Air Pollution and Water Quality

Atmospheric Deposition Initiative

Have you ever watched smoke billow out from a fire? Or seen smokestacks and cars spew clouds of pollutants into the air? What about toxic air pollutants you sometimes hear about on the news but cannot see? Have you ever wondered where they all end up?

For those who have wondered, the answers are becoming clear. A large amount of the pollution we send up into the air is falling back down on our forests, grasslands and agricultural fields, and in our lakes, rivers, streams, wetlands, estuaries and oceans. This type of pollution is called "atmospheric deposition" or "air deposition," because pollutants in the air are deposited onto the land and water. Pollution deposited from the air can reach estuaries in two ways. It can either be deposited directly onto the surface of the water (direct deposition) or deposited onto the landscape and run off into streams and rivers before making its way into an estuary (indirect deposition). Across the country, federal, state, and local groups charged with protecting and improving water quality are discovering that air deposition represents a significant portion of the total pollutant loading. For a general overview of air deposition, visit the Office of Water Air Deposition home page.

Many National Estuary Programs (NEPs) are addressing air deposition as part of their analysis of the threats facing their estuaries. On the East and Gulf Coasts, NEPs including Corpus Christi Bay, Galveston Bay, Tampa Bay, Sarasota Bay, Charlotte Harbor, Albermarle-Pamlico Sound, Delaware Inland Bays, New York-New Jersey Harbor, and Long Island Sound have identified air deposition as a significant source of nitrogen to their estuary.

This atmospherically-deposited nitrogen is added to the nitrogen coming into the estuary from traditional non-point sources such as stormwater runoff and home fertilizer use, and from point sources such as wastewater treatment plants. Together, these sources of nitrogen threaten the water quality and living resources of these estuaries. Excess nitrogen is a significant estuarine pollutant, often leading to water quality problems such as poor water clarity, low levels of dissolved oxygen, and harmful or toxic algal blooms. These water quality problems in turn impact the economic, cultural, and living resources of the estuary. (See the section on challenges facing estuaries for more information on the sources and effects of excess nitrogen and other nutrients.) On the average, atmospheric deposition is responsible for approximately 25% of the nitrogen loading to most of the East and Gulf Coast estuaries studied.

Air deposition of chemical contaminants (or toxics) has also been identified as a problem in several estuaries. Some estuaries already threatened by nitrogen deposition, such as Long Island Sound, Mobile Bay, and Corpus Christi Bay, have also identified air deposition of toxics as a problem. Deposition of toxics has also been identified as a problem in Casco Bay, Santa Monica Bay and San Francisco Bay. Some of the toxics of concern are mercury, copper, PAHs (polycyclic aromatic hydrocarbons), and various organic contaminants. The percentage of toxics due to atmospheric deposition can be very high, as much as 90% in some cases. In some situations estuaries alternate between being a sink (net deposition of pollutants into the water) and a source (net volatilization of pollutants from the water back up to the atmosphere) for contaminants such as mercury and PCBs.

The Office of Air and Radiation Great Waters Program has supported air deposition research and monitoring since 1990. In 1995, the Office of Water established the "Air Deposition Initiative" to support research and cooperation on air-water issues. Together, these two programs sponsored a workshop for the NEPs on air deposition in Edgewater, Maryland in October, 1998. The workshop covered a wide range of information on the monitoring and modeling aspects of atmospheric deposition work and explained the areas where more research is needed to improve estimates of deposition rates and processes. It was also an opportunity for the NEPs and EPA to discuss options for improving our ability to work together to address air deposition issues. The workshop report is now available on the air deposition web site.

As part of the EPA response to issues raised at the workshop, the Coastal Management Branch and the Great Waters Program have dedicated money in 1999 for National Estuary Programs to set up coastal air deposition monitoring sites. Each NEP selected will be responsible for getting matching funds to maintain their site for an additional 4 years. For more information about the NEP coastal air deposition monitoring seed fund, see the announcement on the Atmospheric Deposition web site, or contact John Wilson in the National Estuary Program at (202) 566-1158 or you may contact wilson.john@epa.gov.