Measurements of atmospheric elemental and oxidized mercury and dry deposition to a surrogate surface at a coastal estuary location in Central California

Atmospheric deposition is recognized as a potentially major source of mercury (Hg) to aquatic ecosystems. Hg deposition occurs with precipitation (wet), but also without precipitation (dry) mainly due to the high surface reactivity of the various species of gaseous oxidized mercury (GOM) (HgCl2, HgBr2, HgO, etc.). In some areas where rainfall is sparse or seasonal, dry deposition can be the dominant mechanism of removal of atmospheric Hg and a potential source to aquatic systems. As part of a larger study to quantify inputs of total Hg and monomethyl mercury sources to estuaries along the West Coast of the U.S., the objective of these measurements was to evaluate the atmospheric component of Hg input in order to construct an Hg mass balance for these locations. Measurements of gaseous elemental Hg (GEM), GOM, and deposition of GOM were carried out during the fall of 2009 at Elkhorn Slough on the Monterey Bay, Central California. GEM and GOM were measured with a Tekran 2537/1130 automated system and GOM deposition was measured by deploying a novel passive technique which involves collecting and analyzing ion-exchange membranes for total Hg. These membranes have been shown to take up and retain GOM and not GEM, thereby providing an estimate of dry deposition without the use of micrometeorological models. In this work, preliminary data will be presented and compared with other available data for the region to assess the importance of Hg dry deposition on total Hg input to Elkhorn Slough.