Accumulation of sulfate and carbonate in NE-German groundwaters: A multi-isotope approach

Groundwaters from a Quaternary porous aquifer system in north-eastern Germany and associated surface waters were investigated for their multi-isotope (H, C, O, S) hydrogeochemical composition to identify the sources, sinks and transformations of dissolved sulfur and carbon species, as well as water exchange between the reservoirs. The analysis combined a mass balance approach with physico-chemical modelling. Based on water isotope signatures, some groundwaters appeared impacted by mixing with infiltrating lake water. The isotope composition of dissolved inorganic carbon (DIC) is controlled by the uptake of soil CO2 and the dissolution of carbonate minerals. A contribution from oxidized dissolved organic carbon (DOC) under water-saturated conditions is also indicated. Sulfur and oxygen isotope compositions clearly link the origin of dissolved sulfate to the subterrestrial oxidation of sedimentary sulfides (pyrite, FeS2) which is associated with enhanced loads of dissolved iron but low nitrate concentrations. Some sites indicate further microbial dissimilatory sulfate reduction associated with the oxidation of DOC.

Automated summary

This study investigates the hydrogeochemical composition of groundwater and surface water in north-eastern Germany, focusing on the sources, sinks, and transformations of dissolved sulfur and carbon species, as well as water exchange between different reservoirs. The results suggest that the mixing with infiltrating lake water has impacted some of the groundwater, and the isotope composition of dissolved inorganic carbon is primarily controlled by soil CO2 uptake and carbonate mineral dissolution. The origin of dissolved sulfate is linked to the subterrestrial oxidation of sedimentary sulfides, with some sites also showing microbial dissimilatory sulfate reduction associated with the oxidation of dissolved organic carbon.