Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83, Umeå, Sweden.
Department of Environmental Sciences, University of Basel, 4056, Basel, Switzerland.
Sci Rep. 2017 Nov 22;7(1):16022. doi: 10.1038/s41598-017-16141-7.
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 yr) 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.
泥炭地是甲基汞的主要来源，会污染下游的水生食物网。泥炭地中大量的汞（Hg）即使沉积量大大减少，也可能在一个多世纪内成为 Hg 的来源。然而，由于缺少长期的陆地-大气通量测量，Hg 质量平衡的可靠性可能受到质疑。我们使用一种新颖的微气象系统对 Hg 泥炭地-大气交换进行连续测量，得出了第一个泥炭地的年度 Hg 预算。在一年的时间里，Hg 的逸出量（9.4μg m yr）是溪流 Hg 输出量的七倍，是湿沉降到北方泥炭地的两倍多。泥炭孔隙水中溶解气态 Hg 的测量也表明 Hg 逸出。净通量可能是由于大气 Hg 浓度的最近下降，使泥炭地从一个净汇变成了大气 Hg 的源。这种净 Hg 损失表明，与之前的假设相比，开阔的北方泥炭地和下游生态系统可以从过去的大气 Hg 沉积中更快地恢复。这对北方淡水鱼类中甲基汞的未来水平以及从泥炭剖面估算历史 Hg 积累率具有重要意义。
