Estimating erosion rates on sloping agricultural land in the Yangtze ThreeGorges, China, from caesium-137 measurements

The paper describes the application of caesium-137 measurements for estimat ing soil erosion rates in a small catchment in the Three Gorges region of t he Yangtze River, China. The construction of the Three Gorges Dam has drawn attention to the impact of erosion and sedimentation, but there are relati vely few quantitative estimates of sediment transfer for this area. The sui tability of the fallout radionuclide, caesium-137, for the rapid appraisal of soil redistribution in the steep and dissected terraced landscape of the Three Gorges is investigated here. Previous applications of the technique in Chinese agricultural environments have indicated the difficulty of obtai ning reliable baseline fallout estimation. The integration of monthly rainf all data with a model of global strontium-90 fallout is developed to provid e an independent estimate of baseline fallout, which is consistent with fie ld measurements. The method also enables a mass balance model of caesium-13 7 mobility to be calibrated. Mean annual soil loss during the last four dec ades is estimated at 4500 t km(-2) yr(-1). Erosion rates are strongly relat ed to field slope angles but highly variable spatially. (C) 2000 Elsevier S cience B.V. All rights reserved.