Study On Agricutural Non-Point Pollution In Shuang Yang Reservior Catchment Of JiLin Province

Presently, preferable control and harnessing are applied to nonpoint 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, and the agricultural nonpoint source pollution (ANSP) possesses the max contribution ratio. In our country, the ANSP is also serious. The status of many water areas are unoptimistic, such as the Tai Lake in Jiangsu, the Cao Lake in Anhui, the Fuxian Lake in Yunnan, the Miyun Reservoir in Beijing, the Yuqiao Reservior in Tianjin and the Xinlicheng Reservior in Jilin. The research and control of the ANSP get starting later in our country, so that more work need to be done in the field.As the most important commodity grain production base, the Jilin province is brought the severe potential harm to its environment by plowland over-reclamation, over-fertilization and excessive crop-dusting. At the same time, the climate changes in recent years (especially the precipitation) result in uptight water resources supply in North China. The Shuang Yang reservoir is one of the standby waterhead sites for Changchun that is a hydropenic city. As for Changchun, the important task of the current study is assuring the security of the domestic water supply and meeting the agricultural process water demand, so systematically investigating the water environment contamination, especially the ANSP, in the Shuang Yang reservoir watershed, is practical and meaningful.In this paper, the Shuang Yang reservoir watershed is taken as the study object. A survey is implemented to ravel the circumstantialities of the nature resources and agriculture output in the watershed. Combining qualitative and quantitative analysis, associating field investigation with indoor experiment and supported by the GIS, researches in the followed fields are carried through.The paper profoundly discusses the mechanism of the four processes of the ANSP, namely precipitation and runoff, soil erosion, ground surface solute stripping and soil solute leakage. The BP artificial nerve network package of MATLAB7 is employed to evaluate the water quality of the three rivers around the study area, evaluations of annual water quality changes (1997~2005) about the Yinma River and the Chalu River are given respectively, so is the evaluation about the Shuangyang River (2000~2005), while the discriminatory analysis is drawn to verify the evaluation results which indicate that: from 1997 to 2005, water from the cross-sections of Yantongshan, xingxingshao and Shitoukoumen have preferable quality, generally belong toâ…¡andâ…¢; but form 2000~2005, quality of water from the Xinan cross-section makes people worried, the mean annual water quality belongs toâ…£. The interannual water quality evaluation of the Xinan cross-section shows that water quality isâ…£during the drought period, while water quality isâ…¢in high water period.Collecting water samples from the surface water and the groundwater around the study area, total nitrogen content and total phosphorus content are determined to assess their pollution in the area. Surface water evaluation shows that: the total nitrogen of water in and around the reservoir is badly overproof, while the total nitrogen of the surface water in the upstream area is within the standard. In most places of the study area, the phosphorus is within the standard, while the index is one time higher than the standard in water near the reservoir; groundwater assessment presents that: the total nitrogen content and total phosphorus content are dispersedly distributed in the area, several places are heavily polluted; the GIS is employed to map the distribution maps of the nitrogen and phosphorus in the water. The statistic result of the ANSP in the watershed indicates that the total fertilizer dosage is 8537.4ton in 2006 in the Shuangyang reservoir watershed. During the period of the research, the leaking total nitrogen reaches 457.2ton, and the leaking total phosphorus comes up to 32.9ton; at the same time, the investigation indicates that irrational fertilization and leakage of pesticide are the key source of contamination.Through monitoring the precipitation, the rainfalls whose raininess exceeds 30mm are taken as the main rainfall type of the study area in 2006. In the period, the precipitation agent of erosion R is 93.12, the max R appears in June, while the min R occurs in May. Trough the analysis of concentration of nitrogen and phosphorus in single rainfall, time-variation rules of the concentration of nitrogen and phosphorus are attained; the trend of the total nitrogen concentration outputs of different land-use types is paddy land>corn field>mountain country>timberland, while that of the total phosphorus is corn field>paddy land> mountain country>timberland.By the methods, such as field investigation, testing and analysis and document retrieval etc, the parameters for the ANSP model of the Shuangyang reservovir watershed are determined. The parameters include geological information data, soil parameters, the parameters of fertilizer and pesticide, weather data, the CN of runoff curve and soil erosion factor K etc. When extract the geological information of the watershed and sub-catchment, the simulation of the Shuangyang reservoir AnnANGNPS model is executed. Fitting feedback analysis method is employed to distribute the catchment areas in the Shuangyang reservoir. The optimum grid partition level of the catchments is given, while the model reaches stabilization, and the result indicates the number of the optimum partition grid is 94.With the parameters determined, the AnnAGNSPS model is established, so that the estimations of the total nitrogen, the total phosphorus and the loss of sediment are gained. From the result of the simulation, we can see, during the research period (2006.5~2006.10), 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. 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). It is obvious that the ANSP is closely correlative with the precipitation. When it comes to the spatial distribution, the burden of the total nitrogen, the total phosphorus and the sediment mainly concentrate in the hillslope and irrational fertilization area.The model is validated by the single rainstorm event. 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 in the range 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.The sensitivity analysis is carried out with 8 parameters as follows, E of the SCS curve, Manning's roughness coefficient K, Soil erodibility factor L, soil conservation factor N, slope F, slope length H, slope of main drainage way I, side-slope of main drainage way J. Most of the parameters affect the sediment yield, the result is F>N>L>E>I, K and J. As for the total nitrogen and total phosphorus, the result is F>N>E and L>H, I, J and K.Based on the ANSP feature of the watershed, the pollution harm is ranked in the study area. A place with fine ecological regime and high percentage of vegetation coverage is ranked as faint polluted area, such as the South Dajianggang. A serious polluted area is the place that has steep hillslope, and land over-reclamation and over-fertilization, such as the Northwest Laoyemiao. The schemes and means for the ANSP control and management in the study area are put forward as follows: 1 return the farmland with the hillslope over 25 degrees to forest, the simulation result shows the pollution burden of the total nitrogen, the total phosphorus and the sediment drops 15% respectively at least; 2 reduce 30% fertilization, the simulation result shows the pollution burden of the total nitrogen and the total phosphorus decrease more than 40%, and the burden of sediment is cut down about 10%.