深圳湾红树林沉积物-植物体系汞的分布规律和形态分配特征

摘要

A study quantifying mercury (Hg) distribution and speciation in a continuous system of bulk sediment, rhizosphere sediment, and mangrove species was donducted in Futian mangrove forest, Shenzhen Bay. Sequential extraction procedure was applied to investigate Hg speciation in sediments. The results indicated that Hg concentrations in bulk sediments and rhizosphere sediments were higher than mangrove seedlings. Hg concentrations were lower in stems than that in leaves and roots. Among the three species analyzed in this study, the native species exhibited higher Hg accumulation. InAvicennia marina seedlings, Hg concentration was 45.32 ng·g-1, and 23.49 ng·g-1 inAegiceras corniculatum. The bioconcentration factors and translocation factors showed that the mangrove species were inclined to adopt the metal exclusion strategy due to the plant self-protection from heavy metal stress. Hg speciation in non-rhizosphere sediments followed this order: HgORG>HgVOL>HgR>HgEX>HgCAR>HgFM. Hg speciation in rhizosphere sediments were HgVOL>HgORG>HgR>HgFM>HgEX>HgCAR. Overall, the bioavailable and potentially bioavailable speciation were found in a higher proportion, whereas non-bioavailable speciation was less. Compared with the native species, the introduced speciesSonneratia caseolaris could accumulate Hg in the form of potentially bioavailable and non-bioavailable speciation in the sediment,which were relatively more stable.%为了解重金属汞在非根际沉积物-根际沉积物-红树植物连续体系中的分布特征和迁移规律，以及沉积物中汞的化学形态特征，于深圳湾福田红树林实地采集红树植物幼苗样品及其林下沉积物样品，采用连续提取法对沉积物中汞的各种化学形态进行提取，通过冷原子荧光光谱仪进行定量分析。研究对象包括福田红树林3种常见红树植物，包括白骨壤（Avicennia marina）、桐花树（Aegiceras corniculatum）2个本土种和海桑（Sonneratia caseolaris）1个引进种，并以无植被覆盖的光滩作为空白对照。结果表明，在沉积物-红树植物体系中，根际和非根际沉积物中的总汞含量均高于红树植物幼苗。进入植物体后，汞在茎中的含量均小于根和叶。本土种植株表现出较强的汞积累能力。白骨壤幼苗汞积累量最高，质量分数达到45.32 ng·g-1，其次为桐花树幼苗，汞质量分数为23.49 ng·g-1。3种红树植物对汞的生物积累因子在0.02~0.35范围内，迁移因子处于0.4~0.99范围内，均低于1，表明它们从土壤吸收、并向地上部分运输汞的能力较弱，倾向于采取金属排斥策略，以实现植物体的自我保护。非根际沉积物中汞的各个化学形态质量百分比表现为有机结合态>可挥发态>残渣态>可交换态>碳酸盐结合态>铁锰氧化物结合态，根际沉积物中汞表现为可挥发态>机结合态>残渣态>铁锰氧化物结合态>可交换态>碳酸盐结合态，总体表现为生物可利用态和潜在可利用态质量分数较高，不可利用态较少。与本土种相比，引进种海桑能够将更多汞以稳定性相对较高的生物不可利用态和潜在可利用态形式固定于土壤中，表现出较好的治理汞污染能力。