| With the rapid development of economy, the pollution of small watershed became more and more serious, and it is an urgent need to carry out the remediation work. Based on the investigation of social condition and pollution sources, nitrogen and phosphorus discharged from industy point source minicipal source livestock source and fertilizer in the typical small watershed such as Yangong and Dasong river watershed were computed, and the distribution of nitrogen and phosphorus output from agricultural non-point source pollution was also calculated by the AnnAGNPS model in this thesis.The types of agricultural non-point source pollution were deeply classified, and pollution the loading constituted were analysed.Annual average output loading was simulated by AnnAGNPS model. The results showed that there were 107.6 tons particle nitrogen, 229 tons dissolved nitrogen, 27.2 tons particle phosphorus and 1.4 tons soluble phosphorus discharged from Yangong river watershed, and there were 47.7 tons particle nitrogen, 232 tons dissolved nitrogen, 12.1 tons particle phosphorus and 0.65 tons soluble phosphorus discharged from Dasong river watershed. In non-point pollution of both watersheds,the dissolved nitrogen was the main form of TN loading, whereas the particle phosphorus was the dominant form of TP.At Yangong and Dasong river watershed, the landuse are mainly the woodland and paddy-field, so the spatial of distribution pollutants is well-proportioned, But the output of nitrogen and phosphorus in woodland is smaller than that in paddy-field.The monthly output loading varied significantly, the loading was positively correlated with rainfall and 75% of total pollutants were exported from both watersheds from April to September. Annual N and P loading with ten-years weather data were simulated by AnnAGNPS model, the ruslts showed that yearly output of particle-N&P were positively correlated with rainfall,while it was not fitted for dissolved- N& P loading.Agricultural non-point source pollution is the major pollution source at the constitute of N&P pollution loading. It constituted 60%> 58% of total N&P pollution loading in Yangong river watershed respecyively. The contribution order for TN pollution loading discharged from all the pollution sources were as follows: municipal source) soil erosion) fertilizer) livestock source) industry source; the order for TP pollution loading was: municipal source) soil erosion) livestock source) fertilizer) industry source. Agricultural non-point source pollution was take up 57%> 43% of total N&P pollution loading in Dasong river watershed respectively. The order for TN &TP pollution loading were: municipal source) fertilizer) soil erosion) livestock source) industry source. |
