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首页> 外文期刊>Environmental Science & Technology >The Rise and Fall of Mercury Methylation in an Experimental Reservoir
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The Rise and Fall of Mercury Methylation in an Experimental Reservoir

机译：实验水库中甲基化的兴衰

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For the past 9 years, we experimentally flooded a wetland complex (peatland surrounding an open water pond) at the Experimental Lakes Area (ELA), northwestern Ontario, Canada, to examine the biogeochemical cycling of methyl mercury (MeHg) in reservoirs. Using input-output budgets, we found that prior to flooding, the wetland complex was a net source of approximately 1.7 mg MeHg ha{sup}(-1) yr{sup}(-1) to downstream ecosystems. In the first year of flooding, net yields of MeHg from the reservoir increased 40-fold to approximately 70 mg MeHg ha{sup}(-1) yr{sup}(-1). Subsequently, annual net yields of MeHg from the reservoir declined (10-50 mg MeHg ha{sup}(-1) yr{sup}(-1)) but have remained well above natural levels. The magnitude and timing of Hg methylation in the flooded peat portion of the wetland reservoir were very different than in the open water region of the reservoir. In terms of magnitude, net Hg methylation rates in the peat in the first 2 years of flooding were 2700 mg ha{sup}(-1) yr{sup}(-1), constituting over 97% of the MeHg produced at the whole-ecosystem level. But in the following 3 years, there was a large decrease in the mass of MeHg in the flooded peat due to microbial demethylation. In contrast, concentrations of MeHg in the open water region and in zooplankton, and body burdens of Hg in cyprinid fish, remained high for the full 9 years of this study. Microbial activity in the open water region also remained high, as evidenced by continued high concentrations of dissolved CO{sub}2 and CH{sub}4. Thus, the large short-term accumulation of MeHg mass in the peat appeared to have only a small influence on concentrations of MeHg in the biota; rather MeHg accumulation in biota was sustained by the comparatively small ongoing net methylation of Hg in the flooded pond where microbial activity remained high. In large reservoirs, where the effects of wind and fetch are greater than in the small experimental reservoir we constructed, differences can occur in the timing and extent of peat and soil erosion, effecting either transport of MeHg to the food chain or the fueling of microbial activity in open water sediments, both of which could have important long-term implications for MeHg concentrations in predatory fish.
机译：在过去的9年中，我们以实验方式在加拿大安大略省西北部的实验湖区（ELA）上淹没了湿地综合体（围绕开放水塘的草地），以检查水库中甲基汞（MeHg）的生物地球化学循环。使用投入产出预算，我们发现在洪水之前，湿地综合体是下游生态系统的净来源，大约为1.7 mg MeHg ha {sup}（-1）yr {sup}（-1）。在洪水的第一年，来自储层的MeHg净产量增加了40倍，达到约70 mg MeHg ha {sup}（-1）yr {sup}（-1）。随后，来自储层的MeHg的年净产量下降了（10-50 mg MeHg ha {sup}（-1）yr {sup}（-1）），但仍远高于自然水平。湿地水库水淹泥炭部分中汞甲基化的幅度和时间与水库开放水域中的汞甲基化程度和时机有很大不同。从数量上看，水淹头两年泥炭中的汞净甲基化率是2700 mg ha {sup}（-1）yr {sup}（-1），占整个甲基汞产量的97％以上-生态系统级别。但是在接下来的3年中，由于微生物脱甲基作用，淹没的泥炭中的MeHg的质量大大降低。相比之下，在整个研究过程的9年中，开放水域和浮游动物中的MeHg浓度以及塞浦路斯鱼类中Hg的身体负担仍然很高。开放水域中的微生物活性也仍然很高，这是由持续高浓度的溶解的CO {sub} 2和CH {sub} 4所证明的。因此，泥炭中大量的MeHg短期累积似乎对生物区系中的MeHg浓度只有很小的影响。相反，在充满微生物活性的高水淹池塘中，由于汞的甲基化持续进行，甲基汞在生物区系中的积累得以维持，汞的甲基化水平相对较低。在大型水库中，风和取水的影响大于我们建造的小型实验水库，泥炭和土壤侵蚀的时间和程度可能会发生差异，从而影响甲基汞向食物链的运输或微生物的加油在开放水域沉积物中的活性，这两者都可能对掠食性鱼类的甲基汞浓度具有重要的长期影响。

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