Distribution Characteristics And Pollution Risk Assessment Of Heavy Metals In Heihe River Basin Based On GIS

In recent years,with the increase of population and the rapid development of social economy,the pollution of water environment in the Heihe River Basin was becoming more serious,which had a certain impact on the social and economic development of the Heihe River Basin.Based on the investigation of the heavy metal factors in the Heihe River Basin in April 2015(normal water period),July(high water period)and December(low water period),this paper analyzed and studied the spatial and temporal distribution characteristics of the heavy metals.The principal component analysis was used to analyze the main heavy metal factors affecting the water quality of the Heihe River Basin and their influence degree,and the cluster analysis and multidimensional scaling method were used to categorize ten sub basins,and the water quality index method and Nemerow comprehensive pollution index method were used to assess the risk of heavy metal pollution in Heihe River Basin.Based on the related maps of the Heihe River Basin and the heavy metal data of water quality,the visualized maps of spatial and temporal distribution and the risk of heavy metal pollution of water quality were drawn by the Kriging interpolation method combined with the GIS.In order to provide basic data and theoretical basis for comprehensive treatment of water environment,and sustainable utilization and protection of water resources in Heihe River Basin,the distribution of heavy metals in water quality and the identification of polluted key areas and sources were studied through comparison and analysis of water quality evaluation methods.The main results of this study are as follows:(1)Through the analysis of the spatial and temporal distribution characteristics of heavy metal factors in the Heihe River Basin,some heavy metal factors showed obvious seasonal variation.The average value of cadmium(Cd)and zinc(Zn)was relatively small in December,which was relatively large in 4 and July,showing a certain seasonal variation.Lead(Pb),chromium(Cr),copper(Cu)and arsenic(As)were relatively large in December,and relatively small in April and July.Mercury(Hg)was the largest in July,and relatively small in April and December,which showed V shape.The concentrations of Cd and Hg showed an increasing trend in the whole basin,and the concentrations of Pb,Cr,Cu,Zn and As were no great change little from upstream to downstream.The changing rule of heavy metals is not only related to seasonal changes,but also to regional environment.(2)Based on the principal component analysis,the heavy metal factors were divided into several main components.The anterior several principal components reflected all the water quality information,and evaluated the correlation of heavy metal factors in each period.According to the results of one year’s analysis,the factors of heavy metals in Heihe River Basin were Hg>Pb>Cd>Cu>Zn>Cr>As.Hg,Cd,Pb,Cu and Zn were the main factors affecting the water quality of Heihe River Basin for the most part of the year,mainly from industrial wastewater,domestic sewage,agricultural sewage,mineral at the bottom of the river and supplemental water of groundwater,and inorganic salt in the soil dissolved by rainwater runoff.(3)The classification results of the cluster analysis and multidimensional scaling method of ten sub basins in April 2015,July and December were basically similar.The North River and the East juyan lake basin were classified as one category.The eight treasure River,Heihe River Basin’s stream of midstream,Ejina River and Zhangye wetland were classified as one category.The Shandan River was classified as one category.The buffalo ditch,pear garden river and red water river were classified as one category,which was somewhat deviant.There are only individual differences in a year,and there is no difference between right and wrong.Comparing the two methods,the results complement and correct each other.(4)The assessment results of water quality and Nemerow comprehensive pollution index were consistent.From the seasonal trend,the main pollution level was December>July>April.From the edge of the river,the overall pollution of the Heihe River Basin was no pollution,and the overall pollution from the upstream to the lower reaches was gradually rising.Among them,there were some pollution risks in Heihe River Basin’ s trunk stream,the north big river and the East juyan lake basin.(5)The collection data was collated,and GIS was used to visualize the real heavy metal status of water quality.The visualization chart was reliable,simple and practical,and the visual effect was good.Through drawing,the distribution and distribution law of seven kinds of heavy metals were realized clearly in the ten sub basins,and the key areas of pollution was also identified,and provided basic data and theoretical basis for the comprehensive treatment of water environment in the Heihe River Basin,sustainable utilization and protection of water resources.