Riverbanks contribute substantially to sediment yield in German loess-soil catchments

Loess soils are a major source of stream sediment in agricultural areas, but few studies have focused on the relative contributions of surface and riverbank erosion in temperate climates. This study aimed to discriminate surface and subsurface sources of suspended sediment in three typical mesoscale loess-soil catchments (75–209 km 2 ) in central Germany. We used a sediment fingerprinting method that included radionuclide ( 137 Cs, 210 Pb ex ), spectral, and geochemical tracers to assess the relative contribution of riverbank erosion and the suitability of these tracers for loess-soil catchments. We conducted nine field campaigns, collecting a total of 237 samples with tracer specific fingerprinting strategies, and measured suspended sediment concentrations using turbidity sensors in eight nested sub-catchments in the three catchments. Results showed that riverbank contributed a high percentage of fine sediment, with estimates of 47.9 (2–95)% from radionuclide tracers and 46.2 (3–86)% from spectral tracers. The radionuclide tracers 137 Cs and 210 Pb ex had sufficient statistical discriminatory power across 17 site campaigns in all three catchments. In contrast, the spectral tracers had lower discriminatory power and were applicable in only 12 site campaigns. The geochemical tracers failed to discriminate sediment sources in most of the campaigns due to their low discriminatory power between surface and subsurface loess soils. The mean sediment delivery ratio across all three catchments was 8.2 (2–17)%. The high share of riverbank erosion observed at all sites was related to the lack of riparian vegetation in these predominately arable catchments and low to moderate mean erosion rates of arable land. The results highlight the effectiveness of using multiple fingerprinting tracers to develop cost-efficient measures that reduce fine-sediment yields in loess-soil catchments in central Germany.