Assessment of Particulate Nitrogen and Phosphorus Losses with Soil Erosion in Upper Watershed of Three Gorges Reservoir

Particulate nitrogen and phosphorus (PP and PN) attached to sediment from agricultural land is the main cause of water body eutrophication in the Three Gorges Reservoir. In order to identify the spatial-temporal distribution of PN and PP source and their loads imported to the reservoir, a mathematical model of annual sediment discharge for the upper reaches of the reservoir was proposed based on the Universal Soil Loss Equation (USLE). Integrated with the non-point source (NPS) pollution model, the PN and PP pollution loads in 1990-2006 were estimated. The simulation results show that the lower reaches of the Jinsha River, the upper reaches of the Minjiang River and the Bailong River sub-basin in the Jialing River basin are the main sources of PN and PP pollution. These regions should become the focus of the sediment and NPS pollution control in future. The sediment yield, PN and PP loads have decreased because of the key soil and water conservation project in upper Yangtze River since 1989. Compared with the loads in 1990, the PN and PP loads in 2006 have reduced by 61.7% and 54.7%, respectively.