Risk Of Phosphorus Loss In The Watershed Of Miyun Reservoir

Accelerated by human activity, eutrophication has become a difficult problem of the world, especially in our country. Many researches have revealed that eutrophication is related to agriculture non-point pollution closely.As an important water source, Miyun reservoir plays a crucial role in Beijing. The water quality of Miyun reservoir is at medium-eutrophication situation, which is mainly caused by the non-point source pollution (NPS) in the watershed, and Phosphorus (P) is the limited factor. So, it is important to study on P loss sensitivity in this watershed.In this paper, risk of P loss in Miyun Reservoir Watershed is estimated by P Index. Many kinds of factors such as, soil erosion, distance to water body, runoff, soil P test, application rate and method of P fertilizer, and so on are needed to calculate P Index. These factors are obtained by using GIS, experimentation, field survey and so on.PI distribution is classified by five grades of lowest, low, medium, high, highest, which occupies 56.32%, 36.26%, 4.12%, 2.50%, and 0.81% of total areas. The high-risk region is only 3.3% of total researched area, mainly on east and mid and near to rivers, these area is recognized as critical source area (CSA).According to the result of analysis of CSA and distribution of each factor, landuse is found to be the key factor to P loss. PI is high where these is farmland, the P test and application rate of P fertilizer these is high. When the other factor is the same as each other, the region's PI is high that is near to the river.Based on the analysis result upon, the author put forward effective management, including nutrient management and land management.