Nitrogen Traveling to Rocky Mountain National Park is Largely from Eastern Plains, Study Says

Note to Editors: Click on the news release header to obtain a photo of Jeff Collett and Sonia Kreidenweis with the news release.

The highest concentrations of trace nitrogen affecting ecology in Rocky Mountain National Park originate from sources east of the park, according to initial results of a new study by Colorado State University researchers.

Atmospheric scientists in the College of Engineering will present the results at the American Geophysical Union meeting in San Francisco today.

Scientists have spent recent decades identifying increases in nitrogen in the park, but no one has clearly identified the most important nitrogen source types or regions. The National Park Service, with additional support from the Colorado Department of Health and the Environment and the U.S. Environmental Protection Agency, commissioned CSU scientists to improve understanding of airborne nitrogen and sulfur within the park.

Led by Professors Jeff Collett and Sonia Kreidenweis in the Department of Atmospheric Science, the CSU team captured and evaluated airborne particles and trace gases in the region in spring and summer 2006. Measurements were taken within Rocky Mountain National Park, east and west of park boundaries and near the northeast, northwest and southeast corners of the state. The team took daily measurements using filters and devices that capture gases.

"We collected airborne particulate matter and certain trace gasses like ammonia and nitric acid – some of the more common forms of deposited nitrogen," Collett said. "Nitrogen is an important fertilizer and nutrient in many environments, but if you put in too much, you can change the behavior of the ecosystem. The state, the National Park Service and the EPA have been looking at these ecosystem impacts and agree that something needs to be done."

Much of the work evaluating effects on the ecosystem in Rocky Mountain National Park has been done by Jill Baron, senior research scientist in Colorado State’s Natural Resource Ecology Laboratory within the Warner College of Natural Resources, with the U.S. Geological Survey and colleagues. Among the negative effects of increased nitrogen in the park are the proliferation of grasses and fewer wildflowers in the tundra and spruce trees that are more vulnerable to drought and insects, Baron has said.

The study by Collett and Kreidenweis is not yet complete. In addition to further analysis of the large dataset generated during the field campaign, an extensive computer simulation is underway by other scientists working with the National Park Service. These regional scale simulations will consider the emission, transport and deposition of nitrogen affecting park resources. Collett said the team needs the results of the computer simulation before coming to any final conclusions about nitrogen sources affecting the park.

The 2006 field study measured ammonia and nitric acid gases and their counterparts, ammonium and nitrate, in aerosol particles. The highest concentrations in the park occurred during periods when winds brought air to the park from the east side of the Continental Divide. Nitrate and nitric acid are derived from nitric oxides emitted by any kind of combustion process such as power plants, wildfires or automobiles. Agriculture is an important contributor to ammonia emissions.

Large storms with heavy snowfall can often bring those particles and trace gases up against the mountains. The particles and gases are collected by rain or snow and deposited into the park ecosystem. While direct deposition of particles and gases contribute to total nitrogen inputs to the park, wet deposition in rain and snow is more substantial.

"It’s not all coming from the west. Those storms can take pollutants from the east and bring them into the park," Kreidenweis said. "What we don’t know from measurements in the park is whether the pollutants originated as mostly Colorado emissions or whether there were contributions from farther east or from Texas. It’s a key question for the modeling."

"Much has been done historically to reduce emissions from automobiles and power plants. Work is under way at CSU to look at how to reduce ammonia emissions from agriculture and fertilizer use," Collett said. "All these things cost money, but I think the long-term view is that there probably needs to be action to reduce nitrogen inputs to the park. Hopefully, some of those actions can be done in a voluntary way once people are aware of the problem."