Whole-Ecosystem Climate Manipulation Effects on Total Mercury within a Boreal Peatland

Abstract

Abstract Mercury is a ubiquitous pollutant that accumulates in peatlands, an ecosystem highly sensitive to climate change. We examined the effects of increasing temperature and elevated atmospheric carbon dioxide (CO2) on the concentration of total mercury (THg) in peatland soil and porewater. This research was performed at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment, an ecosystem-scale manipulation in an ombrotrophic bog in northern Minnesota, USA, which includes five temperature levels (above- and below-ground warming), with ambient or enhanced CO2 concentration. The effect of temperature on THgporewater concentration was dependent on depth but overall, increasing temperature led to increased THgporewater concentrations. The ratio of THgpeat to THgporewater decreased, indicating that THg moved from the peat into porewater under warmer conditions. Increased temperature resulted in decreased water table height, and as the water table dropped, increased THgporewater concentrations were observed, as well as decreased THgpeat concentration. The effect of elevated CO2 on THg concentrations in peat and porewater was less clear but in the top portion of the depth profile (0 cm to -40 cm), a negative correlation between elevated CO2 and THgpeat and a positive correlation between elevated CO2 and THgporewater concentration was observed. Our findings indicate with projected climate change, we may see enhanced concentrations of mercury in peatland porewaters that are available for export to surface waters, with potential implications for bioaccumulation in downstream aquatic communities.