[USA] Scientists agree Lake Okeechobee discharges, not septic tanks, caused a 2016 St. Lucie River algae bloom that wrecked the environment and water-related businesses.
This was after much debate over what caused the bloom. Residents have been reminded of the importance of septic tank cleaning and repair to make sure nearby water isn’t contaminated by any leaks caused by lack of maintenance.
While septic tank leaks can sometimes cause harm to a river’s pH, it has now been found that they aren’t part of the issue that caused this particular algae bloom. Instead, it was the discharges from a nearby lake.
But the ongoing debate is this: Did algae carried from the lake into the river turn into the thick, toxic, noxious, guacamole-like blooms by feeding on nutrients from septic tank runoff?
Three scientists TCPalm interviewed this week offered three different points of view:
Septic tank nutrients fed the algae, said Brian Lapointe, a research professor at Florida Atlantic University’s Harbor Branch Oceanographic Institute near Fort Pierce.
The algae was already dead or dying when it hit the river, so it didn’t feed on septic tank nutrients, said Edward J. Phlips, a professor of algal physiology and ecology at the University of Florida Center for Aquatic and Invasive Plants.
The algae was alive and feeding, but on agricultural fertilizers in the lake water, not septic tank nutrients in the river, said Edith “Edie” Widder, founder and lead scientist at the Ocean Research & Conservation Association in Fort Pierce.
The year-old issue arose again this week thanks to a video released Wednesday by the Florida Chamber of Commerce.
“You don’t see those really high, dense mats of algae until they actually hit the nutrient-rich portion of the estuary,” says Ernie Barnett, the Florida Land Council’s executive director and South Florida Water Management District’s former second in command.
Barnett’s argument originates with research by Lapointe, whom the statewide chamber paid to produce this and four previous videos about Florida’s water woes.
Lapointe maintains septic tank runoff is one of the primary sources of pollution in the lagoon. He admitted to TCPalm in July 2016 that septic leaks didn’t cause that year’s bloom, but added: “When the algae from the lake enters the estuary, it encounters high concentrations of what we call ‘active’ nutrients; and that makes the blooms explode.”
That’s not what happened, Phlips countered. The algae bloom didn’t “explode” in the estuary; in fact, the algae didn’t even bloom.
“To say the algae ‘bloomed’ in the estuary is a misnomer,” Phlips said; it was dying.
Healthy algae, he said, can be found at all depths of a water body. The 2016 algae bloom in Lake O, for example, could be seen as scum on top of the water but was below the surface as well.
Once algae in the water discharged from Lake O reached the St. Lucie, Phlips said, “it got stressed by the non-ideal conditions, the slightly elevated salinity.”
The stressed-out algae floated to the water’s surface.
“When algae floats to the surface and becomes scum, it’s not happy,” Phlips said. “It’s on its way out. The dying algae floated to the surface of the water, then winds blew it, massive amounts of it, into bays and canals and marinas.”
The algae mass didn’t explode, Phlips said, “it got concentrated.”
Lapointe’s response: “I don’t buy that at all, and I think the evidence proves I’m right.”
First, Lapointe pointed to data from remote-controlled water monitors showing the Lake O discharges had removed practically all the salinity from the areas of the St. Lucie plagued by the blooms before the algae stared blooming.
In fact, a LOBO monitor maintained by Harbor Branch in the river off downtown Stuart indicates low salinity from mid-May to mid-July 2016, the period of the worst algae blooms.
“That part of the St. Lucie was basically a freshwater lake for over a month before the algae arrived,” he said. “So there was no stress on the algae from salinity. It was a living, growing organism as long as the water remained salt-free.”
Lapointe said samples he took during the bloom showed algae was “assimilating,” or feeding.
Other data from the Florida Department of Environmental Protection, Lapointe said, shows the algae got more toxic as it grew in the estuary – a result, he thinks, of taking in all that nitrogen.
“Algae that’s taking in nitrogen and getting more toxic isn’t dead,” he said.
Pros and cons
Both arguments have good points and weak ones, Widder said.
Phlips is right that the algae was floating, Widder said, but it wasn’t dying: A lot of dead algae would have dropped oxygen levels in the water and possibly caused fish kills, but that didn’t happen.
And unlike Lapointe’s contention, the algae probably didn’t feed on nutrients from septic tanks, she said.
Freshwater from Lake O tended to float on top of the heavier, saltier water in the estuary, Widder said, and the two layers didn’t mix much.
“Which means most of the nutrients fueling the bloom were probably carried with the freshwater from the lake,” Widder added.
The two layers, freshwater over saltier water, also has been credited with keeping salt-loving oysters in the estuary alive despite the prolonged discharges.
Make the switch
Still, both Lapointe and Phlips support switching homes on septic tanks to municipal sewer systems – Phlips just not as adamantly as Lapointe.
Switching from septic to sewer “is a great idea,” Phlips said. “There’s no disputing that septic tanks contribute nutrients and pollution to water bodies like the lagoon and the St. Lucie River. But if you expect making the switch will make the blooms go away, it won’t.”
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