The nitrogen cycle has been profoundly altered by human activities, and that in turn is affecting human health, air and water quality, and biodiversity in the U.S., according to a multi-disciplinary team of scientists writing in the 15th publication of the Ecological Society of America's Issues in Ecology. In "Excess Nitrogen in the U.S Environment: Trends, Risks, and Solutions," lead author Eric Davidson (Woods Hole Research Center) and 15 colleagues from universities, government and the private sector review the major sources of reactive nitrogen in the United States, resulting effects on health and the environment, and potential solutions.  

Nitrogen is both an essential nutrient and a pollutant, a byproduct of fossil fuel combustion and a fertilizer that feeds billions, a benefit and a hazard, depending on form, location and quantity. "Nitrogen pollution touches everyone's lives," says Davidson, a soil ecologist and executive director of the Woods Hole Research Center. "This report highlights the latest understanding of how it's harming human health, choking estuaries with algal growth, and threatening biodiversity, such as by changing how trees grow in our forests." Its authors, a diverse mix of agronomists, ecologists, groundwater geochemists, air quality specialists, and epidemiologists, connect the dots between all of the ways that excess nitrogen in the environment affects people, economics and ecology. They argue for a systematic, rather than piecemeal, approach to managing the resource and its consequences. "We're really trying to identify solutions," emphasizes Davidson.

There is good news: effective air-quality regulation has reduced nitrogen pollution from U.S. energy and transportation sectors. On the other hand, agricultural emissions are increasing. Ammonia, a byproduct of livestock waste, remains mostly unregulated, and is expected to increase unless better controls on ammonia emissions from livestock operations are implemented. Additionally, crop production agriculture is heavily dependent on synthetic nitrogen fertilizer to increase crop yields, but approximately half of all nitrogen fertilizer applied is not taken up by crops and is lost to the environment.

"Nitrogen is readily mobile, and very efficiently distributed through wind and water," says author James Galloway, a biogeochemist at the University of Virginia. Airborne nitrogen from agricultural fields, manure piles, automobile tailpipes, and smokestacks travels with the wind to settle over distant forests and coastal areas.

The report reviews agricultural solutions, and notes that applying current practices and technologies can reduce nitrogen pollution from farm and livestock operations by 30 percent to 50 percent. It tabulates strategies to help farmers optimize efficient use of fertilizer, rather than just maximize crop yield, including buffer strips and wetlands, manure management, and ideal patterns of fertilizer application. It also considers the cost of implementing them, and programs for buffering farmers against losses in bad years.

"There are a variety of impacts due to the human use of nitrogen," says Galloway. "The biggest is a positive one, in that it allows us to grow food for Americans and people in other countries, and we don't want to lose sight of that." Balancing inexpensive abundant food against the damage done by nitrogen escaping into the environment is a conversation the authors would like to hear more prominently in policy arenas. "Yes, we have to feed people, but we also need clean drinking water, clean air, and fisheries in the Gulf of Mexico," emphasizes Davidson. "The science helps to show those tradeoffs, and where we most stand to gain from improved nutrient management in agriculture."

Cited among the impacts from nitrogen pollution:
More than 1.5 million Americans drink well water contaminated with nitrate, a regulated drinking water pollutant, either above or near EPA standards, potentially placing them at increased risk of birth defects and cancer, which are noted in the report.