湛江东海岛红树林湿地表层土壤重金属空间分布特征及生态风险评价

Spatial Distribution and Ecological Risk Assessment of Heavy Metals in the Surface Soils of Mangrove Wetland in Donghai Island, Zhanjiang

近年来随着沿海地区工农业的迅速发展,大量污染物汇集于河口与海湾区,使得红树林湿地重金属污染也日趋严重。为探究东海岛红树林湿地表层(0~15 cm)土壤重金属污染现状,于2017年6月沿东海岛海岸线典型红树林分布区布设了7个站位(由东南向西北方向依次为YC、SYC、JJC、XWC、TMHHK、DCMT和DTSD)进行采样,测定样品中As、Cd、Cr、Cu、Hg、Ni、Pb、Zn 8种重金属元素质量分数并分析其空间分布特征,采用潜在生态危害指数进行污染及潜在生态风险评价,结合相关性分析和主成分分析方法探讨其重金属来源。结果表明,(1)东海岛红树林湿地表层土壤8种重金属的质量分数平均值均超过雷州半岛土壤环境背景值,但未超过国家土壤环境质量一级标准限值。(2)单因子污染指数显示,东海岛红树林湿地表层土壤各重金属元素总体上到达中等污染程度。(3)潜在生态风险评价结果显示,东海岛红树林湿地表层土壤重金属污染总体上属于中等潜在生态风险;其中Hg潜在生态风险参数最高,平均值为105.524,属于强潜在生态风险,其余7种重金属元素均属于轻微潜在生态风险。(4)从潜在生态风险空间分布特征看,东海岛红树林表层土壤重金属空间差异较明显,其中XWC站位的潜在生态风险指数为351.690,为强潜在生态风险(主要来自Hg、Cd和As污染),YC、TMHHK、DCMT和DTSD 4个站位为中等潜在生态风险,SYC和JJC表现为轻微潜在生态风险。(5)统计分析结果表明,东海岛红树林湿地表层土壤中As、Cr、Cu、Ni、Pb和Zn这6种重金属元素之间具有强相关性,结合实地调查结果推测其来源主要与水产养殖排污及农业面源污染有关;而Cd和Hg之间的相关性不明显,推测其来源分别与船舶污染和生活排污有关。

With the rapid development of agriculture and industry in coastal areas in recent years,heavy metal pollution of mangrove wetlands is becoming more serious due to the large amount of pollutants collected in estuaries and bay areas.In order to research the pollution features of heavy metals in the surface soil(0~15 cm)of the mangrove wetland in Donghai Island,7 stations(YC,SYC,JJC,XWC,TMHHK,DCMT and DTSD in turn,from Southeast to Northwest)were designed along the island coastline in typical mangrove areas and soils samples were collected in June 2017.The mass fraction of As,Cd,Cr,Cu,Hg,Ni,Pb and Zn was determined,and their spatial distribution characteristics were analyzed.The potential ecological risk index was used for pollution assessment,and the sources of heavy metals were discussed by the correlation analysis and principal component analysis.The results were as follows:(1)The average mass fraction of 8 heavy metals in the surface soil of Donghai Island exceeded the environment background value,but did not exceed the first level of National Soil Environment Quality Standard.(2)The single factor pollution index showed that the heavy metal elements of the surface soil of the mangrove wetlands in the Donghai Island were generally moderately polluted.(3)The potential ecological risk assessment indicated that heavy metals pollution in the surface soil of the mangrove wetland in Donghai Island reached medium level in general.Among them,Hg owned the highest value of potential ecological risk with an average of 105.524,reaching strong potential ecological risk,while slight potential ecological risk for the others.(4)The spatial distribution characteristics of potential ecological risk assessment suggested obviously spatial differentiation of heavy metals in the surface soil of the mangrove wetland in Donghai Island.The potential ecological risk index of the XWC station was 351.690,which was a strong potential ecological risk(mainly from Hg,Cd and As pollution).The 4 stations of YC,TMHHK,DCMT and DTSD were medium potential ecological risk,while the SYC and JJC stations were slight.(5)The statistical analysis results showed that there were strong correlations among heavy metals such as As,Cr,Cu,Ni,Pb and Zn in the surface soil of Donghai island mangrove wetland.Combined with the results of field survey,it was concluded that the source of the heavy metals was mainly related to the pollutant from aquaculture industry and agricultural non-point source pollution.While the correlation between Cd and Hg and other elements was not obvious,it was speculated that their sources were in turn related to vessel pollution and domestic waste discharge.