Study Of Non-point Source Pollution In Shuangyang Reservoir Based On AnnAGNPS Model

Presently, preferable control and harnessing are applied to non-point source pollution (NSP) worldwide, but the surface water contamination caused by the NSP is getting outstanding increasingly. The investigation indicates that the NSP is the main cause which leads to the surface water contamination, while the agricultural non-point source pollution (ANSP) is gernerally attributed to surface water contamination. The research and control of the ANSP start late in our country, a considerable amount of work needs to be undertaken in this field.In this paper, the Shuang Yang reservoir watershed is taken as the study object, and it's one of the standby water supplies for Changchun. The important task of the current study in Changchun, a hydropenic city , is assuring the security of the domestic water supply and meeting the agricultural demand, so systematically investigating the water environment contamination, especially the ANSP, in the Shuang Yang reservoir watershed, is practical and meaningful.A survey is implemented to ravel the circumstantialities of the nature resources and agriculture output in the watershed. Combining qualitative and quantitative analysis, field investigation and indoor experiment, supported by the GIS, researches in the followed fields are carried through:(1) Nitrogen is the main pollution factor concluded on the evaluation of water quality for the basin surface water in recent years. Due to over-cultivation, excessive fertilizer and agricultural chemical in a large area of farmland around water, the great amount of fertilizers and agricultural chemicals enter to the reservoir, which directly causes the shuangyang river water with high nitrogen density.(2) The main pollution load is Agriculture Non-point Source Pollution fixed by the statistics from the present situation of Non-point source pollution on entire basin. During the period of the research, the leaking total nitrogen reaches 271.9ton, and the leaking total phosphorus comes up to18.513ton, Agricultural non-point source pollution occupies the entire basin81%, the sanitary sewage accounts for 13% and the poultry pollution accounts for 6%, at the same time, the investigation indicates that irrational fertilization is the key source of contamination(3) The main downfalls and rainfall-runoff capacity that cause non-point source pollution are fixed up by rainfall-runoff simulation. There are only 12 downfalls are able to form surface runoff since May, among which 6 downfalls with single rainfall-runoff above 10mm.(4) The parameters for the ANSP model of the Shuangyang reservovir watershed are determined by field investigation, testing analysis and document indexl etc,and the AnnAGNSPS model is established. (5) Used the AnnAGNPS model, during the research period, in the shuangyang reservoir watershed the burden of the total nitrogen, the total phosphorus and the sediment is 341.6ton, 25.86ton and 43691.7ton respectively.Non-point source pollution situation of the Shuangyang reservoir basin is analysed from the following three parts as per the results of the model simulation:(1) As for temporal distribution, the burden of the total nitrogen, the total phosphorus and the sediment mainly concentrate in June, July and August (80% for both the total nitrogen and the total phosphorus, 74% for the sediment). On the analysis time, Has chosen the pollution load and the rainfall amount and rains therunoff fitting at the same time, looked from the fitting result, with rains the runoff to analyze the non-point source pollution loadto conform to the actual situation.(2) As for spatial distribution, the burden of the total nitrogen, the total phosphorus and the sediment mainly concentrate in the hillslope and irrational fertilization area, such as the northwest of Xiao Shipeng and Zhuang Jiatun, ect,.(3) Analysed by harm rank, a serious polluted area is the place that has steep hillslope, land over-reclamation and over-fertilization, mainly in the Northwest Laoyemiao.The model is validated by the single rainstorm. The result shows the simulation of the total nitrogen has a good agreement, its discrepancy of the total nitrogen falls within 10%, while the discrepancy of the sediment is between 14% and 21%, which is a poorer agreement. As for the total phosphorus, as a whole, the simulation shows great uncertainty, and yields large discrepancy, though the discrepancies of several rainfalls are small. So the model has a weaker ability to simulate the total phosphorus. At last, the effective ways on control of basin water eutrophication are rational fertilizer,formula fertilizer and the less quantity of fertilizer, which obtained from the non-point source pollution stimulation through different degree of fertilizer in the farmland.