Pollutants may be changing wilderness ecology
Sometimes when plants grow well, it’s bad for the environment.
A U.S. Forest Service official is concerned that high levels of nitrogen compounds found in high alpine lakes in the Maroon Bells-Snowmass Wilderness area are coming from air pollution. Nitrogen compounds can function as a fertilizer, aiding the rapid growth and spread of weeds not native to the area.
It’s difficult to determine, though, whether the nitrogen in the lakes is swept out of the air by rain and snow, or whether it comes from the soil and rock in the areas that drain into the lakes. Dennis Haddow, U.S. Forest Service air program manager for the Rocky Mountain region, said further testing needs to be done.
“We’ll be able to make that determination by looking at snow chemistry in the area of the lakes,” Haddow said. A project to analyze snow near five test lakes is planned for March or April, when the snowpack is at its peak.
The Forest Service has teamed up with the Aspen Wilderness Workshop in a project to monitor the water quality in five lakes in the Aspen area. Those involved in the project anticipated that the water chemistry might be affected by the nearby geology.
“We had a difficult time choosing the lakes because of this,” Haddow said. “The Maroon Bells (wilderness) has some of the most complex geology anywhere,” he explained. The quantity of nitrates found in the lakes was unexpectedly high. Likely sources for the nitrogen are the soils or bedrock, but other sources are also possible.
Nitrogen compounds are products of combustion, and are produced by both vehicle engines and other combustion sources such as coal-fired power plants.
Vehicle traffic and power plants could be implicated by the results of snow-pit testing. Nitrates, compounds made up of nitrogen and oxygen, and sulfates, composed of sulfur and oxygen, are carried by air away from combustion sources, Haddow said. As air rises to pass over mountain ranges, it cools, causing moisture to drop out as rain or snow, carrying pollutants with it.
“The higher in elevation you go,” Haddow said, “the more sulfate and nitrate you find in the snowpack.” In the intermountain West, the amount of sulfur compounds deposited on the ground is decreasing while the amount of nitrates is increasing. In Western Colorado, prevailing westerly winds mean that most air pollutants come from sources further west.
Haddow said he’s concerned about the overall increase in nitrogen, because some nitrates act as fertilizer, throwing the natural balance off.
“Plants in the Maroon Bells-Snowmass Wilderness have evolved over about 10,000 years in a low-nitrogen environment,” Haddow said. For this reason, they are unable to use nitrogen as a fertilizer to any major extent, while many non-native plants thrive on nitrogen compounds.
This imbalance allows non-native weeds to outcompete the naturally slow-growing alpine species, Haddow said, contributing to the spread of weeds.
An additional concern with nitrogen compounds is they can promote the growth of the green algae that can sometimes be seen in high-elevation lakes. Haddow said this problem is made worse by the length of winters in the high country. With the lakes under ice for as long as eight to 10 months, the algae dies, and as it decomposes, it takes available oxygen from the water, killing both fish and the insect larvae they eat.
Under Colorado laws, Haddow said, sources of various nitrogen oxides that produce less than 250 tons of airborne nitrogen don’t have to apply any controls. This contrasts with the neighboring states of Wyoming and Utah, which both require any new source of sulfur dioxide or oxides of nitrogen to apply what are known as the “best available” controls.
Christopher Dann, public information officer for the state of Colorado Air Pollution Control Division, said in urban areas such as Colorado’s Front Range cities, the greatest source of nitrogen in the air is motor vehicles, with power plants and manufacturing also producing significant amounts.
But Dann said a quick search of department records showed that the only likely source of nitrogen in any quantity west of the Maroon Bells wilderness is a coal-fired power plant at Cameo, outside Grand Junction.
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