Gaseous mercury emissions from soil following forest loss and land use changes: Field experiments in the United States and Brazil

Forest ecosystems are a sink of atmospheric mercury, trapping the metal in the canopy, and storing it in the forest floor after litter fall. Fire liberates a portion of this mercury; however, little is known about the long-term release of mercury post deforestation. We conducted two large-scale experiments to study this phenomenon. In upstate New York, gaseous mercury emissions from soil were monitored continually using a Teflon dynamic surface flux chamber for two-weeks before and after cutting of the canopy on the edge of a deciduous forest. In Brazil, gaseous mercury emissions from soil were monitored in an intact Ombrophilous Open forest and an adjacent field site both before and after the field site was cleared by burning. In the intact forest, gaseous mercury emissions from soil averaged −0.73 ± 1.84 ng m−2 h−1 (24-h monitoring) at the New York site, and 0.33 ± 0.09 ng m−2 h−1 (daytime-only) at the Brazil site. After deforestation, gaseous mercury emissions from soil averaged 9.13 ± 2.08 ng m−2 h−1 in New York and 21.2 ± 0.35 ng m−2 h−1 at the Brazil site prior to burning. Gaseous mercury emissions averaged 74.9 ± 0.73 ng m−2 h−1 after burning of the cut forest in Brazil. Extrapolating our data, measured over several weeks to months, to a full year period, deforested soil is estimated to release an additional 2.30 g ha−1 yr−1 of gaseous mercury to the atmosphere in the Brazilian experiment and 0.41 g ha−1 yr−1 in the New York experiment. In Brazil, this represents an additional 50% of the mercury load released during the fire itself.