[Simulation of nonpoint source pollution load in Maoping River watershed].

The nitrogen and phosphorous transport in the Maoping River watershed was modelled using the SWAT model, which simulates the water cycle and the transformation of nutrients. The model was first calibrated by comparing the observed and the simulated data from May to October 2004, and then validated. The Nash-Sutcliffe coefficient (R2), the mean square root error (RMSE) and the relative error(CV) were used to test the agreement between observed and simulated data. The validated model was then be used to simulate the nutrients load in Maoping River watershed. The Nash-Sutcliffe coefficient of flow, nitrogen and phosphorous was 0.71, 0.51 and 0.62 with the minimum relative error 1.8%, 1.1% and 10% respectively. Despite achieving the relatively lower resemblance between observed and simulated phosphorous and nitrogen load the model showed good agreement in simulating runoff. The results showed that 102.5t nitrogen and 9.46t phosphorous entered intoYangtze River during May to October 2004. One of the important reason that caused the water quality deterioration can be attributed to the nonpoint source pollution.