Ecological rehabilitation reducing erosion as implied by mineral magnetism of reservoir sediments on Guizhou Plateau, SW China

This paper explored whether magnetic characteristics of reservoir sediments compared to catchment soils could indicate ecological rehabilitation reducing erosion on Guizhou Plateau, SW China. Soil profiles were sampled in a catchment where a reservoir was built in 1964 in northeast Guizhou. E h was measured for these profiles when they were being sampled. A 28 cm long sediment core was recovered from the reservoir in April 2019. Precipitation data for 1964–2018 were acquired and land-use data for 11 years included in this period were derived by interpreting remote-sensing images. Magnetism measurements were made on the soils and sediments and analyses of 137 Cs activity and particle size on the sediments. The land-use data suggested that forestland has increased and farmland decreased since 1986 due to an ecological rehabilitation started in the early 1980s. The spatial pattern of soil magnetism was inferred caused by varying levels of gleization as confirmed by the E h variability. That provided implications for interpreting temporal variations of sediment magnetism. Magnetic variables (χ lf , χ ARM , IRM 300mT , SIRM, χ fd % and IRM 300mT /SIRM) were higher in the sediments deposited in 1964–1986 when forestland was small and farmland large, suggesting considerable contributions of the magnetically strong, non-gleyed soils from the distant slopes to the sediments and thus intense erosion. The values decreased in the sediments of 1986–2018 when forestland increased and farmland decreased, implying relatively increased contributions from the magnetically weak, gleyed soils closely around the reservoir and hence declined erosion. Changes of sediment particles supported this reconstruction. The decline of erosion was ascribed to the ecological restoration because variations in precipitation were insignificant. Similar changes were also identified in other parts of Guizhou and attributable to a province-wide campaign of such ecological rehabilitation.