We are using a variety of approaches, including both field work on atmospheric deposition of nitrogen and the development of several models, to better determine the sources of nutrient pollution (particularly nitrogen) to coastal waters, to determine how climatic variation and change affects the delivery of this pollution to the coast, and to provide practical approaches for managers to use to reduce the problem.

Nitrogen is the largest pollution problem in the coastal water of the United States, and an estimated two-thirds of the coastal rivers and bays in are moderately or severely degraded. The nutrient enrichment (eutrophication) that results from excess nitrogen inputs to coastal systems leads to hypoxia and anoxia (waters with little or no oxygen), loss of plant and animal diversity, degradation and loss of seagrass beds, and other ecological changes that degrade habitat quality. Nitrogen pollution comes from many sources, including sewage discharges, runoff from agricultural fields and feed lots, and the atmospheric deposition of nitrogen onto the landscape with subsequent leakage downstream to coastal waters. These sources are poorly known for most watersheds, and a better assessment of sources and the climatic factors that influence the delivery of nitrogen to coastal ecosystems is essential for more cost-effective management of nitrogen pollution.

Our efforts fall into three general areas: the first assesses the importance of atmospheric deposition of nitrogen as a pollution source to coastal waters; the second determines how climate variation and climate change affect the flux of nitrogen from the landscape to coastal waters; and the third requires the development of improved models for managers and stakeholders to evaluate how management options may reduce nitrogen and phosphorus pollution, and how these management decisions may interact with climate change. In the past year, we have made substantial progress on the first two of these three. We have demonstrated that some of the emissions of nitrogen pollution from vehicles are deposited in close proximity to highways; this was not previously recognized, and the implication is that near-source deposition of nitrogen may be a much larger source of nitrogen pollution to coastal systems than previously thought. And we have shown that watersheds in wetter environments export a significantly larger portion of the net anthropogenic nitrogen inputs to them (~35 percent to 40 percent, vs. 10 percent to 20 percent in more dry environments). We have projected that future climate change, which is likely to lead to more wet environments in areas such as the watershed of Chesapeake Bay, may partially or even totally undermine management efforts to reduce nitrogen pollution.

We presented our results to a briefing of the President`s Science Advisory and senior staff at the White House in November 2006. We also presented them at the annual meeting of the National Atmospheric Deposition Program. Our results are leading to a re-assessment of the management programs to reduce nitrogen pollution to Chesapeake Bay, and are being used as part of the reassessment by EPA do set policies for nutrient reduction in the Mississippi River Basin and the northern Gulf of Mexico (through the EPA Gulf Hypoxia Advisory Panel, on which Howarth serves). And our research is being used as the basis for similar research and management efforts in portions of Europe, such as that of the Swedish-funded MARE program to reduce nitrogen pollution to the Baltic Sea.

Watershed management

• Coastal Hypoxia Program, National Oceanic and Atmospheric Administration.
• Woods Hole SeaGrant Program.

• Christy Tyler (Ecology and Evolutionary Biology)
• Don Scavia (University of Maryland)
• Denise Breitberg (Smithsonian Inst.)
• Gilles Billen (University of Paris)
• Beth Boyer (Univ. of Calif, Berkeley)
• Eric Davidson (Woods Hole Research Center)
• Christoph Homburg (University of Stockholm)