolute error (MAE) of worst-affected lake, Esthwaite, rose by 0.14 °C (from 1.75 to 1.89 °C), driven by higher day-to-day temperature volatility (R² = 0.78). For this lake, extending the training set from 5 to 20 years or shortening sampling from 14 to 3 days reduced summer MAE by 0.11 and 0.17 °C, effectively offsetting the volatility caused by climate change. In winter, forecast error declined for four lakes because warmer, more stratified conditions simplified surface-layer dynamics. Thus, modest investments in monitoring cadence or historical record length can preserve forecast skill, even under extreme climate change. More broadly, this highlights a largely unexplored potential use for climate scenario projections: informing the design of climate resilient lake monitoring systems.

Les matières en suspension jouent un rôle central dans les lacs en transportant et en stockant divers polluants. Issues des apports du bassin versant ou de processus internes, elles sont à l'interface entre la colonne d’eau et le sédiment. Leur écotoxicité potentielle constitue un indicateur pertinent de l'état de santé global du lac. Grâce à la plateforme LéXPLORE, nous avons réalisé un suivi mensuel de la qualité écotoxicologique et chimique des matières en suspension du Léman pendant une année.

Speicherkraftwerke sind zentral für die Energiewende, führen jedoch durch ihre flexible Energieproduktion zu häufigen Abflussschwankungen (Schwall-Sunk) in alpinen Fliessgewässern. Dieser Beitrag zeigt, dass die ökologischen Auswirkungen von Schwall-Sunk nicht nur durch einzelne Abflussschwankungen, sondern auch durch deren hohe Frequenz bestimmt werden: Durchschnittlich kommt es unter Schwall-Sunk-Betrieb zu drei Abflussschwankungen pro Tag, was 20- bis 60-mal häufiger ist als unter einem natürlichen Abflussregime. Die Folge sind kumulative ökologische Auswirkungen, zum Beispiel infolge wiederholten Fischstrandens und wiederholter Invertebratendrift. Diese Wirkmechanismen entfalten sich auf Ebene der Kleinlebensräume
(auf Englisch Patch), wo der Schwall-Sunk-Betrieb zu einer stark erhöhten Dynamik führt. So nehmen die Lebensraumbeständigkeit und -verfügbarkeit sowie die räumlich-zeitliche Vernetzung ab. Drei neue Messgrössen (M1, M2, M3) erfassen diese kleinräumige Dynamik und ermöglichen eine räumlich differenzierte Einschätzung kumulativer ökologischer Auswirkungen, beispielsweise durch die Bewertung alternativer Sanierungsmassnahmen.

Les centrales hydroélectriques à accumulation jouent un rôle clé dans la transition énergétique, mais leur production flexible entraîne de fréquentes fluctuations de débit (éclusées) dans les cours d'eau alpins. Cet article montre que les impacts écologiques des éclusées ne résultent pas seulement d'événements isolés, mais surtout de leur fréquence élevée : en moyenne, trois fluctuations de débit par jour, soit 20 à 60 fois plus que sous des régimes naturels. Cette forte fréquence engendre des effets écologiques cumulatifs, tels que l'échouage répété des poissons ou la dérive répétée des invertébrés. Ces mécanismes s'expriment à l'échelle des taches (en anglais patch) et s'accompagnent d'une dynamique fortement accrue des habitats. En d'autres termes, la persistance et la disponibilité des habitats diminuent, de même que leur connectivité spatio-temporelle. Trois nouvelles métriques (M1, M2, M3) permettent de quantifier cette dynamique à fine échelle et d'évaluer de manière spatialement explicite les impacts écologiques cumulatifs, notamment dans le cadre de la comparaison de
scénarios d’assainissement.

Lakes are expected to experience longer summer stratification and shorter winter mixing due to climate-induced warming. These changes will impact biogeochemical cycles, but how shifts in mixing might influence lake nitrogen removal via denitrification remains unconstrained. Here we used ¹⁵N-tracer assays, molecular techniques and flux measurements to establish the seasonal dynamics of denitrification in a eutrophic lake in Switzerland. We find that denitrification was disproportionately active during the winter mixed regime, potentially driven by a previously unrecognized chitinolytic–denitrifying microbial consortium. Moreover, denitrification was strongly governed by the relative availabilities of particulate organic carbon and nitrate. Leveraging these insights enabled accurate simulation of denitrification in a lake model, revealing that a worst-case climate scenario may shorten the mixing period by ~27 days and reduce denitrification by 8–13%, increasing nitrogen export to downstream ecosystems. We conclude that lake microbial denitrification, and its associated denitrifying consortium, will be weakened by climate change.

Palaeoenvironmental records along the eastern coast of Thailand remain sparse, with only a few studies attempting to reconstruct past climatic and environmental conditions. However, additional palaeoenvironmental, palaeoclimatic and sea-level records are needed to improve our understanding of coastal evolution and local environmental changes. This study investigates mangrove sediment from the Prasae Estuary Mangrove (PEM) complex in Rayong Province, eastern Thailand. The PEM complex is an estuarine fringing mangrove influenced by the mixed tidal-fluvial dynamics of the Prasae River mouth. The region's low-relief geomorphology includes intertidal mudflats, wetlands and relict sand deposits associated with relatively high sea levels during the Late Holocene. To reconstruct sea-level changes, beach ridge deposits from the area were dated using optically stimulated luminescence. The results indicate a progressive seaward-younging pattern of the beach ridges, implying shoreline progradation of at least 2 km over the past 1240±40 years in response to a gradual marine regression of less than 2 m during the Late Holocene. The formation of these beach ridges created favourable conditions for the mangrove forest to colonize the Thung Prong Thong area between 690 and 210 years ago. Geochemical analyses of mangrove sediments, including elemental composition (C, N) and δ¹³C values, indicate a predominance of terrestrial organic matter input, primarily from freshwater discharge and mangrove leaf litter. The accumulation of substantial amounts of organic carbon in the soil highlights the role of mangroves as important carbon sinks. Over the past 38 years, land-use changes, particularly the conversion of mangrove areas into shrimp farms, have led to an estimated carbon release of approximately 14 800 Mg C (mega gram carbon = 1000 kg) to the atmosphere. However, conservation efforts have at the same time contributed to the expansion of mangroves and increased carbon sequestration along the PEM coast, resulting in a net increase in carbon stock accumulation of ~17 500 to ~22 800 Mg C. Given the substantial impact of land-use changes on carbon stocks, this study underscores the importance of sustainable land management and long-term monitoring of coastal mangrove ecosystems.

Nickel (Ni) is a bio-essential trace metal for marine phytoplankton, serving as a cofactor in key enzymes. Its nutrient-like distribution and the mirrored distribution of δ⁶⁰Ni in seawater suggest that δ⁶⁰Ni could serve as a tracer of biological Ni cycling. However, particulate Ni (pNi) remains understudied despite its important role. Here, we present three coupled dissolved and particulate δ⁶⁰Ni profiles from distinct biogeochemical regimes across the Subtropical Front in the Australian sector of the Southern Ocean.
In surface waters, pNi is isotopically lighter than co-located dissolved Ni, and particulate Ni/P in the mixed layer falls within the range observed for phytoplankton, reflecting an association with organic matter. These results support previous studies suggesting that phytoplankton preferentially remove isotopically light Ni. In the subtropics, higher surface productivity corresponds to elevated mixed layer pNi concentrations, below which pNi declines, associated with the regeneration of organic matter. However, particulate δ⁶⁰Ni shows limited variation, implying minimal isotope fractionation during this process. At subantarctic stations, pNi concentrations remain relatively constant, while particulate δ⁶⁰Ni decreases with depth in the upper 300 m. Moreover, δ⁶⁰Ni offsets between the dissolved and particulate phases are smaller than for the subtropical counterpart, likely associated with different phytoplankton assemblages. At greater depth, particulate Mn/P increases, and Ni/P ratios exceed those of phytoplankton. This suggests a shift in pNi association from organic-rich to Mn-rich phases, with minimal change in total particulate δ⁶⁰Ni. These findings suggest a more complex internal cycling of Ni in the oceans than one driven solely by biological processes.

Chromium (Cr) cycling in hydrothermal systems, particularly within sediments and pore waters, remains poorly constrained, limiting the robust application of Cr isotopes as paleo-redox proxies. Here we present the first integrated investigation of Cr concentrations and stable isotopes (δ⁵³Cr) in seawater, sediments and pore waters, across a ∼60 km transect from the Rainbow hydrothermal field on the Mid-Atlantic Ridge.
Our results show that the non-buoyant hydrothermal plume acts as a significant local sink for seawater Cr, driven by reductive removal of Cr(VI) by hydrothermal Fe(II) and subsequent scavenging onto Fe(oxy)hydroxide particles. This process is associated with a strong isotopic fractionation (ε = −2.90 ± 0.22 ‰). Relative to background seawater (3.01 nmol kg⁻¹, δ⁵³Cr = +1.13 ± 0.02 ‰, n = 4), plume waters exhibit Cr removal of up to 1.27 nmol kg⁻¹ and seawater δ⁵³Cr enrichment to + 2.67 ± 0.03 ‰, with hydrothermal influence detectable up to 60 km from the vent source.
The hydrothermal imprint is also preserved in sediments and pore waters. Pore water [Cr] ranges from 2.69 and 48.40 nmol kg⁻¹ with δ⁵³Cr values between −0.31 ± 0.06 ‰ to +0.88 ± 0.03 ‰, while sediment leachates display lower δ⁵³Cr values (−1.19 ± 0.04 ‰ to −0.24 ± 0.02 ‰) and [Cr] between 0.36 and 3.6 µg g⁻¹. Bulk sediments contain substantially higher Cr concentrations (10–220 µg g⁻¹) with δ⁵³Cr values (−0.32 ± 0.03 ‰ to −0.01 ± 0.0 2 ‰) consistent with mixed detrital and authigenic inputs. Isotopic mass-balance calculations demonstrate that Cr release from sediments into pore waters is accompanied by significant isotope fractionation, with preferential mobilization of isotopically heavy Cr(VI).
Remobilization of scavenged Cr into pore waters produces a diffusive benthic Cr flux to overlying bottom waters of 0.15 to 0.46nmol cm⁻² yr⁻¹ and is associated with additional isotopic fractionation (+0.21 ± 0.07 ‰ to + 1.01 ± 0.04 ‰; 2 SD). Together, these results reveal complex interactions between hydrothermal scavenging, sedimentary recycling and redox-driven Cr transformations. Our findings underscore the importance of sediment–pore water processes in shaping marine Cr isotope signatures and highlight the need to account for diagenetic modification when interpreting Cr isotope records as paleo-redox proxies.

Accelerated soil erosion due to land use is a far-reaching problem for today's society. Soil degradation leads to outwash and redistribution of soil organic matter, which not only impacts soils but also adjacent ecosystems by downstream eutrophication of freshwater bodies. Despite the severity of the problem and the ever-growing footprint of agriculture, little is known about the long-term effects of past soil degradation periods on catchment soils and lake systems. This study addresses this question by analyzing a sediment sequence retrieved from Lake Lavijärvi, located near the city of Sortavala, north of Lake Ladoga in the Republic of Karelia, Russia, which has witnessed a period of intensive farming at the beginning of the twentieth century, followed by abandonment of the land post-World War II. We applied a multi-proxy approach using geophysical properties, the geochemical and isotopic composition of the bulk sediment, as well as the distribution of sedimentary leaf waxes and their relative ages (compound-specific radiocarbon dating). With the beginning of industrialization (ca. 1900 CE), we observed severe soil erosion, evident as maxima in magnetic susceptibility and Ti concentrations, as well as high sediment mass accumulation rates. Intensive farming led to a reduction of soil-carbon-residence times (mean transfer time, MTT), indicated by the washout and deposition of pre-aged soil organic carbon. During the same time, the lake became eutrophic and varves were deposited, due to a surplus of soil-derived nutrients. Decreasing MTT after World War II reflected depopulation and land abandonment that resulted in stabilization of catchment soils. Even though soil erosion declined and the trophic status of Lake Lavijärvi returned to more oligotrophic conditions during the post-war period, the lake still suffers from anoxia today. We show that land-use legacies exert a major influence on freshwater ecosystems decades after land-use relaxation.

Vegetation Optical Depth (VOD) from L-band microwave radiometry is widely used to monitor vegetation water status and ecosystem dynamics, but existing SMAP and SMOS products at 25–40 km resolution cannot resolve fine-scale canopy heterogeneity. We develop and evaluate a framework for estimating forest Global Navigation Satellite System Transmissometry (GNSS-T)-calibrated VOD at 30 m resolution by fusing Sentinel-1A Synthetic Aperture Radar (SAR), Harmonized Landsat–Sentinel-2 optical reflectance, GEDI lidar canopy structure, and climate variables (precipitation and air temperature aggregated over same-day, 7-, 30-, and 60-day windows), all calibrated using ground-based (GNSS-T). A self-supervised learning (SSL) framework based on Vision Transformers, pretrained on unlabeled satellite imagery and fine-tuned with GNSS-derived VOD from five forest sites in the United States and Switzerland, generally outperforms Random Forest and XGBoost across SAR-only, optical-only, and fusion configurations. Feature importance analysis reveals that medium-term climate drivers, particularly 60-day precipitation and 7-day temperature, consistently outrank SAR backscatter, while SAR captures rain-driven VOD peaks that optical sensors miss due to cloud screening. The framework demonstrates robust temporal generalization across deciduous and evergreen forest types, though spatial generalization remains the critical next step as the GNSS-T network expands. These results establish GNSS-T-calibrated multi-sensor fusion with domain-specific SSL pretraining as a viable pathway toward operational 30 m L-band VOD estimation.

Floods bring pulse and rupture to river ecosystems. In near-natural rivers with high habitat heterogeneity, some habitats buffer harsh conditions during floods and serve as refugia for aquatic organisms, sustaining river resilience. Despite their crucial ecological role, refugia have been poorly studied and barely considered in the restoration of modified rivers with severely reduced habitat heterogeneity. This highly replicated study assessed how flow intensity influences habitat heterogeneity and refugia availability for macrophytes and macroinvertebrates in river reaches with varying levels of human modification. Hydraulic field data was combined with hydrodynamic modelling across three reach morphologies (heavily modified, slightly modified, restored) in ten Swiss rivers. For the 30 reaches investigated, habitat heterogeneity in flow velocity and bed shear stress as well as refugia availability were simulated at mean flow (Q_M) and six flood intensities (HQ₁-HQ₁₀₀). Habitat heterogeneity in flow velocity and bed shear stress was significantly higher in restored compared to heavily modified reaches across all flow intensities (+17% and +34%, respectively). Across the three reach morphologies, increasing flow intensity significantly reduced habitat heterogeneity in flow velocity (−45%) and in bed shear stress (−43%) averaged from Q_M to HQ₁₀₀. Refugia availability for macrophytes declined by 29 percentage points and for macroinvertebrates by 17 percentage points from HQ₁ to HQ₁₀₀. Even at high flood intensities (5-year floods and beyond), refugia were available in restored and slightly modified reaches, e.g., along riverbanks. Refugia availability was positively correlated with habitat heterogeneity. This study highlights the potential of river restoration to foster the resilience of modified river ecosystems by promoting refugia availability through increased habitat heterogeneity. The results suggest that floods of varying intensities should be explicitly considered in restoration planning based on the expectation that disturbances such as floods are likely to increase in the face of climate change.

Tropical lakes are significant sources of atmospheric methane. Understanding and reconstructing methane cycling in these systems is critical for constraining its climatic impact. Certain N-containing bacteriohopanepolyols (BHPs), potentially associated with methane-oxidizing bacteria (MOB), show promise as biomarkers for aerobic methane oxidation (AMO), yet their behavior in natural settings is not fully understood. Here, we present seasonal variations of BHPs, particularly MOB-associated BHPs, from the seasonally stratified tropical Huguangyan maar lake (HGY maar lake) in China over a full year. Various BHPs were detected in this study. Bacteriohopanetetrol-34S (BHT-34S), 3-methyl-bacteriohopanetetrol (3Me-BHT), and bacteriohopanepentol (BHpentol) peaked in summer, likely associated with bacterial biomass or increased water temperature. Nucleoside BHPs, including adenosylhopane, adenosylhopane_HG-diMe, and Me-adenosylhopane_HG-Me, were more abundant in deep waters during several months with no relation with soil input, supporting in situ production. Importantly, alongside established MOB biomarkers such as aminopentol and aminotetrol, ethenolamine-BHhexol and N-formylated-aminopentol also show high potential for tracing MOB. Their abundances were significantly elevated in bottom waters from May to September during stratification, with pronounced peaks during October overturn. Methylcarbamate-aminoBHPs (MC-aminoBHPs) showed somewhat distinct patterns, being enriched only in deep waters during stratification but without the pronounced October peak, potentially indicating different MOB communities or environmental conditions favoring their production under low-oxygen and high-ammonium conditions. MOB-associated BHPs exhibited strong seasonal patterns aligning with dissolved methane concentrations and AMO variations in most seasonally stratified lakes. This study reveals, for the first time from a BHP perspective, the seasonal dynamics of AMO in HGY maar lake, including intensified AMO in the hypolimnion during stratification and lake-wide AMO during October overturn. Our findings support the application of N-containing BHPs as effective biomarkers for tracing AMO in lakes.

As climate change leads to more frequent droughts, understanding forest ecosystem health becomes increasingly critical. Monitoring forest canopy water content provides valuable insights into their resilience to these stressors. Space-based optical vegetation indices like the normalized difference water index (NDWI) are often used to monitor the water content over more extended time periods in large areas. However, the top-of-canopy view of satellites limits the sensitivity as they neglect the lower canopy and understory vegetation. This study explores the seasonal correspondence between the NDWI retrieved from Sentinel-2 satellite data and in situ measured vegetation optical depth (VOD). We use a unique time series of concurrent and complementary measurements acquired in two contrasting forest ecosystems (i.e., an evergreen coniferous and a deciduous broadleaf forest) spanning four seasons. VOD is calculated from global navigation satellite system (GNSS) data measured with one receiver antenna above and one below the canopy, assessing the full vertical extent of the forest canopy. In addition, we used the Sentinel-2 derived enhanced vegetation index (EVI), eddy flux based evapotranspiration (ET) estimates, and measurements of soil moisture, air temperature, precipitation, and shortwave incoming radiation to facilitate our interpretation. Our results showed a large seasonal variation in VOD and NDWI in the deciduous forest, a pattern that coincided with a large variation in biomass, as expected and indicated by the EVI. We saw indications that a short-term summer drought in 2022 affected VOD and ET but not the NDWI in the deciduous forest. In contrast, in the evergreen forest, we found a pronounced seasonality of canopy water content only for ET, while VOD and NDWI followed different trajectories. We conclude that the satellite-based NDWI tended to saturate at higher levels of canopy water content. VOD showed a sensitivity to changing canopy water content, as indicated by ET and soil moisture dynamics, as well as to changing canopy biomass, as suggested by varying EVI. These initial exploratory insights into the sensitivity of VOD could stimulate discussions within the community and potentially help optimize the sampling design of future VOD networks.

Methane (CH₄) accumulation in the oxic metalimnion is a common yet poorly resolved feature of deep stratified lakes. In Lake Geneva, lateral transport from the Rhône delta has been suggested but lacks spatial validation. Here, we quantify the role of lateral advection in shaping metalimnetic CH₄ using high-resolution in situ CH₄ measurements, δ¹³C-CH₄ analyses, and a three-dimensional Lagrangian particle-tracking model. Elevated metalimnetic CH₄ (up to 1143 nM) near the Rhône delta becomes isotopically enriched, likely from prolonged residence and partial oxidation during summer stratification. While additional sources may contribute, comparisons of in situ measurements with particle-tracking simulations suggest circulation gyres may distribute deltaic CH₄. Moreover, isotope- and transport-based indicators suggest more coherent coupling in the epilimnion than in the metalimnion. These results demonstrate that horizontal advection can be an important driver of metalimnetic CH₄ and highlight the importance of circulation-driven lateral transport for assessing CH₄ fluxes from large, stratified lakes.

Many European lakes have suffered oxygen declines from recent eutrophication raising the question as to which conditions are representative of their pre-impact state. Here we present a palaeoecological record revealing that deepwater oxygen in small lakes can be variable over long timescales and subject to human influence for millennia. Remains of chironomids and other invertebrates indicate that Bichelsee (Switzerland) shifted from a stable, oxygen-rich to a dynamic, oxygen-poor state before major human activity. Initially, increased human activity and clearcutting coincided with improved oxygen conditions for deepwater midge larvae. However, from the Roman Age onwards, similar disturbances were associated with low oxygen and reduced deepwater invertebrate populations. These results demonstrate that small European lakes can have multiple, contrasting pre-impact reference states, and that ecological effects of human activity, even their directionality, may shift over time. Furthermore, repeated cycles of impact and recovery can occur over millennia, complicating assumptions about their baseline conditions.

Seasonality in environmental conditions plays a fundamental role in shaping lake ecosystems. However, patterns of seasonality vary worldwide, and these patterns are shifting over time amid global change. Thus, it is increasingly important to evaluate how seasons and seasonality are represented in lake ecosystem research. Here, we used a literature review and global data analysis to synthesize approaches for conceptualizing seasons and seasonality in lakes. We found that a wide range of criteria are used to delineate discrete seasons in published literature, including fixed dates (e.g., months, solstice/equinox), environmental thresholds (e.g., temperature and precipitation cutoffs), and lake-specific indicators (e.g., ice cover, plankton phenology). Analyzing data from lakes worldwide, we found that using different criteria to define the same season resulted in divergent interpretations of ecosystem states. Based on our synthesis, we offer recommendations for how to incorporate seasonality into lake research and communications amid global change.

Cryptic pigmentation is a key phenotypic adaptation that helps many benthic invertebrates evade visual predators. However, little is known about whether and how the expression of pigmentation phenotypes that match the habitat background is influenced by the availability of nutritional resources. Here we investigated whether variation in both the background and the nutritive composition of benthic substrates affect the expressed pigmentation of a freshwater isopod, Asellus hilgendorfii. We collected isopods and their predominant substrate from 17 locations across Hokkaido, northern Japan, and quantified substrate background and nutritional composition (total protein, 18 amino acids, and C:N and C:P ratios). We found that variation in isopod pigmentation was better explained by the substrate's nutritive composition than by its background darkness. Specifically, isopods were more pigmented when substrates had intermediate C:P ratios, lower C:N ratios, and a higher proportion of tryptophan – an essential amino acid involved in the isopods' pigmentation pathway. These results are consistent with previous experiments showing that isopods reared under diets with higher protein concentrations developed more pigmentation, advancing our understanding about the environmental sources of phenotypic variation in natural populations. By demonstrating that nutritional constraints may shape the expression of key phenotypic adaptations in natural populations, our study opens new directions for exploring how organisms navigate adaptive landscapes; particularly in those organisms that rely on pigmentation for signaling and camouflage. Finally, we demonstrate how macronutrients, amino acids, and elemental ratios can serve as biotracers in ecological studies of adaptation, offering new opportunities to examine how stoichiometric traits influence phenotypic plasticity and adaptive capacity, especially in detritivorous taxa.

Cold-water Density Currents (CDCs) resulting from winter differential cooling and flowing down lateral slopes of a lake (winter cascading) can entrain sediment and contribute to cross-shore transport to its deeper layers. Field investigations along Lake Geneva's northern shore reveal how CDCs induce sediment resuspension. Acoustic backscattering demonstrated that sediment resuspension is absent at 10-m depth on the steep slope (~30°) just beyond the edge of the shallow coastal shelf where CDCs were initiated but occurred intermittently at 30-m depth where the flow reached higher velocities (slope reduced to ~4.5°). This suggests that CDCs resuspend sediment on the sloping bed (but not on the shelf edge) and potentially transport it to deeper layers, causing sediment focusing (i.e., thicker sedimentation in deeper zones). During CDCs, resuspension occurs in short bursts, often at the head of CDC impulses, creating plumes that can extend to ~1.5 m above the lakebed. Velocity profiles near the bed were well fitted by a logarithmic profile, from which the Shields parameter was determined and compared to the critical Shields stress. However, the strong time-variability of the downslope velocity prevents computation of a representative Shields parameter needed to determine sediment resuspension. The CDC velocity at 1 m above the bed (above ~9 cm s⁻¹) correlated well with high backscattering echo level (indicating sediment resuspension) and was a better predictor for resuspension than the Shields parameter. Since CDCs were found to occur ~25% of the days in winter, CDC-induced resuspension potentially affects lake ecosystem dynamics.

The ongoing global sea-level rise urges us to better understand the dynamics of coastal processes for predicting future changes. Sedimentary deposits reflect past coastal environments but require precise chronological data to place evidence into a temporal context. While radiocarbon dating is widely employed, it is associated with several methodological challenges and frequently there is an absence of datable material in coastal deposits. Luminescence dating provides an important advantage over radiocarbon by directly determining the time of sediment deposition. However, this method is affected by problematic issues such as partial bleaching, bioturbation and dose rate assessment, which can lead to inaccurate age determinations. As a case study demonstrating good scientific practice in luminescence dating, we investigated deposits from the Chanthaburi Plain, Thailand, for reconstructing past coastal dynamics. Luminescence screening is used to identify potential signal disturbances and select appropriate sample positions in the drill cores. Luminescence dating was performed on 13 samples accompanied by detailed analysis regarding dose rate with a focus on water content and radioactive disequilibrium. The dated samples indicate depositional ages ranging between 7.2 and 4.6 ka. Comparison with radiocarbon ages (18 samples) reveals that plant material often represents modern roots and that molluscs tend to systematically underestimate the sedimentation age, likely due to partial recrystallisation. Our data suggest at c. 6.5 ka, a location of the coastline ~8.1 km inland from the present position. At around 4.6 ka, the coastline was about 7.2 km from the present shore. Together with previously published data, this indicates a sea-level regression from the Middle Holocene highstand towards the Late Holocene.

Restrictions in the soil water availability can strongly impact crop productivity. The increasing frequency and severity of drought events, as a result of global warming, has made the assessment of drought stress effects on vegetation of utmost importance for meeting humanity's agricultural production needs. Recent advances in remote sensing of solar-induced chlorophyll fluorescence (SIF) provide a basis for new approaches to directly assess crop water status, since SIF is closely related to photosynthesis and, thus, to early plant physiological processes triggered by limitations in the water supply. This study provides new insights into the effect of varying levels of plant available water (PAW) in the soil on SIF emissions. We used several SIF datasets acquired with the high-performance airborne imaging spectrometer HyPlant during five subsequent vegetation periods (2018, 2019, 2020, 2021 and 2022), each having a different precipitation regime. We normalized the SIF maps for the underlying effects of canopy structure, calculated SIF emission efficiency (eSIF) and selected various crop fields including sugar beet, wheat and potato. Maps of eSIF were compared with spatial PAW patterns, which were derived from a forward soil infiltration model. Our results show positive correlation between eSIF and PAW in rainfed sugar beet fields at early growing stage, which remained consistent when accounting for variations in the leaf area index (LAI). This suggests that eSIF variations in sugar beet reflect the spatial reduction of photosynthesis caused by reduced PAW. In irrigated potato fields, conversely, no eSIF-PAW correlations were found. This indicates the absence of leaf-level water stress in these well-irrigated fields. In rainfed winter wheat fields that were already in a late developmental stage, the variations in the SIF signal were dominated by locally different ripening, i.e., chlorophyll degradation, and therefore not representative of changing PAW. With this study, we could demonstrate that normalized airborne SIF measurements are related to the functional water stress response in different crops. This study supports future investigations on the development of SIF-based tools for the improvement of water management in agriculture.

Lakes, ponds, and reservoirs (hereafter: "lakes") are important sources of the greenhouse gases carbon dioxide (CO₂) and methane (CH₄). Emissions of CO₂ and CH₄ from lakes are regulated in part by in-lake processes, including the production and storage of gases in the lower parts of the water column (bottom waters). However, while substantial efforts have been made to improve estimates of greenhouse gas emissions from lakes, limited data on gas concentrations along depth profiles have prevented the incorporation of bottom-water processes in global emission estimates. Here, we present GHG-depths: the largest existing dataset of depth-profile CO₂ and CH₄ measurements worldwide, including 522 lakes across 38 countries and all seven continents. These data include contributions from 45 research teams and 56 published studies, totaling 2558 discrete sampling events. As global change continues to alter biogeochemical cycling in lakes, these data can help improve mechanistic models to better predict greenhouse gas production and emission from lakes worldwide.

Calibrating process-based lake models can be challenging, especially for newcomers. Existing literature is extensive but often assumes substantial statistical expertise and is scattered across models and disciplines, making it less accessible to new practitioners. This paper provides an overview of the modelling workflow with emphasis on calibration, which is the most resource-intensive task. Rather than offering a one-size-fits-all recipe, we present approaches that help cope with common challenges, including limited direct measurements, conflicting objectives, and risks of overfitting. Drawing on literature, survey responses, and our own experience, we chart five preparatory steps: clarifying model aims, assessing data suitability, configuring the model, preparing for calibration, and performing sensitivity analysis. We discuss manual versus automatic calibration, emphasising the value of mixed, iterative stepwise strategies that incorporate prior knowledge to constrain parameters to realistic values. Validation is considered as an assessment of whether the model adequately serves its intended purpose. By outlining these steps and considerations, we aim to reduce effort, improve results, and advance lake model development and application.

Forest structure, tree diameter, and above-ground biomass (AGB) are central variables in trait-based ecology and forest management, and recent advances in Unmanned Aerial Vehicle (UAV) and LiDAR surveys have substantially improved tree-level phenotyping of these attributes. Building on these developments, machine learning (ML) applications are increasingly used to refine tree diameter estimates and, by extension, improve AGB predictions derived from allometric relationships. Here, we evaluated the capacity of shallow learning methods to leverage local contextual information surrounding a tree of interest to improve predictions of stem diameter and tree-level AGB over 33 ha of a Norway spruce forest (Davos, CH). Our objectives were to (i) characterize gradients of tree height, (ii) examine group-level morphology of tree assemblages as an indicator of forest structural organization and (iii) assess whether these patterns can be leveraged to improve tree diameter and AGB predictions. We segmented the LiDAR point cloud scene into individual canopies and focused on LiDAR-derived tree canopy features. We then used local indicators of spatial association of tree heights to characterize local context and identify tree assemblages within the forest. Assemblage-level metrics were first analysed to characterize forest spatial structure and ecological similarity, and subsequently evaluated as additional predictors in ML regression experiments for tree diameter. Performance was compared between twin regression methods that either incorporated assemblage metrics (i.e. context-aware) or did not. Improvements provided by context awareness were assessed in terms of accuracy gained in estimating tree diameter and AGB. We evaluated three shallow learning methods using nested cross-validation and considered two datasets from the same site: one spatially sparse, based on scattered sampling plots, and one spatially continuous. In both sparse and continuous datasets, we found enhanced prediction performance in context-aware regressions, with RMSE for tree diameter estimation reduced by 4.1% and 0.8%, respectively, suggesting that heterogeneous local context supports improved estimates. Practical implication: Gradients of tree height can reflect underlying ecological drivers of forest structure, and this structural information may be leveraged to enhance predictions of tree diameter and AGB. The proposed method is fully native to UAV LiDAR data.

Carbon dioxide fluxes associated with weathering and carbon export in river basins are highly spatially variable, with some locations acting as sinks whilst others represent CO₂ sources. Chemical weathering and the associated carbon fluxes are strongly modulated by bedrock geology, with orogenic systems constituting locations where metamorphic lithologies can be found juxtaposed with sedimentary rock mélanges. Hydrological processes also converge in mountain belt interiors, where water in the shallow critical zone can intersect with gas-rich fluids derived from deeper tectonic processes. The Engadin Valley in the Swiss Alps provides a natural geological setting to examine how these competing controls impact weathering and dissolved inorganic carbon (DIC) fluxes in alpine rivers. Using the radiocarbon and stable isotope composition of river DIC, alongside the dissolved products of weathering, we observed an increase in the fractional contribution of riverine DIC derived from metamorphic processes coincident with a distinct lithological transition from the upper to the lower Engadin Valley.
DIC export from the upper Engadin Valley is dominated by silicate weathering of igneous and metamorphic terrains, while Δ¹⁴C_DIC values < -100 ‰ suggest some of this DIC could originate from pre-aged organic sources from soils, permafrost thaw or glaciated catchments. Riverine DIC concentrations increase from headwaters to the most downstream station in the lower Engadin Valley, mirrored by a sharp drop in Δ¹⁴C_DIC values, while the magnitude of this decrease varies seasonally. This decline in Δ¹⁴C_DIC values, which is counter to the trend expected due to increasing exchange with atmospheric CO₂ downstream, is consistent with contributions from geogenic carbon sources, specifically DIC from weathering of carbonate minerals and petrogenic organic carbon (OC), spatially intertwined with inputs CO₂ from metamorphic processes. Overall, seasonal variations in hydrological processes and associated flow pathways appear to modulate DIC contributions from bedrock weathering, while metamorphic CO₂ inputs occur in a quasi-constant manner. This study demonstrates that geogenic CO₂ sources in the shallow critical zone contribute significantly to the riverine DIC pool, leading in the Engadin valley to a potential shift in CO₂ fluxes from uptake via silicate weathering upstream to potential CO₂ release downstream, highlighting both the importance and complexity of carbon cycle processes in mountainous river basins.

The availability of trophic niches is a key driver of biodiversity, promoting adaptive radiation through evolutionary processes. However, most research has focused on how species adapt to trophic niches as adults, largely overlooking the fact that many taxa undergo significant ontogenetic dietary shifts. Here, we address this gap by investigating individual dietary shifts in an incipient adaptive radiation of Arctic charr (Salvelinus alpinus), where distinct piscivorous and planktivorous lacustrine morphs have diverged. Using eye lens isotopes, we reconstructed dietary histories at the individual level, tracing resource use from maternal nutrients to adult diet. Our analyses revealed three key dimensions in which ontogenetic dietary shifts diverge: early-life diets, the stability of dietary transitions, and the degree of plasticity in dietary shifts. These findings suggest that the early phases of adaptive radiation are accompanied by a complete divergence of ontogenetic dietary shifts. We advocate for a more integrated approach to understanding dietary shifts within evolutionary processes and call for further exploration of these patterns across diverse taxa.

Understanding the mechanisms shaping food chain length (FCL) has long been central to food web ecology. FCL is a key determinant of stability, energy flow efficiency, and biodiversity maintenance, but there is an ongoing debate about its underlying drivers. It is particularly important in meta-ecosystems, where predator trophic position (TP) is influenced by multiple energy channels. In this study, we focused on spiders in riparian ecosystems, which rely on resources linked to distinct energy channels: blue (algal herbivory), green (terrestrial herbivory), and brown (terrestrial detritivory). We applied nitrogen isotope analysis of amino acids to estimate the TP of both spiders and their prey. This method is a powerful tool for determining TP from a single sample and even allows for capturing decomposer trophic steps. However, the TP estimate requires special care for riparian spiders, as spiders show a specific trophic discrimination factor (TDF_Glx-Phe), and that energy channel use can confound the TP estimate. Our detailed food web resolution supports the use of specific parameters for spiders, particularly the low trophic discrimination factor (TDF_Glx-Phe ~ 2‰), and raises caution about the importance of estimating resource use of predators to estimate their TP. We show that the primary factor driving variation in spider TP is the energy channel they utilize, from blue (TP ~ 2.9) to green (TP ~ 3.6) to brown (TP ~ 4.1). This increase was largely due to prey omnivory in green channels, and microbial and fungal decomposers serving as an initial trophic step between litter and invertebrate detritivores in brown channels. We propose that this pattern is likely influenced by differences in basal nutritional quality, which increases from brown (low) to green (medium) and to blue (high) sources. This suggests that shifts in energy channels within meta-ecosystems in the course of global change (e.g., climate warming, eutrophication and land-use change) may significantly impact FCL, with significant consequences for trophic interactions, nutrient fluxes, and biomagnification processes.

Plant wax hydrogen isotopes (δ²H) preserved in lake sediments provide valuable insights into past climatic changes. However, lake catchments often experience local shifts in vegetation type that can yield distinct isotopic signatures in the sediments, potentially obscuring hydroclimatic signals. Here, we compile regional plant wax data and test different approaches to correct for the impact of changes in vegetation type over time to isolate precipitation δ²H values (δ²H_prc) since the Younger Dryas (12.9–11.7 ka) from a sediment record from Rotsee (central Switzerland). Our method intercomparison shows that n-alkane relative abundances produced the most accurate δ²H_prc estimates, agreeing with an independent speleothem fluid-inclusion δ²H record from Milandre Cave. This indicates that sedimentary plant wax δ²H values represent a vegetation-weighted community signal. Precipitation was ²H-depleted during the Younger Dryas (∼−75‰), and then δ²H_prc values increased sharply into the Holocene. During the early Holocene (∼10 ka), δ²H_prc values of ∼−55‰ were reached, consistent with maximum summer insolation, followed by a gradual long-term decline toward the present, reflecting Neoglacial cooling and consistent with modern δ²H_prc values (∼−67‰). Importantly, while plant wax δ²H values declined sharply due to deforestation beginning in the Roman period, this impact is effectively corrected for by using the relative abundance of n-alkanes. These findings underscore the need for site-specific vegetation corrections to produce robust hydroclimate reconstructions from plant-wax isotopes, especially in lakes with small catchments, thereby enhancing comparability of sedimentary records with climate models and deepening our understanding of past climate–vegetation–human interactions.

Precise synchronization of paleoclimate records is essential for inferring the dynamics and past evolution of the climate system. For the last glacial period, the time scales of ice cores from the Greenland and Antarctic ice sheets have been synchronized by the use of cosmogenic radionuclides, atmospheric gas concentrations, and traces of large volcanic eruptions. Here we identify the sulfate deposition signatures of the same 300 volcanic eruptions in different Greenland and Antarctic ice cores to obtain an inter-hemispheric volcanic ice-core synchronization of the entire last glacial period and the early Holocene (10–110 ka). Compared to earlier bipolar volcanic synchronizations, we close a gap in the period 16.5–24.5 ka and extend the synchronization to cover the 10–12 ka and 60–110 ka intervals. Furthermore, we increase the density of bipolar match points and make updates and corrections of the existing bipolar and unipolar synchronizations. The volcanic synchronization is in agreement with existing bipolar synchronizations from independent ¹⁰Be and methane matching. The bipolar volcanic synchronization allows us to determine the precise phasing of interhemispheric abrupt climate events throughout the last glacial period, particularly those associated with Dansgaard-Oeschger (D-O) events. Our improved synchronization and extended time period allow us to show that at the time of the D-O warming transitions, the average Antarctic temperature reaches a maximum within decades after the Greenland temperature maximum. This rapid Antarctic warming is superimposed on the well-known millennial-scale thermal bipolar-seesaw warming in Antarctica commonly attributed to oceanic heat transport and confirms earlier work that the abrupt change observed in Greenland is associated with a direct atmospheric circulation change at a global scale.
The exception to this pattern occurs for the EDML ice-coring site located in the Atlantic sector of Antarctica, potentially related to sea-ice conditions in the Weddell Sea. Comparison to state-of-the-art climate model simulations shows excellent agreement in the overall bipolar climate phasing at the warming transitions and allows for analysis of the climate-system behavior at those transitions. The model simulations suggest that the abrupt Antarctic warming response observed is connected with an interhemispheric atmospheric response involving a global scale reorganization of the zonal mean atmospheric circulation. The abrupt D-O surface warming signal in the Northern Hemisphere is teleconnected into an abrupt Antarctic surface warming through changes in the Southern Hemisphere eddy-driven jet and anomalous circulation changes in the associated Ferrel and Polar cells.

Naturnahe Flusslandschaften gehören zu den artenreichsten Lebensräumen der Schweiz, sind aber gleichzeitig stark beeinträchtigt. Mit der gesetzlich verankerten Revitalisierung und einer schweizweit einheitlichen Wirkungskontrolle haben Bund und Kantone die Grundlage geschaffen, um Fliessgewässer ökologisch aufzuwerten und ihre Wirkung langfristig messbar zu machen.

Les paysages fluviaux comptent parmi les milieux les plus riches en biodiversité de Suisse. À condition d'être proches d'un état naturel! Or, ils sont souvent très altérés. En inscrivant dans la loi la revitalisation des cours d'eau et en mettant en place un système unifié de contrôle des effets des mesures engagées, les autorités fédérales et cantonales ont créé une base solide pour revaloriser les rivières et rendre les résultats de cette démarche mesurables à long terme.

We present a data set of trace gas (TG; CH₄, N₂O and H₂S) concentrations and associated hydrochemical parameters (temperature, EC, pH, ORP, TOC, DOC, HCO₃^-, Cl^-, SO42−, NO₃^-, δ¹³C_DIC) in the water columns of Polish inland freshwater lakes. This data set acts as the first comprehensive source of information on the distribution of TG in lakes of central-eastern Europe. Despite the fact that this region displays relatively high limnicity, it is considerably understudied with regard to the occurrence of TG in lakes. This data set was created to fulfill this gap in biogeochemical knowledge and to provide data which can improve assessing and modelling of TG emissions from aquatic systems. The observations were collected monthly between July 2019 and September 2022 from different water depths in representative sites of three lakes in central (L. Łódzko-Dymaczewskie and L. Dębno) and western (L. Trześniowskie) Poland. The lakes showed different trophic conditions, depths as well as catchment characteristics. The database involves 358 records of CH₄/N₂O and 507 values of H₂S.

The COVID-19 pandemic inadvertently offered a condition to evaluate how abrupt human-activity reductions affect freshwater ecosystems, particularly water turbidity. Using satellite-derived data from 774 lakes worldwide (2017–2022), here we show turbidity declined significantly in highly turbid zones of lakes following COVID-19 containment, with minor effects elsewhere. Globally, average peak turbidity decreased 7.0% in 2020 relative to 2019; 5.9% was directly attributable to containment measures, independent of climate. Without these measures, peak turbidity would have been ~5% higher (0.45 Nephelometric Turbidity Units) during 2020–2022. Lakes in regions with stricter containment and higher anthropogenic footprint exhibited larger declines and faster rebounds post-restriction. Among individual lakes, 75.2% experienced average peak turbidity reductions. For 168 lakes, containment-driven improvements averaged –18.6%, strongly correlated with reduced night-time light as a proxy for anthropogenic inputs. By disentangling human and climatic influences, our study provides globally relevant, actionable insights for targeted lake restoration strategies.

