Hurricane Floyd: Fearing the Worst
 
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Within days after Hurricane Floyd, North Carolina officials feared the worst for its coastal and estuarine ecosystems. Floodwaters flushed the contents of fuel tanks, pig waste lagoons, and human sewage treatment plants into the state’s rivers and sounds and, ultimately, out into the Atlantic Ocean. The carcasses of pigs, chickens, and other dead animals floated in the soup of pesticides, fertilizer, and topsoil carried in the massive runoff. Even the sheer volume of the freshwater itself was a threat to the plant and animal species that prefer brackish or salt water.
 

 

Hurricane Floyd Series:
Hurricane Floyd's Lasting Legacy
Fearing the Worst
Sedimental Reasons

Sediments from Floyd

Garcy Ward, environmental specialist with the Pamlico Rapid Response Team, said there was concern among scientists that any number of these pollutants would cause massive fish kills. His team’s job is to monitor daily the river’s health by making a whole suite of in situ measurements and firsthand observations. They routinely measure temperature as well as oxygen and salinity levels at multiple sites along the Pamlico. But they were also on the lookout for signs of anomalous algae blooms, unusually high levels of bacteria, or even Pfiesteria (a toxic dinoflagellate that has multiple life forms in which it can feed off sunlight, algae, and even the living tissue of fish and shellfish).

"People were afraid the runoff would fuel an algae bloom, but it never happened," Ward observed. "We did see a small fish kill in a small, isolated pocket off the Pamlico River. It was a mixed bag of fish--spot, bass, some menhaden. But this is not unusual, and it was hard to pinpoint the cause of death because they had been dead a couple of days when we found them. It’s possible they were killed by low oxygen levels."
 

 

Flood runoff in the aftermath of Hurricane Floyd carried an immense load of sediment—including soil, sand, sewage, fertilizer and pesticides—into the sea. This image, from the Sea-viewing Wide Field of View Sensor (SeaWiFS) on September 23, 1999, shows the sediments being swept into the Atlantic by the Gulf Stream. (Image courtesy SeaWiFS Project, NASA GSFC)

Ward’s team observed that both salinity and dissolved oxygen levels quickly dropped to almost zero in the days following Floyd. He explains that there are two main factors that can cause low oxygen: (1) outflow from swamps and (2) decomposing organic matter in the flood runoff. Swamp waters tend to have low dissolved oxygen because they are rich in decomposing organic matter (the process of bacterial decomposition uses up a lot of oxygen). Outflow from eastern North Carolina’s swamps mingling with river and estuarine waters probably helped bring down oxygen levels. Also, there was a lot of organic matter in the runoff, both carried from sources of human and animal waste as well as vegetation sloughed off from river banks and flooded lands. Again, bacterial decomposition of these organic materials sucked oxygen from the water.

But Ward says the biggest single impact was the decrease in salinity levels. "Prior to the storm, salinity levels in the Pamlico River were the highest I had seen in a long time," he notes. "1999 was a bad drought year with low rainfall and high temperatures."

Typical summertime salinity levels in the Pamlico are anywhere from 6 to 10 parts (of salt) per thousand (parts of water). But as recently as August, due to the drought, the salinity level crept up to 14 parts per thousand. Before Hurricane Floyd, shrimp industry officials were predicting a very high harvest--shrimp prefer saltier water and conditions were certainly right in the rivers and estuaries. Then came the massive outflow of highly polluted freshwater and, almost overnight, the expectation changed to one of total loss. Whereas the dissolved oxygen levels recovered in a matter of weeks, it took several months for salinity levels to return to normal levels.
 

  flooded sewage lagoon

Overflowing rivers in the aftermath of Hurricane Floyd flooded many storage lagoons that contained livestock sewage. The resulting runoff carried animal waste and threatened the health of estuaries along the Atlantic coast. (Photograph courtesy U. S. Geological Survey Center for Integration of Natural Disaster Information)

salinity, september 9, 1999

salinity, september 29, 1999

North Carolina is home to about 8,000 commercial fishermen and the fishing industry is a vital part of the state’s economy. So, in December, industry representatives met with Governor Jim Hunt and state legislators to establish a $11.4 million relief plan to offset the anticipated $19 million impact to the 1999 harvest. Ironically, by the time that meeting was held, fishermen were catching record numbers of shrimp and crabs off the Carolina Coast.

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These maps show salinity levels (parts per thousand) in North Carolina's Pamlico River. (see full series of salinity vs. depth) In early September, before the storm (top image), the water was more saline than it would be in a normal summer. At the end of September (bottom image) the water was almost completely fresh. Grey areas indicate waters where no data were collected. (Images courtesy Pamlico River Rapid Response Team)

  Salinity Content in the Pamlico River
 
   
depth
Salinity-August 17, 1999
 
  Salinity

These maps show profiles of salinity (parts per thousand) in North Carolina's Pamlico River. In August and early September, before the storm, the water was more saline than it would be in a normal summer. At the end of September and later in the fall the water was almost completely fresh. Grey areas indicate waters where no data were collected. (Images courtesy Pamlico River Rapid Response Team)

depth
Salinity-September 8, 1999
 
depth
Salinity-September 22, 1999
 
depth
Salinity-September 27, 1999
 
depth
Salinity-October 7, 1999
 
depth
Salinity-October 13, 1999
 
depth
Salinity-October 26, 1999
Salinity Distance

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  The Ones That Got Away (Almost)   Page 1Page 3

Given the severity of the runoff and the pollution it carried, many scientists were surprised at how little impact it seemed to have on North Carolina’s aquatic ecosystem. In previous years, there were large fish kills after both Hurricanes Fran and Bonnie due to runoff and sewage sapping oxygen from the water.

