A synthesis of rates and controls on elemental mercury evasion in the Great Lakes Basin.

Rates of surface-air elemental mercury (Hg(0)) fluxes in the literature were synthesized for the Great Lakes Basin (GLB). For the majority of surfaces, fluxes were net positive (evasion). Digital land-cover data were combined with representative evasion rates and used to estimate annual Hg(0) evasion for the GLB (7.7 Mg/yr). This value is less than our estimate of total Hg deposition to the area (15.9 Mg/yr), suggesting the GLB is a net sink for atmospheric Hg. The greatest contributors to annual evasion for the basin are agricultural (∼55%) and forest (∼25%) land cover types, and the open water of the Great Lakes (∼15%). Areal evasion rates were similar across most land cover types (range: 7.0-21.0 μg/m(2)-yr), with higher rates associated with urban (12.6 μg/m(2)-yr) and agricultural (21.0 μg/m(2)-yr) lands. Uncertainty in these estimates could be partially remedied through a unified methodological approach to estimating Hg(0) fluxes.