Spatial Characteristics And Pollution Assessment Of Soil Heavy Metals Based On GIS

In recent years,because of the unreasonable mining,agricultural production and industrial production,soil heavy metal contents areincreasing.It poses a serious threat to human health and land and has caused wide public concern.Soil heavy metal contents,their spatial distribution law and assessment of soil heavy metal pollutionare very important to the determination of soil heavy metal pollution,prevention and treatment of soil heavy metal pollution at a later stage and safeguarding the health of the people.GIS and geostatistics were used to analyze the characteristics and spatial distribution characteristics of 8 heavy metal elements in this study.Study areas included four regions of Lianyun,Guanyun and Guannan.Contents and spatial distribution characteristics of Cr,Cu,Ni,Pb,Zn,As,Hg and Cd were studied Single factor pollution index,comprehensive pollution of the inner melo and potential ecological risk index methods were applied to investigate the degree and trend of soil heavy metal pollution in these areas.The results are as follows:(1)Using traditional statistical analysis method,the contents of 8 heavy metal elements in four regions were analyzed.Over-standard rates of Cr,Cu,Ni,Pb and Zn in Lianyun area were relatively high based on soil background value of Jiangsu province.Over-standard rates of Hg,Cd and As were relatively low.The sampling points of Cu,Ni,Zn,Cd and As in Guanyun county were all over the standard,and over-standard rates of Cr and Pb were high.Hg had no over-standard point.The overstandard rates of Cr,Cu,Ni,Pb,Zn,Cd and As in Guannan were relatively high.There were no over-standard points for Hg in this area.Based on soil environmental quality standard,except that As had no over-standard point,there were a certain number of over-standard points of the remaining seven kinds of heavy metal elements in Lianyun District.There were over-standard points for Ni and As in Guanyun County.There were over-standard points for Cu,Ni,Zn and Cd in Guannan(a)area.There were overstandard points for Ni and Cd in Guannan(b).Cd and Cu in Guannan County(a)and Cd in Guannan County(b)are more severe than the standard.(2)Statistical analysis of 8 heavy metal contents in four regions indicated thatnugget/sill ratios of Cr,Cu,Ni,Pb,Zn and As in Guanyun,Cu,Ni,Pb,Zn,As and Cd in Guannan(a),Cr,Cu,Ni,Pb and Zn in Guannan(b)were all less than25%,indicating strong spatial autocorrelation and weak spatial variability.They were mainly influenced by natural factors.The nugget/sill ratios of Cr,Cu,Ni,Pb,Zn,As,Hg,Cd in Lianyun District,Cd in Guanyun county and Cr in Guanyun(a)were between25% and 75%,indicating that they were both influenced by natural factors and human factors.The nugget/sill ratio of Hg in Guanyun,Guannan(a)and Guannan(b)was 0,indicating that the spatial autocorrelation was strong,and the variation was entirely affected by natural factors.(3)Spatial visualization expression was conducted using ordinary kriging interpolation.The high-value areas of Cr,Cu,Ni,Pb,Zn and Cd were all located in the northeast region except As and Hg,and the heavy metal contents of the Southeast region were relatively low.Cr and Zn were distributed in band from northeast to southwest.The distribution of Cu,Pb and Cd in the whole region was irregular,and Ni was distributed as patches in the whole area from the center to the surrounding area.The 8heavy metal elements in Guanyun county all had large porphyritic distribution,Cu and Hg were not classified.The whole content of Cu,Hg,and Cr was low,respectively.The whole content of Cd was high.Ni concentration was high in the northern part of the region,the high-value area of Zn and As were located in the north and the eastern region,and the high-value area of As was located in the north and the southeast,and low-value areas of Pb were loacated in the middle and northeastern part.The low-value areas of Cd were located in the northern part and east part.Cr concentration in the southeast part of the area was lower than background value of Jiangsu province in Guannan(a).Cu and Cd concentration in most parts of the area were higher than the national two level standard value respectively,and they were regularly distributed like island.Ni had obvious accumulation phenomenon in the central regions.Ni content in the whole area was distributed from center to around.Pb and Zn were regularly distributed like island,and the high-value area was located in the north central part.The content of Hg was low in the whole study area.Cr,Ni content in western region was higher than that in the eastern region in Guannan(b).The content of Cu,Pb Hg and Cd was relatively low.High-value area of Zn was located in the south.The five high-value regions of As were distributed in patches.(4)Through correlation analysis and principal component analysis,it is found that the pollution sources of 8 heavy metal elements in regions were judged:Characterization by principal component analysis in Lianyun District,Ni,Zn,As and Cr were located in the first principal component,and Cr had a very significant correlation with Ni and Zn in correlation analysis.Accumulation of Cr,Ni and Zn is mainly affected by natural factors.Ni and Zn are also influenced by human factors.The accumulation of As in Guanyun was mainly affected by organic manure,chemical fertilizer and pesticide application.The Cu was highly correlated with Ni and Zn according to correlation analysis in Ganyan county(a).Cu,Ni and Zn were located in the first principal component according to principal component analysis.Cu,Ni and Zn are mainly affected by industrial activities.Cd is affected by industrial production and agricultural activities.Cd and Zn were significantly correlated in Guannan(b),and Cd and Zn were in the first principal component according to principal component analysis.Cd and Zn are affected by industrial activities and agricultural production.As is mainly affected by agricultural activities.(5)Different evaluation methods were used to evaluate the pollution of 8 heavy metals in regions.In the result of single factor pollution index assessment,all heavy metals in Guanyun County are clean samples.The pollution level in Lianyun District was relatively light with only a few pollution samples.In Guannan County(a),the proportion of minor pollution points of Cd,Cu,and Ni was 45.45%,42.42%,and24.24%,respectively.The pollution of Cd in Guannan County(b)is relatively serious.The point of slight pollution was 64.15%.The evaluation results of comprehensive pollution assessment results and potential ecological risk indicators show that,Lianyun District and Guanyun county is dominated by mild pollution.Their overall potential ecological hazards are lighter.Guannan County(a)is heavily polluted and has the highest potential ecological risk,which is mainly caused by the hazards of Cd.Guannan County(b)is dominated by moderate pollution,and some regions are at a medium level of potential ecological risk.The location and scope of pollution area can be showed visually on interpolation maps finished through geostatistic method and GIS software.