Analysis Of Non-point Source Pollution In Fujiang River Basin Based On SWAT Model

Based on Fujiang River Basin,the study aim at studying the mechanism of the impact of surface rainfall and underlying surface conditions on the non-point source pollution and its uncertainty,and the influence of hydrological processes on non-point source flux and attenuation processes in the channel.Choosing ammonia nitrogen(NH3),total nitrogen(TN),total phosphorus(TP)and permanganate index(Imn)as four key objects to water pollution,systematically investigate the status of pollutant discharge in Fujiang River Basin,and calculate the discharge from point and non-point sources.Based on ArcGIS,the basic data such as DEM,soil distribution,land use,weather data and the source discharge are mapped out,and then build the SWAT model,calibrate and verify the accuracy of the model parameters based on the observed river discharge data and water quality data.Based on the Sobol sensitivity method,analyse the effects of the source intensity of the pollutants,runoff and the background pollution in soil on the non-point source pollution load.Based on the flow and pollutant flux calculated by the SWAT model,analyse the variation of non-point pollution load under the change of rainfall conditions,and discuss the influence of the rainfall process in different hydrological periods and different hydrological years;Then analyse the pollution equilibrium characteristics in the channel,calculate the contribution of non-point source pollution load in the water environmental capacity and characteristics of non-point source pollution load from different source in different hydrological periods;Based on the information entropy and complexity measure,analyse the uncertainty of the non-point pollution load under different meteorological conditons;Finally characterize the underlying surface information,put forward the runoff factors and the discharge factors,and analyse the influence to non-point pollution and its uncertainty.The results show that the contribution of the non-point source pollution load to water pollution is significant,and the compositional structure of the non-point source pollution load in the river channel is different from the emission source.The non-point source of TN emission accounts for 79%,livestock and poultry farming emission in the non-point source accounts for 68%,and 15%in rural life and 17%in farmland fertilizer.In contrast,the contribution of non-point source TN to the pollution load flux of the river channel is 85%,and the contribution of livestock and poultry farming,rural life and farmland fertilizer to non-point pollution load flux are 50.8%,27.5%,and 21.7%,respectively.Obviously the contribution of non-point sources and farmland fertilizer in the channel increases,the contribution of livestock and poultry farming is decreased.78%of TP emissions come from non-point sources,of which 77%are from livestock and poultry farming,16%from rural areas and 7%from farmland fertilizers.The contribution of non-point source TP to the pollution load flux of the river channel is 83%,of which the contribution of livestock and poultry farming,rural life and farmland fertilizer to the non-point source pollution load flux are 30%,17%,and 53%,respectively.Comparing with the emmission of TP pollution,the contribution of farmland fertilizer increases.Emission of non-point source pollution of NH3 accounts for 70%,of which the livestock and poultry farming,rural life and farmland fertilizer account for 55%,26%and 19%respectively.IMn non-point source accounts for 70%,of which 85%for livestock and 15%for rural life.According to the comparative analysis of source emission of pollutants and pollution flux in the channel,the contribution of farmland fertilizer has increased.The non-point source pollution load flux of TP and IMn in the abundance and dry seasons account for a significant difference in the proportion of water environment capacity.In the wet season,the TP non-point source flux accounts for 44.4%of the water environment capacity,the average water season is 22.9%,and the dry season is 5.7%;IMn wet season accounts for 24%,the average water season is 18.65%,and dry season is 6.1%.Specifically NH3 non-point source fluxes account for a small difference in the proportion of water environment capacity during the different hydrological period:the wet season,the average water season and The dry season are 13.3%,14.5%,and 11.4%,respectively.The non-point source pollution load has significant differences with the change of underlying surface conditions.Uncertainty analysis shows that under different conditions,the uncertainty of non-point source load is significantly affected by the dominant factor of the underlying surface,which TN and IMn are affected to a greater extent by the variation of underlaying non-point source discharge,while TP and NH3 are significantly affected by the soil background information and the underlying surface runoff factors.Rainfall is the direct driving force of non-point source pollution load.Changing meteorological conditions,the uncertainty of non-point source pollution load changes significantly.The results show that the uncertainty and complexity of the hydrological flow process are significantly smaller than the uncertainty of the non-point source pollution load,and the magnitudes of the uncertainty and complexity parameters of TP and IMn change significantly more than NH3 and TN.For the Fujiang River basin,under the rainfall of less than 1050mm,with the increase of rainfall,the fluctuation complex of non-point source pollution load increases significantly,the entropy and the average information increment decreases,and the uncertainty of non-point source pollution load significantly reduces,so that the predictability of non-point source pollution load increases.After the rainfall is more than 1050mm,the larger the rainfall,the greater the uncertainty and complexity will be,which is not conducive to the prediction of the non-point pollution load.Further analysis shows that under different rainfall conditions,the factors affecting the non-point source flux of the section have changed:When the rainfall is less than the critical value,the process of the non-point pollution into river is mainly affected by different underlying surface rainfall runoff and the startup status of non-point source pollutants,with little influence factor and small uncertainty,which is sensitive to the change of rainfall;When the rainfall super critical value,the process of the non-point pollution into river is more affected by the underlying surface information?rainfall process?the different non-point pollution emission and the migration process.The impact is more of a change in the macroscopic natural state of the basin,with an increase in the number of influencing factors,an increase in uncertainty,and a reduced sensitivity to rainfall changes.