Geochemistry And Potential Ecological Risk Of Heavy Metal Elements In The Surface Sediments Of The Beihai Inter-tidal Zone

Inter-tidal zone responds sensitively to natural processes and hμman activities, its environment and changes are closely connected with our living space, quality and sustainable development.The distribution and geochemical characteristic of heavy metal elements in the surface sediment are the chief content in environment quality assessment of coastal zone.In this thesis, a series of samples collected during the survey on inter-tidal zone around the Beihai city of Guangxi province were analyzed to reveal the content and spatial distribution of heavy metals, then their correlation with grain size, major and trace elements distribution were discussed to illustrate the impact and control factors for the distribution of heavy metal elements. Environmental quality assessment and potential ecological risk of the heavy metal elements in the surface sediment were conducted.The distribution characteristics of grain size and major and trace elements in the surface sediment were quite restricted by the depositional environment and corresponding hydrodynamic condition. The sediments of the study area are mostly sand, clayey sand and sandy clay, and show great apatial variations. Sediments in the bay have higher elements contents and finer grain size than those on the open coast.There were different heavy metals contents in the surface sediment from different sea areas and different sampling locations. The content of heavy metals in the Lianzhou bay and Yingluo bay was comparatively higher, and the other regions were lower.Correlation analysis and factor analysis indicate the enrichment of Pb, As and Cr depended on clay composition and their surface adsorption action. It is showed that Zn, Cu, Cd and Hg are not closely correlated with the typical oxide, such as SiO₂, Al₂O₃ and Fe₂O₃ et al., or the biological source (CaO, Sr and TOC). It implied that Zn, Cu, Cd and Hg were seriously contaminated by hμman pollution and they come from different pollution sources. Based on the ratio analysis between the goal element and Al2O3 in the same profile, the content of heavy metals in clay fraction of coarse sediment was obviously higher, and the content of heavy metals in coarse fraction of fine sediment was lower.National specifications for marine sediment quality and the potential ecological risk were used to assess the heavy metals pollution degree in inter-tidal zone. The results indicated that most surface sediments are in clean and noncontaminated. In most sampling spot, the Eri and RI of heavy metals are low ecological risk, except that two sampling spots belong to moderate ecological risk. The heavy metals PER order is Hg > Cd > As > Cu > Pb > Cr > Zn, the local PER order in Beihai is Lianzhou Bay > Yingluo Bay > Tieshangang Bay > Yintan section.