It may be global warming -- or it may be just a fluke -- but the Chesapeake Bay is starting to heat up.
Bay water temperatures have risen 1 to 3 degrees Fahrenheit above normal in the past six years, according to a new U.S. Environmental Protection Agency study.
"We're unsure of the cause," EPA Administrator William K. Reilly said, but the warmer water temperatures are making it harder to shrink the "dead zone" in the bay, where fish and shellfish cannot survive in oxygen-starved waters.
Reilly disclosed the draft study finding yesterday in Harrisburg, Pa., where he was chairing a meeting of federal, state and local officials involved with the bay cleanup effort.
The bay's "warming trend," he warned, may call into question one of their key goals.
The bay restoration agreement signed in 1987 by EPA, Maryland, Pennsylvania, Virginia and the District of Columbia calls for cutting nutrient pollution of the bay 40 percent by the end of the decade.
Computer studies of the bay had indicated that a reduction of that size could boost the levels of dissolved oxygen that could sustain life in bay waters.
But if the bay's water temperature remains elevated, then reducing nutrients 40 percent may not be enough to restore oxygen levels in the bay's depths to where fish can survive, EPA officials say.
"Forty percent nutrient reduction by 2000 needs to be reexamined in light of this warming trend and the changing nature of the bay itself," Reilly said.
State and federal environmental officials already have begun reevaluating their nutrient reduction strategy. But one Maryland scientist questioned whether the EPA study really had identified a long-term trend that could affect the bay cleanup effort.
Six years is "really a pretty short time," given natural fluctuations in climate, said Robert Magnien, chief of bay monitoring for the Maryland Department of the Environment.
Nutrients -- from sewage plants, farm and urban runoff and from auto exhaust -- over-enrich the bay, sparking algae blooms that consume the oxygen dissolved in the water.
Maryland has spent $100 million upgrading sewage plants so they can remove more nutrients, and other states have spent similarly large amounts. Levels of one key nutrient, phosphorus, have dropped 20 percent, while the other, nitrogen, has increased slightly, EPA officials say.
But there has been no noticeable improvement in oxygen levels in most of the bay so far, the EPA study found.
"We have not seen dissolved oxygen respond in the way we'd hoped to due to the waste reductions," said Charles Spooner, deputy director of EPA's Chesapeake Bay program office in Annapolis.
A spirited scientific debate has been going on for the past few years over whether a global warming trend has begun because of rising levels of carbon dioxide in the atmosphere. EPA's Spooner suggested that the bay's warming may stem from unseasonably warm winters the mid-Atlantic region has experienced in recent years.
In any case, higher water temperatures "rob the bay of some of its ability to absorb and hold oxygen," he explained.
But Magnien, the Maryland bay scientist, downplayed the significance of the EPA study.
"It's something we probably should check out," Magnien said, "but we shouldn't leave anybody with the impression we're heading in the wrong direction or this is going to totally negate all our cleanup activity."
It is too early to expect to see much change in the main bay, Magnien contended. Water quality has begun to improve in some bay tributaries, like the Potomac and Patuxent rivers, where sewage plants have been improved, he noted.