Using reservoir deposits to reconstruct the impact of recent changes in land management on sediment yield and sediment sources for a small catchment in the Black Soil region of Northeast China

Sediment deposits in lakes and reservoirs can provide a basis for reconstructing the erosional response of the upstream catchment. Recent studies undertaken in the Loess Region of China have successfully used the flood couplets contained in the sediment deposits behind check dams to reconstruct records of annual sediment yield and document the impact of changes in land management. However, flood couplets are rarely found in other areas of the world and there is a need to develop alternative approaches to establish the chronology for sediment deposits. Lead-210 dating techniques offer such potential, by making it possible to establish the age of the individual sections of a core. This contribution reports a study of the sediment deposits accumulated in a reservoir at the outlet of a small 3.46 km2 catchment in the Black Soil region of Northeast China. This region suffered serious soil erosion during the last century and this resulted in changes in land management aimed at reducing erosion rates. The sediment deposits in the reservoir covered the period 1974–2004, when such changes occurred. The study was designed to explore the potential for using excess lead-210 to establish the chronology for the reconstruction and for extending the scope of such studies by using sediment source fingerprinting techniques to include complementary information on changes in sediment source. The study successfully reconstructed the record of annual sedimentation depth, a surrogate for sediment yield. This showed that the annual sediment yield from the catchment decreased by about 60% as a result of improved land management introduced in the late 1970s and early 1980s. Sediment source fingerprinting techniques were also successfully used to identify three primary sources, namely topsoil (interrill and rill) erosion from cultivated and uncultivated areas and gully erosion and apportion their contributions to the annual sediment yields. The findings indicated that interrill and rill erosion and gully erosion were both important sediment sources throughout the period covered, contributing 47.9% and 42.0% of the sediment, respectively, that gully erosion increased in importance during years with high magnitude events, and that there was a general trend for rill and interrill erosion to decrease and for gully erosion to increase over the period 1974–2004. The study is seen as demonstrating the potential for using lead-210 measurements in combination with sediment source fingerprinting techniques to reconstruct the impact of changes in land use and land management on erosion processes and sediment yields.