Recent soil erosion in the Hongfeng catchment on the Guizhou Plateau, SW China revealed by analysis of reservoir sediments and soil loss modeling

摘要

The Guizhou Plateau in SW China is dominated by carbonate rocks and karst landforms. Erosion rates are low, but soils are thin and soil erosion remains a serious problem. Hongfeng Lake is the largest reservoir on the Guizhou Plateau. A 35-cm-long sediment core was retrieved from the reservoir and six soil profiles were sampled in the catchment. Cs-137 activity was measured in the core to establish a chronological framework. Sediments and soils were analyzed for particle size, TOC, TN and mineral magnetism. Soil erosion that occurred between 1960 and 2003 was inferred from stratigraphic variations in particle size, TOC, C/N and magnetism of the sediments, aided by similar analyses on soils. Erosion was generally low from 1960 to 1987, but intensified thereafter, until about 1996. Between ca. 1996 and 2003, erosion declined. Land use data were derived from remote sensing images for 1973, 1990, 1993, 1996, 2000, 2003, 2006, 2010 and 2013, and running the Conversion of Land Use and its Effects at Small Region Extent (CLUE-S) model for 1976, 1979, 1982, 1985 and 1988. Precipitation, Digital Elevation Model (DEM) and soil-property data were also collected. Using these data, we determined input variables [rainfall erosivity (R), soil erodibility (K), slope length and gradient (LS), vegetation cover and management (C) and erosion control practices (P) for the Revised Universal Soil Loss Equation (RUSLE) Model]. Annual soil loss (A) was estimated for the Hongfeng Reservoir catchment for each year using the RUSLE model. Annual soil loss for 1973, 1976, 1979, 1982 and 1985 was generally low, with an average of 38.5 t ha(-1) a(-1). For 1988, 1990, 1993 and 1996, average annual soil loss increased to 57.7 t ha(-1) a(-1). The average for 2000 and 2003 declined to 46.6 t ha(-1) a(-1). Variations in the modeled annual soil loss are consistent with what was measured in the sediment record, implying that erosion events were recorded in the sediments despite temporary storage of sediments in the large, relatively flat catchment. Erosion was low and may have declined even more from 2003 to 2013. Despite the temporal variability, erosion was generally more intense in the west and east than in the central part of the catchment. Topography, rainfall and vegetation are the main factors that influenced soil erosion in the catchment.