Spatial And Temporal Evolution Of Water Environment And Its Reasons Analysis In Hulun Lake

Hulun Lake is located in the northern part of China and is located at high latitudes and it is a typical steppe lake in the cold and arid regions.Its special hydrology,hydrochemistry and aquatic ecology determine that the properties of Hulun Lake are different from those in humid and plateau lakes.In recent years,the water environment of Hulun Lake is not optimistic,and water quality and eutrophication are serious.Therefore,in order to deeply understand the water environment of Hulun Lake,it is necessary to carry out research on the distribution of important pollutants and the causes of water quality in Hulun Lake.Based on the water quality data from 2013 to 2019,this paper uses a variety of statistical methods such as Arcgis spatial interpolation,correlation analysis,redundant analysis methods,and principal component analysis.Explore the spatial and temporal distribution of pollutants,identify and screen environmental factors that affect water quality and eutrophication in Hulun Lake.And use the VAR model to determine the contribution rate of important water quality factors to water quality and eutrophication.At the same time,based on the output coefficient model,compare and analyze the load of non-point source pollutants in 2015 and 2019.The purpose is to reveal the evolution of water bodies,provide some scientific guidance for the formulation of water resources protection measures,and provide theoretical support for the ecological management of Hulun Lake.The main results are as follows:1.In terms of time distribution,TN and TP increased significantly,COD increased first and then decreased,and the change of chlorophyll a was opposite to that of COD.In terms of spatial distribution,the distribution of TN,TP,COD,and chlorophyll a all have the characteristics of relatively small content in the center of the lake.In the vertical distribution,TN,TP,and chlorophyll a have the highest water content in the lower layer during the freezing period and the highest water content in the surface layer during the non-freezing period.The vertical distribution of COD is the opposite.The TN,TP and COD in the ice are"<" type distributions,which meet the characteristics of upper ice>lower ice>middle ice.2.After calculating the comprehensive nutrition status index,GC value,and comprehensive pollution index of Hulun Lake from 2013 to 2019,the following results are obtained:The range of TLI in Hulun Lake in the past 7 years ranges from 54.025 to 78.494,all of which are in the state of eutrophication.The eutrophication shows a trend of first increase,then decrease and then increase;The average value of GC during the freezing period is 4.238,and the average value of the comprehensive pollution index of water quality is 4.381,the average non-freezing period GC is 4.386,and the average water pollution index is 3.593.The comprehensive pollution indexes are all greater than 2,and are in a state of heavy pollution.3.Through correlation analysis,RDA analysis,principal component analysis and variance decomposition,the factors affecting the eutrophication and water quality of Hulun Lake were analyzed.After the analysis,it was determined that the contributions of TN and TP to chlorophyll a during the freezing period were 9%and 7%,and the contribution rates of TP and DO to water quality were 9%and 7%;During the non-freezing period,TN and TP contributed 10%and 7%to chlorophyll a,and 11%and 24.5%to water quality.4.By estimating the pollutant fluxes of the two rivers flowing into the lake,it can be concluded that the fluxes of TN,TP and COD in the Kherlen River and Wuerxun River have increased in 2019 compared with 2015.Using the output coefficient model,it is concluded that the water body bears the most pollutants,accounting for 70.39%and 70.13%of the total land use types of the two periods,respectively.Among them,the total load of TN,TP and COD in 2019 decreased by 2.38 × 103 t/year,4.90 × 102 t/year and 7.63 × 103 t/year respectively compared with 2015.Among different livestock types,cattle produce the most pollutant load,followed by pigs.Among the non-point source pollution sources in Hulun Lake,TN entering the lake mainly comes from livestock,TP mainly comes from different land use types and rivers,and the COD content mainly comes from river imports.In recent years,Hulun Lake has been mainly affected by TN and COD input.In 2015 and 2019,TN input accounted for 70.94%and 58.96%of the total.