CU study: Nitrogen is changing tundra
Posted: Mon Jul 31, 2006 4:51 pm
CU study: Nitrogen is changing tundra
Soils can absorb only so much, researchers say
By Todd Neff, Camera Staff Writer
July 31, 2006
Nitrogen from human activity is changing the face of alpine tundra in the mountains above Boulder, a long-term University of Colorado study has concluded. The findings add to a mounting body of evidence that the reach of urban, industrial and agricultural activity extends to Colorado's apparently pristine peaks.
William Bowman, a CU biology professor and director of the CU Mountain Research Station, is leading an eight-year study on Niwot Ridge in the mountains above Boulder.
Nitrogen compounds delivered through wind, rain and snow act as a fertilizer and eventually acidify ecosystems. In alpine environments, the native flora have evolved with little tolerance for such treatment. When tenuous alpine soils can bear no more, nitrogen compounds leak into streams, which get more acidic and can eventually kill trout and trees.
In June's journal Ecological Applications, Bowman and colleagues established an annual nitrogen "critical load" of 4 kilograms per hectare for Niwot Ridge's tundra plants. A hectare is 2.47 acres; the critical load for a pollutant is the level above which some part of the ecosystem will be harmed.
Bowman estimates the Niwot Ridge tundra is already soaking up 6 kilograms of nitrogen per year.
"It's at six, and it's increasing," Bowman said.
The study also found that the average number of species on a given plot increased with added nitrogen, as certain sedges and grasses that thrived amid the added nitrogen moved in. Bowman said such diversification could be temporary as the encroachers dominate over time and crowd out tundra plants less able to adapt.
For now, nitrogen deposition is a greater threat to mountain tundra than global warming, Bowman said.
Bowman is also leading a three-year, $100,000 study for the National Park Service. It involves similar tundra testing in Rocky Mountain National Park and in Montana's Glacier National Park, which is further removed from human activity.
Rocky Mountain National Park biologist Karl Cordova said Park Service officials wanted a study specific to the park despite it being just a few miles from Niwot Ridge.
One difference appears to be the nitrogen load. Rocky Mountain National Park's eastern slope collects about 4 kilograms per hectare †™‚¢‚¢¢¢¬…¡‚¬‚¢¢¢‚¬Å¡‚¬‚
or 33 percent less nitrogen †™‚¢‚¢¢¢¬…¡‚¬‚¢¢¢‚¬Å¡‚¬‚
annually than the Niwot Ridge site. Scientists don't know why.
The park is piling up nitrogen at a pace of about 20 times the assumed natural background rate, Park Services officials estimate.
Bowman's work follows the April publication in the same journal of a 20-year study of the impact of nitrogen on microscopic algae at Rocky Mountain National Park's Loch Vale Watershed. That study, led by U.S. Geological Survey ecologist Jill Baron, set 1.5 kilograms per hectare as the critical load for the park's most sensitive aquatic life.
Park Superintendent Vaughn Baker used her research as the basis for establishing a park-wide critical load of the same number in May.
Baron said that limit should protect about everything in the park. She said the challenge now is to identify the nitrogen sources, which, she said are not at all clear.
"A lot of sources come from the east, but how far east? The Front Range? Nebraska and Iowa? For the state or anyone to start doing regulation, they need to know," Baron said.
Contact Camera Staff Writer Todd Neff at (303) 473-1327 or [email protected].
Soils can absorb only so much, researchers say
By Todd Neff, Camera Staff Writer
July 31, 2006
Nitrogen from human activity is changing the face of alpine tundra in the mountains above Boulder, a long-term University of Colorado study has concluded. The findings add to a mounting body of evidence that the reach of urban, industrial and agricultural activity extends to Colorado's apparently pristine peaks.
William Bowman, a CU biology professor and director of the CU Mountain Research Station, is leading an eight-year study on Niwot Ridge in the mountains above Boulder.
Nitrogen compounds delivered through wind, rain and snow act as a fertilizer and eventually acidify ecosystems. In alpine environments, the native flora have evolved with little tolerance for such treatment. When tenuous alpine soils can bear no more, nitrogen compounds leak into streams, which get more acidic and can eventually kill trout and trees.
In June's journal Ecological Applications, Bowman and colleagues established an annual nitrogen "critical load" of 4 kilograms per hectare for Niwot Ridge's tundra plants. A hectare is 2.47 acres; the critical load for a pollutant is the level above which some part of the ecosystem will be harmed.
Bowman estimates the Niwot Ridge tundra is already soaking up 6 kilograms of nitrogen per year.
"It's at six, and it's increasing," Bowman said.
The study also found that the average number of species on a given plot increased with added nitrogen, as certain sedges and grasses that thrived amid the added nitrogen moved in. Bowman said such diversification could be temporary as the encroachers dominate over time and crowd out tundra plants less able to adapt.
For now, nitrogen deposition is a greater threat to mountain tundra than global warming, Bowman said.
Bowman is also leading a three-year, $100,000 study for the National Park Service. It involves similar tundra testing in Rocky Mountain National Park and in Montana's Glacier National Park, which is further removed from human activity.
Rocky Mountain National Park biologist Karl Cordova said Park Service officials wanted a study specific to the park despite it being just a few miles from Niwot Ridge.
One difference appears to be the nitrogen load. Rocky Mountain National Park's eastern slope collects about 4 kilograms per hectare †™‚¢‚¢¢¢¬…¡‚¬‚¢¢¢‚¬Å¡‚¬‚
or 33 percent less nitrogen †™‚¢‚¢¢¢¬…¡‚¬‚¢¢¢‚¬Å¡‚¬‚
annually than the Niwot Ridge site. Scientists don't know why.
The park is piling up nitrogen at a pace of about 20 times the assumed natural background rate, Park Services officials estimate.
Bowman's work follows the April publication in the same journal of a 20-year study of the impact of nitrogen on microscopic algae at Rocky Mountain National Park's Loch Vale Watershed. That study, led by U.S. Geological Survey ecologist Jill Baron, set 1.5 kilograms per hectare as the critical load for the park's most sensitive aquatic life.
Park Superintendent Vaughn Baker used her research as the basis for establishing a park-wide critical load of the same number in May.
Baron said that limit should protect about everything in the park. She said the challenge now is to identify the nitrogen sources, which, she said are not at all clear.
"A lot of sources come from the east, but how far east? The Front Range? Nebraska and Iowa? For the state or anyone to start doing regulation, they need to know," Baron said.
Contact Camera Staff Writer Todd Neff at (303) 473-1327 or [email protected].