| The Taihu Lake Basin is densely populated and economically developed.With the development of industry and agriculture,the problem of water environment pollution in Taihu Lake has become increasingly prominent.Non-point source pollution has gradually become the main reason for affecting water environment safety due to its wide range of pollution,few monitoring data and difficult control.The land use change under the action of human activities can significantly affect the non-point source pollution,which is of equal significance to the control of non-point source pollution.Therefore,this study takes the Taihu Lake Basin as the research object.By collecting the digital elevation model,land use data,soil data,meteorological data,hydrological data and agricultural management data in the basin,a watershed SWAT model is constructed to simulate the spatiotemporal distribution of non-point source pollution loads in the Taihu Lake Basin.Based on the five-phase land use data in 1980,1990,2000,2010 and 2020,analyze the impact of land use change on source pollution,so as to provide a basis for water environment management in the basin.The conclusions of this study are as follows:(1)The measured runoff data from 2008 to 2018 at the three hydrological stations of Lanshanzui,Wangjiangjing and Jishuigang was used to calibrate the parameters and validate the model.Results shows that the correlation coefficient R2 are greater than 0.70 and the Nash-Suttcliffe(Ens)are greater than 0.50 for runoff which shows that the constructed SWAT model is suitable for this watershed,and the follow-up research and analysis can be carried out.(2)On the time scale,the total nitrogen and total phosphorus in the Taihu Lake Basin dropped from 95700 tons and 26000 tons in 1980 to 52100 tons and 7600 tons in 2020,respectively.The amount of total nitrogen decline is large and the rate of decline of total phosphorus is fast.On the spatial scale,the distribution of total nitrogen and total phosphorus output intensity is similar,and the high-value areas are mainly located in Jiaxing City,Jiashan County,Haiyan County in the southeast of the basin,and Jurong City and Langxi County in the northwest.(3)During the study period from 1980 to 2020,cultivated land was the main and most drastic land use type in the Taihu Lake Basin.The land use changes in the Taihu Lake Bsin in the past 40 years are mainly manifested in the large-scale shrinkage of cultivated land and the rapid expansion of construction land.(4)From the perspective of landscape pattern factors,the dominant factors of changes in total nitrogen and total phosphorus loads in the Taihu Lake Bsin are landscape aggregation factors-cohesion and largest patch index.From the point of view of rainfall/sediment production,the correlation between total nitrogen and rainfall/sediment production is more closely;the sediment production is more related to total nitrogen and total phosphorus.From the perspective of different slopes,the total nitrogen and total phosphorus loads showed a “U”-shaped relationship with high at both ends and low in the middle.The loads are higher at low grades(0°～ 15°)and high grades(>30°),and lower at medium grades(15°～ 30°).Regardless of the slope,the total nitrogen and total phosphorus loads producted by cultivated land were the highest.From the perspective of different soil types,from 1980 to 2020,the highest loads of total nitrogen and total phosphorus were all man-made accumulated soils,and those with the lowest loads were dune quicksand soils.(5)From the perspective of changes in pollutant loads in the Taihu Lake Basin from 1980 to2020,the spatial distribution of changes in total nitrogen and total phosphorus loads were similar,both high in the northwest and low in the southwest.The contribution of each land use type to the change of total nitrogen load in descending order: forest land,cultivated land,grass land,water area,construction land,unused land.The contribution of each land use type to the change of total phosphorus load in descending order: cultivated land,forest land,construction land,water area,grass land,unused land.(6)Different land use types have different reductions in total nitrogen and total phosphorus in the process of transformation.The reduction of total nitrogen was higher when grassland and cultivated land were converted to forest land.The conversion of cultivated land to forest land and the conversion of construction land to cultivated land has a higher reduction in total phosphorus. |
