The prior post had discussed how climate change had influenced the introduction of mercury into arctic water bodies through permafrost slumping. As mentioned previously, elemental [Hg0] and ionic [Hg(II)] mercury undergoes biotic methylation through microbial activity into its more toxic form, methylmercury [MeHg]. These microbes contain a specific gene pair (hgcAB) and are found in some iron or sulphate reducing bacteria (Gilmour et al., 2018). At the same time, demethylation also occurs as a reaction to light and microbial activity. The rates of both methylation and demethylation are affected by climate change, with different responses in arctic freshwater and marine systems.

 

Freshwater systems

Figure 1: Thermal stratification of lake (Department of Environment and Science, Queensland, 2013)

In freshwater bodies like lakes, Hg methylation and demethylation occur mostly in the anoxic hypolimnion (Fig.1) and sediments, while photodemethylation is restricted to the upper sections of the water column (Lehnherr, 2014). A study by Jackson (2019) on Artic sediment cores to estimate MeHg production in the past 100 years had concluded that warming phrases of climate change had led to a decrease in net sediment methylation. This is due to the thermally induced alterations in the community structure of phytoplankton, which provide nutrients to microbes. Additionally, the input of organic carbon due to permafrost slumping could increase photodemethylation in clear lakes and decrease it in turbid systems (Braaten, 2018).

 

Marine systems

In marine systems, methylation occurs within the water column instead of in sediment (Chetelat et al., 2022) and is thought to be associated with the mineralisation of organic matter, which releases the bonded mercury (Zhang et al., 2020). Climate change is expected to increase the primary productivity of plankton, providing increased nutrients for the methylating microbes (Heimbürger et al., 2015). Conversely, the melting of sea ice may promote the irradiation of the sea’s surface, encouraging MeHg demethylation (Point et al., 2011).

 

Overall, climate change alters the rate of methylmercury production within Arctic water bodies, undergoing different processes within freshwater and marine systems. However, the ultimate effect of climate change on methylmercury production still remains unknown as the numerous interacting factors and processes within the Artic system have to be considered. With the rising global use of coal consumption (IEA, 2022) and its mercury by-products, the issue of Arctic mercury pollution will persist and may possibly worsen.

 

References

Braaten, H. F. V., de Wit, H. A., Larssen, T., & Poste, A. E. (2018). Mercury in fish from Norwegian lakes: The complex influence of aqueous organic carbon. The Science of the Total Environment, 627, 341–348.

Chételat, J., McKinney, M. A., Amyot, M., Dastoor, A., Douglas, T. A., Heimbürger-Boavida, L.-E., Kirk, J., Kahilainen, K. K., Outridge, P. M., Pelletier, N., Skov, H., St. Pierre, K., Vuorenmaa, J., & Wang, F. (2022). Climate change and mercury in the Arctic: Abiotic interactions. The Science of the Total Environment, 824, 153715–153715.

Department of Environment and Science, Queensland (2013) Coastal and subcoastal non-floodplain soil lake – Hydrology, WetlandInfo website, accessed 6 April 2023. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/ecology/aquatic-ecosystems-natural/lacustrine/non-floodplain-soil-lake/hydrology.html

Gilmour, C. C., Bullock, A. L., McBurney, A., Podar, M., Elias, D. A., & Oak Ridge National Lab. (ORNL), T. N. (U. S., Oak Ridge. (2018). Robust Mercury Methylation across Diverse Methanogenic Archaea. MBio, 9(2).

Heimbürger, L.-E., Sonke, J. E., Cossa, D., Point, D., Lagane, C., Laffont, L., Galfond, B. T., Nicolaus, M., Rabe, B., & van der Loeff, M. R. (2015). Shallow methylmercury production in the marginal sea ice zone of the central Arctic Ocean. Scientific Reports, 5(1), 10318–10318.

IEA. (2022, December 16). The world’s coal consumption is set to reach a new high in 2022 as the energy crisis shakes markets. International Energy Agency. Retrieved from: https://www.iea.org/news/the-world-s-coal-consumption-is-set-to-reach-a-new-high-in-2022-as-the-energy-crisis-shakes-markets

Jackson, T. A. (2019). Stratigraphic variations in the δ201Hg/δ199Hg ratio of mercury in sediment cores as historical records of methylmercury production in lakes. Journal of Paleolimnology, 61(4), 387–401.

Lehnherr, I., 2014. Methylmercury biogeochemistry: a review with special reference to Arctic aquatic ecosystems. Environ. Rev. 22 (3), 229–243.

Point, D., Moors, A. J., Hobson, K. A., Vander Pol, S. S., Pugh, R. S., Roseneau, D. G., Becker, P. R., Sonke, J. E., Donard, O. F. X., & Day, R. D. (2011). Methylmercury photodegradation influenced by sea-ice cover in Arctic marine ecosystems. Nature Geoscience, 4(3), 188–194.

Zhang, ZY., Li, G., Yang, L., Xin-Jun, W., & Guo-Xin, S. (2020). Mercury distribution in the surface soil of China is potentially driven by precipitation, vegetation cover and organic matter. In Environmental Sciences Europe.