| In this paper,the area of Jianxin Village of Xiba Town,Wutongqiao District is 650000.0m2.A total of 70 surface soil samples and two profiles of soil profiles are collected.The soil samples are decomposed by high temperature closed digestion and soil is determined by ICP-MS.There are 6 kinds of heavy metals in Cr,Cd,Pb,As,Cu and Zn.The groundwater chemical characteristics are obtained through laboratory tests.Through the statistical analysis,normal transformation and test,trend analysis and optimal semivariogram selection of six heavy metals in farmland soil,six kinds of heavy metals in the study area were interpolated by ordinary Kriging interpolation,and the soil in the study area was obtained.The optimal variation direction and content spatial distribution map of heavy metals.The difference in the change of heavy metal content in vertical sections of different types of soil was studied.The pollution characteristics of the study area were evaluated by qualitative analysis and Geo-accumulation index method and Nemero comprehensive pollution index method.The main findings are as follows:(1)Through data processing,a total of 62 samples conformed to the normal,lognormal and partial lognormal distribution.Cr,Cd and Zn all exceeded the soil background value of Sichuan Province.(2)By comparing the cross-validation methods,the optimal semi-variograms of six heavy metal elements are obtained: the Cr distribution has an exponential semivariogram model,the Cd and As distributions have a spherical semi-variogram model,and the Pb and Cu distributions have a Gaussian half.In the variogram model,the distribution of Zn has a K Bessel semivariogram model.According to the spatial trend analysis,the content of Pb has no trend effect,the trend effect of Cr,Cu and Zn content is 2nd order,and the trend effect of Cd and As element content is 3rd order.(3)The spatial correlation of the six elements is: Cu>Cd>Pb>Zn>As>Cr.The spatial variability of Cr and Cu is similar.The spatial structure variability is smaller from northeast to southwest than northwest to southeast.The spatial variability of Cd and As is similar.The spatial structure variability is greater from northeast to southwest than northwest.The southeast is upward;the spatial variability of Pb and Zn is similar,and the spatial structure of the opposite sex is north to south and larger than east to west.(4)Cr and Cu are higher in the living area of Xiba Town,Cd and Zn are concentrated in the Chengdu-Ninghuan Expressway and on both sides of the village road,and Pb and As are concentrated around the mine.The soil physical properties of the soil in the vertical direction are greatly affected.The content of Cu and Pb in the sandy soil decreases first and then decreases with the change of depth.The contents of Cr,Zn and As increase first and then decrease with depth,while Cd and depth decrease.Negative correlation.The content of heavy metal Cu in clay soil does not change with depth.The content of Cd,Zn,Pb and As decreases first and then increases with the change of depth.The content of Cr increases first and then decreases with depth.(5)The contents of heavy metals in the six soils were high in the east and high in the north,and low in the north and west.The second region was mainly affected by the distribution of pollution sources.In addition to the influence of elevation,the distribution characteristics were also very different around the watershed.The farther away from the watershed and the landform The smaller the relationship of the unit.The six heavy metals in the topsoil migrate,diffuse and accumulate with the flow of groundwater.Among them,As is the most obvious,and the enrichment of Cr,Cd and Cu along the direction of the water level is obvious,and the concentration of Pb decreases along the groundwater.The basic characteristics of shallow groundwater have little to do with the distribution of heavy metals in the study area.(6)Ground accumulation index method for soil heavy metal pollution evaluation,the soil Cd pollution is moderate pollution,Cr,Zn is slightly polluted,the soil in the study area is basically not contaminated by Pb,As and Cu.The single factor index method showed that Cd in soil was heavier pollution,and Cr,Pb,Cu and Zn were mildly polluted.The results of the Nemero comprehensive pollution index method are severely polluted by the Chengdu-Ninghuan Expressway and the vicinity of the village road.The northwestern hilly belt and Xiba Town are slightly polluted,and the rest are moderately polluted.The results of three evaluations indicate that the pollution degree is from large to small: Cd>Zn>Cr>Cu>Pb>As. |
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