| Summary: | Knowledge of the behavior and fate of Hg in the atmosphere is increasing. However, assessment of natural and anthropogenic sources is uncertain, the mechanisms by which Hg is removed from the atmosphere are poorly understood, and linkages between inputs of anthropogenic Hg, especially from the atmosphere, and the bioaccumulation MMHg in sensitive aquatic ecosystems has not yet been established. This project will address questions relating to natural and anthropogenic contributions from global and localized sources, the identification of Hg deposition with a regional origin (e.g., U.S.), and the examination of spatial and temporal trends (e.g., increases, declines) in atmospheric Hg deposition for predictive/modeling purposes. This research is focused on current measurement, reconstruction, quantification, and interpretation of the modern and historical variation in atmospheric Hg fluxes associated with the mid and sub-tropical latitudes of North America. Hypotheses Studies will take place in the lacustrine environs of the Tongass National Forest of southeastern Alaska and Cormack, Newfoundland. This work will be complemented by event-scale Hg and 210 Pb depositional investigations at the respective lake study-areas and at several key geographic regions which display a range of variation in Hg deposition as determined from the Mercury Deposition Network (MDN). The specific regions are the West Coast North America, Mid-Continent U.S., East Coast North America, and the southeastern U.S. Our program benefits from the cooperation and assistance of interested colleagues associated with current operations and facilities (National Parks, and the MDN sites). We will address the following hypotheses: 1) Atmospheric mercury deposition in southeastern Alaska can be viewed as an integrated sample of global Hg pollution in the Northern Hemisphere, and therefore represents a component of the Hg deposition experienced by sites closer to local and regional emission sources. 2) Atmospheric mercury deposition in Canada's maritime provinces is elevated above the northern hemispheric average by regional contributions from the industrialized Northeast/Midwest and can be separated into global and regional components by a comparison of sedimentary archives. 3) The linear correlation between Hg and 210 Pb found in rainwater from other remote and semi-remote locations is observed in southeastern Alaska, and this behavior can be used to constrain the global-scale wet atmospheric flux of Hg to lakes and watersheds of temperate North America. 4) At less remote sites, enhanced atmospheric Hg deposition that is locally/regionally derived, is indicated by deviations from Hg and 210 Pb relationship observed in southeastern Alaska. 5) Sediment archives will show, when corrected for climatology using 210 Pb, that the Pacific and Atlantic seaboards of North America received equivalent preindustrial atmospheric Hg fluxes, and provide a baseline for assessing the global component of anthropogenic Hg deposition at any given locality.
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