Assessing the Potential for Re-emission of Mercury Deposited in Precipitation from Arid Soils Using a Stable Isotope

摘要

A solution containing ~(198)Hg in the form of HgCl_2 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 ~(198)Hg after it was applied,and then emissions decreased exponentially.Within the first 6 h after the isotope was added to the soil,approx 12 ng m~(-2) of ~(198)Hg 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,approx 200 ng m~(-2) or 2% of the ~(198)Hg isotope was emitted from the soil,and we estimate that approx 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 ~(198)Hg 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.