Computer Predicts Stricter Goal Needed To Curb Nitrogen Runoff Into Chesapeake Bay

A simple computer model that predicts the effects of nitrogen runoff on the Chesapeake Bay "dead zone" confirms that the current runoff is too high, and a multi-state bay restoration goal to reduce runoff is not sufficient, researchers said on Aug 30.

"The model confirms from a new perspective that we know what's required to decrease the hypoxic levels in the Chesapeake Bay," said Donald Scavia, a University of Michigan professor. "It's a matter of political will to put in place the practices that will get it done."

The computer model was developed by Scavia of the School of Natural Resources and Environment (SNRE). His collaborators were recent SNRE graduate Emily Kelly and James Hagy III of the U.S. EPA, National Health and Environmental Effects Research Laboratory, Gulf Ecology Division.

The bay is about 200 miles long on the east coast, from Maryland to Virginia, and supports thousands of species of plants, fish and animals. Chesapeake 2000 is the current agreement in place that sets guidelines and goals for restoring the bay. Currently, the goal is to reduce total nitrogen pollution into the water by 35 percent from the mid-1980s levels. Maryland, Pennsylvania, Virginia, the District of Columbia, and the federal government and the Chesapeake Bay Commission voluntarily participate in the agreement.

The computer model indicates that this reduction will not be enough, Scavia said. It will decrease the size of the dead zone in an average year to about half of the values reported between 1980 and 1990, or equivalent to values reported between 1950 and 1970. But because of uncertainty in weather and climate, the model indicates that to reach those levels in most years would require a larger reduction: 53 percent.

Hypoxia is a condition where oxygen concentrations dip so low that most marine life can't survive. Hypoxia, or the dead zone, occurs when increased nutrient runoff causes algae blooms, which sink into bottom waters and are decomposed by bacteria, a process that consumes oxygen. When oxygen is consumed faster than it can be replaced, a dead zone results.

The model predicts the size of the dead zone based on nitrogen loading. For years, environmentalists and scientists have warned that the area must be cleaned and runoff reduced. Agricultural runoff caused by fertilizers is the main cause, and most current efforts to decrease nitrogen from this source are voluntary, Scavia said.

"Even though there are commitments by the states that feed into the Bay, there hasn't been much progress in reducing the size of the dead zone," Scavia said.

The new computer model developed by Scavia, Kelly and Hagy actually sits between two popular methods of forecasting, said Scavia. One method of forecasting is purely statistical, based on previous data. The other is based on developing very complicated models requiring input of detailed physical variables including weather, tides and other factors. This method can be expensive and time consuming.

The new model is a good middle ground between the other methods. It's easy to use and accurate. It takes into consideration both the primary driver -- nitrogen loading -- and uncertainty associated with variations in weather and climate, Scavia said. The model will be available for officials and scientists to use in selling appropriate goals for the bay.

Additional information on the research can be found at

Donald Scavia:

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