The Study Of Metal Correlation In The Soil And Rock And Soil Environmental Quality In Karst Region Of North In Guangxi Longzhou

The heavy metals in soil are mainly derived from three ways as follows: 1.The parent material of the soil.2.Human activities.3.The weathering process.Previous studies showed that there appeared abnormal phenomenon of heavy metals in soil across most of the karst area.excluding the impact of human activities,heavy metals content and weathering process of parent material have become the main controlling factors of soil heavy metals content.Longzhou County in the north of the Guangxi Chongzuo city is taken as the study area in this paper.By a combination method of the field sampling and laboratory analysis and according to the test results of heavy metals content in soil and rock,the correlation and the potential pollution risk of heavy metal elements in soil of sample region are systematically studied and evaluated,using the methods of correlation analysis,spatial interpolation,single factor pollution index,geoaccumulation index and Nemerow comprehensive pollution index.The main research contents are as follows:(1)In the middle of July,2016,186 samples were collected in the field,which includes about 100 soil samples and 86 sock samples.The collection points are mainly concentrated in several villages and towns in Longzhou county,Chongzuo,Guangxi Zhuang Autonomous Region that includes Shanglong village,Wude village,Xiangshui town,Jinlong town and Nonggang nature reserve.(2)Among the 7 sock samples of heavy metals including Cr,Ni,Cu,Zn,As,Cd and Pb which were collected from Devonian system stratum,the average values of As and Cd were more than the average values of the earth's crust elements 1.21 and 1.44 times respectively,and the rest of 5 elements were all less than the average values of the earth's crust elements.Among the average contents of the 7 sock samples of heavy metals including Cr,Ni,Cu,Zn,As,Cd and Pb which were collected from Calcareous,Permian and Cambrian system strata,the average value of Cd in 3 strata was 4.45,3.39 and 1.89 times as high as the average value of the earth's crust elements respectively.There was a slight enrichment of Cb in rock,and the rest of the 6 elements were all less than the average value of the earth's crust elements.(3)In the 100 soil samples that were collected from the study area,the contents of 6 kinds of heavy metals except Pb were all more than the second level of national soil environmental quality standard value,in addition,the amounts of samples that were more than the second level of national soil environmental quality standard value were 37,89,16,67 84,and 91 respectively.The over-standar rates were 37%,89%,16%,67%,84% and 91%,The over-standard rates of 6 elements from high to low were Cd > Ni > As > Zn > Cr > Cu.(4)the data analyzed by linear correlation and partial correlation showed that in the soil of the study area,Ni-Cu,Zn-Pb and As-Pb all showed a highly significant and positive correlation on a significant level(P)that is less than 0.01,and it showed a highly significant positive correlation between Cu and Zn on a significant level(P)that is less than 0.05.It means that these heavy metal elements were very likely from the same sources of pollution.In addition,the correlation indexes between Cr and Zn,Cr and As,Zn and As,Ni and Pb,Cd and Pb,Cu and Cd were negative values,which elucidated that there was an antagonistic or competitive adsorption between heavy metals in soil.(5)After a correlation analysis of the total amount of 7 kinds of heavy metal elements in rocks and soils,analysis data showed that the contents of Cr,Ni and Cu in rocks showed a negative correlation with that in soil but the degree is too low to make sense.The contents of Zn and As in socks showed a positive correlation with that in soils,but the degree of correlation was too low to make sense,either.The correlation index of the contents of Cd in soil and sock is 0.492,and P<0.01,it means that both them showed a extremely significant positive correlation on the 0.01 level.(6)On the basis of the total amount of heavy metals,the soil environmental quality are systematically evaluated,using the method of single factor pollution index,geoaccumulation index and Nemerow comprehensive pollution index.On account of that the pollution index value kept changing along with the change of methods adopted,there might be a slight difference in the results of assessment.