Primary production is the most fundamental ecological process in surface waters. Bio-optical models allow for the estimation of aquatic primary production from optical remote sensing data, providing a cost-effective alternative to incubation measurements. Existing bio-optical models use different parameters for common model components, namely: (1) the vertical resolution of chlorophyll-a, (2) the planar-to-scalar irradiance conversion factor, and (3) the photosynthesis-irradiance relationship. Using a unified modelling framework, we evaluate the impact of these three model components for optically complex inland and transitional waters by testing 16 model configurations against a comprehensive in situ dataset spanning oligotrophic to eutrophic conditions in Lake Geneva, three Estonian lakes, and three stations in the Baltic Sea. Our results demonstrate that the choice of photosynthesis-irradiance function is the most critical component, causing a 23.2 percentage range in median magnitude error and a 0.26 range in median vertical shape correlation. In contrast, using depth-resolved chlorophyll-a profiles shows a modest impact on primary production estimates, while the choice of irradiance conversion factor has a negligible impact. Time-series analysis further reveals that while the models successfully reproduce seasonal dynamics, their ability to resolve short-term variability is limited. Our findings underscore that model accuracy is constrained by the parameterisation of model components, uncertainties in empirical constants, and the in situ validation data itself. This highlights the need to prioritise the refinement of photosynthesis-irradiance relationships alongside community efforts to develop standardised validation datasets that include concurrent measurements of carbon isotope incubations and inherent optical properties.

The global spread of antimicrobial resistance (AMR) is a serious public health concern, driven by widespread antibiotic use and the global environmental circulation of antibiotic-resistant bacteria and resistance genes (ARGs). Wastewater treatment plants (WWTPs) are important sources of anthropogenic AMR entering large rivers, which serve as vital water resources but facilitate downstream dissemination. The drivers and dynamics of AMR propagation along river systems remain poorly understood. As Switzerland's longest and one of its largest rivers, the Aare, situated in the upper Rhine watershed, plays a central role in the 'water castle of Europe'. This study examines the impact of WWTP discharges, some receiving high loads of hospital effluent, on ARG distribution along the 288 km Aare river-continuum. Using quantitative PCR targeting 14 ARGs conferring resistance to eight antibiotic classes, combined with 16S rRNA gene amplicon sequencing, we conducted a high-resolution spatial survey to assess shifts in the riverine ARG content and microbiome. Concentrations of trace metals and nutrients were analyzed as tracers of anthropogenic inputs. Results revealed a progressive increase in ARG abundance downstream, driven by WWTP effluents enriched in ARGs. Effluents had 70-fold higher mean ARG concentrations than upstream waters, raising downstream levels up to 141-fold. Major tributaries such as the Reuss and Limmat sustained elevated ARG levels, while passage through lakes markedly reduced concentrations. This study provides the first detailed baseline for ARG prevalence along a large swiss river system, from pristine headwaters to pollution-affected lower reaches and insights into aquatic AMR dynamics and guidance for future monitoring.

Bacterial endosymbionts of the family Candidatus Azoamicaceae obligately associate with anaerobic ciliates belonging to the class Plagiopylea. The symbionts' unique role for their host involves anaerobic respiration of nitrate and generation of adenosine triphosphate (ATP), analogous to the role of mitochondria in aerobic eukaryotes. As this symbiosis remains so far uncultured, insights into its functioning have been mainly inferred from environmental metagenomes. Here, we investigated the distribution and environmental role of this symbiosis in the anoxic basins of two freshwater lakes, Zug and Lugano (Switzerland), over a course of several years. We found that the environmental niche of the ciliate host is defined by the combined effects of sulfide, oxygen, and nitrate, the latter of which is essential for the symbiont's respiratory function. Moreover, the distribution and abundance of ciliates with denitrifying endosymbionts in the water column suggest that they may substantially contribute to nitrate consumption in Lake Zug. Our microscopic analyses further demonstrated a coordinated division of the Ca. Azoamicus ciliaticola symbionts and their ciliate hosts, implying a vertical inheritance of denitrifying symbionts. These observations offer new insights into the evolution of ciliates with denitrifying endosymbionts and their ecological role in oxygen-depleted lake waters.

Accelerating urbanization exerts a profound impact on the aquatic environment, altering the hydrological cycle, deteriorating water quality, and redistributing water resources. However, water exchange relationships and pollution patterns in such networks are complex and poorly understood due to disturbances resulting from natural processes and anthropogenic activities. This study coupled hydrochemical analysis with stable isotopes in the Dongsha River–Lake Networks (DRLN), China, to elucidate the spatiotemporal dynamics of urban water cycling and the response of water quality to hydrological connectivity. Isotopic signatures effectively traced diverse water sources, revealing a clear distinction between evaporation-dominated lakes and urban rivers, with the latter exhibiting higher sensitivity to precipitation. Driven by regional rainfall and seasonal pumping regulations, water exchange and hydrological connectivity were significantly enhanced during the wet season, as evidenced by isotopic homogenization and MixSIAR results. Hydrological connectivity plays a crucial role in shaping water pollution patterns by governing the transport pathways of pollutants. A pronounced "dual-effect" of hydrological connectivity on urban water quality was identified. Artificial diversion from the high-quality Yangtze River source effectively diluted anthropogenic pollutants in proximal receiving rivers, but this buffering capacity diminished with increasing spatial distance. Conversely, enhanced seasonal connectivity acts as a pollutant vector, facilitating the intrusion of contaminated local water into urban rivers and exacerbating downstream water quality degradation. The use of stable isotopes provides a critical and feasible tool to diagnose hydrological regimes and water exchange in urban systems, offering valuable insights into the water quality management related to connectivity in complex urban river and lake systems.

Methane (CH₄) production in lacustrine sediments is known to be spatially heterogeneous, varying both horizontally and vertically. Porewater methane concentrations often differ between locations within a lake and with depth within the sediment profile. The drivers of this heterogeneity are often not well understood. Here, we explore methane cycling in the sediments of Lake Constance, the 2^nd largest perialpine lake in Europe, with well-documented sedimentary methane production. We use a novel radiocarbon (¹⁴C) based approach to determine the origin and age of buried carbon pools, as well as that of CO₂ and CH₄ in sediment porewaters at two locations with contrasting sediment supply, dominated by either allochthonous or autochthonous inputs. We show that porewater CO₂ is predominantly derived from inorganic carbon inputs, whereas CH₄ is produced from a mixture of CO₂-derived and organic carbon-derived substrates. At the allochthonous-dominated location, a larger fraction of the CH₄ seemed to be produced from organic substrates than in the autochthonous location, where the ¹⁴C signals of CO₂ and CH₄ were more comparable to one another. Furthermore, ¹⁴C contents of lignin-derived phenols and fatty acids, as proxies for mineral-associated and free organic matter respectively, suggest that the "recalcitrant" carbon pool contributes to the methane production in centennial-aged sediments. Microbial community data further suggest active methane production in these old sediments, challenging concepts of permanent organic carbon burial in deeper sediment layers and on the recalcitrance of the buried material.

The Land Surface Temperature (LST) is well suited to monitor biosphere–atmosphere interactions in forests, as it depends on water availability and atmospheric/meteorological conditions above and below the canopy. Satellite-based LST has proven integral in observing evapotranspiration, estimating surface heat fluxes and characterising vegetation properties. Since the radiative regime of forests is complex, driven by canopy structure, components radiation properties and their arrangement, forest radiative temperatures are subject to strong angular effects. However, this depends on the scale of observation, where scattering mechanisms from canopy – to satellite – scales influence anisotropy with varying orders of magnitude. Given the heterogeneous and complex nature of forests, multi-angular data collection is particularly difficult, necessitating instrumentation distant enough from the canopy to obtain significant canopy brightness temperature and concurrent observations to exclude turbulence/atmospheric effects. Accordingly, current research and understanding on forest anisotropy at varying scales (from local validation level to satellite footprint) remain insufficient to provide practical solutions for addressing angular effects for upcoming thermal satellite sensors and associated validation schemes. This study presents a novel method founded in the optical remote sensing domain to explore the use of microcanopies that represent forests at different scales in the footprint of a multi-angular goniometer observing system. Both Geometric Optical (GO) and volumetric scattering dominated canopies are constructed to simulate impacts of anisotropy in heterogeneous and homogeneous canopies, and observed using a thermal infrared radiometer. Results show that heterogeneous canopies dominated by GO scattering are subject to much higher magnitudes of anisotropy, reaching maximum temperature differences of 3 °C off-nadir. Magnitudes of anisotropy are higher in sparse forests, where the gap fraction and crown arrangement (inducing sunlit/shaded portions of soil and vegetation) drive larger off-nadir differences. In dense forests, anisotropy is driven by viewing the maximum portion of sunlit vegetation (hotspot), where the soil is mostly obscured. Canopy structural metrics such as the fractional cover and gap fraction were found to have significant correlation with off-nadir differences. In more homogeneous canopies, anisotropy reaches a lower magnitude with temperature differences up to 1 °C, driven largely by volumetric scattering and components radiation properties. Optimal placement of instrumentation at the canopy-scale (more heterogeneous behaviour due to proximity to the canopy and small pixel size) used to validate satellite observations (more homogeneous behaviour due to larger pixel size) was found to be in cases of viewing maximum sunlit vegetation, for dense canopies. Given upcoming high spatial resolution sensors and associated validation schemes needed to benchmark LST and downstream products such as evapotranspiration, a better understanding of anisotropy over forests is critical to provide accurate, long-term and multi-sensor products.

Reliable paleotemperature proxies are essential for reconstructing past climate. To refine interpretation of the MBT'_5ME index, based on bacterial brGDGT lipids, a year-long study was conducted in Rotsee, Switzerland, a seasonally stratified lake with a 4–21°C temperature range. Suspended particulate matter was collected monthly from the epilimnion and the hypolimnion, complemented by surface sediments and surrounding soils. Both intact polar (IPL) and core lipid (CL) brGDGTs were analyzed alongside 16S rRNA gene data to disentangle environmental (temperature, dissolved oxygen, and pH) and biological (microbial community) controls on brGDGT compositions. In the stratified epilimnion, MBT'_5ME values showed a muted response to summer warming (r = 0.59, p < 0.1), whereas the isomer ratio (IR) correlated more strongly with temperature (r = 0.68, p < 0.05). MBT'_5ME and IR were also significantly correlated (r = 0.93, p < 0.0001), providing a novel diagnostic tool to identify sedimentary GDGTs derived from surface waters. In the seasonally anoxic hypolimnion, MBT'_5ME correlated with pH (r = 0.79, p < 0.01) and IR with dissolved oxygen (r = −0.65 and p < 0.05). Microbial DNA analysis revealed low Acidobacterial abundances (<0.4% of reads), suggesting MBT'_5ME patterns are not solely driven by this phylum. Instead, hypolimnion IPL-brGDGTs correlated with gene abundance of several other bacteria, indicating broader microbial contributions. Surface sediments reflected an integrated water column signal, while also showing evidence for additional in situ IPL-brGDGT production. Overall, findings demonstrate that stratification onset drives MBT'_5ME variability, while epilimnion temperature exerts stronger control on IR, refining their application in paleoclimate proxies.

Lakes in sub-Sahelian Africa are facing growing ecological threats from climate change and human, yet most research has focused on a handful of well-known large lakes. This study analyses 137 lakes, many previously understudied, and identifies consistent seasonal co-variability patterns across meteorological variables, satellite-derived lake physical and biogeochemical variables, and morphological and anthropogenic characteristics. We identify four distinct clusters of lakes, shaped by the atmospheric variability and its synchrony with water temperature seasonality. Within each cluster, we observe three seasonal patterns of chlorophyll-a concentration tied to wet and dry seasons. These patterns align with regional climatic threats in Africa, such as shifts in rainfall seasonality, altered frequency of tropical cyclones and wildfires, thus positioning our study as a framework to assess lake vulnerability across the sub-Sahelian region.

Models are simplified descriptions of reality and are intrinsically limited by the assumptions that have been introduced in their formulation. With the development of automatic calibration toolboxes, finding optimal parameters that suit the environmental system has become more convenient. Here, we explore how optimization toolboxes can be applied innovatively to uncover flaws in the physical formulations of models. We illustrate this approach by evaluating the effect of simplifications embedded in the formulation of a widely used hydro-thermodynamic model. We calibrate a Delft3D model based on temperature profiles for a case study, Lake Morat (Switzerland), through the DYNO-PODS optimization tool. The results show that higher values of the light extinction coefficient can compensate for neglecting the fraction β of short-wave radiation absorbed at the surface of the water. This leads to unrealistic values of the light extinction coefficient, as the optimization pushes its value toward the limit of no transparency, consistent with the need to reproduce a significant absorption at the surface. Although it is well known that β is significantly larger than zero, its absence from the model was never noticed as critical. Automatic calibration tools provide valuable diagnostic insights into the physical robustness of models, enabling more precise evaluation of their structural integrity and performance.

Ongoing global warming caused by a steady increase in carbon dioxide in the atmosphere urgently needs to be mitigated. This is possible if phytoplankton biomass is increased in the ocean, as this will remove additional atmospheric CO₂. In the Southern Ocean, Fe is a well-known growth-limiting element, but the role of the other micronutrients remains very unclear. Our aim is to describe the evolution of each nutrient in the Southern Ocean throughout the year and to identify nutrients that limit phytoplankton growth. Therefore, we created a model that calculates nutrient consumption rates and available nutrient pools, fueled by deep winter mixing and diapycnal supply. Annual consumed nutrient amounts are smaller than their labile dissolved pools, but this is not true for limiting elements Fe and Co (from the sub-Antarctic zone [SAZ] to the Antarctic zone [AZ]) and Zn and Si (only in the SAZ). Since we found several limiting elements, fertilization with multiple nutrients would be required to promote large-scale carbon capture.

As the Earth system is exposed to large anthropogenic interferences, it becomes ever more important to assess the resilience of natural systems, i.e., their ability to recover from natural and human-induced perturbations. Several, often related, measures of resilience have been proposed and applied to modeled and observed data, often by different scientific communities. Focusing on terrestrial ecosystems as a key component of the Earth system, we review methods that can detect large perturbations (temporary excursions from a reference state as well as abrupt shifts to a new reference state) in spatio-temporal datasets, estimate the recovery rate after such perturbations, or assess resilience changes indirectly from stationary time series via indicators of critical slowing down. We present here a sequence of ideal methodological steps in the field of resilience science, and argue how to obtain a consistent and multi-faceted view on ecosystem or climate resilience from Earth observation (EO) data. While EO data offers unique potential to study ecosystem resilience globally at high spatial and temporal scale, we emphasize some important limitations, which are associated with the theoretical assumptions behind diagnostic methods and with the measurement process and pre-processing steps of EO data. The latter class of limitations include gaps in time series, the disparity of scales, and issues arising from aggregating time series from multiple sensors. Based on this assessment, we formulate specific recommendations to the EO community in order to improve the observational basis for ecosystem resilience research.

We report 17 new solar activity cycles with periodicities ranging from 1,700 to 18,000 years. Using Bayesian spectral analysis we determined for each cycle period, amplitude and phase for the past 145,000 years. These results were obtained by analyzing ¹⁰Be in the 2775 m long EDML ice core from Dronning Maud Land, Antarctica. In addition, we have augmented the ¹⁰Be data with synchronous ice accumulation and δ¹⁸O data obtained from the same ice core; with paleomagnetic dipole moment data derived mainly from ocean sediments; and with calculated global insolation data. There is a close agreement between the ¹⁰Be periodicities in the first and the last 70 kyr intervals. We have developed a new analytical technique we call the “frequency domain differentiation technique” (FDDT) that distinguishes between the periodicities due to (a) variations in the cosmic ray intensity and (b) climate effects related to the accumulation rate. In a first step we have calculated the ¹⁰Be flux and then selected all periodicities which are common within 1 % in at least 2 of the investigated parameters (¹⁰Be concentration, ¹⁰Be flux, accumulation rate, δ¹⁸O, and insolation). Using these data we identified a total of 42 statistically significant periodicities. 20 of them are found in the ¹⁰Be concentration which we separated into 3 groups of origins: Four due to ¹⁰Be production only (group 1: 18012, 6508, 5782, 3833 yr), thirteen being a combination of production and accumulation related (system) effects with the production components being generally larger than the system components (group 2: 15503, 13837, 8441, 7722, 7136, 4695, 4556, 4110, 3961, 3292, 3104, 2025, 1680 y), and three being related to system effects only (group 3: 23971, 21101, 11637 y). In a second step we used independent paleomagnetic information to distinguish between heliomagnetic and geomagnetic periodicities in the ¹⁰Be production. We find an overall good agreement between the ¹⁰Be flux and the dipole moment in the time domain. In the frequency domain there is evidence for system effects in the geomagnetic data. Due to inconsistencies between the paleomagnetic records we do not draw conclusions regarding a potential geomagnetic origin of the ¹⁰Be cycles found in the EDML ice core.

Copepods are a major group of the mesozooplankton and thus a key part of marine ecosystems worldwide. Their fitness and life strategies are determined by their functional traits which allow different species to exploit various ecological niches. The range of functional traits expressed in a community defines its functional diversity (FD), which can be used to investigate how communities utilize resources and shape ecosystem processes. However, the spatial patterns of copepod FD and their relation to ecosystem functioning remain poorly understood on a global scale. Here, we use estimates of copepod community composition derived from species distribution models in combination with functional traits and indicators of ecosystem functioning to investigate the distribution of multiple facets of copepod FD, their relationships with species richness and ecosystem processes. We also project how anthropogenic climate change will impact the facets of copepod FD. We find that the facets of FD respond to species richness with variable strength and directions: functional richness, divergence, and dispersion increase with species richness whereas functional evenness and trait dissimilarity decrease. We find that primary production, mesozooplankton biomass and carbon export efficiency decrease with species richness, functional richness, divergence and dispersion. This suggests that ecosystem functioning may be disproportionally influenced by the traits of a few dominant species in line with the mass ratio hypothesis. Furthermore, climate change is projected to promote trait homogenization globally, which may decrease mesozooplankton biomass and carbon export efficiency globally. The emergent covariance patterns between copepod FD and ecosystem functions we find here strongly call for better integrating FD measurements into field studies and across scales to understand the effects of changing zooplankton biodiversity on marine ecosystem functioning.

Aim: Shark Bay, a UNESCO World Heritage site in Western Australia, is highly vulnerable to climate change, yet its fish biodiversity remains poorly understood at fine spatial scales. We integrated environmental DNA (eDNA) metabarcoding with high-resolution remote sensing to assess and extrapolate fish diversity patterns, providing a scalable framework for biodiversity monitoring in dynamic coastal ecosystems.
Location: Shark Bay, Western Australia.
Methods: We analysed 270 water samples across 560 km² using fish-specific 16S and 12S rRNA metabarcoding, comparing our results to earlier studies using conventional methods including seining, trawling, fisheries reports, and fish traps. We linked biodiversity patterns to key environmental variables, including depth, salinity, sea surface temperature, and habitat characteristics derived from high-resolution satellite imagery. To predict fish biodiversity across unsampled areas, we employed machine-learning models, enabling spatial extrapolation of eDNA data across the seascape.
Results: eDNA metabarcoding identified 106 fish species across 132 genera and 71 families, with substantial overlap with conventional monitoring but broader coverage at higher taxonomic levels. Fish richness increased with decreasing salinity, high channel habitat coverage, and moderate depths with high seagrass coverage. We delineated five distinct fish communities (A–E): two shallow seagrass communities—one in sparse seagrass (A) and another in dense seagrass (B), one in channel habitats (C) with the greatest fish diversity; one in deep sandy waters (D) and one in medium-depth, seagrass-free areas (E). Additionally, we detected several tropical species, suggesting poleward shifts due to rising water temperatures.
Main Conclusions: This study highlights the utility of combining marine eDNA metabarcoding with remote sensing to detect fine-scale biodiversity. The integration of machine learning enables spatial upscaling and timely responses to habitat changes, enhancing marine conservation and management. By identifying key environmental drivers of fish diversity, this approach supports proactive conservation strategies, providing a scalable model for biodiversity monitoring under climate change.

The sloping boundaries of stratified aquatic systems, such as lakes, are crucial environmental dynamic zones. While the role of sloping boundaries as energy dissipation hotspots is well established, their contribution to triggering large-scale motions has received less attention. This review delves into the development of thermally driven cross-shore flows on sloping boundaries under weak wind conditions. We specifically examine 'thermal siphons' (TS), a dynamical process that occurs when local free convection transforms into a horizontal circulation over sloping boundaries. Thermal siphons result from bathymetrically induced temperature (i.e. density) gradients when a lake experiences a uniform surface buoyancy flux, also known as differential cooling or heating. In the most common case of differential cooling of waters above the temperature of maximum density, TS lead to an overturning circulation characterised by a downslope density current and a surface return flow within a convective environment. Field observations, laboratory experiments and high-fidelity simulations of TS provide insights into their temporal occurrence, formation mechanisms, water transport dynamics and cross-shore pathways, addressing pivotal questions from an aquatic system perspective. Fluid mechanics is a fundamental tool in addressing such environmental questions and thereby serves as the central theme in this review.

The simultaneous interaction of lake breeze (LB) flows, complex terrain circulations and urban environments has so far received limited attention in the scientific literature. Here, we use the Weather Research and Forecasting model to investigate the aero- and thermodynamical interaction between Lake Geneva, the Swiss cities of Lausanne and Geneva and their rugged alpine landscape. To better isolate the role of urban areas, we compare results from a set of year-long simulations representing both realistic urban and hypothetical rural landcover scenarios. The results show that the urban areas of Lausanne and Geneva have a negligible effect on the dynamical evolution of LB, mostly consisting of wind deceleration caused by increased surface drag. However, the daytime excess heat over Lausanne results in a shift of the local anabatic wind regime onset time, one hour ahead, and a 1 km spatial displacement northward of the location of opposing flow collision. Urban-induced changes in heat advection can further lead to warmer air temperatures over the lake or cooler urban conditions along the lake shore. Our study shows that, although with due magnitude differences, mid-sized cities may have similar effects on wind and heat dynamics as larger metropolises in different landscapes and climates.

Measurements of water colour and clarity are used to track the environmental status of lakes, estuaries and oceans. The oldest standardised methods for measuring water clarity and colour are the Secchi disk and Forel-Ule colour scale. Both techniques were developed in the 19th century and require use of the human eye. Despite the advent of optoelectronic-based sensing, these visual methods are still used today, owing to their sensitivity, affordability, simplicity and long history of use. Recently, a hand-held device was developed for measuring the Secchi depth and Forel-Ule colour (presented in two formats, named the mini- and midi-Secchi disk). Designed to be small, light and convenient-to-use, it is well suited for participatory science projects that involve monitoring water colour and clarity. To date, over 900 mini- and midi-Secchi disks have been distributed to citizens and scientists, primarily through six projects, with data mostly transferred via mobile phone applications to data servers and dashboards. In this paper, we describe the methods used in the projects and show some characteristics of the datasets collected so far. We showcase how the device can be used for scientific applications, such as verifying satellite data products, gaining new scientific insights, and supporting public engagement and education. Finally, we provide suggestions for methodological improvements and future developments.

Satellite and airborne synthetic aperture radar (SAR) systems are frequently used for topographic mapping. However, their limited scene aspects lead to reduced angular coverage, making them less effective in environments with complex surface structures and tall objects. This limitation can be overcome by drone-based SAR systems, which are becoming increasingly advanced, but their potential for three-dimensional (3-D) imaging remains largely unexplored. In this article, we utilize multiaspect SAR data acquired with a K-band drone system with 700 MHz bandwidth and investigate the potential 3-D point cloud retrievals in high resolution. Through a series of experiments with increasingly complex 3-D structures, we evaluate the accuracy of the derived point clouds. Independent references - based on light detection and ranging (LiDAR) and 3-D construction models - are used to validate our results. Our findings demonstrate that the drone SAR system can produce accurate and complete point clouds, with average Chamfer distances on the order of 1 m compared to reference data, highlighting the significance of multiple aspect acquisitions for 3-D mapping applications.

The Arctic is warming several times faster than the rest of the globe. Such Arctic amplification rapidly changes hydrometeorological conditions with consequences for the structuring of cold-adapted terrestrial and aquatic ecosystems. Arctic ecosystems, which have a relatively small buffering capacity, are particularly susceptible to hydrometeorological regime shifts thus frequently undergo system-scale transitions. Abrupt ecosystem changes are often triggered by disturbances and extreme events that shift the ecosystem state beyond its buffering threshold capacity thus irreversibly changing its functioning (ecosystem tipping). The tipping depends on spatial and temporal scales. At the local scale, feedback between soil organic matter and soil physics could lead to multiple steady states and a tipping from high to low soil carbon storages. On the continental scale, local tipping is smoothed and the changes are rather gradual (no clear tipping threshold). However, due to the centennial timescale of soil carbon and vegetation dynamics, Arctic ecosystems are not in equilibrium with the changing climate, so a tipping could occur at a later time. Earth Observation (EO) is useful for monitoring ongoing changes in permafrost and freshwater systems, in particular extreme events and disturbances, as indicators of a possible tipping point. Lake change observations support gradual rather than abrupt transitions in different permafrost regions until a hydrological tipping point where lake areas start to decline leading to regional drying. Due to floodplain abundance, floodplains should be considered separately when using satellite-derived water extent records to analyse potential tipping behaviour associated with lakes. Reduction in surface water extent, increasing autocorrelation of water level of larger lakes and the impact of extreme events on ground ice can all be observed with satellite data across the Arctic. The analysis of Earth System simulations suggests significant impacts of changes in permafrost hydrology on hydroclimate in the tropics and subtropics, but there is no clear threshold in global temperature for these shifts in hydroclimate.

Human activities significantly alter natural river flows, impacting ecosystem functioning and biodiversity worldwide. Hydropeaking, resulting from intermittent on-demand hydropower generation, introduces sub-daily flow fluctuations exceeding natural variability. While the effects of single hydropeaking events are well-studied, the cumulative impacts of frequent hydropeaking requires further exploration. This study aims to develop metrics that captures changes in habitat dynamics at the patch scale (i.e. individual micro-habitats within the habitat mosaic) due to reoccurring hydropeaking. Using hydrodynamic simulations, we introduce three patch-scale metrics to quantify habitat dynamics with high spatial (0.5 m) and temporal (10 min) resolution: (M1) Habitat probability within patches, assessing spatio-temporal diversity of habitats; (M2) Habitat shifts within patches, evaluating habitat persistence for sessile organisms (e.g. vegetation, invertebrates); and (M3) Spatial shifts of habitats, indicating habitat relocation affecting mobile species (e.g. adult fish). Using eight hydro-morphological scenarios representing different levels of anthropogenic modification of flow and morphology, we demonstrate that these metrics effectively quantify changes in habitat dynamics at patch-scale. The results highlight the ecological relevance of these metrics and their potentially utility for river management. By identifying areas susceptible to ecological impacts, these metrics may serve as tools for hydropeaking mitigation, enabling more targeted and spatially explicit habitat management and restoration.

Over the past millennium, the tropical Pacific Islands of Remote Oceania have experienced significant transformations caused by different waves of human settlement and climatic variability. However, many sites remain to be explored for their archeological potential, and the complex climatic setting of the tropical Pacific further complicates our understanding of past environmental and societal changes. In this study, we applied a multi-proxy approach to sediment cores extracted from ponds on the west coast of Espiritu Santo, Vanuatu to investigate past human-climate-environment dynamics. Through the analysis of human-associated proxies including fecal markers, palmitone (a specific lipid biomarker for taro), crop pollen and sedimentary charcoal, we inferred changes in human presence and activities. We reconstructed past hydroclimate from leaf wax hydrogen isotopes (δ²H_LW) and past temperatures from branched glycerol dialkyl glycerol tetraethers (brGDGTs). Changes in pollen reveal major shifts in local and regional vegetation. In our record, the period from 1000 to 1300 CE was characterized by warm/wet conditions concomitant with demographic expansion inland. Around 1400 CE, pollen, leaf wax distributions, and δ²H_LW data indicated a drier period. The coincident decrease in palmitone, despite high charcoal and fecal marker concentrations, suggested that drier conditions might have rapidly restricted taro cultivation, but not the overall population, which declined more than a century later. We hypothesize that the establishment of one of the earliest European settlements in Oceania in 1606 CE further disrupted local demographics with the introduction of epidemic diseases. This study contributes to our understanding of the intricate relationship between human activities, climatic fluctuations, and landscape modifications in Remote Oceania over the past millennium.

Winter dissolved nickel (dNi) and particulate nickel (pNi) concentrations were measured in the Southern Ocean (GEOTRACES GIpr07 transect) to investigate biogeochemical cycling within the water column and over seasonal timescales. Concentrations of dNi ranged from 1.98 to 8.21 nmol kg⁻¹ with low surface concentrations and maxima in deepest sampled water masses. Combining our winter data with the GEOTRACES Intermediate Data Product (2021) shows insignificant seasonal dNi variation in surface waters north of the Antarctic Polar Front, indicating the dominance of year-round mixing processes. However, lower summer concentrations than winter in the Antarctic Zone (∆0.23 nmol kg⁻¹) suggest a role for biological processes at high latitudes. For pNi, concentrations ranged from 5 to 49 pmol kg⁻¹ with higher values in surface/near-surface water masses. Vertical attenuation factors (b values) for pNi (0.19 ± 0.06) and particulate phosphorus (pP; 0.43 ± 0.10) suggest a greater retention of Ni in particles than P, invoking scavenging processes or refractory Ni phases. Water mass analysis shows that remineralization of pNi contributes a maximum of 6% of the highest measured dNi. Instead, dNi distributions and macronutrient relationships were largely explained by phytoplankton uptake in surface waters, and mixing and advection of Atlantic and Antarctic origin water masses, each with different preformed nutrient compositions. Winter trace metal measurements provide new perspectives regarding the balance between biological and physical drivers in the Southern Ocean. For Ni, the biological component is small with respect to physical mixing processes and over the timescales in which water masses accumulate Ni during their transport.

Antimicrobial resistance (AMR) is among the top 10 public health threats, with nearly 5 million deaths in 2019 linked to AMR-related bacterial infections. (1) A One Health approach is needed to combat AMR.
Healthcare-based surveillance (HBS) of AMR provides incomplete information about the scope of the AMR threat. HBS screens only patients seeking medical attention, lacking community-level representativeness, and suffers from underreporting. (2) Consequently, researchers are turning to wastewater-based surveillance (WBS) to complement HBS. (3) WBS can provide information about AMR circulating within communities and hospitals, offering a comprehensive understanding of AMR prevalence. However, the surveillance targets and data obtained from WBS are distinct from those derived from HBS, creating uncertainty regarding their utility to the public health sector and ability to yield policy relevant information. In May 2024, participants in a workshop during the 7^th Environmental Dimension of Antimicrobial Resistance (EDAR7) conference (Montréal, Canada) sought to answer four questions aimed at advancing the policy relevance of AMR data generated by WBS.

The rate of technological innovation within aquatic sciences outpaces the collective ability of individual scientists within the field to make appropriate use of those technologies. The process of in situ lake sampling remains the primary choice to comprehensively understand an aquatic ecosystem at local scales; however, the impact of climate change on lakes necessitates the rapid advancement of understanding and the incorporation of lakes on both landscape and global scales. Three fields driving innovation within winter limnology that we address here are autonomous real-time in situ monitoring, remote sensing, and modeling. The recent progress in low-power in situ sensing and data telemetry allows continuous tracing of under-ice processes in selected lakes as well as the development of global lake observational networks. Remote sensing offers consistent monitoring of numerous systems, allowing limnologists to ask certain questions across large scales. Models are advancing and historically come in different types (process-based or statistical data-driven), with the recent technological advancements and integration of machine learning and hybrid process-based/statistical models. Lake ice modeling enhances our understanding of lake dynamics and allows for projections under future climate warming scenarios. To encourage the merging of technological innovation within limnological research of the less-studied winter period, we have accumulated both essential details on the history and uses of contemporary sampling, remote sensing, and modeling techniques. We crafted 100 questions in the field of winter limnology that aim to facilitate the cross-pollination of intensive and extensive modes of study to broaden knowledge of the winter period.

Bacteriohopanepolyols (BHPs) are structurally diverse compounds produced by a wide range of bacteria making them ideal candidates as chemotaxonomic biomarkers and indicators of bacterially-driven biogeochemical processes in the geological record. In this study, we characterize changes in the BHP distribution in the Black Sea over the past 20 thousand years (ka), as the basin underwent three distinct environmental phases: (i) an oxic lacustrine phase where the Black Sea was disconnected from the global ocean; (ii) a transition period marked by the initial influx of marine water into the basin; and (iii) a marine phase where the basin was permanently euxinic. During the lacustrine phase we observe a high abundance and diversity of nucleoside BHPs (Nu-BHPs) that are likely derived from elevated terrigenous inputs as well as production of Nu-BHPs in the brackish-to-fresh water column. The transition phase is marked by a decrease in the abundance of most Nu-BHPs and an increase in the abundance of methoxylated-BHPs as well as BHPs such as aminobacteriohopanetriol which are ubiquitous across a wide range of environments including soils as well as marine and freshwater settings. The euxinic marine phase (7.2 ka-present) can be divided into two stages based on changes in BHP composition. The early stage is characterised by a high abundance of aminobacteriohopanetetrol and aminobacteriohopanepentol, which were likely produced by methanotrophs at the oxycline. A shallow oxycline likely allowed for increased transport of these BHPs to the sediment. The later marine phase is characterised by a decline in these BHPs, likely due to a deepening of the oxycline and reduced transport of BHPs from the oxycline to the sediment. The changes in BHP distributions throughout the record may either be attributed to shifts in the bacterial communities or physiological adaptations of bacteria to the changing environment. Throughout the record, diagenetic products of BHPs (e.g., anhydro-bacteriohopanetetrol) were detected. These degradation products, however, remain a small proportion of the overall BHP composition, indicating excellent preservation conditions throughout the record. This study offers new insights into changes in microbial communities and biogeochemical processes that occurred in the Black Sea during the Last Deglaciation and Holocene in response to substantial shifts in the hydrology and oxygen conditions of the basin.

To assess the long-term impact of climate change and human influence on lakes and their sedimentary carbon storage, paleo-environmental approaches using well-dated lake sediment cores can be employed. Here, we reconstruct carbon mass accumulation rates for organic and inorganic carbon since 13 ka BP in Rotsee, a perialpine lake near the Swiss Alps, using a 12-m sediment core. A multiproxy approach (XRF, carbon and nitrogen isotopes, organic macromolecule chemical compositions, aDNA) was used to explore changes in the lake system that affect sedimentary carbon storage. The Early Holocene (11.8–7 cal ka BP) was characterized by a mixed phytoplankton and watershed-derived provenance of organic matter, and the deposition of inorganic and organic sedimentary carbon. Warming during the Holocene Thermal Maximum (9.8–8.8 cal ka BP) increased sedimentary carbon storage. In the Mid- to Late Holocene (7–1 cal ka BP), the sedimentary record indicates an increased influx of allochthonous, vascular plant-derived organic matter, and low production or conservation of phytoplankton-derived carbon. Organic carbon storage increased, while inorganic carbon became negligible. Larger deforestation events, potentially during Neolithic times (around 4 ka BP), but especially during Roman times (2 ka BP), coincided with further increased organic carbon MARs. Recent sediments, influenced by eutrophication in the last century, show higher carbon accumulation rates compared to earlier Holocene periods. Rotsee serves as a case study of how climate warming and human land use changes have influenced lake development and sedimentary carbon6 storage, with broader implications for understanding carbon dynamics in high altitude lakes and their future carbon balance.

Carbon dioxide (CO₂) fluxes in regulated Alpine rivers are driven by multiple biogeochemical and anthropogenic processes, acting on different spatiotemporal scales. We quantified the relative importance of these drivers and their effects on the dynamics of CO₂ concentration and atmospheric exchange fluxes in a representative Alpine river segment regulated by a cascading hydropower system with diversion, which includes two residual flow reaches and a reach subject to hydropeaking. We combined instantaneous and time-resolved water chemistry and hydraulic measurements at different times of the year, and quantified the main fluxes by calibrating a one-dimensional transport-reaction model with measured data. As a novelty compared to previous inverse modeling applications, the model also included carbonate buffering, which contributed significantly to the CO₂ budget of the case study. The spatiotemporal distribution and drivers of CO₂ fluxes depended on hydropower operations. Along the residual flow reaches, fluxes were directly affected by the upstream dams only in the first 2.5 km, where the supply of supersaturated water from the reservoirs was predominant. Downstream ofthe hydropower diversion outlets, the fluxes were dominated by systematic sub-daily fluctuations in CO₂ transport and evasion fluxes (“carbopeaking”) driven by hydropeaking. Hydropower operational patterns and regulation approaches in Alpine rivers affect fluxes and their response to biogeochemical drivers significantly across different temporal scales. Our findings highlight the importance of considering all scales of CO₂ variations for accurate quantification and understanding of these impacts, to clarify the role of natural and anthropogenic drivers in global carbon cycling.

(Sub)tropical inland waters are important greenhouse gas (GHG) sources, yet limited observations have long hindered broad analyses of GHG variability across this diverse region. Here, through a meta-analysis, we have examined the rates and drivers of GHG emissions from flowing and standing (sub)tropical inland waters. We find considerable spatial variation in fluxes, largely related to differences in hydroclimate, geomorphology, land cover and human disturbance. Flowing waters emit more carbon dioxide (3,387_2,121^5,702 TgCO₂ yr⁻¹, expressing median_{first quartile}^{third quartile}), methane (10.6_0.1^28.8 TgCH₄ yr⁻¹) and nitrous oxide (0.62_0.35^1.10 TgN₂O yr⁻¹) than standing waters (114₇₃²¹⁹ TgCO₂ yr⁻¹, 5.4_2.1^9.1 TgCH₄ yr⁻¹ and 0.03_0.02^0.05 TgN₂O yr⁻¹, respectively). (Sub)tropical inland waters release 4,238₂₄₇₃⁷³⁷⁵ TgCO₂-equivalents annually, with first- to third-order streams contributing 75% of riverine emissions and lakes larger than 100 km² contributing 59% of standing water emissions. Our results suggest emissions from (sub)tropical waters are 29–72% lower than earlier estimates, a downward revision with important implications for global GHG budgets.

Many species of river riparia are threatened by habitat loss due to altered flood and sediment regime, and associated shifts in vegetation structure. However, their ecological niche is often obscure, especially in inconspicuous organisms such as lichens, hindering their conservation and use as indicator species in river restoration. We studied if variation in sediment size distribution, gravel bank elevation and vegetation structure drive presence-absence and fertility (fruit body production) in the endangered, soil-dwelling lichen Stereocaulon incrustatum along two Swiss braided rivers, using binomial generalized linear mixed effect models in a Bayesian framework. Data was sampled on 811 plots randomly placed along 41 transects perpendicular to the main channels. Presence probability was highest on the most elevated plots, at 30% vascular plant cover in the herb layer, and 30–40% cobble cover, and increased with moss cover. Fruit body production probability was highest under closed canopies of woody plants > 3m. We show that in braided rivers, S. incrustatum is most likely found on elevated, coarse-grained sediments with increased moss but moderate vascular plant cover. This indicates a niche comprising relatively stable riparian environments, where a dry, cryptogam-dominated vegetation establishes on raw soils and competition with vascular plants is moderate. Fertile thalli are mostly found under closed canopies and high densities, suggesting a shift to sexual reproduction with increasing habitat age. While rare but strong disturbances are therefore necessary for habitat creation, older, densely populated habitat patches may harbor important source populations for colonization, thereby representing focal areas for conservation.

Flow pulses play a vital role in maintaining the ecological functioning of natural river systems. However, anthropogenic flow regulation, particularly from hydropower operations, can introduce rapid and unnatural pulses that negatively impact aquatic biota. This study investigated the effects of hydropeaking-induced rapid fluctuations on macroinvertebrate drift at the patch scale. Using a portable flume, we simulated rapid flow pulses on 45 patches characterised by either slow or fast current habitat conditions, within a prealpine river reach that supports an unimpacted macroinvertebrate community. This in situ experimental approach allowed us to bridge the gap between laboratory flumes and observational studies in regulated rivers. Current velocity (V40—mean current velocity at 40% of the water depth from the bottom) was the primary driver of increases in drift intensity when no distinction was made between habitat type. In patches with slow current (V40 < 0.5 m/s), drift intensity was primarily influenced by V40, whilst in patches with fast current (V40 > 0.5 m/s), the change in current velocity (V40% – percentage change in V40 between baseline and stress phases of experiment) was more influential. V40% significantly shaped drift composition in patches with slow current. Our findings show that flow pulses, such as those caused by hydropeaking, significantly affect macroinvertebrate drift, with responses varying at the patch scale according to habitat-specific hydraulics and local benthic assemblages. This study advances river management by emphasising the importance of patch-scale processes for effective hydropeaking mitigation. By highlighting habitat-specific sensitivities, our findings support the development of more spatially targeted conservation strategies to enhance biodiversity and ecosystem resilience in flow-altered river systems worldwide.

