Abteilung Wasserressourcen und Trinkwasser

Taiwan’s mid-20th-century Blackfoot disease epidemic highlighted the public health implications of geogenic arsenic in groundwater and prompted extensive water-supply interventions. Despite these measures, arsenic persists in aquifers, continuing to affect drinking water, irrigation, and aquaculture. This study developed a scalable machine learning model to identify areas across Taiwan at risk of groundwater arsenic concentrations exceeding the WHO guideline of 10 µg/L. The model demonstrated robust performance (mean AUC 0.93, balanced accuracy 0.87). A detailed evaluation and interpretation of the principal predictor variables governing arsenic dissolution provides insights into geochemical and hydrogeological controls on mobilization. Furthermore, the resulting hazard map of Taiwan was used to estimate the human population at risk as well as the locations and types of exposed agriculture and aquaculture. Hotspots are clustered in the Chianan, Pingtung and Lanyang plains, where many rural communities still rely on untreated groundwater. Population exposure is substantial, with an estimated 148,000 people at risk in 2023, which is about half the 303,000 reported in 1998. Agricultural impacts are also considerable: >80 % of aquaculture areas, and 33 % of paddy rice fields occur within high-risk zones. Several high-risk zones lie outside Taiwan's Groundwater Control Areas, revealing regulatory blind spots. By connecting Taiwan's historical arsenic crisis to novel predictive tools, this work supports evidence-based strategies to reduce current exposures and prevent future public arsenic-related health impacts.

Mountainous regions such as Switzerland, which are characterized by highly complex geological and hydrogeological conditions, hold significant geothermal potential linked to tectonic settings and deep hydrothermal flow systems. However, geothermal exploration in such regions is challenged by geological and hydrogeological complexity, data scarcity, high uncertainty, administrative hurdles, as well as environmental and economic risks associated with drilling. Robust quantitative tools that maximize the value of the limited information available on the subsurface are needed to assess geothermal potential, productivity, and sustainability. Here, a step-by-step framework for the assessment of regional hydrothermal flow systems is presented. The framework consists of 3D geological modeling, 3D thermohydraulic modelling (3D-TH-model), and a systematic sensitivity analysis for the identification of the optimal structural model complexity. The framework is demonstrated on the hydrothermal systems of the Upper Aarmassif in the Swiss Alps. Results showed that thermal upwelling in the system is driven by strong topographic gradients and upward flux along more permeable tectonic faults and thrusts. The upwelling results in significantly elevated groundwater temperatures near the surface in the Rhône Valley, with temperatures exceeding 70 °C at depths of 1000 m and reaching ~100 °C at depths of 2000 m. These model outputs were verified by the few available vertical borehole temperature profiles, horizontal tunnel temperature profiles, groundwater recharge rates and hydraulic head distribution, ¹⁴C-based groundwater residence times, and geothermometrically identified hydrothermal-reservoir-temperature estimates. The framework provides the basis for risk-reduced geothermal exploration, thereby supporting sustainable geothermal development—a significant step towards a decarbonized energy future.

Reproduction of hydrodynamic and hydrologic processes in complex coastal lagoons requires the development and calibration of linked numerical model implementations, that can show accuracy even in extreme weather scenarios. To achieve that, robust datasets for a wide variety of parameters are needed to validate the model. This study aimed to develop and validate a hydrodynamic model linked to a groundwater and a watershed model, for the microtidal Mar Menor coastal lagoon located in the southeastern Spain. Special concern was given to flash flood events, which, although infrequent, are proved to trigger mass mortality of species inside the lagoon. To achieve that, a ROMS numerical implementation was developed and linked to atmospheric (HARMONIE-AROME), groundwater (SUTRA), and watershed (TETIS) models. The model results were compared with a robust dataset with hydrodynamic, salinity, and water temperature data. Special attention was given to the September 2019 Cut-off Low (CoL) flash flood event. The model demonstrated high accuracy in reproducing the lagoon's dynamics under normal conditions, including the currents in the narrow inlets connecting the lagoon with the Mediterranean Sea. After the CoL event, an extraordinary hydrological scenario developed — characterized by strong vertical stratification that persisted for over a month — explained by the lack of sufficient shear instability to overcome buoyancy forces induced by density gradients, despite the occurrence of a two-layer opposite direction flow. Runoff associated with the CoL event also led to a nearly 20 % reduction in the lagoon's Water Renewal Time.

Sulfur functional groups are abundant in natural organic compounds, pesticides and pharmaceuticals. Kinetic data of their aqueous reaction with ozone is only available for a very small set of compounds and sometimes contradictory, making predictions on their fate during ozonation processes difficult. Therefore, second-order rate constants k_O₃ were determined for 37 sulfur-containing compounds and trends in reactivity were identified. For the determination of k_O₃ via competition kinetics, aldicarb was established as pH-independent competitor (k_O₃=1.0×10⁶ M⁻¹s⁻¹). Sulfides (thioethers) react very fast with ozone (k_O₃≈2×10⁶ M⁻¹s⁻¹). Exceptions are sulfides, which are π-conjugated to electron-withdrawing groups (e.g., thiocarbamates, k_O₃≈10⁰−10³ M⁻¹s⁻¹), and β-lactam antibiotics (k_O₃≈10³ M⁻¹s⁻¹), which are deactivated to different degrees. Thiols exhibit pH-dependent reactivities, though the dependency is much smaller than previously reported, ranging from k_O₃+SH≈10⁴ M⁻¹s⁻¹ to k_O₃+S⁻≈10⁶ M⁻¹s⁻¹, but an unprecedented pH-dependency is observed. A deactivating effect of neighboring groups renders the reactivity of the disulfide cystine and similar compounds pH-dependent (k_O₃(pH3)≈10² M⁻¹s⁻¹, k_O₃(pH7)≈10⁵ M⁻¹s⁻¹) while disulfides without acidic functional groups exhibit pH-independent reactivities (k_O₃≈2×10⁵ M⁻¹s⁻¹). Further oxidized functional groups like sulfoxides or thiosulfinate esters are unreactive (k_O₃≈10⁰−10¹ M⁻¹s⁻¹), but sulfinates are very susceptible to ozonation (k_O₃≈2×10⁶ M⁻¹s⁻¹). A definitive explanation for this difference is still lacking. For non-N-alkylated isothiazolones, an unexpected pH-dependency is observed, similar to cysteines. The reactivity at pH 7 differs by 4 orders of magnitude, whether or not N-alkylated (k_O₃≈10² M⁻¹s⁻¹, k_O₃≈10⁶ M⁻¹s⁻¹, respectively). Overall, the data presented provides novel insights into the ozone reactivity of sulfur compounds as a basis for a better assessment of their fate during ozonation.