FAU study pins Indian River Lagoon pollution problems on septic tanks

When it comes to pollution in the Indian River Lagoon, everyone has a boogeyman.

In a year when record manatee deaths were scrutinizing lagoon pollution, some blame Lake Okeechobee’s freshwater runoffs for eelgrass evisceration. Others point to a flood of rainwater choking the estuary with nutrient-rich fertilizers from nearby farms.

For Brian Lapointe, a scientist with the Harbor Branch Oceanographic Institute, one polluter should bear most of the blame: human waste leaking from septic tanks.

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“It’s the greatest boogeyman we can do something about to really save the lagoon,” Lapointe said in a recent interview with TCPalm.

Lapointe, an eminent researcher who routinely cites septic systems as the main source of pollution in the St. Lucie River and Indian River Lagoon, previously confirmed to TCPalm that Lake Okeechobee is the largest source of harmful algal blooms in the St. Lucie River estuary .

For a study published last month in the Marine Pollution Bulletin, researchers from Lapointe and Florida Atlantic University looked at water quality at 20 locations in four Indian River County’s drainage basins. According to the study, the team found:

  • Even “properly functioning” sewage treatment plants pollute nitrogen in shallow groundwater
  • The nutrient load was higher during the rainy season
  • Shallow ecosystems, like the central Indian River Lagoon, have a hard time flushing or diluting pollution, making them more susceptible to contaminated groundwater
  • Florida’s sediments – sandy soil and limestone – are not suitable for removing nutrient pollution from sewage treatment plants
  • The problem is “likely widespread” in the 156 mile long lagoon.

The study completed about six years ago but is now being published after lengthy peer review and amid the surge in manatee deaths, Lapointe said.

In 2015, researchers measured nitrogen isotopes in groundwater and surface water to pinpoint sources of nitrogen affecting the lagoon. According to Lapointe, they used sucralose – an artificial sweetener that sewage treatment plants or sewage treatment plants don’t completely purify – as a detector for human wastewater.

“Our research shows that sewage is generally the largest part of the problem” – particularly in the northern part of the lagoon, Lapointe said.

Are septic tanks the biggest problem?

Wastewater is “the main driver” of the algal bloom, said Lapointe. But when he pressed for it, he admitted that his research did not determine the total percentage in which sewage contributes to total lagoon pollution.

“I’m not saying that no fertilizer is coming in, but in the studies we are doing on groundwater … the (isotope) accumulation levels correspond to the wastewater, not the synthetic fertilizers used on the farms.” said Lapointe.

Brian Lapointe, research professor at Florida Atlantic University's Harbor Branch Oceanographic Institute, speaks at the Everglades Coalition's annual conference in Naples, January 2014.

It’s not the first time that Lapointe’s research has come to similar conclusions about the effects of sewage on the lagoon. In 2018, a FAU study found that fertilization bans reduce the nutrients in the lagoon, but do not stop the algae bloom. A year earlier, he had stated that septic tank runoff in the summer of 2016 was a major contributor to the toxic blue-green algae blooms in the St. Lucie River.

When announcing the new research, FAU largely disregards the fertilizer runoff as the main cause of the harmful algal blooms in the lagoon.

“For more than a decade, fertilizer leaching and associated rainwater runoff has been the leading cause of harmful algal blooms in Florida’s Indian River Lagoon,” the university wrote in a press release announcing its findings.

“Despite the numerous fertilization ordinances for residential areas that have been enacted since 2011, the water quality, harmful algal blooms and the loss of seaweed … have continued to deteriorate.”

More than a boogeyman

There isn’t just one pollution boogeyman who haunts the lagoon. Indeed there are many.

The Florida Institute of Technology in Brevard County cited the increasing development and “a deadly chain reaction started from fertilizers and sewage” that have decimated marine life over the decades.

According to the regional non-profit Marine Resources Council, nitrogen enters the lagoon, one of the most biodiverse estuaries in the country, from many sources:

  • Water contaminated by fertilizers
  • Leaky wastewater infrastructure
  • Septic tanks
  • Animal waste
  • Black mud or “filth” that covers about 11% of the lagoon floor.

All of these polluters enter the lagoon via storm sewers, canals and seepage water.

“Nitrogen … in excess can be devastating, causing algal blooms and lowering dissolved oxygen in water, which suffocates life,” the council wrote in its 2021 lagoon report.

Septic tanks are, of course, part of the problem. About 40% of the septic tanks on the east coast of Florida are in the six counties bordering the lagoon, which equates to more than 300,000 systems. In the counties of Indian River and Martin, over 50% of all wastewater disposal is taken over by sewage treatment plants, according to studies by the FAU.

One of five septic tanks on the barrier island of Vero Beach has failed, recent mandatory inspections have shown.

During the five-year inspections and pumping operations, 19.4% of the beach water treatment plants showed signs of failure, potentially adding pollutants to the lagoon, according to Rob Bolton, the city’s water and sanitation director.

“This is a pervasive and insidious problem that gets worse over time,” said Lapointe. “If you move to Florida, buy a house with a septic tank near the water. … But our groundwater is closely related to our surface water in Florida. It really is a water system. I don’t think people really understand. “

For more news, follow Max Chesnes on Twitter.

Max Chesnes is a TCPalm environmental reporter who focuses on the problems of the Indian River Lagoon, St. Lucie River, and Lake Okeechobee. You can stay up to date with Max on Twitter @MaxChesnes, email him at [email protected] and call him at 772-978-2224.

Read more of Max’s stories.

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