Catchment soil erosion and river sediment transport decoupled under global change (ErRiSed)

• Applicants: Professor Dr. Peter Fiener; Privatdozent Dr. Thomas Hoffmann
• Subject Area: Physical Geography
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 551865089

In a recent study Hoffmann et al (2022) analyzed the temporal trends of suspended sediment concentrations (SSC) in German waterways between 1990 and 2010. Their results indicate a widespread and strong decrease of SSC up to 50% within 20 years. The declining SSC is in strong contrast to the likely development of soil erosion during the same time. Increases in rainfall erosivity and intensified land use due to biofuel production suggest that sediment supply to headwater river channels through soil erosion increased in Germany during the last decades. These contradictory developments suggest an enhanced disconnection of large river systems from the sediment feeding headwater streams. The specific controls and processes of that trigger this disconnection remains speculative. We aim to identify the key drivers of this contradiction accounting for changes in sediment supply, transport pathways, and sediment connectivity along the sediment cascade from eroding hillslopes to the outlet of major rivers. Here we focus on the Main catchment (Germany), because there are several long-term suspended sediment monitoring stations within the Main river channel and its contributing tributaries. Furthermore, the catchment of the river Main covers various lithologies, which support the detection of suspended sediment sources in the trunk river, using fingerprinting techniques. In work package 1, we reconstruct decadal trends and seasonal shifts of drivers of sediment production on arable land within the Main catchment since 1990. Furthermore, we aim to identify changes in landscape structures affecting sediment connectivity and analyze trends and seasonal shifts of suspended sediment concentration in tributary rivers and along the Main river. WP 2 aims to analyze changes in sediment flux and connectivity at the catchment scales using the soil erosion model WaTEM/SEDEM and sediment fingerprinting approaches. To trace sediment sources within the river channel network of the Main catchment we wish to apply Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) in combination with fallout radionuclides (7Be and 210Pbex). To understand the controls on changing sediment connectivity in the Main catchments between 1990 and 2020 (WP 3) we apply catchment scale sediment connectivity approaches and a hydraulic sediment transport model along the river Main. This framework will be used to unravel the discrepancy between the driving factors of hillslope soil erosion and suspended sediment transport in the larger waterways. This project will provide valuable knowledge to improve sediment management in large rivers facilitating a good ecological status of rivers in Germany, as required by the European Water Frame Directive.

• DFG Programme: Research Grants