The Chesapeake Bay is North America's largest estuary. Restoring it to its former productivity is an immense undertaking with enormous implications for Maryland and Virginia. The economic value of the Chesapeake to both states, according to conservative estimates by the Maryland Department of Economic and Employment Development, approaches $700 billion. This figure includes land value premiums that people will pay for waterfront, waterview or water-access residences, as well as the annual incomes generated by major economic activities that depend on the bay.

Declines in the bay's environmental quality translate into real economic loss. With so much money at stake, there is strong governmental and citizen support for action. States in Chesapeake Bay's 64,000-square-mile watershed, extending from New York to Virginia, have spent hundreds of millions of dollars to upgrade sewage treatment plants, reduce urban and agricultural runoff, and limit discharges from industrial smokestacks.

They are trying to reduce nutrient inputs and strictly limit inputs of toxic contaminants. Management actions can be costly, so they must be based on sound technical information. For example, will a 40 percent nutrient reduction be enough? And how will we know if we succeed?

Pioneer Research Effort

A key indicator of Chesapeake Bay's environmental quality is dissolved oxygen, which is vital to survival of estuarine organisms. Each spring, dissolved oxygen declines in the deeper bay waters, and large areas of its productive bottom become lifeless throughout the summer due to this hypoxia.

Maryland and Virginia Sea Grant pioneered a major, coordinated research effort to examine hypoxia -- its causes and frequency, the species it affects and the way it can be controlled. The Hypoxia Research Program, funded by NOAA, began in 1985 to identify the major factors, particularly nutrient enrichment, that contribute to oxygen depletion, and to determine the effects of hypoxia on the bay's ecosystem.

This program focused on ecosystem-level interactions of nutrients, the production and consumption of organic material, changes in the food web and development of oxygen depletion. The scientific and management communities have recognized the results of this research, results that apply to similar problems in coastal waters throughout the world. Researchers believe, however, that oxygen depletion may be a natural feature of bottom waters in the deep channel of the estuary. Fresh water flowing seaward passes over dense, saltier water that flows into the bay. The result is a barrier layer, called the pycnocline, that prevents oxygenated surface waters from mixing with waters below.

Oxygen depletion has increased in severity and duration since colonial settlement. Deforestation, increased sediment runoff from farms and developed areas, and growing human population have altered the watershed. Significant changes in the bay's ecosystem and its trophic structure have occurred as a result.

Too Many Nutrients

Excessive nutrient enrichment has exacerbated natural oxygen depletion. Annual cycles of phytoplankton growth in spring are the result of nutrients flowing into the bay from hundreds of streams and rivers. Excessive nutrient loading from point and nonpoint sources stimulates the growth of more algae than higher organisms can consume. Severe oxygen depletion occurs in bottom waters as bacteria decompose the dead algae.

The goal of restoring dissolved oxygen concentrations needs to be based on what is realistic historically in Chesapeake Bay's bottom waters. Modest increases in oxygen concentrations may be the best that can be achieved with 40 percent nutrient reduction goals, but they will still have profound effects on the system. Small increases in oxygen levels in bottom waters will help restore a functioning benthic community, increase habitat for commercially important fish and shellfish, and reduce the flux of toxics and nutrients from bottom sediments to the overlying water.

The network of complex feedback loops among physical, biological and geochemical processes is integral to controlling oxygen depletion. Consequently, a small initial improvement in dissolved oxygen can cause a chain of events that will further improve the Chesapeake Bay system.

Reaching Out With Results

A major thrust of the federal-state Chesapeake Bay restoration program is the reduction of nutrient inputs from land and other sources into the bay's many tributaries. Successful nutrient reduction depends on setting realistic water quality criteria for each tributary and establishing strategies for meeting them. The results of continuing Sea Grant research on the factors regulating oxygen depletion are helping scientists and resource managers refine the three-dimensional models that serve as the major tool in these efforts. Equally important, Sea Grant is working with state and business leaders to help communities explore innovative ways for raising funds to meet their goals. Sea Grant is helping to marshal the collective expertise of business, government and universities to improve our efforts to restore the economic vitality of the Chesapeake Bay.