Département Ressources aquatiques et eau potable

Groundwater is a central component of the Earth system. However, our understanding of how it is dynamically interlinked with the atmosphere, hydrosphere, cryosphere, biosphere, geosphere, and anthroposphere remains limited. In the pursuit of understanding groundwater dynamics across diverse global settings, we present GROW (the global-scale integrated GROundWater package). This analysis-ready, quality-controlled dataset combines depth to groundwater and level time series from 55 countries, 91% from North America, India, Europe, and Australia, with associated Earth system variables. The dataset contains >200,000 time series with either daily, monthly, or yearly temporal resolution, accompanied by 36 time series or static attributes of meteorological, hydrological, geophysical, vegetation, and anthropogenic variables (e.g., precipitation, drainage density, rock type, NDVI, land use). 34 data flags regarding well features (e.g., coordinates and country), as well as time series characteristics (e.g., gap fraction or autocorrelation), facilitate quick data filtering. GROW provides a foundation for understanding large-scale groundwater processes in space and time, as well as for calibrating and evaluating models that simulate groundwater dynamics within the Earth system.

The micronutrient selenium (Se) exhibits a narrow range between essentiality and toxicity. In soils, Se speciation influences its mobility and plant availability, with implications for addressing unsafe Se levels in plant-based nutrition. We investigated how Se speciation varies with the molecular composition of organic matter (OM) in 92 Swiss topsoils spanning different land uses (i.e., croplands, grasslands, and forests). OM composition was characterized using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), while Se speciation was determined in NaOH extracts using size exclusion chromatography coupled to UV and elemental mass spectrometry (SEC-UV-ICP-MS/MS). We found that Se speciation strongly relates to OM decomposition status and pH, and drastically differs between soil land uses. Cropland soils exhibited higher proportions of Se oxyanions and small hydrophilic organic Se, whereas forest and grassland soils contained more larger, aromatic organic Se compounds. Overall, these larger Se forms correlated with fresh and/or poorly decomposed, plant-derived OM, while oxyanions and small hydrophilic Se were linked to decomposed OM. Additionally, Se extractability by NaOH decreased with increasing soil pH, which may be due to stronger SOM stabilization, microbial processes, or higher Ca contents at higher pH. These results have important implications for Se plant availability considering land use changes and SOM degradation.

Groundwater, enhanced through managed aquifer recharge (MAR), plays a central role in mitigating current and future water stress. Here we evaluate anthropogenic and natural water isotopes as tracers of groundwater flow dynamics within alluvial MAR systems. High-resolution sampling (daily/weekly) of stable isotopes (δ¹⁸O and δ²H) and tritium (³H), influenced by nuclear power plant effluents, is used to trace and quantify the movement of infiltrated river water through an alluvial aquifer along the Rhine River in Switzerland. Time-series deconvolution is applied to quantify the tracer-based travel time distribution and to predict travel times throughout the entire MAR scheme. The results demonstrate the suitability of ³H as a quasi-conservative travel time tracer in systems where the infiltrating river water is marked by nuclear power plant discharges—a situation prevalent along the banks of many large river basins globally. Deuterium excess proved equally effective as a bulk travel time tracer, reflecting distinct seasonal meltwater signals expected in major European rivers. These findings quantify MAR recovery rates and wellhead protection zones, supporting sustainable groundwater management under natural and anthropogenic pressures.

Cyanobacteria produce complex mixtures of secondary metabolites (cyano-metabolites), some of which are toxic and pose a growing concern for water utilities. While physical treatments such as filtration can efficiently remove cells, their lysis can release dissolved cyano-metabolites. This study investigated the efficiency of laboratory-scale sand filtration to abate 19 cyano-metabolites representing various structural classes. Furthermore, abatement of cyano-metabolites in a full-scale sand filtration is presented. Most cyano-metabolites showed abatement similar to or higher than the biodegradable benchmark micropollutants atenolol, paracetamol, and valsartan. Among cyano-metabolites, anabaenopeptins and cyanopeptolins had the highest abatement, while cyclamides and microcystin-LR had the lowest abatement. Abiotic controls and formation trends of 10 identified biotransformation products demonstrated that biodegradation played a major role in their removal. Laboratory-scale sand filters showed a sharp increase in biodegradation efficiency within days due to their adaptation to cyano-metabolites. Increasing the contact time and temperature both enhanced the abatement of most compounds, which could be kinetically modeled. High cyano-metabolite concentrations suppressed their own relative abatement, possibly due to metabolic enzyme inhibition or saturation. These findings suggest that sand filtration can serve as a dual-barrier against cyano-metabolites, including particle removal and biodegradation. However, biodegradation will be affected by the temperature and cyano-metabolite intake dynamics.