Department of Environmental, Earth and Atmospheric Sciences, University of Massachusetts, Lowell, Massachusetts 01854, USA.
Division of Atmospheric Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, Nevada 89512, USA.
Nature. 2017 Jul 12;547(7662):201-204. doi: 10.1038/nature22997.
Anthropogenic activities have led to large-scale mercury (Hg) pollution in the Arctic. It has been suggested that sea-salt-induced chemical cycling of Hg (through 'atmospheric mercury depletion events', or AMDEs) and wet deposition via precipitation are sources of Hg to the Arctic in its oxidized form (Hg(ii)). However, there is little evidence for the occurrence of AMDEs outside of coastal regions, and their importance to net Hg deposition has been questioned. Furthermore, wet-deposition measurements in the Arctic showed some of the lowest levels of Hg deposition via precipitation worldwide, raising questions as to the sources of high Arctic Hg loading. Here we present a comprehensive Hg-deposition mass-balance study, and show that most of the Hg (about 70%) in the interior Arctic tundra is derived from gaseous elemental Hg (Hg(0)) deposition, with only minor contributions from the deposition of Hg(ii) via precipitation or AMDEs. We find that deposition of Hg(0)-the form ubiquitously present in the global atmosphere-occurs throughout the year, and that it is enhanced in summer through the uptake of Hg(0) by vegetation. Tundra uptake of gaseous Hg(0) leads to high soil Hg concentrations, with Hg masses greatly exceeding the levels found in temperate soils. Our concurrent Hg stable isotope measurements in the atmosphere, snowpack, vegetation and soils support our finding that Hg(0) dominates as a source to the tundra. Hg concentration and stable isotope data from an inland-to-coastal transect show high soil Hg concentrations consistently derived from Hg(0), suggesting that the Arctic tundra might be a globally important Hg sink. We suggest that the high tundra soil Hg concentrations might also explain why Arctic rivers annually transport large amounts of Hg to the Arctic Ocean.
人为活动导致北极地区大规模汞（Hg）污染。有人认为，海盐诱导的 Hg 化学循环（通过“大气汞消耗事件”或 AMDEs）和通过降水的湿沉降是 Hg 以氧化形式（Hg（ii））进入北极的来源。然而，除了沿海地区之外，几乎没有证据表明 AMDEs 的发生，而且它们对净 Hg 沉降的重要性也受到了质疑。此外，北极地区的湿沉降测量显示，通过降水进行 Hg 沉降的水平是全球最低的，这引发了对高北极 Hg 负荷来源的质疑。在这里，我们提出了一个全面的 Hg 沉降质量平衡研究，并表明北极内陆苔原中约 70%的 Hg 来自气态元素 Hg（Hg（0））的沉降，只有一小部分来自降水或 AMDEs 中 Hg（ii）的沉降。我们发现，普遍存在于全球大气中的 Hg（0）形式的沉降全年都在发生，并且通过植被吸收 Hg（0），夏季沉降会增强。苔原生态系统对气态 Hg（0）的吸收导致土壤中 Hg 浓度升高，Hg 质量大大超过温带土壤中的水平。我们在大气、积雪、植被和土壤中同时进行的 Hg 稳定同位素测量支持了我们的发现，即 Hg（0）是苔原的主要来源。从内陆到沿海的一个横断面的 Hg 浓度和稳定同位素数据表明，土壤 Hg 浓度始终来源于 Hg（0），这表明北极苔原可能是一个重要的全球 Hg 汇。我们认为，高浓度的苔原生态系统土壤 Hg 可能也解释了为什么北极河流每年向北极海洋输送大量 Hg。