Lentic waters integrate atmosphere and catchment processes, and thus ultimately capture climate signals. However, studies of climate warming effects on lentic waters usually do not sufficiently account for a change in heat flux from the catchment through altered inflow temperature and discharge under climate change. This is particularly relevant for reservoirs, which are highly impacted by catchment hydrology and may be affected by upstream reservoirs or pre-dams. This study explicitly quantified how the catchment and pre-dams modify the thermal response of Rappbode Reservoir, Germany's largest drinking water reservoir system, to climate change. We established a catchment-lake modeling chain in the main reservoir and its two pre-dams utilizing the lake model GOTM, the catchment model mHM, and the stream temperature model Air2stream, forced by an ensemble of climate projections under RCP2.6 and 8.5 warming scenarios. Results exhibited a warming of 0.27/0.15°C decade⁻¹ for the surface/bottom temperatures of the main reservoir, with approximately 8%/24% of this warming attributed to the catchment warming, respectively. The catchment warming amplified the deep water warming more than at the surface, contrary to the atmospheric warming effect, and advanced stratification by about 1 week, while having a minor impact on stratification intensity. On the other hand, pre-dams reduced the inflow temperature into the main reservoir in spring, and consequently lowered the hypolimnetic temperature and postponed stratification onset. This shielded the main reservoir from climate warming, although overall the contribution of pre-dams was minimal. Altogether, our study highlights the importance of catchment alterations and seasonality when projecting reservoir warming, and provides insights into catchment-reservoir coupling under climate change.

Mesomediterranean vegetation with abundant evergreen broadleaved trees and shrubs is dominant along the coast of northern Greece. Well-dated palynological records are available from the inland submediterranean zone, where evergreen broadleaved trees and shrubs are absent or rare, but less is known about the vegetation history of the coastal area. For instance, it is unclear when and why evergreen broadleaved vegetation expanded during the Holocene. Here we present a new record from a mesomediterranean site, Limni Volvi, near the coast of the Aegean Sea. To understand Holocene vegetation history, we combined palynology, microscopic charcoal analysis and biogeochemical proxies (Ti, Ca, RABD_655–680max). At the start of the Holocene, open steppe vegetation and high fire activity prevailed around Limni Volvi. Afforestation by deciduous trees was likely delayed compared to sites further inland, due to the lack of moisture at the start of the Holocene, but vegetation composition was generally similar (i.e. submediterranean), with barely any evergreen broadleaved element. Around 8150 cal. BP (6200 cal. BC) trees and shrubs declined in the open woodlands or parklands, and the landscape returned to steppe conditions at 8000 cal. BP (6050 cal. BC), likely because of drier and colder conditions during the "8.2 ka event." Around the same time, cultural indicators suggest the start of Neolithic agriculture in the region. The present-day mesomediterranean vegetation with evergreen oaks only began to develop after 6000–5000 cal. BP (4050–3050 cal. BC), likely in response to increasing winter temperatures and reduced frost occurrence, further advantaged by human impact during the past 3600 years.

This study reports the outcomes of the third Atmospheric Correction Intercomparison Exercise (ACIX-III Aqua), which evaluated the performance of atmospheric correction (AC) methods for hyperspectral PRISMA satellite data over inland and coastal waters. The exercise included five AC processors (ACOLITE, hGRS, iCOR, MIP, and POLYMER), the standard PRISMA Level 2C product, and an adjacency correction tool (T-Mart) tested with ACOLITE. A total of 239 cloud-free PRISMA scenes from 2019 to 2024 were compared with in situ data of remote sensing reflectance, gathered from both hyperspectral and multispectral radiometers across eight distinct optical water types (OWTs). The accuracy of each AC method varied with spectral band, but all showed largest and lowest discrepancies with in situ data at 443 nm and 560 nm, respectively. All AC methods showed the best agreement with in situ data in greenish waters (OWT 4b) and highest uncertainties were yielded in humic-rich waters (OWT 7). Consistently with the previous ACIX-Aqua study focused on multispectral data, no single AC method outperformed the others across all OWTs. The study confirmed the ongoing challenges of AC over optically complex waters, yet the exercise allowed the community to advance in developing AC methods for hyperspectral satellite images and supporting the development of future operational hyperspectral missions, such as PRISMA Second Generation (PRISMA 2G) and CHIME.

Over the last decades, the chromium (Cr) stable isotope system (referred to as δ⁵³Cr) has emerged as a proxy to reconstruct past oxygenation changes in Earth’s atmosphere and oceans. Although Cr is a promising paleoproxy, uncertainties remain as to the modern marine Cr cycle, and limited data are yet available in large swaths of the ocean, including the Atlantic Ocean. Here we present dissolved seawater Cr concentrations ([Cr]) and δ⁵³Cr along a meridional transect from the North to the South Atlantic (AMT 29). Chromium concentrations range from of 2.51 to 3.96 nmol kg⁻¹ (n = 68) and δ⁵³Cr values range from +0.86 ± 0.04 ‰ (2SEM) to +1.20 ± 0.02 ‰ (2SEM) (n = 68). In contrast to data from other ocean basins [Cr] and δ⁵³Cr show only a weak correlation (δ⁵³Cr vs. Ln([Cr]) R² = 0.17), inconsistent with a closed-system Rayleigh distillation model. These results can mainly be explained by horizontal advection and water mass mixing, which our data demonstrate are the dominant processes controlling [Cr] and δ⁵³Cr distributions throughout much of the Atlantic, while the impact of in situ biogeochemical cycling is comparatively minor. There is, indeed no clear impact of biological productivity nor of dysoxic environments in the (sub)tropical Atlantic on the cycling of Cr along the transect. This is likely explained by insufficiently depleted oxygen concentrations and relatively low biological productivity, resulting in these processes being of secondary importance relative to water mass mixing in shaping the distribution of Cr in the low- to mid-latitude Atlantic Ocean.

Rapid urbanization changes the water cycle in urban areas, which exacerbates pollution and ecological degradation in water bodies. This problem can be effectively addressed by green-gray-blue infrastructures system, of which water transfer project and sponge city project are two key strategies, but have never been placed together as a system. Therefore, taking Dong-Sha Lake basin in Wuhan, China as an example, this research aims to investigate the potential of green-gray-blue infrastructures system composed of water transfer project and sponge city project to improve urban lake water quality, in which their seasonal performance and efficiency are innovatively discovered, and the annually efficient operation schemes are proposed. The SWMM model and MIKE 21 model are utilized for simulation. The results indicate that the green-gray-blue solution can reduce the total nitrogen (TN) concentration in urban lakes by 40 %–60 % annually, with water transfer project functioning in dry season and sponge city project functioning in flood season; the inlet-outlet arrangement and diversion discharge are primary factors influencing the performance of water transfer with the closer distance to inlet or outlet and the larger discharge contributing to the higher pollutants removal rate but perhaps less efficiency; the green infrastructures (GIs) paving area is the main index of sponge city projects; when its portion reaches 50 %, the TN concentration in urban lakes can be reduced over 50 % annually. The research provides an excellent example of green-gray-blue system to address urban water quality issues, with a particular focus on the combination of water transfer and sponge city projects.

Sun-induced fluorescence (SIF) from phytoplankton has historically been used as a proxy for chlorophyll-a concentration (chl-a) estimates in water bodies using optical Earth observation data. However, the relationship is often affected by spectral features caused by elastic scattering, and by the shifting incidence of different fluorescence quenching mechanisms. This study found that disentangling Photochemical Quenching (PQ) and Non-Photochemical Quenching (NPQ) cases improves SIF-based chl-a estimates. Further, we defined strategies which can distinguish the two quenching mechanisms. We assembled a unique dataset collected between 2018 and 2022 by an autonomous profiler in Lake Geneva (Western Europe). We used NPQ-influenced chl-a estimates from the fluorometer and NPQ-corrected chl-a estimates to distinguish between PQ and NPQ cases. The correlation between SIF yield and chl-a is weak when considering the entire dataset (R² = 0.37; Median Absolute Percentage Difference (MAPD) = 74%). It increases strongly when comparing PQ cases (R² = 0.72, MAPD = 49%) and NPQ cases (R² = 0.48, MAPD = 68%) separately. Analyzing a subset of in situ measurements acquired around Sentinel-3 overpasses (±3 hours) improved the performance metrics for both PQ cases (R² = 0.82, MAPD = 35%) and NPQ cases (R² = 0.43, MAPD = 61%). However, when applying the same approach to Sentinel-3 OLCI data, we found that the errors in remote sensing reflectance products disable such an adaptation. We conclude that enhanced atmospheric correction in the red-NIR region for oligo-mesotrophic lakes is needed to demonstrate the upscaling of our in situ-based results. This will enhance satellite-based SIF yield retrievals and subsequently, obtain SIF-related phytoplankton physiology products.

Amid unprecedented biodiversity loss and water scarcity, calls for corporate responsibility are becoming louder and have led to emerging non-financial disclosure frameworks with demanding data needs. While the role of satellite remote sensing (RS) is highly anticipated to address data needs and boost transparency, critical thought on what is feasible and how to strategically integrate its insights for ambitious corporate biodiversity and water disclosure is lagging behind. To address this, we propose applying a systems perspective to represent the complex, multi-scale interactions between biodiversity, water systems, and corporate operations, and to guide how to integrate RS contributions to analyze the full spectrum of impacts and risks—ranging from direct and concurrent to cascading, cumulative, and emergent. We highlight seven guiding (non-exhaustive) principles for leveraging satellite RS data to assess corporate biodiversity and water impacts and risks. This process requires an effective system boundary (1) set spatially, temporally, and process-wise. Within which, biodiversity and water's multi-dimensionality (2) needs to be addressed to monitor the spatio-temporal dynamics (3) that characterize ecosystem responses. To attribute risk and impact of detected changes, interactions need to be defined by causality (4) and directionality (5), and ultimately consider compound impacts (6) across commodities, supply chains and portfolios, as well as cross-system interactions (7), for example, between climate change, water and biodiversity. We review each of these principles and related challenges individually, providing a system theory definition, relevant RS capabilities, and research directions. Addressing these seven principles will be crucial to harness satellite RS's potential for comprehensive biodiversity and water disclosure for strong corporate accountability.

Research and management of hydropeaked rivers largely overlook the ecological impacts of recurring flow fluctuations, such as fish stranding, on ecosystem health. This article synthesizes scientific and grey literature, field studies, and experiments to assess the effects of frequent hydropeaking on fish. Findings show that hydropeaking frequency significantly affects the ecological integrity of alpine rivers, with an average of three daily down-ramping events. Despite some evidence of behavioral adaptation of fish to recurrent flow fluctuations, this adaptation appears insufficient to counter the cumulative effect of a series of single hydropeaking events. Larval and juvenile fish are particularly vulnerable, with stranding impacts extending to the population and community levels. Effective mitigation should prioritize reducing the cumulative impact of recurring hydropeaks while ensuring single-event ramping rates and flow amplitudes remain within ecological limits. To effectively safeguard sensitive habitats, targeted mitigation efforts informed by an understanding of habitat dynamics are critical. Furthermore, maintaining lateral connectivity within river systems is essential for supporting resilient fish populations, especially where hydropeaking mitigation possibilities are limited. Finally, this study identifies future research directions on hydropeaking frequency and its ecological effects.

Climate extremes such as droughts are expected to increase in frequency and intensity with global change. Therefore, it is important to map and predict ecosystem responses to such extreme events to maintain ecosystem functions and services. Alongside abiotic factors, biotic factors such as the proportion of needle and broadleaf trees were found to affect forest drought responses, corroborating results from biodiversity–ecosystem functioning (BEF) experiments. Yet it remains unclear to what extent the behavior of non-experimental systems at large scales corresponds to the relationships discovered in BEF experiments. Using remote sensing, the trait-based functional diversity of forest ecosystems can be directly quantified. We investigated the relationship between remotely sensed functional richness and evenness and forest drought responses using data from temperate mixed forests in Switzerland, which experienced an extremely hot and dry summer in 2018. We used Sentinel-2 satellite data to assess aspects of functional diversity and quantified drought response in terms of resistance, recovery, and resilience from 2017 to 2020 in a scalable approach. We then analyzed the BEF relationship between functional diversity measures and drought response for different aggregation levels of richness and evenness of three physiological canopy traits (chlorophyll, carotenoid/chlorophyll ratio, and equivalent water thickness). Forest stands with greater trait richness were more resistant and resilient to the drought event, and the relationship of trait evenness with resistance or resilience was hump-shaped or negative, respectively. These results suggest forest functional diversity can support forests in such drought responses via a mixture of complementarity and dominance effects, the first indicated by positive richness effects and the second by negative evenness effects. Our results link ecosystem functioning and biodiversity at large scales and provide new insights into the BEF relationships in non-experimental forest ecosystems.

The effect of metals on freshwater microbiomes is poorly understood compared to other factors, such as nutrients or climate. While deleterious effects of metals on plant and animal biodiversity are well documented, the role of metals in shaping the biodiversity, composition and functional potential of sediment microbial communities remains unknown. Therefore, we explored if metal concentrations can be linked to alterations in biodiversity and composition of freshwater sediment microbial communities. We collected sediments from 34 streams and lakes in Switzerland and grouped them based on their metal content. Microbial diversity and community composition were determined using 16S rRNA gene amplicon sequencing. Most of the sediments were not contaminated with metals according to Sediment Environmental Quality Criteria, although some stations exceeded the limits for Cu, Zn, and Pb. Nevertheless, correlational analysis indicated links of metal concentrations to various aspects of sediment microbial biodiversity. Al concentrations were significantly (p < 0.05) correlated with microbial richness. We further observed a predominantly negative correlation between some metals and abundances of dominant taxa. Predicted microbial functional potential analysis indicated that different types of metals have different effects on microbial functional potential. For example, Mn exhibited a significant positive correlation with nitrogen fixation potential, whereas Cu, Pb, and Zn displayed a significant negative correlation. Overall, our findings indicate that metal concentrations may alter microbial community diversity and functional potential in freshwater sediments even at ambient concentrations. Further research into the role of metals as drivers of microbial biodiversity and factors in biodiversity loss is warranted.

The biogeochemistry of Cr and its cycling in Earth's surface environments is reviewed. A synthesis and critical evaluation of the major processes controlling Cr mobility and isotope composition (δ⁵³Cr) is presented, taking a source to sink view beginning with Cr mobilization from Earth's crust. Transport and cycling in inland waters and input to the oceans are discussed. Anthropogenic mobilization of Cr results in contributions to the atmosphere and inland waters that are of similar orders of magnitude as natural processes. The principal sources of Cr to the oceans are rivers and diffusive fluxes from marine sediments. Internal cycling of Cr in the ocean is largely controlled by reductive removal onto particles, particularly in O₂-depleted waters, and redistribution through ocean circulation. Chromium removal from the oceans occurs primarily in organic carbon-rich, O₂-poor shelf sediments. Despite theoretically poor mobility of Cr(III), reductive removal in anoxic waters is non-quantitative. As a result, isotope fractionation drives δ⁵³Cr offsets in removed Cr as well as residual dissolved Cr(III), which accumulates in anoxic water, compared to the corresponding source. The implications for δ⁵³Cr-based reconstructions are discussed, along with an outlook for future proxy applications based on the processes controlling Cr incorporation into sediments. The roles of different source and sink processes are quantified in an updated mass balance for the global ocean. Finally, priority topics for future research are suggested, which at present are the primary uncertainties of the modern Cr biogeochemical cycle and aspects of the Cr isotope mass balance.

The discharge of wastewater treatment plant (WWTP) effluent containing bacteria and viruses has significant ecological and public health implications for aquatic ecosystems. While viruses infecting bacterial hosts are abundant and diverse in wastewater, their environmental fate, host association, and functional impact in affected river ecosystems remain poorly understood. Using a metagenomic approach, we characterized double-stranded DNA viral communities across nine WWTPs and impacted riverine habitats, including water, suspended particles, sediment, and epilithic biofilm. River water was the most affected habitat by WWTP effluent, with viral diversity increasing by 22 % (±15 %) downstream. In contrast, no significant differences were observed in either viral or bacterial community structures across locations in biofilm or sediment. Among 38,826 viral operational taxonomic units (vOTUs) recovered from 148 metagenomes, 18 % were shared exclusively between effluent and downstream habitats, primarily with river water (99 % of the vOTUs). These wastewater-associated vOTUs were predicted to infect key bacterial taxa involved in carbon and nitrogen cycling (e.g., Nitrosomonas and Methylomonadaceae) and potential human pathogens (e.g., Vibrio and Ralstonia). Additionally, WWTP effluent increased the diversity of virus-encoded auxiliary metabolic genes, especially those involved in carbon, nutrient, and drug metabolism, suggesting potential roles in shaping host fitness and environmental adaptation. Overall, our findings demonstrate that WWTP effluent drives coupled changes in viral and bacterial communities in river water, highlighting the potential ecological consequences of virus-host interactions in wastewater-impacted aquatic environments.

Extremely thinned layers and possible folding make the dating of the deepest sections of ice cores especially challenging. Cosmogenic radionuclides have the potential to provide independent age estimates. The ³⁶Cl/¹⁰Be ratio is largely independent of production rate changes that affect individual radionuclides and has an effective half-life of 384 kyr, making it an ideal tool for dating the new 1.5 Myr old ice core that the Beyond EPICA Oldest Ice Core project aims to retrieve at Little Dome C in East Antarctica. However, the loss of ³⁶Cl through hydrogen chloride outgassing at low accumulation sites complicates its application and the long-term decay of the ³⁶Cl/¹⁰Be ratio in ice has not been studied. Here, we show that ³⁶Cl is preserved in glacial periods and that the ³⁶Cl/¹⁰Be ratio decreases more slowly than expected from physical decay over the last 900 kyr. While the glacial ³⁶Cl flux decreases at the expected rate of physical decay within the uncertainty, the ¹⁰Be flux decreases faster, which may be linked to a post-depositional mobility of ¹⁰Be in deep ice and leads to the slower decrease of the ³⁶Cl/¹⁰Be ratio. In addition to this long-term trend, the ³⁶Cl/¹⁰Be ratio fluctuates around a fitted decay curve, which is likely caused by different climate sensitivities of the transport and deposition pathways of the individual radionuclides. Both effects need to be better understood and quantified to improve age estimates based on the ³⁶Cl/¹⁰Be ratio.

Reconstructions of past changes in algal community composition provide important context for future alterations in biogeochemical cycling. However, many existing phytoplankton proxies are indicative of individual algal groups and are not fully representative of the whole community. Here, we evaluated hydrogen isotope ratios of algal lipids (δ²H_Lipid) as a potential proxy for phytoplankton community composition. We sampled the water column of Rotsee, a small eutrophic lake in Switzerland, every second week from January 2019 to February 2020 and analyzed distributions and the relative offsets between δ²H_Lipid values (δ²H_{Lipid1/Lipid2}) from short-chain fatty acids, phytosterols and phytol. Comparing these data with phytoplankton cell counts, we found that δ²H_{C16:0 Acid/Sterol} and δ²H_{Sterol/Phytol} values reflect shifts within the eukaryotic algal community. To assess whether the selected phytoplankton groups were the main sources of the selected lipids, we further modeled algal δ²H_{Lipid1/Lipid2} values based on δ²H_{C16:0 Acid}, δ²H_Sterol and δ²H_Phytol values from batch cultures of individual algal groups and their biovolume in Rotsee and evaluated the role of heterotrophy on δ²H_{Lipid1/Lipid2} values using a model incorporating δ²H_{C16:0 Acid} and δ²H_Sterol values from microzooplankton. Annually-integrated and amount-weighted δ²H_{Lipid1/Lipid2} values measured in Rotsee were within 2 to 20 ‰ of the mean of modeled algal δ²H_{Lipid1/Lipid2} values, demonstrating a strong link with the phytoplankton community composition, while δ²H_{Lipid1/Lipid2} values including microzooplankton lipids had a larger offset. Additionally, cyanobacterial biovolume was positively correlated with the ratio of phytol and phytosterols (phytol:sterol ratio) as well as the ratio of unsaturated C18 and C16:0 fatty acids (C18:C16 ratio). Our results support the application of sedimentary δ²H_{Lipid1/Lipid2} values in eutrophic lakes as a proxy for past phytoplankton community assemblages. Moreover, the calculation of sedimentary phytol:sterol and C18:C16 ratios provides an additional proxy for reconstructing cyanobacterial blooms.

The Arctic cryosphere is the epicentre of acute global change impact, with abrupt warming and amplification driving rapid sea ice decline and irreversible glacial ice loss. A key challenge is understanding how the cryosphere meltdown will impact Arctic marine carbon cycles and ecosystems. Here, we use organic geochemical biomarkers to trace the contribution of different planktonic groups to organic carbon in Arctic fjord sediments (Kongsfjorden, Svalbard) during past warmer and colder (than present) climate states. We show that phytoplankton community structures changed abruptly with variable sea ice cover and glacial ice loss. Our results imply that future deglaciation of Svalbard fjords will likely increase primary productivity in a “blue” (summer ice-free) scenario; however, the potential for fjords to serve as hotspots of marine organic carbon burial will likely be constrained due to warmer, stratified waters and reduced meltwater-induced supply of critical nutrients.

Forest ecosystems are vital for biodiversity, climate regulation, and ecosystem services. Their resilience depends not only on species diversity but also on intraspecific variation—the genetic and phenotypic differences within species—which underpins adaptive capacity to environmental change. However, large-scale, continuous monitoring of intraspecific variation remains challenging. Here, we present a remote sensing approach using Sentinel-2 time series of five vegetation indices as proxies for pigment content, canopy structure, and water content to detect intraspecific variation in seven tree species across a broad environmental gradient in Switzerland. Using pure-species plot data from the Swiss National Forest Inventory, we decomposed variation into spatial, temporal, and spatiotemporal components. We found that spatial variation dominated in evergreen species (48–86%), while temporal variation was more pronounced in deciduous species (56–82%), reflecting their stronger seasonality. These findings demonstrate that species-specific Sentinel-2 time series can effectively track intraspecific variation, providing a scalable method for forest monitoring. This approach opens new pathways for studying forest adaptation, informing management strategies, and guiding species selection for conservation under changing climate conditions.

Monitoring tree phenology is key to understanding forest dynamics under climate change. Events like leaf unfolding and senescence affect ecosystem productivity, tree mortality, and species interactions. While in situ phenology observations provide valuable ground information, they are typically restricted in spatial and temporal coverage and may be influenced by observer-related inconsistencies. Here, we derived species-specific phenology metrics from Sentinel-2 satellite data for Switzerland’s two dominant tree species: beech (Fagus sylvatica) and spruce (Picea abies). We extracted start (SOS), peak (POS), and end (EOS) of season metrics and compared them to in situ observations to study interannual, regional, and topographic variation. Sentinel-2-derived metrics differed significantly from the in situ observations for the SOS and EOS of Fagus sylvatica and the SOS of Picea abies. Sentinel-2 metrics indicated a shorter growing season – later SOS (5 days for Fagus sylvatica; 3 days for Picea abies) and earlier EOS (13 days for Fagus sylvatica). Despite these offsets, satellite data captured similar annual and regional trends. POS closely tracked SOS trends, but offered more reliable sampling opportunities due to more stable vegetation conditions and typically lower cloud cover during summer. Satellite-derived EOS may reflect stress responses missed by ground observations. Elevation trends also differed, with in situ data showing steeper slopes of the SOS-elevation relationships. Limitations of satellite data remained in mountainous regions due to topography and cloud cover, limiting sampling sizes. Overall, satellite remote sensing can complement in situ observations by facilitating observations across large geographic and temporal domains. In contrast, in situ observations provide long-term historical data unaffected by atmospheric conditions or possible technical issues of satellites.

Phytoplankton play a key role in biogeochemical cycles, impacting atmospheric and aquatic chemistry, food webs, and water quality. However, it remains challenging to reconstruct changes in algal community composition throughout the geologic past, as existing proxies are suitable only for a subset of taxa and/or influenced by degradation. Here, we investigate if compound-specific hydrogen isotope ratios (δ²H values) of common algal lipids can serve as (paleo)ecological indicators. First, we grew 20 species of algae – representing cyanobacteria, diatoms, dinoflagellates, green algae, and cryptomonads – in batch cultures under identical conditions and measured δ²H values of their lipids. Despite identical source water δ²H values, lipid δ²H values ranged from −455 ‰ to −52 ‰, incorporating variability associated with chemical compound classes and taxonomic groups. In particular, green algae synthesized fatty acids with higher δ²H values than other taxa, cyanobacteria synthesized phytol with relatively low δ²H values, and diatoms synthesized sterols with higher δ²H values than other eukaryotes. Second, we assessed how changes in algal community composition can affect net δ²H values of common algal lipids in 20 experimental outdoor ponds, which were manipulated via nutrient loading, and the addition of macrophytes and mussels. High algal biomass in the ponds, which was mainly caused by cyanobacterial and green algal blooms, was associated with higher δ²H values for generic fatty acids, relatively stable δ²H values for phytol and the dinoflagellate biomarker dinostanol, and lower δ²H values for the more cosmopolitan sterol stigmasterol. These results are consistent with expectations from our culture-based analyses, with both datasets indicating large taxon-specific changes that are unlikely to be driven by bacterial heterotrophy. This suggests that measuring δ²H values of multiple lipids from sediment and calculating ²H-offsets between them can resolve changes in algal community composition from changes in source water isotopes. With an appropriate availability of sedimentary lipids, this approach could permit the reconstruction of both taxonomic variability and hydroclimate from diverse sedimentary systems.

Beach ridges are depositional landforms that provide information related to coastal evolution, storm activity and sea-level variations. However, beach ridges are sometimes modified by aeolian processes, storm washover and/or human activity. Therefore, systematic investigations are required to use beach ridges as an archive of palaeoenvironmental conditions and sea-level changes. In this study, a multidisciplinary approach involving ground-penetrating radar, sedimentological analysis and optically stimulated luminescence as well as radiocarbon dating was used to reconstruct sedimentary processes and past sea-level changes that formed beach ridges in the coastal zone of Nakhon Si Thammarat province, Lower Gulf of Thailand. Ground-penetrating radar data reveal evidence of beach progradation coupled with the presence of beach scarps and washover deposits. This implies that the formation of the beach ridges occurred under swash processes on the beachface and was later punctuated by erosion during storm surges, leading to the deposition of washover sediments. During a storm, elevated seawater transported moderately to poorly sorted medium-to-coarse sand onto a higher position along the beach profile, resulting in an elevation of the beach ridge of up to 4.6 m above mean sea-level. In addition, aeolian processes contributed to vertical accretion by depositing well-sorted fine sand on the surface of the beach ridges. The dating results indicate that the formation of the beach ridges occurred approximately between 8.6 ka and 6.1 ka and can be attributed to an upper sea-level limit of 1.8 to 2.3 m above present-day mean sea level. Both allogenic (e.g. sea-level and climate variability) and autogenic (e.g. sediment supply and wave action) factors play crucial roles in the formation and evolution of beach ridges. Therefore, the multidisciplinary approach of this study enhances the understanding of these composite depositional processes and improves palaeoenvironmental reconstructions derived from beach ridges.

Waterborne pathogens pose a serious threat to public health, emphasizing the need for reliable and efficient water treatment technologies. Wastewater treatment plants employ a range of processes to reduce microbial contamination, with membrane filtration emerging as a promising solution due to its ability to physically remove pathogens without the production of harmful chemical by-products. This study investigates the effectiveness of a gravity-driven membrane (GDM) filtration system for pathogen removal from wastewater and evaluates the associated public health risks with and without treatment. A quantitative microbial risk assessment model was employed to estimate infection probabilities for various waterborne pathogens. The results demonstrated a significant decrease in pathogen concentrations following treatment, with up to a 10⁴-fold reduction in norovirus infection risk. Three critical factors influencing membrane performance were identified: membrane integrity, pore size characteristics, and membrane fouling. Maintaining membrane integrity was found to be essential for ensuring consistent pathogen removal. While nominal pore size is commonly used to predict rejection efficiency, the overall pore size distribution was found to have a greater influence on virus retention. Additionally, although membrane fouling is often considered detrimental, it was shown to enhance virus removal by up to two orders of magnitude. These findings underscore the potential of GDM systems for effective virus removal and highlight the importance of proper membrane design, maintenance, and monitoring in ensuring long-term operational efficiency and maximizing public health protection in wastewater treatment applications.

Spatial environmental heterogeneity is an important driver of aquatic biodiversity. Ecological and evolutionary theory often consider spatial heterogeneity as being driven by exogenous factors, yet heterogeneity can also be generated and modified by organisms. Here we used a mesocosm experiment to investigate if consumers influence the build-up of spatial heterogeneity. We expected that consumer effects on heterogeneity would depend on consumer composition and differ among response variables. We constructed metacommunities consisting of three mesocosms and manipulated the presence and composition of consumers, using four treatment levels: (1) no consumers, (2) two genotypes of Daphnia galeata, (3) D. galeata and Daphnia longispina, and (4) D. galeata and a hybrid of D. galeata × D. longispina. We then continuously increased heterogeneity among the three patches of each metacommunity by adding nutrients and dissolved organic carbon (DOC), respectively, to two of the three mesocosms. We found that consumers affected the build-up of heterogeneity, but the direction and magnitude of this effect differed among consumer compositions. Metacommunities with only D. galeata had increased heterogeneity in phytoplankton biomass, whereas metacommunities with D. longispina or the hybrid had low phytoplankton heterogeneity. The differential effects of Daphnia taxa on phytoplankton heterogeneity cascaded down to the abiotic environment and resulted in taxon-specific effects on heterogeneity in light extinction, dissolved inorganic nitrogen, and total inorganic carbon. Our results imply that changes in consumer species (e.g., due to environmental change or invasion) might affect not only the local environment but could also impact heterogeneity among environments, with important consequences for aquatic biodiversity.

Many components of the Earth system feature self-reinforcing feedback processes that can potentially scale up a small initial change to a fundamental state change of the underlying system in a sometimes abrupt or irreversible manner beyond a critical threshold. Such tipping points can be found across a wide range of spatial and temporal scales and are expressed in very different observable variables. For example, early-warning signals of approaching critical transitions may manifest in localised spatial pattern formation of vegetation within years as observed for the Amazon rainforest. In contrast, the susceptibility of ice sheets to tipping dynamics can unfold at basin to sub-continental scales, over centuries to even millennia. Accordingly, to improve the understanding of the underlying processes, to capture present-day system states and to monitor early-warning signals, tipping point science relies on diverse data products. To that end, Earth observation has proven indispensable as it provides a broad range of data products with varying spatio-temporal scales and resolutions. Here we review the observable characteristics of selected potential climate tipping systems associated with the multiple stages of a tipping process: This includes i) gaining system and process understanding, ii) detecting early-warning signals for resilience loss when approaching potential tipping points and iii) monitoring progressing tipping dynamics across scales in space and time. By assessing how well the observational requirements are met by the Essential Climate Variables (ECVs) defined by the Global Climate Observing System (GCOS), we identify gaps in the portfolio and what is needed to better characterise potential candidate tipping elements. Gaps have been identified for the Amazon forest system (vegetation water content), permafrost (ground subsidence), Atlantic Meridional Overturning Circulation, AMOC (section mass, heat and fresh water transports and freshwater input from ice sheet edges) and ice sheets (e.g. surface melt). For many of the ECVs, issues in specifications have been identified. Of main concern are spatial resolution and missing variables, calling for an update of the ECVS or a separate, dedicated catalogue of tipping variables.

Phytoplankton play a central role in aquatic ecosystems, influencing biogeochemical cycles, food web dynamics, and overall water quality. Monitoring their composition is essential for assessing water ecosystem health and detecting environmental changes. Chlorophyll-a concentration is widely used as a proxy for phytoplankton abundance in inland waters. Together with colored dissolved organic matter and total suspended matter, these parameters can be retrieved from remote sensing reflectance data. However, identifying the detailed taxonomic composition of phytoplankton in lakes remains a major challenge. Spectral matching algorithms offer promising solutions to overcome this limitation. In this study, we investigated the potential of retrieving phytoplankton taxa composition from high-resolution in situ spectroscopy measurements by applying radiative transfer inversion and validating the results against phytoplankton abundance data obtained from an imaging microscope. First, we assessed the performance of our approach in retrieving four phytoplankton taxa under cloud-free conditions. Then, we extended the analysis to two seasons, covering multiple consecutive blooms using data acquired independently of cloudiness. The high agreement between the imaging microscopy results and those obtained from in situ spectroscopy indicates that remote sensing with radiative transfer inversions can track the evolution of phytoplankton blooms. The results suggest that low phytoplankton concentrations and the lack of unique spectral features for some taxa may prevent the accurate identification of phytoplankton composition through spectroscopy. In addition, the natural variability in cell size, along with physiological changes such as fluctuations in intracellular chlorophyll-a content, impacts the empirical conversion from cell cross section to intracellular chlorophyll-a content.

Harmful algal blooms (HABs) caused by the dinoflagellate Alexandrium minutum can pose risks to human and ecosystem health. HABs of different species can coexist in coastal waters and accumulate near the shoreline, challenging their detection through Earth observation (EO). In this study, we use in situ geo-bio-optical and taxonomical data from the Rías Baixas (NW Spain) to develop a new method for identifying high-concentration blooms of A. minutum and its application to Sentinel-2 Multispectral Instrument (S2 MSI). Our approach named A. minutum index (AMI) was developed to capture the low absorption and high backscattering properties of A. minutum cells between 560 and 570 nm. We tested and validated the performance of three atmospheric correction algorithms (AC) (C2RCC, POLYMER and ACOLITE) using matchups between in situ and satellite-derived R_rs. Results show that C2RCC had the lowest error across most wavelengths. Applying AMI to S2 MSI indicates that our approach can accurately identify high-concentration blooms of A. minutum (F1 score: 70 %, Kappa: 68.3 %, balanced accuracy: 87.7 %, MCC: 68.3 %) and discriminate blooms of A. minutum from other phytoplankton species. We compared AMI with three existing indices for detecting HABs in coastal waters and found that our approach achieved a better performance, with the NDTI, RGCI and NDCI yielding F1 scores of 21.28, 21.74, and 0.0 % and MCC values of 15.0, 15.0 and 0.0 %, respectively. We also investigated the spatial resolution of S2 MSI to Sentinel-3 Ocean and Land Colour Instrument (S3 OLCI) for mapping fine-scale variations in A. minutum blooms. We found that the higher spatial resolution data from S2 MSI were highly useful for detecting small-scale variations in A. minutum in nearshore waters, enabling their detection in the mid-inner part of the Rías, where aquaculture activities are more prominent. This study also showcases the significance of accurate AC in near-shore waters, where high-concentration blooms can be more prevalent. Our findings show that greater errors in AC are observed in near-shore pixels, where the socio-economic and environmental impact of HABs are typically more severe.

For over a century, ecologists have used the concept of trophic state (TS) to characterize an aquatic ecosystem's biological productivity. However, multiple TS classification schemes, each relying on a variety of measurable parameters as proxies for productivity, have emerged to meet use-specific needs. Frequently, chlorophyll a, phosphorus, and Secchi depth are used to classify TS based on autotrophic production, whereas phosphorus, dissolved organic carbon, and true color are used to classify TS based on both autotrophic and heterotrophic production. Both classification approaches aim to characterize an ecosystem's function broadly, but with varying degrees of autotrophic and heterotrophic processes considered in those characterizations. Moreover, differing classification schemes can create inconsistent interpretations of ecosystem integrity. For example, the US Clean Water Act focuses exclusively on algal threats to water quality, framed in terms of eutrophication in response to nutrient loading. This usage lacks information about non-algal threats to water quality, such as dystrophication in response to dissolved organic carbon loading. Consequently, the TS classification schemes used to identify eutrophication and dystrophication may refer to ecosystems similarly (e.g., oligotrophic and eutrophic), yet these categories are derived from different proxies. These inconsistencies in TS classification schemes may be compounded when interdisciplinary projects employ varied TS frameworks. Even with these shortcomings, TS can still be used to distill information on complex aquatic ecosystem function into a set of generalizable expectations. The usefulness of distilling complex information into a TS index is substantial such that usage inconsistencies should be explicitly addressed and resolved. To emphasize the consequences of diverging TS classification schemes, we present three case studies for which an improved understanding of the TS concept advances freshwater research, management efforts, and interdisciplinary collaboration. To increase clarity in TS, the aquatic sciences could benefit from including information about the proxy variables, ecosystem type, as well as the spatiotemporal domains used to classify TS. As the field of aquatic sciences expands and climatic irregularity increases, we highlight the importance of re-evaluating fundamental concepts, such as TS, to ensure their compatibility with evolving science.

Inland waters play an important role in the terrestrial carbon cycle by burying carbon in aquatic sediments while simultaneously releasing CO₂ to the atmosphere and laterally exporting carbon along the land-ocean aquatic continuum. Especially in hardwater lakes, the close connection between primary production and calcite precipitation results in a poorly understood balance of carbon burial and release, with stronger coupling of organic and inorganic processes than in softwater lakes. To better understand these dynamics, we analyzed organic and inorganic carbon fluxes in a yearlong (June 2022 to June 2023) sediment trap study in Lake Geneva, the largest natural lake in Western Europe. Two sediment traps – one deployed in the subaqueous delta of the upper Rhône River, the other in the lake's deepest basin – were sampled monthly. Analyzing radiocarbon (¹⁴C) signatures of particulate organic and inorganic carbon allowed us to resolve allochthonous (external) and autochthonous (internal) contributions to absolute carbon fluxes. We found that the flux of autochthonous particulate inorganic carbon in the river-proximal deltaic site was approximately four times higher than in the distal one. This is likely the result of calcite precipitation driven by increased fluvial supply of nutrients and suspended carbonate-bearing particles. Sediment core analysis in the same location suggests efficient preservation of this calcite over centennial timescales, which we conservatively estimate around 7–10 Gg C yr⁻¹ lake-wide. This indicates at least partial offset of the CO₂ released during calcite precipitation and is an important flux to be considered in mechanistic carbon cycle models.

Organic carbon (OC) burial in lake sediments is comparable to that in marine sediments globally. However, climatic and carbon cycle implications depend on the origin of buried OC. This study utilizes high-resolution radiocarbon (¹⁴C) measurements in combination with stable carbon isotopes (¹³C) and total organic carbon/total nitrogen ratios to constrain sources and ages of OC deposited since the early 20^th century in Lake Constance, the second-largest lake in central Europe. We differentiate between aquatic, pre-aged soil, and fossil rock-derived (petrogenic) OC. The shape and magnitude of the ¹⁴C bomb spike recorded in the sediment profile indicate the sequestration of recently synthesized biospheric OC with a complex overlay from different OC sources. We find that soil-derived OC is the dominant component of sedimentary OC, with a mean transit time in the catchment of around 110 yr. Additionally, we quantified the ¹⁴C dynamics of dissolved inorganic carbon in the lake, which can be modeled with a mean transit time of around 10 yr. An ordinary kriging spatial analysis revealed that the Alpine Rhine delta and the profundal areas are the primary loci for allochthonous OC deposition. Lake-wide surface sediment OC fluxes were spatially heterogeneous but averaged 52.0 gC m⁻² yr⁻¹, where 26.7 gC m⁻² yr⁻¹ of mostly stable, allochthonous OC are buried long term. This study highlights the necessity of accounting for both pre-aged and fossil OC sources, as well as spatial heterogeneity, when assessing the response of lakes and, more broadly, source-to-sink systems to ongoing climate and ecosystem change.

The continued rise of antibiotic resistance and adoption of the One Health approach necessitates reliable methods for detection and quantification of antibiotic resistance genes (ARGs) in complex environmental matrices. Here we present a consolidated set of TaqMan quantitative PCR assays for quantification of clinically relevant and emerging ARGs in complex environmental matrices.
• We systematically designed five new primer sets, six TaqMan probes and verified and adapted four previously published relevant primer/probe sets from literature and evaluated their specificity in silico against current database.
• For external quantification, two sets of gBlock standard libraries were designed. We experimentally validated the specificity, sensitivity, and efficiency of the assays with positive strain control DNA, negative strain control DNA, general no target controls, extraction blank controls, negative controls, and environmental test samples (i.e., metagenomic DNA from complex environmental matrices) to comprehensively assess each assays’ performance.
• Optimization included iterative testing of both primer and probe concentration, annealing temperature, and annealing time. Results demonstrated robust and reliable detection and quantification of ARGs in clinical isolates and wastewater effluents with high sensitivity, specificity, and efficiency.
This makes the assays suitable for surveillance in wastewater or various environmental matrices, in support of efforts to mitigate dissemination of antibiotic resistance.

Motivations: Urban drainage systems (UDS) play a crucial role in protecting public health and aquatic ecosystems by transporting wastewater to treatment plants. However, they
are also a significant source of pollution due to aging infrastructure, leakages, and combined sewer overflows. Quantifying and mitigating these emissions is challenging. Traditional sampling campaigns offer limited temporal and spatial coverage, while conventional contact-based sensors often fail in harsh sewer environments due to fouling. Therefore, there is a critical need for innovative monitoring tools that can measure water quality indicators (WQIs) under these challenging conditions.

Objectives: This thesis investigates the use of diffuse reflectance spectrophotometry (DRS) as an in-situ method for measuring wastewater quality in UDS. DRS combines the strength of spectral analysis with fouling-free, low-maintenance remote measurement, overcoming limitations of conventional sensors. So far, implementation of this method for WQI monitoring in UDS has not been reported. This thesis addresses three main research objectives (ROs). The first is to evaluate the detectability of relevant WQI in raw wastewater with DRS (RO1). The second is to optimize conversion of DRS measurements into WQIs with data-driven models (RO2). The third is to study the effect of measurement geometry and UDS environment variability on DRS measurements to prepare for realworld implementation (RO3).

