| With the rapid development of agriculture and industry,the input of nitrogen(N)and phosphorus(P)increased owing to the non-point source pollution,which caused the water deterioration and water eutrophication of Nansi Lake.The output risk assessment and influencing factors analysis of non-point source pollution were carried out.This study can provide important reference for the comprehensive prevention of non-point source pollution and the sustainable development of ecological environment.However,the non-point source pollution output risk is different in different regions,due to geographical location,topography,climate,socio-economic development,temperature and precipitation.The Nansi Lakes Basin Slope Grade was extracted based on DEM data by using Spatial Analyst Tools of ArcGIS10.1.Then apply to Hydrologic Analysis function,the drainage,river figures were extracted and the drainage basin was delimited.The method of output risk model was used.The output value of non-point source pollution was estimated by taking the sub-basin as the minimum unit in Nansi Lake Basin.The characteristics of risk changes in different land use,slope and county-level were analyzed.Combined CA-Markov model with Regression Model,the land use pattern and the export risk distribution in 2020 were simulated.The main conclusions of this study are as follows:(1)In 2013,the average risk probability of nitrogen reached 0.52.The average risk value of P reached 0.09.Nitrogen is the most main basin non-point source pollutants.The output risk of non-point source pollution in the east of lakes was less than the west.The larger the slope,the less the risk of non-point source pollution;Different counties and cities have different risks,and N risk was higher than P risk The risk of P was less in all counties.The output risk value of non-point source pollution had close relationship with land cover and slope.(2)During 1990-2015,farmland and arable land were the main land use types in the study area,accounting for more than 85% of the total area.The TN and the TP risk changes were significantly different.The TN output risk value was distributed in 0-0.64.The TP output risk value was distributed in 0-0.12.N was the main pollutant.The TN risk increased gradually from 1990 to 2005,decreased significantly during 2005-2005,and increased sharply during 2010-2015.The TP risk decreased gradually during 25 years.From the perspective of space,the low risk areas distributed mainly in the eastern basin of Nansi Lakes,and the high risk areas was mainly in the west region of the lake.(3)The land use change in 2020 was predicted.Compared with 2015,the arable land is increasing,the area of unused land is unchanging,and the other land use types is reducing to different degrees.The TN risk is reducing slightly.TP risk is unchanging.It is necessary for the local government to focus on improving the agricultural science and technology and reducing fertilizer use in order to control the status quo of non-point source pollution in Nansi Lakes Basin. |
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