Research On Agricultural Non-Point Source Pollution Load In Xiaojiang River Watershed Of The Three-gorge Reservoir Region Based On AnnAGNPS Model

The agricultural non-point source pollution as the main cause of water pollution which became the focal point of worldwide attention. It is difficult for monitoring and quantitative analysis. The computer simulation based on mathematic models is a good approach to solve these problem. The distributed-parameter, batch process, continuous simulation model such as AnnAGNPS model became the important method to simulate the pollution load,identify the critical pollution sources, study the agricultural management measures. Because of its serious environmental pollution, complex topography, mini land, scattering management, diversified farming measures, it's better to use mathematic models to simulate pollution loads, not the field monitoring or artificial rainfall in the Three-gorge Reservoir Region.Little research has been used in the AnnAGNPS model,the study amost focus on small-scale. Present research mainly study Xiao Jiang watershed in the Three Gorges reservoir region,it has 250m from the Three Gorges dam. It can give us the implication to control the pollution sources when use the AnnAGNPS model to build databases, analyse sensitiveness, simulate the runoff, silt, nutrient output, identify the critical pollution sources, study the three agriculture management how to influence pollution loads,all of these is This rearch provides reference value for the follow study. Presentresearch'conclusion to be as follows:(1) Present research introduces methods of constructing data set for AnnAGNPS in the case of Xiaojiang River watershed located in the Three Gorges Region. The data set mainly focuses on climate, topography, landuse, soil, crop, non-crop, crop management, fertilizer, pesticide information and runoff curve number data.(2)Main 8 factors determining non-point pollution output were identified through sensitivity analysis, including curve number, K, conservation of water and soil factor, crops management factor, slope, slope length, Manning and the chemical fertilizer. This parameters have different effects to runoff yields, sediment yields, total nitrogen and total phosphorus.(3) AnnAGNPS was applied to estimate runoff, sediment yields, N and P loads from Xiaojiang River Watershed in the Three Gorges reservoir region from 2002 to 2004. Time series data of the same time periods on runoff, sediment yields from Baotawo gauge station (which covers an area of 62% of the whole catchment) and nutrient loads from the outlet of Xiao Jiang catchment were used to calibrate and validate simulation datas. It shows that the results are reliable to use.(4) It shows that the result of runoff simulation is more precise than sediment and nutrition loads simulation. Annual (2002-2008) output of sediment from watershed outlet is 277.81×104 tons, while annual loads of total nitrogen and total phosphorous are 7949.38 tons and 463.74 tons, respectively. All non-point source pollutants are of similar generation trends, which are varying with season, being positive correlative with precipitation, and determined by fertilization, cultivation as well as land surface condition.(5) The results shows that the non-point source pollution loads are different for spatial division and land-use types. The unit area loads in turn are waters, construction land, cultivated land, forest land, grass land, the total quantity loads in turn are farming, forest land, construction land, waters, grass land.(6) The results shows that the non-point source pollution loads are mainly from the soil erosion and the chemical fertilizer loss by dry lands on slopes, so it's important to control this areas'pollution.Though the study of three agriculture management practices, it indicates that some methods have obviously function to reduce the pollution loads, such as returning farmland to forest and change the slope.