Methanotrophs, in particular methane-oxidizing bacteria (MOB), regulate the release of methane from lakes, and often co-occur with methylotrophs that may enhance methane-oxidation rates. Assessing the interaction and physiological status of these two microbial groups is essential for determining the microbial methane buffering capacity of environmental systems. Microbial membrane lipids are commonly used as taxonomic markers of specific microbial groups; however, few studies have characterized the changes of membrane lipids under different environmental conditions. For the case of methane-cycling microorganisms, this could be useful for determining their physiological status and potential methane buffering capacity. Here we investigated the changes in membrane lipids, bacteriohopanepolyols (BHPs) and respiratory quinones, produced by MOB and methylotrophs in an enrichment co-culture that primarily consists of a methanotroph (Methylobacter sp.) and a methylotroph (Methylotenera sp.) enriched from a freshwater lake under different methane concentrations, temperatures, and salinities. To assess whether the lipid response is similar in methanotrophs adapted to extreme environmental conditions, we also characterize the BHP composition and respiratory quinones of a psychrotolerant methanotroph, Methylovulum psychrotolerans, isolated from an Arctic freshwater lake and grown under different temperatures. Notably, in the Methylobacter-Methylotenera enrichment the relative abundance of the BHPs aminobacteriohopanepentol and aminobacteriohopanepolyols with additional modifications to the side chain increased at higher temperatures and salinities, respectively, whereas there was no change in the distribution of respiratory quinones. In contrast, in the Methylovulum psychrotolerans culture, the relative abundance of unsaturated BHPs increased and ubiquinone 8:8 (UQ_8:8) decreased at lower temperatures. The distinct changes in lipid composition between the Methylobacter-Methylotenera enrichment and the psychrotolerant methanotroph at different growth temperatures and the ability of the Methylobacter-Methylotenera enrichment to grow at high salinities with a singular BHP distribution, suggests that methane-cycling microbes have unique lipid responses that enable them to grow even under high environmental stress.

The primary production of fjords across the Arctic and Subarctic is undergoing significant transformations due to the climatically driven retreat of glaciers and ice sheets. However, the implications of these changes for upper trophic levels remain largely unknown. In this study, we employ both bulk and compound-specific stable isotope analyses to investigate how shifts at the base of fjord food webs impact the carbon and energy sources of consumers. Focusing on two rapidly changing fjords in Southern Greenland, we used the migratory Arctic char as an indicator species, sampling populations along environmental gradients within the fjords, building upon the assumption that char populations feed primarily close to their natal stream, thereby integrating a dietary gradient. Our analysis of bulk stable isotopes in Arctic char tissue confirmed this premise, revealing a consistent change in resource use from the outer to the inner fjord, which nonetheless served as preferred feeding grounds. Essential amino acid analysis further indicated shifts in carbon and nitrogen sources, consistent with changes in nutrient use near glacier inputs characterized by low turbidity and high iron levels. Notably, these changes in the source of primary production were associated with shifts in trophic positions and the transfer of polyunsaturated fatty acids, with Arctic char in glacier-influenced inner fjords feeding at lower trophic level (size-corrected) and accumulating higher levels of high-quality docosahexaenoic acid (DHA). These findings highlight the usefulness of new analytical tools in revealing that glacial retreat can substantially alter food web dynamics, enhancing both carbon flow and the nutritional quality of fish in fjord ecosystems. The two Southern Greenland fjords studied could represent the future of other fjords, where retreating glaciers become land-terminating and glacial inputs decrease. Our study underscores the critical role of glacier dynamics in affecting high-level consumers, such as salmonids, with implications for fjords globally.

The 8.2 ka event, the most abrupt climatic anomaly of the Holocene, disrupted global climate by weakening the Atlantic Meridional Overturning Circulation (AMOC) due to meltwater influx, triggering widespread climatic and environmental changes. While its impacts are well-documented in and around the North Atlantic, responses in Southeast Asia remain uncertain due to sea level fluctuations and limitations in existing paleoclimate data. This study presents a new multi-proxy analysis of a sediment core from the Kuan Kreng peat swamp forest in southern Thailand. Lithostratigraphy and geochemical analyses (total organic carbon and biomarkers) reveal environmental shifts between coastal lagoon and peat swamp ecosystems primarily driven by early- to mid-Holocene sea level changes. Our record delineates two distinct transitions: (1) from a marine-influenced lagoon to the onset of a peat swamp (8025 ± 20 yr BP) and (2) a subsequent return to lagoon conditions. Evidence based on n-Fatty Acid Methyl Ester (n-FAMEs) suggests that sea level regression due to the 8.2 ka event may have begun before the transition from lagoon to peatland indicated by lithostratigraphy. Branched-glycerol dialkyl glycerol tetraethers (brGDGTs) also indicate environmental changes and possibly cooler temperatures around 8.0 ka BP. Comparisons with published records from the Thai-Malay Peninsula refine the understanding of regional environmental changes, suggesting that the 8.2 ka event likely triggered a temporary regression at the study site, with variations in the monsoon intensity and ITCZ shifts playing a key role in hydroclimate changes.

Nearly half (46%) the world’s population is now served by non-sewered sanitation. In urban areas of low- and middle-income countries, this translates to onsite storage of wastewater in tanks and pits until it can be collected and transported by road to treatment, which is commonly referred to as fecal sludge management. The microbial communities that develop during storage of this wastewater remain understudied, leaving practitioners and scientists to speculate on best management practices such as downstream treatment and climate mitigation measures. In this study, we collected samples from 135 randomly selected containments across the city of Lusaka, Zambia, and evaluated statistical relations of 16S rRNA gene sequence data to types and volume of wastewater going into containments, disturbances (i.e., emptying events), characteristics of accumulated wastewater during storage, and metrics of downstream treatment processes. At the phyla level, 80% of the identified microorganisms belonged to Firmicutes, Proteobacteria and Bacteroidota. Focusing in at the genera level, microbial diversity and composition were statistically related to volumes of water usage, properties of wastewater in containments (total organic carbon, total kjeldahl nitrogen, ammonium nitrogen, pH), and metrics of stabilization and dewatering performance. In Lusaka, a core community was identified with 104 of the 1,247 identified genera being present in >90% of the containments. In contrast, 936 genera were present in <60% of the containments, indicating that niche or transient organisms may also be important in unravelling metabolic processes such as sulfur reduction, methanogenesis, and ammonia tolerance. Community similarity was independent of time since last emptied, indicating stability of microbial communities over time. Identified metabolic differences between pit latrines (i.e., less water usage) and septic tanks (i.e., more water usage) indicate that methanogens more actively convert organic matter to methane in the more dilute wastewater in septic tanks, which could be globally relevant for greenhouse gas mitigation from non-sewered sanitation.

Monitoring the health of essential freshwater and coastal ecosystems like lakes and estuaries requires estimating water quality indicators (WQIs) like chlorophyll-a from remote sensing data. Machine learning (ML)-based regression tools are a popular choice for this estimation task. Training such models requires a labeled dataset comprising of co-located measurements of remote sensing variables and WQIs. To address this need, practitioners primarily use co-located in situ measurements of remote sensing reflectance and WQIs to train ML models. While these ML models outperform other analytical/empirical methods for the chlorophyll-a estimation tasks on labeled in situ datasets, their performance deteriorates quite significantly when applied to satellite datasets. Using satellite-based training datasets is infeasible given the paucity of co-located measurements of satellite-derived variables and WQIs, especially for newer sensors. To address the discrepancy between the training (in situ) datasets and application (satellite) datasets, we will leverage domain adaptation (DA), i.e., an ML trick to transfer knowledge from a source (in situ) domain with abundant labeled examples to a related target domain with little or no labeled data (satellite). To demonstrate the effectiveness of this approach, we implement Domain Adaptation for REgression by aligning inverse GRAM matrices (DARE-GRAM) for the chlorophyll-a estimation task. This regression-specific domain adaptation technique uses the labeled source (in situ) data and unlabeled satellite data (i.e., only the remote sensing reflectance) to build a model with improved chlorophyll-a estimation for satellite datasets. We test this approach using data from two popular multispectral sensors, namely, Sentinel-2 MultiSpectral Instrument (MSI) and Sentinel3 Ocean and Land Colour Imager (OLCI). The DARE-GRAM shows improvements of between 20-50% across a wide range of regression metrics, indicating a comprehensive improvement in the estimation performance relative to classical ML methods. The DARE-GRAM method also shows significantly improved agreement for chlorophyll-a estimates from near-simultaneous acquisitions from the different sensors. This improved harmony is expected to be an important step in creating consistent crosssensor products.

Turbidity currents, gravity-driven sediment-laden flows, govern material transport and shape underwater landscapes across diverse environments. While extensively studied in marine settings, their dynamics in freshwater systems remain underexplored. We present multi-temporal, multi-scale observations from the Aare Delta of Lake Brienz (Switzerland), combining Acoustic Doppler Current Profiler measurements with high-resolution repeated bathymetric surveys to capture turbidity currents and resulting morphological changes. A single turbidity current reached near-bed velocities of 0.65 m/s and induced upslope migration of a cyclic step by at least 4 m within minutes. Characterisation of overall bedform migration across the channel network over five years highlights the cumulative imprint of turbidity currents and frames these short-term changes within the broader context of channel reworking. Together, our results show striking similarities in overall flow structure, bedform morphologies, and dynamics between freshwater and marine systems, underscoring the value of lacustrine settings as accessible, scaled-down environments for advancing turbidity current research.

Understanding recent rapid environmental and climatic changes requires placing them in a long-term context derived from reconstructions from natural archives. Membrane lipids such as glycerol dialkyl glycerol tetraethers (GDGTs) are increasingly recognized as vital proxies for paleoenvironmental and climatic reconstructions. While this field is rapidly evolving, with frequent publications introducing new calibrations, indices, and ratios derived from a growing range of compounds, there remains a notable lack of automated workflows for subsequent data processing. In response, we introduce GaDGeT, a comprehensive software designed to streamline GDGT data analyses, including the calculation of concentrations, fractional abundances, and published GDGT-indices and ratios. Users input raw HPLC peak area datasets, and GaDGeT automatically processes and organizes the results into structured output directories as CSV files. Implemented in the open-source language R, it ensures reproducibility and transparency. GaDGeT’s platform-independent, modular design makes it accessible and adaptable for researchers of varying expertise levels and enables the software to evolve alongside advancements in the field. GaDGeT currently focuses on data processing and output generation rather than visualization. The software is continuously updated with additional calibrations, and its open framework allows users to extend the tool with their own functions and indices. We encourage users to consult the original publications for appropriate interpretation and to share their HPLC peak area files to promote transparency, support peer review, and enhance the scientific utility of GDGT datasets.

This report summarizes a pilot study conducted by the Eionet Working Group (WG) on antimicrobial resistance (AMR) monitoring in European surface waters. With AMR recognized as a major public health threat, the study aimed to develop a harmonized approach for collecting and reporting AMR data in surface waters, supporting revisions of EU water directives.
Led by the European Environment Agency (EEA) and the European Topic Centre Biodiversity and Ecosystems (ETC-BE), the WG developed methodologies and practical guidelines covering sampling, analysis, data reporting, and quality control. Sampling focused on rivers downstream of urban wastewater treatment plants (WWTPs). Target indicators included six gene markers (e.g., 16S rRNA, intl1, aadA1) via qPCR and culturing of E. coli and ESBL-producing E. coli (ESBL-Ec).
Ten of fourteen nominated countries participated, using qPCR as the main method for its cost-effectiveness. WHO’s Tricycle protocol was applied for culturing due to the absence of standardized EU methods for water. A custom data reporting template aligned with EEA’s WISE-6 model was also developed.
Results showed AMR gene abundance followed a clear gradient: WWTP inlet > outlet > downstream > upstream, consistent with previous studies. Gene removal by WWTPs ranged between 94.5%-99.9%, and ESBL-Ec levels varied between countries (0–14.5%). Wastewater treatment effectively reduced both E. coli and ESBL-Ec by over 99%.
The pilot faced challenges including funding limits, varied national capacities, and differing technical expertise. Despite this, it was viewed as a successful step toward EU-wide AMR monitoring. Priority areas for future EU-wide monitoring were identified and include defining objectives, harmonizing methods, improving QA/QC, and establishing a centralized reporting system.

Accurate forecasting of algal blooms in lakes can support effective freshwater management. However, observational datasets for calibrating and validating algal bloom forecasting models such as the General Lake Model - Aquatic Eco Dynamics (GLM-AED) are often scarce, which impedes robust model calibration and forecasting ability. Satellite remote sensing can help fill these gaps by offering high-frequency, large-scale measurements of phytoplankton chlorophyll-a concentration (mg m^-3), but satellite chl-a products often carry high uncertainty. Here we introduce a novel approach to quantify uncertainty in satellite chl-a based on conformal prediction, with the aim of integrating robust chlorophyll-a products into GLM-AED. Using Sentinel-2 imagery from two eutrophic lakes in the UK, Esthwaite Water and Loch Leven, we obtain remotely sensed chlorophyll-a with low systematic signed percentage bias (-1.22 % and 0.38) and moderate median symmetric accuracy (15.87 and 43.02 %) using Polymer atmospheric correction. We effectively flag potentially uncertain chlorophyll-a estimates (coverage factor: 75.6 - 81 %). Integrating the screened remotely sensed chlorophyll-a estimates improved GLM-AED algal bloom forecasts by 50 % in Loch Leven and 13 % in Esthwaite Water, with the greater improvement in Loch Leven attributed to its higher initial model errors. In contrast, incorporating unscreened chlorophyll-a estimates into GLM-AED increases validation errors on average by 32 %. Our findings show that process-based model predictions can substantially benefit from incorporating additional satellite-derived chlorophyll-a estimates. At the same time, they highlight a crucial need for robust uncertainty quantification to support downstream applications such as algorithm validation, biological monitoring in data-scarce regions, and water management decision-making. Moreover, because conformal prediction is model-agnostic and satellite-derived chlorophyll-a products are globally accessible, our study paves the way for large-scale, well-calibrated bloom forecasting through process-based models.

Lake Cadagno is a meromictic alpine lake characterized by permanent stratification, which creates a permanent anoxic environment that supports the growth of anoxygenic phototrophic sulfur bacteria. The seasonality and interseasonality of these microorganisms were examined over a three-year period (2019–2021) through regular monitoring of the water column. A variety of physical–chemical parameters, including temperature, conductivity, light, oxygen and sulfide concentrations, and the community composition of anoxygenic phototrophic sulfur bacteria in the chemocline were recorded, to observe potential influence of external weather conditions. Our findings indicate that, despite the lake’s consistent physical and chemical stratification, the composition of the anoxygenic phototrophic sulfur bacteria community exhibited notable variations in response to external environmental factors, including changes in rainfall and light irradiance. Specifically, we observed different growth dynamics in the purple (PSB) and green (GSB) sulfur bacteria communities over the three years of monitoring. These variations underscore the complexity of biogeochemical cycles in meromictic lakes and the impact of external environmental factors on this ancestral microbial community dynamics. The results provide valuable insights into the stability of redox-stratified environments, offering a modern analog for ancient aquatic ecosystems. This research emphasizes the importance of long-term regular monitoring to capture interannual dynamics and assess the implications of climate change on such unique ecosystems.

Projected increases in drought frequency and strength in Central Europe in the next two decades due to anthropogenic climate change pose challenges for European temperate forests. Understanding the correlation between drought stress, local conditions, and forest responses is crucial for effective forest management and climate mitigation measures. We examine how local water dynamics determine the response of Swiss forests during the European drought in 2018. We particularly investigate how increased atmospheric water demand, reduced soil water availability, and increased exposure of forests to potentially harsh abiotic conditions at the edge of the forest affect forest health. We used Sentinel-2 data to calculate the normalized difference water index (NDWI) as proxy for forest health. Weather data, data from a process based hydrological model, a digital elevation model, and airborne LiDAR data were used to assess hydrological drivers. Our analysis revealed that forest exposure and water availability were more important than atmospheric water demand in explaining forest drought resistance. Regions with more limited water availability (47 % of Switzerland) had systematically higher proportions of forest areas that exhibited weak drought resistance (R² = 0.56 for moderate NDWI decrease and 0.55 for severe NDWI decrease). Forest exposure (i.e. the degree to which a forest patch stands out from the surroundings) could best explain weak drought resistance, with strong statistical relationships (R² = 0.69, R² = 0.50). Finally, atmospheric water demand had only a moderate effect on weak drought resistance (R² = 0.45 and 0.27). Our findings highlight the complex interplay of local water dynamics and forest responses to drought, while providing insights on how forest structure and exposure conditions at local scales affect responses and need to be considered when examining forest health under changing climatic conditions.

Microbial methane production is a key reaction involved in the terminal step of anaerobic degradation of organic matter. The energy substrates of methane-producing microorganisms are largely generated during the breakdown of larger organic molecules by fermentative microorganisms, wherein the products of fermentation may vary with the chemical compositions of these larger molecules. Due to differences in energy substrates among methane-producing microorganisms, it is thus possible that organic matter compositional variations select for different communities of methane producers. Here, we investigate the sources and compositions of OC in sediments of Lake Geneva and how both are potentially linked to methane production. Differences in dominant long-chain fatty acid abundances and carbon isotopic compositions suggest the predominance of diagenetically altered phytoplankton-derived OC at a profundal site (PS) and temporally highly variable sources of both aquatic and terrestrial OC in a deltaic location. Despite these differences, radiotracer-based methanogenesis rate measurements and stable isotopic signatures of methane indicate significant methane production that is dominated by CO₂ reduction (>95 % of total methanogenesis) in both locations. Matching this interpretation, members of well-known CO₂-reducing Methanoregula sp. dominate both sites. Similarly, no clear effect of OC source on methane production rates was evident. Our data demonstrate that OC of diverse sources and diagenetic states supports microbial methane production, but the data do not indicate a clear impact of the OC source on the dominant methanogenic pathway or the community structure of methanogenic microorganisms in lacustrine sediments.

The rapid worldwide formation and expansion of glacial lakes has increased the likelihood of glacial lake outburst floods, threatening lives and infrastructure, particularly in vulnerable mountain communities. Given the rapid increase in the popularity of artificial intelligence methods for remote sensing of glacial lakes, a comprehensive review is essential. We survey a decade (2015–2024) of research on glacial lake monitoring from space, with a focus on classical machine learning and deep learning approaches. We identify key trends, research gaps, and best practices for future studies. Most studies rely on optical imagery, especially Landsat-8 and Sentinel-2, while Sentinel-1 serves as a complementary radar source. However, monitoring glacial lakes in mountainous regions remains a challenge on cloudy days due to the limitations of radar and the unusability of optical data. Deep learning, particularly U-Net and DeepLab derivatives, dominates learning-based glacial lake studies but remains computationally demanding. Critical challenges involve balancing performance gains against trade-offs in data availability, computational cost, and model transferability. Geographic and methodological gaps, especially in regions experiencing rapid lake growth, underscore the need for broader spatial coverage and improved spatiotemporal model generalization. Moreover, transitioning from a focus on static seasonal mapping to frequent multi-temporal monitoring is beneficial for understanding glacial lake evolution and outburst flood hazards. Adapting emerging deep learning architectures to integrate multispectral, hyperspectral, and radar data could enhance glacial lake detection capabilities. Furthermore, thorough inter-method comparisons, benchmarking with rigorous evaluation metrics, and open-sourcing datasets and code would facilitate robust, large-scale glacial lake monitoring efforts.

Aquatic and terrestrial ecosystems are linked through the reciprocal exchange of materials and organisms. Aquatic-to-terrestrial subsidies are relatively small in most terrestrial ecosystems, but they can provide high contents of limiting resources that increase consumer fitness and ecosystem production. However, they also may carry significant contaminant loads, particularly in anthropogenically impacted watersheds. Global change processes, including land use change, climate change and biodiversity declines, are altering the quantity and quality of aquatic subsidies, potentially shifting the balance of costs and benefits of aquatic subsidies for terrestrial consumers. Many global change processes interact and impact both the bright and dark sides of aquatic subsidies simultaneously, highlighting the need for future integrative research that bridges ecosystem as well as disciplinary boundaries. We identify key research priorities, including increased quantification of the spatiotemporal variability in aquatic subsidies across a range of ecosystems, greater understanding of the landscape-scale extent of aquatic subsidy impacts and deeper exploration of the relative costs and benefits of aquatic subsidies for consumers.

We use a zero-dimensional stochastic dynamo model describing the coupled oscillatory behavior of the toroidal and poloidal components of the solar magnetic field. The model includes a time delay, arising from the assumption that the two field components are generated in spatially segregated locations, and a quenching of the α-effect for amplitudes of the toroidal magnetic field outside a range defined by a lower and an upper threshold. We apply two distinct simulation-based Bayesian inference methods to calibrate the model parameters. The first approach employs a Simulated Annealing Approximate Bayesian Computation algorithm, based on the comparison of relevant features extracted from observed data with their counterparts from simulated data. The second one leverages a sequential neural posterior density estimation method known as Automatic Posterior Transformation. The inference was carried out using two different data sets: the observed sunspot record and a recent millennial solar activity reconstruction based on ¹⁴C cosmogenic radionuclides from tree rings. The different methods and data sets produce remarkably consistent posterior distributions for the model parameters. Bayesian inference results corroborate the hypothesis presented in a previous publication that the solar dynamo might be operating close to a critical bifurcation point characterized by the coexistence of two modes akin to normal and Grand Minima regimes. We show that the calibrated dynamo model, despite its simplicity, can be used to make predictions about solar cycles.

The operational practice of "hydropeaking" allows hydropower plants to cover peaks and deficits in energy demand, but it also impacts river ecosystems. The assessment of hydropeaking impacts plays an important role in safeguarding ecosystem services, but is challenging due to the relative importance of impacts at different sites. To compare impacts in hydropeaking rivers, we elicit expert judgment on the relative impacts of hydropeaking on river ecosystem services. Using the best-worst scaling (BWS) method, we compare the impact on the three categories of river ecosystem services (provisioning, regulating and cultural). Our respondents include 98 hydropower experts. Our analysis accounted for individual heterogeneity to assess how perceptions vary across regions, attitudes and representative river characteristics. We find trade-offs between provisioning and regulating services at the regional and local levels, which represents a key issue in dealing with climate change and ecosystem degradation. The best-affected services were water for power generation, raw materials, water for industrial activities and water for irrigation. The worst-affected services were fisheries and aquaculture, maintenance of population and habitat, and wild animals. Our results have implications for the safeguarding of river ecosystem services and the design of regulatory and incentive schemes for mitigation.

Abstract: In March 2014, typical coastal ice fields—so-called "kolobovnik"—with a total area of about 25 km², were found in the central part of the Southern Basin of Lake Baikal. A core of bottom sediments was collected from a depth of 1246 m in the area of their discovery. The composition of Baikal sediments and sedimentary matter extracted from ice monoliths (kolobovnik admixture) has been analyzed. Low concentrations of biogenic silica and diatom valves, the dominance of benthic species, and a coarser grain size composition of the kolobovnik admixture when compared to surface bottom sediments indicate that the source of the kolobovnik is the shallow zone of the lake. The data prove the existence of recent ice transport in Southern Baikal.

This study investigates in detail natural processes of modern sedimentation in South Baikal. The article presents data on the total flux of sedimentary matter, collected between March 1999 and March 2021. The quantity and composition of the recovered material is largely determined by SiO_2bio, which is directly dependent on annual blooms of diatoms in the lake. Since 2010, particle fluxes have generally increased. At the same time, there was a change in the dominant diatom species. So called “Melosira years” were replaced by years with increased productivity of species of the genus Synedra. Presumably, this happened due to climate change.

Детально исследованы процессы современного осадконакопления в Южном Байкале. В статье представлены данные об общих потоках осадочного материла, собранные с марта 1999 г. по март 2021 г. Количество и состав извлеченного материала во многом определя-ется SiO2био, который напрямую зависит от ежегодного цветения диатомовых водорослей в озере.С 2010 г. потоки частиц в целом возросли. Одновременно с этим произошла смена доминирующих видов диатомей. Так называемые “мелозирные годы” сменились годами с повышенной урожай-ностью видов рода Synedra. Предположительно это произошло в связи с изменением климата.
 

Functional diversity can be assessed remotely from optical sensors using vegetation index-based plant traits. Without effective corrections, employed reflectance values are affected by absorption and scattering processes in the atmosphere and on the ground, which modify radiance and irradiance values used for the reflectance retrieval. Additionally, the anisotropic nature of vegetation canopies induces observation and illumination angle-dependent reflectance variations. Often, however, the reflectance retrieval is not accurate enough to compensate for these effects in the atmosphere and on the surface, resulting in uncertain reflectance values. Furthermore, the effects in retrieved reflectance values propagate into derived products, like the vegetation indices used for calculating functional diversity, where they manifest as apparent differences between temporally close observations of the same area. A key to compensating for these effects lies in the capacity and consideration of several processing steps, such as atmospheric, topographic, and anisotropy correction.
To date, it is unknown how these effects and their correction influence the estimation of functional richness. Here, we estimate functional richness based on three differently retrieved reflectance datasets in the overlapping area of three consecutively acquired flight lines with short temporal differences but with three distinct acquisition geometries. We analyze how atmospheric, topographic, and anisotropy effects influence functional richness estimates and how functional richness varies due to different observation and illumination angles.
We show that reflectance data before correction for atmospheric, topographic, and anisotropy effects yield up to 15% larger median functional richness estimates compared to data after respective corrections. We discuss under which circumstances comprehensive data processing can reduce between-observation differences. Furthermore, we show that resulting functional richness estimates correlate with the number of shaded pixels (r² ≈ 0.7). Consequently, observations in the solar principal plane with more or fewer shadows can lead to larger or smaller functional richness estimates and to differences compared to observations perpendicular to the solar principal plane.
We conclude with recommendations concerning best-suited data processing and acquisition geometry for reliable and repeatable assessments of functional richness from optical remote sensing data and discuss applications to aerial and space-based observations of functional diversity.

Ocean Bottom Seismometers (OBS) are primarily designed to record seismic signals in marine environments. However, the fundamental principles of their operation as broadband instruments enable a wider range of applications. Here, we demonstrate that OBS systems can also effectively monitor the impact of sudden strong wind events on lakes. We conducted an experiment in Lake Lucerne (Switzerland), at the Muota Delta, using five OBS equipped with hydrophones. In addition, an Acoustic Doppler Current Profiler (ADCP) was moored to record current speed and direction. Comprehensive data analysis of weather measurements reveals a link between a strong wind and seismic signature. A foehn event that occurred on October 10th, 2023 in Switzerland caused a wind-lake interaction that triggered an internal current in the lake, with intensified deep near-bed velocity flowing in the upwind direction. Seismic signals induced by foehn winds correlate strongly with recorded increased sediment load, likely from resuspension or erosion, demonstrating how ocean-bottom seismometer networks can enhance environmental monitoring.

Wasserkraftwerke sollen nach der Fassung eines Fliessgewässers eine minimale Wassermenge im Fluss belassen. Diese Forderung nach Restwasser stellt sicher, dass die naturnahe Charakteristik des Gewässers sowie die Artenvielfalt der Tiere und Pflanzen erhalten bleiben. Ein Rückblick auf Entstehung und Vollzug der Restwasservorschriften enthüllt eine Leidensgeschichte, die angesichts von Klima- und Biodiversitätskrise dringend ein Happy End braucht.

Machine learning models have steadily improved in estimating inherent optical properties (IOPs) from remote sensing observations. Yet, their generalization ability when applied to new water bodies, beyond those they were trained on, is not well understood. We present a novel approach for assessing model generalization across various scenarios, including interpolation within in situ observation datasets, extrapolation beyond the training scope, and application to hyperspectral observations from the PRecursore IperSpettrale della Missione Applicativa (PRISMA) satellite involving atmospheric correction. We evaluate five probabilistic neural networks (PNNs), including novel architectures like recurrent neural networks, for their ability to estimate absorption at 443 and 675 nm from hyperspectral reflectance. The median symmetric accuracy (MdSA) worsens from ≥25% in interpolation scenarios to ≥50% in extrapolation scenarios, and reaches ≥80% when applied to PRISMA satellite imagery. Across all scenarios, models produce uncertainty estimates exceeding 40%, often reflecting systematic underconfidence. PNNs show better calibration during extrapolation, suggesting an intrinsic awareness of retrieval constraints. To address this miscalibration, we introduce an uncertainty recalibration method that only withholds 10% of the training dataset, but improves model calibration in 86% of PRISMA evaluations with minimal accuracy trade-offs. Resulting well-calibrated uncertainty estimates enable reliable uncertainty propagation for downstream applications. IOP retrieval uncertainty is predominantly aleatoric (inherent to the observations). Therefore, increasing the number of measurements from the same distribution or selecting a different neural network architecture trained on the same dataset does not enhance model accuracy. Our findings indicate that we have reached a predictability limit in retrieving IOPs using purely data-driven approaches. We therefore advocate embedding physical principles of IOPs into model architectures, creating physics-informed neural networks capable of surpassing current limitations.

Inland waters play a crucial role in the global carbon cycle, with lakes integrating carbon from various sources within their catchment in addition to that fixed by local primary productivity. Isotopic measurements of carbon pools can differentiate contributions from these sources, with natural abundance radiocarbon (¹⁴C) a particularly powerful tool due to the large range in ¹⁴C characteristics among carbon sources. Here, we present ¹⁴C measurements of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) from monthly water column samplings over the course of a year in Lake Geneva, a large oligotrophic hard water perialpine lake in Western Europe. We find that DIC in the lake is significantly ¹⁴C-depleted relative to the atmosphere primarily due to the dissolution of carbonate rocks in the lake's catchment. Variability in DI¹⁴C is largely tied to the Rhône River inflow, where DI¹⁴C values were also found to vary seasonally. DOC has a ¹⁴C signature similar to that of DIC, reflecting the fact that much of the lake DOC pool is autochthonous. However, more ¹⁴C-depleted DOC was observed in July and tied to increased river discharge from snow and glacier melt within the upper Rhône River basin. These observations shed light on carbon sources and dynamics within Lake Geneva and its alpine catchment and highlight the importance of preaged dissolved carbon inputs to the largest natural lake in Western Europe.

Cyanobacteria are ubiquitous aquatic organisms with a remarkable evolutionary history reaching as far as 1.9 Ga. They play a vital role in ecosystems yet also raise concerns due to their association with harmful algal blooms. Understanding the historical patterns and drivers behind these blooms is crucial for effective ecosystem management. Lake-sediment cores are valuable natural environmental archives, recording the histories of such blooms. Among others, phycocyanin, a pigment specific to cyanobacteria, emerges as a promising biomarker for reconstructing past cyanobacterial bloom events. However, due to the physicochemical properties of phycocyanin, there is no validated method available to extract and measure this pigment from complex sediment matrix. This study explores the applicability of hyperspectral imaging (HSI), a non-destructive technique, as a novel approach for high resolution in-situ detection and quantification of phycocyanin in lake sediments. Our experiments show that phycocyanin can be detected by HSI with an absorption trough at 620 nm (relative absorption band depth, RABD₆₂₀). We established a semi-quantitative calibration of the spectral index RABD₆₂₀ by conducting spiking experiments with phycocyanin standard (known phycocyanin mass) on organic-rich and mineral-rich sediments of varying water contents. We also assessed potential interference from chlorophyll a, another photosynthetic pigment, ensuring the reliability of hyperspectral phycocyanin measurements. Our findings demonstrate a significant correlation (R² ranging from 0.37 to 0.997) between the RABD₆₂₀ index and associated phycocyanin amounts in organic-rich and minerogenic sediments. This indicates the potential of the spectral index to directly measure in-situ biomarker concentrations on split sediment cores. Although confounding factors such as water and chlorophyll a content can influence the spectral signal, this method offers a rapid and non-destructive approach for studying historical cyanobacterial blooms in sedimentary records. This opens promising grounds for various applications, including ecosystem-health assessment and environmental change monitoring.

Study region: Central Europe, Gniezno Lake District, Poland
Study focus: The purpose of this study is to depict and explain long-term trends in surface water temperatures (LSWT) and chemical composition in Lake Licheńskie (LLi), which since 1960s has been involved in a cooling system of two electric power plants (PP) and thus has been prone to thermal pollution (TP). For the analyses we used 24-year long stationary monitoring and satellite data.
New hydrological insights for the region: We estimated that LLi was 3.81°C warmer than natural lakes in the region and demonstrated that the TP displayed spatial and seasonal variability. The data shows that owing to a reduction in the PP activity the LSWT has constantly been decreasing at a rate of 0.09°C·y⁻¹. Because, the lake has also been supplied with saltwater and highly alkaline effluents from nearby brown coal mine, LLi has been prone to salinization and alkalinization. The former process is still ongoing but alkalinization is declining, which is interpreted as a self-recovery of the lake triggered by a reduction in brown coal mining in the region. The knowledge of environmental conditions in the lake as well as its long-term changes is crucial for developing lake management strategies in the face of planned incorporation of the lake in a cooling system of the new nuclear power plant in the vicinity of the lake.

Turbidity is a key indicator of water quality and has significant impacts on underwater light availability of lakes. But the spatiotemporal variability of turbidity, which is important for understanding comprehensive changes in the water quality and status of aquatic ecosystems, remains unclear on a global scale. In this study, the spatial distribution pattern, seasonal variability, spatiotemporal variability, and influencing factors of turbidity in 774 lakes worldwide have been investigated using the turbidity product of Copernicus Global Land Service (CGLS) derived from Sentinel-3 OLCI. We found that 63.4% of lakes show low turbidity (≤ 5 Nephelometric Turbidity Units). The ranking of turbidity by climate zone is as follows: arid climate > tropical climate > temperate climate ∼ polar climate > cold climate. Turbidity decreased significantly in 40% of studied lakes, and increased significantly in 32% lakes. The lake with low turbidity has less seasonal variation, and there is a large seasonal variation in lake turbidity in the tropical and polar climate zones of Northern Hemisphere. Positive covariates to turbidity of global lakes include wind speed of lake, slope, surface runoff, and population in the catchment. Conversely, negative covariates include lake area, volume, discharge, inflow of lake, and GDP. Abundant water volume, favorable flow conditions, and more financial investments in lake management can help to reduce turbidity. These findings highlight the spatiotemporal changes of global lake turbidity and underlying mechanisms in controlling the variability, providing valuable insights for future lake water quality management.

Urbanization impacts Earth’s systems by increasing CO₂ emissions, creating urban heat islands (UHI), and affecting climate, energy use, and public health. Understanding urban microclimates and energy and CO₂ balances is crucial for designing effective climate change adaptation and mitigation strategies. This paper presents preliminary results from the UrbaNature project, focusing on vegetation’s role in urban microclimates. The goal is to develop a 3D microscale ecophysiological model for CO₂, water, and energy exchanges between plants and the urban atmosphere, including a 3D radiation exchange model for urban canyons with tree canopies. Using high-resolution digital surface models (DSMs), land cover, and leaf area index (LAI), we construct a 3D urban landscape of isometric voxels categorized as buildings, trees, terrain, or empty. This landscape supports radiation exchange simulations via a ray tracing algorithm, computing parameters like sky view factor (SVF), and light transmission coefficient, stored in look-up tables (LUTs). Meteorological data from an urban tower in Basel, Switzerland, is used to evaluate the model’s accuracy by comparing simulation results with ground-level station data. Preliminary results show that the model effectively replicates observed shortwave radiation patterns, highlighting its potential to enhance urban climate research and understanding of urban energy balance.

An array of lake sediment proxies including paleobotanic, geochemical, and historical records has been used to determine former environments of Bugbee Pond, a small, mesotrophic pond in northeastern Minnesota. Much research has been produced on the history of climate and vegetation change of the region, yet we have little information on the impact of human settlement. This well-dated, high resolution, multi-proxy record is important for its length and concentration on the historic period. The lake itself became established by ~7000 years ago. Pollen evidence suggests a transition between the regional Prairie Period to the Great Lakes mixed conifer – hardwood forest was established in the region at this time. XRF data suggest dry basin accumulation early in the record after ~7000 cal yr BP, but lake levels substantially increased by ~5600 cal yr BP, during a regionwide climatic transition to more humid conditions. Birch and boreal conifers increased after about 3800 cal yr BP; further increases in boreal conifers occurred by ~2000 cal yr BP. Anthropogenic vegetation changes during the Historic period, beginning in the late 19th century, is well represented by forest clearance of white pine (Pinus strobus), followed by increases in early successional species and an increased sediment accumulation rate due to land clearance. Establishment of farming communities locally are shown by occurrence of corn (Zea mays) and oat (Avena sativa) pollen, and pasturing and grazing are documented by Rumex, Fabaceae and Poaceae pollen, as well as coprophilous fungi, such as Sordaria. The increase and subsequent decline in Pb and S concentrations in the uppermost sediments are mirrored by historically documented, nearby industrial activities.

Les cartes historiques telles que la carte Siegfried fournissent des informations précieuses sur les paysages d'autrefois et leur utilisation par l'homme. Grâce à des méthodes d'apprentissage automatique, il est possible de déduire des données raster et vectorielles spatialement explicites de rivières, de lacs ou de zones humides à partir de ces cartes historiques. Des métriques écologiquement significatives pour la recherche et la pratique peuvent être calculées à partir de ces données, comme le nombre de confluences dans un bassin versant ou la modification de la composition des habitats. Dans cet article, nous présentons une sélection de résultats du projet de recherche HistoRiCH et concluons par des recommandations pour une utilisation prudente
des géodonnées obtenues à partir de cartes historiques.

Historische Karten wie die Siegfriedkarte liefern wertvolle Einblicke in frühere Landschaften und deren Nutzung durch den Menschen. Mit Machine Learning Methoden lassen sich aus den historischen Karten räumlich explizite Raster- und Vektordaten von Flüssen, Seen oder Feuchtgebieten ableiten. Daraus können ökologisch aussagekräftige Metriken für Forschung und Praxis berechnet werden wie z. B. die Anzahl Einmündungen in einem Einzugsgebiet oder die Veränderung der Lebensraumzusammensetzung. In diesem Artikel stellen wir ausgewählte Resultate des Forschungsprojekts HistoRiCH vor und schliessen mit Empfehlungen für eine umsichtige Nutzung von Geodaten, die aus historischen Karten gewonnen wurden.

Historical maps such as the Siegfried Map provide valuable insights into past landscapes and their utilisation by humans. Machine learning methods can be used to derive spatially explicit raster and vector data of rivers, lakes or wetlands from the historical maps. This can be used to calculate ecologically meaningful metrics for research and practice, such as the number of confluences in a catchment area or the change in habitat composition. In this article, we present selected results from the HistoRiCH research project and conclude with recommendations for the informed use of geodata obtained from historical maps.

Historische Karten wie die Siegfriedkarte liefern wertvolle Einblicke in frühere Landschaften und deren Nutzung durch den Menschen. Mit Machine Learning Methoden lassen sich aus den historischen Karten räumlich explizite Raster- und Vektordaten von Flüssen, Seen oder Feuchtgebieten ableiten. Daraus können ökologisch aussagekräftige Metriken für Forschung und Praxis berechnet werden wie z. B. die Anzahl Einmündungen in einem Einzugsgebiet oder die Veränderung der Lebensraumzusammensetzung. In diesem Artikel stellen wir ausgewählte Resultate des Forschungsprojekts HistoRiCH vor und schliessen mit Empfehlungen für eine umsichtige Nutzung von Geodaten, die aus historischen Karten gewonnen wurden.

The legacy of historic anthropogenic disturbance can significantly affect the structure and function of contemporary freshwater ecosystems. Environmental research and management that neglect anthropogenic legacy are likely to lead to a biased interpretation of present and future ecosystem dynamics. Yet, anthropogenic legacy remains poorly considered, mainly because of the challenges associated with its identification. Synthesizing past progress in legacy research, we present a conceptual framework for the systematic identification of anthropogenic legacy. We focus on the dynamic processes occurring during legacy formation (e.g., disturbance regime, ecosystem trajectories). Based on the review of relevant case studies, we discuss the historical and contemporary sources of information (e.g., communication, cartographic, paleoenvironmental sources) that can be employed for legacy identification. Finally, we provide practical examples of anthropogenic legacy identification in real-world freshwater ecosystems. Produced in multidisciplinary collaboration, this review presents a comprehensive approach to anthropogenic legacy to foster its informed and systematic consideration in freshwater research and management.

Historische Karten wie die Siegfriedkarte liefern wertvolle Einblicke in frühere Landschaften und deren Nutzung durch den Menschen. Mit Machine Learning Methoden lassen sich aus den historischen Karten räumlich explizite Raster- und Vektordaten von Flüssen, Seen oder Feuchtgebieten ableiten. Daraus können ökologisch aussagekräftige Metriken für Forschung und Praxis berechnet werden wie z. B. die Anzahl Einmündungen in einem Einzugsgebiet oder die Veränderung der Lebensraumzusammensetzung. In diesem Artikel stellen wir ausgewählte Resultate des Forschungsprojekts HistoRiCH vor und schliessen mit Empfehlungen für eine umsichtige Nutzung von Geodaten, die aus historischen Karten gewonnen wurden.

Les cartes historiques telles que la carte Siegfried fournissent des informations précieuses sur les paysages d'autrefois et leur utilisation par l'homme. Grâce à des méthodes d'apprentissage automatique, il est possible de déduire des données raster et vectorielles spatialement explicites de rivières, de lacs ou de zones humides à partir de ces cartes historiques. Des métriques écologiquement significatives pour la recherche et la pratique peuvent être calculées à partir de ces données, comme le nombre de confluences dans un bassin versant ou la modification de la composition des habitats. Dans cet article, nous présentons une sélection de résultats du projet de recherche HistoRiCH et concluons par des recommandations pour une utilisation prudente des géodonnées obtenues à partir de cartes historiques.

Bloom-forming algae present a unique challenge to water managers as they can significantly impair provision of important ecosystem services and cause health risks to humans and animals. Consequently, effective short-term algae forecasts are important as they provide early warnings and enable implementation of mitigation strategies. In this context, machine learning (ML) emerges as a promising forecasting tool. However, the performance of ML models is heavily dependent on the availability of appropriate training data. Consequently, it is essential to determine the volume of data necessary to develop reliable ML forecasts. Understanding this will guide future monitoring strategies, optimize resource allocation, and set realistic expectations for management outcomes. In this study, we used 30 years of fortnightly measurements of 13 different parameters from a lake in the English Lake District (UK) to examine the impact of training data duration on the performance of ML models for forecasting chlorophyll-a two weeks in advance. Once training data availability exceeded four years, a Random Forest model was found to consistently outperform naive benchmarks (mean absolute percentage error 16.4 % lower than the best-performing benchmark). With more than 5 years of training data, model performance generally continued to improve, but with diminishing returns. Furthermore, it was found that equivalent and, in some cases, better performance could be achieved by only using a subset of the most important input features. Additionally, it was found that reducing the sampling frequency had negative impacts on performance, both due to the reduced number of training observations available, and increased forecast horizon. Our findings demonstrate that for lakes ecologically similar to the study site, a consistent and regular sampling programme focused on monitoring a limited number of key parameters can provide sufficient observations for generating short-term algae forecasts after approximately five years of data collection. Importantly, this result provides justification for the initiation of new monitoring programmes for sites where algal blooms are a concern, and suggests that there are likely many pre-existing monitoring datasets which would be suitable for training algae forecast models.

