CHAPEL HILL - Water testing and a flight over North Carolina's Pamlico Sound - the nation's largest lagoonal estuary - provided new evidence this week that the catastrophic flooding and runoff following Hurricane Floyd will damage the sound and connected waters.
Both commercial and recreational fisheries could be hurt along much of the southeastern U.S. coast between Virginia and northern Florida, according to a University of North Carolina at Chapel Hill marine scientist.
The first direct assessment of potentially adverse marine life conditions took place Wednesday (Oct. 6). During the survey, researchers observed low oxygen in the sound and strikingly different-colored water.
"The chocolate-colored sediment plume associated with flood discharge from Floyd has now extended into Pamlico Sound and also is making its way down Core Sound," said Dr. Hans Paerl, Kenan professor of marine sciences.
"We found low oxygen 'dead zone' conditions in bottom waters in a region of the sound under the influence of the sediment plume," Paerl said. "This is obviously not a good development. In addition, nutrient enrichment associated with the plume has the potential for triggering fall and early spring phytoplankton blooms which could further fuel the low-oxygen conditions."
If the excessive freshwater discharge continues into next spring, scientists should detect a low-density freshwater "lens" covering denser saltwater, much like oil floating on vinegar in unshaken salad dressing, he said.
Resulting isolation of salty bottom water prevents oxygen replenishment from the atmosphere, leading to development of the oxygen-deficient dead zone. Algal blooms can exacerbate the condition, because decaying blooms will ultimately sink to the bottom, further contributing to oxygen depletion. Bottom water with little or no dissolved oxygen would prove uninhabitable to finfish and shellfish.
"It's also possible that nuisance algal blooms -- in particular potentially toxic blue-green algae -- normally seen in the freshwater portions of our estuaries will get a foothold in the surface waters of the sounds," he said. "We are particularly concerned about Core Sound, as this is one of North Carolina's most prized fisheries habitats."
Because water entering the Pamlico Sound system, which also is the second largest estuary in the United States, remains for about a year, nutrients and pollutants washed into the system will be there long enough to affect an entire growth cycle of algae, Paerl said. That will give a broad spectrum of algal species the opportunity to reproduce rapidly.
Most water leaving the sound leaves by evaporation instead of through the three narrow inlets - Okracoke, Oregon and Barton's -- that connect it with the open ocean, he said. The sound acts like a giant bathtub trapping polluted fresh water.
"We need to carefully and thoroughly monitor the situation immediately not just for North Carolina's sake but also because the Pamlico Sound system provides a nursery and refuge for the entire southeast coastal fishery," the scientist said. "At present, we can only speculate on the rate of development and expansion of the dead zone, and the ecosystem's ability to recover from this catastrophic event."
In a joint effort between UNC-CH's Institute of Marine Sciences, the Duke Marine Laboratory and the National Oceanographic and Atmospheric Administration's Beaufort Fisheries Laboratory, N.C. scientists have begun a series of cruises to obtain long-term hydrographic, water quality and algal growth measurements and document the sound's recovery. N.C. Sea Grant is supporting the initial work.
Dr. Mark Sobsey of the UNC-CH School of Public Health and N.C. Division of Marine Fisheries staff will test water samples for microorganisms that can cause human disease. Dr. Pat Tester of the NOAA Fisheries Laboratory also will sample water and monitor satellite images of turbidity, color and algal abundance.
Among the many marine species that could suffer are clams, oysters, scallops, crabs and a variety of commercial and sport fish species, Paerl said.
"Because of human conversion of the forests and wetlands to farmland and urban and industrial acreage during the past few centuries, the natural nutrient filtering capacity of the sound's watershed has been greatly reduced," he said. "That makes the receiving waters more prone to nutrient and other contaminant pollution following a catastrophe like Hurricane Floyd."
Pamlico Sound's lagoon-like enclosed shape, which has made it an ideal nursery for fish, also makes it extremely sensitive to pollution, because substances entering the system tend to stay for a long time. In contrast, Chesapeake Bay -- only slightly larger than Pamlico -- is a more forgiving system since more bay water exchanges with the coastal ocean at its wide entrance near Norfolk.
Despite its toll, some good may eventually come from Floyd, including renewed awareness of the importance of forests and wetlands as pollutant filters and recognition of the environmental risks associated with intensive agricultural and urban development in coastal river floodplains, Paerl said.
Photo Note: A color photo of a sediment plume in Pamlico Sound can be downloaded at http://www.unc.edu/news/newsserv/pics/plume.jpg
Note: Paerl can be reached at 252-726-6841, Ext. 133.