| The heavy metal elements in sediments which from Shimian County of Dadu River Valley was employed to research the geochemistry distribution. Through geological investigation and analysis of the sampling of 1:50000 geological survey,I have found out the distribution and amounts characteristics of heavy metals which include As、Cd、Cr、Cu、Hg、Ni、Pb. Correlation analysis and cluster analysis were used to study the relationship among heavy metal elements in sediments. This study used the index of geo-accumulation evaluation and the potential ecological risk evaluation to assess contaminate degree and distribution feature of the heavy mentals in the sediments. Following primary conclusion are as follows:In the Shimian County section of Dadu River basin sediment, except As average content is lower than the average background value of Yangtze River sediment, the average content of 8 heavy metal in Dadu River sediment are generally higher than the 5 kinds of background value. The minimum values are all less than 5 kinds of reference background value. As Chinese sediment background value for an example, The maximum value of eight elements are several times to hundreds of times to element background values. For example, the maximum value of Cd is 192 times of the background value and the maximum value of Pb is 1044 times of the background value. So the Dawen River sediments have accumulated heavy metal obviously, and greatly affected by human activities.From the point of enrichment coefficient, heavy metal content have enriched in high degree in the Shimian County section of Dadu River basin sediment. Comparing with the background value of the main stream of Yangtze River, enrichment of heavy metal elements is Pb>Cd>Hg>Ni>Cr>Zn>As>Cu. From the point of variation coefficient, the coefficient of variation of every point is larger different from each other. The variation coefficient of As, Cd, Cu, Hg, Pb were all above 2, which belongs to strong differentiation type.Correlation analysis of heavy metals shows that As, Cd, Cu, Pb and Zn are in a significant correlation. There was a significant positive correlation between Cr and Ni. The correlation between Hg and other elements are relatively poor. The results of cluster analysis showed that 8 kinds of metal elements in the sediments can be divided into As-Cu-Pb, Cd-Zn, Hg and Cr-Ni four categories. Which indicates that the heavy metal pollution in the study area is a common result of human action and natural effect.Two common methods which were Index of Geoaccumulation and the Potential Ecological Risk Index and one evaluation criterion which was national sediments evaluation criterion were implementing to evaluate potential ecological risk of heavy metal elements in sediments which from the Shimian County section of Dadu River. The evaluation results of the two methods are highly consistent. Cd is classified into moderate-severe contamination, and strong-extremely strong ecological risk. Moderate pollution level and above is 75, and strong ecological risk and above is 257. Cd is the largest contributor to the potential ecological risk index, Cu and Pb next to it. Pb belongs to moderate-severe contamination, and moderate-strong ecological risk, then Hg belongs to moderate-comparatively heavy contamination and moderate-comparatively strong ecological harm. As and Cu belong to moderate-comparatively heavy contamination and moderate-strong ecological harm.Cr、Ni and Zn belong to moderate-heavy contamination and moderate-Mild ecological harm. The Pollution of heavy metals was medium ecological harm and moderate-comparatively heavy contamination in sediments from the Shimian County section of Dadu River basin,especially Cd、Pb and Zn. |
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