FAU study: Septic tanks add to Treasure Coast’s algae woes
Nitrogen from the tanks found to feed blooms that start in Lake O.
Lake Okeechobee is not the lone culprit in the recurring algae blooms that plague Treasure Coast waterways, but an accomplice aided by thousands of nitrogen-spewing septic tanks, according to a recently published Florida Atlantic University study.
A peer-reviewed FAU paper that appeared in December’s issue of the journal Harmful Algae, says that algae in freshwater lake discharges grows exponentially when it reaches the St. Lucie River because of heavy nitrogen levels specific to septic tanks.
The fresh lake water weakens the brackish water ecosystem then the algae feeds on the reactive forms of nitrogen, such as ammonium and nitrate, that come from the tanks, according to the report.
Brian LaPointe, lead author of the study and a research professor at FAU’s Harbor Branch Oceanographic Institute, said the study was able to trace the nitrogen’s source not to fertilizer — long blamed for the growth — but to human sources.
“This is compelling evidence that the problem we are seeing with the algae blooms, even though they can originate in the lake and be carried into the estuary, is exacerbated by elevated nitrogen that is locally sourced from septic tanks,” LaPointe said. “Not to say there aren’t fertilizers there, but our work shows the wastewater signal is a major contributor supporting the bloom.”
Sucralose, an artificial sweetener, that was found in water samples was a key clue in identifying septic tanks as a contributing factor. Sucralose is not broken down by the body, and “not used by cattle.”
LaPointe presented the research, which he said was paid for by the Martin County Utilities
Department, at the National Harmful Algae Bloom conference in November.
“Everyone wants to blame this on the farms and there is a lot of denial about the wastewater problem,” LaPointe said. “People overlook the role of population growth on the Indian River Lagoon, and a lot of that growth has relied on septic tanks.”
A 2015 study by LaPointe found there are more than 300,000 septic tanks in a five-county area between the Jupiter Inlet and the Ponce Inlet in Volusia County. But LaPointe said Monday it could be closer to 600,000 because decades-old septic tanks may not be recorded in county records.
“It’s too many people, and too much poop,” said Bill Louda, an FAU research professor who studies phosphorus and nitrogen amounts in Florida’s waterways. “Once the bloom is in the lake and it makes it into the estuaries it gets more nutrients from the septic tanks and that perpetuates it and lets it grow to tremendous proportions.”
LaPointe’s study of water quality in the St. Lucie Estuary has been ongoing, but the septic tank component was criticized and dismissed by environmentalists in 2016 when a widespread algae bloom grew in the estuary after the Army Corps of Engineers began releasing Lake Okeechobee water to lessen pressure on the aging Herbert Hoover Dike.
The blame for the bloom was put squarely on Lake Okeechobee discharges, triggering legislation that fast-tracked the building of a new reservoir south of the lake to hold overflow instead of sending it east to the St. Lucie and west to the Caloosahatchee Estuary.
Gov. Rick Scott, who declared a state of emergency in 2016 in response to the algae outbreak, also proposed $60 million in last year’s state budget to help homeowners switch from septic tanks to sewer systems in response to the algae bloom.
“It has long been thought that the algal blooms found in Lake Okeechobee, which are caused by pollution such as runoffs from farms, were solely responsible for driving the blooms and their toxins in the St. Lucie Estuary,” LaPointe said.
Treasure Coast environmentalists are skeptical of LaPointe’s findings, arguing the amount of nitrogen from septic tanks is minuscule compared to what’s coming from agriculture.
“It isn’t all about septic tanks,” said Mark Perry, executive director of the Florida Oceanographic Society in Stuart. “I don’t want to discount that they could be a problem if they are located in a bad area, but let’s not lose focus on the big problem and that is Lake Okeechobee discharges and agricultural runoff.”
But LaPointe argues it’s flawed to look at total nitrogen output because it’s only specific forms called “reactive nitrogen” that feed algae growth.
“The harmful blooms aren’t just in the St. Lucie Estuary, we are seeing problems up and down the Indian River Lagoon,” he said.