Oxygen Levels In Bay Disputed

The statistics on oxygen-depleted water are considered another key measure of the bay cleanup's progress.

The Bay Program says that the volume of oxygen-depleted, or hypoxic, water has shown a downward trend since 1985. The University of Maryland researchers found no trend since 1985. Under a longer view, the data showed an increase in the problem that has accelerated in recent years.

The discrepancy in the findings appears to arise from a difference in how researchers defined "oxygen-depleted." Scientists agree that when measuring from 1985 there has been no sign of improvement in hypoxic waters in the bay under the usual definitions.

The Bay Program's report of improvement relies on a broader definition of hypoxic, which some scientists believe is a valuable gauge.

"We used different statistical methods and we looked at different levels of oxygen," said David Jasinski, a water monitoring data analyst with the Environmental Protection Agency's Chesapeake Bay Program office. "There is an improving trend."

He described the trend as "slight."

The divide over the amount of oxygen-depleted water echoes the debate over whether the primary measure of bay progress should be the Bay Program's computer model or actual water samples.

While the computer model shows significantly reduced pollution flows, observed water monitoring data from rivers entering the bay indicate far less progress, particularly for phosphorus.

Program officials note that the river sampling data from the U.S. Geological Survey cover about 80 percent of the watershed and miss significant pollution reductions at many improved sewage treatment plants. The model, they have said, takes the entire bay into account and can adjust for rainfall fluctuations, which affect pollution flows.

But the model has proven an inconsistent guide.

Donald F. Boesch, president of the University of Maryland's Center for Environmental Science, has criticized the Bay Program for what he calls "the over-reliance on the virtual reality of models."

The assumptions behind the computer model likely will be revised again within three years, and again could shrink the amount of progress reported, said Tom Simpson, a consulting scientist to the program from the University of Maryland.

"The more we learn about this, the more we learn our [assumptions about agricultural pollution] have been too optimistic," said Simpson, who is working with the Bay Program to adjust its assumptions about agricultural practices. "I'd expect the revisions will have to reflect that."