Abstract
Purpose Quantifying and understanding fine sediment transfers from catchment sources to large river deltas is crucial for effective, integrated river basin management. This study aimed to identify the source areas of fine sediments contemporary deposited along the Rhine River. Methods We sampled fresh fine sediment deposits along the Rhine mainstem after a single minor high-water event in summer 2023, and analysed the element concentrations, on which we performed a principal component analysis (PCA). To calculate the source areas of the event sediments and their downstream transfer, we calibrated a spatial sediment transfer model on the scores of the PC that was interpreted to be primarily controlled by the geogenic composition of the source sediments using auxiliary data on source area geochemistry of the Rhine basin. Results The model calibration results revealed the relative importance of nearby sediment sources over sources further upstream. The relative contribution of the upstream sources of the sediment load of the 2023 summer event dwindled by 0.42% on average per kilometre downstream transport. This implied that although the Swiss part of the Rhine basin upstream from the Aare confluence contributed 64% to the 2023 event discharge, it contributed for only 25% to the total sediment load to the Rhine delta. Conclusion The pursued sediment fingerprint tracing approach provides meaningful insights in the provenance of the freshly deposited 2023 event sediments and the role of river channels and banks as temporary sources and sinks of fine sediments. These components remain undetected in traditional long-term sediment mass budgets of rivers but are essential for a proper understanding of the transfer of fine sediments and associated contaminants at the river basin scale.