View article

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. Increasing temperature led to increased THgporewater concentrations and these increases were correlated with physical (water table height) and chemical (pH, dissolved sulfate, total dissolved iron, solid-state sulfur speciation) environmental factors. The ratio of THgpeat to THgporewater decreased with warming, indicating that THg moved from the peat into porewater. In the top portion of the depth profile (0 cm to-40 cm), a net movement of THg from peat to porewater was observed with elevated CO2. This finding is likely due to indirect effects of elevated CO2 such as the lowering of the water table and changes in the proportion of plant species. Porewaters had more detectable changes in THg than peat. Peat with higher proportions of organic disulfide were observed to retain more THg in the solid phase than peat with higher proportions of organic monosulfide (thiols). Overall, we observed that temperature and CO2 had significant but subtle effects on THg in porewater. Our findings indicate with projected climate change, we …