The effects of Isabel may be felt for years on the Chesapeake Bay, scientists said yesterday, from untreated sewage dumped into the water to potentially significant shoreline and beach erosion.
Although Isabel appeared to be less severe than Tropical Storm Agnes - dropping less than half of the average 8 inches of rain recorded in the 1972 storm - bay experts said they still expect to see environmental consequences in the coming weeks and months.
"This storm comes on top of a lot of other rainfall all summer long, so it's just going to add more fuel to the fire this year," said Donald F. Boesch, president of the University of Maryland Center for Environmental Science. "We're likely to see more nutrients, more sediment, and a lot of areas with lost real estate, particularly low-lying areas on the Eastern Shore."
In the short term, state and local officials were warning of the health effects that could come from untreated sewage that was flowing into rivers. In some areas yesterday, people were swimming or wading through flooded streets.
"People should avoid contact with the contaminated waters, and wash thoroughly if they do come into contact with those waters," said Elise Armacost, a spokeswoman for Baltimore County, where as many as nine sewage pumping stations were submerged by the storm.
As many as 40 of the county's pumping stations were operating on generators yesterday, but nine in the Middle River, Dundalk and Essex areas were covered by flood waters and unable to pump sewage from those neighborhoods to treatment plants. Two were restored by yesterday afternoon, and more are expected to be fixed as the waters recede, Armacost said.
Three of Anne Arundel County's seven wastewater treatment plants - which typically handle 17.6 million gallons of sewage a day - were knocked off line by power outages. The county's largest plant, Cox Creek, was back on line by 2 p.m. yesterday, and County Executive Janet S. Owens said she hoped the other two would be operating by nightfall.
Other sewage plants that were not working - and dumping raw sewage into waters - included one in Prince George's County and at least two in Washington County, said Alan J. Williams of the Maryland Department of the Environment.
But Williams said there could be more. "It's complicated by the fact that the state is closed," he said. There are "lots of failures" that haven't been addressed yet, he said.
The sewage may also limit the state's oyster season, which is scheduled to start Oct. 1, according to the Maryland Department of Natural Resources. If testing indicates unsafe levels of human waste, the state could close some oyster beds - a move that could be a significant blow to an industry that is suffering from record low harvests.
Scientists said they expect the broader environmental consequences from Isabel to include erosion and runoff of nutrients and sediment - though no one was sure how severe it would be.
"We're nowhere near the ballpark of the effect of Hurricane Agnes on the bay," said Bob Wood, a fisheries biologist with the National Oceanic and Atmospheric Administration's Chesapeake Bay office in Annapolis, referring to the storm that is believed to have killed two-thirds of the bay's underwater grasses.
Although Agnes dropped an average of 8 inches of rain across the region, many areas saw only 3 inches or less in Isabel.
"High pressure systems on either side helped reduce the access of the storm to moisture and helped usher it northward more quickly," Wood said. "I think that helped to keep it from producing as much rain as we had thought it might."
Nevertheless, the bay's fragile condition may mean that smaller storms such as Isabel could leave a deeper impression than larger storms from decades ago, said Theresa Pierno of the Chesapeake Bay Foundation.
"When you have a weakened system, which we have in the Chesapeake Bay, it's not able to respond as quickly," Pierno said. "The system has fewer buffers and wetlands, there's much more sediment built up. With this kind of trauma, it can be very difficult to recover."
Sediment can cover beds of aquatic vegetation, which are considered crucial for wildlife habitat and water clarity. "We suspect this will have a devastating impact on our efforts to restore bay grasses," Pierno said.
In the meantime, nutrients swept into the bay through runoff and sewage discharges could feed unusual fall algae blooms, Boesch said. "It's still warm enough to have some algae production, but usually at this time of the year the nutrient supply in the bay is pretty well burned out."
When algae die, the bacteria that feed off them deprive the bay of oxygen - creating "dead zones" for fish and crabs.
Meanwhile, Michael Kearney, a geography professor at the University of Maryland, College Park who specializes in wetlands and coastal areas, planned to head out as soon as today to begin surveying areas of the Eastern Shore for flooding and erosion.
"There's so much low-lying development in the Chesapeake Bay, from Norfolk, Va., up to Maryland's Eastern Shore," Kearney said. "I would think that in the next several months, as the data come out, you'll find a significant amount of erosion in a lot of areas."
Sun staff writers Greg Garland, Andrea Siegel and Cyril T. Zaneski contributed to this article.