By Katy Human
Camera Staff Writer

Pollution from cars, farms and power plants on the Front Range is changing mountain lake ecosystems and might eventually cause water quality problems in Boulder and other communities east of the Continental Divide, according to a new University of Colorado study.

A lake northwest of Nederland supports a very different group of organisms than it did several decades ago, even though it lies in the city of Boulder's carefully protected watershed, said CU researcher Diane McKnight.

"Here we are protecting the watershed with no hikers, no driving, no activities but research ... yet it's still changing," she said. "Protecting the alpine water quality and ecosystems will require more regional cooperation. ... Boulder can't go it alone."

McKnight and her colleagues have been digging into the ecological history of several mountain lakes in Boulder's watershed by studying the bottom sediment layers. The scientists pieced together the history of one lake back to the 1780s.

"The changes began in 1940," McKnight said. "That's coincident with the introduction of the use of nitrogen fertilizer."

Soon, vehicles and power plants began spewing even more nitrogen pollution into the air.

Upslope winds sweep nitrogen-rich particles and gas into the mountains, where the nutrient rains or snows out on slopes. Eventually, the excess nitrogen can end up in lakes, where it feeds algae.

The nutrient favors bottom-dwelling species, McKnight said, so not only does the lake support more algae, it supports a different sort of algal community than in the past.

Climate change may exacerbate the problem: McKnight and others have watched the lakes' ice cover gradually thin during the last 20 years. "The lake ice is potentially more transparent," she said. More light would foster even more algal growth.

Algae can impact water supplies in several ways, McKnight said. The organisms produce dissolved organic carbon, which, at high levels, can combine with chlorine in water treatment plants to make harmful chemicals.

Algae also simply alter the taste of drinking water, she said, and many cities with algae problems manage it with chemicals.

"The city of Boulder hasn't had to manage it — so far," McKnight said.

She presented her results in a talk Wednesday afternoon at the spring American Geophysical Union Meeting in Washington, D.C.

Jill Baron, a nitrogen researcher with the U.S. Geological Survey in Fort Collins, has found higher nitrogen levels in lakes on the eastern side of the Continental Divide than in lakes on the Western Slope.

"It's the Front Range, urban, suburban sources," she said. "And it's not just cars. A substantial portion are these off-road vehicles associated with construction, and farm machinery. They're not regulated. Period."

Baron estimates that in the Front Range, about 65 percent of nitrogen oxide emissions come from mobile sources, 20 percent from power plants, and 5 to 10 percent from livestock operations.

Nitrogen pollution can also turn lakes acidic, she said. It acts more slowly than the sulfur dioxide typically associated with acid rain, but "ultimately, these lakes will acidify and we will have dead fish," Baron said.

She called the environmental changes a manifestation of growth and energy consumption. They're reversible, however, she said: Controlling car emissions, cleaning up power plants and using alternative energy would help.

Contact Katy Human at (303) 473-1364 or humank@thedailycamera.com.

May 30, 2002

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