“We have identified forest fires as a principal factor
in the mercury cycle because of the ability of fire to volatilize
mercury sequestered in forest floor organic material.”
“These findings, when combined, show that fire history plays
an important and previously under-appreciated role in the mercury
cycle in northern forests. Forest fire burning through a watershed
decreases the mercury load contributed to the aquatic system in
response to short- (during the fire) and long-term (years following
fire) mercury losses. The decrease in mercury load apparently
can persist for decades,even as the mercury content of soils gradually
increases due to continued atmospheric input. Although
many other factors must be considered, fires may lessen the possibility
of severe mercury contamination in fish by cleansing a watershed
of mercury that had been sequestered at the forest floor by decades
of accumulation.”
Please see their website for more information: http://minerals.usgs.gov/east/environment/indexmercLSNP.htm
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“Photochemical reactions have long been known to affect
the phase, redox state, partitioning, transport, and fate of many
metals in aquatic environments. Probably no metal is more affected
by exposure to sunlight (photosensitivity) in terms of its environmental
behavior than Hg. Sunlight drives two important photochemical
processes involving mercury: photochemical reduction and photochemical
demethylation. Photochemical Hg reduction involves both redox
and phase changes, from ionic Hg (II) to dissolved gaseous Hg
(0). Dissolved gaseous mercury (DGM) is sparingly soluble in water,
and will seek to evade from the water to the atmosphere, thereby
removing Hg from the aquatic environment. Methylmercury
(MeHg), the most bioaccumulative form of Hg, is also photosensitive
and can undergo photochemical degradation to Hg (II), and then
possibly reduced to DGM. This two step process serves
two important roles, demethylation of MeHg to a less toxic form
of Hg, and then possibly elimination of Hg from the aquatic ecosystem
by evasion.”
Please see their website for more information: http://sofia.usgs.gov/projects/evergl_merc/evmercabsfrsf3.html
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