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The hydrological dynamics of hillslopes, particularly subsurface stormflow (SSF), exhibit intricate variability in space and time. Existing studies are often confined to single slopes or limited storm events, resulting in uncertainties when applying findings to other slopes or catchments. To address this, a comprehensive understanding of hillslope hydrological dynamics and factors influencing spatial and temporal SSF patterns is essential for upscaling and model validation. Linked to hillslope hydrology is the export of organic carbon to streams, yet spatial carbon sources remain unclear due to limited knowledge of SSF flow paths within slopes. We propose a hydro-biogeochemical approach, measuring water-soluble organic matter (WSOM; concentration, absorbance, and fluorescence) at 480 locations across 100 hillslopes in four contrasting catchments (Sauerland, Ore Mountains, Black Forest, Alps). This approach aims to establish empirical relationships between landforms, bedrock, and soil properties, quantifying spatial variability and stability of subsurface hydrological processes (e.g., flow directions, transit times, hydrochemical and biochemical composition). Distributed sampling of WSOM along soil profiles (6 samples per profile) will assess vertical and lateral subsurface flow paths in unsaturated and saturated zones, aiding spatial discretization of SSF source areas. Preliminary results will provide depth profiles of WSOM in the four catchments spanning low to high mountain ranges (Sauerland, Ore Mountains, Black Forest, Alps), facilitating the detection of SSF source areas.
Chifflard et al. (Fri,) studied this question.