Spatial And Temporal Distribution Characteristics Of Water Quality And Eutrophication Assessment In Daihai Lake

Located in Ulanqab City,Inner Mongolia Autonomous Region,Daihai Lake is one of the important inland lakes in the region.It is an important ecological barrier around Beijing,Tianjin and Hebei.In recent years,the ecological environment of Daihai basin has been deteriorating,the water quantity has decreased,the lake surface has shrunk,and the water quality has deteriorated.In order to make clear the water environment condition of Daihai Lake and the temporal and spatial distribution law of important pollutants,based on the water quality data from April 2019 to October 2020,this paper comprehensively uses spatial interpolation by Arc GIS,correlation analysis,PCA and other statistical methods to deeply explore the temporal and spatial distribution of pollutants.The eutrophication status of Daihai Lake was evaluated by TLI,the fuzzy comprehensive evaluation,RAGA-PPE.The results show that:（1）Daihai Lake is alkaline as a whole,DO,BOD₅,NH₃-N and other water quality indicators are relatively good,The concentration of COD_Cr,COD_Mn,TP,TN were higher.Most of the water quality indicators showed obvious seasonal changes in time distribution.The spatial distribution of lake water quality has little difference among seasons.There is close correlations between the indicators.（2）The results showed that the comprehensive pollution index of Daihai Lake was significantly different in time and space.The comprehensive pollution index p of 11 months in the study period exceeded 2.00,which belonged to heavy pollution,accounting for 57.9%;In other months,the comprehensive pollution index p was between 1.00 and 2.00,which belonged to moderately polluted water quality.In both 2019 and 2020,the pollution is heavy in July and August.The results of principal component analysis showed that BOD₅,COD_Mn,TP、COD were the main factors affecting the water quality evaluation.（3）The eutrophication of Daihai Lake was evaluated by TLI,fuzzy comprehensive evaluation method and RAGA—PPE.The results showed that the eutrophication of Daihai Lake was mild to moderate.The projection pursuit model considers the different contribution of each evaluation index to the nutritional status,solves the problem of weight assignment,and reveals the internal relationship between each water quality index,which makes the evaluation results more reasonable.