The Dead Zone   Page 1Page 3

The Pamlico Sound was already in bad shape before the heavy September flood runoff. For years, pollutants had been accumulating in the waters around the mouth of the river. Luczkovich, and his colleagues at ECU, have been studying the "flushing rate" of the state’s estuaries for years. (This term describes how long it takes for an average molecule of water to pass through the system and out to sea.) In general, he says, the Pamlico Sound is a low flushing rate system, on the order of 11 months.


North Carolina

"There is a ‘zone’ that appears each summer in the Pamlico where there is typically very little freshwater input," Luczkovich says. "Researchers from UNC-Wilmington conducted a benthic survey in Pamlico Sound and found large areas that were devoid of benthic life." ("Benthic" means relating to or occurring at the bottom of a body of water.) The researchers were looking for worms, plants, and other life forms that form the foundation of the marine food chain. (Hackney et al. 1998)

"Instead, they found high levels of heavy metals and other contaminants from runoff," Luczkovich continues. "So the Pamlico Sound was already impacted by human pollution. You could consider parts of it a ‘dead zone’ even before the storm hit." (The term "dead zone" refers to a region where there is too little, or no, dissolved oxygen to support life.)

Map of North Carolina, including the Neuse and Pamlico Rivers, both affected by Hurricane Floyd.

depth Dissolved Oxygen-September 8, 1999
Dissolved Oxygen

The process of bacterial decomposition uses up a lot of oxygen. Due to high levels of organic material in the runoff entering the Pamlico River, dissolved oxygen levels (see full time series of dissolved oxygen vs. depth) dropped substantially in the days and weeks following the hurricane. (Images courtesy Pamlico River Rapid Response Team)

depth Dissolved Oxygen-September 27, 1999
Dissolved Oxygen Distance

Although there were no major fish kills from the Floyd event, ecologists are particularly concerned at what might happen this summer when the waters warm up. It is possible that the size of the Pamlico’s dead zone could expand dramatically, or that additional dead zones could occur.

"Will a larger than normal dead zone appear?" Luczkovich asks. "That’s a good question. We don’t know, but there is the potential."

He adds that the larger than usual influx of nutrients--such as nitrogen and phosphorus--could also produce larger than normal blooms of phytoplankton this summer. Because the lifespan of an average phytoplankton is short (12 to 48 hours), they turn over rapidly. As they grow, phytoplankton produce oxygen at the surface. But when they die, they sink to the bottom and decompose, thereby consuming oxygen. Luczkovich notes that if there is a larger than usual bloom in the Pamlico Sound this summer, the waters could become stratified, with very oxygen-rich waters near the surface but much less oxygen toward the bottom. If that happens, he says, we could see large fish kills.

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