| The Beiyun River originates from the western mountainous area of Beijing and flows through Beijing urban area and Tong Zhou Sub-center,which undertakes the tasks of water supply,flood control and landscape,and is an important ecological corridor connecting Beijing-Tianjin-Hebei Area.In recent years,with the development of the city,many kinds of ecological environment risk problems such as point and non-point source pollution,soil erosion,mountain hazards and so on in the the upper Beiyun River basin are highlighted.Quantitative analysis and comprehensive risk partitioning of the above ecological environment risks is an important prerequisite and basis for comprehensive watershed management.Based on the GIS,the study uses the estimation model of rural domestic waste pollution load,potential non-point source pollution index,SWAT model and sensitivity coefficient method to simulate and analyse the risk spatial distribution characteristics of point source pollution,non-point source pollution,soil erosion and mountain hazards in the the upper Beiyun River basin(above Shahe reservoir).It calculates the four risk weight by the mean square deviation decision-making method,synthesizes the comprehensive risk distribution map of the river basin,analyzes the single risk and comprehensive risk in the basin,divides the risk level,and put forward comprehensive watershed management measures according to the risk zoning.The main conclusions are as follows:(1)The risk spatial distribution characteristics of point source pollution in the upper Beiyun River basin is characterized by high in southeast and low in northwest.The proportion of extremely low,low,medium,high and extremely high risk areas is respectively 73.1%?6.6%?7.0%?5.3% and 8.0%;The extremely high risk areas are mainly concentrated in the plain towns with dense population and primary tributaries.And the extremely low risk areas are mainly distributed in the northwest mountainous areas with sparse population.(2)The risk spatial distribution characteristics of non-point source pollution in the upper Beiyun River basin is also characterized by high in southeast and low in northwest.The proportion of extremely low,low,medium,high and extremely high risk areas is respectively 52.4%?0.5%?12.4%?25.1% and 9.6%;The extremely high risk areas are mainly concentrated in both sides of the river in southeast plain areas with dense population.The extremely low risk areas are mainly distributed in the northwest mountainous areas with sparse population and far away from the river,and the main land use is forest.(3)SWAT model can accurately simulate runoff and soil erosion in the upper Beiyun River basin.The R2 is 0.89 and 0.78,and the NSE is 0.75 and 0.73.The soil erosion intensity in the study area is mainly micro erosion and light erosion,and the area proportion is 70.9% and 29.1%.The micro erosion is mainly concentrated in the plain area,while the slight erosion is mainly distributed in the northern mountainous areas.The risk spatial distribution characteristics of soil and water loss in the upper Beiyun River basin is characterized by high in northwest and low in southeast.The proportion of extremely low,low,medium,high and extremely high risk areas is respectively 23.1%?9.6%?27.5%?20.5% and 19.3%.The extremely high risk areas are mainly concentrated in the northern mountainous areas with steep terrain,and the extremely low risk areas are mainly concentrated in the downstream of plain river network with better soil and water conservation.(4)The risk spatial distribution characteristics of mountain hazards in the upper Beiyun River basin is also characterized by high in high in northwest and low in southeast.The proportion of extremely low,low,medium,high and extremely high risk areas is respectively 16.3%?25.3%?25.8%?18.4% and 14.2%;The extremely high risk areas are mainly concentrated in the mountainous areas with dense disaster points and disaster environment,while the extremely low risk areas are mainly concentrated in the plain areas with flat terrain and no conditions for disaster development.(5)The results of mean square deviation decision show that the weight coefficients of point source pollution risk,non-point source pollution risk,soil erosion risk and mountain disaster risk in the upper Beiyun River basin are respectively 0.20?0.35?0.26 and 0.19.It shows that the risk of non-point source pollution has the largest relative impact on the comprehensive risk of ecological environment,followed by the risk of soil erosion,and the impact of mountain disaster is the smallest.(6)The proportion of areas with extremely low,low,medium,high and extremely high risk are 14.5%?40.7%?20.0%?17.8% and 7.0% respectively in the upper Beiyun River basin.The extremely high risk areas are mainly concentrated in both sides of river in plain areas with dense population;The extremely low risk areas are mainly concentrated in the southwest and northern mountainous areas with steep terrain and sparse population. |
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