Hurricanes might flood waterfront properties, but there's nothing like them for flushing pollutants out of the Chesapeake Bay and other estuaries.
Researchers studying hurricanes' effects found that the storms' "scouring activity" cleaned two North Carolina waterways and wiped out the same microorganism that killed fish and sickened humans on Maryland's lower Eastern Shore in 1997.
"It's very encouraging news," said JoAnn Burkholder, an ecologist at North Carolina State University and the study's lead author.
Burkholder's team focused on the effects of Hurricanes Dennis, Floyd and Irene in 1999 and Hurricane Fran in 1996 on Pamlico Sound and the Neuse River watershed in North Carolina.
"These events may serve essential functions of ecosystem renewal," the authors wrote in last week's Proceedings of the National Academy of Sciences.
Scientists collected water samples from 21 monitoring stations and based calculations of water flow on federal estimates. They found that both waterways recovered rapidly and -- despite a dip in crab populations -- did not sustain lasting damage.
Burkholder is credited with discovering Pfiesteria piscicida, the microscopic organism blamed for fish kills and human illness that appeared on the Shore seven years ago. However, some researchers argue that Pfiesteria was not to blame.
In the latest study, Burkholder noted that the hurricanes cut blue crab populations in the North Carolina waterways. But she said they increased populations of most other marine life, improved water quality and washed away most of the Pfiesteria.
The storms probably had the same effects on the Chesapeake Bay, she said: "Estuaries seem to be able to withstand the impact of hurricanes and bounce back in just a few years."
But other experts cautioned that the Chesapeake -- the nation's largest estuary -- is a vastly different waterway from North Carolina's Pamlico Sound, which includes the Cape Hatteras area.
The bay's size and the development around it make it more vulnerable to damage when nutrients wash in during major storms, said William Goldsborough, a senior scientist for the Chesapeake Bay Foundation.
Although hurricanes might flush toxins out of the bay, he said, they also destroy marshes and dump chicken manure, farm fertilizer and sewage.
"When there's a storm, the bay gets a lot bigger volume of water and all the things that come with it," he said.
The key to the bay's health lies in controlling development and upgrading sewage treatment plants, according to Goldsborough and other experts.
Burkholder's results conflict with the findings of a 2001 study that predicted long-lasting impacts from the 1999 hurricanes. But both Burkholder and the 2001 author said the earlier findings were based on more limited information.
Scientists say they're just beginning to understand the effects of hurricanes and tropical storms on estuaries, which can vary with wind speed and rain volume, the rate of rainfall and weather patterns during the months before the storm. A storm after an extensive drought, for example, will wash more nutrients into the water.
"We're going to see more of these storms, we're going to see sea level rising and a whole lot of effects," said William Dennison, a scientist at the University of Maryland Center for Environmental Science. "This is something we better get used to and understand."