CHAPEL HILL - In as few as six weeks in late summer and early autumn 1999, three major hurricanes -- Dennis, Floyd and Irene -- walloped and partially drowned great swaths of eastern North Carolina under more than three feet of rain. Floodwaters at some sites rose more than 20 feet.
Besides their human toll, the storms powerfully altered the nation's largest lagoonal estuary, Pamlico Sound, new studies show. They flushed unprecedented amounts of nutrients and sediments into this key Mid-Atlantic fisheries nursery, sickening and killing countless thousands of fish and shellfish and greatly diluting the shallow waterway's natural saltiness.
The studies, published as a single paper in the May 8 issue of the Proceedings of the National Academy of Sciences, showed floodwaters displaced three-fourths of the sound's volume. Salinity also declined by two-thirds, and the sound's annual intake of nitrogen jumped by at least 50 percent in the aftermath. "Within six weeks, the entire water content of Pamlico Sound was replaced by the flood," said Dr. Hans W. Paerl, Kenan professor at the University of North Carolina at Chapel Hill's Institute of Marine Sciences and lead author of the paper. "Normally, that would take a year because the sound has only four small inlets restricting exchange with the sea."
Freshwater algae and higher organisms that normally live far up in the freshwater tributaries feeding the Pamlico Sound were driven far down into the sound, Paerl said. This was accompanied by a period of low-oxygen conditions in the sound's bottom waters, restricting habitat for shellfish and finfish." Resident crab, shrimp and fish communities either scurried out of the system, took up residence near the inlets or, in some cases, just died.
"While extensive low-oxygen conditions were documented during fall 1999, we didn't see equivalent low oxygen during the summer of 2000 because that spring and summer were very windy, keeping the waters well-mixed," the scient
Contact: David Williamson
University of North Carolina at Chapel Hill