ANNAPOLIS — While the effects of tropical storm Fran were immediately seen last week in swollen and muddied tributaries, environmental officials and scientists say it is too early to tell the real story of the impact on the Chesapeake Bay.
Several national, state and private agencies are conducting studies to gauge the effect of the storm on the delicate ecosystem. Results will be released over the next few months, officials said.
These studies will test for sediment and nutrients that have washed into the bay. A major concern is an excess of the nutrients phosphorus and nitrogen, which feed algae that in turn can harm fish and crab populations.
According to scientists at the U.S. Geological Survey, the Potomac River at Washington, D.C., peaked at 17.81 feet and raged with a flow rate of 202 billion gallons of water a day.
Those figures combined to average about 6.7 times the normal flow for the month, the highest level since 1931 when the agency started recording the data.
“At this point, no one knows what impact these floods will have on the Chesapeake Bay,” said Linda Zynjuk, a hydrologist for the survey. “We do know, however, that during the January 1996 flood, the Potomac River transported about 2.5 billion pounds of sediment, 20 million pounds of nitrogen and 2 million pounds of phosphorus into the bay.”
Levels could be higher after Fran, Zynjuk warned, given that in January, the frozen ground prevented excessive erosion.
Bruce Michael, chief of the water and habitat quality division program for the Maryland Department of the Environment, said the Potomac’s salinity up to the 301 bridge was the lowest the agency has marked at this time of year since it started such records in 1984.
Low salinity, or salt water content, can affect such wildlife as oysters, which need certain levels to live.
Kent Mountford, a biologist for the U.S. Environmental Protection Agency’s Chesapeake Program, described the most recent storm as “more of a lower bay event” because of the pass that Fran took. The center of the storm did not hit the Chesapeake, he noted.
The topography of the area causes tidal flooding that washes contaminants off streets and washes away materials gathering in marshes, Mountford observed.
The Chesapeake Program sails ships on the water every two weeks, measuring about 19 different things, including salt, oxygen, nutrients and plankton.
Mountford added that in the 1600s, such catastrophic floods did not occur as they do today. The then-expansive forests soaked up a lot of water and sediment, preventing as much from reaching the bay.
Bill Goldsborough, a senior scientist for the Chesapeake Bay Foundation, made a similar point.
“By virtue of all the things we have done to the watershed, its resilience to events like this is impaired,” he said.
Goldsborough said the loss of woodlands and wetlands and the clearing of stream banks has allowed a larger volume of water to flow down the watershed more quickly.
“We need to guard against the conclusion that this is just a natural event,” he said.
Robert Magnien, director of the Maryland Department of Natural Resources’ tidewater ecosystem assessment division, called Fran’s aftermath a “mixed situation.”
Sediments can bury bay grasses, damaging wildlife habitat, he noted. But given that bay grasses are dying off at this time of year, harm would be minimal.
Magnien said he wouldn’t know the complete story until he went out to do some tests. But he knew this much already: Such an increase in water volume is “a stress on the bay system.”
Glen Bese, chairman of the Maryland chapter of the Sierra Club, worried that changes in climate believed to be caused by global warming were responsible for more frequent big storms.
Infusions of fresh water will change the salinity of the bay, and with it the bay’s biological character, he warned. A “greater concern has got to be the long-term effects,” Bese said. -30-