Heavy Metals In Sediments Of The Minjiang Estuary Wetlands And Assessment

The total concentration, chemical speciation of elements (Cu, Pb, Zn, Cd, Ni, Fe, Mn) were determined in surface sediment collected from different wetlands of Minjiang estuary. The concentration of core sediments came from different tidal wetlands were analyzed also. Based on which, the spatial distributions, accumulation, speciation, migration were investigated. Different ecological assessment methods, which based on total concentration and chemical speciation of elements, were applied to comprehensive assess the environment quality and ecological risk. Migration and transformation of exogenous heavy metals in wetland sediments were studied by soil incubation method and soil column experiment. Attempt to establish the vigor values of heavy metal to assess the ability of migration and transformation.Concentration of heavy metals in wetland sediments of the Minjiang estuary lie between the higher level for Chinese estuarine, and lie between the mid to higher range for abroad estuarine.The character of heavy metals concentrations in Minjiang estuary was the middle estuary higher than the both sides of the estuary. In other words, the contents of heavy metals of Tajiaozhou wetland and Shanyutan wetland were lower than the Yangzhong-village tidal wetland and Bianfuzhou wetland. It is quite different that the contents of heavy metals when the wetland sediments were treated with different vegetation or different land uses. Overall, the hierarchical order of heavy metal concentrations in different vegetation is as follow:Cmalaccensis Lam. Var. bervifolius Bocklr. wetland, Kandelia candel(L.) Druce wetland, phragmites australis (Cav.) Trin. ex Steud. wetland, and artificial wetland (paddy soil). The order of heavy metal pollution in different land uses is as follow:fishpond, growing grass beach, the barren wetland and paddy soil.The order of heavy metals concentrations of different core sediment is as follow: Mn>Zn>Cu>Pb>Cd, after analyzed the core sediments that collected from different wetland of Minjiang estuary. In different wetlands, the contents of Cd came from Tajiaozhou far higher than the other wetland, and Cu, Zn concentrations of Bianfuzhou was higher than the other wetland.The modified BCR-sequential extraction technique was used to analyzed the chemical speciation(acid-soluble, reducible, oxidisable and residual) of heavy metals (Cu, Pb, Zn, Cd, Mn, Ni, Fe) in surface sediments came from the Minjiang estuary wetland. Pb in surface sediments are mainly in reducible (Fe-Mn oxides) fraction, with the contents up to 39.23%. The major chemical speciation of Cu, Zn, Ni and Fe is residual, with the contents 56.23%,51.22%,76.88% and 81.97%, respectively. Cd and Mn are mainly in acid-soluble fraction, secondly is reducible fraction.Transform of chemical forms of exogenous heavy metals in the sediments were studied with soil incubation and core sediment incubation method. Results showed that exogenous heavy metals existed in the wetland sediments mainly in available and potentially available form, and the change of residual form concentration is little. It's mainly transform into F1 and F2 when the exogenous heavy metals came into the sediments. In the whole incubation, the migration of heavy metal in vertical direction is moving continuously mainly with F1 and F2 forms.The assessment result of the heavy metals of Minjiang estuary wetland sediment by different Sediment Quality Criteria (SQC) method is not consistent. It is consensus that Cu, Cd contribution to the Minjiang estuary pollution assess by 6 kinds SQC is small, and there are large differences contribution to the Minjiang estuary pollution in different SQC about Ni, Zn and Pb. Hong Kong, Australia and New Zealand SQC evaluated that the heaviest pollution is Zn, but others SQC evaluation result argued that Ni pollution is the largest. According to the analysis of Marine sediment quality (GB 18668-2002), the heavy metal pollution of Minjiang estuary is mainly comprised by Zn. According to the geo-accumulation, the heavy metal pollution is mainly come from Cd and Zn. According to the potential ecological risk index, Minjiang estuary was suffered from medium ecological harm and its potential ecological risk was mainly come from Cd. According to RSP (Ratio of secondary phase and primary phase), which belong to based on chemical speciation of elements, showed that the pollution of Minjiang estuary wetland mainly from Pb, Cd and Mn.Exogenous heavy metals in wetland sediments mainly transformed into acid-soluble, reducible and oxidisable, the ratio of F1, F2, F3 and F4 can indicated the ability of heavy metals migration and transformation. It is named Vigor values of heavy metals. The Vv(Vigor values of heavy metals)>3 in the whole zone is Pb, Cd and Mn, showed 3 heavy metals belongs to strong migration and transformation. The Vigor values of heavy metals can be ordered as follow:Mn>Cd>Pb>Zn>Cu>Ni>Fe.