Miyun reservoir

the mere surface water source of drinking water in Beijing

is facing with serious threat of eutrophication in recent years.Non-point source pollution has become the primary factor resulting in water quality deterioration when point source pollution was gradually controlled in the Miyun reservoir.Nonpoint source pollution has remarkable variation on spatial distribution and the pollutant coming from specific landscape units usually accounts for the majority of the pollutant load in watershed.These landscape units are the critical nonpoint pollution areas.Measures should be taken on them in order to control nonpoint source pollution with limited resources.As a simple model developed in past years

the USLE(Universal Soil Loss Equation) is still one of the most widely used soil erosion models through continuing revisions and modifications presently.Because the parameters of USLE are relatively simple and easy to obtain

this model integrated with GIS may be used in soil erosion investigation in large regions.Based on the widely used GIS platform

the USLE is used for raster calculation to create the distribution map of critical nonpoint source pollution areas in the Miyun reservoir watershed.The distribution map produced in this study may provide helpful reference for the further investigation on the identification of critical areas for the nonpoint source pollution.