Assessing the sources, sinks, and fluxes of nitrogen in large watersheds and coastal regions, including the influence of climate variability and climate change
CALS Impact Project
We presented our results to a briefing of the President`s Science Advisory panel 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 reassessment of management programs to reduce nitrogen pollution to Chesapeake Bay and are being used as part of the reassessment by EPA to 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 Bob Howarth serves).
Finally, our project is being used as the basis for similar research and management efforts in parts of Europe, such as the Swedish-funded MARE program to reduce nitrogen pollution to the Baltic Sea.
impact statement issue
Nitrogen pollution is the biggest problem in the coastal waters of the United States, and an estimated two-thirds of coastal rivers and bays 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 atmospheric deposition of nitrogen onto the landscape with subsequent leakage to downstream, 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 cost-effective management of nitrogen pollution.
impact statement response
Our research has three basic objectives: the first is to assess the importance of atmospheric deposition of nitrogen as a pollution source to coastal waters; the second is to determine how climate variation and climate change affect the flux of nitrogen from the landscape to coastal waters; and the third is 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 objectives. We have demonstrated that nitrogen emissions from vehicles are deposited near highways, implying that near-source deposition of nitrogen may be a much larger source of nitrogen pollution to coastal systems than previously thought.
Additionally, we have shown that watersheds in wetter environments export a significantly larger portion of the net anthropogenic nitrogen inputs to coastal systems (35 to 40 percent, vs. 10 to 20 percent in drier environments). We have projected that future climate change, which is likely to lead to wetter environments in areas such as the watershed of Chesapeake Bay, may partially or even totally undermine management efforts to reduce nitrogen pollution.
impact statement summary
Nitrogen pollution is the biggest problem in the coastal waters of the United States, and an estimated two-thirds of coastal rivers and bays are moderately or severely degraded. We are using a variety of approaches, including field work on atmospheric deposition of nitrogen and the development of several models, to: 1) better determine the sources of nutrient pollution (particularly nitrogen) to coastal waters, 2) determine how climatic variation and change affect the delivery of this pollutant to the coast, and 3) to provide practical approaches to managers to reduce the problem.
