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 U.S., 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," said 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," said 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 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," said 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."
The following impacts from nitrogen pollution are cited:
- 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.
- Agricultural and sewage system nutrient releases are likely linked to coral diseases, bird die-offs, fish diseases, and human diarrheal diseases and vector-borne infections transmitted by insects such as mosquitoes and ticks.
- Two-thirds of U.S. coastal systems are moderately to severely impaired due to nutrient loading. There are now nearly 300 hypoxic (low oxygen) zones along the U.S. coastline.
- Air pollution continues to reduce biodiversity, with exotic, invasive species dominating native species that are sensitive to excess reactive nitrogen. For example, in California, airborne nitrogen is impacting one third of the state's natural land areas, and the expansion of N-loving, non-native, highly flammable grasses in the western U.S. has increased fire risk.
The report is published by Ecological Society of America's Issues in Ecology, and can be viewed in Issue 15 at http://www.esa.org/science_resources/issues_ecology.php
The Woods Hole Research Center addresses the great issues for a healthy planet through science, education, and policy. We combine satellite remote sensing with field research to study, model, map, and monitor Earth's chemistry and ecology, and we use this knowledge to address the planet's great issues. We work around the Earth, from local to global scales, including the Amazon and Cerrado of South America, the Congo Basin and East Africa, the high latitudes of North American and northen Eurasia, and across the United States. We are unique in the depth of our science capability in combination with our commitment to the environment.