Late Holocene sediment source changes in the Yellow River basin, China

Information on sediment sources in river basins is crucial for the rational distribution of soil and water conservation measures. The Yellow River in China has an overground channel in its downstream, which is prone to be breached during floods and has been elevated mainly by siltation of coarse particles in the river load. Soft sandstone strata underlaying an area in the middle reaches were found to be one of the principal coarse sediment sources of the river. Using a sediment fingerprinting mixing model with geochemical elements as tracers, we fingerprinted the changes in source apportionments from the region underlain by soft sandstone strata and the region with other substrata in the river basin in the past 2600 years. Source sediment samples were collected from the sediment deposits at the outlets of the main tributaries in the middle reaches, and target sediment samples were collected from alluvial fans in the lower reaches of the river. Geochemical properties of the samples were used as source fingerprints. Using the range test and Kruskal-Wallis H-test and considering the chemical reactivity of the tracer, five geochemical tracers were selected. The results showed that the sediment contribution (<63 mu m) of the basins in the region underlain by soft sandstone strata was in the range of 4.2 %-56.0 %, 19.6 % on average. Combining the relative source contributions with the total river load in historical periods, the reconstructed sediment yields from both sources showed an increasing trend with time, but the increasing rate was lower in the region underlain by soft sandstone strata where human interference was weaker historically. This study can serve as a reference for sediment fingerprinting in large catchments, and our findings have implications for future water and soil conservation in the Yellow River basin.