Bay suddenly healthiest in years, naturally Dry weather cut flow of pollutants

October 29, 1992|By Timothy B. Wheeler | Timothy B. Wheeler,Staff Writer

The Chesapeake Bay's troubled waters last summer were the healthiest they have been since 1984, the U.S. Environmental Protection Agency says. But the weather had far more to do with the recovery than did any pollution-control efforts.

No one is saying that the bay has been restored from decades of decline.

But the amount of oxygen measured in the bay's deep waters this year was higher than during any summer since testing began eight years ago, according to the EPA's bay office in Annapolis.

Scientists say the dry winter and spring reduced the flow of fresh water and nutrients -- phosphorus and nitrogen -- from the Susquehanna River into the bay.

Those nutrients feed massive blooms of algae in early spring. When the algae die and sink to the bottom, their decay consumes the oxygen needed by fish, crabs and shellfish.

By late summer, a vast "dead" zone of water stretches down the middle of the bay from the Bay Bridge to the mouth of the Rappahannock River in Virginia.

The Susquehanna River dominates the bay, however, supplying more than half of all the estuary's fresh water and a major portion of its nutrients that come from sewage, from fertilizer washing off farm fields and suburban lawns and from air pollution raining down on the bay's 64,000-square-mile watershed.

But in the first few months of the year, the river's flow was down by as much as half, scientists say.

As a result, the growth of algae in the bay was delayed and weaker than usual, scientists say. Algae sampled at the mouth of the Choptank River last spring were about half their normal level, said Robert Magnien, chief of bay monitoring and special projects for the Maryland Department of the Environment.

"We're not attempting to take credit for it," said Joseph Macknis, water monitoring coordinator in EPA's Annapolis bay office. "And we're not saying it's a trend, either."

Even so, some officials say the improvement in the water quality is heartening, even if it has been caused by something as uncontrollable and unpredictable as the weather.

"It doesn't say we've finished the cleanup of the bay, but it does confirm the responsiveness of the bay" to changes, said Mr. Magnien.

Oxygen levels also were up because the bay's water mixed better than it has in recent years, thanks in part to cooler temperatures last summer.

In warmer months, the bay tends to stratify, or form layers, with denser oxygen-poor water sinking to the bottom.

The bay's responsiveness to "good" weather "doesn't surprise anybody," said Michael Hirshfield, senior science adviser for the Chesapeake Bay Foundation.

"We would have been really depressed if we'd had bad [water quality] under these circumstances."

But last summer's experience suggests that the estuary will benefit from the $400-million-a-year effort by Maryland, Pennsylvania and Virginia to reduce nutrient flows 40 percent by the end of the decade, Mr. Magnien said.

The levels of one key nutrient, phosphorus, already have come down about 19 percent, while those of nitrogen have increased slightly.

"It's certainly heading in the right direction," said William Matuszeski, chief of the EPA's bay office.

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