Background Environmental reservoirs of antibiotic resistance pose a threat to human and animal health. Aquatic biofilms impacted by wastewater effluent (WW) are known environmental reservoirs for antibiotic resistance; however, the relative importance of biotic factors and abiotic factors from WW on the abundance of antibiotic resistance genes (ARGs) within aquatic biofilms remains unclear. Additionally, experimental evidence is limited within complex aquatic microbial communities as to whether genes bearing low sequence similarity to validated reference ARGs are functional as ARGs.

Results To disentangle the effects of abiotic and biotic factors on ARG abundances, natural biofilms were previously grown in flume systems with different proportions of stream water and either ultrafiltered or non-ultrafiltered WW. In this study, we conducted deep shotgun metagenomic sequencing of 75 biofilm, stream, and WW samples from these flume systems and compared the taxonomic and functional microbiome and resistome composition. Statistical analysis revealed an alignment of the resistome and microbiome composition and a significant association with experimental treatment. Several ARG classes exhibited an increase in normalized metagenomic abundances in biofilms grown with increasing percentages of non-ultrafiltered WW. In contrast, sulfonamide and extended-spectrum beta-lactamase ARGs showed greater abundances in biofilms grown in ultrafiltered WW compared to non-ultrafiltered WW. Overall, our results pointed toward the dominance of biotic factors over abiotic factors in determining ARG abundances in WW-impacted stream biofilms and suggested gene family-specific mechanisms for ARGs that exhibited divergent abundance patterns. To investigate one of these specific ARG families experimentally, we biochemically characterized a new beta-lactamase from the Planctomycetota (Phycisphaeraceae). This beta-lactamase displayed activity in the cleavage of cephalosporin analog despite sharing a low sequence identity with known ARGs.

Conclusions This discovery of a functional planctomycete beta-lactamase ARG is noteworthy, not only because it was the first beta-lactamase to be biochemically characterized from this phylum, but also because it was not detected by standard homology-based ARG tools. In summary, this study conducted a metagenomic analysis of the relative importance of biotic and abiotic factors in the context of WW discharge and their impact on both known and new ARGs in aquatic biofilms.

Swiss geosciences are at the heart of major national and global challenges that our society is facing, including climate change and weather extremes, long-term environmental trends, natural hazards (e.g. landslides, floods, seismic and volcanic events), the energy transition towards a green and blue economy, sustainable management of natural resources (e.g. water, soils, ecosystems, critical metals, building materials), and the increasing interest towards extra-terrestrial life and resources. In order to remain at the forefront of geosciences research and provide the fertile environment necessary for groundbreaking findings addressing these societal challenges, the Swiss Geosciences Community proposes five large infrastructures, organised into four pillars built on a common datadriven research foundation. [...]

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are common in lake sediments, where they are frequently employed to infer mean annual air temperatures (MAAT) or air temperatures of months above freezing (MAF) using the MBT'_5Me lipid paleothermometer. The reliable reconstruction of such temperatures, however, requires robust calibration functions. Here, we investigated brGDGT distributions in surface sediments from 41 freshwater lakes located along an altitudinal gradient across the Alps (Central Europe) and spanning a MAAT range from 1.3 to 12.9 °C. Linear regression analysis demonstrates that fractional abundances of brGDGTs are strongly correlated with MAAT and MAF allowing to establish regional MBT'_5Me-based transfer functions: MAAT (°C) = −2.19 + 31.91 × MBT'_5Me (r² = 0.72; RMSE = 1.51 °C) and MAF (°C) = 4.81 + 15.64 × MBT'_5Me (r² = 0.64, RMSE = 0.92 °C). Stepwise forward selection yielded the following, alternate temperature calibrations: MAAT (°C) = 7.11 + 67.66 × Ib – 13.54 × IIIa (r² = 0.72; RMSE = 1.47 °C) and MAF (°C) = 5.19 + 16.22 × Ia (r² = 0.66; RMSE = 0.98 °C). Our results demonstrate that the above calibration functions allow precise temperature reconstructions using lacustrine sediment records. However, our data also show that high-altitude lakes are more prone to warm bias and that lakes characterized by comparatively high abundances of 6-methyl brGDGTs show aberrant behaviors with temperature offsets up to ∼7 °C. Determining the IR_6Me, as an independent control complementary to the MBT'_5Me, is thus essential to validate the robustness of brGDGT-based temperature reconstructions of past climates. A cut-off value of 0.50 for the IR_6Me is here proposed, after which MBT'_5Me-reconstructed MAATs from lacustrine archives should be regarded as unreliable.

The global nitrogen (N) cycle has been strongly altered by anthropogenic activities, including increased input of bioavailable N into aquatic ecosystems. Freshwater sediments are hotspots with regards to the turnover and elimination of fixed N, yet the environmental controls on the microbial pathways involved in benthic N removal are not fully understood. Here, we analyze the abundance and expression of microbial genes involved in N transformations using metagenomics and -transcriptomics across sediments of 12 Swiss lakes that differ in sedimentation rates and trophic regimes. Our results indicate that microbial N loss in these sediments is primarily driven by nitrification coupled to denitrification. N-transformation gene compositions indicated three groups of lakes: agriculture-influenced lakes characterized by rapid depletion of oxidants in the sediment porewater, pristine-alpine lakes with relatively deep sedimentary penetration of oxygen and nitrate, and large, deep lakes with intermediate porewater hydrochemical properties. Sedimentary organic matter (OM) characteristics showed the strongest correlations with the community structure of microbial N-cycling communities. Most transformation pathways were expressed, but expression deviated from gene abundance and did not correlate with benthic geochemistry. Cryptic N-cycling may maintain transcriptional activity even when substrate levels are below detection. Sediments of large, deep lakes generally showed lower in-situ N gene expression than agriculture-influenced lakes, and half of the pristine-alpine lakes. This implies that prolonged OM mineralization in the water column can lead to the suppression of benthic N gene expression.

The pathway of dense river inflows into lakes, which affects the lake water quality, is not accurately predicted by existing models. The pathway of a dense riverine inflow in a lake with a submerged canyon is analyzed based on measurements during a 4-month period of weakening lake stratification and weakening density excess between river and epilimnion. In line with models, the dense riverine inflow plunges upon entering the lake, continues as an underflow on the sloping lake bottom, and finally intrudes at its level of neutral buoyancy. Underflow and interflow velocities are O(0.1 m s⁻¹). The river inflow is finally trapped in the pycnocline most of the time, even when the river's density excess and the lake's stratification are marginal. This trapping in the pycnocline is explained by the reduction of the inflow density excess due to the intense plunging mixing, which is an order of magnitude larger than that obtained in confined laboratory flumes. The pathway of the dense riverine inflow is affected by interactions of the underflow with the lake bottom and sedimentary processes. A canyon carved by the underflows confines and accelerates the underflow, which enhances its capacity to entrain and carry sediment. The entrainment of sediment that was previously deposited on the canyon bottom accelerates the underflow. Due to both effects, the underflow can temporarily break through the pycnocline and reach the hypolimnion. Existing models explain these observations qualitatively, but a quantitative prediction would require better parameterizations of the plunging mixing and the sedimentary processes.

In this study, we investigated the temporal and spatial quantitative changes in the concentration of antibiotic resistance gene (ARG) markers in a municipal wastewater treatment plant (WWTP). Four ARGs conferring resistance to different classes of antibiotics (ermB, sul1, tet[W], and bla_CTXM) and a gene used as a proxy for ARG pollution (intl1) were quantified in two separate sampling campaigns covering two and half years of operation of the WWTP. First, a systematic monthly monitoring of multiple points in the inlet and the outlet revealed an absolute decrease in the concentration of all analyzed ARGs. However, the relative abundance of sul1 and intl1 genes relative to the total bacterial load (estimated using the universal marker 16S rDNA) increased in the outlet samples as compared to the inlet. To pinpoint the exact stage of removal and/or enrichment within the WWTP, a second sampling including the stages of the biological treatment was performed bimonthly. This revealed a distinct enrichment of sul1 and intl1 genes during the biological treatment phase. Moreover, the temporal and spatial variations in ARG abundance patterns within the WWTP underscored the complexity of the dynamics associated with the removal of ARGs during wastewater treatment. Understanding these dynamics is pivotal for developing efficient strategies to mitigate the dissemination of ARGs in aquatic environments. Practitioner points: Regular monitoring of ARG markers in WWTPs is essential to assess temporal and spatial changes, aiding in the development of effective mitigation strategies. Understanding the dynamics of ARG abundance during biological treatment is crucial for optimizing processes and minimizing dissemination in aquatic environments. Increased relative abundance of certain ARGs highlights potential enrichment during wastewater treatment, necessitating targeted interventions. Systematic monitoring of multiple points within WWTPs can provide valuable insights into the efficacy of treatment processes in reducing ARG levels over time. The complexity of ARG abundance patterns underscores the need to develop holistic approaches to tackle antibiotic resistance in wastewater systems.

Climate change exerts a profound impact on lakes, eliciting responses that range from gradual to abrupt transitions. When reaching critical tipping points, the established lake dynamics stand to undergo substantial modifications, setting off a chain reaction that reverberates through the entire ecosystem. This lake shift ripples into related ecosystem services and even influences the well-being of human communities. Despite the importance of lake shifts, we lack a systematic overview of their occurrence, mainly due to the lack of systematic data at the global scale. We reviewed the literature focusing on climate-related lake shifts and assessed how satellite Earth Observation (EO) has contributed to the research topic, and what we can unlock from this novel data. Our results show that EO data are used in only 9% of studies on lake shifts, although this fraction has increased since 2012. EO data is most commonly used to assess shifts in surface extent, ice coverage, or phytoplankton phenology. These variables are directly observable and the spatio-temporal resolution of EO satellites is of great advantage. But lake shifts can also be identified indirectly from EO data, as in the example of the vertical mixing of lake water, which can be described on the basis of surface patterns. In all possible applications, we expect increasing use of EO satellites in the future, including the development of early warning systems that promise to provide timely alerts regarding impending lake shifts, thus serving as a vanguard against abrupt alterations that could ripple through interconnected ecosystem services.

Remote Oceania was among the last places settled by humans. However, the timing of initial human settlements and the early introduction of horticulture remain debated. We retrieved a sediment core close to Teouma, the oldest cemetery in Remote Oceania that reveals evidence of initial settlement, horticulture practice, and concurrent climatic conditions on the island of Efate, Vanuatu. Sedimentary biomarkers indicating human presence (coprostanol and epicoprostanol), and taro cultivation (palmitone), increase simultaneously, attesting to the early introduction of horticulture by first settlers. The precipitation signal preserved in leaf waxes shows that the initial settlement occurred during a period of increasing wetness—climatic conditions favourable for the establishment of horticulture. The timing of these events is constrained by a high-resolution radiocarbon chronology that places the first unequivocal trace of human activity and horticulture at 2800 years ago. These findings advance our understanding of human history in the Pacific.

Patagonia is a unique area for climate studies, exposed to the strong Southern Hemisphere Westerly Winds (SWW) and modulated by the Southern Annular Mode (SAM). Patagonia is also affected by volcanic eruptions of the Andean Mountain Range, and is rich in lacustrine environments, which are ideal for paleocological and paleoclimatological reconstructions. Sediments of Patagonian lakes provide an excellent opportunity to study the responses of aquatic communities to major climatic and environmental events in still pristine freshwater ecosystems. Here, we present a high-resolution paleolimnological reconstruction using testate amoebae and chironomid assemblages and compare it with organic and inorganic sediment geochemistry (Ca, K, Ti, N, TOC, TOC/N, δ¹⁵N, δ¹³C) from a sediment core of Laguna Polo (49°S, Santa Cruz, Argentina) covering the last ca. 1300 years. Our results imply a warm-dry and productive environment from around 1300–1400 CE, a cold and less productive environment from ca. 1400–1700 CE, broadly corresponding to the Little Ice Age (LIA). The latter period is followed by high volcanic activity between ca. 1700 and 1960 CE. The tephra layers are known from other records in the vicinity and are preliminarily attributed to the eruptions of the adjacent Lautaro Volcano. A warm-stenothermic chironomid assemblage indicates a progressive increase in temperature in the most recent time after the last eruption, attributed to Lautaro Volcano in 1960 CE.

Catchment urbanisation results in urban streams being exposed to a multitude of stressors. Notably, stressors originating from diffuse sources have received less attention than stressors originating from point sources. Here, advances related to diffuse urban stressors and their consequences for stream benthic communities are summarised by reviewing 92 articles. Based on the search criteria, the number of articles dealing with diffuse urban stressors in streams has been increasing, and most of them focused on North America, Europe, and China. Land use was the most common measure used to characterize diffuse stressor sources in urban streams (70.7 % of the articles characterised land use), and chemical stressors (inorganic nutrients, xenobiotics, metals, and water properties, including pH and conductivity) were more frequently reported than physical or biological stressors. A total of 53.3 % of the articles addressed the impact of urban stressors on macroinvertebrates, while 35.9 % focused on bacteria, 9.8 % on fungi, and 8.7 % on algae. Regarding ecosystem functions, almost half of the articles (43.5 %) addressed changes in community dynamics, 40.3 % addressed organic matter decomposition, and 33.9 % addressed nutrient cycling. When comparing urban and non-urban streams, the reviewed studies suggest that urbanisation negatively impacts the diversity of benthic organisms, leading to shifts in community composition. These changes imply functional degradation of streams. The results of the present review summarise the knowledge gained to date and identify its main gaps to help improve our understanding of urban streams.

La urbanización de las cuencas expone a los arroyos urbanos a multitud de factores de estrés. Destacan aquellos que tienen su origen en fuentes difusas, los cuales han recibido menos atención que aquellos estresores procedentes de fuentes puntuales. Este estudio resume los avances relacionados con los estresores urbanos difusos y sus consecuencias para las comunidades bentónicas fluviales, a partir de la revisión de 92 artículos. En base a los criterios de búsqueda, el número de artículos que tratan sobre estresores urbanos difusos en arroyos ha ido en aumento, la mayoría de ellos centrados en América del Norte, Europa y China. Los usos del suelo fueron la variable más utilizada para caracterizar las fuentes difusas de estrés (el 70.7 % de los artículos caracterizó los usos del suelo), y los factores de estrés químico (nutrientes inorgánicos o propiedades del agua, como pH o conductividad) se mencionaron con más frecuencia que los factores de estrés físico o biológico. El 53.3 % de los trabajos abordaron el impacto de los estresores urbanos difusos sobre los macroinvertebrados, mientras que el 35.9 % se centraron en bacterias, el 9.8 % en hongos y el 8.7 % en algas. En cuanto al funcionamiento de los ecosistemas, prácticamente la mitad de los trabajos (43.5 %) analizó cambios en la dinámica de las comunidades, el 40.3 % en la descomposición de materia orgánica y el 33.9 % en los ciclos de los nutrientes. Al comparar los arroyos urbanos y no urbanos, los trabajos revisados sugieren que la urbanización afecta negativamente a la diversidad de organismos bentónicos, provocando cambios en la composición de la comunidad. Estos cambios implican la degradación funcional de los arroyos. Los resultados de la presente revisión resumen los conocimientos adquiridos hasta hoy e identifican sus principales carencias a fin de ayudar a mejorar nuestra comprensión de los arroyos urbanos.

The highly biodiverse Lake Poso, located in Central Sulawesi, Indonesia, can be considered one of the least studied ancient lakes in the world. Here, we present a comprehensive analysis of Lake Poso's hydrology and hydrochemistry, shedding light on factors that may have contributed to the exceptional biodiversity. Riverine and lake water chemical compositions indicated a soft water lake and relative major cation and anion abundances of Ca²⁺ ≫ Mg²⁺ > Na⁺ > K⁺ and HCO₃^– ≫ SO₄²⁻ > Cl⁻, primarily a result of the high annual precipitation and chemical weathering of calcareous-siliceous metamorphic bedrock. Lake Poso’s nutrient concentrations were low (average DIN/TDP mass ratio of 6.2 and 50.9 for the lake surface water and its tributaries, respectively), indicating that most of the inlets were P-limited and that the lake was likely P-limited as well. Metal pollutants indicated a minor to moderate impact of anthropogenic land use (∼32 % of the catchment area). Water isotopic compositions of the different tributaries clearly delineated rivers draining higher elevation catchments with lower δ²H and δ¹⁸O from those draining lower elevation catchments with higher δ²H and δ¹⁸O. Surface lake water isotopic compositions indicated detectable evaporation from the lake leading toward more enriched isotope compositions than the integrated source signal. Overall, the findings suggested that Lake Poso remains relatively resilient to anthropogenic land use and related nutrient and pollutant inputs. However, ongoing alterations to its hydrological balance due to significant changes in land use may drive the lake towards higher trophic levels in the future.

The extent of littoral influence on lake gas dynamics remains debated in the aquatic science community due to the lack of direct quantification of lateral gas transport. The prevalent assumption of diffusive horizontal transport in gas budgets fails to explain anomalies observed in pelagic gas concentrations. Here, we demonstrate through high-frequency measurements in a eutrophic lake that daily convective horizontal circulation generates littoral-pelagic advective gas fluxes one order of magnitude larger than typical horizontal fluxes used in gas budgets. These lateral fluxes are sufficient to redistribute gases at the basin-scale and generate concentration anomalies reported in other lakes. Our observations also contrast the hypothesis of pure, nocturnal littoral-to-pelagic exchange by showing that convective circulation transports gases such as oxygen and methane toward both the pelagic and littoral zones during the daytime. This study challenges the traditional pelagic-centered models of aquatic systems by showing that convective circulation represents a fundamental lateral transport mechanism to be integrated into gas budgets.

Das interdisziplinäre Forschungsprogramm «Wasserbau und Ökologie» des Bundesamts für Umwelt vereint seit 21 Jahren erfolgreich Wasserbauingenieur:innen sowie Ökolog:innen des ETH-Bereichs zur Erarbeitung von wissenschaftlichen Grundlagen zum nachhaltigen Wasserbau und zur Biodiversität entlang von Fliessgewässern. Die Programmphase «Lebensraum Gewässer – Sedimentdynamik und Vernetzung» wurde unlängst abgeschlossen, und die wissenschaftlichen und praxisorientierten Produkte sind auf der Webseite www.rivermanagement.ch verfügbar. Die aktuelle Programmphase mit dem Titel «Resiliente Fliessgewässer: Refugien – Vernetzung – Trittsteine» baut auf den gewonnenen Ergebnissen auf und vertieft die interdisziplinäre Zusammenarbeit. Der vorliegende Beitrag greift exemplarisch einige Ergebnisse der letzten Phase auf und zeigt, wie diese weiterbearbeitet werden.

Le programme de recherche interdisciplinaire « Aménagement et écologie des cours d’eau » de l’Office fédéral de l’environnement réunit depuis 21 ans avec succès des ingénieurs hydrauliciens et des écologistes du domaine des EPF afin d’élaborer des bases scientifiques pour l’aménagement durable des cours d’eau et de la biodiversité le long de ces derniers. Le dernier projet « Milieux fluviaux – dynamique sédimentaire et connectivité » du programme s’est achevé récemment et des produits scientifiques et pratiques sont disponibles sur le site www.rivermanagement.ch. Le projet actuel, intitulé « Cours d’eau résilients: refuges – connectivité – relais », s’appuie sur les résultats acquis précédemment tout en approfondissant la collaboration interdisciplinaire. Le présent article reprend à titre d’exemple quelques résultats du dernier projet et montre comment ils continuent à être développés.

L'état global de la qualité des lacs en Suisse a tendance à s'améliorer, mais de nombreux problèmes d'oxygénation dans le fond des lacs persistent. Ce phénomène, lié aux concentrations actuelles et passées de phosphore, demeure préoccupant. La modélisation au coeur de cette étude vise à guider le choix d'approches simples mais appropriées pour la gestion des lacs. Deux exemples d'applications pour les lacs de Schiffenen et de Baldegg sont illustrés.

À chaque éclusée, les contraintes hydrauliques s'intensifient dans les habitats individuels au sein de la mosaïque d'habitats du cours d'eau. Ces contraintes hydrauliques peuvent entraîner une dérive passive des macroinvertébrés, au cours de laquelle une partie des individus sont arrachés du fond du lit. À long terme, ce phénomène entraîne une modification de la composition et de la biomasse de la communauté des macroinvertébrés.
    Dans notre étude de terrain, nous avons utilisé un chenal expérimental portatif pour quantifier, dans différents types d’habitats, l'intensité de la dérive des macroinvertébrés provoquée par une augmentation des contraintes hydrauliques telle qu'elle pourrait être causée par les éclusées. Nos résultats montrent que cette augmentation des contraintes hydrauliques peut avoir des effets différents selon les types d'habitats. Dans les habitats à courant lent (vitesse d'écoulement <0,5 cm/s), la hausse de la vitesse d'écoulement est le paramètre déterminant pour l’intensification de la dérive passive. Dans les habitats à courant rapide (> 0,5 cm/s), le paramètre dominant est en revanche le rapport entre la vitesse d'écoulement maximale et minimale (rapport des vitesses d'écoulement).
    Pour réduire de façon ciblée le risque de dérive des macroinvertébrés causé par les éclusées, les mesures devraient viser à (i) limiter l'augmentation de la vitesse d'écoulement dans les habitats à courant lent et à (ii) maintenir le rapport des vitesses d'écoulement aussi bas que possible dans les habitats à courant rapide. Cela exige une considération explicite (par modélisation, par exemple) de la distribution aussi bien spatiale que temporelle des contraintes hydrauliques dans les tronçons soumis aux éclusées.

Bei Schwall-Sunk-Betrieb erhöhen sich mit jedem Schwall die hydraulischen Kräfte in den einzelnen Habitaten des Habitatmosaiks. Dies kann zur passiven Drift von Makroinvertebraten führen, bei der Individuen unfreiwillig von der Flusssohle abgelöst werden. Längerfristig beeinträchtigt dies die Zusammensetzung und Biomasse der Makroinvertebraten-Gemeinschaft.
    In unserem Feldexperiment haben wir mit einer tragbaren Versuchsrinne die passive Drift von Makroinvertebraten unter erhöhten hydraulischen Kräften, wie sie beim Schwall-Sunk-Betrieb auftreten können, gemessen. Unsere Resultate zeigen, dass sich eine Erhöhung der hydraulischen Kräfte in unterschiedlichen Habitattypen unterschiedlich auswirken kann. In langsam durchflossenen Habitaten (Fliessgeschwindigkeit < 0,5 cm/s) ist die Zunahme der Fliessgeschwindigkeit ausschlaggebend für die Erhöhung der passiven Drift. In schnell durchflossenen Habitaten (> 0,5 cm/s) hingegen ist das Verhältnis zwischen minimaler und maximaler Fliessgeschwindigkeit (Fliessgeschwindigkeitsverhältnis) hauptverantwortlich für die Zunahme der passiven Drift.
    Um das durch den Schwall-Sunk-Betrieb verursachte Driftrisiko von Makroinvertebraten gezielt zu reduzieren, sollten Massnahmen darauf abzielen, dass (i) in langsam durchflossenen Habitaten die Fliessgeschwindigkeit möglichst wenig erhöht und (ii) in schnell durchflossenen Habitaten das  Fliessgeschwindigkeitsverhältnis möglichst gering gehalten wird. Dies bedarf einer expliziten Betrachtung (z. B. Modellierung) der räumlichen, aber auch zeitlichen Verteilung der hydraulischen Kräfte in einer Schwall-Sunk-Strecke.

Bei Schwall-Sunk-Betrieb erhöhen sich mit jedem Schwall die hydraulischen Kräfte in den einzelnen Habitaten des Habitatmosaiks. Dies kann zur passiven Drift von Makroinvertebraten führen, bei der Individuen unfreiwillig von der Flusssohle abgelöst werden. Längerfristig beeinträchtigt dies die Zusammensetzung und Biomasse der Makroinvertebraten-Gemeinschaft.
    In unserem Feldexperiment haben wir mit einer tragbaren Versuchsrinne die passive Drift von Makroinvertebraten unter erhöhten hydraulischen Kräften, wie sie beim Schwall-Sunk-Betrieb auftreten können, gemessen. Unsere Resultate zeigen, dass sich eine Erhöhung der hydraulischen Kräfte in unterschiedlichen Habitattypen unterschiedlich auswirken kann. In langsam durchflossenen Habitaten (Fliessgeschwindigkeit < 0,5 cm/s) ist die Zunahme der Fliessgeschwindigkeit ausschlaggebend für die Erhöhung der passiven Drift. In schnell durchflossenen Habitaten (> 0,5 cm/s) hingegen ist das Verhältnis zwischen minimaler und maximaler Fliessgeschwindigkeit (Fliessgeschwindigkeitsverhältnis) hauptverantwortlich für die Zunahme der passiven Drift.
    Um das durch den Schwall-Sunk-Betrieb verursachte Driftrisiko von Makroinvertebraten gezielt zu reduzieren, sollten Massnahmen darauf abzielen, dass (i) in langsam
durchflossenen Habitaten die Fliessgeschwindigkeit möglichst wenig erhöht und (ii) in schnell durchflossenen Habitaten das Fliessgeschwindigkeitsverhältnis möglichst gering
gehalten wird. Dies bedarf einer expliziten Betrachtung (z. B. Modellierung) der räumlichen, aber auch zeitlichen Verteilung der hydraulischen Kräfte in einer Schwall-Sunk-Strecke.

À chaque éclusée, les contraintes hydrauliques s'intensifient dans les habitats individuels au sein de la mosaïque d'habitats du cours d'eau. Ces contraintes hydrauliques peuvent entraîner une dérive passive des macroinvertébrés, au cours de laquelle une partie des individus sont arrachés du fond du lit. À long terme, ce phénomène entraîne une modification de la composition et de la biomasse de la communauté des macroinvertébrés.
    Dans notre étude de terrain, nous avons utilisé un chenal expérimental portatif pour quantifier, dans différents types d'habitats, l'intensité de la dérive des macroinvertébrés provoquée par une augmentation des contraintes hydrauliques telle qu'elle pourrait être causée par les éclusées. Nos résultats montrent que cette augmentation des contraintes hydrauliques peut avoir des effets différents selon les types d'habitats. Dans les habitats à courant lent (vitesse d’écoulement < 0,5 cm/s), la hausse de la vitesse d'écoulement est le paramètre déterminant pour l'intensification de la dérive passive. Dans les habitats à courant rapide (> 0,5 cm/s), le paramètre dominant est en revanche le rapport entre la vitesse d'écoulement maximale et minimale (rapport des vitesses d'écoulement).
    Pour réduire de façon ciblée le risque de dérive des macroinvertébrés causé par les éclusées, les mesures devraient viser à (i) limiter l'augmentation de la vitesse d'écoulement dans les habitats à courant lent et à (ii) maintenir le rapport des vitesses d'écoulement aussi bas que possible dans les habitats à courant rapide. Cela exige une considération explicite (par modélisation, par exemple) de la distribution aussi bien spatiale que temporelle des contraintes hydrauliques dans les tronçons soumis aux éclusées.

Marine sediments are one of the largest organic carbon (OC) sinks on Earth. Yet, major knowledge gaps remain in our understanding of sedimentary OC cycling, particularly regarding temperature-induced alteration processes of OC from different sources. Here, we investigate OC-rich sediments of Guaymas Basin (Gulf of California) across two hydrothermal areas, one with only conductive geothermal heating and the other additionally experiencing seepage of hydrocarbon-rich fluids from deeper layers. We use Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) to investigate diagenetic OC changes and show that cold control sites in both hydrothermal areas are dominated by similar contributions of lipid-derived compounds, nitrogenous (likely protein-derived) compounds, carbohydrates, and polyaromatic hydrocarbons (PAHs). These OC compound groups are largely derived from phytoplankton detritus from overlying water. Conductively heated sediments, which reach in situ temperatures of ∼ 80 °C, have similar general OC compositions and contents to these cold sites, but show evidence of diagenetic modifications of individual carbohydrate groups in deeper layers. By contrast, strong decreases in carbohydrate and nitrogenous compound abundances at the seep sites indicate that these compound groups are not only modified but also selectively degraded at the higher temperatures (>80 °C) of these sites. Increases in pyrolysis products of PAHs, prist-1-ene, and alkanes with depth, moreover, show that import of OC by deep hydrothermal fluids contributes significantly to sedimentary OC pools mainly in deeper layers of these sites. Our study provides the first comprehensive analysis of major OC compound groups in Guaymas Basin sediment and indicates that the supply of OC by hydrothermal fluid flow only has minor impacts on particulate organic matter compositions at the seafloor, even at active seep sites. We furthermore show that temperatures up to ∼ 80 °C already result in thermochemical modifications of organic matter (OM) that are potentially linked to the onset of kerogen formation. The sequence and time scales of chemical modifications and activations in relation to temperature are an important subject for future investigations.

It has been debated whether wastewater treatment plants (WWTPs) primarily act to attenuate or amplify antibiotic resistance genes (ARGs). However, ARGs are highly diverse with respect to their resistance mechanisms, mobilities, and taxonomic hosts and therefore their behavior in WWTPs should not be expected to be universally conserved. We applied metagenomic sequencing to wastewater influent and effluent samples from 12 international WWTPs to classify the behavior of specific ARGs entering and exiting WWTPs. In total, 1079 different ARGs originating from a variety of bacteria were detected. This included ARGs that could be mapped to assembled scaffolds corresponding to nine human pathogens. While the relative abundance (per 16S rRNA gene) of ARGs decreased during treatment at 11 of the 12 WWTPs sampled and absolute abundance (per mL) decreased at all 12 WWTPs, increases in relative abundance were observed for 40% of the ARGs detected at the 12th WWTP. Also, the relative abundance of mobile genetic elements (MGE) increased during treatment, but the fraction of ARGs known to be transmissible between species decreased, thus demonstrating that increased MGE prevalence may not be generally indicative of an increase in ARGs. A distinct conserved resistome was documented in both influent and effluent across samples, suggesting that well-functioning WWTPs generally attenuate influent antibiotic resistance loads. This work helps inform strategies for wastewater surveillance of antibiotic resistance, highlighting the utility of tracking ARGs as indicators of treatment performance and relative risk reduction.

Fresh produce is suggested to contribute highly to shaping the gut resistome. We investigated the impact of pig manure and irrigation water quality on microbiome and resistome of field-grown lettuce over an entire growth period. Lettuce was grown under four regimes, combining soil amendment with manure (with/without) with sprinkler irrigation using river water with an upstream wastewater input, disinfected by UV (with/without). Lettuce leaves, soil, and water samples were collected weekly and analyzed by bacterial cultivation, 16S rRNA gene amplicon sequencing, and shotgun metagenomics from total community DNA. Cultivation yielded only few clinically relevant antibiotic-resistant bacteria (ARB), but numbers of ARB on lettuce increased over time, while no treatment-dependent changes were observed. Microbiome analysis confirmed a temporal trend. Antibiotic resistance genes (ARGs) unique to lettuce and water included multidrug and β-lactam ARGs, whereas lettuce and soil uniquely shared mainly glycopeptide and tetracycline ARGs. Surface water carried clinically relevant ARB (e.g. ESBL-producing Escherichia coli or Serratia fonticola) without affecting the overall lettuce resistome significantly. Resistance markers including biocide and metal resistance were increased in lettuce grown with manure, especially young lettuce (increased soil contact). Overall, while all investigated environments had their share as sources of the lettuce resistome, manure was the main source especially on young plants. We therefore suggest minimizing soil-vegetable contact to minimize resistance markers on fresh produce.

Microbial biodiversity is fundamental to maintain ecosystem functioning in seasonally variable ecosystems. However, it remains unclear how alterations in water availability caused by episodic drying compromise the ability of stream microbes to maintain multiple functions simultaneously (e.g., primary production and carbon cycling). Using data from 32 streams, we investigated how the phenology of annual drying influences stream sediment microbial biodiversity and their capacity to sustain multifunctionality. Our results showed that stream multifunctionality and most bacteria did not respond to changes in drying phenology. Only two bacterial groups, the drying-resistant Sphingobacteriia and the drying-sensitive Acidobacteria_Gp7, exhibited positive associations with multifunctionality; whereas, bacterial diversity showed a negative correlation with functions. Among these biodiversity aspects, Sphingobacteriia showed the strongest capacity to maintain multifunctionality at low and moderate performance levels. Our findings will help to better understand the mechanisms through which biodiversity sustains the functioning of seasonally variable streams and their responses to global change.

Hydrological drought, characterized by a significant deficiency in rainfall events, promotes natural desiccation processes. The reduction in water recharge and the loss of freshwater ecosystems pose urgent challenges in the face of increasing global population and the escalating demand for water resources.

The variability in the duration of no-flow periods can have profound implications for ecosystem functioning, specifically impacting the microbiota residing in streambed sediments and the vital processes they perform. The streambed serves as an ecotone where microorganisms form biofilms, playing critical roles in in-stream biogeochemical cycles and greenhouse gas emissions. Consequently, prolonged desiccation periods and subsequent rewetting episodes can disrupt, limit, or alter the functions and structure of microbial communities, thereby compromising the overall functioning of aquatic ecosystems. Understanding how streambed microbial communities respond to prolonged desiccation events is crucial.

This revision manuscript provides a synthesis of recent empirical and experimental studies that have explored various aspects of streambed microbial communities in the context of diverse drying-rewetting periods. A special focus is placed on highlighting key microbial community structural and functional responses that could be used as endpoints of responses to desiccation. In particular, we showed the greater expression of the phenol-oxidase activity among the intermittent streambeds submitted to long-term drought. This result suggested a potential begin of transition from freshwater to terrestrial systems. Additionally, we observed a tendency of decreasing bacterial diversity in the dry conditions together with a change in the relative abundance of certain microbial taxa and a general shift from Gram-negative to Gram-positive bacteria. All of these evidences strengthened the similarity between the dry streambed systems studied and a (dry)-soil environment, suggesting that prolonged and unusual dry periods could boost the terrestrial transition of the aquatic intermittent ecosystem. By summarizing these findings, we aim to enhance our understanding of the responses exhibited by streambed microbiota in the face of desiccation events. The synthesized results may further provide potential diagnosis and/or management tools for intermittent freshwater ecosystems functioning.

La sequía hidrológica, caracterizada por una deficiencia significativa de las precipitaciones, favorece los procesos naturales de desecación. La reducción de la recarga de agua y la pérdida de ecosistemas de agua dulce plantean retos urgentes ante el aumento de la población mundial y la creciente demanda de recursos hídricos.

La variabilidad en la duración de los periodos sin caudal puede tener profundas implicaciones para el funcionamiento de los ecosistemas, afectando específicamente a la microbiota que reside en los sedimentos de los lechos de los ríos y a los procesos vitales que llevan a cabo. El lecho de los ríos es un ecotono en el que los microorganismos forman biopelículas que desempeñan un papel fundamental en los ciclos biogeoquímicos y en las emisiones de gases de efecto invernadero. Por consiguiente, los periodos prolongados de desecación y los subsiguientes episodios de rehumectación pueden perturbar, limitar o alterar las funciones y la estructura de las comunidades microbianas, comprometiendo así el funcionamiento general de los ecosistemas acuáticos. Es crucial comprender cómo responden las comunidades microbianas de los lechos de los ríos a los episodios de desecación prolongada.

Este manuscrito de revisión ofrece una síntesis de estudios empíricos y experimentales recientes que han explorado diversos aspectos de las comunidades microbianas de los lechos de los ríos en el contexto de diversos periodos de desecación-remojo. Se hace especial hincapié en destacar las respuestas estructurales y funcionales clave de la comunidad microbiana que podrían utilizarse como puntos finales de las respuestas a la desecación. En particular, mostramos la mayor expresión de la actividad fenol-oxidasa entre los microorganismos de los ríos intermitentes.

Nitrit ist eine ökotoxikologisch problematische Substanz und führt auf Kläranlagen zur Bildung von klimaschädlichem Lachgas. Auf nitrifizierenden Belebtschlammanlagen kann Nitrit saisonal akkumulieren und erhöhte Ablaufwerte treten auf. Hier diskutieren wir die Häufigkeit von Überschreitungen des Nitrit-Richtwerts auf Schweizer ARA und schlagen Gegenmassnahmen vor.

Freshwater algae exhibit complex dynamics, particularly in meso-oligotrophic lakes with sudden and dramatic increases in algal biomass following long periods of low background concentration. While the fundamental prerequisites for algal blooms, namely light and nutrient availability, are well-known, their specific causation involves an intricate chain of conditions. Here we examine a recent massive Uroglena bloom in Lake Geneva (Switzerland/France). We show that a certain sequence of meteorological conditions triggered this specific algal bloom event: heavy rainfall promoting excessive organic matter and nutrients loading, followed by wind-induced coastal upwelling, and a prolonged period of warm, calm weather. The combination of satellite remote sensing, in-situ measurements, ad-hoc biogeochemical analyses, and three-dimensional modeling proved invaluable in unraveling the complex dynamics of algal blooms highlighting the substantial role of littoral-pelagic connectivities in large low-nutrient lakes. These findings underscore the advantages of state-of-the-art multidisciplinary approaches for an improved understanding of dynamic systems as a whole.

Iron-rich, ferruginous waters were the dominant geochemical regime for most of Earth's history. Modern ferruginous waters are found in stratified, sulfur-poor lakes, and serve as crucial analogs for biogeochemical cycling throughout Earth's past. Here we present the first depth-resolved data of physical structure, nutrients and trace elements from Lake Poso (Indonesia), a deep oligotrophic ancient lake. Lake Poso is ferruginous, with anoxia below ~ 90 m depth, placing it among the world's largest ferruginous lakes. Physical stratification is weaker than other tropical anoxic lakes, indicating sensitivity for paleoclimate reconstructions. Trace elements and nutrients are predominantly shaped by the oxic–anoxic transition. Manganese– and Fe oxyhydroxide–driven biogeochemical cycling occurs at distinct depth horizons, with Co and Ni controlled by Mn and showing shallow release in anoxic waters, while V, Cr, P, and As are controlled by Fe, with release in surface sediments and diffusive transport. Chromium is nonquantitatively removed in anoxic waters, in contrast to widespread assumptions in Cr-based paleoreconstructions. Oxycline U and Se removal corresponds to a local N minimum, suggesting biological reduction and/or uptake. These first ferruginous water Se data also show removal in sediments, indicating sediment signals reflect multiple removal processes and informing Se-based paleoreconstructions, while the absence of sediment U removal contrasts other anoxic basins. A comparison with other ferruginous lakes demonstrates how local influences drive deviations from expectations in other systems, and highlight common, generalizable ferruginous basin features. Therefore, these data will guide research in ferruginous settings across space and time, and improve paleoreconstructions from ferruginous sediment records.

Forests substantially mediate the water and carbon dioxide exchanges between terrestrial ecosystems and the atmosphere. The rate of this exchange, including evapotranspiration (ET) and gross primary production (GPP), depends mainly on the underlying vegetation type, health state, and the composition of abiotic environmental drivers. However, the complex 3D structure of forest canopies and the inherent top-view perspective of optical and thermal remote sensing complicate remote sensing-based retrievals of biotic and abiotic factors that eventually determine ET and GPP. This study investigates the sensitivity of remote sensing approaches to 3D variation of abiotic and biotic environmental drivers. We use 3D virtual scenes of two structurally different Swiss forests and the radiative transfer model DART to simulate the 3D distribution of solar irradiance and reflected radiance in the forest canopy. These simulations, in combination with LiDAR data, are used to derive the absorbed photosynthetic active radiation (APAR) and the leaf area index (LAI) in 3D space. The 3D variation of both parameters was quantified and analyzed. We then simulated images of the top-of-canopy bi-directional reflectance factor (BRF) and compared them with the hemispheric-conical reflectance factor (HCRF) data derived from HyPlant airborne imaging spectrometer measurements. The simulated BRF data was used to derive APAR and LAI, and the results were compared to their respective 3D representations. We unravel considerable spatial differences between both representations. We discuss possible reasons for the disagreement, including a potential insensitivity of the inherent top-of-canopy view for the real 3D product dynamics and limitations of the processing of remote sensing data, especially the approximation of effective surface irradiance. Our results can help understanding sources of uncertainties in remote sensing based gas exchange products and defining mitigation strategies.

In large and stratified lakes, substantial methane stocks are often observed within the metalimnion. The origin of the methane (CH₄) accumulated in the metalimnion during stratification, which can sustain significant emissions during convective mixing, is still widely debated. While commonly attributed to the transport of methane produced anaerobically ex situ, recent evidence suggests that oxic in situ methane production could also contribute to metalimnetic methane peaks. Here, we assessed the origin, that is, pelagic CH₄ production or transport of sublittoral CH₄ through the interflow, of metalimnetic methane in Lake Geneva, the largest lake in Western Europe. Microbial diversity data do not support the hypothesis of oxic methane production in the metalimnion. In contrast, both spatial and temporal surveys of methane show that maxima occur at depths and sites most affected by the Rhône River inflow. Methane δ¹³C values point to an anaerobic sublittoral methane source, within a biogeochemical hotspot close to the river delta region, and an efficient transport across several kilometers in a vertically well-constrained metalimnion. Our current findings emphasize the indirect role of river interflows for the long-range transport of CH₄ produced in sediment biogeochemical hotspots, even for large lakes where sublittoral habitats represent a fairly limited fraction of the lake volume.

