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Earth’s nitrogen cycle profoundly affected by humans

Nitrogen pollution affects wide range of land, sea ecosystems

Even high mountain lakes are feeling the sting of nitrogen pollution.

By Summit Voice

SUMMIT COUNTY — Nitrogen pollution is becoming one of the most pervasive global environmental problems, with nutrient pollution from agricultural runoff and sewage leading to coral diseases, bird die-offs, fish diseases, human diarrheal diseases and vector-borne infections transmitted by insects such as mosquitos and ticks.

About two-thirds of U.S. coastal systems are moderately to severely impaired due to nutrient loading and 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 nitrogen-loving, non-native, highly flammable grasses in the western U.S. has increased fire risk in the region.

These conclusions are part of a sobering assessment by a multi-disciplinary team of scientists led by Eric Davidson of the Woods Hole Research Center who reviewed the major sources of reactive nitrogen in the U.S., resulting effects on health and the environment, and potential solutions.

Publishing their findings in a leading ecological journal, the researchers said the planet’s  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.

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.”

The researchers argue for a systematic, rather than piecemeal, approach to managing the resource and its consequences.

“We’re really trying to identify solutions,” Davidson said.

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, explaining that application of existing technologies and best management practices can reduce nitrogen pollution from farm and livestock operations by 30 to 50 percent.

“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 at http://www.esa.org/science_resources/issues/FileEnglish/issuesinecology15.pdf

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