SUDOCQU: Soil moisture’s Uncertain influence on riparian DOC quantity and QUality

• Applicant: Dr. José L. J. Ledesma, Ph.D.
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 524850178

Management of catchments, the areas of the landscape where water from precipitation is received and routed via surface runoff, needs scientific understanding for preserving freshwater services. Near-stream zones, aka ‘riparian zones’, are the portions of land where direct interaction between soils and surface waters occurs and play a pivotal role in controlling surface water chemistry, especially in forest headwater catchments drained by small streams. The mobilization of dissolved organic carbon (DOC) from riparian zones to streams is of particular relevance: DOC is a master variable in catchment biogeochemistry and its removal during drinking water treatment is necessary and depends on both DOC quantity (i.e. its concentration) and DOC quality (i.e. its molecular composition). Among the factors determining DOC quantity and quality in forest headwaters, soil moisture is paramount because it controls DOC accumulation, production, decomposition, and mobilization. However, limited soil moisture data are available from forest headwaters and, specifically, from their riparian zones. Furthermore, future changes in soil moisture associated to climate change are expected but uncertain and predictions miss the key aspects of riparian zone dynamics. Comprehensive studies that consider spatial heterogeneities (topographic and vertical) and temporal scales (from short-term and seasonal to long-term changes) are needed to increase our knowledge on how riparian soil moisture drive DOC quantity and quality. The objective of this project is to integrate vertical and topographic heterogeneity in soil moisture and DOC quantity and quality in the riparian zone of forest headwaters, with the aim to better understand mobilization processes and implications for surface water chemistry across temporal scales, including modelled changes associated with future climate. Existing field infrastructure at the temperate forest headwater catchment Rappbode (Harz mountains, Germany) will be complemented with a network of soil moisture sensors and suction cups placed at different layers in representative riparian profiles. Field sampling campaigns will ensure appropriate data collection and DOC quality will be characterized using Fourier transform ion cyclotron resonance mass spectrometry and UV absorbance. Future simulations of soil moisture will consider the range of climate projections for the study area and will be realized using the rainfall-runoff model PERSiST. Collaboration between KIT, UFZ-Leipzig, the Spanish National Research Council, and the Swedish University of Agricultural Sciences will ensure appropriate method application and result interpretation. The project will contribute to an advanced understanding of riparian soil processes that drive surface water chemistry in forest headwaters and will inform about potential future changes in stream DOC quantity and quality that can help decision-makers of the drinking water industry in applying adaptation strategies.

• DFG Programme: Research Grants
• International Connection: Spain, Sweden
• Co-Investigators: Dr. Oliver Lechtenfeld; Dr. Andreas Musolff
• Cooperation Partners: Dr. Susana Bernal, Ph.D.; Dr. Martyn Futter, Ph.D.