AS A CLASS I AREA, ACADIA NATIONAL PARK (Maine) is afforded the highest level of air quality protection under the federal Clean Air Act Amendments (1990). Acadia hosts the highest peaks along the East Coast (~1,530 feet [466 m]), and its steep slopes and proximity to coastal fog create an environment conducive to intercepting polluted air masses (Weathers et al. 1986). Investigators have documented elevated deposition of contaminants, including mercury (Hg), at Acadia (Norton et al. 1997; Bank et al. 2007; Johnson et al. 2007; Kahl et al. 2007), which in certain areas of the park causes at least as much Hg contamination in tree swallow chicks and eggs as in birds living at a mercury-contaminated Superfund site in Massachusetts (Longcore et al. 2007).

PRIMENet, a long-term watershed research program at Acadia (Tonnessen and Manski 2007), has shown that the legacy of wildfire affects Hg in watersheds and biota for decades or longer (Bank et al. 2005; Johnson et al. 2007; Kahl et al. 2007). Because their needles have more surface area than deciduous leaves and they keep their foliage year-round, coniferous forests, like the spruce-.r forests of an unburned Acadia watershed, are more effective than postfire deciduous forests at canopy scavenging of atmospheric Hg (Grigal 2002; Johnson et al. 2007). That is, conifer forests collect more dust and dry particles on their foliage than deciduous trees. Dry-deposited Hg is washed to the forest floor in subsequent rain, fog, and snow events and collected as “throughfall” (Grigal 2002; Miller et al. 2005; Weathers et al. 2006; Johnson et al. 2007). Throughfall allows investigators to assess deposition across heterogeneous, forested areas by deploying a large number of samplers and comparing chemistry data with patterns in landscape features (Weathers et al. 2006).

Reports in the scientific literature suggested that Hg concentrations in snow throughfall might be low, though data were sparse (Nelson 2007). Therefore, the goal of this research was to collect winter throughfall Hg data and assess Hg mobility in forested research watersheds in Acadia to establish the importance of this Hg load to the terrestrial ecosystem (Nelson 2007).