Description:

Over the past decades, major German rivers have shown a marked decline in suspended sediment concentrations. This trend cannot be explained by large-scale river engineering works and stands in contrast to rising soil erosion rates driven by land use practices and climate change. Such observations raise important scientific questions about the processes controlling sediment transfer in large river systems, particularly the role of small-scale infrastructure changes and agricultural practices evolution in headwater areas.

This research project focuses on the Main River watershed in Bavaria (27,300 km?), a tributary of the Rhine, where a decline in suspended sediment has been observed.?
The project aims to identify the key drivers behind the observed decline in suspended sediment concentrations by analysing changes in sediment supply, transport pathways, and connectivity from hillslopes to river outlets between 1990 and 2020 in interaction with global change. Structured in three phases, it combines extensive analyses of climate and land use changes, sediment connectivity, and sediment source identification along the river network. The WaTEM/SEDEM model will be used to evaluate the evolution of erosion prone areas and connectivity, while fallout radionuclides and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) will help trace the evolution of sediment sources. In parallel, river morphology will be mapped to identify the evolution of physical features influencing sediment transfer.

By integrating these approaches, the project seeks enhance our understanding of the anthropic and climate interplay of sediment dynamics in the Main River basin, to support sustainable sediment management, and contribute to achieving the good ecological status mandated by the European Water Framework Directive. Ultimately, it addresses the paradox of increasing erosion yet declining sediment flux, with implications for mitigating the ecological and societal impacts of soil degradation and sustaining freshwater health.