Study points to high mercury release from forest fires due to climate change

Study points to high mercury release from forest fires due to climate change

18 September 2006

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Canada — Vastly increased emissions of highly toxic mercury are an unexpected result of climate change in Canada’s northern woods, says the United States Geological Service.

New data suggest wildfires release 15 times more of the poisonous element into the air than previously thought, more than every U.S. coal-fired power plant combined. And those emissions could double again as the boreal forest grows hotter and drier.

“This could be quite significant,” said Mike Flannigan of the Canadian Forest Service, who co-authored the recently published scientific paper.

Scientists have long known that forest fires release mercury into the atmosphere. But researchers assumed peatlands – widespread in the vast boreal forest stretching across nearly every Canadian province and far into the territories – released the potent neurotoxin at the same rate as trees and other so-called “first fuels.”

But Flannigan and his American colleagues found that mercury tends to concentrate in boggy peatlands.

“As water flows through, peat filters mercury out of the water,” Flannigan said.

For thousands of years, that mercury has been accumulating in peatlands, where it is buried and away from plants, animals and humans. But when peatlands burn, mercury is released into the atmosphere, eventually falling to earth where it combines with sulphur to form mercury’s most toxic form.

And as climate change creates drier boreal forests with longer droughts, especially in the global warming hotspot of northern Canada, fires are likely to burn both larger areas and deeper into peatlands once protected by groundwater.

“We’re bringing it up to the surface again where it is more toxic,” said Jennifer Harden of the U.S. Geological Survey.

That means forest fires are much larger contributors to mercury in the environment than scientists believed.

Flannigan said those factors mean climate change could double the group’s current estimate that peat-burning forest fires release 341 tonnes per year across the world’s northern forests.

That compares with about 48 tonnes annually for all American power plants, or 1,000 tonnes a year from all natural sources in North America.

“When you think of climate change, this doesn’t immediately spring to mind,” Flannigan said. “This is indirect but potentially very important.”

Harden, who called mercury emissions carbon’s “toxic twin,” said her group’s estimates were deliberately conservative.

She said they assumed a 10 per cent drop in the boreal forest water table. Some areas, however, are likely to experience a 30 per cent drop, exposing even more peat for burning.

Most of that mercury would be distributed throughout the northern hemisphere. But because about 10 per cent of it would come down with ash from the fire, northern Canada would be likely to receive the heaviest concentration, she suggested.

Mercury attacks the nervous and endocrine systems and can cause death. It also can severely affect infants and has caused birth defects.

As methylmercury, its most toxic form, mercury becomes more concentrated in animals as it moves up the foodchain.


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