Geothermal activity is a natural source of mercury (Hg) to surface environments, but its contributions as part of the larger geogenic flux to the global Hg budget are poorly understood, in part due to large geographic gaps in emissions data where no measurements have been made. In this study we report the results of a field campaign over 2021 and 2022 on the highly active volcanic island country of Iceland. Six geothermal sites across the country were investigated for soil gaseous elemental mercury (GEM) and total Hg (THg) concentrations through a series of measurements made across the diffuse degassing surface. At 10 cm depth, soil GEM concentrations were often hundreds and in some cases thousands of times higher than ambient surface air concentrations. Geothermal soils were also highly enriched in THg due to the sorption of hydrothermal Hg on the characteristically fine, thermally-altered clays and silts. Soil “hotspots” displayed THg concentrations exceeding 100 µg g comparable to levels in areas heavily contaminated by anthropogenic activity and in Hg-rich mineral soils. Strong correlations were observed between soil GEM, THg and soil temperature, and intensive measurements made at small spatial scales (∼1 m) demonstrated the representativeness of individual sampling points. By adapting an active sampling gradient method for determining soil–air gas fluxes, we estimate an Icelandic geothermal GEM flux of 1.8 kg a and a total Icelandic GEM flux, including non-geothermal areas, of ∼18 kg a. This work shows that Icelandic geothermal activity can generate high GEM and THg concentrations in the local soil environment, but its contribution to global Hg cycling appears to be minor.

中文翻译：

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冰岛地热活动产生的汞：土壤中富集度高，大气中排放量低


地热活动是地表环境中汞 (Hg) 的天然来源，但作为更大的地源通量对全球汞预算的一部分，人们对它的贡献知之甚少，部分原因是排放数据存在巨大的地理差距，尚未进行测量。在这项研究中，我们报告了 2021 年和 2022 年在高度活跃的火山岛国冰岛进行的实地考察结果。通过在扩散脱气表面进行的一系列测量，对全国六个地热点的土壤气态元素汞 (GEM) 和总汞 (THg) 浓度进行了调查。在 10 厘米深度，土壤 GEM 浓度通常比周围表面空气浓度高数百倍，在某些情况下高数千倍。由于热液汞在细小热变粘土和粉砂上的吸附，地热土壤中 THg 也高度富集。土壤“热点”显示 THg 浓度超过 100 µg g，与受人类活动严重污染的地区和富含汞的矿质土壤的水平相当。土壤GEM、THg和土壤温度之间观察到很强的相关性，并且在小空间尺度（~1 m）上进行的密集测量证明了各个采样点的代表性。通过采用主动采样梯度法来确定土壤-空气气体通量，我们估计冰岛地热 GEM 通量为 1.8 kg a，冰岛 GEM 总通量（包括非地热区域）约为 18 kg a。这项工作表明，冰岛地热活动可以在当地土壤环境中产生高浓度的 GEM 和 THg，但其对全球汞循环的贡献似乎很小。