Im Rahmen der Wirkungskontrolle des Ausbaus der ARA Falkenstein in der Dünnern werden ba-sierend auf dem Untersuchungskonzept für den Ausbau der ARA Falkenstein Untersuchungen der Fischpopulationen und des Makrozoobenthos durchgeführt. Diese Methoden ermöglichen eine Aussage über den Zustand der Lebensgemeinschaften von Wasserwirbellosen und Fischen. Zusätzlich werden ausgewählte chemische Untersuchungen durchgeführt. Werden hierbei auch Umweltschadstoffe gemessen (z.B. basierend auf dem NAWA-Programm), ermöglichen chemi-sche Untersuchungen eine Erfassung der Stoffkonzentrationen in Gewässern und eine Abschät-zung des damit verbundenen Risikos für Auswirkungen auf Wasserlebewesen. Um eine möglichst aussagekräftige Beurteilung zu ermöglichen, sind jedoch zusätzlich ökotoxikologische Untersu-chungen empfehlenswert, da chemische Stoffe, wie Herbizide, Insektizide und Pharmazeutika Wasserorganismen auf verschiedenen biologischen Skalen, vom Individuum bis zur Gemein-schaft, beeinträchtigen können. [...]

When antimicrobial resistant bacteria (ARB) and genes (ARGs) reach novel habitats, they can become part of the habitat’s microbiome in the long term if they are able to overcome the habitat's biotic resilience towards immigration. This process should become more difficult with increasing biodiversity, as exploitable niches in a given habitat are reduced for immigrants when more diverse competitors are present. Consequently, microbial diversity could provide a natural barrier towards antimicrobial resistance by reducing the persistence time of immigrating ARB and ARG. To test this hypothesis, a pan-European sampling campaign was performed for structured forest soil and dynamic riverbed environments of low anthropogenic impact. In soils, higher diversity, evenness and richness were significantly negatively correlated with relative abundance of >85% of ARGs. Furthermore, the number of detected ARGs per sample were inversely correlated with diversity. However, no such effects were present in the more dynamic riverbeds. Hence, microbiome diversity can serve as a barrier towards antimicrobial resistance dissemination in stationary, structured environments, where long-term, diversity-based resilience against immigration can evolve.

Pastoral farming formed a key element of Norse subsistence strategies in South Greenland but with climatic changes of the Little Ice Age they may have reached their limit. Most recently, studies into hydrological changes across the Norse period (10th–15th century AD) revealed a severe drying trend that was coincident with the Norse demise during the early to mid-15th century AD. This study examines lake sediments from a central area of the Norse Eastern Settlement in Greenland. By means of palynology this study investigates whether climatic changes were responsible for decreasing hay yields and a consequent lack of winter fodder. The results suggest that droughts were likely only minor drivers of vegetation change. In fact, we demonstrate a complex entanglement of cooling trends, substrate impoverishment in the catchment of the sampled lake and human adaptation processes. The latter is manifested in a shift in usage of the farm towards a shieling/ dairy production. We conclude that the high amount of labour required to maintain hay yields while counterbalancing the lack of soil nutrients and the shortening of the growing season could be among the many driving forces in the process of Norse farming reorganization in South Greenland. Furthermore, the results allow for the discussion of a potential first palynological evidence of Norse water management in South Greenland.

Lakes represent a vital source of freshwater, accounting for 87% of the Earth’s accessible surface freshwater resources and providing a range of ecosystem services, including water for human consumption. As climate change continues to unfold, understanding the potential evaporative water losses from lakes becomes crucial for effective water management strategies. Here we investigate the impacts of climate change on the evaporation rates of 23 European lakes and reservoirs of varying size during the warm season (July–September). To assess the evaporation trends, we employ a 12-member ensemble of model projections, utilizing three one-dimensional process-based lake models. These lake models were driven by bias-corrected climate simulations from four General Circulation Models (GCMs), considering both a historical (1970–2005) and future (2006–2099) period. Our findings reveal a consistent projection of increased warm-season evaporation across all lakes this century, though the magnitude varies depending on specific factors. By the end of this century (2070–2099), we estimate a 21%, 30% and 42% average increase in evaporation rates in the studied European lakes under RCP (Representative Concentration Pathway) 2.6, 6.0 and 8.5, respectively. Moreover, future projections of the relationship between precipitation (P) and evaporation (E) in the studied lakes, suggest that P-E will decrease this century, likely leading to a deficit in the availability of surface water. The projected increases in evaporation rates underscore the significance of adapting strategic management approaches for European lakes to cope with the far-reaching consequences of climate change.

Long-chain diols are biomarkers commonly used in the marine realm to reconstruct several environmental parameters such as sea surface temperature and salinity. However, they are also produced in lacustrine and slow-flowing river environments, a characteristic that has proved to be useful to trace past riverine inputs in coastal sedimentary records. So far, their use in lacustrine settings is sparse as their controls are not well-known. Previous studies in two lakes have shown that long-chain diol distribution is linked to changes in temperature (in a small Spanish alpine lake), but also to water column stratification (in a large deep Swiss lake). To understand the controls on i) the presence of long-chain diols in lakes, and ii) the distribution of long-chain diol isomers, surface sediments from 52 Swiss lakes were studied. Long-chain diols are present in 57% of the lakes, and machine learning (i.e., random forest model) showed that their presence is mainly controlled by mean annual air temperature, sodium and potassium concentrations and area of the lakes. Long-chain diol isomer relative distribution seems to react to temperature, nutrient (here nitrate) and oxygen concentrations in the lakes. This new insight was tested on a short sedimentary core from Lake Zurich, and compared with other biomarker proxies (based on branched and isoprenoid glycerol dialkyl glycerol tetraethers), as well as with historical record of nutrient contents and temperature. Variations in the long-chain diol index (LDI) mirror measured temperature, but also reacted to changes in nutrients and oxygenation in the lake. This study highlights the potential of long-chain diols as a proxy to trace both nutrients and temperature in lakes, potentially on geological timescales.

Methane (CH₄) accumulation in the well-oxygenated lake epilimnion enhances the diffusive atmospheric CH₄ emission. Both lateral transport and in situ oxic methane production (OMP) have been suggested as potential sources. While the latter has been recently supported by increasing evidence, quantifying the exact contribution of OMP to atmospheric emissions remains challenging. Based on a large high-resolution field data set collected during 2019-2020 in the deep stratified Lake Stechlin and on three-dimensional hydrodynamic modeling, we improved existing CH₄ budgets by resolving each component of the mass balance model at a seasonal scale and therefore better constrained the residual OMP. All terms in our model showed a large temporal variability at scales from intraday to seasonal, and the modeled OMP was most sensitive to the surface CH₄ flux estimates. Future efforts are needed to reduce the uncertainties in estimating OMP rates using the mass balance approach by increasing the frequency of atmospheric CH₄ flux measurements.

Lakes emit substantial amounts of carbon dioxide (CO₂) into the atmosphere, but why they do remains debated. The long-standing vision of lakes as solely respirators of the organic matter leaking from the soils has been challenged by evidence that inorganic carbon produced by weathering of the catchment bedrock could also support lake CO₂ emissions. How inorganic carbon inputs ultimately generate lake CO₂ outgassing remains a blind spot. We develop and introduce a calcite module in a coupled one-dimensional physical-biogeochemical model that we use to simulate the carbon cycle of the large Lake Geneva over the past 40 years. We mechanistically demonstrate how the so-far neglected process of calcite precipitation boosts net CO₂ emissions at the annual scale. Far from being anecdotal, we show that calcite precipitation could explain CO₂ outgassing across various lakes globally, including some of the largest lakes in the world.

A growing interest in lacustrine alkenones as a proxy for continental paleotemperature reconstructions accompanied important methodological improvements over the past two decades. New gas chromatography (GC) columns were used for alkenone analysis, that drastically improved alkenone separation, especially for freshwater lakes. However, these recent advances are sometimes not sufficient in separating compounds that interfere with alkenones in the resulting chromatograms and concurrently, new chemical procedures were implemented to further clean up the samples. Here we investigate the impact of two clean-up procedures, saponification and silver-nitrate purification, on alkenone distribution, alkenone quantification, and C₃₇ alkenone-based indices, including the U₃₇^K index. The silver-nitrate purification modified the C₃₇ alkenone distribution and thus the C₃₇ alkenone-based indices, especially the U₃₇^K index, in 6 out of the 9 studied samples by further retaining alkenones with more double bonds. These changes would result on an average error of 3 °C in reconstructed temperatures. Saponification also influenced the C₃₇ alkenone distribution mainly by removing co-eluting compounds, thereby improving the quality of the results. Both saponification and purification resulted in the reduction of the C₃₇ alkenone concentration by almost half. Clean-up steps should thus be used carefully, paying particular attention to any change in alkenone distribution and concentration. Limiting the use of additional clean-up steps reduces the risk of modifying the alkenone distribution.

Lacustrine alkenones are increasingly reported in freshwater lakes worldwide, which makes them a very promising proxy to reconstruct past continental temperatures. However, a more systematic understanding of ecological preferences of freshwater alkenone-producers at global scale is lacking, which limits our understanding of alkenones as a proxy in lakes. Here we investigated 56 Swiss freshwater lakes and report Group 1 alkenones in 33 of them. In twelve of the lakes containing alkenones, a mixed Group 1/Group 2 alkenone signature was detected. We used a random forest (RF) model to investigate the influence of 15 environmental variables on alkenone occurrence in Swiss lakes and found sodium (Na⁺) concentration and mean annual air temperature (MAAT) to be the most important variables. We also trained a RF model on a database that included Swiss lakes and all freshwater lakes worldwide, which were previously investigated for alkenone presence. Water depth appeared as the most important variable followed by MAAT and Na⁺, sulfate and potassium concentrations. This is very similar to results found for freshwater and saline lakes, which suggests that Group 1 and Group 2 alkenone occurrence could be controlled by the same variables in freshwater lakes. For each tested variable, we defined the optimal range(s) for the presence of alkenones in freshwater lakes. The similarity of the results for the Swiss and global models suggests that the environmental parameters controlling the occurrence of freshwater alkenone producers could be homogenous worldwide.

Biodiversity loss is increasing worldwide, necessitating effective approaches to counteract negative trends. Here, we assessed aquatic macroinvertebrate biodiversity in two river catchments in Switzerland; one significantly degraded and associated with urbanisation and instream barriers, and one in a near-natural condition. Contrary to our expectations, environmental heterogeneity was lower in the near-natural stream, with enhanced productivity in the degraded system resulting in a greater range of environmental conditions. At face value, commonly employed alpha, beta and gamma biodiversity metrics suggested both catchments constituted healthy systems, with greater richness or comparable values recorded in the degraded system relative to the near-natural one. Further, functional metrics considered to be early indicators for anthropogenic disturbance, demonstrated no anticipated differences between degraded and near-natural catchments. However, investigating the identity of the taxa unique to each river system showed that anthropogenic degradation led to replacement of specialist, sensitive species indicative of pristine rivers, by generalist, pollution tolerant species. These replacements reflect a major alteration in community composition in the degraded system compared with the near-natural system. Total nitrogen and fine sediment were important in distinguishing the respective communities. We urge caution in biodiversity studies that employ numerical biodiversity metrics alone. Assessing just one aspect of diversity, such as richness, is not sufficient to track biodiversity changes associated with environmental stress. We advocate that biodiversity monitoring for conservation and management purposes must go beyond traditional richness biodiversity metrics, to include indices that incorporate detailed nuances of biotic communities that relates to taxon identity.

Nitrogen oxides (NO_x Combining double low line NO + NO₂) are air pollutants which are co-emitted with CO₂ during high-temperature combustion processes. Monitoring NO_x emissions is crucial for assessing air quality and for providing proxy estimates of CO₂ emissions. Satellite observations, such as those from the TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel-5P satellite, provide global coverage at high temporal resolution. However, satellites measure only NO₂, necessitating a conversion to NO_x. Previous studies have applied a constant NO₂-to-NO_x conversion factor. In this paper, we develop a more realistic model for NO₂-to-NO_x conversion and apply it to TROPOMI data of 2020 and 2021. To achieve this, we analysed plume-resolving simulations from the MicroHH large-eddy simulation model with chemistry for the Bełchatów (PL), Jänschwalde (DE), Matimba (ZA) and Medupi (ZA) power plants, as well as a metallurgical plant in Lipetsk (RU). We used the cross-sectional flux method to calculate NO, NO₂ and NO_x line densities from simulated NO and NO₂ columns and derived NO₂-to-NO_x conversion factors as a function of the time since emission. Since the method of converting NO₂ to NO_x presented in this paper assumes steady-state conditions and that the conversion factors can be modelled by a negative exponential function, we validated the conversion factors using the same MicroHH data. Finally, we applied the derived conversion factors to TROPOMI NO₂ observations of the same sources. The validation of the NO₂-to-NO_x conversion factors shows that they can account for the NO_x chemistry in plumes, in particular for the conversion between NO and NO₂ near the source and for the chemical loss of NO_x further downstream. When applying these time-since-emission-dependent conversion factors, biases in NO_x emissions estimated from TROPOMI NO₂ images are greatly reduced from between -50 % and -42 % to between only -9.5 % and -0.5 % in comparison with reported emissions. Single-overpass estimates can be quantified with an uncertainty of 20 %-27 %, while annual NO_x emission estimates have uncertainties in the range of 4 %-21 % but are highly dependent on the number of successful retrievals. Although more simulations covering a wider range of meteorological and trace gas background conditions will be needed to generalise the approach, this study marks an important step towards a consistent, uniform, high-resolution and near-real-time estimation of NO_x emissions - especially with regard to upcoming NO₂-monitoring satellites such as Sentinel-4, Sentinel-5 and CO₂M.

Emissions of microbially produced methane (CH₄) from lake sediments are a major source of this potent greenhouse gas to the atmosphere. The rates of CH₄ production and emission are believed to be influenced by electron acceptor distributions and organic carbon contents, which in turn are affected by anthropogenic inputs of nutrients leading to eutrophication. Here, we investigate how eutrophication influences the abundance and community structure of CH₄ producing Archaea and methanogenesis pathways across time–resolved sedimentary records of five Swiss lakes with well–characterized trophic histories. Despite higher CH₄ concentrations which suggest higher methanogenic activity in sediments of eutrophic lakes, abundances of methanogens were highest in oligotrophic lake sediments. Moreover, while the methanogenic community composition differed significantly at the lowest taxonomic levels (OTU), depending on whether sediment layers had been deposited under oligotrophic or eutrophic conditions, it showed no clear trend in relation to in situ distributions of electron acceptors. Remarkably, even though methanogenesis from CO₂-reduction was the dominant pathway in all sediments based on carbon isotope fractionation values, taxonomic identities, and genomes of resident methanogens, CO₂-reduction with hydrogen (H₂) was thermodynamically unfavorable based on measured reactant and product concentrations. Instead, strong correlations between genomic abundances of CO₂-reducing methanogens and anaerobic bacteria with potential for extracellular electron transfer suggest that methanogenic CO₂-reduction in lake sediments is largely powered by direct electron transfer from syntrophic bacteria without involvement of H₂ as an electron shuttle.

Background: Seasonal movements of animals often result in the transfer of large amounts of energy and nutrients across ecosystem boundaries, which may have large consequences on local food webs through various pathways. While this is known for both terrestrial- and aquatic organisms, quantitative estimates on its effects on food web structure and identification of key pathways are scarce, due to the difficulty in obtaining replication on ecosystem level with negative control, i.e. comparable systems without migration. Methods: In this study, we estimate the impact of Arctic charr (Salvelinus alpinus) migration on riverine ecosystem structure, by comparing multiple streams with strictly resident populations above natural migration barriers with streams below those barriers harboring partially migratory populations. We compared density estimates and size structure between above and below populations. Diet differences were examined through the analysis of stomach contents, changes in trophic position were examined by using stable isotopes. To infer growth rate of resident individuals, back-growth calculation was performed using otoliths. Results: We find higher densities of small juveniles in partially migratory populations, where juvenile Arctic charr show initially lower growth, likely due to higher intraspecific competition. After reaching a size, where they can start feeding on eggs and smaller juveniles, which are both more frequent in partially migratory populations, growth surpasses that of resident populations. Cannibalism induced by high juvenile densities occurred almost exclusively in populations with migration and represents an altered energy pathway to the food web. The presence of large cannibalistic charr feeding on smaller ones that have a similar trophic level as charr from strictly resident populations (based on stomach content) coupled with steeper δ¹⁵N-size regression slopes illustrate the general increase of food chain length in systems with migration. Conclusions: Our results thus suggest that the consumption of migration-derived resources may result in longer food chains through middle-up rather than bottom-up effects. Furthermore, by occupying the apex of the food chain and feeding on juvenile conspecifics, resident individuals experience reduced competition with their young counterparts, which potentially balances their fitness with migratory individuals.

Subaqueous paleoseismic studies used soft sediment deformation structures (SSDS) to discern the shaking strength of past earthquakes, as the deformation degree of SSDS related to Kelvin Helmholtz Instability evolves from disturbed lamination and folds to intraclast breccia with higher peak ground accelerations (PGA). We lack comparative studies of different sediment types with SSDS related to earthquakes from different seismogenic sources to comprehend how these factors modulate earthquake-induced deformation. Here, we compile sediment records with seven earthquake-triggered SSDS from 10 lakes with organic-, carbonate-, siliciclastic-, and diatom-rich sediment from three subduction zones and one collisional setting. We target basin sequences with slope angles <0.65° to reduce the influence of gravitational downslope stress. We find that even minimal increases in slope angle, maximal 1°, lead to higher deformation degrees and, for some earthquakes, SSDS are only present at >0.65°. Fine-grained clastics enhance sediment susceptibility to deformation, whereas abundant diatoms reduce it, demonstrating the influence of composition. Deformation correlates best with PGA and the vicinity of the earthquakes, suggesting that high frequency shaking promotes deformation. In addition, deformation only occurs above a minimum magnitude dependent on sediment composition, and higher deformation degrees in our studied basin sedimentary sequences only above M_w 4.9 for all sediment types, suggesting that sufficient duration of shaking—magnitude correlates with duration—is essential for SSDS development. We advise taking multiple cores on gentle slopes to study SSDS—additional to basin cores—to resolve small magnitude local earthquakes and relative differences in frequency content of past events.

Sentinel-2 satellite data enables multispectral monitoring of the earth at a high temporal revisit rate. Combining this information with a network of optical ground measurements enables a more detailed and a more complete understanding of terrestrial ecosystems. However, independent optical ground measurements often lack consistency, especially when comparing different sites in geographically remote locations. Using the very high temporal and spectral resolution offered by the automated field spectrometer systems FloX and RoX (Fluorescence Box and Reflectance Box, respectively, JB-Hyperspectral Devices GmbH, Duesseldorf, Germany), we investigated continuous time series ranging over three years and in ten different locations across Europe, Africa, America and Asia. The continuous records of ground-measured reflectance were first validated against Sentinel-2 top of canopy (TOC) reflectance to evaluate the consistency of the in-situ network. Our results suggest a good agreement of ground-measured reflectance with Sentinel-2 TOC reflectance in vegetation and snow with R² around 0.79 in the 833 nm band and R² up to 0.94 in the bands around 559 nm and 492 nm, demonstrating good consistency across the network. Spatial misalignment of Sentinel-2 pixel-sizes with respect to the different footprint sizes of the ten automated spectrometers on the ground, atmospheric uncertainties, sub-optimal instrument setup and spatial-temporal variable landscape heterogeneity were identified as the most relevant sources of uncertainties in the network. Comparing the Normalized Difference Vegetation Index (NDVI), Transformed Chlorophyll Absorption in Reflectance Index (TCARI) and Enhanced Vegetation Index (EVI) between ground and satellite revealed a decreasing agreement with increasing complexity of index formulation. The best agreement between satellite and ground was exhibited by NDVI with R² around 0.96 and relative error of 4.3% investigating vegetation and snow across all ten sites. Furthermore, we identified a seasonal pattern in residuals of NDVI between ground and satellite in an alpine ecosystem in northern Italy, which was associated with increased spatial heterogeneity due to the effects of diverse vegetation phenology and snowfall. In contrast, a random distribution of residuals was recognized in a rather uniform oak forest canopy in southern France. Clustering Sentinel-2 pixels with respect to their temporal patterns in NDVI identified similar areas seen as homogenous in the canopy of Torgnon, Italy, and Observatoire de Haute-Provence (OHP), France, each. The very high temporal resolution of NDVI measured on the ground confirmed overlap with matched homogenous areas, but must consider seasonal landscape heterogeneity. Using well-standardized and globally homogenous Sentinel-2 TOC reflectance enabled the assessment of uncertainties in ten field spectrometer sites around the world. The standardization of the automated field spectrometers, their data products and data annotation were essential prerequisites that enabled joint validation against Sentinel-2. Harmonizing optical ground measurements with respect to a satellite is promising for future research to ensure the valid intercomparison and transfer of data products across different sites in a network worldwide.

Constructing a robust ocean color (OC) record (e.g., water transparency, phytoplankton absorption) for long-term assessments of coastal and inland water ecosystems from past, present, and future missions requires high-quality spectral remote sensing reflectance (R_rs) products. Using the GLORIA dataset [1], we evaluated the quality of R_rs products from the Moderate Resolution Imaging Spectroradiometer (MODIS on Terra and Aqua), Medium Resolution Imaging Spectrometer (MERIS), and Visible Infrared Imaging Radiometer Suite (VIIRS) processed via the 2-band heritage atmospheric correction method (a combination of near-infrared and shortwave infrared bands) available in the SeaWiFS Analysis Data Analysis System (SeaDAS). Overall, retrieval residuals are consistent within a few percent among the four missions. Median residuals ranged from ~20% in the ~550 nm band to > 60% in the ~412 nm bands. Spectrally averaged root mean squared differences for all the missions were ~ 0.0024 sr^-1 with one standard deviation of ~0.001 sr^-1. The corresponding (median) biases in the visible bands varied from -60 to -3%, with the largest biases identified in MERIS and VIIRS products. Despite the lower sensitivity of band-ratio algorithms to residuals in specific spectral regions (e.g., OC3 chlorophyll-a algorithm is less prone to residuals in R_rs(λ > 600 nm)), other algorithms or downstream products that leverage all the visible bands are highly compromised. We underscore the need to improve the quality of R_rs products, thereby enabling the reconstruction of baseline OC products of high caliber in global coastal and inland waters that are often near human activity.

Climate change is contributing to rapid changes in lake ice cover across the Northern Hemisphere, thereby impacting local communities and ecosystems. Using lake ice cover time-series spanning over 87 yr for 43 lakes across the Northern Hemisphere, we found that the interannual variability in ice duration, measured as standard deviation, significantly increased in only half of our studied lakes. We observed that the interannual variability in ice duration peaked when lakes were, on average, covered by ice for about 1 month, while both longer and shorter long-term mean ice cover duration resulted in lower interannual variability in ice duration. These results demonstrate that the ice cover duration can become so short that the interannual variability rapidly declines. The interannual variability in ice duration showed a strong dependency on global temperature anomalies and teleconnections, such as the North Atlantic Oscillation and El Niño–Southern Oscillation. We conclude that many lakes across the Northern Hemisphere will experience a decline in interannual ice cover variability and shift to open water during the winter under a continued global warming trend which will affect lake biological, cultural, and economic processes.

Siberia experienced a prolonged heatwave in the spring of 2020, resulting in extreme summer drought and major wildfires in the North-Eastern Siberian lowland tundra. In the Arctic tundra, plants play a key role in regulating the summer land surface energy budget by contributing to land surface cooling through evapotranspiration. Yet we know little about how drought conditions impact land surface cooling by tundra plant communities, potentially contributing to high air temperatures through a positive plant-mediated feedback. Here we used high-resolution land surface temperature and vegetation maps based on drone imagery to determine the impact of an extreme summer drought on land surface cooling in the lowland tundra of North-Eastern Siberia. We found that land surface cooling differed strongly among plant communities between the drought year 2020 and the reference year 2021. Further, we observed a decrease in the normalized land surface cooling (measured as water deficit index) in the drought year 2020 across all plant communities. This indicates a shift towards an energy budget dominated by sensible heat fluxes, contributing to land surface warming. Overall, our findings suggest significant variation in land surface cooling among common Arctic plant communities in the North-Eastern Siberian lowland tundra and a pronounced effect of drought on all community types. Based on our results, we suggest discriminating between functional tundra plant communities when predicting the drought impacts on energy flux related processes such as land surface cooling, permafrost thaw and wildfires.

Industrial activities of a silk dyeing factory in Thalwil, on the shore of Lake Zurich, Switzerland, caused extreme Sn contamination of lake sediments. In this study, we determine the contamination source, spread, and age using a multiproxy approach. We used X-ray fluorescence spectroscopy (XRF) core scanning and further geochemical analyses to assess the contamination spreading and thickness in the sedimentary column. We found elevated Sn levels throughout sediments of Lake Zurich, ranging from 177 gkg^-1 in front of the former silk factory to 0.05 gkg^-1 at the southeast end (background: ca. 0.006 gkg^-1). The rapid concentration drop away from the shore suggests quick precipitation of a sparingly soluble inorganic Sn compound, which is confirmed by Scanning Electron Microscope Imaging in tandem with Energy-dispersive XRF spectroscopy (SEM-EDX) data. The Sn XRF profile of a varved core indicates a contamination onset in the early 1890s, a maximum around 1900, and a gradual decrease to low levels in the 1940s. High Sn concentrations in turbidite layers from the deep basin indicate that mass movements physically remobilised Sn. However, in stable conditions, in-situ porewater measurements (conc. < 0.5 μgL^-1) using dialyse plates show little Sn remobilisation into the lake water (0.05 mga^-1m^-2). The low remobilisation, reducing conditions, and high sulphide contents in the contaminated layers suggest that Sn is firmly bound to the sediments. Combined with the low toxicity of Sn, we conclude that the Sn contamination poses no threat to lake biota or drinking water production.

While it is commonly accepted that ecosystem dynamics are nonlinear, what is often not acknowledged is that nonlinearity implies scale-dependence. With the increasing availability of high-resolution ecological time series, there is a growing need to understand how scale and resolution in the data affect the construction and interpretation of causal networks—specifically, networks mapping how changes in one variable drive changes in others as part of a shared dynamic system ("dynamic causation"). We use Convergent Cross Mapping (CCM), a method specifically designed to measure dynamic causation, to study the effects of varying temporal and taxonomic/functional resolution in data when constructing ecological causal networks. As the system is viewed at different scales relationships will appear and disappear. The relationship between data resolution and interaction presence is not random: the temporal scale at which a relationship is uncovered identifies a biologically relevant scale that drives changes in population abundance. Further, causal relationships between taxonomic aggregates (low-resolution) are shown to be influenced by the number of interactions between their component species (high-resolution). Because no single level of resolution captures all the causal links in a system, a more complete understanding requires multiple levels when constructing causal networks.

In a warming world, the input of glacier meltwater to inland water ecosystems is predicted to change, potentially affecting their productivity. Meta-ecosystem theory, which posits that the nutrient availability in the recipient ecosystem can determine the extent of cross-ecosystem boundary utilization, can be useful for studying landscape-scale influences of glacier meltwater on inland waters. Here, we investigate how the input of glacier meltwater in a river system in Southern Greenland influences the utilization of marine subsidies in freshwater fish. Our study system comprised four sites, with controls for glacial meltwater and marine subsidies, harboring a partially migrating population of arctic char, meaning that some individuals migrate to the ocean and others remain in freshwaters, and two fully resident populations as a freshwater reference. We assessed the incorporation of marine carbon in freshwater resident char using both bulk and amino acid stable isotope analysis of muscle tissue. In the population with partial migration, marine subsidies were a significant resource for resident char individuals, and estimates of trophic position suggest that egg cannibalism is an important mechanism underlying the assimilation of these marine subsidies. In proglacial streams, namely those with high glacial meltwater, the total dependence on marine subsidies increased and reached 83% because char become cannibals at smaller sizes. In the configuration of our focal meta-ecosystem, our results suggest that the importance of marine subsidies to freshwater fish strengthens within increasing meltwater flux from upstream glaciers.

1. Global change drives multiple facets of biodiversity including interaction diversity, which is fundamental for ecosystem functioning. However, studying trophic interactions is challenging in meta-ecosystems, that is ecosystems connected by spatial flows of energy, materials and organisms across ecosystem boundaries. While analytical methods based on abundances of polyunsaturated fatty acids (PUFAs) and stable isotopes of amino acids (AAs) are being increasingly used, it has never been explored if both approaches could be: (i) combined in mixing models to enhance precision in dietary inference (ii) compared to disentangle transfers of various PUFAs and proteins in food webs in the wild.
2. We explore the utility of analytical approaches based on PUFA abundances and AA isotopes to resolve resource transfers in a natural riparian food web. We focus on spiders and their potential prey from blue, green and brown sources to address three important and persisting methodological issues in food-web ecology, namely whether (i) essential AA carbon isotopes can resolve protein origin from blue, green and brown resources, (ii) PUFA relative abundance and AA isotopes can be combined in a mixing model to provide higher precision estimates (i.e. narrower intervals) and (iii) combining the two approaches can unveil the coupling of protein and PUFA transfers in food webs. 3. Our research demonstrates the power of AA isotopes and PUFAs to distinguish blue, green, and brown sources and their transfer up to consumers. We show that combining PUFA relative abundance and AA isotopes in a mixing model provides overall estimates similar to the individual estimates but significantly increases precision. In addition, we showcase how combining approaches unveil the coupling of protein and PUFA transfers. For instance, we show that most PUFAs are less concentrated from prey to predators, relative to proteins, highlighting uncoupling of PUFAs and protein transfer along food chains.
4. We show for the first time the effectiveness of combining AA isotopes and PUFA abundances, particularly relevant for complex trophic interactions in a meta-ecosystem context. Our study illustrates the trophic uncoupling of proteins and PUFAs, highlighting the necessity in combining both approaches.

Food webs are crucial for understanding how carbon and nutrients flow within ecosystems, influencing sustainability and carbon fluxes. Ecosystems are interconnected, exchanging energy, nutrients, and organic matter—a concept captured by meta-ecosystem theory. Consequently, changes in one ecosystem can have cascading effects on others. This interconnectedness becomes increasingly important as global change drives significant alterations in food webs. Therefore, there is a pressing need to characterize food web functioning in complex settings, such as meta-ecosystems, and to study how these webs are impacted by global change. [...]

Given the use of machine learning-based tools for monitoring the Water Quality Indicators (WQIs) over lakes and coastal waters, understanding the properties of such models, including the uncertainties inherent in their predictions is essential. This has led to the development of two probabilistic NN-algorithms: Mixture Density Network (MDN) and Bayesian Neural Network via Monte Carlo Dropout (BNN-MCD). These NNs are complex, featuring thousands of trainable parameters and modifiable hyper-parameters, and have been independently trained and tested. The model uncertainty metric captures the uncertainty present in each prediction based on the properties of the model—namely, the model architecture and the training data distribution. We conduct an analysis of MDN and BNN-MCD under near-identical conditions of model architecture, training, and test sets, etc., to retrieve the concentration of chlorophyll-a pigments (Chl a), total suspended solids (TSS), and the absorption by colored dissolved organic matter at 440 nm (a_cdom (440)). The spectral resolutions considered correspond to the Hyperspectral Imager for the Coastal Ocean (HICO), PRecursore IperSpettrale della Missione Applicativa (PRISMA), Ocean Colour and Land Imager (OLCI), and MultiSpectral Instrument (MSI). The model performances are tested in terms of both predictive residuals and predictive uncertainty metric quality. We also compared the simultaneous WQI retrievals against a single-parameter retrieval framework (for Chla). Ultimately, the models’ real-world applicability was investigated using a MSI satellite-matchup dataset (N = 3'053) of Chla and TSS. Experiments show that both models exhibit comparable estimation performance. Specifically, the median symmetric accuracy (MdSA) on the test set for the different parameters in both algorithms range from 30% to 60%. The uncertainty estimates, on the other hand, differ strongly. MDN’s uncertainty estimate is ∼50%, encompassing estimation residuals for 75% of test samples, whereas BNN-MCD’s average uncertainty estimate is ∼25%, encompassing the residuals for 50% of samples. Our analysis also revealed that simultaneous estimation results in improvements in both predictive performance and uncertainty metric quality. Interestingly, the trends mentioned above hold across different sensor resolutions, as well as experimental regimes. This disparity calls for additional research to determine whether such trends in model uncertainty are inherent to specific models or can be more broadly generalized across different algorithms and sensor setups.

After years of partial winter mixing in Lake Zurich (Switzerland), a complete turnover of the water column reoccurred during winter/spring 2021. It was favored by a cold, windy winter and a small difference of water temperatures between the surface zone and a hypolimnion (deep water zone) that had gradually warmed during the previous years. The trend of declining phytoplankton spring blooms due to incomplete winter mixing was interrupted by mass development of algae due to the upwelling of nutrients accumulated in the hypolimnion. The effects of this singular deep mixing on the microbial food web during spring were studied in a high-frequency sampling campaign and compared with data from two years of partial winter mixing (2020 and 2022). A particular focus was put on the quantitative composition of the ciliate assemblage. Our results showed that not all organisms reacted equally to the nutrient (phosphorus) boost in the surface zone. Centric diatoms and cryptophytes profited most directly from the deep mixing, outcompeting the otherwise dominant cyanobacterium Planktothrix rubescens. Heterotrophic bacteria and their top predators, the ‘heterotrophic nanoflagellates’ trophic guild, were less affected by the nutrient supply and showed only short-lived increases of maximal biomass. The assemblage composition of ciliate morphotypes was highly resilient over the three years, presumably due to the range of acceptable food items of the predominant omnivorous species. However, numerous ciliate morphotypes showed brief mass development in 2021, and Balanion planctonicum, small Urotricha species and tintinnids were significantly more frequent than in 2020/2022. Small interception-feeding morphotypes apparently profited from the rich supply of their cryptomonad food, and tintinnid morphotypes additionally benefited from the availability of building material (e.g., centric diatom shells) for their loricae. In summary, we show that effects of lake warming in deep stratifying lakes are not as unidirectional as previously presumed, and we reveal resilience of the pelagic ciliate morphotype assemblage to lake warming related interannual variability in Lake Zurich.

Global warming particularly impacts terrestrial and aquatic ecosystems in the Arctic. To constrain the sensitivity of Arctic lakes and make meaningful predictions about future change under global warming, we need to examine their response to previous warm phases. Lake sediments from Greenland's deglaciated area offer valuable archives to investigate past climate variability and associated lake changes.
Here, we applied hyperspectral imaging and lipid biomarker thermometry to a Holocene-length sediment record from Lake 578 in the Eastern Settlement of the Norse (61.08° N, 45.62° W; ∼155 m a.s.l) to investigate local temperature, productivity, and anoxia histories. We calibrated branched glycerol dialkyl glycerol tetraethers (brGDGTs) with summer mean water temperatures (SMWT) using a previously published site-specific calibration and analyzed pigment fluxes based on hyperspectral imaging. Notably, the anoxia reconstructions were corroborated with two independent proxies (GDGT-0/Crenarchaeol and bacterio pheophytins). We investigated the lake's environmental history and identified periods of significant change by employing generalized additive models (GAMs).
Our results reveal significant transitions in Lake 578 driven both by natural climate shifts and anthropogenic impacts. During the early Holocene, low SMWT and productivity coupled with high anoxia suggest strong seasonality and prolonged inverted thermal stratification, possibly enhanced by extended ice cover. The mid-Holocene showed higher SMWT and productivity along with low anoxia, indicating a dimictic lake system. The early Holocene temperature rise lagged that of to the Northern Hemisphere, but closely followed the Atlantic-Fennoscandian stack. The Holocene Thermal Maximum (7.5–4.5 cal ka BP) aligns with other regional reconstructions. After 3 cal ka BP, we observed a Neoglacial cooling characterized by increased anoxia and reduced temperatures due to enhanced stratification. At around 1.0 cal ka BP, Lake 578 saw a surge in productivity and anoxia, which we attribute to land use and lake damming by the Norse. Despite a post-Norse decline in productivity and disappearance of anoxia, the lake never reverted to its pre-Norse state, with modern sheep farming further intensifying productivity in recent decades. While early Holocene anoxia resulted from natural cold temperature stratification, anoxia during the Norse period was anthropogenically induced.
This research underscores the value of integrating lipid biomarkers with hyperspectral imaging for detailed reconstructions of changes within Arctic lakes. It provides crucial insights for anticipating the ecologic and climatic resilience of Arctic lakes to ongoing global warming and anthropogenic influence.

Lacustrine methane emissions are strongly mitigated by aerobic methane-oxidizing bacteria (MOB) that are typically most active at the oxic-anoxic interface. Although oxygen is required by the MOB for the first step of methane oxidation, their occurrence in anoxic lake waters has raised the possibility that they are capable of oxidizing methane further anaerobically. Here, we investigate the activity and growth of MOB in Lake Zug, a permanently stratified freshwater lake. The rates of anaerobic methane oxidation in the anoxic hypolimnion reached up to 0.2 µM d⁻¹. Single-cell nanoSIMS measurements, together with metagenomic and metatranscriptomic analyses, linked the measured rates to MOB of the order Methylococcales. Interestingly, their methane assimilation activity was similar under hypoxic and anoxic conditions. Our data suggest that these MOB use fermentation-based methanotrophy as well as denitrification under anoxic conditions, thus offering an explanation for their widespread presence in anoxic habitats such as stratified water columns. Thus, the methane sink capacity of anoxic basins may have been underestimated by not accounting for the anaerobic MOB activity.

Past changes in the input/output, and internal cycling, of bioavailable nitrogen (N) in marine and lacustrine environments can be reconstructed by analyzing the N isotopic composition (δ¹⁵N) of organic matter in the sedimentary record. To verify, and eliminate, potential biases of bulk sedimentary δ¹⁵N (δ¹⁵N_bulk) signatures by diagenetic alteration and external N inputs, we applied, for the first time, the diatom-bound N isotope (δ¹⁵N_db) paleo-proxy to lake sediments. By comparing δ¹⁵N_bulk and δ¹⁵N_db in a sedimentary record from eutrophic Lake Lugano (Switzerland), we demonstrate that changing redox conditions influence the degree of N-isotopic alteration of the bulk sediment, emphasizing the need for caution when interpreting δ¹⁵N_bulk in paleolimnological studies. Furthermore, in combining δ¹⁵N_db measurements with X-ray fluorescence scanning and state-of-the-art molecular biomarker analyses, we reconstruct nutrient cycling and paleoenvironmental conditions in the lake over the past ~ 125 yr. Coeval with the period of severe eutrophication in Lake Lugano in the 1960s, our proxy data indicate that export production, δ¹⁵N_db, and the concentration of heterocyst glycolipids (a biomarker for N₂-fixing cyanobacteria) increased simultaneously. Together, these data suggest that the rise in δ¹⁵N_db is likely the result of enhanced water-column denitrification in response to increased phytoplankton productivity. We hypothesize that greater export production during eutrophication led to anoxic conditions in the hypolimnion as a result of enhanced organic matter remineralization, raising water-column denitrification. Enhanced N loss and remobilization of phosphorous (P) from the sediments under anoxic conditions lowered the N : P ratio in the lake, fostering cyanobacterial N₂ fixation in surface waters.

The removal of organic particulate matter, predominantly phytoplankton, in eutrophic coastal seas and estuaries is considered an ecosystem service performed by large bivalve assemblages. Mussel farming has been proposed as a measure to mitigate eutrophication, as filtration directly reduces the concentration of chlorophyll a (Chl a), a primary ecological indicator. Seston depletion is typically assessed by in situ investigation, which generally lacks spatiotemporal coverage of features relative to greater ecosystem dynamics. To assess the scale and structure of this service, the present study couples multiple measurement approaches, including moored stations, synoptic transect surveys, flow cytometry, a preliminary drone survey technique, and satellite remote sensing within and around a large mussel farm. Significant depletion patterns were observed with all methods, and mixing gradients could be detected hundreds of meters beyond the farm, with repeatable patterns but distinct findings between methods. The intensity of the depletion signal was correlated with mussel biomass loads, ambient conditions, and hydrodynamic regimes, ranging from 5% to 91% relative Chl a depletion and Secchi depth increases of up to 2 m. Changes in particle size distributions were impacted in all downstream areas, as well as phytoplankton diversity. Observed depletion gradients with satellite imagery were consistent with other measurements and can be used to complement in situ field measurements. The findings of this study, will inform carrying capacity assessments, farm configuration, and development of impact assessment programs on seston removal for bivalve aquaculture.

Three-dimensional lake hydrodynamic model is a powerful tool widely used to assess hydrological condition changes of lake. However, its computational cost becomes problematic when forecasting the state of large lakes or using high-resolution simulation in small-to-medium size lakes. One possible solution is to employ a data-driven emulator, such as a deep learning (DL) based emulator, to replace the original model for fast computing. However, existing DL-based emulators are often black-box and data-dependent models, causing poor interpretability and generalizability in practical applications. In this study, a data-driven emulator is established using deep neural network (DNN) to replace the original model for fast computing of three-dimensional lake hydrodynamics. Then, the Koopman operator and transfer learning (TL) are employed to enhance the interpretability and generalizability of the emulator. Finally, the generalizability of DL-based emulators is comprehensively analyzed through linear regression and correlation analysis. These methods are tested against an existing hydrodynamic model of Lake Zurich (Switzerland) whose data was provided by an open-source web-based platform called Meteolakes/Alplakes. According to the results, (1) The DLEDMD offers better interpretability than DNN because its Koopman operator reveals the linear structure behind the hydrodynamics; (2) The generalization of the DL-based emulators in three-dimensional lake hydrodynamics are influenced by the similarity between the training and testing data; (3) TL effectively improves the generalizability of the DL-based emulators.

Per- and polyfluoroalkyl substances (PFAS) pose significant environmental and health risks due to their ubiquitous presence and persistence in water systems. Herein, the efficacy of piezocatalysis using barium titanate nanoparticles under ultrasound irradiation for the degradation and defluorination of perfluorooctane sulfonate (PFOS) in water is investigated. The research demonstrates a substantial 90.5% degradation and 29% defluorination of PFOS after 6 h of treatment, highlighting the potential of piezocatalysis as a promising approach for PFAS degradation. Additionally, the quantification of degradation products elucidates the transformation pathways of PFOS, suggesting a stepwise chain-shortening mechanism. The findings underscore the importance of continued research in optimizing piezocatalytic processes and exploring synergistic approaches with other advanced oxidation methods to effectively address PFAS contamination challenges. These efforts are essential for advancing sustainable water treatment strategies and mitigating the environmental and health hazards associated with PFAS contamination.

