Bird feces, regrowth could hold key to water contamination

by Cole Dittmer
Wednesday, May 1, 2013

In an ongoing study of Wrightsville Beach’s stormwater system, Dr. Rachel Noble of the University of North Carolina Chapel Hill’s Institute of Marine Science in Morehead City has been working with the town to determine the root of bacterial contamination that triggers swimming advisories during summer months. 

An annual issue since the North Carolina Department of Environment and Natural Resources began regular testing in 2007, the town has not been able to pinpoint the exact source and source location despite other studies by the University of North Carolina Wilmington. 

However, with new molecular DNA testing Noble recently presented to the Wrightsville Beach Board of Aldermen, contamination levels from the town’s gull and shorebird population registered the highest among all other sources. Noble’s study has concentrated on the two watersheds on the eastern side of Banks Channel that have experienced the highest number of swimming advisories — Iula and Snyder streets.  

Despite these results, Noble said her research team still does not know how much gull contamination contributes to the total enterococcus and E. coli levels — the bacteria DENR tests for when determining when to close water bodies. 

“There is still a disconnect between what concentration of that gull marker you could expect in fresh bird feces and what concentration of enterococcus you would expect,” Noble said. “We know that the gull contamination is not trivial; we know it is an important part of the picture, but we don’t yet know how to place the importance into the context of the big picture.”

Further testing of fresh gull contamination is needed for Noble to determine the correlation; but if gull contamination does prove to be a significant contributor, town stormwater manager Jonathan Babin said it would prove to be a hard problem to fix. 

“It is one of those tough situation where we have bird sanctuaries at both ends of the island,” Babin said. “We talked about doing some kind of gull program, even just putting plastic owls out there on top of the Blockade Runner to see if that would deter birds from hanging out up there, but I haven’t heard anything else about what the next step may be.” 


In addition to determining the impact gull contamination has on the bacteria levels in Banks Channel, Noble said a phenomenon called regrowth could also hold the key to pinpointing the source of the contamination. 

A characteristic she has seen from Florida to Maryland, regrowth occurs when bacteria like E. coli and enterococcus settle into dark, muddy surfaces like the bottoms of storm drains such as those that collect from Snyder and Iula streets and empty into Banks Channel, or in the silt-like substance at the bottom of Banks Channel itself. 

“What we have actually seen through preliminary data we have already collected in the town of Wrightsville Beach is that there is a layer of muck that accumulates in the bottom of storm drains,” Noble said. “When we actually look at the concentration of enterococcus and E. coli in that muck we find quite a bit of it and it leads us to believe that during warm months … there is a source of constant regrowth in the bottom of these storm drains that is likely conveying a baseline amount of enterococcus and E. coli to the system.”

If Noble can determine whether the bacteria is growing and thriving in those conditions, or merely lying dormant, she could then determine that baseline level the regrowth is consistently supplying to the system. With that knowledge she would then be able to separate the level of fresh contaminants from the baseline during a storm event to see which source is contributing more bacteria. 

“In order to understand what sort of remediation strategies will work in this area it is important to get a handle on this regrowth because it is a real phenomenon,” she said. “It is an area of research that is just expanding and the regrowth question adds a wrinkle to how the EPA allows people to manage water bodies because what they are finding is, in some areas, you can say the water body is impaired but it is not really impaired with fresh contamination, it is suffering from a perfect storm of circumstances.” 

Steve Dellies, assistant to the director of Wrightsville Beach public works, said given the number of past studies that have failed to deliver exact sources of contamination, he is hopeful Noble’s regrowth study will lead to answers. 

“What I am hoping to find out in particular with the regrowth is if it even plays a roll,” Dellies said. “If it does, that’s good; that may point to the actual source or what we are dealing with. If it does not appear to be a source or even a contributor, then we have to step back because I’m running out of answers at this point.”

Swimming advisories

One project Noble has been developing that she is confident will deliver results is a quicker, more efficient way to test bacterial content in water bodies like Banks Channel to post swimming advisories more immediately. The sample culture system DENR uses to test water quality takes 24 hours to process, adding in a lag time for posting the advisories and possibly placing the public at risk, Noble said. 

“We have developed a new molecular test based on DNA that only takes a few hours,” she said. “What we do now is take a water sample on the beach, say Monday morning, and on Tuesday morning we might put up a sign, but the beach was contaminated on Monday. We want to be able to take a sample at 8:30 a.m. and have a sign up by no later than 10 a.m. to better serve the public and protect them from these potentially harmful contaminants.” 

The continued cooperation of the town of Wrightsville Beach will be crucial in drawing conclusions to her studies, Noble said. At the board of aldermen’s April 29 budget workshop, the board approved more funding for Noble’s studies for the town’s Fiscal Year 2013-14 budget. 


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