Desert Research Institute, Division of Atmospheric Sciences, Reno, Nevada 89512, USA.
Sci Total Environ. 2010 Mar 1;408(7):1691-700. doi: 10.1016/j.scitotenv.2009.12.008. Epub 2010 Jan 13.
Mercury (Hg) levels in terrestrial soils are linked to the presence of organic carbon (C). Carbon pools are highly dynamic and subject to mineralization processes, but little is known about the fate of Hg during decomposition. This study evaluated relationships between gaseous Hg emissions from soils and carbon dioxide (CO(2)) respiration under controlled laboratory conditions to assess potential losses of Hg to the atmosphere during C mineralization. Results showed a linear correlation (r(2)=0.49) between Hg and CO(2) emissions in 41 soil samples, an effect unlikely to be caused by temperature, radiation, different Hg contents, or soil moisture. Stoichiometric comparisons of Hg/C ratios of emissions and underlying soil substrates suggest that 3% of soil Hg was subject to evasion. Even minute emissions of Hg upon mineralization, however, may be important on a global scale given the large Hg pools sequestered in terrestrial soils and C stocks. We induced changes in CO(2) respiration rates and observed Hg flux responses, including inducement of anaerobic conditions by changing chamber air supply from N(2)/O(2) (80% and 20%, respectively) to pure N(2). Unexpectedly, Hg emissions almost quadrupled after O(2) deprivation while oxidative mineralization (i.e., CO(2) emissions) was greatly reduced. This Hg flux response to anaerobic conditions was lacking when repeated with sterilized soils, possibly due to involvement of microbial reduction of Hg(2+) by anaerobes or indirect abiotic effects such as alterations in soil redox conditions. This study provides experimental evidence that Hg volatilization, and possibly Hg(2+) reduction, is related to O(2) availability in soils from two Sierra Nevada forests. If this result is confirmed in soils from other areas, the implication is that Hg volatilization from terrestrial soils is partially controlled by soil aeration and that low soil O(2) levels and possibly low soil redox potentials lead to increased Hg volatilization from soils.
汞（Hg）水平与土壤中的有机碳（C）的存在有关。碳库高度动态，易受矿化过程的影响，但人们对 Hg 在分解过程中的命运知之甚少。本研究在受控实验室条件下评估了土壤气态 Hg 排放与二氧化碳（CO(2)）呼吸之间的关系，以评估 C 矿化过程中 Hg 向大气潜在损失的情况。结果表明，在 41 个土壤样本中，Hg 与 CO(2)排放之间存在线性相关性（r(2)=0.49），这种效应不太可能是由温度、辐射、不同的 Hg 含量或土壤湿度引起的。排放物和基础土壤基质的 Hg/C 比的化学计量比较表明，有 3%的土壤 Hg 发生了逸出。然而，即使在矿化过程中排放出极少量的 Hg，鉴于陆地土壤中封存的大量 Hg 库和 C 储量，这在全球范围内可能也是重要的。我们诱导了 CO(2)呼吸速率的变化，并观察到 Hg 通量的响应，包括通过改变腔室空气供应从 N(2)/O(2)（分别为 80%和 20%）变为纯 N(2)来诱导厌氧条件。出乎意料的是，在 O(2)剥夺后，Hg 排放几乎增加了四倍，而氧化矿化（即 CO(2)排放）大大减少。当用灭菌土壤重复进行时，这种对厌氧条件的 Hg 通量响应缺失，这可能是由于厌氧菌还原 Hg(2+)或间接的非生物效应（例如土壤氧化还原条件的改变）所致。本研究提供了实验证据，表明 Hg 的挥发，可能还有 Hg(2+)的还原，与内华达山脉两个森林土壤中的 O(2)可用性有关。如果这一结果在其他地区的土壤中得到证实，那么这意味着陆地土壤中的 Hg 挥发部分受土壤通气控制，土壤中低 O(2 水平和可能的低土壤氧化还原电位会导致土壤中 Hg 挥发增加。
