Peatlands are a major source of methylmercury that contaminates downstream aquatic food webs. The large store of mercury (Hg) in peatlands could be a source of Hg for over a century even if deposition is dramatically reduced. However, the reliability of Hg mass balances can be questioned due to missing long-term land-atmosphere flux measurements. We used a novel micrometeorological system for continuous measurement of Hg peatland-atmosphere exchange to derive the first annual Hg budget for a peatland. The evasion of Hg (9.4 µg m−2 yr−1) over the course of a year was seven times greater than stream Hg export, and over two times greater than wet bulk deposition to the boreal peatland. Measurements of dissolved gaseous Hg in the peat pore water also indicate Hg evasion. The net efflux may result from recent declines in atmospheric Hg concentrations that have turned the peatland from a net sink into a source of atmospheric Hg. This net Hg loss suggests that open boreal peatlands and downstream ecosystems can recover more rapidly from past atmospheric Hg deposition than previously assumed. This has important implications for future levels of methylmercury in boreal freshwater fish and the estimation of historical Hg accumulation rates from peat profiles.
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机译:泥炭地是甲基汞的主要来源,它污染了下游水生食物网。即使沉积物大大减少了,一个世纪以来,泥炭地中大量的汞(Hg)仍可能是汞的来源。但是,由于缺少长期的陆地-大气通量测量,汞质量平衡的可靠性可能会受到质疑。我们使用一种新颖的微气象系统来连续测量汞泥炭地-大气交换,以得出泥炭地的第一个年度汞预算。一年中汞的逸出量(9.4 µg m −2 sup> yr −1 sup>)是流汞出口量的七倍,是湿流汞出口量的两倍以上大量沉积到北方泥炭地。泥炭孔隙水中溶解的气态汞的测量结果也表明汞逸出。净流出可能是由于近期大气汞浓度的下降而导致的,这使泥炭地从净汇变成大气汞的来源。汞的净损失表明,开放的北方泥炭地和下游生态系统可以从过去的大气汞沉积中更快地恢复。这对北方淡水鱼中甲基汞的未来水平以及根据泥炭剖面估算历史汞累积速率具有重要意义。
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