A 42-yr soil erosion record inferred from mineral magnetism of reservoir sediments in a small carbonate-rock catchment,Guizhou Plateau,southwest China

Shibanqiao Reservoir (25°56′56.5′′ N, 105°26′44.5′′ E and ∼1400 m a.s.l.), southwest Guizhou Plateau, SW China, was built in 1958. It lies in an area of sub-tropical monsoon humid climate in a carbonate-rock-dominated catchment of 6 km². Two sediment cores (24 and 23 cm long) were retrieved from the reservoir, and four soil profiles were sampled in the catchment. Mineral magnetism was measured on all sediment and soil samples. Soil and sediment magnetic measurements together with analyses of sediment ¹³⁷Cs activity, particle-size, TOC, and C/N revealed changes in soil erosion between 1960 and 2002. During some phases, erosion (probably as splashing and/or sheeting) was relatively low and tended to take place only in the topsoil as indicated by high ARM/SIRM of the sediments. During other phases, erosion (probably as rilling and/or initial gullying) was relatively intense and thus disturbed the deeper soils, as expressed by high IRM_−100mT/SIRM. Most of the changes in relative intensity of erosion can be ascribed to fluctuations in precipitation. Changes in land use/land cover or human activities may account, in part, for changes in soil erosion inferred for four more roughly identified periods.