Unregulated agricultural ammonia threatens national parks’ ecology

A press release on Harvard's website: Thirty-eight U.S. national parks are experiencing “accidental fertilization” at or above a critical threshold for ecological damage, according to a study published in the journal Atmospheric Chemistry and Physics and led by Harvard University researchers. Unless significant controls on ammonia emissions are introduced at a national level, they say, little improvement is likely between now and 2050.

The environmental scientists, experts in air quality, atmospheric chemistry, and ecology, have been studying the fate of nitrogen-based compounds that are blown into natural areas from power plants, automobile exhaust, and—increasingly—industrial agriculture. Nitrogen that finds its way into natural ecosystems can disrupt the cycling of nutrients in soil, promote algal overgrowth and lower the pH of water in aquatic environments, and ultimately decrease the number of species that can survive.

“The vast majority, 85 percent, of nitrogen deposition originates with human activities,” explains principal investigator Daniel J. Jacob, Vasco McCoy Family Professor of Atmospheric Chemistry and Environmental Engineering at the Harvard School of Engineering and Applied Sciences (SEAS). “It is fully within our power as a nation to reduce our impact.”

Existing air quality regulations and trends in clean energy technology are expected to reduce the amount of harmful nitrogen oxides (NOx) emitted by coal plants and cars over time. However, no government regulations currently limit the amount of ammonia (NH3) that enters the atmosphere through agricultural fertilization or manure from animal husbandry, which are now responsible for one-third of the anthropogenic nitrogen carried on air currents and deposited on land.

“Ammonia’s pretty volatile,” says Jacob. “When we apply fertilizer in the United States, only about 10 percent of the nitrogen makes it into the food. All the rest escapes, and most of it escapes through the atmosphere.”

...In many previous studies, environmental scientists have identified the nitrogen levels that would be ecologically harmful in various settings. The new Harvard-led study uses a high-resolution atmospheric model called GEOS-Chem to calculate nitrogen deposition rates across the contiguous United States, and compares those rates to the critical loads. The findings suggest that many parks may already be suffering....

A bear in Smoky Mountains National Park, National Park Service photo