Using Mercury Stable Isotopes to Quantify Bidirectional Water-Atmosphere Hg(0) Exchange Fluxes and Explore Controlling Factors

Knowledgeof the bidirectional fluxes and Hg isotope fractionationduring water-atmosphere Hg(0) exchange remains limited. Thisstudy reports the MDF and odd-MIF of Hg isotopes as well as emissionand deposition fluxes during water-atmosphere Hg(0) exchangeprocesses. In this study, exchange fluxes andHg isotope fractionation duringwater-atmosphere Hg(0) exchange were investigated at threelakes in China. Water-atmosphere exchange was overall characterizedby net Hg(0) emissions, with lake-specific mean exchange fluxes rangingfrom 0.9 to 1.8 ng m(-2) h(-1), whichproduced negative & delta;Hg-202 (mean: -1.61 to -0.03 & PTSTHOUSND;)and & UDelta;Hg-199 (-0.34 to -0.16 & PTSTHOUSND;)values. Emission-controlled experiments conducted using Hg-freeair over the water surface at Hongfeng lake (HFL) showed negative & delta;Hg-202 and & UDelta;Hg-199 in Hg(0) emittedfrom water, and similar values were observed between daytime (mean & delta;Hg-202: -0.95 & PTSTHOUSND;, & UDelta;Hg-199: -0.25 & PTSTHOUSND;) and nighttime (& delta;Hg-202:-1.00 & PTSTHOUSND;, & UDelta;Hg-199: -0.26 & PTSTHOUSND;).Results of the Hg isotope suggest that Hg(0) emission from water ismainly controlled by photochemical Hg(0) production in water. Deposition-controlledexperiments at HFL showed that heavier Hg(0) isotopes (mean & epsilon;Hg-202: -0.38 & PTSTHOUSND;) preferentially deposited to water,likely indicating an important role of aqueous Hg(0) oxidation playedduring the deposition process. A & UDelta;Hg-200 mixing modelshowed that lake-specific mean emission fluxes from water surfaceswere 2.1-4.1 ng m(-2) h(-1) and deposition fluxes to water surfaces were 1.2-2.3 ng m(-2) h(-1) at the three lakes. Resultsfrom the this study indicate that atmospheric Hg(0) deposition towater surfaces indeed plays an important role in Hg cycling betweenatmosphere and water bodies.