Featured Research Highlight

Warming Increases Methylmercury Production in Arctic Soils

The Science

Climate warming not only influences the degradation of stored soil organic carbon and climate feedback but also the production and bioaccumulation of methylmercury toxins in natural ecosystems. Researchers determined the effects of warming on methylmercury production in an Arctic soil during an eight-month anoxic incubation experiment and found that net methylmercury production increased >10 fold in a permafrost active layer soil of 8°C compared to colder (-2°C) temperatures. More importantly, it was found that the biosynthesis of methylmercury is strongly coupled with processes such as methanogenesis and iron reduction during soil organic carbon degradation.

The Impact

Results show that climate warming and permafrost thaw could potentially enhance methylmercury toxin production by an order of magnitude, impacting Arctic terrestrial and aquatic ecosystems by increased exposure to mercury through bioaccumulation and biomagnification in the food web.

Summary

Rapid temperature rise in Arctic permafrost impacts not only the degradation of stored soil organic carbon (SOC) and climate feedback, but also the production and bioaccumulation of methylmercury (MeHg) toxin that can endanger humans, as well as wildlife in terrestrial and aquatic ecosystems. Little is known concerning the effects of rapid permafrost thaw on microbial methylation and how SOC degradation is coupled to MeHg biosynthesis. Here we describe the effects of warming on MeHg production in an Arctic soil during an eight-month anoxic incubation experiment. Net MeHg production increased >10 fold in both organic- and mineral-rich soil layers at 8°C compared to colder (-2°C) temperatures. The type and availability of labile soil organic carbon (SOC), such as reducing sugars and ethanol, were particularly important in fueling the rapid initial biosynthesis of MeHg. Freshly amended mercury was more readily methylated than preexisting mercury in the soil. Additionally, positive correlations between mercury methylation and methane and ferrous ion production indicate linkages between SOC degradation and MeHg production. These results show that climate warming and permafrost thaw could potentially enhance MeHg production by an order of magnitude, impacting Arctic terrestrial and aquatic ecosystems by increased exposure to mercury through bioaccumulation and biomagnification in the food web.

Publication

Yang, Z., W. Fang, X. Lu, G. Sheng, D. E. Graham, L. Liang, S. D. Wullschleger, and B. Gu. 2016. “Warming Increases Methylmercury Production in an Arctic Soil.” Environmental Pollution 214: 504-509. DOI: 10.1016/j.envpol.2016.04.069

Metadata: Organic Carbon Transformation and Mercury Methylation in Tundra Soils from Barrow Alaska. DOI:10.5440/1235032

 

The ORNL Mercury SFA is sponsored by the Subsurface Biogeochemical Research (SBR) program within the U.S. Department of Energy's Office of Biological and Environmental Research.