Ammonia and Fertilizers Impact US National Parks in a Big Way

Our national parks may be in more trouble than we thought. Scientists have discovered that thirty-eight U.S. national parks are experiencing "accidental fertilization" at or above a critical threshold for ecological damage. Unless significant controls on ammonia emissions are introduced, in fact, it's likely that there will be little improvement between now and 2050.

Increased fertilization in our environment is not wholly surprising. Human activities are steadily increasing the load that finds its way into lakes and rivers. Yet the 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. This can ultimately decrease the number of species that can survive.

Although there are existing air quality regulations and trends in clean energy that are expected to reduce the amount of harmful nitrogen oxides, there are no government regulations that currently limit the amount of ammonia that enters the atmosphere. This could potentially pose a major issue for environmental systems.

"Ammonia's pretty volatile," said Daniel Jacob, one of the researchers, in a news release. "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 order to examine how this type of pollution might affect environmentally sensitive areas, the researchers employed models. More specifically, they used a high-resolution atmospheric model called GEOS-Chem in order to calculate nitrogen deposition rates across the contiguous United States. They then compared these rates to the critical loads. Unfortunately, they found that many parks may already be suffering.

In Eastern temperate forests, like those in Great Smoky Mountains National Park, the most sensitive elements of the ecosystem are the hardwood trees. These trees start to suffer when nitrogen deposition reaches approximately 3 to 8 kilograms per hectare per year. The scientists have discovered that the actual rate of deposition is 13.6 kg/ha/yr, which far exceeds that threshold. In addition, the scientists discovered that lichens in the forests of Mount Rainier National Park have also exceeded their own threshold.

"The lichens might not be noticed or particularly valued by someone walking around a national park, but they're integral for everything else that's dependent on them," said Raluca Ellis, one of the researchers, in a news release.

The findings reveal the importance to decreasing this fertilizer load in the future. More specifically, it shows that regulations should be in place in order to help counteract the current pollution.

"It's a national issue, and I think that's why having the national perspective was so important," said Jacob. "We've shown that most of the nitrogen deposition to parks in the United States is coming from domestic sources. It's not coming from China; it's not coming from Canada--it's something we can deal with, but we need to deal with it at the national level."

The findings are published in the journal Atmospheric Chemistry and Physics.