Abstract:

Located in the coastal buffer zone, mangrove wetlands act as a significant source and sink of heavy metal pollutants. This study aims to explore the accumulation and migration patterns of heavy metal pollutants in soil-mangrove system, and as well reveal the relationship between the morphological characteristics of soil heavy metals and the absorption and enrichment abilities of mangroves to heavy metals. The mass fractions and morphological characteristics of eight kinds of heavy metals in both surface soil and mangrove plant Avicennia marina were studied. The enrichment and transfer characteristics of heavy metals in mangrove plants were analyzed using bioconcentration coefficient and transfer coefficient, and, the correlation analysis was conducted to quantify the correlation between the available heavy metal content in soil and the heavy metal content in plant. The results show that: (1) The average mass fractions of heavy metals in mangrove soil of Nansan Island rank as Zn>Cu>Cr>Pb>Ni>As>Hg>Cd. The average mass fraction of 8 heavy metals do not exceed the national soil environmental quality standard. As for speciation characteristics, except As and Hg, the effective contents of the other six heavy metal elements are more than 70%, which implies high secondary release potential. (2) There are differences regarding the accumulation of heavy metals in various parts of plants. In general, the mass fraction is the highest in root. No positive correlation is found between enrichment ability and transfer ability. The available content of Cr and Ni in the soil of the study area is relatively high, but its accumulation in Avicennia marina is not obvious, which is primarily due to the relatively stable oxidizable state of this element in the soil. High contents of acid extracted state and reducible state can promote the bioavailability of heavy metals in mangrove soil. (3) Avicennia marina is found to have strong bio-concentration of Cd and Hg, and is widely distributed in the study area. It can be used as a pioneer plant for ecological restoration of mangrove wetland. (4) The correlation coefficient between the available content of heavy metals in mangrove soil and the mass fraction of heavy metals in plants shows that the contents of Cr, Ni and Pb in mangrove roots are positively correlated with the available state of respective element in soil, while the other elements are negatively correlated. As and Pb in stems are positively correlated with their available state contents in soil, and the other elements are negatively correlated. Cr and Zn in leaves are negatively correlated with their available state contents in soil, while the other elements are positively correlated, but the correlation is not significant on the whole.

Key words: Avicennia marina, heavy metals, speciation characteristics, transfer coefficient, bio-concentration coefficient, mangrove

摘要：

位于海陆缓冲带的红树林湿地是重金属污染物重要的源与汇。为探究红树林土壤-红树植物系统对重金属污染物的累积及迁移规律,揭示土壤重金属形态特征与红树植物对重金属吸收富集能力的关系,以湛江南三岛红树林为研究对象,对表层土壤和红树植物白骨壤（Avicennia marina）的8种重金属质量分数与土壤重金属形态特征进行了研究。采用生物富集系数和转移系数分析红树植物对重金属元素的富集与转移特征,结合相关性分析方法探讨了土壤中重金属有效态含量与植物体内重金属含量的相关关系。结果表明：（1）南三岛红树林土壤中重金属平均质量分数表现为锌 (Zn)>铜 (Cu)>铬 (Cr)>铅 (Pb)>镍 (Ni)>砷 (As)>汞 (Hg)>镉 (Cd),8种重金属的平均质量分数均未超过国家土壤环境质量标准。从形态特征看,除砷（As）和汞（Hg）外,其余6种重金属元素有效态含量比例均大于70%,具有较高的二次释放潜力。（2）不同重金属元素在红树各部位的累积存在差异,总体上根部的质量分数最高;且红树的富集能力与转移能力并非呈正相关关系。研究区土壤中铬（Cr）和镍（Ni）有效态含量较高,但在白骨壤体内累积不明显,主要与土壤中该元素以相对较为稳定的可氧化态为主有关;而酸提取态和可还原态含量较高则可以促进红树林土壤中重金属的生物有效性。（3）白骨壤对镉（Cd）和汞（Hg）这两种元素具有较强的生物富集作用,且白骨壤在研究区分布较广数量较多,可作为红树林湿地生态恢复的先锋植物。（4）南三岛红树林土壤中重金属有效态含量与植物体内重金属质量分数的相关系数表明,红树根部铬（Cr）、镍（Ni）和铅（Pb）与土壤中该元素的有效态呈正相关,其余元素为负相关;茎部砷（As）和铅（Pb）与土壤中该元素的有效态呈正相关,其余元素为负相关;而叶片中铬（Cr）和锌（Zn）与土壤中该元素的有效态呈负相关,其余元素为正相关,且总体上相关性不显著。

关键词: 白骨壤（Avicennia marina）, 重金属, 形态特征, 转移系数, 生物富集系数, 红树林