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

A solution containing Hg-198 in the form of HgCl2 was added to a 4 m(2) area of desert soils in Nevada, and soil Hg fluxes were measured using three dynamic flux chambers. There was an immediate release of Hg-198 after it was applied, and then emissions decreased exponentially. Within the first 6 h after the isotope was added to the soil, similar to 12 ng m(-2) of Hg-198 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, similar to 200 ng m(-2) or 2% of the Hg-198 isotope was emitted from the soil, and we estimate that similar to 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.