Island Non-point Source Pollution Simulation And Control Scenario Analysis Based On InVEST Mode

With the gradual control of point source pollution,non-point source pollution has become the main cause of water quality deterioration due to its strong concealment,randomness and high harmfulness.Xishan Island in Taihu Lake is surrounded by water,and pollutants are discharged directly into the lake,which makes the water pollution more intuitive.Therefore,it is of great significance to study and control the non-point source pollution in the island for the water quality protection of Taihu Lake.In this paper,Xishan Island,Suzhou City,Jiangsu Province,was taken as the research area,Using meteorological data,land use data,soil data,digital elevation models,and other data,the parameter localization calculation of the In VEST model was completed to simulate the spatiotemporal distribution characteristics of non-point source pollution on the island from 2011 to 2020.With the powerful spatial analysis capability of GIS,hotspot analysis of ammonia and phosphorus output loads and spatial autocorrelation analysis were conducted to explore the risk zones of nitrogen and phosphorus output loads.Based on the simulation results of non-point source pollution,the influencing factors of non-point source pollution were analyzed,and different scenarios for reducing non-point source pollution were proposed and evaluated for their effectiveness,providing reference for controlling non-point source pollution.The main conclusions are as follows:(1)DEM,precipitation,land use,soil,NDVI and other data were used to calculate the required parameters of the In VEST model,and carried out the localized calculation of Zhang coefficient.the average value from 2011 to 2020 was 8.5,and through the test of measured data,the simulation result of the model is good.(2)The average total water yield of Xishan Island from 2011 to 2020 was 6.26×10~7m~3,with a coefficient of variation of 0.32,indicating an obvious range of change.On the whole,the water yield in the eastern region was higher than that in the western region.The average N output load was 2.07×104kg and P output load was 3815.09kg in 10 years.The N and P output load showed a decreasing trend in general,and the coefficient of variation was 0.04 and 0.05,respectively,with a small range of change.Spatial distribution is uneven,the eastern region is obviously higher than other regions.(3)Hot spots of N and P output load were concentrated in the eastern cultivated land.Hot spots and sub-hot spots of N output accounted for 5.77%and 3.25%of the study area,and P output accounted for 6.61%and 2.20%,respectively.The Moran’s I index of N and P output load was greater than 0.5.The results showed that N and P output load had strong spatial autocorrelation.(4)The N and P output load risk water area of Xishan Island accounted for 4.83%,15.14%of the total area,mainly distributed in the northeastern cultivated area of Xishan Island;The export risk of P is higher than that of N,so the emission of P should be strictly limited to curb the export risk of P.(5)Different land use types had different levels of non-point source pollution.The unit water yield of construction land was the highest(1221.56mm),the total water yield of grassland was the highest(3.2×10~7m~3),and the N and P output load of cultivated land was the highest(9745.49kg and 2305.71kg,respectively).Because the cultivated land is concentrated in the area with low slope,the lower the slope of Xishan Island,the higher the N and P output load.The correlation between precipitation and water yield was the highest,and the correlation between N and P output load and fertilizer application was the highest.(6)Reducing fertilizer application by 20%,converting 20%of cultivated land into forest land,and converting garden land with slope of more than 20°into forest land can all reduce N and P output load.The reduction rate of N and P output is the highest in reducing fertilization,while the reduction rate of N and P output is the lowest in returning garden to forest.According to the actual situation,combined with three control measures,more targeted to reduce non-point source pollution.