Mercury air/surface exchange over terrestrial background surfaces of the eastern United States and its policy implications

Quantifying the mercury (Hg) released from terrestrial surfaces and establishing background levels of Hg is important for constructing the global Hg budget and developing effective remediation strategies for point and non-point sources. Two systematic field campaigns examining the spatial and temporal variability of Hg-air surface exchange in forests in the eastern USA were conducted and compared to a separate study in an area without a canopy. A policy review and analysis of Hg abatement strategies were undertaken in association with the field results for considering a policy alternative to bridge the gap between the scientific and policy communities.; Mercury fluxes were collected for 11 months in 2004 within Standing Stone State Forest in Tennessee using the dynamic flux chamber method. The Hg fluxes for the litter-covered forest floor were very low (mean annual daytime flux = 0.4 +/- 0.5 ng m-2 h-1, n = 301). A seasonal trend of lower emission in the spring and summer (closed canopy) compared to the fall and winter (open canopy) seemed visible. Mercury fluxes were measured in the early summer of 2005 within various types of forests along the eastern seaboard from South Carolina to Maine. The fluxes were consistently very low and similar for the various forest types (overall daytime mean flux = 0.2 +/- 0.9 ng m-2 h-1, n = 310, for all six sites monitored). The mean soil Hg flux for the open site was 0.1 +/- 0.6 ng m-2 h-1 (n = 82). These three studies seem to suggest a spatial similarity for fluxes.; This research seems to suggest that the contribution to the global atmospheric pool by Hg from forested background surfaces is probably small and could be re-emission of Hg deposited. The temporal, rather than spatial, variability of the Hg flux may be more important. The factors driving Hg exchange found for enriched soils may not hold for these background surfaces. This indicates that in scaling Hg fluxes for terrestrial background systems, the flux from litter-covered surfaces and low Hg substrates void of canopies may be modeled collectively but more investigation is warranted to verify this approach.