The Study Of Non-Point Source Pollution And Health Assessment For Sibao Reservoir In Jiangmen City

Water environmental pollution is one of the urgent problems to be solved in China,and it also threatens the allocation of water resources.Sibao Reservoir is the largest reservoir in Heshan City,Jiangmen City,and an important water source for surrounding towns.The non-point source pollution generated by the reservoir watershed has an impact on the water quality and ecological health of the reservoir area.Controlling non-point source pollution of the reservoir and protecting the ecological environment are important for ensuring the water supply security.This paper takes Sibao Reservoir in Jiangmen City as the research object,uses SWAT model to simulate non-point source pollution in the watershed,conducts water quality assessment and comprehensive health assessment of the reservoir,and conducts a comprehensive analysis from the watershed to the water body.The main results are as follows:（1）Based on the spatial and attribute data of the Sibao Reservoir watershed,a non-point source pollution model for the Sibao Reservoir watershed was established.On the time scale,the annual change trend of sediment,TN and TP from 2009 to 2018 was basically the same as rainfall.In the flood season of typical hydrological year,TN accounted for 60.3%to 79.4%,and TP accounted for 60.6%to 91.1%.On the spatial scale,the sub-watershed with more cultivated land had stronger nitrogen and phosphorus loss,and the sub-watershed with mostly steep mountains was easy to cause soil erosion and the intensity of nitrogen and phosphorus loss was also large relatively.In terms of pollution load per unit area of the watershed,cultivated land accounted for the largest proportion,followed by forest land and shrub forest.So measures such as reducing fertilizers and returning farmland to forests can effectively reduce nitrogen and phosphorus losses.（2）Conduct continuous water quality monitoring in Sibao Reservoir,and use single-factor evaluation method,BP neural network method and principal component analysis to analyze water quality by selecting 7 evaluation indicators including DO,BOD₅,COD_Cr,COD_Mn,TP,TN and NH₃-N.Select 5 indicators such as transparency,TP,TN,NH₃-N and chlorophyll a,and use the index method to evaluate the eutrophication of the reservoir.The results of single factor evaluation and BP neural network were roughly the same,indicating that the water quality of the reservoir was generally between class III-IV.Principal component analysis showed that the water quality was mainly affected by COD_Mn,TP,TN and NH₃-N.The results of the index method showed that the reservoir was in a state of mild eutrophic,and the degree of eutrophication in the catchment area was higher.（3）Establish a comprehensive health assessment system for the Sibao Reservoir,and divide into 5 primary indicators of hydrology and water resources,physical structure,water quality,biology and social service functions and 16 specific secondary indicators.The analytic hierarchy process and the entropy method were used to combine the subjective and objective weights to determine the weight of each index.The set-pair analysis method was used to evaluate the health of the reservoir comprehensively.The results indicated that the Sibao Reservoir was at a healthy level.Water quality indicator in the guidelines layer was at sub-health level,and there was a risk of developing the reservoir to an unhealthy trend.（4）According to the non-point source pollution situation of the watershed,the water quality and health assessment of the reservoir,the pollution control measures for the water source area of Sibao Reservoir were proposed.