Zur Identifizierung von vertikalem Grundwasseraustausch mittels formationsspezifischer Schwefel- und Strontium-Isotope (Süddeutsches Schichtstufenland)

In the southwest German scarp land, the groundwater in the karst aquifer of the Upper Muschelkalk displays hydrochemical characteristics that suggest inflow from both overlying and underlying aquifers. The elevated levels of sulphate, sodium, and chloride can be attributed to the dissolution of evaporites, which are prevalent in the Germanic Triassic, particularly in the Middle Muschelkalk and Gipskeuper layers. To determine the sources of these inflows into the Upper Muschelkalk, sulphur and strontium isotopes (δ³⁴S, ⁸⁷Sr/⁸⁶Sr) are utilized as tracers specific to each formation. The stratigraphic origin of the isotope tracers, which suggests leakage, can be utilized to estimate the direction of hydraulic gradients between aquifers. This approach enables a consistent interpretation of groundwater hydraulics, supporting the idea that cross-formation flow is a plausible scenario for explaining the observed mixing processes. Thus, the use of contrasts in hydrochemistry and isotopes helps to visualize unmeasurable processes and allows a quantification of the inflow rates into the Upper Muschelkalk. Calculations based solely on hydraulic data are deemed unreliable due to their lack of accuracy.