University of Montana researcher Cory Cleveland contends that many mountain ecosystems, hammered by years of pollution, may be approaching toxic conditions.

Cleveland, an assistant professor in UM’s College of Forestry and Conservation, was part of a team that studied nitrogen pollution in the Tatra Mountains of Slovakia. Atmospheric deposition of nitrogen was heavy there during the 20th century because of the industrialization of Eastern Europe.

Because deposition of atmospheric pollutants, especially nitrogen, are projected to increase dramatically during the coming decades, the researchers wanted to understand how a high-country ecosystem already impacted by decades of pollution would respond to new inputs. So they purposely added varying levels of nitrogen fertilizer to several study plots above the tree line in Tatra National Park.

“We added nitrogen at rates that are essentially equivalent to what you might expect going into the future,” Cleveland said, “and we saw big changes in the ecosystem. Plant growth decreased, and soil chemistry was altered.”

Results of the study were published in the November issue of Nature Geoscience.

Nitrogen makes up 78 percent of the atmosphere, where it’s a harmless gas. However, human activities such as burning fossil fuels or manufacturing fertilizers can turn nitrogen into forms with a host of negative environmental consequences.

If leeched into streams, lakes and ultimately the ocean, nitrogen can cause algal blooms, oxygen deprivation and aquatic dead zones. Human infants drinking nitrate-laced groundwater can get blue baby syndrome, a blood disorder that prevents hemoglobin from carrying oxygen to the body’s cells and tissues.

Nitrogen compounds emitted from many human activities can rise into the atmosphere and fall downwind as precipitation. Because mountains get more rain and snow, and alpine ecosystems above the tree line don’t produce the biomass to take up the nitrogen, it builds up in soil.

“It’s kind of scary when you consider how much we depend on mountain ecosystems,” Cleveland said. “A lot of places obtain all of their drinking water from the melting of mountain snow.”

The study started in the summer of 2002. After arriving in Slovakia, it took three hours for the UM researcher and his partners to backpack into their study area, carrying both fertilizer and the water needed to mix it.

“We added three levels of nitrogen, and under every treatment we saw declines in plant biomass,” Cleveland said. “There were few significant changes in the composition of species, but the species that were there grew a lot less.”

He believes that with increasing nitrogen deposition, the acidity of the soil is increased. This causes some of the essential nutrients that plants need to become mobile and leech out of the system.

“We saw declines in things like calcium and magnesium,” Cleveland said, “and we saw increases in iron. Iron only becomes detrimental to plants growing in extremely acidic soil because acid can convert iron into a form that plants can take up. So we saw iron increases in the plants as well, and at high concentrations this can become toxic to plants.”

So are alpine areas in Western Montana currently threatened by nitrogen deposition? No, Cleveland said, because the mostly sedimentary rocks of Big Sky mountains are buffered pretty well against inputs of acidity. Montana also is fortunate to lack major industrial centers due west that send high levels of nitrogen up into the high country. However, many other mountain ranges around the globe may be on the brink of big changes.

Cleveland’s partners in the study were William Bowman of the University of Colorado, Luboš Halada and Juraj Hreško of the Slovak Academy of Sciences, and Jill Baron of the U.S. Geological Survey.

In this era of global warming and atmospheric carbon dioxide buildup, Cleveland contends, few scientists and fewer members of the public are concerned about the nitrogen cycle.

“But human activities have essentially doubled the amount of nitrogen that circulates throughout the world every year,” he said. “We sometimes feel like this issue is overlooked a little bit. We should be paying attention to this other element.”

Cory Cleveland, assistant professor, Department of Ecosystem and Conservation Sciences, UM College of Forestry and Conservation, 406-243-6018, [email protected]