The Study On Agricultural Non-Point Source Pollution Modeling In The Small Watershed Based On ArcGIS

Water environment pollution, one of the major environmental problems to be solved, has become a serious threat to the survival and development of the human society. Although the point source pollution has been furthest controlled in recent years, the impact of non-point source pollution on the aquatic environment is gradually revealed. As the characteristics of the non-point source pollution exist, such as uncertainty, complexity, and the broad sphere of influence, it may be hard to monitor all non-point source pollution in field effectively.In the past time, non-point source pollution was mainly studied artificially. A lot of manpower and resources was spent on mapping, planning, data processing, and analysis, which resulted in simulation with error-prone, low efficiency, and low quality. Based on the geographic information system (GIS) software platform, agricultural non-point source pollution research in the small watershed can be improved significantly in efficiency and quality by the functions such as data entry, processing, management, analysis, calculation, and other function of geographic information systems. Therefore, with the introduction of spatial information technology such as GIS, remote sensing to the research of agricultural non-point source pollution, making the modeling, management, analysis and other study of non-point source pollution move forward into the era of digital and information technology. GIS and remote sensing technologies have gradually become the powerful tools of simulation, management, comprehensive analysis of agricultural non-point source pollution in the small watershed.On the basis of the study on component GIS and watershed agricultural non-point source pollution models, Addressing the needs of the study on agricultural non-point source pollution in Three Gorges Reservoir Area, taking the foundation of mechanism of analysis and theory Construction of the small watershed agricultural non-point source pollution as a starting point, a method that a small watershed in agricultural non-point source pollution model integrated seamless with object-oriented programming language environment and the secondary development platform ArcEngine is explored. Taking Shenjia river watershed in Zhongxian for example, the simulation results of agricultural non-point source pollution model in the small watershed were validated with measured data. The results show that the establishment of a small watershed agricultural non-point source pollution model simulate the Shen River Basin sediment, dissolved nitrogen, the adsorption of nitrogen, dissolved phosphorus, adsorbed phosphorus values well. The main innovative achievements are as following.(1) In this study, starting from the analysis of fromation causes of small watershed agricultural non-point source pollution, the mechanism of surface runoff, soil erosion, migration of the pollutant load of N and P is studied in detail. By comparison of non-point source pollution model and its mechanism of major domestic and foreign agricultural, parametric model suit for the study area is selected and some factor were amended. The theoretical framework of the Three Gorges Reservoir Area agricultural non-point source pollution model is built. Taking Component-based geographic information system as platform, under the object-oriented programming language environment, non-point source pollution model is embedded in the development platform, thereby the Three Gorges Reservoir Area agricultural non-point source pollution model is established.(2) The terrain factor of the model has been calculated by an optimized algorithm in the study. By an automatically generated function for slope length, the accuracy and practicality of the model is greatly improved. The slope length factor in the modified Universal Soil Loss Equation (MUSLE) is amended in the model to increase the practicality and simulation accuracy of the model. Aimed at sloving the disadvantage of traditional model in failure of predicts in steep slope, an optimized algorithm is used to achieve prediction in this case. The vegetation cover and management factor in the MUSLE is modified and improved the utility and simulation accuracy of the model. vegetation indices from remote sensing images is used to calculate the vegetation cover, the estimation of vegetation cover and management factor is realized, which improved the practicality of the model and simulation accuracy significantly.(3) The highest depth of surface runoff in rainstorm simulated is as high as 62.72 mm, which is mainly distributed in the southeast of study basin. The biggest peak flows in rainstorm simulated is up to 189.33 m3/s. In the simulation, the area which produced the soil erosion more than 500 t is mainly in the where both slope and slopelength are relatively larger in the southeast of study area. Amount of soil erosion of Dryland is the greatest one, followed by forest field and paddy field. The biggest amount of dissolved nitrogen (nitrate nitrogen) pollutant simulated by our model in the study area losing through surface runoff is 6.20 kg/hm2. The biggest amount of adsorption of nitrogen (organic nitrogen) pollutant is 1.20 kg/hm2. The biggest amount of dissolved phosphorus pollutant losing through the surface runoff of loads is 0.26 kg/hm2. The biggest amount of adsorbed phosphorus pollutants (organic phosphorus and mineral phosphorus) is 0.31 kg/hm2, larger values of these indicators are mainly distributed in the southeast part of the study area. validation of Measured data from the study area show that there is a good correlation between the measured data and simulation data. The application of the model in small river scale in Three Gorges Reservoir Area has good prospect.