Influence of the Forest Canopy on Total and Methyl Mercury Deposition in the Boreal Forest

Abstract

Atmospheric mercury deposition by wet and dry processes contributes mercury to terrestrial and aquatic systems. Factors influencing the amount of mercury deposited to boreal forests were identified in this study. Throughfall and open canopy precipitation samples were collected in 2005 and 2006 using passive precipitation collectors from pristine sites located across the Superior National Forest in northern Minnesota, USA. Samples were collected approximately every 2 weeks and analyzed for total (THg) and methyl mercury (MeHg). Forest canopy type and density were the primary influences on THg and MeHg deposition. Highest THg and MeHg concentrations were measured beneath conifer canopies (THg mean=19.02 ng L −1 ; MeHg mean=0.28 ng L −1 ) followed by deciduous throughfall (THg mean= 12.53 ng L −1 ; MeHg mean=0.19 ng L −1 ) then open precipitation (THg mean=8.19 ng L −1 ; MeHg mean= 0.12 ng L −1 ). The greater efficiency of conifers at scavenging THg and MeHg from the atmosphere may increase the risk of mercury related water quality issues in conifer-dominated systems.

Atmospheric gaseous elemental mercury (GEM) concentrations and mercury depositions at a high-altitude mountain peak in south China

“…This was probably due to dry deposition of MeHg to foliage. The average fractions of THg present as MeHg in precipitation and throughfall were 1% and 1.1%, respectively, which were comparable or lower than values reported for Europe and North America (Porvair and Verta, 2003;Hall et al, 2005;Witt et al, 2009), as well as an upland forest in Mt. Gongga in southwest China (Fu et al, 2010).…”

“…Leigong were comparable or lower than those reported in North America and Europe (Schwesig and Matzner, 2000;St. Louis et al, 2001;Hall et al, 2005;Choi et al, 2008;Witt et al, 2009). This is quite different from atmospheric GEM concentrations, which were elevated compared to sites in Europe and North America.…”

Terrestrial organic matter biomarkers as tracers of Hg sources in lake sediments

“…Moreover fluxes of T-Hg in forest floor leachates are lower in coniferous stands than in deciduous stand, with a difference in annual T-Hg fluxes estimated at 23% with respect to vegetation composition for lakes in the Adirondak region (Demers et al 2007). Several studies have also shown that open forest areas, grasslands and scrublands are sites of lower Hg deposition leading to reduced [T-Hg] in litterfall as in addition to lower Hg fluxes in soils (Sheehan et al 2006;Poulain et al 2007;Nelson et al 2007;Witt et al 2008). Second, in these studied watersheds, a previous study revealed that coniferous and open areas are mainly found in very low slope and illdrained areas that act as buffer zones for TOM transfer to the lake (Teisserenc 2009).…”

“…Second, in these studied watersheds, a previous study revealed that coniferous and open areas are mainly found in very low slope and illdrained areas that act as buffer zones for TOM transfer to the lake (Teisserenc 2009). These results are particularly significant as the role of vegetation on Hg uptake and transfer in a watershed is a key parameter to understand Hg cycle in the boreal ecosystem (Grigal 2003;Sheehan et al 2006;Demers et al 2007;Poulain et al 2007;Witt et al 2008).…”

Modeling and Mapping of Atmospheric Mercury Deposition in Adirondack Park, New York

“…We calculated throughfall Hg deposition from precipitation Hg deposition by adjusting to an enrichment factor K (i.e., the ratio of throughfall/precipitation Hg deposition fluxes). The enrichment factor K varies by tree type [60], which differ in their ability to capture, adsorb, and mobilize Hg forms. For the deciduous forest, we used an enrichment factor of 1.03 (throughfall Hg deposition 12.0 g m yr, and precipitation Hg deposition 11.6 g m yr) found by Choi et al [61] for the deciduous forest in the Adirondacks.…”