Examination of mercury inputs by throughfall and litterfall in the Great Smoky Mountains National Park

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Throughfall and litterfall represent two major pathways which comprise the bulk of the mercury that reaches the forest floor. In an effort to quantify total mercury deposition to forests, throughfall and litterfall samples were collected at three elevations in the Great Smoky Mountains National Park (GSMNP) between April and November in 2008 and 2009. The mean (±standard error) volume-weighted throughfall total mercury concentration across all three sites ranged from 13.62 ng L−1 (±0.86) to 18.23 ng L−1 (±0.77) with a slight trend of higher throughfall mercury concentration at the high elevation spruce-fir sites relative to the low elevation mixed-hardwood site. The mean (±standard error) throughfall total mercury deposition across all sites ranged from 2.07 μg m−2 (±0.09) to 4.09 μg m−2 (±0.38). Mean (±standard error) mass-weighted litterfall concentration ranged from 37.2 ng g−1 (±1.36) to 62.87 ng g−1 (±1.94) and statistically higher (p = 0.02, p < 0.05) mean concentrations were observed at the higher elevation sites. The mean (±standard error) litterfall mercury deposition across all three sites ranged from 10.34 μg m−2 (±0.69) to 29.30 μg m−2 (±0.44). Although, no statistically (p = 0.05, p < 0.05) significant difference was observed between the sites for either throughfall or litterfall deposition, both increased from 2008 to 2009 at the lower elevation site. Mean litterfall deposition (17.93 μg m−2) dominated Hg input for the two years studied over mean throughfall deposition (3.20 μg m−2). Meanwhile, the mean throughfall concentration (17.8 ng L−1) dominated the mean open area precipitation input (6.03 ng L−1) at the high elevation site, suggesting evidence for a dry deposition component from the forest canopy. While the study was limited in scope, the results do provide some basic data that adds to understanding Hg inputs to the terrestrial ecosystem in general and in the GSMNP specifically.