Ammonia emissions from agricultural fertilizers are threatening sensitive ecosystems in U.S. national parks, a study led by Harvard researchers has found. Thirty-eight national parks are seeing nitrogen deposition levels at or above the threshold for ecological damage,
the study says. In natural ecosystems, excess nitrogen can disrupt nutrient cycling in soil, cause algal overgrowth, and make aquatic environments acidic. While some of that nitrogen comes in the form of nitrogen oxides (NOx) from power plants and vehicle exhaust, existing air quality regulations and new clean energy technologies are helping reduce NOx emissions. Ammonia emissions from agricultural operations, however, are expected to climb as demand for food and biofuels surges. Daniel Jacob, who led the study, said that because ammonia is volatile, only 10 percent of the nitrogen makes it into the food, with much of it escaping through the atmosphere and being deposited across the landscape. According to the report, published in Atmospheric Chemistry and Physics, hardwood trees, such as those shown above, are most sensitive to excess nitrogen in eastern temperate forests, while in western national parks lichens appear to suffer first.