HARRISBURG, Pa. -- The waters of the Chesapeake Bay have warmed nearly 3 degrees in the past six years, a trend that may be related to global warming and could make cleaning up the bay harder, EPA officials said yesterday.
Scientists discovered the average temperature increase recently as they analyzed why the bay had not responded better to reductions in pollution.
"We are unsure of the cause, but the warming temperatures are making it harder to keep oxygen in the
water -- even as we reduce the amount of pollutants," said EPA chief William K. Reilly at a meeting on the Chesapeake Bay cleanup yesterday.
For the past six years, scientists have taken the bay's temperature and other measurements in 50 locations 28 times a year.
"There is a statistically significant increase in temperature over the period of the monitoring," said Edward Stigall, chief of the EPA's technical program section in Annapolis. "There is a global warming, that is the only conclusion one can draw."
PD However, he said, it is not clear whether the warming is man-in
duced or a natural cycle that will change. A cooling trend could begin next year, he acknowledged.
What is clear is that the warming is not a result of something in the water, but rather an increase in the temperature in the air. pTC "There has been no monstrous power plant built on Chesapeake Bay," Mr. Stigall said.
The average warming appears to be caused by warmer winters not hotter summers, according to Charles Spooner, deputy director of the EPA Chesapeake Bay Program office in Annapolis. Because the winters have not been as cold, he said, the water running off the land is not from melting ice but from warmer rain water.
Warmer bay water could affect some aquatic species. Diseases which would be killed by cold water might continue to live in the warmer winter weather. And algae, which are detrimental to many species, might flourish earlier in the spring, Mr. Spooner said.
The trend has not showed up in any other estuary or coastal waters, Mr. Stigall said, because no other area has collected as much data as that available for the Chesapeake.
If the trend continues, the amount of nitrogen and phosphorus being dumped into the bay would have to be reduced even further than it is now to achieve any improvement in the water.
The goal to reduce nutrients by 40 percent by the year 2000 is now under review.
An excess of nutrients in the water will cause algae blooms, which consume oxygen and reduce the amount of sunlight that gets to the bottom of the bay.
Since the loads of nitrogen to the bay have decreased by 20 percent in the past five years, scientists expected to see an improvement in the level of oxygen necessary for all aquatic life.
But instead, they found the amount of oxygen had actually decreased. When they looked further they found part of the problem was that the waters had warmed, Mr. Stigall said.
But they also turned up another discouraging conclusion. Some of the most common phytoplankton that feed on nutrients in the bay can change their diet. When more nitrogen is available they will use that instead of phosphorus.
The result, Mr. Stigall said, is that both nitrogen and phosphorus will have to be reduced before an improvement in the water is seen.