The research goal is the investigation of environmental processes of recent sedimentation in the Arctic Ocean area. A short core (length – 37 cm) was taken from the Northern part of the Chukchi Sea. Analytical methods included macroscopic sedimentological description by smear-slides, dating by γ-measurements of ¹³⁷Cs and ²¹⁰Pb, diatom and palynological analyses. Sedimentation rates at the research site have been determined to be 1 mm y^-1. Thus, the age of the cored sediments spans approximately 400 years, which includes the period of the Little Ice Age. Abundant cold-water diatom species and spores of terrestrial plants within the lower part of the sediment core are characteristic for cold climate conditions, which dominated the Little Ice Age. The occurrence of Jurassic, Cretaceous, and Neogene species of spores and pollen in the Holocene deposits are the evidence of coastal abrasion and the subsequent transfer of the material to the coring site by currents. Southern, subtropical, and tropical species of diatoms within the upper, more recent part of the core reveal the transfer of material by currents from the Pacific Ocean to the Arctic Ocean through the Bering Strait. The results of biostratigraphic analyses indicate environmental changes during the last 400 years, revealed in bottom sediments of the Northern part of the Chukchi Sea.

Im Spannungsfeld dreier Krisen. Der Klimawandel schreitet voran, der Biodiversitätsverlust verschärft sich und die Energieversorgung ist angespannt. Diese drei globalen Herausforderungen betreffen sowohl die Gewässer und Auengebiete als auch die gesamte Wasserwirtschaft, insbesondere die Wasserkraft. Im Schnittpunkt der drei Krisen steht das politisch umkämpfte Restwasser.

As climate change intensifies, understanding the dynamics of lake evaporation is imperative, especially in semi-arid regions where water resources are already scarce. This study examines the regulatory role of lake depth on evaporation rates, focusing on a terminal lake in a semi-arid region: Dali Lake in China. Using the Complementary Relationship Lake Evaporation model, we simulated the heat and temperature lag time of Dali Lake, an 8 m deep lake, due to its heat storage capacity. This approach was validated through moderate-resolution imaging spectroradiometer (MODIS)-based surface temperatures of Dali Lake and adjacent Ganggenor Lake. Dali Lake, by storing heat during the warmer months, maintains lower surface temperatures compared with the shallower Ganggenor Lake. Under the same climatic conditions, Dali Lake has an annual evaporation of 980 mm, which is 45 mm less than that of Ganggenor Lake, which has an annual evaporation of 1024 mm. To further study the impact of lake depth, we simulated the heat storage and evaporation of Dali Lake during the Holocene, when the lake reached up to 34 m average depth, representative of the maximum depth reached by Dali Lake. During the Holocene, under constant climate conditions, the annual evaporation would be 44 mm/year less than the average evaporation from 1984 to 2016. Average annual evaporation decreased with increasing depth, showing a significant reduction during warmer months, while the release of heat during the ice-cover period did not result in additional evaporation. Our results highlight the important relationship between lake depth and evaporation under climate change, emphasizing the necessity for depth-specific water management strategies in semi-arid regions.

The Southern Hemisphere Westerlies (SHW) are a vital part of the Southern Hemisphere's coupled ocean-atmosphere system and play an important role in the global climate system. The SHW affect the upwelling of carbon-rich deep water and exchange of CO₂ from the ocean to the atmosphere by driving the Antarctic Circumpolar Current. On seasonal to millennial timescales, changes in the strength and position of the SHW are associated with temperature and precipitation changes throughout the extratropical Southern Hemisphere. Understanding the behaviour of the SHW under different background climate states is important for anticipating its future behaviour and remains a subject of ongoing research. Terrestrial paleoclimate records from lake sediments are valuable for reconstructing past atmospheric change and records from the handful of sub-Antarctic islands provide the opportunity to develop datasets to document spatio-temporal patterns of long-term SHW behaviour. Here, we generate palynological, microcharcoal, and sedimentological reconstructions (including CT imagery, μXRF analysis, magnetic susceptibility, and loss-on-ignition) on lake sediments from the Kerguelen Islands (49°S) to constrain variability in Holocene vegetation, climate, and atmospheric circulation (SHW position). Due to the influence of the SHW on the Kerguelen Islands, the influx of long-distance transported (LDT) pollen and microcharcoal from southern Africa serve as proxies for the meridional position of the SHW. In contrast with the stable conditions that prevailed on the Kerguelen Islands over the past 8,600 cal yr BP, our findings reveal a highly dynamic Early Holocene period. Consistent with local palynological evidence of warmer conditions, a high influx of LDT pollen and charcoal from southern Africa suggest that the SHW core belt was located further south of the Kerguelen Islands during this time. Comparison against paleoclimate records from the surrounding region and beyond suggests that the inferred changes might be explained by changes to our planet's interhemispheric thermal gradient, triggered by North Atlantic cooling in response to melting of the last remnants of the Laurentide Ice Sheet.

Knowledge of actual crop transpiration (T) is important for advanced crop management but challenging to obtain due to the large spatial and temporal variation of T. Remote sensing offers various possibilities to assess T dynamics, while particularly sun-induced chlorophyll fluorescence (SIF) has been demonstrated as a sensitive empirical proxy for T. Despite this success, the advancement of the mechanistic understanding of how SIF relates to T dynamics is key for the future development and implementation of robust and reliable SIF-based T products. This study aims to contribute insights by experimentally assessing the sensitivity of several SIF-based T estimation strategies for evolving soil water limitation. We investigated extensive in situ and airborne data acquired during a water limitation experiment in a maize canopy in northern Italy. We evaluated five empirical strategies to integrate SIF in a T modelling framework based on the Penman-Monteith (PM) and the Ball-Berry-Leuning (BBL) concepts. Our results indicate that replacing model parameters sensitive to canopy conductance with SIF results in the best agreement between modelled and measured T under evolving water limitation. Our study contributes expanding existing knowledge with empirical insights on the sensitivity of SIF based T approaches under increasing soil water limitation at short time scales.

Storage hydropower plants, which are an important component of energy production in Switzerland, can lead to hydro- and thermopeaking, affecting river habitats and organisms. In this study, we developed an approach for integrating water temperature simulations into a habitat model to assess the impact of both hydro- and thermopeaking on the availability of suitable fish habitats. We focused on the habitat requirements of juvenile brown trout (Salmo trutta) in a semi-natural braided floodplain along the Moesa River (Southern Switzerland) in early summer. First, we defined different scenarios (with and without hydropeaking) based on the local hydrological and meteorological conditions. Second, we used a two-dimensional depth-averaged hydro- and thermodynamic model to simulate the spatial distributions of water depth, flow velocity, and water temperature. Third, we applied generalized preference curves for juvenile brown trout to identify hydraulically suitable habitats, and developed a new index to assess the availability of thermally suitable habitats. Finally, we quantified the extent to which hydraulically and thermally suitable habitats overlap in space and time. During both base and peak flow phases, most of the hydraulically and thermally suitable habitats are located in the side channels. High flow conditions combined with strong cold-thermopeaking lead to a higher thermal heterogeneity. However, disconnected habitats originate in the dewatering zone, increasing the risk of stranding as well as thermal stress. By helping to better understand the effects of thermopeaking on the availability of fish habitats, our approach could contribute to the design and evaluation of ecological restoration in hydropeaking rivers.

Aquatic fungi are highly diverse organisms that play a critical role in global biogeochemical cycles. Yet it remains unclear which assembly processes determine their co-occurrence and assembly patterns over gradients of drying intensity, which is a common stressor in fluvial networks. Although aquatic fungi possess drying-specific adaptations, little is known about how functional similarity influences co-occurrence probability and which functional traits are sorted by drying. Using field data from 15 streams, we investigated how co-occurrence patterns and assembly processes responded to drying intensity. To do so, we determined fungal co-occurrence patterns, functional traits that best explain species co-occurrence likelihood, and community assembly mechanisms explaining changes in functional diversity over the drying gradient. Our results identified 24 species pairs with positive co-occurrence probabilities and 16 species pairs with negative associations. The co-occurrence probability was correlated with species differences in conidia shape and fungal endophytic capacity. Functional diversity reduction over the drying gradient is generally associated with non-random abiotic filtering. However, the assembly processes changed over the drying gradient, with random assembly prevailing at low drying intensity and abiotic filtering gaining more importance as drying intensifies. Collectively, our results can help anticipate the impacts of global change on fungal communities and ecosystem functioning.

Accumulation of methane in oxic waters of lakes and the ocean has been widely reported. Despite the importance for the greenhouse gas budget, mechanistic controls of such "methane paradox" remain elusive. Here, we use a combination of CH₄ concentration and isotopic (δ¹³C_CH4, δD_H2O and δ¹⁸O_H2O) measurements, plankton incubations and microbial community assessments to demonstrate the existence of the methane paradox in oxygenated waters of a meromictic lake (Lake Cadagno, Switzerland). Following mass dynamics using water isotopes, we exclude the possibility that the accumulation of CH₄ at the thermocline results solely from lateral transport. Interannual variability in the magnitude of the methane paradox (between 0.5 and 5 μmol L^-1) is associated to stratification patterns, changes in zooplankton biomass and planktonic detritus accumulation along density gradients, as well as fluctuating microbial cell numbers. The links between hydrodynamic conditions, aggregation of planktonic detritus and its microbiome, as well as the accumulation of CH₄ in the water column are further supported by high-resolution echosounder revealing backscatter maxima at the top of the thermocline, where detritus is effectively trapped, and by oxic incubations showing that CH₄ is produced in zooplankton detritus (0.046 nmol L^-1 to 0.095 CH₄ mg dry mass L^-1 d^-1). Our results also show that detritus-hosted methanogenesis is stimulated through the addition of methylphosphonate, suggesting that zooplankton-associated microbiomes exploit organic phosphorus compounds to release CH₄. Understanding the variability of the methane paradox in relation to changing hydrodynamics and plankton communities will be crucial to predict the future role of lakes in the global methane budget.

Alteration in the river flow regime due to intermittent hydropower production (i.e., hydropeaking) leads to biodiversity loss and ecosystem degradation worldwide. Due to the increasing shear of volatile green energy (i.e., wind and solar), hydropeaking frequency is deemed to increase in the coming decades. However, our mechanistic understanding of how the frequency of repeated hydropeaking (i.e., series of multiple events) affects ecological processes is still limited. Here, we reflect on the impacts of altered flow frequency and relative duration on the persistency of aquatic habitats. We focus on the habitats at patch-scale, being this the scale representing what organisms perceive when interacting with their environment. With a showcase we explore a temporally explicit approach to quantify altered habitat dynamics at patch-scale due to hydropeaking. We then review how changes in habitat dynamics and persistency may affect ecological processes. Our findings suggest that (i) a time-series approach allows to account for the inherent multi-event nature of hydropeaking; (ii) hydropeaking can increase the dynamics of single habitat patches by at least one order of magnitude if compared to unregulated rivers; (iii) altered habitat dynamics at the patch scale can affect the survival of more sessile species and life cycle stages (e.g., invertebrates) or the energy budget of mobile species and life cycle stages (e.g., adult fish). However, the ecological significance and potential environmental thresholds of patch-scale dynamics and persistency are still poorly investigated and need further attention. Moreover, methods for the aggregation of habitat dynamics and persistency from the patch to the reach-scale are not available yet.

Interdisciplinary approaches are required to tackle complex environmental issues as freshwater ecosystems face unprecedented pressures globally. The emerging Ecohydraulics field of research should, therefore, take steps towards developing true interdisciplinarity to adapt to a continuing changing world. This study contributes to the ongoing discussion on interdisciplinarity in Ecohydraulics and shapes its growth by identifying key actions, actors and implementation strategies that can strengthen it. Based on an online questionnaire and a workshop involving over 150 early and established careers, we present a list of 20 prioritised actions that will help engage the research community towards specific goals and will result in increased interdisciplinary outcomes. While early career researchers (ECRs) have taken the lead on creating this roadmap, its implementation should be a joint responsibility of both ECRs, established career scientists, groups, and institutions within Ecohydraulics. The list of identified actions and assigned responsibility should, therefore, be considered a conversation starter. Continued revision of the here-stated approaches will be required in the future as the field of research and its community progresses. With this contribution, we resume a critical reflection on where the Ecohydraulics field of research and community stand today and suggest where resources should be invested in the long-term to consolidate the inherent interdisciplinarity in Ecohydraulics.

Long-term effects of climate change on lakes globally will include a substantial modification in the thermal regime and the oxygen solubility of lakes, resulting in the alteration of ecosystem processes, habitats, and concentrations of critical substances. Recent efforts have led to the development of long-term model projections of climate change effects on lake thermal regimes and oxygen solubility. However, such projections are hardly ever confronted with observations extending over multiple decades. Furthermore, global-scale forcing parameters in lake models present several limitations, such as the need of significant downscaling. In this study, the effects of climate change on thermal regime and oxygen solubility were analyzed in the four largest French peri-alpine lakes over 1850–2100. We tested several one-dimensional (1D) lake models' robustness for long-term variations based on up to 63 years of limnological data collected by the French Observatory of LAkes (OLA). Here, we evaluate the possibility of forcing mechanistic models by following the long-term evolution of shortwave radiation and air temperature while providing realistic seasonal trends for the other variables for which local-scale downscaling often lacks accuracy. Based on this approach, MyLake, forced by air temperatures and shortwave radiations, predicted accurately the variations in the lake thermal regime over the last 4 to 6 decades, with RMSE < 1.95 ^∘C. Over the previous 3 decades, water temperatures have increased by 0.46 ^∘C per decade (±0.02 ^∘C) in the epilimnion and 0.33 ^∘C per decade (±0.06 ^∘C) in the hypolimnion. Concomitantly and due to thermal change, O₂ solubility has decreased by −0.104 mg L⁻¹ per decade (±0.005 mg L⁻¹) and −0.096 mg L⁻¹ per decade (±0.011 mg L⁻¹) in the epilimnion and hypolimnion, respectively. Based on the shared socio-economic pathway SSP370 of the Intergovernmental Panel on Climate Change (IPCC), peri-alpine lakes could face an increase of 3.80 ^∘C (±0.20 ^∘C) in the next 70 years, accompanied by a decline of 1.0 mg L⁻¹ (±0.1 mg L⁻¹) of O₂ solubility. Together, these results highlight a critical alteration in lake thermal and oxygen conditions in the coming decades, and a need for a better integration of long-term lake observatories data and lake models to anticipate climate effects on lake thermal regimes and habitats.

Introduction: Bioconvection, a phenomenon characterized by the collective upward swimming of motile microorganisms, has mainly been investigated within controlled laboratory settings, leaving a knowledge gap regarding its ecological implications in natural aquatic environments. This study aims to address this question by investigating the influence of bioconvection on the eco-physiology of the anoxygenic phototrophic sulfur bacteria community of meromictic Lake Cadagno.
Methods: Here we comprehensively explore its effects by comparing the physicochemical profiles of the water column and the physiological traits of the main populations of the bacterial layer (BL). The search for eco-physiological effects of bioconvection involved a comparative analysis between two time points during the warm season, one featuring bioconvection (July) and the other without it (September).
Results: A prominent distinction in the physicochemical profiles of the water column centers on light availability, which is significantly higher in July. This minimum threshold of light intensity is essential for sustaining the physiological CO₂ fixation activity of Chromatium okenii, the microorganism responsible for bioconvection. Furthermore, the turbulence generated by bioconvection redistributes sulfides to the upper region of the BL and displaces other microorganisms from their optimal ecological niches.
Conclusion: The findings underscore the influence of bioconvection on the physiology of C. okenii and demonstrate its functional role in improving its metabolic advantage over coexisting phototrophic sulfur bacteria. However, additional research is necessary to confirm these results and to unravel the multiscale processes activated by C. okenii’s motility mechanisms.

Gravity currents contribute to the transport of heat and mass in atmospheric and aquatic environments. In aquatic systems subject to daily surface cooling, gravity currents propagate through turbulent convective surroundings. Yet, the effects of thermal convection on aquatic gravity currents remain to be quantified. This paper demonstrates how the interaction between penetrative convection and downslope gravity currents impacts the fluid dynamics and transport across littoral aquatic systems. We performed field experiments in a wind-sheltered lake experiencing differential cooling to resolve the dynamics of thermally driven gravity currents in convective environments. Our in situ observations reveal that convective plumes penetrate gravity currents, generating large vertical fluctuations that foster the erosion of the stratified layer. This enhanced vertical mixing destroys the stratified downslope flow and limits the basin-scale transport. Our results demonstrate that the interaction between penetrative convection and downslope gravity currents controls the littoral-pelagic connectivity in aquatic ecosystems.

Abrupt changes in the Atlantic meridional overturning circulation (AMOC) are thought to affect tropical hydroclimate through adjustment of the latitudinal position of the intertropical convergence zone (ITCZ). Heinrich Stadial 1 (HS1) involves the largest AMOC reduction in recent geological time; however, over the tropical Indian Ocean (IO), proxy records suggest zonal anomalies featuring intense, widespread drought in tropical East Africa versus generally wet but heterogeneous conditions in the Maritime Continent. Here, we synthesize proxy data and an isotope-enabled transient deglacial simulation and show that the southward ITCZ shift over the eastern IO during HS1 strengthens IO Walker circulation, triggering an east-west precipitation dipole across the basin. This dipole reverses the zonal precipitation anomalies caused by the exposed Sunda and Sahul shelves due to glacial lower sea level. Our study illustrates how zonal modes of atmosphere-ocean circulation can amplify or reverse global climate anomalies, highlighting their importance for future climate change.

The factors that govern the geographical distribution of nitrogen fixation are fundamental to providing accurate nitrogen budgets in aquatic environments. Model-based insights have demonstrated that regional hydrodynamics strongly impact nitrogen fixation. However, the mechanisms establishing this physical-biological coupling have yet to be constrained in field surveys. Here, we examine the distribution of nitrogen fixation in Lake Tanganyika – a model system with well-defined hydrodynamic regimes. We report that nitrogen fixation is five times higher under stratified than under upwelling conditions. Under stratified conditions, the limited resupply of inorganic nitrogen to surface waters, combined with greater light penetration, promotes the activity of bloom-forming photoautotrophic diazotrophs. In contrast, upwelling conditions support predominantly heterotrophic diazotrophs, which are uniquely suited to chemotactic foraging in a more dynamic nutrient landscape. We suggest that these hydrodynamic regimes (stratification versus mixing) play an important role in governing both the rates and the mode of nitrogen fixation.

Lake Tanganyika’s pelagic fish sustain the second largest inland fishery in Africa and are under pressure from heavy fishing and global warming related increases in stratification. The strength of water column stratification varies regionally, with a more stratified north and an upwelling-driven, biologically more productive south. Only little is known about whether such regional hydrodynamic regimes induce ecological or genetic differences among populations of highly mobile, pelagic fish inhabiting these different areas. Here, we examine whether the regional contrasts leave distinct isotopic imprints in the pelagic fish of Lake Tanganyika, which may reveal differences in diet or lipid content. We conducted two lake-wide campaigns during different seasons and collected physical, nutrient, chlorophyll, phytoplankton and zooplankton data. Additionally, we analyzed the pelagic fish–the clupeids Stolothrissa tanganicae, Limnothrissa miodon and four Lates species–for their isotopic and elemental carbon (C) and nitrogen (N) compositions. The δ¹³C values were significantly higher in the productive south after the upwelling/mixing period across all trophic levels, implying that the fish have regional foraging grounds, and thus record these latitudinal isotope gradients. By combining our isotope data with previous genetic results showing little geographic structure, we demonstrate that the fish reside in a region for a season or longer. Between specimens from the north and south we found no strong evidence for varying trophic levels or lipid contents, based on their bulk δ¹⁵N and C:N ratios. We suggest that the development of regional trophic or physiological differences may be inhibited by the lake-wide gene flow on the long term. Overall, our findings show that the pelagic fish species, despite not showing evidence for genetic structure at the basin scale, form regional stocks at the seasonal timescales. This implies that sustainable management strategies may consider adopting regional fishing quotas.

Many compounds produced by cyanobacteria act as serine protease inhibitors, such as the tetrapeptides aeruginosins (Aer), which are found widely distributed. The structural diversity of Aer is intriguingly high. However, the genetic basis of this remains elusive. In this study, we explored the genetic basis of Aer synthesis among the filamentous cyanobacteria Planktothrix spp. In total, 124 strains, isolated from diverse freshwater waterbodies, have been compared regarding variability within Aer biosynthesis genes and the consequences for structural diversity. The high structural variability could be explained by various recombination processes affecting Aer synthesis, above all, the acquisition of accessory enzymes involved in post synthesis modification of the Aer peptide (e.g., halogenases, glycosyltransferases, sulfotransferases) as well as a large-range recombination of Aer biosynthesis genes, probably transferred from the bloom-forming cyanobacterium Microcystis. The Aer structural composition differed between evolutionary Planktothrix lineages, adapted to either shallow or deep waterbodies of the temperate climatic zone. Thus, for the first time among bloom-forming cyanobacteria, chemical diversification of a peptide family related to eco-evolutionary diversification has been described. It is concluded that various Aer peptides resulting from the recombination event act in chemical defense, possibly as a replacement for microcystins.

Lake Kivu is one of the African Great Lakes lying in the Albertine Rift. It provides livelihoods to 5.7 million people living in the two riparian countries of the Democratic Republic of the Congo and the Republic of Rwanda. Lake Kivu is currently experiencing numerous stressors, including fish habitat destruction, pollution, invasive species, weak governance and law enforcement as well as conflict between riparian countries. One of the biggest challenges on Lake Kivu is the limitation of coordinated and consistent research on the lake. Scientific attention to large lakes is often not seen as a high enough priority by the riparian countries, despite the lake sustaining millions of people's livelihoods, and contributes to the GDP of both countries. Although we have a fair understanding of the basic geology, physics, chemistry, and biology of the lake, there is a need for stronger long-term monitoring and research frameworks to gain more comprehensive understanding of the changes resulting from human uses and global warming. These would be needed to develop good policies and management decisions for sustainable and long-term health and use of the lake's resources. This manuscript presents an opinion of experts on what is known about the current lake's current status and its resources as well as about what should be done. It highlights key threats, issues and gaps that needs to be urgently addressed, and provides specific and strategic ways forward for long-term monitoring and management, essential to achieving a healthy Lake Kivu, able to sustain its dependents.

Die Sedimentdynamik und Vernetzung in Flusslandschaften sind Schlüsselelemente für die ökologische Funktion und den Hochwasserschutz. Im interdisziplinären Forschungsprojekt «Lebensraum Gewässer - Sedimentdynamik und Vernetzung» erforschten Wasserbau- ingenieur:innen und Ökolog:innen des ETH-Bereichs gemeinsam mit dem Bundesamt für Umwelt (BAFU) Massnahmen zur Förderung funktionaler Lebensräume und der Sedimentdynamik in Fliessgewässern. Die wichtigsten Forschungsergebnisse werden in einer Publikation der Reihe Umwelt-Wissen des BAFUs der Öffentlichkeit zugänglich gemacht. Mit einem Flyer für Schweizer Gemeinden wird zudem auf das langjährige Forschungsprogramm «Wasserbau und Ökologie», die neu gestaltete Webseite www.rivermanagement.ch und die Vermittlung der Erkenntnisse durch «Stop-Motion-Filme» aufmerksam gemacht. Der Flyer wird an alle Schweizer Gemeinden verschickt.

La dynamique sédimentaire et la connectivité dans les milieux fluviaux sont des éléments clés pour la fonction écologique et la protection contre les crues. Dans le projet de recherche intenlisciplinaire «Milieux fluviaux - dynamique sédimentaire et connectivité», des spécialistes en aménagement et en écologie des cours d'eau du domaine des EPF, en collaboration avec l'Office fédéral de l'environnement (OFEVI, ont étudié des mesures pour promouvoir les habitants fonctionnels et la dynamique sédimentaire dans les cours d'eau. Les principaux résultats de la recherche font l'objet d'une publication dans la série Connaissance de renvironnement de l'OFEV. De plus, un flyer destiné aux communes suisses informe sur le programme de recherche «Aménagement et écologie des cours d'eau», mené depuis de nombreuses années, ainsi que sur le nouveau site Internet www.rivermanagement.ch, ou des animations en volume servent à la transmission des connaissances. Le flyer sera envoyé à toutes les communes suisses.

Dissolved iron (dFe) availability limits the uptake of atmospheric CO₂ by the Southern Ocean (SO) biological pump. Hence, any change in bioavailable dFe in this region can directly influence climate. On the basis of Fe uptake experiments with Phaeocystis antarctica, we show that the range of dFe bioavailability in natural samples is wider (<1 to ~200% compared to free inorganic Fe′) than previously thought, with higher bioavailability found near glacial sources. The degree of bioavailability varied regardless of in situ dFe concentration and depth, challenging the consensus that sole dFe concentrations can be used to predict Fe uptake in modeling studies. Further, our data suggest a disproportionately major role of biologically mediated ligands and encourage revisiting the role of humic substances in influencing marine Fe biogeochemical cycling in the SO. Last, we describe a linkage between in situ dFe bioavailability and isotopic signatures that, we anticipate, will stimulate future research.

Carbohydrates are a ubiquitous constituent of organisms and contribute significantly to sedimentary organic carbon pools. Yet, the factors that control the degradation and long-term preservation of sedimentary carbohydrates are not well understood. Here, we investigate carbohydrate pool sizes and chemical compositions in high-altitude, meromictic Lake Cadagno (Switzerland) over a 13,500-year-old sedimentary succession that has recorded past changes from oxic to anoxic conditions and consists mostly of intercalations of lacustrine sediments and terrestrial-derived sediments. Analyses of the organic matter chemical composition by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) show that carbohydrates are selectively preserved over other organic matter constituents over time. The carbohydrate pyrolysis products levosugars (potentially cellulose-derived) and (alkyl)furans and furanones (potentially pectin-derived) dominate both lacustrine and terrestrially derived sediment layers, suggesting aquatic and terrestrial-derived sources of these compounds. Carbohydrate monomer analyses indicate galactose and glucose as dominant monomers and show no clear differences between aquatic and terrestrial organic matter. No clear impacts of past changes in redox conditions on carbohydrate compositions were observed. Our study shows that carbohydrates are a major contributor to sedimentary organic carbon burial in Lake Cadagno and indicates the effective preservation of both aquatic and terrestrial derived carbohydrates over millennia in lake sediments.

As motivation to address environmental dissemination of antimicrobial resistance (AMR) is mounting, there is a need to characterize mechanisms by which AMR can propagate under environmental conditions. Here we investigated the effect of temperature and stagnation on the persistence of wastewater-associated antibiotic resistance markers in riverine biofilms and the invasion success of genetically-tagged Escherichia coli. Biofilms grown on glass slides incubated in-situ downstream of a wastewater treatment plant effluent discharge point were transferred to laboratory-scale flumes fed with filtered river water under potentially stressful temperature and flow conditions: recirculation flow at 20 °C, stagnation at 20 °C, and stagnation at 30 °C. After 14 days, quantitative PCR and amplicon sequencing were used to quantify bacteria, biofilms diversity, resistance markers (sul1, sul2, ermB, tetW, tetM, tetB, blaCTX-M-1, intI1) and E. coli. Resistance markers significantly decreased over time regardless of the treatment applied. Although invading E. coli were initially able to colonize the biofilms, its abundance subsequently declined. Stagnation was associated with a shift in biofilm taxonomic composition, but there was no apparent effect of flow conditions or the simulated river-pool warming (30 °C) on AMR persistence or invasion success of E. coli. Results however indicated that antibiotic resistance markers in the riverine biofilms decreased under the experimental conditions in the absence of exposure to external inputs of antibiotics and AMR.

Real-time quantitative PCR (qPCR) has been widely used to quantify gene copy numbers in microbial ecology. Despite its simplicity and straightforwardness, establishing qPCR assays is often impeded by the tedious process of producing qPCR standards by cloning the target DNA into plasmids. Here, we designed double-stranded synthetic DNA fragments from consensus sequences as qPCR standards by aligning microbial gene sequences (10–20 sequences per gene). Efficiency of standards from synthetic DNA was compared with plasmid standards by qPCR assays for different phylogenetic marker and functional genes involved in carbon (C) and nitrogen (N) cycling, tested with DNA extracted from a broad range of soils. Results showed that qPCR standard curves using synthetic DNA performed equally well to those from plasmids for all the genes tested. Furthermore, gene copy numbers from DNA extracted from soils obtained by using synthetic standards or plasmid standards were comparable. Our approach therefore demonstrates that a synthetic DNA fragment as qPCR standard provides comparable sensitivity and reliability to a traditional plasmid standard, while being more time- and cost-efficient.

Special attention has been given to chromium (Cr) as a paleoproxy tracing redox cycling throughout Earth’s history, due to differences in the solubility of its primary redox species at Earth’s surface (Cr(III) and Cr(VI)) and isotope fractionation associated with their interconversion. In turn, chromium’s paleoproxy potential has motivated studies of the modern ocean to better understand which processes drive its cycling and to constrain their impact on the Cr isotope composition (δ⁵³Cr) of seawater. Here, we present total dissolved seawater Cr concentrations and δ⁵³Cr along the GEOTRACES GP13 section. This section is a zonal transect extending from Australia in the subtropical southwest Pacific Ocean. Surface signals of local biological Cr cycling are minimal, in agreement with distributions of dissolved major nutrients as well as biologically-controlled trace metals in this low productivity, oligotrophic environment. Depth profiles have Cr concentration minima in surface waters and maxima at depth, and are largely shaped by the advection of nutrient- and Cr-rich subsurface waters rather than vertically-driven processes. Samples close to the sediment-water interface indicate important benthic Cr fluxes across the section.
The GP13 transect crosses the hydrothermally-active Kermadec Arc. Hydrothermal fluids (consisting of <15% background seawater) were collected from three venting sites at the Brothers Volcano (along the Kermadec Arc). These fluids yielded near-crustal δ⁵³Cr values (-0.17 to +0.08‰) and elevated [Cr] (7.5-23 nmol kg^-1, hydrothermal endmember [Cr] ≈ 8-27 nmol kg^-1), indicating that the Kermadec Arc may be an isotopically light Cr source. Dissolved [Fe] enrichments have been reported previously in deep waters (∼1600-3000 m) along the GP13 transect, east of the Kermadec Arc. These same waters show elevated [Cr] compared to Circumpolar Deep Water ([Cr] = 3.88 ± 0.11, δ⁵³Cr = 0.89 ± 0.08, n = 32), with an average [Cr] accumulation of 0.71 ± 0.11 nmol kg^-1 (1 SD), and an estimated δ⁵³Cr of +0.46 ± 0.30‰ (2 SD, n = 9) for the accumulated Cr. Comparing high-temperature vent and neutrally buoyant plume data, hydrothermal-sourced Cr is likely negligable compared to Cr contributions from other processes (benthic fluxes, release from particles), and the advection of more Cr-rich Pacific Deep Water. It is unlikely that hydrothermal vents would be a major contributor within the regional or global biogeochemical Cr cycle, even if hydrothermal fluxes change by orders of magnitude, and therefore δ⁵³Cr trends in the paleorecord may be attributable, at least in part, to major changes in other controls on Cr (e.g. widespread anoxia).

Inland and coastal waters provide key ecosystem services and are closely linked to human well-being. In this study, we propose a semi-analytical method, which can be applied to Sentinel-2 MultiSpectral Instrument (MSI) images to retrieve high spatial-resolution total suspended solids (TSS) concentration in a broad spectrum of aquatic ecosystems ranging from clear to extremely turbid waters. The presented approach has four main steps. First, the remote sensing reflectance (R_rs) at a band lacking in MSI (620 nm) is estimated through an empirical relationship from R_rs at 665 nm. Second, waters are classified into four types (clear, moderately turbid, highly turbid, and extremely turbid). Third, semi-analytical algorithms are used to estimate the particulate backscattering coefficient (b_bp) at a reference band depending on the water types. Last, TSS is estimated from b_bp at the reference band. Validation and comparison of the proposed method with three existing methods are performed using a simulated dataset (N = 1000), an in situ dataset collected from global inland and coastal waters (N = 1265) and satellite matchups (N = 40). Results indicate that the proposed method can improve TSS estimation and provide accurate retrievals of TSS from all three datasets, with a median absolute percentage error (MAPE) of 14.88 %, 31.50 % and 41.69 % respectively. We also present comparisons of TSS mapping between the Sentinel-3 Ocean and Land Colour Instrument (OLCI) and MSI in Lake Kasumigaura, Japan and the Tagus Estuary, Portugal. Results clearly demonstrate the advantages of using MSI for TSS monitoring in small water bodies such as rivers, river mouths and other nearshore waters. MSI can provide more detailed and realistic TSS estimates than OLCI in these water bodies. The proposed TSS estimation method was applied to MSI images to produce TSS time-series in Lake Kasumigaura, which showed good agreements with in situ and OLCI-derived TSS time-series.

In this study, the speciation and isotopic composition of Zn were traced across the sediments of a freshwater lake that experienced one hundred years of strong eutrophication, in order to assess the potential of sedimentary Zn isotopes to record such an environmental disturbance. The results indicate that the sedimentary Zn isotope signal varied with the change from pre-eutrophic to eutrophic conditions in the investigated lake. The average δ⁶⁶Zn_JMC value of the dominantly allochthonous lithogenic sediments deposited during the pre-eutrophic period was +0.27‰ ±0.05‰ (i.e. similar to the δ⁶⁶Zn_JMC value of +0.28‰ ±0.05‰ proposed for Bulk Silicate Earth), while enhanced autochthonous biochemical sedimentation during the eutrophic period resulted in significantly lower δ⁶⁶Zn_JMC values down to +0.04‰ ±0.06‰. Synchrotron-based X-ray absorption spectroscopy data revealed a concomitant change in Zn speciation from a dominant fraction of Zn in clay minerals during the pre-eutrophic period to a major fraction of Zn in ZnS during the eutrophic period. A linear regression relating the sedimentary Zn isotope signal to the fraction of Zn in ZnS indicated δ⁶⁶Zn_JMC values of +0.27‰ ±0.06‰ and 0.00‰ ±0.08‰ for Zn in clay minerals and in ZnS, respectively. The enrichment of light Zn in ZnS in the eutrophic sediments is tentatively attributed to enhanced biological uptake of light Zn in the water column, which resulted in an enhanced flux of organic-bound Zn towards the sediments and further transformation of organic Zn into ZnS upon biomass mineralization during early diagenesis. This hypothesis is in agreement with the fractionation towards lighter Zn reported for both biological uptake of Zn and ZnS precipitation. The results of this study emphasize the potential of sedimentary Zn isotopes to register past eutrophic periods in freshwater lakes, and thus to serve as a probe of paleo-environmental conditions and/or past land use at the catchment scale.

In total, 28 of the 29 fish species reported from the Lake Kivu basin occur in the littoral zone of the lake, but information about their structure, occurrence, and the habitats affecting their distribution is largely lacking. The lake’s inshore area is poorly heterogenous, with rock and macrophyte habitats representing the major habitats. The lack of heterogeneity in the habitats is probably an important factor influencing species richness, abundance, and the association between the species and habitats. We evaluated the fish diversity, abundance, and habitat parameters across 14 sites representing the major habitats of the lake, using data collected between April 2018 and October 2019. We calculated Hull and Jaccard indices and applied uni- and multivariate statistical approaches to the collected data. We identified 18 fish species in the lake. In the north, 17 species were found, with high abundance in rocky sites but low abundance in sandy habitats. In the south, 15 species were reported. We identified 12 species in the Ishungu Basin where the site with rock substrate had high abundance and 13 species in the Bukavu Basin with weak species richness and low abundance across degraded sites. Lamprichthys tanganicanus, a non-native species, was abundant in rocky (north) and macrophyte sites (south). Sand, rock, conductivity, depth, dissolved oxygen, and water transparency were significant parameters that could explain the fish distribution in the north while dissolved oxygen, vegetation cover, depth, and conductivity were significant in the south. A monitoring programme of the fish fauna in Lake Kivu is needed.

Freshwater systems have undergone drastic alterations during the last century, potentially affecting cross-boundary resource transfers between aquatic and terrestrial ecosystems. One important connection is the export of biomass by emergent aquatic insects containing omega-3 polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA), that is scarce in terrestrial systems. Because of taxon-specific differences in PUFA content and functional traits, the contribution of different insect groups should be considered, in addition to total biomass export. In this context, one important trait is the emergence mode. Stoneflies, in contrast to other aquatic insects, crawl to land to emerge instead of flying directly from the water surface, making them accessible to ground-dwelling predators. Because stoneflies are especially susceptible to environmental change, stream degradation might cause a mismatch of available and required nutrients, particularly for ground-dwelling predators. In this study, we estimated emergent biomass and EPA export along two streams with different levels of habitat degradation. The EPA content in aquatic insects did not differ with different degrees of habitat degradation and total biomass export in spring was with 7.9 ± 9.6 mg m^-2 day^-1 in the degraded and 7.3 ± 8.5 mg m^-2 day^-1 in the natural system, also unaffected. However, habitat degradation substantially altered the contribution of crawling emergence to the total export in spring, with no biomass export by stoneflies at the most degraded sites. The EPA content in ground-dwelling spiders was correlated with emergent stonefly biomass, making up only 16.0 ± 6.2 % of total fatty acids at sites with no stonefly emergence, but 27.3 ± 3.0 % at sites with highest stonefly emergence. Because immune function in ground-dwelling spiders has been connected to EPA levels, reduced crawling emergence might impact spider fitness. Functional traits, like emergence mode as well as nutritional quality, should be considered when assessing the effects of stream degradation on adjacent terrestrial ecosystems.

Climate change and reduction in nutrient loads have significant effects on primary production and phytoplankton growth dynamics. Since in the last few decades in many regions, nutrients in lakes were reduced simultaneously as the climate changed. Yet, it remains unclear which of the two has impacted primary production the most. In this study, we couple the General Ocean Turbulence Model with the Ecological Regional Ocean Model to disentangle the effects of climate change and reoligotrophication on primary production (PP) in Lake Geneva, Switzerland–France. We apply a data assimilation method to calibrate the model with the observations from the past (1981–1990) and validate it against the in situ data from the present decade (2011–2019). Both decades represent different climate conditions and trophic states of the lake. We show that the model is skilful to reproduce assimilated and unassimilated observations from both periods. According to our results, the effect of reoligotrophication on PP is marginally higher than that of warming, leading to a net decrease in primary production by 10% from the past to the present. The areal phosphorus supply in Lake Geneva, in spite of a decrease by ∼70%, is still characteristic of a meso-to-eutrophic ecosystem. This points towards an incomplete reoligotrophication of the lake. The effects of future climate change on winter mixing and PP dynamics have also been studied. Although there would be a significant reduction in deep mixing, the autotrophic production in Lake Geneva is expected to increase by ∼20% by the end of twenty-first century, largely due to stimulation in biomass build-up of temperature-dependent algae (e.g. dinoflagellates and cyanobacteria). Considering our results to represent other large temperate lakes with similar trophic status and water residence time as Lake Geneva, future climate scenarios are expected to bring back symptoms of eutrophication.

Wastewater treatment plants (WWTPs) are key sources of antimicrobial resistance genes (ARGs) that could influence the resistomes of microbial communities in various habitats of the receiving river ecosystem. However, it is currently unknown which habitats are most impacted and whether ARGs, like certain chemical contaminants, could be accumulated or enriched in the river ecosystem. We conducted a systematic metagenomic survey on the antibiotic resistomes of WWTP effluent, four riverine habitats (water, suspended particles, sediment, epilithic biofilm), and freshwater amphipod gut microbiomes. The impact of WWTP effluent on the downstream habitats was assessed in nine Swiss rivers. While there were significant differences in resistomes across habitats, the wastewater resistome was more similar to the resistome of receiving river water than to the resistomes of other habitats, and river water was the habitat most strongly impacted by the WWTPs effluent. The sulfonamide, beta-lactam, and aminoglycoside resistance genes were among the most abundant ARGs in the WWTP effluents, and especially aadA, sul1, and class A beta-lactamase genes showed significantly increased abundance in the river water of downstream compared to upstream locations (p < 0.05). However, this was not the case for the sediment, biofilm, and amphipod gut habitats. Accordingly, evidence for accumulation or enrichment of ARGs through the riverine food web was not identified. Our study suggests that monitoring riverine antimicrobial resistance determinants could be conducted using "co-occurrence" of aadA, sul1, and class A beta-lactamase genes as an indicator of wastewater-related pollution and should focus on the water as the most affected habitat.

The development of algorithms for remote sensing of water quality (RSWQ) requires a large amount of in situ data to account for the bio-geo-optical diversity of inland and coastal waters. The GLObal Reflectance community dataset for Imaging and optical sensing of Aquatic environments (GLORIA) includes 7,572 curated hyperspectral remote sensing reflectance measurements at 1 nm intervals within the 350 to 900 nm wavelength range. In addition, at least one co-located water quality measurement of chlorophyll a, total suspended solids, absorption by dissolved substances, and Secchi depth, is provided. The data were contributed by researchers affiliated with 59 institutions worldwide and come from 450 different water bodies, making GLORIA the de-facto state of knowledge of in situ coastal and inland aquatic optical diversity. Each measurement is documented with comprehensive methodological details, allowing users to evaluate fitness-for-purpose, and providing a reference for practitioners planning similar measurements. We provide open and free access to this dataset with the goal of enabling scientific and technological advancement towards operational regional and global RSWQ monitoring.

