Heavy Metals' Distribution And Environment Evaluation Of The Tidal Surface Sediments In Some Representative Islands Of Guangxi

In recent years, as the development of coastland, the island tidal zone of Guangxi has greatly changed because of human activities such as mariculture, coastal tourism and etc. The thesis particularly chooses the representative islands as study area, such as Weizhou Island which is near by the mainland, Longmen Island and Xicun Island which are far off the mainland. According to the analysis of heavy metals, grain size, TOC and CaCO3 in the tidal surface sediment, the following results are showed.The content level of heavy metals in Weizhou tidal zone is lower. All 7 elements are less than State StandardⅠ. Content of Cu, Pb, Cd and Cr is slightly higher than it in Grangxi offing sediments. The content level of Longmen and Xicun is observably higher than Weizhou, but only Cu's content runs over the State StandardⅠ.Heavy metals'distribution of Weizhou is erratic in the direction which is perpendicular to the coastline. But in the landscape orientation, Section W05 and XKZ have more enrichment level. In Longmen and Xicun zone, heavy metals'contents are slightly higher in low tidal zone than in middle and high tidal zone. For regional distribution, Xicun is higher than Longmen because of difference of water motivity and bedload removal of Qinzhouwan.The correlation of Pb, Zn, Cr is positive in Weizhou tidal zone, the same as Hg, Cd, As. They have similar source or transfer mode. But they have no correlation with grain size and TOC, because the sediments of this area have no granule component below 63μm. In Longmen and Xicun tidal zone except for LM-02, the correlation of Hg, Pb, Zn, Cr, As, grain size and TOC is observably positive, and it is showed that the 5 elements mainly comes from nature. There are a great deal of Cu, Pb and Zn which come from human activities in LM-02. Cu has no correlation with other elements and its source or transfer mode is particular. While heavy metals mainly come from nature, sediment environment will effect the grain size, TOC and CaCO3 and finally effect the content of heavy metals. But when human activity is the main source, it will effect the distribution of heavy metals directly.According to the results of Index of Geoaccumulation and Potential Ecological Risk Indices, the tidal environment is well in Weizhou Island. Only Cu is slightly polluted in some area and the Potential Ecological Risk Indices are extremely low. In Xicun tidal zone, Pb and Cu are polluted and Xicun's RI is higher than Weizhou's. Cu is polluted in Longmen tidal zone. Furthermore, Pb and Zn are polluted in LM-02. The RI of Longmen Island is equivalent with Xicun besides LM-02 has a high ecological risk.