Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 36, Issue 23, Pages 5034-5040Publisher
AMER CHEMICAL SOC
DOI: 10.1021/es025572t
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The METAALICUS (Mercury Experiment To Assess Atmospheric Loading In Canada and the US) project is a whole ecosystem experiment designed to study the activity, mobility, and availability of atmospherically deposited mercury. To investigate the dynamics of mercury newly deposited onto a terrestrial ecosystem, an enriched stable isotope of mercury (Hg-202) was sprayed onto a Boreal forest subcatchment in an experiment that allowed us, for the first time, to monitor the fate of new mercury in deposition and to distinguish it from native mercury historically stored in the ecosystem. Newly deposited mercury was more reactive than the native mercury with respect to volatilization and methylation pathways. Mobility through runoff was very low and strongly decreased with time because of a rapid equilibration with the large native pool of bound mercury. Over one season, only similar to8% of the added Hg-202 volatilized to the atmosphere and less than 1% appeared in runoff. Within a few months, approximately 66% of the applied Hg-202 remained associated with above ground vegetation, with the rest being incorporated into soils. The fraction of 202Hg bound to vegetation was much higher than seen for native Hg (<5% vegetation), suggesting that atmospherically derived mercury enters the soil pool with a time delay, after plants senesce and decompose. The initial mobility of mercury received through small rain events or dry deposition decreased markedly in a relatively short time period, suggesting that mercury levels in terrestrial runoff may respond slowly to changes in mercury deposition rates.
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