Heavy Metals In The Mangrove Wetland Of China

Mangrove wetland with special,habitat is located in the transitional zones from land to ocean,its ecological environment is controlled by the marine environment, and influenced closely by the land-based area environment.Because of population's increasing,the city and basic industrial and agricultural rapidly development in recent years had led to serious heavy metal pollution in the wetland.Environmental pressure in mangrove wetland increased day by day.Heavy metals including Cr,Cu,Zn,As,Cd and Pb were chosed as research object in the mangrove Nature reserve of Sanya,Dongzhaigang,Daguansha, Beilunhekou,Qinzhouwan,Shankou,Zhanjiang,Yaishan,Shenzhen Futian,Yunxiao, Fugong,Luoyangqiao,Yaojiayu and Ewan.Contents of those heavy metals were analyzed with ICP-MS.Tessier sequential extraction procedures were conducted to reveal their speciations' properies.In order to discuss accumulation and transition of metals in the sediments,the relationships among heavy metals contents,speciation, and physical chemical properties of sediment were analyzed.With the content of the heavy metals in the sediment,the environmental quality of main mangrove sediment in China was evaluated.The results were showed as follows and hoped to can guideline the reserve and restoration of mangrove wetland.1.The content range of pH in mangrove sediment was 5.06-7.19,the average value was 6.23.The content range of the organic matter is 1.49%-4.38%,the average value was 2.73%.The range of degree of salt was 6.27‰-20.10‰in the mangrove sediment,the average value was 10.72‰.The soil in Sanya,Daguansha,Beilunhekou was sandy,the others were loam and clay.2.The average value of Cr,Cu,Zn,As,Cd and Pb in sediment were 18.193 ug/g, 22.774 ug/g,86.119 ug/g,8.142 ug/g,0.213 ug/g and 75.867 ug/g respectively. Compared with the background value,the content of Cu,Zn,Cd and Pb were relatively high.The order of six heavy metals content in mangrove sediment was Zn＞Pb＞Cu＞Cr＞As＞Cd.According to the environmental factor of multi-regression model,the most important environmental factor influencing the content of heavy metal were the organic matter and particle machinery.The content of heavy metals in sediment of mangrove was also closely related with the degree of heavy metal pollution which the nearby city discharged.3.The heavy metals speciation in main mangrove sediment mainly existed in the form of residue and bound to organic/sulfides.The exchangeable,bound to carbonate and bound to Fe-Mn oxides were relatively low.The proportion of heavy metal residue accounted for the total content were 57.95%(Cr),47.93%(Cu),72.22% (Zn),50.65%(As),52.34%(Cd),64.35%(Pb) respectively;The proportion of organic and sulfides form of Cr,Cu,As and Pb accounted for the total quantity were 40.08%,27.75%,30.40%,34.68%respectively,which were relatively high.It might related with the condition of abundant sulfur,high organic and reductive in mangrove sediments.The residue and bound to organic/sulfides were stable,which were difficult to release to the environment,and had little potential harmfulness to the biological.4.Throught intergrating results of servral appraisal methods,the pollution degree of main mangrove areas was:Shenzhen Futian＞Dongzhaigang＞Fugong＞Beilunhekou＞Taishan＞Ewan＞Luoyangqiao＞Yaojiayu＞Yingluowan＞Daguansha＞Sanya＞Qinzhouwan.The environment quality of mangrove wetlands was influenced by territory environment strongly.5.The content of heavy metal in up layer sediments is higher than that of deep layer in profile samples,which indicated that the emission of heavy metals have the trend of increasing in the sediment,and also indicated that discharge of pollutant increased tightly with the coastal economic development.The heavy metals pollution history in sediment demonstrated that the most serious pollution of heavy metals appeared in the early-1980s.6.Mangrove plants can absorb heavy metals from environment and accumulate them in the body.The ability of plants' to absorb and accumulate heavy metal was different.The absorption and accumulation ability to the heavy metals of plants was not only related with floristic component and organs,but also related with heavy metal content,the heavy metal speciation and the habitat.The accumulation ability of mangrove plants to Cd wree relatively strong,the Cd accumulation index of mangrove plants(without Lumnitzera racemosa) was greater than 1.Among them the accumulation index of Cu,Zn and Cd of Hibiscus tiliaceus was 1.977,1.079 and 8.708 respectively,possess some characteristics ultra accumulation characteristics of plant.