Application Of SWAT Model In Non-point Source Pollution Simulation Of Tiaoxi Watershed

Non-point source pollution (NPS) was an important factor for water environmental deterioration and Lake Eutrophication. It is essential to control NPS to improve water quality in our country. Taihu Lake is the third largest freshwater lake in China. With economic and social development, an increasing amount of pollutants have been discharged into Taihu Lake and resulted in water pollution-eutrophication in particular. Agricultural non-point source pollution is a major source of water pollution source in Taihu Lake. Tiaoxi is an inflow river surrounding Taihu Lake, and is also the main drinking water source for local community.SWAT model developed by USDA Agricultural Research Service(ARS) was applied to estimate the NPS in Tiaoxi Watershed. By calibrating and validating with the observed data, the NPS model for study area was established. The pollution load of NPS in Tiaoxi Watershed was estimated and the factors for NPS were discussed with the model. The main content and results were as follows:(1) The database for SWAT in the study area was established to ensure the successful operation. The data from Pingyao and Gangkou stations were used for calibration and validation. Error analysis showed that the simulation results were fine and the model was applicable for the study area.(2) SWAT model was used to calculate the runoff, sediment and nutrient load in Tiaoxi Watershed. The results showed that there existed a good positive correlation between sediment and rainfall. According to the simulation results of 2008, nutrient load was higher in the north and east of the watershed.(3) According to the model results, farmland was the main source of sediment and pollutions, which produced much more nutrient load in unit area than other land use types. The runoff and the load of nutrients varied during the whole year and reached the peak in the rainy season. There existed positive correlation between discharge and rainfall. The same trend was also found in the output of sediment and nutrient load. Therefore the rainy season is the key time for the NPS control. The average slope of sub-basins was another important factor to the output of the load of sediment, organic nitrogen and nitrate.(4) Scenario analysis based on the fertilizer application showed that reduction of chemical fertilizer could reduce the output of NPS, but not significantly.