Research On Non-Point Source Pollution Caused By Land Use Allocation Of Dianchi Watershed Based On SWAT Model

With the effective governance and control of point source pollution, non-point source pollution has displaced point source pollution as the primary pollution source of affecting the quality of water environment. Non-point source pollution occurs under the influence of many factors. Among them, land use is the key factor, which comprehensive reflects the human activities. As one of the three national focused lake bodies, the water pollution of Dianchi Lake has attracted tremendous attention. For a long time, control of point source pollution has little effect, and the pollution situation has not been improved obviously. Also, Dianchi watershed passes through vast area with complicated topography. In watershed, the land use activity is frequent and so much not enough reasonable in structure and layout.Therefore, this paper choosing Dianchi watershed as study area carries out series research surrounding land use and non-point source pollution. With the support of ArcGIS, SWAT model in Dianchi watershed is constructed. On this basis, it explores the effects of land use structure on non-point source pollution from two aspects of quantity structure and space layout, aiming at providing a scientific basis for land rational utilization and water environment governance in watershed. The final achievements are as follows:(1) Establishment the non-point source pollution model (SWAT model) suitable for Dianchi watershed. By using the ArcGIS as platform, the digital elevation model (DEM) and soil type map are acquired. Besides, in order to build the basic database for model, it should collect and organize the data of soil properties, meteorological, hydrologic and so on. Then, based on the actual monitoring data from2005to2008in Kunming station, Ganhaizi station and Haikou station, the sensitive parameters are adjusted to meet the requirements for certainty coefficient of R2and Nash-Suttcliffe coefficient. Consequently, it thinks that the model can be applied to the study.(2) Through the non-point source pollution simulations of land use allocation of2008and F1in2020, the impact of different quantitative structure of land use to non-point source pollution is analyzed. It turns out that, except for the runoff, the other pollution load under F1in2020are all less than that in2008. It shows, relative to2008, the land use allocation of F1in2020is headed in the direction of reduce pollution load in general and it does have been optimized on the population structure. Also, it directly quantitative proofs that, the quantity structure of land use has a great influence on non-point source pollution. The difference of quantity and spatial structure of land use will lead to different load out.(3) Through the simulations of land use allocation of Fland F2in2020, the impact of different spatial structure with same quantity structure is analyzed. It shows that, all the pollution loads of F1are less than that under F2. The different pollution load simulations of the two kind configuration schemes also suggest that, the aggregate space layout of one land use type is more effectively than the distributed layout pattern of land use in reducing the non-point source pollution for the whole watershed. What’s more, the two kinds land use allocation of F1and F2have the same number structure but different spatial distribution. It illustrates that, even under the same quantity structure, the spatial structure of different can also cause of different non-point source pollution load output.(4) Through the simulations of each sub basin of F1and F2in2020, the distribution maps show that, the unit pollution loads are not the same. When sub basins increase with cultivated land and construction land, the pollution load largely increase; when forest land and grassland widely distributed in sub basin, the non-point source pollution can be effectively weakened. Intensity analysis shows in the sub basin with little change of land use pattern, the unit pollution load changes little too; however, in the sub basin with great change of land use pattern, the unit pollution load also along with it change much.(5) On the whole, the region of north and edge of east in watershed are the most severe soil and water loss area, but with little nitrogen and phosphorus pollution; while the region of middle with construction land and arable land are more serious of nitrogen and phosphorous pollution than sediment loss. It indicates that, the areas with serious sediment pollution do not coincide with the areas with serious nitrogen and phosphorus pollution. So, the control of pollution load should be according to the pollution characteristics of different sub-basins.