Study On The Driving Force Response Of Water Environment Evolution In Dongting Lake

Dongting lake is the second largest freshwater lake in China.In recent years,with the rapid economic and social development as well as the continuous increase of polluting emissions,its environmental quality has decreased significantly.In order to grasp the driving influence of human activity intensity on water environmental quality and provide beneficial support for its improvement as well as the sustainable basin socio-economic development.In this study,EKC model analysis,correlation analysis,multiple linear regression analysis and polynomial regression fitting were used to systematically analyze the driving effects of economic development and the change of land use pattern on the evolution of water environmental quality in Dongting lake during the 15 years from 2003 to 2017,the main conclusions were drawn as follows:（1）According to the historical evolution analysis of the main water quality indexes in Dongting lake from 2003 to 2017,TN and TP are the main pollution factors,the concentration level of TN in recent ten years has significantly increased compared with that in 2003-2007,while the nutrient index has also been on the rising level.The analysis of lake sediment polluting condition showed that the concentration of TN and TP in the sediment core was relatively stable,and the average concentration from the bottom（30cm）to the surface was between 504.48-854.00 mg/kg and 481.32-891.74mg/kg respectively;Among the heavy metals in the sediments,the concentrations of elements Cd,As and Pb increased significantly from 2003 to 2017,increasing by 87.56%,17.45%and 14.56%respectively,which were higher than Taihu lake,Poyang lake,Hongze lake and Chaohu lake in the middle and lower Yangtze river.The analysis results of the potential ecological risk of heavy metals showed that Cd and Hg were the key factors with the contribution rate as high as 61.96%and 30.29%respectively.（2）Based on the response analysis of socio-economic indicators and water environmental quality indicators in Dongting lake in the past 15 years,it is shown that its water quality is greatly affected by the primary industry,secondary industry,tertiary industry and urbanization rate,among them,the change of TN is mainly driven by the correlation between the development of primary production（regression fitting coefficient R²=0.7298）and urbanization rate（R²=0.6669）.TP is greatly affected by the development of primary production（R²=0.6954）,agricultural non-point source pollution and domestic sewage discharge are the main factors leading to the change of TN and TP concentration.COD_Mn is mainly driven by the development of secondary industry（R²=0.7458）and tertiary industry（R²=0.7136）,the concentration of COD_Mnchanges due to the discharge of industrial and mining wastewater as well as pollutants from the catering industry.The statistical analysis results of economic indexes and sediment indexes show that in recent years,the rise of Cd and Hg pollution levels in sediments in Dongting lake is closely related to the development of secondary production in the basin,and the leading mode of secondary production development in the Dongting lake with mineral exploitation is the main factor that leading to this result.（3）According to the analysis of remote sensing image of Dongting lake from2003 to 2017,the change of land use pattern is mainly reflected in the trend of land transfer from cultivated land to construction land,in which the cultivated land decreased by 740.19 km² and the construction land increased by 778.99 km².In the process of land use transfer in Dongting lake,the driving effect on water quality is mainly reflected in the correlation between cultivated land,construction land,NH₃-N and COD_Mn,with the decrease of cultivated land area,agricultural non-point source pollution decreases,NH₃-N concentration value decreases,construction land increases,urbanization process speeds up,and COD_Mn concentration value increases,moreover,the greater the land use degree in Dongting lake,the more increasing accordingly with eutrophication index of comprehensive water quality index,and the water quality will gradually deteriorate;The response relationship between sediment pollution and watershed land use in Dongting lake is not significant,indicating that the circulation of land pattern in the 15-year time period has not formed a prominent correlation in lake sediments.（4）Through the comparative analysis of social economy and water environment,land use and water environment in Dongting Lake Basin,it is found that the dynamic evolution process of water quality in Dongting Lake has a strong correlation with economic development and land use,and economic development is stronger than the driving effect of land use on water quality evolution;while the evolution process of sedimentary facies environment is more inclined to the indicating effect of economic development,especially the important one Metal pollution.