Simulation Of Non-point Source Pollution And Its Influencing Factors In Chenhu Wetland Based On SWAT Model

The study area was selected in the Chenhu Nature Reserve.In 2013,the Chenhu Wetland Nature Reserve was included in the ’ International Important Wetland List ’ and became the fifth international important wetland in China.The rich and diverse ecosystems in the wetland area provide important habitats for many rare and endangered species.Since the 20 th National Congress of the Communist Party of China,China has comprehensively promoted ecological revitalization.Wuhan has gradually attached importance to the treatment and protection of the international important wetlands of the sunken lake,and comprehensively intercepted point source pollution.In order to effectively prevent and control the non-point source pollution of the submerged lake wetland,it is necessary to understand the distribution of non-point source pollution in the study area,and model simulation and prediction analysis is one of the main means to understand the risk of non-point source pollution.In order to effectively prevent and control the non-point source pollution of the submerged lake wetland,it is necessary to study the distribution of non-point source pollution in the study area,and the model simulation and prediction analysis is one of the main means to understand the risk of non-point source pollution.Therefore,by collecting the digital elevation model data,land use data,soil data,meteorological data,hydrological data and agricultural management data of the sunken lake wetland,this paper constructs a non-point source pollution model of the sunken lake wetland to simulate the non-point source nitrogen and phosphorus pollution load of the sunken lake wetland.The temporal and spatial distribution of non-point source pollution from 2003 to 2022;the spatial distribution of non-point source pollution in 2000,2005,2010 and2020 was simulated every 5 years.In order to find the distribution law of non-point source pollution in sunken lake wetland,and provide a theoretical basis for the treatment of non-point source pollution,the main results are as follows :(1)Conduct a long-term investigation of the Chenhu wetland and build a basic database of the Chenhu wetland reserve.Based on the relevant data,a SWAT model was built for the Chenhu Wetland Reserve.The SWAT-CUP software was used to analyze the sensitivity of 30 common parameters,and the top 15 parameters were selected for calibration.The calibration period and validation period for hydrological parameters,total nitrogen,and total phosphorus exhibited R~2 values greater than 0.6,and the NashSutcliffe Efficiency(NSE)exceeded 0.5 The model was calibrated and verified,and the applicability of the model in the submerged lake wetland reserve was analyzed.The calculation and analysis results show that the SWAT model can be applied to the sunken lake wetland reserve.(2)By studying the relationship between rainfall and non-point source pollution in Chenhu Wetland Reserve from 2000 to 2020,the results show that non-point source pollution in Chenhu Wetland Reserve is positively correlated with rainfall.The SWAT model simulation results show that the non-point source nitrogen and phosphorus loads in the Chenhu Wetland Reserve in 2016 and 2020 are much higher than those in other years.This is because the rainfall in these two years is too high,resulting in an increase in nitrogen and phosphorus loads.(3)The Chenhu wetland reserve is divided into 13 sub-basins.On the time scale,the nitrogen and phosphorus loads in the Chenhu Wetland Reserve increased from379.85 tons and 52.91 tons in 2003 to 864.77 tons and 120.97 tons in 2020,respectively.On the spatial scale,the distribution of total nitrogen and total phosphorus output intensity is similar,mainly No.1 and No.2.(4)The contribution of nitrogen and phosphorus load of different land use types in Chenhu Wetland Reserve and its surrounding areas from large to small is cultivated land > town > bare land > forest land.(5)Because the contribution of cultivated land to non-point source pollution is the largest,and the area accounts for about 60.6 %.Therefore,the scenario hypothesis of returning farmland to lake is carried out to explore the reduction of non-point source pollution under the two scenarios of returning farmland area 20 % and returning farmland area 40 %.Scenario 1 : Returning farmland to 20 % can reduce phosphorus load by 37 % and nitrogen load by 32 %.Scenario 2 : Returning 40 % of farmland can reduce phosphorus load by 50 % and nitrogen load by 48 %.Therefore,the management work should focus on the cultivated land.