Spatial Analysis On Soil Heavy Metal And Pollution Evaluation In Chongming

The characteristics of the spatial distribution of the heavy metal contents in soils of Chongming county,Shanghai,was studied,and the degrees of their pollution was evaluated.The heavy metals in soil analyzed included Cd,Cu,Pb,Cr and Zn.When earring out the analysis,the Geostatistion Analyst module of ArcGIS was used.The main analysis included:(1)the calculation of semi-variance function and the choice of the fittest model and parameters;(2)the choice of an appropriate Kriging method through cross-validation;(3)drawing the spatial distribution map of the heavy metal contents,analyzing the trends of spatial variation and the influential factors through the spatial interpolation.Statistical softwares like Excel and SPSS were also used for data analysis in order to calculate and assess the variation of different heavy metal contents,and the single factor quality index(SI),Nemerrow complex index(NI) and the potential ecological risk index(PJ).The conclusions were listed as follow:1.The regulations of the spatial variation of the heavy metal elements in soils in Chongming county was as follows:the ratios of nugget value to sill value was Cu＞Cr＞Zn＞Pb＞Cd,the ratios nugget value to sill value was larger than 75%,the relationship between Cu and Cr showed weak spatial correlation.The ratios of nugget value to sill value of Cd,Pb and Zn was between 25%and 75%,the inter-relationships showed moderate spatial correlation.2.Through analyzing with the Geostatistical Analyst module in ArcGIS,the error ratios of the spatial interpolation of each model was obtained.The results showed that the error ratio of Zn was higher,and those of Cd,Cu,Pb and Cr were lower.3.The sequence of degrees of pollution of heavy metals in soils of Chongming county were Cd＞Zn＞Cu＞Cr＞Pb.Among these heavy metals,Cd was the major one. The average SPI of Cd in the soil samples was 1.05,reaching the light degree of pollution.The values of the comprehensive pollution index of these five heavy metals calculated from all soil sample data,ranged from 0.22 to 2.59,with an average of 0.88, reaching the alarm degree of pollution.However,the overall situation of heavy metals in soils of Chongming were relatively clean,because there were still 72.39%of soil samples showing the cleanness.Based on the national standards for the evaluation of soil quality,through our analysis,in addition to Cd,the other four heavy metal elements were in the main range less than 40 in general,indicating that the eco-toxicity of Cu,Pb,Cr and Zn were limited.Eco-toxicity of Cu,Pb,Cr and Zn were relatively low.All soil samples were in low-risk,but the eco-toxicity of Cd was relatively high.The sequence of risks of these five heavy metal elements in soils of Chongming was Cr＜Zn＜Pb＜Cu＜Cd.4.The result of statistical analysis revealed a close correlation between Cd and Pb, as well as Pb and Cr.A close correlation also existed between Cu and Pb,Zn respectively.