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Rethinking recovery rates from mercury (Hg) pollution by reconciling evasion of legacy Hg pollution from peatlands with historical records of Hg accumulation and isotope signatures in peat profiles
PI: Chuxian Li
Anthropogenic mercury (Hg) emissions to the atmosphere have increased the concentration of this potent neurotoxin in terrestrial and aquatic ecosystems. Efforts to control this pollution have reduced atmospheric concentrations of gaseous elemental mercury (GEM) over Fennoscandia by 50% in the past 30 years. The first annual Hg mass-balance for a boreal peatland that measured peat-atmosphere exchange revealed so much evasion of the Hg pollution legacy from the peat back to the atmosphere that the mire will have recovered in decades, rather than in centuries as previously assumed. Producing this mass balance was a methodological challenge, but explaining it presents a scientific challenge. We propose that the long history of atmospheric Hg pollution, followed by sharp reductions in atmospheric Hg concentrations, switched the peatland from being a net accumulator of atmospheric Hg for millennia to suddenly becoming a net GEM emitter to the surrounding environment. We propose to test whether a recent reversal in the direction of Hg exchange between peatlands and atmosphere can be modeled by changing GEM concentrations. This model will be constrained by historical peat archives of Hg concentration and isotopic composition, as well as novel measurements of pore atmosphere Hg isotopes. This will provide information on the effectiveness of Hg emission controls for reducing Hg contamination in freshwater fish where peatlands influence aquatic Hg bioaccumulation.