FAU study shows nitrogen from human waste significant driver of Lake O algae blooms

Lake Okeechobee is ready for the next step.

New research published in the journal Harmful Algae shows that managing phosphorus levels in Florida’s waterways is insufficient to combat algae blooms in Lake Okeechobee.

The study comes from Florida Atlantic University’s (FAU) Harbor Branch Oceanographic Institute, which found that nitrogen from human waste is a significant driver of those blooms.

A release from FAU summarized the researchers’ findings.

“Historically, Lake Okeechobee has only been considered to be impaired for phosphorus, leading to targeted efforts aimed at reducing phosphorus runoff from agricultural sources in the watershed,” reads the release. Researchers found that putting the sole spotlight on phosphorus is mistaken.

“Inorganic nitrogen levels were elevated in urbanized estuaries and the Kissimmee River, which extends north through the Kissimmee Chain of Lakes to the greater Orlando area, and its water flows into Lake Okeechobee. Furthermore, the expanding urbanization in Orlando was identified as a contributing factor to the increasing prevalence of these blooms in Lake Okeechobee.”

The study did note that phosphorus is also a contributor to those blooms. Historically, that fact has been used to push for more regulation of runoff from nearby farms, which contained significant amounts of phosphorus in the past.

However, as reported by the South Florida Sun-Sentinel in 2016, less than 6% of the phosphorus in Lake Okeechobee came from land south of Lake Okeechobee, where farms are prevalent. That’s due in significant part to farmers’ efforts to cut down on phosphorus discharges per the 1994 Everglades Forever Act, as reports have shown consistent progress in meeting environmental standards under the law.

Now, regulators and lawmakers appear to have an entirely new target to address to rehabilitate Lake O.

Brian Lapointe, Rachel Brewton, Malcolm McFarland, and Nicole Stockley were the researchers who worked on the FAU study.

Lapointe has studied this issue for years, briefing the Legislature on findings related to lake pollution.

“Based on our study findings, strategies focused only on reducing phosphorus aren’t sufficient,” said Lapointe, the study’s senior author and a research professor at FAU Harbor Branch.

“To tackle toxic cyanobacterial blooms, we need to cut back on both nitrogen and phosphorus. Managing both nutrients is crucial because of their combined impact, which often lead to more severe and persistent harmful algal blooms. In urban areas like the St. Lucie and Caloosahatchee River watersheds, human waste is a major source of these nutrients.”

The study’s findings suggest that development near estuaries that feed into the lake is a driver of the added nitrogen in the lake.

“When water and Microcystis is released from Lake Okeechobee into the estuaries, the growth response is like ‘Miracle Grow,’” Lapointe said. “We found the highest concentrations of ammonium, nitrate and phosphate in the estuaries. These nutrients are commonly associated with human waste. Specifically, we observed elevated nitrogen isotope levels, indicating that human waste is a significant source of this nitrogen.”

The FAU release also highlighted other findings supporting the idea that human waste is a big problem.

“The biggest blooms were observed in the Pahokee Marina and Cape Coral, which were strongly affected by human waste,” reads the release.

Lapointe confirmed that studying other parts of the state reinforced that idea.

“Evidence from the Florida Keys shows similar trends of nitrogen enrichment, and our research indicates that such changes may be happening throughout the entire watershed,” Lapointe said.

Brewton, a co-author and an assistant research professor at FAU Harbor Branch, highlighted the effects of nitrogen in a statement provided by FAU.

“Microcystis blooms and their toxicity in Lake Okeechobee and the St. Lucie Estuary are influenced by nitrogen levels, and our study shows that nitrogen enrichment is increasing. It’s crucial to reduce nitrogen to control harmful algal blooms along the lake’s waterway and downstream estuaries,” Brewton said.

“Given the high nitrogen load from the Upper Kissimmee River, cutting these inputs should be a top priority. Although Lake Okeechobee doesn’t have a Total Maximum Daily Load established for nitrogen as it does for phosphorus, the St. Lucie and Caloosahatchee estuaries do, and recent plans for the lake’s tributaries aim to address nitrogen reductions.”

Ultimately, Lapointe said that better understanding the causes behind algae blooms and other issues impacting Florida’s waterways is vital to keeping the state’s ecosystem healthy.

“These blooms don’t only impact Florida’s vital water resources but also have national implications for public health, environmental quality and economic well-being,” Lapointe said. “Understanding these changes helps us address the challenges of safeguarding our waters and ensures clean, safe water for communities across the country.”