Dep. of Forest Resources, Univ. of Minnesota, 1530 Cleveland Ave. N, St. Paul, MN, 55108.
Northern Research Station, USDA Forest Service, 1831 Hwy 169 East, Grand Rapids, MN, 55744.
J Environ Qual. 2020 Mar;49(2):404-416. doi: 10.1002/jeq2.20046. Epub 2020 Mar 6.
Biogeochemical processes in northern peatland ecosystems are influenced by seasonal temperature fluctuations that are changing with the climate. Methylmercury (MeHg), commonly produced in peatlands, affects downstream waters; therefore, it is important to understand how temperature transitions affect mercury (Hg) dynamics. We investigated how the freeze-thaw cycle influences belowground peat pore water total Hg (THg), MeHg, and dissolved organic carbon (DOC). Four large, intact peat columns were removed from an ombrotrophic peat bog and experimentally frozen and thawed. Pore water was sampled across seven depths in the peat columns during the freeze-thaw cycle and analyzed for THg, MeHg, and DOC concentrations. Freezing results showed increased concentrations of THg below the ice layers and limited change in MeHg concentrations. During thawing, THg concentrations significantly increased, whereas MeHg concentrations decreased. Limited bromide movement and depth decreases in THg and DOC concentrations were associated with increased bulk density and degree of humification in the peat. The experiment demonstrates the effects of the freeze-thaw cycle on Hg concentrations in northern peatlands. Changes to freeze-thaw cycles with climate change may exacerbate Hg cycling and transport processes in peatland environments.
受气候变化影响，北方泥炭地生态系统的生物地球化学过程受到季节性温度波动的影响。在泥炭地中普遍产生的甲基汞（MeHg）会影响下游水域；因此，了解温度变化如何影响汞（Hg）动态变化很重要。我们研究了冻融循环如何影响地下泥炭孔隙水中总汞（THg）、MeHg 和溶解有机碳（DOC）。从一个寡营养泥炭沼泽中取出四个大型完整的泥炭柱进行了实验性的冻结和融化。在冻融循环期间，从泥炭柱的七个深度采样了孔隙水，并分析了 THg、MeHg 和 DOC 浓度。冻结结果表明，冰层下方的 THg 浓度增加，而 MeHg 浓度变化有限。在解冻过程中，THg 浓度显著增加，而 MeHg 浓度下降。溴化物的移动有限，THg 和 DOC 浓度的深度降低与泥炭中较大的密度和腐殖化程度增加有关。该实验证明了冻融循环对北方泥炭地中 Hg 浓度的影响。气候变化引起的冻融循环变化可能会加剧泥炭地环境中 Hg 的循环和迁移过程。
