Research On Non-Point Source Pollution Of Heimiaogou Watershed In Danjiangkou Reservoir Area Based On AnnAGNPS Model

Non-point source pollution(NSP) has become the chief cause of water contamination with the effective control on point source pollution.As the water source of middle route South-to-North Water Transfer Project,the water quality of Danjiang reservoir is pretty well and is suitable for water transfer in general.But it is reported that the water quality of some branches is bad,which are mainly caused by NPS pollution.Therefore,it is important to study the NPS pollution for protecting the water quality of Danjiang reservoir.In this paper,Heimiaogou watershed of Danjiang reservoir was selected for research object,AnnAGNPS model database was constructed based on comprehensive investigation,field surveying,collecting land use and soil information as well as runoff plot experiment;The surface flow,sediment,total nitrogen and total phosphorus data of the Monitoring site were uesd to verify the simulation precision of AnnAGNPS,and the result showed that the suitability of the model was validated in Heimiaogou watershed.The characteristic of NSP was finally quantitative analyzed and the abridged effect of environmental pollution for the best management practices were evaluated by the calibrated AnnAGNPS model.The main results are listed as follow:(1) Runoff prediction is very sensitive to curve number selection,and sediment prediction is sensitive to crop cover and soil disturbance.(2) The correlation coefficients between the simulated results and the observed one of surface runoff,sediment,total nitrogen and total phosphorus are respectively 0.96,0.94,0.82 and 0.75.The simulation precision of AnnAGNPS is runoff＞sediment＞total nitrogen＞total phosphorus.(3) The exporting amount of annual surface runoff is 6.43×10~5 m~3.Sediment is 2.34×10~3 t,and the efflux coefficient is 1409.64 t/km~2·a.The exporting amount of annual total nitrogen and total phosphorus is 4.22 t and 0.54 t,and the efflux coefficients of them are respectively 2.54 t/km~2,0.33 t/km~2.Sol N and Sed P is in the majority,account for 75.47%,87.28%.(4) Critical source area of sediment load contributed 52.8%with the 19%area of the total,and the land use types are crop land and sparse woodland.Critical source area of TN contributed 54.7%with the 21%area of the total,TP contributed 15.6% with the 4.5%area of the total..(5) Monthly output loading changed very strongly and the loading was interrelated positively with rainfall.The output of TN and TP at the outlet were mostly from April to October,and the output of Sediment was mostly from July to September month.(6) AnnAGNPS model has been used for the management practices evaluation. Five management practices were proposed.The result showed that:the practice of reduce cultivate is the best method to reduce sediment,and the 75.45%sediment of the total can be reduced.Returning land for farming to forestry is best for cutting down the runoff,sediment,total nitrogen and total phosphorus,and the reduce ratio are respectively 50.95%,61.18%,32.77%and 24.35%,which is the best management practice for Heimiaogou watershed.