Pollution: Nitrogen levels on the rise in Rocky Mountain National Park

Rocky Mountain National Park officials have recognized for years that Front Range pollution -- from auto exhausts, power plants, emissions from oil wells and refineries, feedlots and more -- pose a threat to the health and welfare of their high-country streams, fish and plants. Now a new study from a team of University of Colorado Boulder researchers confirms that increasing levels of nitrogen deposited in the tundra are changing the makeup of alpine vegetation there. And the changes aren't for the better -- the first in a series of increasingly serious impacts that could alter the park's ecosystem.

"The changes are subtle, but important," says biology professor William Bowman, director of CU's Mountain Research Station, one of the country's leading climate research centers -- the same center that's produced pioneering work on pine beetles and climate change that was discussed in a Westword cover story two weeks ago. "They represent the first step in a series of changes that may be relatively irreversible."

Funded by the National Park Service, the CU team studied soils, plants and levels of nitrogen in an alpine meadow near Chapin Pass in the Mummy Range. Over three years, they gathered evidence that rising levels of nitrogen in the soil corresponded to large increases in a common species of sedge that thrives on nitrogen; over time, the phenomenon is expected to limit diversity and exclude rarer species as the sedge and other nitrogen-favored competitors take over.

If that happens, the plants won't be the only losers. Rising nitrogen levels cause soils to become acidified, Bowman explains in a summary of the study's results released by the university: "Once this happens, soluble aluminum leaches from soils and begins to show up in streams and lakes. This aluminum is quite toxic to many aquatic animals."

Park officials have been monitoring airborne pollutants for decades, and the levels of nitrogen found in the tundra are now many times the levels that could be found there prior to the 1950s, prompting the development of a voluntary plan for major polluters to reduce nitrogen emissions. New management practices in agriculture and industry and Xcel's conversion of some of its coal-burning plants to natural gas are expected to help control future nitrogen levels, but the "reversibility" of the current trend is open to question.

"The take-home message is that the amount of nitrogen deposition reaching the tundra in Rocky Mountain National Park has already passed an important threshold," Bowman says.

For more on the impacts of Front Range pollution on the state's premier national park, see our 2004 feature "Loved to Death."

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