C SSF HILLSLOPE FLOW DIRECTION- Comparing dynamics and pathways of SSF among hillslopes [funded by DFG]
Project staff:
Prof. Peter Chifflard
Jonas Pyschik
Britta Kattenstroth
Dr. Christina Fasching
Prof. Markus Weiler
Abstract:
Project C - Hillslope and Flow direction/ Angle aims to quantify the spatial variability and stability of subsurface hydrological process patterns (flow gradients, flow directions, transit times, hydrochemical and biochemical composition) at the hillslope scale.
Hydrological dynamics of hillslopes, particularly subsurface stormflow (SSF), are highly complex and variable in space and time. Frequently, available studies are often limited to single slopes or few storm events, so that the transfer of these findings to other slopes or catchments is associated with great uncertainties. Thus, for upscaling and model validation a quantification of the hydrological dynamics of hillslopes and the factors influencing the spatial and temporal patterns of subsurface stormflow is urgently needed. Closely related to the hydrological dynamics of hillslopes is the export of organic carbon from the soils to the adjacent stream. But the spatial sources of carbon are still largely unclear because the exact flow paths of SSF within the slope are not well known.
Research Questions:
1. Are the di erent studied hillslopes classi ed by topographic, soil and bedrock properties characterized by typical hydrological behavior and SSF dynamics?
2. When and where is SSF being generated in the di erent hillslopes (cascading e ects)?
3. Are there characteristic depth distributions of stable water isotopes and water-soluble organic matter which can be related to subsurface flow pathways?
4. What parts of a hillslope are connected to the stream during di erent hydrological conditions and how does this impact water fluxes and water quality?
A combined hydro-biogeochemical approach, that measures the hillslope groundwater dynamics including a characterisation of stable isotopes and the water-soluble organic matter (WSOM; concentration, absorbance and fluorescence) along 480 locations at 100 hillslopes in four contrasting catchments from the low to high mountain ranges (Sauerland, Ore Mountains, Black Forest, Alps). This enables us to derive empirical relations among different landforms (i.e., convergent, divergent and planar slope shapes, flow path lengths and valley shapes), bedrock and soil properties and groundwater dynamics to quantify the spatial variability and stability of subsurface hydrological process patterns (e.g., flow directions, transit times, hydrochemical and biochemical composition). A GIS based landscape analysis and a predictive modeling with the RoGeR model will be conducted prior to instrumentation that incorporates topographic, soil and land use information as well as spatial distribution of areas were SSF is expected be dominant, respectively, in order to sample representative hillslopes. Shallow groundwater dynamics due to SSF will be recorded in 480 wells across all equipped hillslopes. Distributed sampling of water stable isotopes and WSOM along the soil profile (12 isotope and 6 WSOM samples per profile; two times during wet and dry conditions) will help to assess the vertical and lateral subsurface flowpaths of water in the unsaturated and saturated zone and the spatial discretization of source areas for SSF. We will use an array of state-of-the-art laboratory equipment and methods (TOC-Analyzer, Fluorescence Spectrometry, Isotope Analyzer) to analyze stable isotopes and WSOM. The use of multivariate statistical techniques and machine learning tools will help to identify temporal and spatial patterns of subsurface hydrological process patterns. We will investigate hillslope-stream connectivity including the extent of contributing area with RoGeR predicting SSF fluxes, directions and dynamics which can later be used for predicting transport of soil organic matter from the hillslope to the stream.
Achievements - Developed a new autosampler for Direct Vapor Equillibration pore water stable isotope analysis - Detected preferential flow using stable water isotopes - Derived SSF flow depth using temperature profiles - Developed a new low cost evaporation save water autosampler
Publications and poster presentations:
- Pyschik, J. & Weiler, M. (2025): Detecting the occurrence of preferential flow in soils with stable water isotopes (preprint). EGU Sphere ...( ), ...
- Pyschik, J.; Kuleshov, A.; Fasching, C.; Chifflard, P.; Blume, T.; Hopp, L. & Weiler, M. (2024.04.15). Insights into Subsurface Stormflow Dynamics Using Multitracer Approaches. Presented at EGU 2024, Vienna.
- Pyschik, J.; Seeger, S.; Herbstritt, B. & Weiler, M. (2025): Technical note: A fast and reproducible autosampler for direct vapor equilibration isotope measurements. Hydrology and Earth System Sciences 29(2), 525--534
- Pyschik, J.; Thoenes, E.; Achleitner, S.; Kohl, B. & Weiler, M. (2025.04.28). Tracing Subsurface Stormflow: Insights into Preferential Flow and Pre-Event Water Contributions from Controlled Sprinkling Experiments. Presented at EGU 2025, Vienna.
2024 - Pyschik, J. & Weiler, M. (2024.09.12). Identifying soil water storage and water mobilization processes using stable water isotopes. Presented at WATSON Final Action Conference, Online.
2023 - Pyschik, J. & Weiler, M. (2023.04.28). Detecting the Occurrence of Preferential Flow in Soils with Stable Water Isotopes. Presented at EGU, Vienna.