Mercury and Carbon Dynamics in Peatland Pore Water during Experimental Warming, Freezing and Thawing.

Biogeochemical processes in northern peatland ecosystems are influenced by seasonal temperature fluctuations that are altering with changes in climate. Mercury is a heavy metal that accumulates in peatland soils where inundation and biogeochemical conditions can lead to the bioaccumulative form methylmercury (MeHg). This study investigates how changes in temperature influences belowground concentrations of total mercury (THg), MeHg, and dissolved organic carbon (DOC) in peat pore waters. Four large peat columns were removed from an ombrotrophic peat bog and exposed to experimental warming, freezing, and thawing. Pore water was sampled across seven depths in the peat columns during the different temperature treatments and analyzed for THg, MeHg, and DOC concentrations. Results indicated that a 2°C air temperature increase during warming was not great enough to change the THg and MeHg concentrations in the peat pore water. Freezing resulted in significant decreases in THg and MeHg concentrations and showed evidence of THg exclusion from the ice structure. During thawing, THg concentrations significantly increased while MeHg concentrations remained low, likely because of low biological activity. These findings fill a gap in peatland research by providing data related to how the freeze-thaw cycle impacts mercury dynamics in peat pore water.