Importance of the Forest Canopy to Fluxes of Methyl Mercury and Total Mercury to Boreal Ecosystems

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• 作者：Vincent L. St. Louis ; John W. M. Rudd ; Carol A. Kelly ; Britt D. Hall ; Kristofer R. Rolfhus ; Karen J. Scott ; Steve E. Lindberg ; and Weijin Dong
• 刊名：Environmental Science & Technology
• 出版年：2001
• 出版时间：August 1, 2001
• 年：2001
• 卷：35
• 期：15
• 页码：3089 - 3098
• 全文大小：266K
• 年卷期：v.35,no.15(August 1, 2001)
• ISSN：1520-5851

文摘

The forest canopy was an important contributor to fluxesof methyl mercury (MeHg) and total mercury (THg) to theforest floor of boreal uplands and wetlands and potentiallyto downstream lakes, at the Experimental Lakes Area (ELA),northwestern Ontario. The estimated fluxes of MeHg andTHg in throughfall plus litterfall below the forest canopy were2 and 3 times greater than annual fluxes by direct wetdeposition of MeHg (0.9 mg of MeHg ha^-1) and THg (71 mgof THg ha^-1). Almost all of the increased flux of MeHgand THg under the forest canopy occurred as litterfall (0.14-1.3 mg of MeHg ha^-1 yr^-1 and 110-220 mg of THg ha^-1yr^-1). Throughfall added no MeHg and approximately 9 mgof THg ha^-1 yr^-1 to wet deposition at ELA, unlike inother regions of the world where atmospheric depositionwas more heavily contaminated. These data suggest that drydeposition of Hg on foliage as an aerosol or reactivegaseous Hg (RGM) species is low at ELA, a finding supportedby preliminary measurements of RGM there. Annual totaldeposition from throughfall and litterfall under a fire-regenerated 19-yr-old jack pine/birch forest was 1.7 mg ofMeHg ha^-1 and 200 mg of THg ha^-1. We found thataverage annual accumulation of MeHg and THg in thesurficial litter/fungal layer of soils since the last forest firevaried between 0.6 and 1.6 mg of MeHg ha^-1 and between130 and 590 mg of THg ha^-1 among sites differing in drainageand soil moisture. When soil Hg accumulation siteswere matched with similar sites where litterfall andthroughfall were collected, measured fluxes of THg to theforest floor (sources) were similar to our estimates of long-term soil accumulation rates (sinks), suggesting that the Hgin litterfall and throughfall is a new and not a recycledinput of Hg to forested ecosystems. However, furtherresearch is required to determine the proportion of Hg inlitterfall that is being biogeochemically recycled withinforest and wetland ecosystems and, thus, does not representnew inputs to the forest ecosystem.