Few manipulative studies have investigated how the drivers of climate change such as warming, elevated carbon dioxide, and changes in precipitation regimes are predicted to influence peatland mercury cycling and subsequent bioaccumulation in downstream communities. Three studies have manipulated conditions to simulate climate change and measured mercury including The Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment in northern Minnesota, the BRACE (Biological Response to A Changing Environment) experiment in central Ontario, and the PEATCOSM experiment in northern Michigan. A synthesis of results indicates that warming increases both total mercury (THg) and methylmercury (MeHg) concentrations in peatland porewater with decreasing THg:MeHg ratios. Extreme hydrological events, either drought or heavy precipitation, also tends to lead to similar responses of increased water and soil THg, MeHg, and THg:MeHg ratios in the zone of water table fluctuations. Similarly, sedge treatments at PEATCOSM led to higher water and soil MeHg. Also, there is evidence that elevated carbon dioxide (eCO₂) increases MeHg pore water concentrations at SPRUCE likely associated increases with ecosystem primary productivity. That evidence is in line with recent research analyzing the long-term streamflow and MeHg concentration record for our reference peatland watershed at the Marcell Experimental Forest. That data indicates that MeHg in stream water has decreased over time due to improved air quality but could increase with increasing air temperatures because of increases in decomposition rates associated with higher watershed-level productivity.

¹ USDA Forest Service, Northern Research Station, Grand Rapids, MN

* Corresponding author: randall.k.kolka@usda.gov