Tracing mercury seawater vs. atmospheric inputs in a pristine SE USA salt marsh system: Mercury isotope evidence
Tracing mercury seawater vs. atmospheric inputs in a pristine SE USA salt marsh system: Mercury isotope evidence
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DOI：
10.1016/j.chemgeo.2012.04.035
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发表时间：
2013-01-16
期刊：
影响因子：
3.9
通讯作者：
Wilson, Alicia M.
中科院分区：
文献类型：
--
作者：
Das, Reshmi;Bizimis, Michael;Wilson, Alicia M.
盐沼可能是沿海海洋生物中甲基汞的重要来源，但盐沼沉积物以及整个沿海环境中汞的来源和循环仍不清楚。我们分析了美国佐治亚州卡布雷塔岛盐沼和邻近高地沙丘的表面和岩芯沉积物的总汞 (Hg-T)、汞同位素和痕量金属浓度，以更好地限制该沿海环境中汞的来源。高地沙子中的 Hg-T 浓度 (1-6 ng/g) 低于沼泽沉积物中的 Hg-T 浓度 (6-16 ng/g)。 Hg-T 与沉积物中总有机物含量 (TOC) 和细粉比例增加呈正相关。无论化学亲和力（即亲铜剂、亲铁剂或亲石剂）如何，痕量金属浓度也与沼泽沉积物中的 Hg-T 呈正相关。所有这些数据都与表面吸附（直接吸附在沉积物上或吸附在有机物上）一致，表面吸附是沼泽沉积物中汞和金属积累的主要机制。表面沉积物显示出奇数汞同位素的显着质量独立分馏 (MIF)：高地沙丘沙的 Delta Hg-199 为零至轻微负值（-0.07 ppm 至 -0.14 ppm），沼泽表面沉积物具有正 Delta Hg-199（0.48 ppm 至 0.79 ppm）。与表面样品一样，岩心沉积物中分选良好的砂层具有较低的 Hg 浓度和零至轻微的负 Delta Hg-199，而富含细颗粒的层具有较高的 Hg 浓度和正 Delta Hg-199 值。在没有任何证据证明细菌介导的甲基化-去甲基化反应导致汞同位素发生 MIF 的情况下，观察到的沼泽和高地沙子之间的汞同位素差异可以用不同的汞来源来解释。我们认为，局部大气汞沉积在反营养高地沙中的汞预算中占主导地位，而沼泽沉积物中的正 MIF 与主要来自海水的汞一致。虽然光还原和逃逸等原位过程可以叠加汞沉积同位素特征，但它们对沉积物的影响目前不受限制。尽管如此，我们的数据表明，汞同位素可以在原始沿海环境和小空间尺度上描绘不同的汞来源。因此，当汞同位素在受人为影响的地点用作汞示踪剂时，应将自然背景同位素变异性作为基线进行评估。 (C) 2012 Elsevier B.V. 保留所有权利。
Salt marshes can be a significant source of MeHg in coastal marine organisms, however the sources and cycling of Hg in salt marsh sediments, and in coastal environments in general, remain unclear. We analyzed surface and cored sediments from a salt marsh and adjacent upland sand dune in Cabretta Island, Georgia, USA, for total mercury (Hg-T), Hg isotopes and trace metal concentrations to better constrain the sources of Hg in this coastal environment. Hg-T concentrations are lower in the upland sands (1-6 ng/g) than in the marsh sediments (6-16 ng/g). Hg-T shows a positive correlation with total organic content (TOC) and increasing proportion of fines in the sediments. Trace metal concentrations also show a positive correlation with Hg-T in the marsh sediments regardless of chemical affinity (i.e. chalcophile, siderophile or lithophile). All these data are consistent with surface adsorption (either directly on to sediments or on to organic matter) as a dominant mechanism of Hg and metals accumulation in the marsh sediments. The surface sediments show significant mass independent fractionation (MIF) of odd Hg isotopes: the upland dune sands have zero to slightly negative Delta Hg-199 (-0.07 parts per thousand to -0.14 parts per thousand) and the marsh surface sediments have positive Delta Hg-199 (0.48 parts per thousand to 0.79 parts per thousand). As in the surface samples, well-sorted sand layers in the cored sediments have low Hg concentrations and zero to slightly negative Delta Hg-199, whereas fine particle-rich layers have higher Hg concentrations and positive Delta Hg-199 values. In the absence of any evidence for MIF of Hg isotopes by bacteria mediated methylation-demethylation reactions, the observed Hg isotope differences between marsh and upland sands can be explained by different sources of Hg. We suggest that local atmospheric Hg deposition dominates the Hg budget in the ombrotrophic upland sand, while the positive MIF in the marsh sediments are consistent with Hg dominantly of seawater origin. While in situ processes, like photoreduction and evasion can overprint the Hg depositional isotope signature, their effect on the sediments is currently unconstrained. Nevertheless, our data show that Hg isotopes can delineate different sources of Hg in a pristine coastal environment and at small spatial scales. Thus natural background isotope variability should be assessed as a baseline when Hg isotopes are used as tracers of Hg in anthropogenically-influenced sites. (C) 2012 Elsevier B.V. All rights reserved.