The bright green scum coating areas of the Cape Fear River’s surface caught everyone by surprise.
Until that summer in 2009, no one had seen Microcystis blooms in the river, which for decades leading up to that point had been monitored for algae.
Sponsor Spotlight
“The community members, researchers, the water utilities, this was a really strange system to have these types of cyanobacterial blooms,” in the Cape Fear, said Madi Polera, a doctoral candidate at North Carolina State University. “Many historic blooms are typically associated with some kind of nearby, still-moving water, like another lake or reservoir, and the blooms appear immediately downstream.”
Even more baffling was the fact that the blooms abruptly stopped appearing in the river in 2012 — and they haven’t appeared since.
The presence of blooms set off a flurry of investigations. Water utilities studied what types of toxins the blooms may have been emitting into the drinking water supply and how to best remove those toxins from the raw water source. Wildlife officials wanted to know how the blooms might affect fisheries, particularly the anadromous fish swimming upstream to spawn.
Two years after the blooms disappeared, researchers in 2014 initiated a forensic-like investigation to rule out any possible explanation of how the algae got into the river, how to prepare for a reoccurrence of the blooms, and seek out ways to prevent the blooms from sprouting up on the river’s surface again.
Polera, one of the authors of the study that was published in March, explained that the investigation was not one where researchers tried to prove anything.
Sponsor Spotlight
The study “was just what is the most likely, the most plausible aspects that we could not rule out,” Polera told Coastal Review via telephone earlier this week.
Microcystis algae blooms are made from a recipe largely of nitrogen and phosphorous. The cyanobacteria thrives in waters like lakes and ponds, blooming during warm summer months before hunkering down into the sediment, where it lies dormant in the winter.
Microcystis blooms produce a few different types of toxins, primarily microcystin. Microcystin can affect the liver and is considered a possible human carcinogen by the Environmental Protection Agency. If ingested, microcystin and the other toxins can cause digestive issues and may cause flu-like symptoms in both humans and animals.
Dogs are especially sensitive to microcystin.
The blooms in the Cape Fear River were localized primarily upstream of Lock and Dam No. 1, an area where conditions are ripe for algae growth because of the lake-like effect the dam has on the water. The dam is near Riegelwood, a community roughly 30 miles upstream of Wilmington and near the drinking water source intake for thousands in the region.
“What we really tried to do was look at everything that we know about the biology of Microcystis and what can contribute to it and kind of go down the list to rule out any possible explanation,” Polera said. “We started with the conditions in the river and we asked what is special about these four summers and at this location that may have changed to now support these blooms that we’ve never seen before.”
Were the summers between 2009 and 2012 particularly hot? Was there an unusual amount of nutrients in the river? Did the turbidity change in a way that would favor Microcystis blooms?
Polera first turned to monitoring data collected between the early 1990s through the 2000s. It was determined that there was nothing particularly unique about those summers or that location.
Researchers then turned way upstream to Jordan Lake where waters, they knew, had harbored other cyanobacteria in the past. Could a chance in the lake have created conditions that allowed Microcystis to incubate there and send it down river?
No. Researchers determined that the blooms that appeared that far downstream could not have possibly gotten there from the lake.
“We’ve never seen blooms at any other areas of the river that have the same type of lake-like characteristics that Lock and Dam 1 does. There were no blooms behind Buckhorn Dam, no blooms behind Lock and Dam 3 and there were occasional surges out of Jordan Lake when they got really big rains that we didn’t see blooms immediately following that,” Polera said.
Next, researchers focused a little closer to Lock and Dam No. 1, turning their attention to major industrial dischargers.
They were able to rule out wastewater treatment plants in Fayetteville and Elizabethtown.
But they could not eliminate Smithfield Foods’ plant in Tar Heel, a tiny town in Bladen County that’s home to the largest pork-processing facility in the country.
After confirming the presence of Microcystis in samples of discharge from the plant, researchers combed through monitoring reports to look at whether there was a correlation between when the facility discharged into the river and when the blooms appeared.
Next, researchers compared the Microcystis found in the plant’s discharge to that found downstream near the dam.
“Yes, there’s chlorophyll in there. Yes, there’s Microcystis. Yes, there’s enough nutrients. Yes, they were discharging during the times. Yes, they were discharging enough based on our calculations and modeling that what was coming out of the discharge was enough to seed the population that we saw downstream. I just can’t find anything in their data and in our sampling to say, no, this wasn’t possible,” Polera said.
One simple way to prevent the possibility of future blooms, she said, is for regulatory agencies to require industries that may have chlorophyll a, which allows algae to use sunlight to convert molecules into organic compounds, to monitor for that particular type of chlorophyll.
The EPA is currently proposing revisions to wastewater discharge standards for meat and poultry products facilities. The revisions would require facilities to reduce the amounts of nutrients and other pollutants they discharge by using “affordable and available wastewater treatment technologies.”
“I think the good news is we have been watching now for over 10 years,” Polera said. “We’ve been prepped and ready to go if it ever does happen again. The water utilities are very prepared, if it does happen, to make sure that nothing gets into the drinking water and they can do that very effectively. As far as the risk goes, the water utilities and researchers that are really keeping an eye on the conditions of the river have it covered. My hope is that with all that preparation and additional monitoring, I would be surprised if we see it again.”