Theory suggests that increasingly long, negative feedback loops of many interacting species may destabilize food webs as complexity increases. Less attention has, however, been paid to the specific ways in which these delayed negative feedbacks' may affect the response of complex ecosystems to global environmental change. Here, we describe five fundamental ways in which these feedbacks might pave the way for abrupt, large-scale transitions and species losses. By combining topological and bioenergetic models, we then proceed by showing that the likelihood of such transitions increases with the number of interacting species and/or when the combined effects of stabilizing network patterns approach the minimum required for stable coexistence. Our findings thus shift the question from the classical question of what makes complex, unaltered ecosystems stable to whether the effects of, known and unknown, stabilizing food-web patterns are sufficient to prevent abrupt, large-scale transitions under global environmental change.

Human impacts such as habitat loss, climate change and biological invasions are radically altering biodiversity, with greater effects projected into the future. Evidence suggests human impacts may differ substantially between terrestrial and freshwater ecosystems, but the reasons for these differences are poorly understood. We propose an integrative approach to explain these differences by linking impacts to four fundamental processes that structure communities: dispersal, speciation, species-level selection and ecological drift. Our goal is to provide process-based insights into why human impacts, and responses to impacts, may differ across ecosystem types using a mechanistic, eco-evolutionary comparative framework. To enable these insights, we review and synthesise (i) how the four processes influence diversity and dynamics in terrestrial versus freshwater communities, specifically whether the relative importance of each process differs among ecosystems, and (ii) the pathways by which human impacts can produce divergent responses across ecosystems, due to differences in the strength of processes among ecosystems we identify. Finally, we highlight research gaps and next steps, and discuss how this approach can provide new insights for conservation. By focusing on the processes that shape diversity in communities, we aim to mechanistically link human impacts to ongoing and future changes in ecosystems.

We introduce the first two-way coupled model for the thermo-viscous damping of a mechanical structure (such as quartz tuning fork) that is forced by the weak acoustic and thermal waves generated when a laser source periodically interacts with a trace gas. The model is based on a Helmholtz system of thermo-visco-acoustic equations in the fluid, together with a system of equations for the temperature and the displacement of the structure. These two subsystems are coupled across the fluid-structure interface via several conditions. With this model, the user specifies the geometry of the structure and the viscous and thermal parameters of the fluid, and the model outputs an effective damping parameter and a signal strength that is proportional to the concentration of the trace gas. This new model is a significant improvement over existing one-way coupled models in which damping effects are incorporated via a priori laboratory measurements. Analytical solutions derived for an annular structure show reasonable agreement between the one-way and two-way coupled models at higher ambient pressures. However, at low ambient pressure the one-way coupled model does not adequately capture thermo-viscous effects.

The United Nations (UN) expectations for 2030 account for a renewable, affordable, and eco-friendly energy future. The 2030 agenda includes 17 different Sustainable Development Goals (SDGs) for countries worldwide. In this work, the 7th SDG: Affordable and Clean Energy, is brought into focus. For this goal, five main challenges are discussed: (i) limiting the use of fossil fuels; (ii) migrating towards diversified and renewable energy matrices; (iii) decentralizing energy generation and distribution; (iv) maximizing energy and energy storage efficiency; and (v) minimizing energy generation costs of chemical processes. These challenges are thoroughly scrutinized and surveyed in the context of recent developments and technologies including energy planning and supervision tools employed in the Global South. The discussion of these challenges in this work shows that the realization of SDG 7, whether partially or in full, within the Global South and global contexts, is possible only if existing technologies are fully implemented with the necessary international and national policies. Among the key solutions identified in addressing the five main challenges of SDG 7 are a global climate agreement; increased use of non-fossil fuel energy sources; Global North assistance and investment; reformed global energy policies; smart grid technologies and real time optimization and automation technologies.

Ein zeitnahes Biomonitoring mit Nanopore-Sequenzierung gewährt neue Einblicke in die biologischen Prozesse einer Abwasserreinigungsanlage (ARA). Im Rahmen des Projekts «MicROcensus» wurde an verschiedenen ARA die Einsatzfähigkeit solcher Mikrobiom-Analysen als Diagnoseinstrument evaluiert. So unterstützen Momentaufnahmemessungen die Ursachenfindung von Prozessinstabilitäten oder Begleitphänomenen. Während wöchentliche Analysen des Mikrobioms – bei Bekanntsein der jahreszeitlichen Dynamiken - als Frühwarnsystem dienen und praxisrelevante Daten für den ARA-Betrieb liefern können.

Sun-induced fluorescence (SIF) as a close remote sensing based proxy for photosynthesis is accepted as a useful measure to remotely monitor vegetation health and gross primary productivity. It is therefore important to develop methods that allow for its precise and reliable retrieval from radiance measurements with spectral resolutions that have been increasing over the past few years. Retrieval methods are catching up to the increasing complexity of the available datasets making use of their whole information extent (spectral, spatial and temporal) but the comparability of different SIF retrievals and consistency across scales is still limited.
In this work we present the new retrieval method WAFER (WAvelet decomposition FluorEscence Retrieval) based on wavelet decompositions of the measured spectra of reflected radiance as well as a reference radiance not containing fluorescence. By comparing absolute absorption line depths by means of the corresponding wavelet coefficients, a relative reflectance is retrieved independently of the fluorescence, i.e. without introducing a coupling between reflectance and fluorescence. The fluorescence can then be derived as the remaining offset. This method can be applied to arbitrary chosen wavelength windows in the whole spectral range, such that all the spectral data available is exploited, including the separation into several frequency (i.e. width of absorption lines) levels and without the need of extensive training datasets.
At the same time, the assumptions about the reflectance shape are minimal and no spectral shape assumptions are imposed on the fluorescence, which not only avoids biases arising from wrong or differing fluorescence models across different spatial scales and retrieval methods but also allows for the exploration of this spectral shape for different measurement setups.
WAFER is tested on a synthetic dataset as well as several diurnal datasets acquired with a field spectrometer (FloX) over an agricultural site. We compare the WAFER method to two established retrieval methods, namely the improved Fraunhofer line discrimination (iFLD) method and spectral fitting method (SFM) and find a good agreement with the added possibility of exploring the true spectral shape of the offset signal and free choice of the retrieval window. On our synthetic dataset, WAFER seems to outperform the SFM and works best in a spectral window only containing solar Fraunhofer lines where we achieve a relative retrieval error of 10% on average. Applied to the real dataset, the method returns reasonable diurnal cycles for SIF and can, due to the decoupling of reflectance and fluorescence retrieval, reveal interesting trends at times when vegetation canopies may experience a midday depression that remain largely unobserved with current methods.

During the Pleistocene, Earth's climate changed dramatically. The mid-Pleistocene transition (MPT; ~1.3-0.7 million years (Ma)) featured an important ice volume increase at both poles. The evolution of large Arctic ice sheets caused the sequestration of methane as free gas and hydrates in subseabed sediments. Ice volume changes, associated with variable pressures and temperatures, perturbed those giant reservoirs, causing methane leakages. Here, we present borehole data from the Arctic-Atlantic gateway region, providing foraminiferal stable carbon isotope and source-specific biomarker evidence that reveals three main seafloor leakage episodes that occurred prior to and across the mid-Pleistocene transition. By combining borehole data with hydrate stability modelling, we propose that tectonic stress changes associated with large ice volume early build-up and wastage during the mid-Pleistocene controlled episodic methane leakages from subsurface reservoirs. Our data indicate methane release, showing a potential scenario for vast Arctic areas storing methane that are now affected by ongoing ice volume decrease.

In ice-covered lakes, near-bottom oxygen concentration decreases for most of the wintertime, sometimes down to the point that bottom waters become hypoxic. Studies insofar have reached divergent conclusions on whether climate change limits or reinforces the extent and duration of hypoxia under ice, raising the need for a comprehensive understanding of the drivers of the dissolved oxygen (DO) dynamics under lake ice. Using high-temporal resolution time series of DO concentration and temperature across 14 mountain lakes, we showed that the duration of bottom hypoxia under ice varies from 0 to 236 d within lakes and among years. The variability of hypoxia duration was primarily explained by changes in the decay rate of DO above the lake bottom rather than by differences in DO concentration at the ice onset or in the ice-cover duration. We observed that the DO decay rate was primarily linked to physical controls (i.e., deep-water warming) rather than biogeochemical drivers (i.e., proxies for lake or catchment productivity). Using a simple numerical model, we provided a proof-of-concept that the near-bed stratification can be the mechanism tying the DO decay rate to the sediment heat release under the ice. We ultimately showed that the DO decay rate and hypoxia duration are driven by the summer light climate, with faster oxygen decline found under the ice of clearer cryostratified alpine lakes. We derived a framework theorizing how the hypoxia duration might change under the ice of alpine lakes in a warmer climate.

In alkaline freshwater systems, the apparent absence of carbon limitation to gross primary production (GPP) at low CO₂ concentrations suggests that bicarbonates can support GPP. However, the contribution of bicarbonates to GPP has never been quantified in lakes along the seasons. To detect the origin of the inorganic carbon maintaining GPP, we analyze the daily stoichiometric ratios of CO₂–O₂ and alkalinity–O₂ in a deep hardwater lake. Results show that aquatic primary production withdraws bicarbonate from the alkalinity pool for two-thirds of the year. Alkalinity rather than CO₂ is the dominant inorganic carbon source for GPP throughout the stratified period in both the littoral and pelagic environments. This study sheds light on the neglected role of alkalinity in the freshwater carbon cycle throughout an annual cycle.

Refugia are habitats where organisms retreat during a disturbance (e.g. flood, drought). Due to their reduced intensity of physico-chemical conditions, refugia allow organisms to withstand a disturbance. Despite their important ecological role, refugia are poorly studied and often neglected in practical management (e.g. river restoration). Through descriptions of field and laboratory experiments, this chapter illustrates the structure and function of flood refugia and emphasizes the role of the sediment regime in refuge provision.

Refugien sind Habitate, in die sich Lebewesen während einer Störung (z. B. Hochwasser, Trockenheit) zurückziehen können. Die Intensität einer Störung ist in Refugien gedämpft; dies ermöglicht den Lebewesen, eine Störung zu überstehen. Refugien sind trotz ihrer wichtigen ökologischen Rolle aber nur unzureichend erforscht und werden im praktischen Management (z. B. bei der Revitalisierung von Fliessgewässern) häufig vernachlässigt. Dieses Kapitel veranschaulicht die Struktur und Funktion von Hochwasserrefugien anhand von Feld- und Laborexperimenten und betont die Rolle des Geschiebehaushalts für die Verfügbarkeit von Refugien.

Les refuges sont des habitats dans lesquels des organismes se mettent à l'abri durant une perturbation (p. ex. crue ou sécheresse). Étant donné qu'ils présentent des conditions physico-chimiques moins sévères, les refuges permettent aux organismes de résister à une perturbation. Bien qu'ils jouent des rôles écologiques importants, peu d'études leur sont consacrées et ils sont souvent négligés dans la gestion pratique (p. ex. revitalisation des eaux). S'appuyant sur des descriptions d'expérience de terrain et de laboratoire, le présent chapitre illustre la structure et la fonction des refuges en situation de crue, en mettant l’accent sur le rôle du régime sédimentaire dans la mise à disposition d'un refuge.

I rifugi sono habitat in cui gli organismi si ritirano durante un evento estremo (p. es. piena o siccità). Considerata la ridotta intensità delle condizioni fisico-chimiche, i rifugi consentono agli organismi di resistere ai disturbi. Nonostante il loro importante ruolo ecologico, i rifugi sono poco studiati e spesso trascurati nella gestione pratica (p. es. la rivitalizzazione dei corsi d'acqua). Attraverso la descrizione di esperimenti sul campo e in laboratorio, il presente capitolo illustra la struttura e la funzione dei rifugi alluvionali evidenziando il ruolo del regime sedimentario nella disponibilità dei rifugi.

Global change increasingly threatens nature, endangering the ecosystem services human wellbeing depends upon. Biodiversity potentially mediates these impacts by providing resilience to ecosystems. While biodiversity has been linked to resilience and ecosystem service supply on smaller scales, we lack understanding of whether mediating interactions between biodiversity and anthropogenic drivers are global and ubiquitous, and how they might differ between systems. Here, we examine the potential for biodiversity to mediate anthropogenic driver-ecosystem service relationships using global datasets across three distinct systems: mountains, islands and deltas. We found that driver-ecosystem service relationships were stronger where biodiversity was more intact, and weaker at higher species richness, reflecting the negative correlation between intactness and richness. Mediation was most common in mountains, then islands, then deltas; reducing with anthropogenic impact. Such patterns were found across provisioning and regulating ecosystem services, and occurred most commonly with climate change and built infrastructure. Further, we investigated the contribution of biodiversity and abiotic and anthropogenic drivers to ecosystem services. Ecosystem service supply was associated with abiotic and anthropogenic drivers alongside biodiversity, but all drivers were important to different ecosystem services. Our results empirically show the importance of accounting for the different roles that biodiversity plays in mediating human relationships with nature, and reinforce the importance of maintaining intact biodiversity in ecosystem functioning.

Billions of tons of hazardous mine waste are stored in thousands of tailings storage facilities around the world. These impoundments represent one of the most important environmental risk factors of industrial mining, since occasional tailings spills or dam failures cause devastating impacts on humans and ecosystems, specifically along river corridors. In this study, we developed a satellite remote sensing methodology to assess the impacts of tailings spills on water quality focusing on the controversial incident that occurred at the Catoca diamond mine in Angola in late July 2021. The spill allegedly caused important river pollution in neighbouring Democratic Republic of the Congo (DR Congo) and led to public health concerns including the loss of human lives - however the mining company denied any responsibility. We processed high resolution imagery acquired by ESA's Sentinel-2 satellites using the Python package Acolite for atmospheric correction and turbidity retrieval, and applied a river skeletonizing algorithm to automatically extract turbidity values for the entire river system. This allowed tracking the propagation of the pollution front from the source at the Catoca mine through the Tshikapa- and the Kasaï River during more than one month and across 1400 km, until the pollution front finally dissipated after discharging into the Congo River. We further analyzed a 6-year time series of virtual stations in the Tshikapa River located up- and downstream of the effluent discharge to compare the impacts of the tailings spill to seasonal variabilities of water quality. Turbidity values caused by the spill largely exceeded the seasonal variability in the Tshikapa River in recent years. These findings confirm that the Catoca tailings spill has significantly affected water quality of the Tshikapa- and the Kasaï River with total suspended solids concentrations that were several 10-fold above drinking water standards in Lunda Norte Province, Angola, and Kasaï Province, DR Congo, making severe public health impacts for residents and fish kills highly probable. After investigating whether this methodology could be applied to other tailings dam failures that have occurred since the Sentinel-2 mission began in 2015, we recommend to apply it to four other incidents in Mexico, Myanmar, Peru and China, respectively. Overall, this Sentinel-2 workflow provides the opportunity to assess the large-scale impacts of pollution incidents in mining areas around the world in locations where hydrological- and water quality data are scarce and monitoring capacities are limited.

1. Lakes are recipients of allochthonous organic matter and nutrients. However, the importance of these subsidies for food webs and how they vary with lake trophic status remains unclear, especially for large lakes.
2. We assessed the source and fate of organic matter and nutrients in seven perialpine lakes across a gradient of trophic status. We measured carbon and nitrogen stable isotopes of amino acids of lake-residing Atlantic trout, Salmo trutta, to determine the source of primary production (i.e., how carbon is fixed in the ecosystem) and how it is transferred through food webs, respectively. Based on essential amino acid carbon fingerprinting, we estimated the probability of organic carbon originating from autochthonous (algal), allochthonous (terrestrial plant), and recycled (bacterial) sources. In addition, we used amino acid δ¹⁵N to track how this primary production is transferred to consumers in general, and by using different trophic amino acids (glutamic acid and alanine), identify the trophic pathways involving either metazoan or protozoans.
3. We found a high likelihood of autochthonous origin of organic carbon (86 ± 9%) in trout that contrasted with allochthonous origins of particulate organic matter and some sediments. We showed that those estimates are good proxies of source reliance. Our results also highlighted the importance of bacterial origin of organic carbon in fish (12%). The likely autochthonous origin of this carbon was supported by trophic markers (Ala δ¹⁵N) that suggest the role of protists in transferring recycled organic carbon up the food web. While the sources of nitrogen sustaining food webs varied among lakes, we found a conserved carbon fingerprinting of fish. Overall, this suggests an uncoupling between the source of nutrients and organic carbon in large perialpine lakes.
4. Across a wide range of trophic status (c. 2 orders of magnitude range of phosphorus concentration), several lines of evidence suggested that perialpine lake food webs shared a common reliance on autochthonous and bacterial production.
5. Our study is the first to quantify the dependence on allochthonous organic carbon in lake food webs based on new amino acid stable isotope markers (carbon fingerprinting and Ala δ¹⁵N) and shows promise for estimating the source of carbon fixation in ecosystems. Our results support previous suggestions that terrestrial organic carbon is a relatively minor source for aquatic consumers despite contributing to the pool of organic matter, and more importantly, its contribution does not vary substantially with trophic status in perialpine lakes.

This article focuses on defining hydromorphological features to be extracted from historical maps by means of digital map processing techniques. The hydromorphological features, evolving through time, can be described quantitatively by the development and application of various ecological metrics to study the spatiotemporal change of the natural and built freshwater environment. With the goal to support future revitalization efforts, this article first reviews the theory on quantifying spatiotemporal change using landscape and ecological metrics, ranging from simple shape metrics (e.g., shoreline length) to more complex hydromorphological indexes (e.g., river braiding index). Second, the hydromorphological features themselves are important to consider in terms of data quality and uncertainty as they might inherit errors due to the low-quality maps, the extraction process, or due to poor definitions used during feature extraction efforts. Errors introduced by poorly defined features can be avoided by the use of a well-structured definition system. Thus, the article concludes in a new concept categorizing hydromorphological features and the changes they can undergo. The definition framework integrates novel perspectives for defining and evaluating features from the Siegfried and old Swiss national map, including key aspects from the theory.

Recent efforts using microstructure turbulence measurements have contributed to our understanding of the overall energy budget in lakes and linkages to vertical fluxes. A paucity of lake-wide turbulence measurements hinders our ability to assess how representative such budgets are at the basin scale. Using an autonomous underwater glider equipped with a microstructure payload, we explored the spatial variability of turbulence in pelagic and near-shore regions of Lake Geneva. Dissipation rates of kinetic energy and thermal variance were estimated by fitting temperature gradient fluctuations spectra to the Batchelor spectrum. In deep waters, turbulent dissipation rates in the surface and thermocline were mild (∼10^-8 W kg^-1) and weakened towards the hypolimnion (∼10^-11 - 10^-10 W kg^-1). The seasonal thermocline exhibited inhibited interior mixing, with extremely low values of mixing efficiency (Ri_f ≪ 0.1). In contrast, in the slope zone, a band of significantly enhanced energy dissipation (∼5 × 10^-8 W kg^-1) extended well above the bottom boundary layer and was associated with strong, efficient mixing (Ri_f > 0.17). The resulting contribution of the slope region to basin-scale mixing was large, with 90% of the basin-wide mixing - and only 30% energy dissipation - occurring within 4 km of the shoreline. This boundary mixing will modify overturning circulation and the transport pathways of dissolved compounds exchanged with the sediments. The dynamics responsible for the shift in the mixing regime, which appears crucial for the mixing budget of lakes, could not be fully unraveled with the collected observations. Additional model data analyses hint at the role of submesoscale instabilities.

Climate change leads to an increased frequency of severe weather events as well as stressful growing conditions. Together these changes may impact the resilience of ecosystems. To keep track of such effects, conservation managers monitor the “ecological integrity” or coherence of ecosystem processes, such as the cycling of carbon and water. Networked phenocams can produce near-continuous observations of leaf function in the context of climate change, capturing declines due to disturbance or stress. Here we explore the application of phenocams to detect responses to disturbance and stress using 14 examples from the PhenoCam Network. We selected these previously published and new examples to include a variety of disturbances in the form of hurricanes, a windstorm, frost, insect defoliation, and stress due to drought. Frost and herbivory disturbances led to both reductions and extensions in the duration of the rising section of the greenness curve, while hurricanes generally led to reductions in the duration of the plateau section and entire leaf-on period. We found that changes of at least ±20% in the duration of the rising section in the seasonal greenness curve, ±20% in the duration of the plateau section following the seasonal greenness peak, and ±10% in the duration of the entire leaf-on period were a reliable signal of leaf functional declines due to disturbance or stress. If such declines become increasingly frequent and severe as a consequence of climate change, this could impact ecological integrity through interruptions to ecosystem processes. Comparing the duration of these periods in a given year to the average for other years with these thresholds resulted in average true detection rates of 86% and false-positive detection rates of 11% when sampling from probability density functions of 344 broadleaf and needleleaf PhenoCam site-years. Here we show that phenocams are powerful ecological integrity monitoring tools, which can be efficiently applied to quantify dynamic responses to disturbance or stress.

The old question of whether the solar dynamo is synchronized by the tidal forces of the orbiting planets has recently received renewed interest, both from the viewpoint of historical data analysis and in terms of theoretical and numerical modeling. We aim to contribute to the solution of this longstanding puzzle by analyzing cosmogenic radionuclide data from the last millennium. We reconsider a recent time series of ¹⁴C-inferred sunspot data and compare the resulting cycle minima and maxima with the corresponding conventional series down to 1610 A.D., enhanced by Schove's data before that time. We find that, despite recent claims to the contrary, the ¹⁴C-inferred sunspot data are well compatible with a synchronized solar dynamo, exhibiting a relatively phase-stable period of 11.07 years, which points to a synchronizing role of the spring tides of the Venus-Earth-Jupiter system.

Arctic charr (Salvelinus alpinus [L.] complex) has been widely used as a model system for studies in evolutionary ecology because of its diversity in feeding ecology, habitat use, life history forms, and associated morphologies observed in matured individuals. However, we still know relatively little about traits exhibited early in life of the species, although the trait diversity of matured individuals may largely be shaped during development. Egg size is a key determinant of various traits exhibited early in life. Therefore, describing egg size variation within- and between-individuals as well as the link between egg size and adult traits will be a useful step in understanding the early life trait diversity of Arctic charr. Here, using Greenlandic Arctic charr, which includes alternative life history forms (i.e. anadromous and resident) and spawning habitat use (i.e. lake and river spawner), we described egg size variation (i.e. clutch-mean egg diameter and within-clutch variation) and explored the link between egg size variation and female body length, life history form, and spawning habitats. As in many other fishes, clutch-mean egg diameter increased with female body length. No significant effect of other female traits on clutch mean-egg diameter was detected, suggesting that female body size variation could be a direct cause of early life history trait variation. On the other hand, we found that the degree of within-clutch variation of the anadromous life history form was higher than that of the resident life history form. The pattern could be interpreted in an adaptive context. For instance, given that the anadromous life history form tends to be semelparous, anadromous females could decrease the likelihood of complete reproductive failure by producing variable-sized offspring within a clutch since at least some offspring are expected to be matched to the prevailing environment.

Die Drift (bzw. Verdriftung) wird als flussabwärts gerichteter Transport von aquatischen Organismen durch die Strömung definiert (Waters, 1972; Brittain & Eikeland, 1988). Die natürliche Drift des Makrozoobenthos in Fliessgewässern hat einen wesentlichen Einfluss auf die Aus- und Verbreitung der Organismen (Palmer et al., 1996; Matthaei et al., 1997). Die Makrozoobenthos-Drift umfasst drei grundlegende Prozesse (Abb. 37): Zuerst löst sich das Makrozoobenthos vom Substrat ab, was als Driftanfang ("drift entry"; A) bezeichnet wird. Dann folgt das Driften in der Wassersäule (Drifttransport; Pfeile AB, AC, AD, AE). Zum Schluss erfolgt das Driftende ("drift exit"), welches entweder durch Prädation (B), durch passives Zurücksinken auf die Gewässersohle (C), durch aktives Absetzen in neue Bereiche oder Strandung (D) oder durch Emergenz, d.h. das Verlassen des aquatischen Habitats (Adultphase; E), erfolgt. [...]

La dérive est le transport, par le courant, d'organismes aquatiques en direction de l'aval (Waters 1972 ; Brittain et Eikeland 1988). La dérive naturelle du macrozoobenthos dans les cours d'eau a une influence considérable sur la dissémination et la propagation des organismes (Palmer et al. 1996 ; Matthaei et al. 1997). La dérive du macrozoobenthos comprend trois processus fondamentaux (fig. 37). D’abord, le macrozoobenthos se détache du substrat : c'est le début de la dérive (« drift entry » ; A). Vient ensuite la dérive dans la colonne d'eau (transport par dérive ; flèches AB, AC, AD, AE). Enfin, c'est la fin de la dérive (« drift exit ») du fait de la prédation (B), de la redescente passive sur le fond du lit (C), du déplacement actif vers de nouvelles zones ou de l’échouage (D), ou de l’émergence, c'est-à-dire la sortie de l’habitat aquatique (phase adulte ; E). [...]

The interdisciplinary project “Resilient Rivers” links research in hydraulic engineering and ecology to explore processes and to evaluate measures related to river restoration. The partners from four different Swiss research institutions together with the Swiss Federal Office for the Environment are pursuing the common objective to develop scientific basics for answering current questions in restoration practice while involving experts from cantonal administrations, private offices and non-governmental organizations. The current project is the fifth phase within the Swiss national research program “Hydraulic Engineering and Ecology” which focusses on flood protection and functional riverscape habitats as well as current challenges such as biodiversity conservation, water use and adaptation to climate change. We introduce the 13 subprojects and highlight research questions, methodology, and collaboration. There are subprojects addressing lateral and longitudinal connectivity with regard to biodiversity of aquatic and terrestrial species, and connectivity will be studied locally at individual sites and on reach scale between different restoration sites. This includes also the study and modelling of hydrochory considering effect of sills and fluvial morphology, among others. Other subprojects are focusing on morphodynamics in river widenings, particularly with regard to sediment supply, flood protection and refuge availability, considering also climate change. Furthermore, instream structures such as engineered log jams are studied with respect to flood protection and habitat provision. The major common feature of all subprojects is the tight collaboration between hydraulic engineers and aquatic and terrestrial ecologists.

The objective of the work was a comprehensive study of Late Holocene bottom sediments from the southern Chukchi Sea and reconstruction of their accumulation conditions. Analytical methods included macroscopic description with smear slides, ²¹⁰Pb dating of sediments, determination of biogenic components, magnetic susceptibility measurements, and grain size distribution, palynological, and mineral analyses. The modern sedimentation rate established at the study point is 8–10 mm/year. Sediments are mainly represented by silts. In the upper part of the core, there are elevated concentrations of SiO_2biog, C_org, and N_tot and decreased magnetic susceptibility values. This is probably due to the increased bioproductivity of the Chukchi Sea in recent years, caused by current climate warming. The palynological composition of the studied deposits reflects the tundra and forest–tundra vegetation on land adjacent to the Chukchi Sea. The presence of Neogene pollen in Late Holocene sediments is evidence of their transfer from eroded ancient sediments.

The paper provides the results of experiments with sediment traps in the deep-water part of the South Basin of Lake Baikal (depth of 1366 m), installed from March 2015 to March 2016 in order to study recent sedimentation within the lake. We present new data on total fluxes of particulate matter and fluxes of biogenic components (SiO_2biog, С_org, and N_tot) at different depths of the water column both for the whole year and for individual periods of the year. Diatom analyses were carried out for all obtained samples. The total flux of sedimentary material averaged 94.9 g/m²/y; the average fluxes of SiO_2biog, С_org, and N_tot were 23.9, 11.6, and 0.94 g/m²/y, respectively. The molar C/N ratio varies from 11 to 21 and indicates a predominance of allochthonous material in almost all samples. Maximum fluxes of sedimentary matter were recorded from 20 June to 20 July 2015. This period corresponds to the bloom of diatoms of the species Synedra acus. This species amounts to >94% of the total diatom content in all samples taken during this year. The recent predominance of Synedra acus in the water column, as well as in the surface bottom sediments of South Baikal, is probably due to the climate warming.

Abstract: Late Holocene sediments have been recovered in a core from the central Chukchi Sea to reconstruct their accumulation conditions. The sediments consist mainly of terrigenous and just partly of biogenic material. Fine sand is dominated by up to 99.8% light fraction minerals, whereas heavy minerals account for not more than 1.4%. Results of magnetic susceptibility, related to the sand and heavy mineral content, decrease from the bottom to the top of the core. The species composition of pollen spectra varies insignificantly throughout the core and, on the whole, reflects the modern vegetation of the Chukchi Sea coast. The increased number of cysts of dinoflagellates and other aquatic palynomorphs, as well as some increased content of coarse-grained material at the upper part of the sediment core, is presumably caused by recent climate warming conditions. Two peaks of ¹³⁷Cs activity at the 7.5 and 1.5 cm in the core are related to radioactive fallout, caused by the accidents at the Chernobyl nuclear power plant in 1986 and the Fukushima nuclear power plant in 2011. The resulting sedimentation rates of 2.5–3 mm/yr correspond well to rates of sedimentation determined by ²¹⁰Pb dating (2.0 mm/yr).

We quantify the lake dynamics, near-bottom turbulence, flux of dissolved oxygen (DO) across the sediment-water interface (SWI) and their interactions during oxygenation in two lakes. Field observations show that the lake dynamics were modified by the bubble plumes, showing enhanced mixing in the near-field of the plumes. The interaction of the bubble-induced flow with the internal density structure resulted in downwelling of warm water into the hypolimnion in the far-field of the plumes. Within the bottom boundary layer (BBL), both lakes show weak oscillating flows primarily induced by seiching. The vertical profile of mean velocity within 0.4 m above the bed follows a logarithmic scaling. One lake shows a larger drag coefficient than those in stationary BBLs, where the classic law-of-the-wall is valid. The injection of oxygen elevated the water column DO and hence, altered the DO flux across the SWI. The gas transfer velocity is driven by turbulence and is correlated with the bottom shear velocity. The thickness of the diffusive boundary layer was found to be consistent with the Batchelor length scale. The dynamics of the surface renewal time follow a log-normal distribution, and the turbulent integral time scale is comparable to the surface renewal time. The analyses suggest that the effect of bubble plumes on the BBL turbulence is limited and that the canonical scales of turbulence emerge for the time-average statistics, validating the turbulence scaling of gas transfer velocity in low-energy lakes.

Uncertainty is an inherent aspect of aquatic remote sensing, originating from sources such as sensor noise, atmospheric variability, and human error. Although many studies have advanced the understanding of uncertainty, it is still not incorporated routinely into aquatic remote sensing research. Neglecting uncertainty can lead to misinterpretations of results, missed opportunities for innovative research, and a limited understanding of complex aquatic systems. In this article, we demonstrate how working with uncertainty can advance remote sensing through three examples: validation and match-up analysis, targeted improvement of data products, and decision-making based on information acquired through remote sensing. We advocate for a change of perspective: the uncertainty inherent in aquatic remote sensing should be embraced, rather than viewed as a limitation. Focusing on uncertainty not only leads to more accurate and reliable results but also paves the way for innovation through novel insights, product improvements, and more informed decision-making in the management and preservation of aquatic ecosystems.

The Tropical Andes is a biodiversity hotspot facing pressure from planned and ongoing hydropower development. However, the effects of dams on the region's river ecosystems, as mediated by physicochemical changes in the water quality, are poorly known. Colombia is unique among its peers in South America with respect to managing central public environmental databases, including surface water quality data sets associated with the environmental monitoring of dams. To assess the relationship between hydropower and Colombian river conditions, we analyze monitoring data associated with 15 dams, focusing on oxygen availability, thermal regimes and sediment losses because these properties are influenced directly by river damming and impose fundamental constraints on the structure of downstream aquatic ecosystems. We find that most Colombian dams (7 of 10) seasonally reduce concentrations of total suspended solids by large percentages (50 %-99 %) through sediment trapping. Most dams (8 of 15) also, via the discharge of warm reservoir surface waters, seasonally increase river temperatures by 2 to 4 °C with respect to upstream conditions. A subset of four dams generate downstream hypoxia (< 4 mg L^-1) and water that is 2 to 5 °C colder than inflows, with both processes driven by the turbination and discharge of cold and anoxic hypolimnetic waters during periods of reservoir stratification. Reliance on monitoring data likely leads us to under-detect impacts: many rivers are only sampled once or twice per year, which cannot capture temporal shifts across seasons and days (i.e., in response to hydropeaking). Despite these blind spots, the monitoring data point to some opportunities for planners and hydropower companies to mitigate downstream ecological impacts. These findings highlight the importance of implementing environmental monitoring schemes associated with hydrologic infrastructure in developing countries.

The Northern Mesoamerican Frontier was a complex multicultural region characterized by frequent human settlement changes and shifts in agricultural conditions during the Late Preclassic period (~400 BCE-150 CE). Here, we report a high-resolution paleoenvironmental record from the varved sedimentary sequence of the crater maar La Alberca which spans the Late Preclassic (~400 BCE-150 CE) to part of the Early Classic period (~150 CE-250 CE) corresponding to Late Chupicuaro phase (400 BCE-100 CE) and Mixtlan phase (0–250 CE). Our work aims to study the paleoenvironmental conditions during the rise of agriculture in the Northern Mesoamerican Frontier and provide insights related to landscape alteration by human activity. To reach these aims, a multiproxy investigation was conducted by means of varve counting, high-resolution XRF scans, magnetic susceptibility, pollen data and fecal stanol biomarkers as a proxy for human population change. Our results reveal two varve type. Type 1 is characterized by the alternation of detrital-organic layers and aragonite layers, type 2 by alternating detrital-organic layers with an organic layer formed by diatom frustules and aragonite layers. This study suggest that the increase of erosion by human activity during the Late Chupicuaro phase (400 BCE-100 CE) and the start of the Mixtlan phase (0–250 CE) coincide with a high percentage of Amaranthaceae pollen, a rise of sedimentation rates, increase in nutrient content and the increase of human waste flux interpreted with the (Coprostanol + epi) :((Coprostanol + epi)+cholestanol biomarker. Moreover, a wetter period (~137 BCE-37 CE) interpreted during the Late Chupiacuaro phase and the start of the Mixtlan phase could suggest favorable environmental conditions for the establishment of agriculture.

For over 50 years Lake Licheńskie (LLi), central Poland, has been involved in the cooling system of two power plants (PP). Owing to the discharge of cooling waters the lake was prone to considerable environmental changes which involved its thermal structure, mixing regime and water parameters. In this study we investigated how the man-made transformations affected greenhouse gas emissions (GHG; CH₄ and N₂O) from the lake. The GHG emissions in Lake Licheńskie were monitored at the deepest site from December 2014 to November 2015 and between March 2022 and February 2023. The values obtained were compared to reference lakes encompassing 10 natural and undisturbed inland and coastal lakes in Poland. Our results revealed that LLi was a net source of CH₄ and N₂O to the atmosphere but the fluxes were low. The mean annual diffusive fluxes were 0.21–0.38 mmol·m⁻² d⁻¹ for CH₄ and 4.90–7.40 μmol·m⁻² d⁻¹ for N₂O. The CH₄ emissions were significantly lower than in most of reference lakes, while the N₂O emissions were comparable. Therefore, the human intervention resulted in reduction of CH₄ release from LLi but it had minor effect on the N₂O. The most likely reason for the low direct fluxes of GHGs from the surface waters was the high flushing rate of the lake and export of dissolved gases to adjacent lakes and canals. Hence, the overall emission from the connected lake and canal system was not mitigated by the man-made changes to the lake system.

Lake Nyos, a deep crater lake, located in the north-west of Cameroon, was permanently stratified below 50 m depth due to subaquatic sources supplying warm, salty and CO₂-enriched water into the deepest reaches. The high CO₂ content in these source waters caused the 1986 limnic eruption. The deep inflowing water is denser than the hypolimnetic water and maintains the stability of the water column, which is double-diffusively stratified. During the dry season in Feb 2002, cooling triggered the formation of a double-diffusive (DD) staircase, a sequence of homogeneously mixed layers separated by distinct stable interfaces. The initiation of the staircase was slightly below the permanent chemocline at ~50 m depth, from where the staircase expanded vertically in a diffusion-type manner for ~750 days to a maximal vertical extension of ~37 m. The staircase pattern caused the upward heat fluxes to increase which depleted the driving temperature gradient. Subsequently, the density ratio increased and reduced the upward heat flux divergence until DD progressively weakened and finally the staircase structure eroded. Based on 39 CTD profiles, we describe the DD phenomenon, explain the three distinct phases of this unique DD event, which lasted for ~ 850 days, and discuss the vertical extension of the DD zone in relation to the rates of new layer formation and layer decay. To our knowledge, this is the only observation over the entire lifespan - "from birth to death" - of a DD event in a natural water body.

Surveillance of antibiotic resistance genes (ARGs) has been increasingly conducted in environmental sectors to complement the surveys in human and animal sectors under the "One-Health" framework. However, there are substantial challenges in comparing and synthesizing the results of multiple studies that employ different test methods and approaches in bioinformatic analysis. In this article, we consider the commonly used quantification units (ARG copy per cell, ARG copy per genome, ARG density, ARG copy per 16S rRNA gene, RPKM, coverage, PPM, etc.) for profiling ARGs and suggest a universal unit (ARG copy per cell) for reporting such biological measurements of samples and improving the comparability of different surveillance efforts.

Forests account for nearly 90 % of the world's terrestrial biomass in the form of carbon and they support 80 % of the global biodiversity. To understand the underlying forest dynamics, we need a long-term but also relatively high-frequency, networked monitoring system, as traditionally used in meteorology or hydrology. While there are numerous existing forest monitoring sites, particularly in temperate regions, the resulting data streams are rarely connected and do not provide information promptly, which hampers real-time assessments of forest responses to extreme climate events.
The technology to build a better global forest monitoring network now exists. This white paper addresses the key structural components needed to achieve a novel meta-network.
We propose to complement - rather than replace or unify - the existing heterogeneous infrastructure with standardized, quality-assured linking methods and interacting data processing centers to create an integrated forest monitoring network.
These automated (research topic-dependent) linking methods in atmosphere, biosphere, and pedosphere play a key role in scaling site-specific results and processing them in a timely manner. To ensure broad participation from existing monitoring sites and to establish new sites, these linking methods must be as informative, reliable, affordable, and maintainable as possible, and should be supplemented by near real-time remote sensing data.
The proposed novel meta-network will enable the detection of emergent patterns that would not be visible from isolated analyses of individual sites. In addition, the near real-time availability of data will facilitate predictions of current forest conditions (nowcasts), which are urgently needed for research and decision making in the face of rapid climate change. We call for international and interdisciplinary efforts in this direction.

Protected agriculture boosts the production of vegetables, berries and fruits, and it plays a pivotal role in guaranteeing food security globally in the face of climate change. Remote sensing is proven to be useful for identifying the presence of (low-tech) plastic greenhouses and plastic mulches. However, the classification accuracy notoriously decreases in the presence of small-scale farming, heterogeneous land cover and unaccounted seasonal management of protected agriculture. Here, we present the random forest-based pixel-level Open field and Protected Agriculture land cover Classifier (OPAC) developed using Sentinel-2 L2A data. OPAC is trained using tiles from Switzerland over 2 years and the Almeria region in Spain over 1 acquisition day. OPAC classifies eight land covers typical of open field and protected agriculture (plastic mulches, low-tech greenhouses and for the first time high-tech greenhouses). Finally, we assess (1) how the land covers in OPAC are labelled in the Sentinel-2 Scene Classification Layer (SCL) and (2) the correspondence between pixels classified as protected agriculture by OPAC and by the best performing Advanced Plastic Greenhouse Index (APGI). To reduce anthropogenic land covers, we constrain the classification task to agricultural areas retrieved from cadastral data or the Corine Land Cover map. The 5-fold cross-validation reveals an overall accuracy of 92% but other classification scores are moderate when keeping the separation among the three classes of protected agriculture. However, all scores substantially improve upon grouping the three classes into one (with an Intersection Over Union of 0.58 as an average among the scores of the three classes and of 0.98 for one single class). Given the recently acknowledged importance of Sentinel-2 Band 1 (central wavelength of 443 nm), the classification accuracy of OPAC for the Swiss small-scale farming is mostly limited by the band's reduced spatial accuracy (60 m). A careful visual assessment indicates that OPAC achieves satisfactory generalization capabilities also in North European (the Netherlands) and four Mediterranean areas (Spain, Italy, Crete and Turkey) without the need of adding location and temporal specific information. There is good agreement among natural land covers classified by OPAC and the SCL. However, the SCL does not have a class for protected agriculture, the latter being often classified as clouds. APGI achieved similar to lower classification accuracies than OPAC. Importantly, the APGI classification task depends on a user-defined space- and time-specific threshold, whereas OPAC does not. Therefore, OPAC paves the way for rapid mapping of protected agriculture at continental scale.

Agriculture relies heavily on the use of plastic mulch films, which increase crop yields and can lower water demands. In recent years, soil-biodegradable mulch films have been marketed to replace the non-biodegradable, conventional polyethylene-based mulch films. These biodegradable mulch films are designed to be ploughed into the soil after use to be biodegraded in situ by soil microorganisms. However, research has shown that part of the mulch film material may be transported from the fields to neighboring environments, including aquatic ecosystems. Research on potential biodegradation of soil-biodegradable plastics in freshwater habitats is lacking. Here, we investigated the mineralization of soil-biodegradable agricultural mulch films in freshwater lake sediments of Lake Lucerne, Switzerland. Two types of commercial soil-biodegradable mulch films were incubated within lake sediment cores, along with traditional polyethylene (PE) plastic, and the production of CO₂ and CH₄ was followed over time relative to non-plastic-containing control sediments. After the 40-week incubation period, the films were visually intact and showed no signs of mineralization. Gas analyses showed no additional production of either CO₂ or CH₄ in the degradable mulch film incubations, compared to the control or PE plastic incubations. We conclude that these two used soil-biodegradable mulch films have a low biodegradability in lake sediments, likely reflecting that the microbial community structure in the lake sediment lacks active microbial degraders. Our results highlight the importance of preventing transport of soil-biodegradable mulch films from agricultural soils to surrounding aquatic environments.