ACCELERATED SOIL-EROSION IN WATERSHEDS OF YUNNAN PROVINCE, CHINA

Soil erosion in agricultural watershed consist of a natural (geologic) component and an accelerated (human-induced) component. There is litt le information available, particularly in developing countries, on the accelerated component of soil and nutrient erosion, or its effect on agricultural sustainability. Lakes and watersheds are physically linke d ecosystems, and lake sediments preserve historical records of materi al export from watersheds. We used paleolimnological methods to calcul ate sediment accumulation rates for four lakes in Yunnan Province, Chi na. We estimated trap efficiencies of three of the lake basins, calcul ated recent erosion rates for their watersheds, and calculated low-dis turbance rates that approximate natural erosion. Human activities in r ecent centuries caused a 15-fold increase relative to natural erosion rates of non-carbonate, clastic materials from two small [350 km2 (135 mi2)] watersheds. Phosphorus export from these watersheds increased a pproximately 19 fold. The degree of human influence appeared to differ between the two larger [2700 km2 (1042 mi2)] watersheds. Accelerated soil and nutrient erosion rates from Yunnan watersheds are high, and m ay ultimately destabilize agricultural productivity and the agrarian e conomy.