Impacts of anthropogenic emissions and meteorology on mercury deposition over lake vs land surface in upstate New York.

Atmospheric deposition is a major input of mercury (Hg) to aquatic and terrestrial ecosystems. To evaluate Hg pollution mitigation strategies for inland lakes, the two Great Lakes (Ontario and Erie) adjacent to New York State (NYS), and rural land areas of Upstate New York, the relative contributions to atmospheric Hg deposition from anthropogenic emission reductions and meteorological variations were investigated using a regional three-dimensional chemical transport model with detailed Hg and bromine chemistry (CMAQ-newHg-Br). Our simulations suggested that NYS in-state emissions and the Northeastern US emission reductions from 2005 to 2011 did not significantly alter Hg wet and dry deposition in all study areas when averaged over time and space. However, such emission changes significantly altered intensive emission sources (>10 lb/year) with subsequent effects on deposition to nearby water bodies. For the Great Lakes, Hg dry deposition was enhanced by a factor of 2-5 in the adjacent model grids (within distances of ~12 km downwind), and the enhancements decreased to negligible values over ~50 km distances. Over land, anthropogenic emissions contributed 30% of the spatial variation in Hg dry deposition and 46% in ambient concentrations of gaseous oxidized Hg (GOM). Spatial and temporal variations in meteorology and foliar characteristics were found to affect both Hg wet and dry deposition. Convective precipitation significantly contributed to spatial and seasonal variations (~65%) in Hg wet deposition over both lake and land surfaces, whereas wind speed and surface heat flux were the main factors contributing to the spatial variation in Hg dry deposition over the lake surfaces through their impacts on dry deposition velocities of GOM and PBM. Leaf area index, which regulates deposition velocity, contributed 14% of the spatial variation in dry deposition flux over land. Variation in solar radiation, which influences photochemical formation of GOM and PBM, explained ~10% of the spatial variation over lake and land surfaces alike. Findings from our highly focused study suggested broad implications. Future climate change will likely serve to enhance Hg concentrations in biota via increases in Hg dry and wet deposition to varying degrees contingent on land surface type. Hence, liminating the health risks of Hg requires mitigation of both anthropogenic Hg emission hotspots and human-induced climate change.