Study On The Elements Geochemistry Characteristics Of Sediments In Mangrove Areas In Northern Hainan Island

Sediments of mangrove areas located in the intertidal zone of sensitive areas of the intersection of marine and terrestrial. The ecological environment is effected by oceans and continent. Because of the inherent characteristics of mangrove areas and residues of plant litter make the sediment content of organic matter relatively high, at the same time the water velocity is slow,anaerobic environment and other factors'influence. These benefit from the deposition and accumulation of major and trace elements from marine and terrestrial.In this paper, a series of samples collected during the survey on sediments of mangrove areas on northern Hainan Island was analyzed to reveal the content and spatial distribution of major and trace elements, study the correlation of the elements in sediments, discusses the control factors of the element'space distribution .Moreover, environment quality assessment and ecological risk assessment of heavy metals in study area. The main conclusions can be summed up as follows:1.The content of major element oxides SiO₂,Al₂O₃,Fe₂O₃ was relatively high in study area, other major element oxides are relatively low, the main element component was SiO₂,Al₂O₃. This shows that the major chemical composition of sediments is silicate and aluminum-silicate.2.Planar spatial distribution of major elements: Al₂O₃,Fe₂O₃,MgO,TiO₂,MnO,Na₂O,K2O contents is highest in mangrove area of dong zhai port; P₂O₅ contents is highest in mangrove area of qing lan port; SiO₂,CaO contents is highest in mangrove area of xin ying port.3.Vertical distribution characteristics of major elements: SiO₂,CaO,P2O5 content showed gradually reduce from sediment surface to deep; form shallow to deep Al₂O₃,Fe₂O₃,MgO,K₂O,TiO₂ content showed the trend of gradual increase; MnO content did not change significantly with depth in different regions of sediment profile; SiO₂,Al₂O₃,Fe₂O₃,MgO,CaO contents have large amplitude in sediment profiles of the three study area, TiO₂,P₂O₅,MnO,K₂O,TiO₂ contents have a lesser extent.4.Correlation analysis: SiO₂ with Al₂O₃,Fe₂O₃,MgO,TiO₂,MnO,P₂O₅ and other major element was a significant negative correlation, especially SiO₂ and Al₂O₃ showed particularly significant negative correlation, and the negative correlation with Na₂O; among MgO,Al₂O₃,Fe₂O₃,TiO₂,MnO,P₂O₅ exist the different levels of positive correlation; TiO₂ with CaO,Na₂O,K₂O has no significant correlation, these indicates the source of complex background.5. Study found that in sediments of mangrove areas on northern Hainan Island the average concentration of trace elements sorts for Zn> Cr> Ni> Cu> Pb> Co> As> Mo> Cd>Hg. Trace elements have different content in different regions, the trace element of surface sediment in mangrove area of dong zhai port and qing lan port, while it is relstively low in mangrove area of xin ying port.6. Trace elements of sediment profiles exist certain rules in the vertical distribution: On the whole, except As element, almost all trace elements were higher in surface than the lower levels of trace elements in Xin ying port, this shows that trace elements enrich in surface sediments of mangrove areas in Xin ying port; 6 trace elements of lowerlayer sediments content was higher than surface sediment of mangrove areas in Dong zhai port; This shows surface sediment effect by eluviation and trace elements enriches in its lower layer; Cd,Cr,Zn enriches in lower layer and As,Co,Cu,Hg,Ni,Pb enriches in surface sediment of mangrove areas in Qing lan port.7. Trace elements correlation analysis in sediments of mangrove areas on northern Hainan Island: Al addition to As,Cd,Hg,Mo and other elements has no obvious correlation, but with a lot of element has the obvious correlation, these elements has a similar features in the geochemical behaviour and impact. SiO₂ with Co,Cr,Cu,Hg,Ni,Pb,Zn shows a significant negative correlation.8. Trace element enrichment are concerned with the components of the sediment particles, also reflect the five elements has similarity in the material source and the migration and accumulation. Cd,Hg,Pb has a high positive load, these shows they has similar with material sources,migration and accumulation. As,Mo elements has different material sources,migration and accumulation from other elements.9. Through the geological cumulative index method and potential ecological risk index method evaluated heavy metals pollution condition and potential ecological risks. The results show that the overall environmental quality is better in Sediments of mangrove areas in northern Hainan Island, heavy metal pollution is not serious, the stations of mangrove ecosystems was in the minor potential ecological harm of pollution, Only the YF-03, HW-01 site in the "heavy " level of risk, Individual stance Cd, As, Cu high unusual values and severe potential ecological risk level was a wake-up call for us, Cu,Hg,As,Cd was the main pollution factor in seven kinds of heavy metal evaluation factors in sediments of mangrove areas on northern Hainan Island.