ALBERT

Description: Lentic small water bodies (LSWB) are widespread globally. They fulfill a variety of ecohydrological tasks and are of central importance for biodiversity in rural areas. Due to their size and location, they interact with their environment in complex ways not found in other types of water bodies. Plant protection products (PPP) and their transformation products (TP) pose a particular risk to them. However, the database of their contamination is low and inhomogeneous and transport pathways have not been sufficiently investigated so far. This study focuses on two LSWB in northern Germany that were monitored for their PSM/TP contamination and hydrological connectivity in a high-resolution measurement campaign from 10/1/20 to 10/31/21. Surface runoff, lateral flow, groundwater, drainage water, and surface water of the LSWB were analyzed for 26 PPP/TP. Based on recorded hydrological data and tracer experiments, water balances were established. Results show multiple findings of up to eight PPP/TP in all samples. In addition, several input and output pathways as well as different temporal dynamics of the various PPP/TP concentrations were identified. A pronounced interaction between the LSWB and the shallow groundwater enabling a PPP/TP exchange was observed. LSWB and shallow groundwater showed a constant and high load of the non-applied TP metazachlor-ESA. Metazachlor-ESA was measured with the highest concentrations of up to 11.66 µg L〈sup〉-1〈/sup〉 in the shallow groundwater and loads of up to 3.12 g in a single inflow per month. For one of the LSWB, a drainage system was a major input pathway for PPP/TP.

Description: Two ephemeral ponds in northern German lowlands, one isolated and another one fed and discharged by drainage pipes, were investigated for an entire year by 577 isotopic water samples. In the isolated pond, winter and most spring pond water samples plotted close to the global meteoric water line (GWML) of the dual isotope plot, while summer samples followed a distinct evaporation line (EL). Groundwater wells either formed individual clusters close to the GMWL with limited evaporative enrichment, or plotted closely to pond water samples including the EL in summer, suggesting high percentages of infiltrated pond water. In the drained pond, evaporative enrichment was also evident but less pronounced. Here, all groundwater wells plotted closely above the GMWL, indicating negligible evaporative enrichment and limited surface water infiltration. In both ponds, EL slopes were typical for lakes with open water surface. Differences between the ponds pointed to differences in microclimate, caused by e.g. tree shading or wind exposition. EL-GWML intersection points marked the main water origin, which was represented by a particular groundwater well in both ponds. Then, two-component mixing models separated instantaneous rainfall from evaporatively enriched pond water. They suggested only small rainfall fractions that increased towards the end of the year. In the isolated pond, a second mixing analysis was possible to show a high fraction (〉 50%) of infiltrated pond water into down-gradient groundwater. These results underline the explorative power of stable water isotopes to determine directions and quantities of surface-groundwater interaction in lowland ponds.