Public Release: 

Study Reports Human Impact On Global Nitrogen Cycling Greater Than Origianally Believed; Rate Of Impact Accelerating

National Sea Grant College Program

NARRAGANSETT, R.I.- Human-induced changes to the global nitrogen cycling patterns are much more significant than previously believed is the finding of three United States-based scientists in a report published in the Netherlands this week (10/22/96), in the peer-reviewed science journal, Biogeochemistry. They attribute the changes to the rapid post-World War II increase in the use of inorganic nitrogen fertilizers, and to atmospheric pollution from fossil fuel combustion.

"We will need more large-scale discussion and assessment of how to deal with this nitrogen problem. We are clearly not just dealing with sewage, but with agricultural practices and atmospheric sources. These are too large-scale and difficult for individual cities and states to deal with. It will require larger geographical governmental units," says Rhode Island Sea Grant Director Scott Nixon, one of the report's principal authors. Joining Nixon in authoring the study are Robert Howarth, Cornell University ecology and systematics professor, and James Galloway, University of Virginia environmental sciences professor.

The report is the result of a two-year study of the nitrogen cycle of the North Atlantic Basin, including the ocean, coastal systems and contributing watersheds from northeastern Canada to the Amazon and from Northwestern Africa to the Baltic Sea. The North Atlantic was chosen because it is the best-studied and most-altered region of its kind, and the scientists say that what was learned can be extrapolated globally, particularly to the developing third world areas of the globe.

Increasing scientific evidence shows that large amounts of reactive nitrogen from the atmosphere can change species composition, kill trees, and impact coastal marine waters-including causing nuisance algal blooms, hypoxia and anoxia, changes in species composition of plankton, elimination of entire food chains, and death of fish and shellfish. Nitrogen is an important bio-stimulant both on land and in the marine environment. Human activities have accelerated the cycling of that element, increasing the amount moving through the atmosphere, the oceans and across the landscape.

The findings represent a significant step forward in understanding of the controls over, and effects of, human-induced changes to nitrogen cycling throughout the globe.

Among the important findings are:

  • Humans have had a much larger impact on the global nitrogen cycle than previously thought.
  • Changes are large and recent. Enormous changes in large-scale nitrogen cycling have occurred in a very short period of time ( much of it in the last 50 years.
  • The major source of nitrogen to waterways is from agricultural and atmospheric sources. Anthropogenic deposition of nitrogen from the atmosphere is the major source of nitrogen in the northeastern and southeastern U.S. These changes are directly related to two huge increases: the use of inorganic nitrogen fertilizers that accelerated dramatically following WW II, and atmospheric pollution from fossil fuel combustion.
  • Nonpoint sources of nitrogen, largely from fertilizer and atmospheric deposition, dominate the sources of nitrogen to rivers and estuaries, while sewage accounts for only some 11 percent.
  • Nitrogen deposition for the entire North Atlantic basin is five times great than in pre-industrial times.
  • The continental shelf is a "sink" for nitrogen from both land and the open ocean, a previously unknown role. (Being a "sink" for nitrogen means that reactive nitrogen is removed from the system and converted by bacteria back to unreactive nitrogen gas that is returned to the atmosphere.)

There is both "good" and "bad" news in the study's conclusions.

The good news is that as estuaries load up with nitrogen ( there has been a three-to-five-fold increase in the last 100 years ( the reactive nitrogen is being transported to the coastal shelf where it is being denitrified. For large urban areas like Boston, or New York the implication is if the continental shelf is a net "sink" for nitrogen, then it is better to put wastewater and sewage outfalls out of bays and estuaries, and onto the coastal shelf, which is better able to absorb it.

The bad news is that the problem is not just watersheds, it is airsheds.

The findings show that nitrogen pollution will be harder to solve as a result. New pollution remediation and controls will be needed to monitor and reduce atmospheric nitrogen sources, such as acid rain, smog, and ozone. For large multi-state estuaries, such as Chesapeake Bay, that means regulations governing control of atmospheric sources, not just waterborne sources, of nitrogen.

Impetus to conduct the study originated at a Rhode Island Sea Grant-arranged conference in May, 1994 that featured 50 scientists from 12 countries in a gathering to look at the buildup of reactive nitrogen on Earth.

The study was sponsored by the following international organizations: the Scientific Committee on Problems of the Environment (SCOPE) of the International Council of Scientific Unions; the United Nations Environmental Program; the World Meteorological Organization; and the Andrew W. Mellon Foundation.

Principal Authors Available for Comment: Scott Nixon, Director, Rhode Island Sea Grant, University of Rhode Island Professor of Oceanography 401-792-6800, (H) 401-789-6439, E-Mail: snixon@gsoun1.gso.uri.edu

Robert Howarth, Cornell University Professor of Ecology and Systematics, 607-255-6175

James Galloway, University of Virginia Professor of Environmental Sciences, 804-924-1303

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