Département Eaux de surface

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.

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.

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.