[Characteristics of Nitrogen and Phosphorus Output and Loss Flux in the Shipanqiu Watershed, Three Gorges Reservoir Area].

As the source of non-point pollution in the Three Gorges Reservoir Area, small watershed is a key control object in alleviating deterioration of water quality. In the Three Gorges Reservoir Area, the Shipanqiu small watershed with various land-use types was selected as the research object, and the water quantity and quality of the outlet section of the watershed were continuously monitored. We carried out analysis of the small watershed runoff loss and nitrogen and phosphorus pollutants with concentration, analyzed the morphology change characteristics of runoff erosion, calculated the small watershed of pollutant emission flux, and analyzed the nitrogen and phosphorus nutrient loss and main human and natural factors, especially in the Three Gorges Reservoir Area of agriculture where nonpoint source pollution research has important practical significance. The results showed that the rainfall in the watershed varied significantly with the seasons, and the rainfall was mainly distributed from April to June, which was the main output period of nitrogen and phosphorus loss in the small watershed, accounting for 58.94% and 67.60% of the total nitrogen and phosphorus load, respectively, in the whole year. The total annual runoff in the Shipanqiu small watershed was 8.02×10 m, and the annual total nitrogen loss flux was 5.04 kg·hm, of which nitrate nitrogen (2.54 kg·hm) was the main part. The total phosphorus output was 0.534 kg·hm, and the soluble total phosphorus (0.422kg·hm) accounted for 79.00% of the total phosphorus flux. The loss flux of total nitrogen was 9.51 times that of total phosphorus, and the non-point source pollution risk of nitrogen was much greater than that of phosphorus. Therefore, for the Shipanqiu small watershed, it is especially important to prevent nitrogen loss in paddy fields when fertilization and rainfall coincide.