Assessing the potential for re-emission of mercury deposited in precipitation from arid soils using a stable isotope

A solution containing ¹⁹⁸Hg in the form of HgCl₂ was added to a 4 m² area of desert soils in Nevada, and soil Hg fluxes were measured using three dynamic flux chambers. There was an immediate release of ¹⁹⁸Hg after it was applied, and then emissions decreased exponentially. Within the first 6 h after the isotope was added to the soil, ∼12 ng m^-2 of ¹⁹⁸Hg was emitted to the atmosphere, followed by a relatively steady flux of the isotope at 0.2 ± 0.2 ng m^-2 h^-1 for the remainder of the experiment (62 days). Over this time, ∼200 ng m^-2 or 2% of the ¹⁹⁸Hg isotope was emitted from the soil, and we estimate that ∼6% of the isotope would be re-emitted in a year's time. During the experiment, dry deposition of elemental Hg from the atmosphere was measured with an average deposition rate of 0.2 ± 0.1 ng m^-2 h^-1. Emission of ambient Hg from the soil was observed after soil wetting with the isotope solution and after a storm event. However, the added moisture from the storm event did not affect ¹⁹⁸Hg flux. Results suggest that in this desert environment, where there is limited precipitation, Hg deposited by wet processes is not readily re-emitted and that dry deposition of elemental Hg may be an important process.