Abstract:

Nonpoint source (NPS) pollution of particulate phosphorus (PP) has recently become an important environmental concern in Three Gorges Reservoir. This study aims to identify the contributing zones of sediment and PP pollution in the upstream watershed of Three Gorges Reservoir and quantify the pollution by simulation method. Firstly, a mathematical model of annual sediment yields was proposed based on the Universal Soil Loss Equation（USLE）. The proposed model introduced a coefficient according to the influence of hydrology condition and human activities on sediment yield. The spatial and temporal distribution of sediment delivery ratio (SDR) in the model was got by topography index interpolation method. Then, an annual load model of PP pollution was established on the basis of the sediment model. The PP pollution in 1990~2006 was simulated by the model integrated with GIS. The simulation results show that subbasins of middle and lower reaches of Jinsha River, Yalong River and Dadu River are the main sources of the NPS pollution of PP, and the Jialing River subbasin has a relatively low degree of soil and particulate nutrients loss due to the “key erosion prevention project in the upper Yangtze River” program began in 1989. The PP pollution imported into the reservoir has declined since the implementation of the soil loss prevention program. Annual average load in the last five years is 16 482 t/a, which have reduced by about 37 % compared with that of in 1990.