Mercury in Water
Rocky Mountain lake is high in toxic metal
By Jeremy P. Meyer Denver Post Staff Writer
Article Last Updated:12/10/2006 11:58:38 PM MST
Loch Vale, a clear, high-elevation alpine watershed, is Rocky Mountain National Park's most photographed lake setting.
What the photos don't capture, researchers say, is that the area has some of the highest mercury levels in Colorado - comparable to polluted Midwest and Northeast lakes where people are warned not to eat the fish.
But unlike those low-elevation lakes, the alpine ecosystem is protecting Loch Vale's fish from the highly toxic mercury.
"From the pure human-health issue, it's better here because the ecosystem is different," said researcher Don Campbell of the U.S. Geological Survey.
"It doesn't process mercury the same way," Campbell said. "Our fish are puny compared to fish there. Fish that eat fish tend to accumulate mercury."
Conditions in the high mountain ecosystem aren't favorable for the biological process that transforms the heavy metal to methylmercury, which is five to 10 times more toxic and more easily passes into animal cells.
"Maybe we're at the point where it isn't in the fish, but we could be around the corner," said Keith Keenan, regional coordinator for Trout Unlimited.
The state health department has already issued consumption advisories on seven lakes and reservoirs where fish have been found with elevated mercury levels. Most are lower-elevation water bodies in southwestern Colorado, and one reservoir is near Pueblo.
Scientists have been studying Loch Vale for 25 years, finding that air pollution is depositing pesticides, insecticides and other long-lasting chemicals.
Mercury loading to sediment in the alpine lakes is four times higher than what it was in pre-industrial times, indicating that the mercury is from man-made sources.
Research suggests that 70 percent of mercury in the atmosphere is from industrial processes, Campbell said.
The most likely source is coal-fired power plants, Campbell said, though it is impossible to determine exactly where it's coming from.
In the mercury cycle, the chemical gets spewed into the atmosphere in an elemental form and can travel the globe for months before being deposited back on land and water.
Higher elevations get more precipitation and therefore get more mercury, Campbell said.
In the Loch Vale study, rains in the spring and summer have produced levels of mercury three to four times higher than in winter.
Campbell said fish may not be the only species being affected by the higher levels of mercury.
"There can be a lot of mercury left in the soils and lake sediments that the fish don't see that other animals see," he said.
"We see some mercury in all the fish that we measure, but most of it is below the human criteria," Campbell said. "The levels we have seen could have effects on other wildlife that eat the fish - birds, eagles and osprey. No one has looked at the effects of mercury on the terrestrial environment."
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