Study On Charateristics Of Agricultural Non-point Source Pollution In Fengyu River Basin Based On SWAT Model

The role of agricultural non-point source pollution (ANPS) in water environment pollution is moreand more outstanding, and agricultural non-point source pollution is becoming the key point of thewater environment problem. It is essential to reduce ANPS to improve water quality. Erhai is a plateaulake in its early eutrophication. Fengyu River is one of the main sources of Erhai. This study choosesFengyu River basin in the Erhai basin to study ANPS, through the method of combining with the SWATmodel and field monitoring. The study on agricultural non-point source load and characteristics inFengyu watershed could be a guidance and reference for Erhai. In this research Fengyu watershed istaken as the research area to study the composition and distribution of agricultural non-point sourcepollution using SWAT model. The main contents and results are as follows:(1) The average concentrations of total nitrogen and total phosphorus is0.76mg/L and0.15mg/Lrespectively in whole period of supervision, which is Ⅲ class water in accordance with the provisionsof national standards for surface water environmental quality. This suggests that the water quality ofFengyu river has appeared different degree of pollution. Based on the whole period of supervision, thepollutant concentration in flood season is higher than that in non-flood season. Results of monitoringheavy rain’s procession show that the concentrations of all pollutants are reduced in undulate downwardtrend with the rainfall.(2) The database for running SWAT in the study area was established, including hydrology monitordata, survey data, lab analysis result, etc. The calibration and validation of SWAT are based onmonitoring data from basin outlet. Error analysis showed that the simulation results are fine and themodel is applicable for the study area.(3) The annual production amount of total nitrogen is50.71t, and the proportion of nitratenitrogen is82.2%in total nitrogen. The annual production amount of total phosphorus is8.74t, and theproportion of inorganic phosphorus is82.2%in total phosphorus.(4) According to the simulation results, nutrient load was higher on both sides of the main riverchannel. In the south and east of the watershed, the main types of landuse are forest and grassland andthe nutrient load is lower. At the same time, the phosphorus loss is given priority to with particle state.So the spatial distribution of phosphorus and soil erosion has higher correlation.(5) 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 loadof nutrients varied during the whole year and reached the peak in the rainy season. There existedpositive correlation between discharge and rainfall. The same trend was also found in the output ofsediment and nutrient load. Therefore the rainy season is the key time for the NPS control. The slope ofsub-basins was another important factor to the the load of sediment and nutrient.(6) Scenario analysis based on the fertilizer application showed that reduction of chemical fertilizercould reduce the output of nitrogen significantly, but phosphorus is not significant. If we hope toreduce the output of NPS from farmland comprehensively, other management measures like the time offertilizer and tht rate of fertilizer should be paid attention to.