Spatial Distribution Characteristics And Ecological Risk Assessment Of Heavy Metals In The Wuma River Basin Of Guizhou Province

In order to research in Chishui tributary-WuMa space river basin distribution features of soil heavy metal content and the status of the ecological risk in Guizhou,through the multivariate statistics,statistics,spatial analysis,spatial interpolation technology,accumulation exponential method and inside plum nemerow index and potential ecological risk index method theory and methods,As the research object of Chishui tributary-WuMa river basin in Guizhou,analysis the eight heavy metals in soil(Ni,Cu and Zn,Pb,Cd,As,Hg and Cr)content,WuMa system studied the space distribution features of soil heavy metal content in river basin and the status of the ecological risk.Preliminary conclusions are as follows:(1)Analysis of heavy metal content and its source in the wuma river basinThe mean values of the heavy metal elements Ni,Cu,Zn,Pb,Cd,As,Hg and Cr were 39.95mg/kg,49.45mg/kg,64.21mg/kg,53.03mg/kg,0.08mg/kg,12.73mg/kg,0.42mg/kg and 92.65mg/kg,respectively.The average value of all heavy metals did not exceed the soil pollution risk screening value of the standard《Soil environmental quality Risk control standard for soil contamination of agricultural land》(pH>7.5).Principal component analysis showed that Zn and Hg had the highest load in the first principal component,indicating that Zn and Hg were from natural sources.The six heavy metal elements,Ni,Cu,As,Pb,Cd and Cr,had the highest loading in the second principal component,which was believed to be from human sources.(2)Spatial variation structure analysis of heavy metals in the wuma river basinThe analysis shows that the heavy metal content in the soil of the wuma river basin is normally distributed.The semi-variogram analysis of the heavy metal content showed that the ratio of the nugget value of Ni,Cu,Pb and Cd to the base station value was greater than 75%,and thespatial correlation of the heavy metal content in the spatial distribution was weak.The ratio of Zn,As and Hg nugget value to base station value was between 25% and 75%,showing a moderate spatial correlation.The ratio of Cr nugget value to base station value was less than 25%,showing a strong spatial correlation.Heavy metal spatial interpolation model selection,Ni,Zn,Cd and Hg with spherical model As the best,Cu with exponential model As the best,Pb and As with linear model the best,As and Cr with gaussian model the best.(3)Spatial distribution characteristics of heavy metals in the wuma river basinThe spatial interpolation analysis based on Arcgis shows that the high content area of Zn is mainly distributed in part of the middle reaches of Wuma town,the high content area of Pb and Cr is scattered in the whole basin,and the high content area of Ni,Cu,Cd,As and Hg is mainly distributed in part of the upper reaches of Maoba town and the lower reaches of Changgang town.Among them,the contents of heavy metals Pb,As and Cr in some parts of the basin are slightly higher than the soil pollution risk screening value,which is a degree of mild pollution,the Pb pollution areas were mainly distributed in the upstream area of feilong village-lianghe village in Maoba town,the middle area of yukong village in Wuma town,and the downstream area of maopo village in Changgang town;As pollution area is mainly located in yangliu village-xiongfeng village-shiliang village of Maoba town;the Cr contaminated areas were mainly distributed in guanyuan village-baiguoshi villageFeilong village of maoba town,and the Wuma town in the middle reaches,and sangshu village-maopo village of Changgang town in the downstream.(4)Evaluation of soil heavy metal pollution in the wuma river basinThe evaluation of soil pollution in the wuma river basin shows that heavy metal pollution is generally light.The soil accumulation index method and the nemero pollution index method show that there is no pollution in Ni,Zn and Cd,while there is light pollution in Hg,Cu,Pb,As and Cr,Hg is middle level pollution.Therefore,it is necessary to take treatment measures for these heavy metals.The evaluation of the potential ecological risk of heavy metals showed that there were no potential ecological hazards in Ni,Cu,Zn,Pb,As and Cr,and there were potential ecological hazards in Cd and Hg.The combined potential ecological risks of eight heavy metals accounted for 50.37% of the total potential ecological risks,and the medium intensity hazard was 13.53%.According to the comprehensive evaluation,there is no pollution of heavy metals Ni and Zn in soil of wuma river basin,and Hg reaches moderate pollution in some sampling areas,so it is necessary to take control measures.The heavy metals Pb As Cr and Cd were slightly polluted in a few sampling areas.Cu is at the alert value in some sampling areas,and preventive measures should be taken in combination with the spatial distribution map of heavy metals.Hg mainly takes control measures in the north of maoba town and the north of changgang town.Control measures for heavy metal Pb,Cr,Cd and As in the contaminated areas;prevention measures of heavy metal Cu in its high content area were taken.According to the comprehensive analysis and evaluation,it is necessary to strengthen the strict management of mineral exploitation,mine sites and township enterprises in the basin,reduce the discharge of industrial wastes,apply chemical fertilizers and pesticides rationally,and carry out scientific irrigation to prevent non-point source pollution.Necessary prevention and control measures should be taken in some areas with light pollution.In addition,environmental protection publicity should be actively carried out to improve people’s awareness of ecological and environmental protection and avoid secondary pollution of heavy metals.