| Soil is the cornerstone of human activities and food production,and soil environmental quality plays an important role in safeguarding human health and food security.The pressure of cultivated land facing China is increasing,and soil heavy metal pollution is becoming more and more serious.As a reserve resource for cultivated land in Henan Province,the back river depression has little systematic research on soil pollution in this area.Therefore,t This study takes the back river area of the lower Yellow River(Kaifeng section)as the research object,the research area is 1327.86km~2,and 156(0-20cm)surface soil is taken by the 3×3km grid method.The contents of eight heavy metals such as cadmium(Cd),chromium(Cr),nickel(Ni),lead(Pb),copper(Cu),zinc(Zn),arsenic(As)and mercury(Hg)were determined.and the background value of tidal soil in Henan Province was compared.Based on geostatistics theory and spatial interpolation theory,combined with GS+9.0,SPSS20.0 and ArcGIS10.2 software,using the Nemero pollution index method,the cumulative pollution index method and the pollution load index method to study the soil heavy metals in the study area.The pollution status and spatial distribution characteristics were discussed.The potential ecological risks of farmland soil in the study area were evaluated.Based on the correlation analysis and principal component analysis methods in the multivariate statistical analysis method,the sources of heavy metals inthe study area were identified.The conclusions of this study are as follows:(1)The overall over-standard rate of soil heavy metals in the study area is not high compared with the background value.The average content of pollution only exceeded the Cd element,and the other seven elements Cu,Ni,Zn,Cr,Pb,As and Hg did not exceed the standard.The excess rate of heavy metal elements in soil was Cd(95.51%)>As(48.08%)>Hg(21.79%)>Cr(16.03%)>Ni(14.10%)>Cu(10.26%)>Pb(9.62%)>Zn(7.05%).The degre e of variation is that Hg is a strong mutation,and Cu,Ni,Zn,Cr,Pb,As,and Cd are moderately mutated,indicating that Hg is greatly influenced by humans.The normal distri bution test shows that Cr,Ni and As are normally distributed,Cu,Zn,Cd and Hg are in logarithmic normal distribution,and Pb is not in normal distribution.(2)The fitting models of heavy metals in the study area have exponential model,spherical model and Gaussian model.Cu,Zn,Cd,As,Hg are exponential models,Cr is a spherical model,and Ni is a Gaussian model.The spatial correlations of Cu,Cr,Cd,As,and Hg are very strong,indicating that they are mainly affected by natural sources in spatial autocorrelation.Ni and Zn are moderately spatially correlated,indicating that they are also affected by natural sources.Impact,The soil heavy metals in the study area showed a certain spatial distribution trend.(3)The optimal interpolation models for eight heavy metals in the study area is the Disjunctive Kriging(DK)with Cu constant,Cr for the second-order Disjunctive Kriging(DK),and Ni for the InverseMultiquadric(IS)Radial Basis Function,Zn is the fourth-order Global Polynomial Interpolation(GPI),Cd is the first-order Universal Kriging Interpolation Method(UK),and As is the InverseMultiquadric(IS)Radial Basis Function,Hg is the first-order Universal Kriging(UK),and Pb is the InverseMultiquadric(IS)Radial Basis Function.(4)The spatial distribution characteristics of Cr and Ni in the study area are similar,and the three elements of Zn,Cd and Hg are similar.The Cu content is generally low in the middle and high on both sides.The overall distribution trend of Cr element is west high and low east;the Ni content distribution is generally low in the middle and higher on both sides;the value of Zn is generally higher.The low level is characterized by the distribution of the surrounding area higher than the central part;the Cd element has a higher value in the southwest,and the middle part is slightly higher than the two sides;the As element generally shows a low-high-low-high trend from west to east.The spatial distribution characteristics of Hg are trending from west to east,while the spatial distribution of Pb from west to east is characterized by high-low-high-low.(5)Eight heavy metal elements in the study area showed different degrees of pollution.Single factor evaluation of soil heavy metals Cd pollution is the most serious,light pollution,the average value of As,Cr,Ni,Hg,Cu,Zn,Pb is less than 1,is no pollution,but the maximum value is greater than 1,indicating a certain degree Pollution.The Nemero comprehensive pollution index indicates that the soil in the study area has begun to be polluted and is dominated by light pollution.The soil accumulation index in the study area is mostly in the degree of non-moderate pollution,and the enrichment is relatively light,of which Cd The cumulative pollution is the most serious,and there is no cumulative pollution of Cr.The pollution load index evaluation area did not show strong pollution and extremely strong pollution.In some areas,it was moderately polluted,accounting for 15.38%,indicating that the overall soil pollution level in the study area was weak.Potential ecological risk assessment of heavy metal elements in the study area,Cd is medium risk,the other 7 are all minor risks,Cd is the main risk factor in the region,RI distribution map indicates that the study area is mainly light pollution,and appears in the local Strong risk level.(6)Among the eight heavy metal elements in the study area,there was no significant correlation between As and Cd,Hg,and there was a significant or extremely significant positive correlation between Cu,Cr,Ni,Zn,Pb;Therefore,Cu,Cr,Ni,Zn,Pb may belong to the same type of pollution source.Principal component analysis extracted two common factors.Among them,the first principal component(PC1)extracted four elements of Zn,Pb,Cd and Hg,which were greatly influenced by human sources,and Cu,Cr,Ni and As were the second principal components.(PC2)Extract elements,which are greatly affected by natural sources. |
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