University of Toronto Scarborough, Department of Physical and Environmental Sciences, 1265 Military Trail, Toronto, Ontario M1C 1A4, Canada; University of Toronto, Department of Geography, 100 St. George Street, Toronto, Ontario M5S 3G3, Canada.
Michigan Technological University, School of Forest Resources and Environmental Science, Houghton, MI 49931, USA; USDA Forest Service Northern Research Station, Houghton, MI 49931, USA.
Sci Total Environ. 2019 Sep 10;682:611-622. doi: 10.1016/j.scitotenv.2019.05.072. Epub 2019 May 11.
Climate change is expected to alter the hydrology and vascular plant communities in peatland ecosystems. These changes may have as yet unexplored impacts on peat mercury (Hg) concentrations and net methylmercury (MeHg) production. In this study, peat was collected from PEATcosm, an outdoor, controlled mesocosm experiment where peatland water table regimes and vascular plant functional groups were manipulated over several years to simulate potential climate change effects. Potential Hg(II) methylation and MeHg demethylation rate constants were assessed using enriched stable isotope incubations at the end of the study in 2015, and ambient peat total Hg (THg) and MeHg concentration depth profiles were tracked annually from 2011 to 2014. Peat THg and MeHg concentrations and the proportion of THg methylated (%MeHg) increased significantly within the zone of water table fluctuation when water tables were lowered, but potential Hg(II) methylation rate constants were similar regardless of water table treatment. When sedges dominate over ericaceous shrubs, MeHg concentrations and %MeHg became significantly elevated within the sedge rooting zone. Increased desorption of Hg(II) and MeHg from the solid phase peat into pore water occurred with a lowered water table and predominant sedge cover, likely due to greater aerobic peat decomposition. Deeper, more variable water tables and a transition to sedge-dominated communities coincided with increased MeHg accumulation within the zone of water table fluctuation. Sustained high water tables promoted the net downward migration of Hg(II) and MeHg. The simultaneous decrease in Hg(II) and MeHg concentrations in the near-surface peat and accumulation deeper in the peat profile, combined with the trends in Hg(II) and MeHg partitioning to mobile pore waters, suggest that changes to peatland hydrology and vascular plant functional groups redistribute peat Hg(II) and MeHg via vertical hydrochemical transport mechanisms.
预计气候变化将改变泥炭地生态系统的水文和维管植物群落。这些变化可能对泥炭汞（Hg）浓度和净甲基汞（MeHg）产生尚未被探索的影响。在这项研究中，从 PEATcosm 采集了泥炭，PEATcosm 是一个户外控制中观实验，在过去几年中，通过操纵泥炭地地下水位制度和维管植物功能群来模拟潜在的气候变化影响。在 2015 年底的研究中，使用富集中稳定同位素孵育评估了潜在的 Hg(II)甲基化和 MeHg 脱甲基速率常数，并且从 2011 年到 2014 年每年跟踪跟踪泥炭总汞（THg）和 MeHg 浓度的深度分布。当降低地下水位时，泥炭 THg 和 MeHg 浓度以及 THg 甲基化的比例（%MeHg）在地下水位波动带内显著增加，但无论地下水位处理如何，潜在的 Hg(II)甲基化速率常数相似。当莎草科植物超过石南科灌木占主导地位时，MeHg 浓度和 %MeHg 在莎草根区显著升高。随着地下水位降低和莎草覆盖度增加，更多的 Hg(II)和 MeHg 从固相泥炭中解吸到孔隙水中，这可能是由于有氧泥炭分解增加所致。更深、更具变异性的地下水位和向莎草为主的群落的转变，与地下水位波动带内 MeHg 的积累增加相一致。持续高水位促进了 Hg(II)和 MeHg 的净向下迁移。近地表泥炭中 Hg(II)和 MeHg 浓度的同时下降以及在泥炭剖面较深的地方积累，加上 Hg(II)和 MeHg 分配到可移动孔隙水中的趋势，表明泥炭地水文和维管植物功能群的变化通过垂直水化学输运机制重新分配泥炭 Hg(II)和 MeHg。
