Mercury in Throughfall and Litterfall Inputs and Stream Export in the Great Smoky Mountains National Park 2007 - 2009

Suzanne Fisher and Mark Wolfe
Tennessee Valley Authority

Several major mercury input and export pathways were sampled at three elevations in the Great Smoky Mountain National Park (GSMNP) between April and October during both 2007 and 2009. Throughfall (TF) which is precipitation that reaches the forest floor after falling through and interacting with the forest canopy and litterfall (LF) which are pieces and fragments of leaves, twigs, bark etc. that fall to the forest floor are two pathways which comprise the bulk of the mercury that reaches the forest floor and ultimately enters nutrient cycling pathways that bring mercury into various trophic levels of the forest ecosystem and eventually to aquatic ecosystems. In a discussion of the causal factors of increased mercury in the Tennessee River Valley and the Northern hemisphere (Joslin, 1994) identified the major inputs to water bodies and the transformational factors that either result in sequestration or higher concentrations of mercury in aquatic environments. Interestingly, Joslin identified Fontana Lake, which is bordered by the GSMNP, and other similar high elevation lakes in the Tennessee Valley as being potentially vulnerable to future increases in mercury levels in fish. This vulnerability was suggested to be attributable to the relatively low acid neutralizing capacity (ANC) and low nutrient levels of lake water which affect within-lake mechanisms that lessen the rate of mercury loss through volatilization and may increase mercury methylation. Mercury and its cycling within various environmental components are of concern to TVA because of the potential for adverse human health impacts in sensitive populations resulting from the presence of methylmercury in fish.

Mercury emissions from coal-fired power plants, particularly those in Asia, together with other various worldwide sources are primary contributors of mercury to the environment. It is thought that regional high elevation sites are potentially affected more than low elevation sites. This study is designed to generate some initial data that may provide some basic understanding of mercury movement within the terrestrial ecosystem of the GSMNP. Sampling was initiated in April 2007 and expanded and focused on primary mercury inputs and exports in 2008 and 2009. Reported here are the results from 2007 through current 2009 collection period.

This study is being carried out at three sites; two high elevation sites - Clingmans Dome (CD) at 6643 ft and Noland Divide (ND) at 5578 ft and a low elevation site - Noland Creek (NC) at 1945 ft. The CD and ND sites are coniferous forest composed of primarily fir (Abies fraseri) at the CD site and spruce (Picea rubens)