Assessing the role of deciduous forests in the biogeochemical cycle of mercury using quaking aspen (Populus tremuloides)

The role of vegetation in accumulating and transforming atmospheric mercury (Hg) was examined using stands of aspen grown within mesocosms in Hg-enriched soil (12 μg g−1). Approximately 80% of the total Hg that accumulated in the aboveground biomass was found in the leaves, and roughly 1% of that Hg was methylated. Aspen grown within the mesocosms in low Hg soil (0.03 μg g−1) exhibited foliar Hg concentrations similar to those of trees grown in the Hg-enriched soil, indicating that almost all of the Hg in the foliage originated from the atmosphere. Using a gas-exchange system, the net flux of Hg vapor for aspen grown in various soil Hg concentrations and exposed to different air Hg concentrations was measured. In low Hg air (2.4 ng m−3) foliage released Hg as a function of soil concentration, and in elevated Hg air (>11 ng m−3) deposition occurred as a function of air concentration.