辽河三角洲湿地生态系统对表层沉积物重金属元素的移除作用

Heavy metal distribution in the wetland sediments of the Liaohe delta: Implications for filter function of wetlands

为了研究辽河三角洲湿地表层沉积物中重金属元素含量及其与有机碳的相关性,探讨湿地对重金属元素的移除作用,对233个辽河三角洲上三角洲平原湿地(典型湿地)表层沉积物样品和150个相邻浅海湿地(浅水湿地)表层沉积物样品,进行了化学分析测试及数理统计分析,并运用多种评价方法进行重金属污染风险评价。结果显示:①重金属元素浓度量级大小均遵循Cr (Zn)>Pb>Cu>As>Cd>Hg的分布规律;②除As和Hg外,其他金属元素浓度均表现为浅水湿地显著低于典型湿地,暗示湿地生态系统对污染物的移除作用;③除Pb和Zn外,其他重金属元素对环境均造成了中度污染;④重金属元素分布受有机碳和粒径大小的显著影响,浓度存在显著的相关性,浅水湿地表层沉积物重金属元素浓度及其与有机碳之间的相关性更显著,揭示有机碳对重金属的螯合作用;⑤在有湿地分布的浅海湿地区,重金属元素浓度均表现为浅水湿地显著低于典型湿地,暗示湿地生态系统对污染物的移除作用,相反,在大规模湿地被改造成农田的锦州海岸带地区,造成了近海浅水湿地的严重污染。该研究揭示了滨海湿地对重金属元素的过滤作用及在缓解环境污染过程中的重要意义。

Heavy metals(As,Cd,Cr,Cu,Hg,Pb,Zn),organic carbon(Corg)and grain size of 223 surface sediment samples in the Liaohe upper delta plain wetland(UDPW)and 150 surface sediment samples in neighboring shallow sea wetland(SSW)were analyzed to evaluate the spatial distribution and assess the risk of metal pollution.Concentrations of heavy metals in sediments from both UDPW and SSW are in the decreasing order of Cr(Zn)>Pb>Cu >As>Cd>Hg.The results of two-sample-t-tests indicate significant higher heavy metal concentrations in UDPW compared with SSW except As and Hg,implying the accumulation or biouptake of particulate metal within the wetland ecosystem and reducing metal input to marine coastal systems.Multiple assessment approaches,namely,the metal enrichment factor(EF),geoaccumulation index(Igeo),contamination factor(CF)and pollution load index(PLI)were jointly used to explore the risks of the anthropogenic contaminations.The results indicate unpolluted nature for Pb and Zn,moderate degree of contamination for the remaining metals both in UDPW and SSW.Furthermore,the distribution of heavy metals is substantially influenced by grain size and the concentration of Corg,and there is significant correlation between the concentrations of heavy metal,especially for the concentration of Corg and heavy mentals in surface sediment samples of shallow sea wetland(r=0.439,p<0.01),revealing the metal chelation acted by organic matter.