An investigation of mercury dynamics in the pore water of peat columns during experimental warming, freezing, and thawing

Abstract

Biogeochemical processes in northern peatland ecosystems are influenced by seasonal temperature fluctuations that are becoming altered with changes in climate. Since mercury is commonly found in peatlands, it is important to understand how temperature impacts mercury dynamics. This study investigates how changes in temperature influences belowground concentrations of total mercury (THg), methylmercury (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 degree Celsius 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. Depth results showed increased bulk density and decreased THg, MeHg, and DOC after 15 cm, which may be indication of the mesotelm layer in the peat columns. 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.