Nitrogen levels increasing in Rocky Mountain NP lakes

DENVER — Airborne nitrogen pollution from vehicle exhaust and farm fertilizer is turning algae in the alpine lakes of Rocky Mountain National Park into junk food for fish, a study says.

A similar phenomenon is occurring in Sweden and Norway, according to the study of about 90 high-elevation lakes set to be published in the journal Science on Friday.

Arizona State University professor James Elser, the study's lead author, said the effect of airborne nitrogen on once-pristine lakes is greater than previously believed. The nitrogen's sources include vehicle exhaust, fertilizer used on farms and livestock feed lots and power plant emissions.

More nitrogen can reduce long-term lake biodiversity because algae become poor food for other microscopic organisms and, ultimately, fish. The algae are high in nitrogen, but low in phosphorous and less nutritious.
Previous studies have documented rising nitrogen levels in Rocky Mountain National Park, 70 miles northwest of Denver.

Elser likened the algae to junk food. "It's like eating marshmallows all day and expecting to grow. You can't do it," he said Thursday.

full story