Matthew Could Impact The Neuse River and Pamlico Sound For Months, Years

Nov 22, 2016

Dr. Hans Paerl's lab at the University of North Carolina at Chapel Hill's Institute of Marine Science in Morehead City.
Credit UNC Institute of Marine Sciences

Local scientists have increased monitoring of the Neuse River and Pamlico Sound following Hurricane Matthew.  Algal blooms and low dissolved oxygen are a few of the problems being detected due to nutrient loads and storm water runoff. 

Eastern North Carolina is recovering from Hurricane Matthew. As officials try to get a handle on the extent of damages, another significant impact is being realized in our waterways.  Researchers are keeping close tabs on the estuary for fish kills and algal blooms due to an influx of pollutants.  Professor of Marine and Environmental Sciences at the University of North Carolina’s Institute of Marine Sciences in Morehead City Dr. Hans Paerl.

ModMon results five days before Hurricane Matthew
Credit Dr. Hans Paerl - UNC Institute of Marine Sciences

“We had nutrients and pollutants that came in from agricultural lands, from urban centers, including storm water runoff, and also from industrial sites and agricultural concerns like animal operations for example.  They all essentially made the mixture that ended up in the river and ultimately into the estuary and into the sound.”

The University of North Carolina and NC State received a joint grant of $180,000 from the National Science Foundation to explore how Hurricane Matthew impacted the Neuse River and Pamlico Sound.  To collect data, researchers are using a modeling and monitoring system called “ModMon” to assess water quality, observe algal growth and measure changing environmental conditions.  There are 11 mid-river sampling sites set up in the estuary.  Researchers collect water samples at these locations and take them back to the lab for analysis. Before Matthew, samples were taken every two weeks.  Now, it’s twice a week. 

“We had a run that occurred just a few days before the hurricane occurred so we have good baseline data to see what they system looked like before the storm impacted it.  And since the storm, after we realized that there was much rain that had fallen in the basin, it was obvious that we needed to do a more intensive set of monitoring.”

ModMon results nine days after Matthew
Credit Dr. Hans Paerl - UNC Institute of Marine Sciences

In the weeks following Matthew, floodwaters carrying pollutants collected in the upper Neuse River basin and gradually flowed east through Goldsboro, Kinston and Vanceboro.  The influx of fresh water funneled into the brakish Neuse River near New Bern and formed a wedge, with freshwater on top and denser saltwater on the bottom.

“And that caused sort of an oil and vinegar type of situation where the bottom water was locked in and couldn’t change with the surface or the atmosphere and given all the nutrients and organic matter that was coming in from various sources, we could see a rapid sag of dissolved oxygen in the bottom water.  And that occurred throughout the Neuse estuary and at the entrance to the Pamlico Sound.”

According to the latest ModMon results, salinity is creeping back into the estuary.  Salinity in the Pamlico Sound is still unusually low but stratification is minimal, for now.  

ModMon results 16 days after Matthew
Credit Dr. Hans Paerl - UNC Institute of Marine Sciences

If low-oxygen levels persist in the Neuse River, finfish and shellfish will attempt to move to a different area.  If they’re not able to relocate fast enough or the area of low-dissolved oxygen is widespread, a fish kill occur.  Oysters, clams and other mollusks are the most susceptible.  In addition to large numbers of dead fish and the putrid smell, large scale fish kills can impact local fisherman and raise consumer concerns about seafood safety.

Dr. Paerl says they are detecting low levels of dissolved oxygen in the Neuse as it extends toward the sound. 

“And we know from the Floyd experience that the sound was covered a low oxygen bottom water for quite a long time, which ultimately impacted the crab fishing for example and bottom fishing for several years.”

The good news Dr. Paerl says is they don’t think this event will be as big as Hurricane Floyd.  The bad news? 

“We’ve had good weather and stable conditions so that allows the oil and vinegar situation to persist out there.” 

ModMon results four weeks after Hurricane Matthew
Credit Dr. Hans Paerl - UNC Institute of Marine Sciences

Using ModMon, Dr. Paerl is able to track the presence of nutrients such as nitrogen and phosphorus, organic waste, as well as pesticides and herbicides and a variety of other chemical pollutants. Some nutrients are bio-reactive meaning they break down quickly, while organic compounds tied up in sediment take time to release into the water column.

“And when we had Floyd back in 1999, we had a very big slug of those sediments and organic matter, constituents that came into the system, and it took almost a year for those sources of nutrients to actually lead to the release of the soluble nutrients that then formed algal blooms the following spring or the following summer.”

The same situation is expected with Hurricane Matthew.  Dr. Paerl is paying close attention to higher concentrations of nutrients, which have the potential to trigger toxic algal blooms that can impact wildlife and disrupt food chains.  According to the latest ModMon results, moderately high levels of chlorophyll extend downstream from the bend at Cherry Branch to the mouth of the river. 

ModMon results five weeks after Matthew
Credit Dr. Hans Paerl - UNC Institute of Marine Sciences

“We’re already seeing some that have followed up immediately after the storm event both in the estuary and in the sound.   Those algal blooms have been relatively harmless.  They are algae that don’t produce toxins or not going to lead to fish kills.  So far so good but the story is only partially told at this point.  I think we’re going to be looking at this for at least a year or so.”

The Pamlico Sound drains into the Atlantic Ocean very slowly so the material that enters the sound takes time to decompose.  After Hurricane Floyd, Dr. Paerl says it took up to two years to release all of the nutrients. 

“And it’s quite possible that the nutrients that will be sitting in the system next spring from this event, if we have a nice sunny spring with good weather and calm conditions, we will see some blooms and hopefully they will not be the blooms that will release toxins and cause additional water quality problems.  But we’re keeping a very close eye on that.”

The National Weather Service has predicted a drier and warmer winter for eastern North Carolina, conditions that would make algal blooms a real possibility. Dr. Paerl and the team of researchers will continue intensive monitoring of the Neuse River and Pamlico Sound throughout the winter and into next spring.