Hurricane Dennis, followed by the intermittent thunderstorms, may have played a role in shifting whole populations of animals eastward toward the ocean, surmises Joe Luczkovich, marine biologist at East Carolina University (ECU). Because the fish and shellfish prefer saltier water, it is possible that all the freshwater runoff in the weeks prior to Floyd prodded these animals to move toward the Atlantic and out of harm’s way.

"It is hard to say if that is the case because we really didn’t get much data during these events," Luczkovich states. "Most folks take their boats out of the water when hurricanes are coming, so no one was out taking [in situ] data. Unfortunately, we are really only seeing a snapshot of conditions before and after [the hurricanes], and not much during."

Ward suggests that Hurricane Floyd may have less severely impacted fish than both Fran and Bonnie because it occurred a month later, when water temperatures were much cooler. "The cooler the water, the higher the capacity for oxygen," he explains. "The conditions that were right [after Floyd] to produce low dissolved oxygen were offset by the cooler temperatures. The fish kills after Bonnie and Fran may have been more of a problem because they occurred during warmer months."
 

  Menhaden with sores

During the summer months over the last 10-15 years, usually after severe events like droughts or hurricanes, researchers have occasionally found populations of dead fish floating in the Pamlico Sound with open wounds on their bellies. State officials feared there would be similar fish kills following Floyd, but none occurred. (Photograph courtesy Pamlico River Rapid Response Team)

An important piece of evidence came from the fishermen. While the catch in the rivers and estuaries was virtually nil, they caught white shrimp in droves just behind the boundary line where the runoff waters ended and the saltwater began. According to Ward, this boundary was actually visible on the surface–on one side the water was almost completely fresh and full of sediment, and the other side was the very salty water that got pushed out from the rivers and estuaries weeks earlier. Hordes of shrimp were schooling just on the seaward side of the line, but staying in close to the boundary, making them an easy catch.

"Basically, [Hurricanes Dennis and Floyd] changed the ecology of the Pamlico River and Sound," Ward observes, "and just moved the fish and shrimp out to sea. Commercial fishermen with boats equipped to fish in the ocean had a big year. But those who are only equipped to fish the rivers were devastated."

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  Sediment boundary

After the hurricane, the boundary between the outflowing rivers and ocean water was unusually sharp. Fisherman profited because shrimp, pushed out of the estuaries by runoff, clustered along the ocean side of the boundary. (Image courtesy Neuse River Estuary Modeling and Montoring)

  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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  Dissolved Oxygen Content in the Pamlico River
 
   
depth Dissolved Oxygen-August 17, 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 dropped substantially in the days and weeks following the hurricane. (Images courtesy Pamlico River Rapid Response Team)

depth Dissolved Oxygen-September 8, 1999
 
depth Dissolved Oxygen-September 22, 1999
 
depth Dissolved Oxygen-September 27, 1999
 
depth Dissolved Oxygen-October 7, 1999
 
depth Dissolved Oxygen-October 13, 1999
 
depth Dissolved Oxygen-October 26, 1999
Dissolved Oxygen Distance

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  That’s Bad...No That’s Good...   Page 3

Alternatively, the Floyd event could have a positive effect on North Carolina’s coastal ecosystem, says Luczkovich. The massive runoff could effectively flush out to sea the pollutants that have been accumulating in the Pamlico over the years.
 

   

"This could improve the long-term health of the Pamlico Sound," Luczkovich says. "When you put a lot of freshwater into the system, it could increase the flushing rate and, ultimately, have a rejuvenating effect."

On average, the Pamlico River has a flushing rate of 20 days. Following Floyd, the river's flushing rate increased to 4 days, or about 5 times the Pamlico's normal turnover rate. It is anyone’s guess at this point what the long-term impact will be on the Carolina Coast. Only time will tell which scenario will emerge—a fish kill disaster, or will there be a happy ending? Scientists, as well as fishermen, are watching closely.

"It’s crazy to try to answer that question now," Luczkovich states. "We don’t know what will happen and we won’t know until we get more data."

But, regardless of what happens this summer, both Luczkovich and Ward emphasize that we won’t really know Floyd’s long-term impact for at least a year and maybe several years.

Regarding reports in news media of the anticipated "massive fish kills," Luczkovich cautions, "It is irresponsible to report certain facts before we know them. [The news reports] show the danger of jumping to conclusions about a complex system that we’re still gathering data on."

Reference
Hackney, Courtney, Jude Grimley, Martin Posey, Troy Alphin, Jeff Hyland, 1998: "Sediment Contamination in North Carolina's Estuaries." Center for Marine Science Research, University of North Carolina at Wilmington, Publication No. 198, 59 pages.

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  Scientist sampling the estuary

Members of the Pamlico River Rapid Response Team continue to monitor the estuary's health. Parameters such as dissolved oxygen, pH, temperature, and salinity can provide early warning of fish kills and algal blooms. (Photograph courtesy Pamlico River Rapid Response Team)