Non-point Source Pollution Control Of Shitoukoumen Reservoir From The Perspective Of Land Use

The current problems facing water pollution in China should not be underestimated,and the long-term massive and random discharge of pollutants makes the water environment management pressure prominent,and the management of non-point source pollution has become the main problem facing China’s water environment management and ecological protection.Management should fully consider the impact of land use when formulating water environment management and protection programs,which requires evaluating the effect of spatial distribution of land on nonpoint source pollution from the perspective of land management.The study was carried out in the Shikoumen Reservoir watershed in Jilin Province,and the optimized land sub-case was simulated using the Conversion of Land Use and its Effects at Small regional extent(CLUE-S)model,and input into the Soil and Water Assessment Tool(Soil and Water Assessment Tool)separately from the base period land use.The results of the study can provide reference and theoretical support to the land management department of the Shiqoumen Reservoir basin in formulating land use planning and subsequent land remediation work.The results show that:(1)The total nitrogen and total phosphorus pollutants in the Shitoukoumen Reservoir basin exhibit significant periodic changes over time,with a gradual increase starting from January and reaching their peak in August.The total nitrogen and total phosphorus loads in that month account for 40.6% and 46.3% of the total annual amount,respectively.Afterwards,they gradually decrease with each month,and there will be significant fluctuations in March and May.(2)The total nitrogen and total phosphorus pollutants in the Shitoukoumen Reservoir basin have obvious spatial distribution characteristics.The areas with high output intensity of total nitrogen load are mostly distributed in the southern part of the study area,and the output intensity is higher in the southwestern part;The total phosphorus load is characterized by a spatial distribution of low around and high in the center,due to poor phosphorus mobility and gradient differences in phosphorus concentration in the soil,and only dissolved phosphorus in the surface soil can migrate with surface runoff.(3)Comparing the optimized scenario and the pollutant load during the base period,it can be found that land use optimization has a certain effect on controlling non point source pollution,with a total nitrogen output decrease of 8.68% and a total phosphorus output decrease of 10.12%.The overall nitrogen concentration has decreased to normal levels,i.e.8kg/hm 2 Below,the peripheral part of total phosphorus decreased to normal level,which is 1.5kg/hm 2,there is no significant decrease in the central part.The months with the highest reduction rate of pollutant load are concentrated in August,and the sub basins with higher reduction rates are mostly distributed in the southeast of the study area.This is because the area is a part of concentrated and continuous expansion of forest land in the optimization scenario.Returning farmland to forest not only reduces the input intensity of pollution sources,but also reduces the diffusion intensity of existing pollution.The nitrogen and phosphorus in the sub watersheds located at the outlet of the Shitoukoumen Reservoir basin are relatively high and the reduction rate is relatively small,which is related to the relatively few changes in land use optimization in the region.Overall,the CLUE-S land optimization model and the SWAT nonpoint source pollution simulation model are applicable to the study area,and the proposed land optimization scheme based on the land use perspective can effectively reduce the intensity of nonpoint source pollution in the study area,among which the reduction of total nitrogen load is higher,which means that the land optimization can better control the diffusion of total nitrogen.