The Accumulation Risk And Origin For Heavy Metals In The Supratidal Wetlands On The West Coast Of Bohai Sea

Wetland is not only an important land but also a precious natural resource.It can provide diversified habitats for many wild animals and plants,especially for birds.However,due to the rapid growth of the population and the industrialization,the waste water,exhaust gases and waste residue of some heavy and chemical industries are discharged in a disorderly manner.Large amounts of heavy metal pollutants entered into the environmental media such as air,water and soil,which is extremely harmful to human beings and ecosystems.In this paper,we tried to select the rainfall-driven supratidal wetlands as the research objects,and to explore the spatial distribution and enrichment degree of heavy metals in those supratidal habitats on the west coast of Bohai Sea.In addition,the influential factors of human activities,hydrology cycle,climate change and soil characters were combined to clarify the accumulated risk for heavy metals in those supratidal wetlands.We also hope to investigate the sources and the input pathways of heavy metals by quantitative ecological methods,such as the cluster analysis?CA?and the principal component analysis?PCA?.Those explorations are helpful for policies making of ecological protection and can provide theoretical and technical support for sustainable utilization of marine space resources.The results are as follows:?1?The average contents of Al,Cr,Cu,Fe and Mn in the supratidal wetlands of Dongying,Changyi,Binzhou and Tianjin were lower than the background values in the local and Bohai Bay,indicating that these elements were mainly originated from soil parent material weathering or few exotic inputs.The average content of Ni in the supratidal wetland of Dongying was 40.91 mg.kg^-1,which exceeded the background values of Ni in the local and Bohai Bay.The average content of Pb in the supratidal wetlands of Binzhou and Tianjin were 30.43mg.kg^-11 and 21.04 mg.kg^-11 respectively,which exceeded the background values of Pb in the local and Bohai Bay.The average values of Zn in the supratidal wetlands of Dongying,Binzhou and Tianjin were 66.94 mg.kg^-1,75.12 mg.kg^-1and 108.13mg.kg^-11 respectively,exceeding the background values of Zn in the local and Bohai Bay.The average contents of As and Cd in the four supratidal wetlands were higher than the background values in the local and Bohai Bay,but the concentrations of As and Cd in the supratidal wetland of Changyi were 12.98 mg.kg^-11 and 0.087 mg.kg^-1,which were significantly lower than those in the other supratidal wetlands.?2?The enrichment factor?EF?values of Cr,Ni,As and Cd in the supratidal wetland of Dongying were larger than or close to 2,indicating that these four heavy metals reached or neared to the level of moderate enrichment in this habitat.The EF values of As and Cd in the supratidal wetlands of Changyi were greater than 2,indicating that there has a moderate enrichment risk for As and Cd in the supratidal habitat of Changyi.EFs of Zn,As and Cd in the supratidal wetland of Binzhou were greater than 2,which suggesting moderate enrichment for those metals in this habitat.The EF of As in the supratidal wetland of Tianjin was greater than 2,reaching a moderate enrichment of the element in this habitat;while the EF values of Zn and Cd were close to 2 and there was also a certain risk for the two metals in this habitat.From the perspective of geo-accumulation index?Igeo?,the Igeo values of all the heavy metals were less than 0 in the four supratidal wetlands.The result revealed that the geochemical elements were found to be accumulated in a certain degree in the supratidal wetlands on the west coast of Bohai Sea,however all those elements did not reach the level of pollution.This conclution was similar to the result of soil quality standards?SQG?in China.?3?The total ecological risk index?RI?for all heavy metals in the four supratidal wetlands was less than 150,which indicated that there was only slight ecological risk in the supratidal regions on the west coast of the Bohai Sea.However,the total risk index in the four supratidal wetlands mainly depended on the single risk index?E_rⁱ?of As and Cd.For RI in the supratidal wetlands of Dongying,Changyi,Binzhou and Tianjin,the contributions of As and Cd?E_rⁱ-As+E_rⁱ-Cd?were 75.5%,78.1%,79.8%and 75.4%respectively.From the perspective of pollution degree,the RI of Cd in the supratidal wetland of Changyi was 5.77,which is lower than 8 and belongs to low risk status.The RI values of Cd were higher 8 in the other three supratidal wetlands,suggesting moderate risk status in the supratidal regions of Dongying,Binzhou and Tianjin.From the perspective of the pollution load index?PLI?,the PLI in the supratidal wetland of Dongying ranged from 2 to 4,indicating that the accumulated risk for heavy metals was moderate in this habitat.The PLI in the supratidal wetlands of Binzhou and Tianjin were between 4 and 8,suggesting high-risk status in the two habitats.The PLI in the the supratidal wetland of Changyi was 0.47,which is lower than 1.5 and indicates no-risk or low-risk status.?4?Based on the results of cluster analysis?CA?,the principal component analysis?PCA?was used as method and the correlation analysis?Spearman?was used as evidence to explore the sources and input pathways of heavy metals in the supratidal wetlands of Bohai Sea.The results showed that the heavy metals of Al,Cr,Mn and Fe are homologous,all these elements were influenced by natural factors and may come from the parent materials and rocks weathering.In contrast with those heavy metals,Pb was found to be tightly correlated to human activities.The heavy metals,such as Cu,Cd and As,may not only come from human activity but also relate to the atmospheric deposition of natural factors.The sources of Ni and Zn might depend on the actual conditions around those supratidal wetlands.For example,Ni was found to be derived from agricultural activities in the supratidal wetland of Dongying,whereas it was originated from the atmospheric deposition in the supratidal wetlands of Tianjin and Changyi.In the supratidal wetland of Binzhou,this metal might be originated from natural sedimentation.In this research,Zn was found to be originated from atmospheric deposition in the supratidal wetlands of Dongying and Binzhou,however,it might be originated from natural sedimentation in the supratidal wetland of Changyi.In the supratidal wetland of Tianjin,Zn was more likely to come from agricultural non-point source pollution.