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Thursday, January 08, 2009
12:30 PM - 2:00 PM
CNLS Conference Room (TA-3, Bldg 1690)


Terrestrial biogeochemistry of Mercury - a new model

Nicole Smith-Downey
University of Texas at Austin

The biogeochemical cycling of mercury (Hg) in the terrestrial environment is of critical importance in understanding the global Hg cycle. In soils, Hg(II) binds to reduced sulfur in organic material, and is protected against reduction until the organic matter is consumed. Here, we develop a global model of soil Hg storage and emissions that ties the lifetime of Hg in soils to the lifetime of the carbon pools it is associated with. Using both preindustrial and present-day simulations of Hg deposition to the land surface, we evaluate the influence of anthropogenic emissions on global Hg storage and emissions. We found that organic soils stored 219,765 Mg Hg in the year 2000, a 26% increase from preindustrial values (175,002 Mg). Mercury accumulates in the most recalcitrant soil pools, but the relative impact of anthropogenic emissions is largest in the most labile pools (280% increase). This may have implications for increases in methyl mercury production since the industrial revolution, because Hg associated with more labile pools is more likely to be methylated than Hg associated with more recalcitrant pools. We find that by the year 2000, decomposition of soils emits 650 Mg Hg yr-1 to the atmosphere, which is equivalent to 33% of anthropogenic emissions. We also show that there is significant inertia in the soil Hg system, and that if emissions continue at 2000 levels into the future, decomposition emissions will increase to 750 Mg yr-1 by 2050 and 950 Mg yr-1 by 2500.

Host: Rajan Gupta