Project Description

Objectives: Terrestrial carbon (C) pools play an important role in uptake, deposition, sequestration, and emission of atmospheric mercury (Hg). Biomass and soil C pools are highly sensitive to climate and land use changes with potentially serious consequences for the fate of an estimated 50,000 Mg of atmospheric Hg associated within C pools. Our overall objective is to assess how global change during the next 100 years is likely to affect Hg cycling processes (i.e., atmospheric Hg uptake, sequestration, and emission) associated with vegetation and soil C pools. We propose to assess how global change will affect plant-derived atmospheric Hg inputs to ecosystems via changes in plant productivity, plant senescence, and litterfall; and how global change impacts on plant, litter, and soil C pools will affect sequestered Hg within these pools and feedback on the future atmospheric Hg burden. Experimental approach: This proposed study includes a systematic determination of Hg in vegetation and soil C pools in terrestrial ecosystems, field and laboratory experimental studies, and modeling components. We aim to (1) collect the first systematic database on Hg pools and fluxes associated with terrestrial C pools by assessing C:Hg ratios of major ecosystem compartments in nine terrestrial ecosystems across the U.S. and combining these data with existing detailed data on plant and soil C pools and turnover rates; (2) perform controlled laboratory and field studies to clarify the fate of sequestered Hg pools during C mineralization (i.e., organic matter decomposition), specifically to what degree Hg is emitted back to the atmosphere; (3) statistically compare Hg pools and fluxes among climatically different sites to establish a hierarchy of climatic factors and drivers which control Hg pools and fluxes associated with terrestrial C; and (4) integrate acquired Hg data into an existing global change C model to scale up data to coterminous U.S. states and to enable prediction of how changes in C dynamics may affect the atmospheric Hg burden during the next 100 years. Expected results: Systematic quantification of Hg levels in major ecosystems will provide the first comprehensive database on Hg pools, plant Hg uptake, sequestration, and Hg turnover associated with terrestrial C pools in the U.S. Fate processes of Hg sequestered in C pools are fundamental to prediction of how anticipated C pool changes in the future will feedback on the future atmospheric Hg burden. Integration of Hg data into an existing global change C model will enable for prediction on how various global change scenarios will affect C-related Hg cycling. Our results will support formulation of strategies by land managers, policy makers, and stakeholders to mitigate atmospheric Hg and stabilize Hg sequestered in terrestrial C pools. Keywords: air pollution effects, atmosphere, biosphere, climate change, air quality, mercury cycling, soil carbon, global warming, human health, modeling, atmospheric deposition, volatilization, sorption.

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