Atmospheric mercury pollution due to losses of terrestrial carbon pools?

Abstract

Plants accumulate significant amounts of atmospheric mercury (Hg) in aboveground biomass, likely sequestering over 1,000 Mg of atmospheric Hg every year. This large mercury uptake could be strong enough to affect tropospheric Hg levels and might be partially responsible for seasonal variations in atmospheric Hg observed at Mace Head, Ireland. The fluctuations of Hg concentrations coincide temporally with the annual oscillation of carbon dioxide (CO2) in the Northern Hemisphere, which is a result of seasonal growth of vegetation. Therefore, declining Hg concentrations in spring and summer may be attributed in part to plant uptake of atmospheric Hg. Further, the increase of Hg concentrations during non-active vegetation periods might partially be due to plant-derived Hg emitting back to the atmosphere during carbon mineralization. The implications of these propositions are that past and future changes in biomass productivity and organic carbon pools may have had—and may continue to have—significant effects on atmospheric Hg levels. Specifically, large losses in soil and biomass carbon pools in the last 150 years could have contributed significantly to observed increases in atmospheric Hg pollution. The roles of vegetation and terrestrial carbon pools should receive detailed consideration on how they might attenuate or exacerbate atmospheric Hg pollution.