Studies On Environmental Geochemistry Of Heavy Metals In Mangrove Wetland Sediments Of Fujian Province

Jiulongjiang estuary mangrove wetland and Zhangjiang estuary mangrove wetland of Fujian province are two of important natural reserves of mangrove in China. In recent years, rapid economic growth and development in the region has led to excessive release of heavy metal pollutants into the wetland. The accumulation of contaminants in wetland sediments is likely to pose serious environmental problems in mangrove ecosystem. In present study, sequential extraction procedures were used to reveal the spatial distribution of total concentration and speciation of 7 heavy metals (Fe, Mn, Zn, Pb, Cu, Ni and Cd) in these two mangrove wetlands. To discuss accumulation and transition principle of metals in the sediments, the relationships between metal contents, speciation and physical chemical properties of sediments were analyzed, and speciation changes of Cd in mangrove (Kandelia candel(L.)) rhizosphere sediments were studied by using rhizobox. Finally, the contents of AVS (Acid volatile sulfide) and SEM (Simultaneously extracted metal) were measured to reveal their spatial distribution in mangrove wetland, and the differences of AVS, SEM mole concentration were adopted to evaluate the condition of metal pollution. The results were showed as follows and hoped to can guideline the reserve and restoration of mangrove wetland.1. Order of total metal concentrations was Fe> Mn >Zn >Pb >Cu >Ni >Cd in the study areas. According to the standard quality of marine sediment in China, Zn, Pb, Cd and Cu polluted the mangrove wetland of Jiulongjiang estuary, and Zn, Pb, and Cu polluted the mangrove wetland of Zhangjiang estuary. The results showed that metal speciation distribution was metal-specific and site-specific. Low percentage of metal was found to bound to residual fraction, except Fe. The Fe-Mn oxide fraction (F3) was dominant for all 7 metals in Jiulongjiang mangrove wetland, and the percentage was 73%(Pb),52%(Fe),51%(Mn),48%(Cu),35%(Zn),31%(Cd), and 28%(Ni)respectively. Both Fe-Mn oxide fraction and bound to organic matter-sulfide fraction (F4) were important for these metals in mangrove wetland of Zhangjiang estuary, and the percentages respectively were: Fe (F3:41%;F4:8%), Mn (F3:35%;F4:25%), Zn (F3:27%;F4:32%), Pb (F3:38%;F4:33%), Cu (F3:26%;F4:...