Mercury (Hg) in the environment poses a significant threat to human and ecological health, and is a major contaminant of concern for water quality. Anoxic sediments in wetlands, lakes, and reservoirs are hotspots for bacterially driven methylmercury (MeHg) production. The factors that influence the mercury cycle are varied, complex, and interrelated. As such, we used a mechanism-based reactive-transport model approach to assess the influence of climate change on various biological and abiotic processes that control net mercury methylation. We applied a thermodynamic-kinetic biogeochemical mercury model (using PHREEQC) to two sites in different climate zones: one in a polar climate with thawing permafrost soils and one in a temperate-Mediterranean climate zone experiencing reduced precipitation and intermittent drought. The model includes methylation reactions coupled to sulfate reduction, iron reduction, and methanogenesis, reductive and oxidative demethylation, and adsorption of Hg to organic matter. We investigated primary factors that influence net Hg methylation, including concentration and form of organic carbon (dissolved, solid, labile); complexation and surface sorption of Hg and availability for methylation; distribution of reduced and oxidized zones under different temperature regimes; and rates of Hg demethylation. Comparison of different model scenarios served to relate the effect of climate change on a global scale to Hg cycling on a local scale.

Assessment of the influence of climate change on mercury methylation on a molecular scale with a mechanistic reaction-transport model

253rd National Meeting (2017)

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