Catchment transit time sensitivity to the type of SAS function for unsaturated zone and groundwater

作者：Hatice Türk, Christine Stumpp, Markus Hrachowitz, Peter Strauß, Günter Blöschl, Michael Stockinger · 年份：2025 · DOI：10.5194/egusphere-2025-2597 · 被引用次数：1 · 研究领域：Soil Moisture and Remote Sensing、Underwater Acoustics Research、Groundwater flow and contamination studies

Abstract. Preferential flow paths in hydrological systems (e.g., macropores or subsurface pipe networks) facilitate rapid water and solute transport, leading to fast streamflow responses and markedly short transit times. While such preferential flow processes are well known in the unsaturated zone and groundwater, it remains uncertain whether catchment-scale isotope-based transport models can accurately represent these fast groundwater flow processes. In this study, we tested the hypothesis that preferential discharge of young groundwater is significant and can be captured by selecting specific StorAge Selection (SAS) functions, i.e., functions that specify if young or old water leaves a storage, at the catchment scale. We systematically compared multiple SAS parameterisations for the unsaturated zone and groundwater using a catchment scale transport model and long-term measurements of hydrogen isotopes (δ2H) data from two headwater catchments (Hydrological Open Air Laboratory, HOAL, catchment in Austria and Wüstebach catchment in Germany). The results indicated that δ2H ratios in streamflow had sufficient information content to identify preferential flow in the unsaturated zone. However, δ2H ratios in streamflow were insufficient to constrain or confirm preferential flow in groundwater, as any seasonal variation of δ2H in pore water was largely dampened by the catchments’ substantial passive groundwater storage volumes. This was further confirmed as the observed attenuated δ...