Along the coast of Northeastern United States the consequences of additions of excessive amounts of nitrogen-containing pollutants to many estuaries in the region has become a significant environmental concern. The Chesapeake Bay, Long Island Sound, Massachusetts Bay, and others are showing the effects of this over fertilization by anthropogenic nitrogen. The sources of this pollution are varied: sewage treatment plants; runoff from agricultural fertilizers and livestock manure; seepage of groundwater contaminated by septic systems that are inadequate or too densely situated; and runoff from lawn fertilizers used by homeowners. Individual estuaries have differing mixes of these sources as the most significant problem to be cleaned up or otherwise mitigated.

The effects of this excessive fertilization include:

1. Blooms of microscopic phytoplankton that can shade and degrade submerged, rooted aquatic plants that provide habitat for many commercially and ecologically important species of fish and shellfish;
2. Loss of essential dissolved oxygen in the water as the algal blooms die and the dead cells are decomposed by microorganisms;
3. Possible changes in the species of phytoplankton in coastal waters from one's that are "good food" for filter-feeding animals to species that are not easily eaten or that have less nutritional value;
4. Declines in abundance and diversity of fin fish and shellfish because of lowered dissolved oxygen concentration;
5. Possible increases in the occurrence of blooms of harmful species of microscopic algae.

The over fertilization of northeastern coastal waters has been recognized for many years and for estuaries like the Chesapeake and Long Island Sound major efforts are underway to control and reduce the amount of nitrogen that people add to these bodies of water. The technique that has been taken to clean up these estuaries has been one termed the "watershed approach." A watershed is the land area that drains into a body of water. To "fix" a nutrient-polluted estuary society must reduce the amount of pollutants that are added, not just directly to the estuary itself, but to the entire watershed that drains into the estuary. This watershed approach has become the new paradigm for controlling water pollution to coastal and increasingly to inland bodies of water.

However, recent research is showing that for some pollutants, particularly nitrogen, society must look beyond just the watershed boundaries to consider a larger area that encompasses the "airshed".

An airshed is the land area that may act as a source of pollutants that, when they leave the atmosphere as wet or dry deposition, fall on the watershed or the water body itself. For example, Chesapeake Bay (http://www.chesapeakebay.net/bayprogram/committ/mdsc/gis/wsh.gif) has a watershed area of 165,000 square kilometers that includes parts of Maryland, Virginia, Pennsylvania, New York, West Virginia, and Delaware. However, the airshed, or the area that may contribute air pollutants that end up in the Chesapeake Bay, is 600,000 square kilometers and extends from Indiana and Kentucky in the west to New York and Canada in the north, to North and South Carolina in the south.

The anthropogenic sources of nitrogen to the atmosphere include fossil fuel power plants, vehicles with internal combustion engines, fertilizers, and livestock manure. The nitrogen oxides produced at the temperatures generated during fossil fuel combustion return to earth as nitrogen-containing nitrates. Estimates for the Chesapeake Bay and Long Island Sound indicate that of the total amount of anthropogenic nitrogen added to their respective watersheds, approximately 20% is from atmospheric deposition. However, the exact role that atmospherically deposited nitrogen plays in fertilizing water bodies is still unclear.

Producers of these air pollutants may be quite distant from the water body that is affected. As a result there is potentially less regulatory pressure in one state to reduce the production of air pollutants whose ultimate effect is on a second, distant state. However, much the same issue of regional air pollution has bee at the core of efforts to reduce acid rain deposition in the northeast and in reducing smog or tropospheric ozone in the same region. Like the "watershed approach" in which pollution controls coordinated at an environmental scale (i.e., the watershed) that crosses municipal and state jurisdictional boundaries, a similar, broader "airshed approach" is needed to control a variety of air pollutants that become water pollutants once deposited in a watershed.

The Federal law that governs much of water pollution control is the Clean Water Act (CWA). Section 320 of the CWA established the National Estuary Program which has acted as the model for developing the "watershed approach" in considering pollution controls throughout an entire watershed rather than on an individual state-by-state basis. The 1990 Clean Air Act is the primary Federal authority for controlling and regulating air pollution. Regulations that reduce acid rain, ozone, and nitrogen oxides all have the effect of reducing nitrogen deposition to watersheds. Additionally, the CAA established the Ozone Transport Commission (OTC) and the Northern Ozone Transport Region in recognition of the regional nature of ozone production and impact.

On 17 July 1997, the EPA promulgated a reduction in the national ambient air quality standard (NAAWS) for ground-level ozone. Significantly, reductions in ozone should have an effect on reducing atmospheric nitrogen deposition to coastal water bodies because of the linkages in the atmospheric processes which produce tropospheric ozone and associated smog.

The reduction of atmospheric nitrogen deposition is not without controversy. Pro and con arguments include:

1. Questions as to the level of scientific understanding of linkages between sources of atmospheric pollutants and the effects of nitrogen fertilization of coastal water bodies;
2. The economics and politics of forcing reductions in pollutants in the Midwest to solve water pollution problems on the east coast;
3. The trade off between the economic costs of pollutant reductions and the ecological and economic benefits of water pollution reduction in the impacted bodies of water.

Deposition of Air Pollution to the Great Waters

This site offers an executive summary from the 1997 report to Congress on the deposition of air pollutants, including nitrogen, to the nation's waters.

Chesapeake Bay and its Ecosystem

This site provides information on the Chesapeake Bay.

Airsheds and Watersheds: The Role of Atmospheric Nitrogen Deposition

This site includes a report from a 1995 workshop on the role of atmospheric deposition of nitrogen to the Chesapeake Bay.

Regional Approaches to Air Pollution Control

A description of several programs designed to address regional air pollution problems is presented at this site.

The New Clean Air Act Ozone Standard

This site offers an EPA fact sheet describing the new National Ambient Air Quality Standard for ozone.

Long Island Sound Study

This is the home page for the Long Island Sound Study. It provides information about pollution and the monitoring program for Long Island Sound.

Duce, R.A., P.S. Liss, J.T. Merrill, E.L. Atlas, P. Buat-Menard, B.B. Hicks, J.M. Miller, J.M. Prospero, R. Arimoto, T.M. Church, W. Ellis, J.N. Galloway, L. Hansen, T.D. Jickells, A.H. Knap, K.H. Reinhardt, B. Schneider, A. Soudine, J.J. Tokos, S. Tsunogai, R. Wollast, and M. Zhou. 1991. The atmospheric input of trace species ot the world ocean. Global Biogeochemical Cycles 5:192-259.

Fisher, D.C. and M. Oppenheimer. 1991. Atmospheric nitrogen deposition and the Chesapeake Bay. Ambio 20:102-108.

Prospero, J.M., K. Barrett, T. Church, F. Dentener, R.A. Duce, J.N. Galloway, H. Levy II, J. Moody, and P. Quinn. 1996. Atmospheric deposition of nutrients to the North Atlantic basin. Biogeochemistry 35:27-73.