[Inversion formula of one-dimensional water quality equation for the export loads of nonpoint sources pollution in headwater area]

An inversion formula for the export loads of nonpoint sources pollution in headwater area was established based on one-dimensional water quality equation, and it was used to calculate the pollution loads for tributaries in the headwater catchment of Laohutan Reservoir, in Huzhou City, Zhejiang Province of China. Monte Carlo method was adopted to determine the sensitivity about each input parameter in the inversion formula. Because each sensitive parameter can be measured directly in the inversion formula, so that this approach can decreased calculation error, which is often caused by the parameter estimation. Furthermore, the inversion formula can be adopted to calculate pollution loading on any time scale. Monthly nonpoint sources pollution export loads in 2007 were calculated by the model in the research catchment. Results showed that pollution loads in stream were significantly positive related with flow rates (r > 0. 90, p < 0.01), and the flow rate was the most sensitive factor in the model, followed by the nutrient concentration and background concentration at the stream end. While, comprehensive degradation coefficient and flow velocity contributed very little influence to the model uncertainty.