Study: Fertilizer bans cut nutrients in Indian River Lagoon, but don't stop algae blooms

Editor's note: This story has been modified from its original version, which had an incorrect phone number.

Fertilizer bans are doing a good job keeping nutrients out of the Indian River Lagoon, but not the type of nutrients that feed algae blooms.

That's the result of research to be presented Thursday during the Indian River Lagoon Symposium at Harbor Branch Oceanographic Institute, a branch of Florida Atlantic University at Fort Pierce.

Between 2010 and 2015, nearly every municipality along the Indian River Lagoon approved laws designed to keep nutrients in fertilizer from running off lawns and into the St. Lucie River and the lagoon. 

Most of the laws ban use of fertilizers with nitrogen and phosphorus during Florida's rainy season from June through September, when excess nutrients can feed algae blooms that shade and kill sea grass, as well as marine animals that depend on sea grass beds.

More: Editorial board gives fertilizer ban a 'thumb up'

"The bans are reducing nutrient levels, particularly nitrogen, in the lagoon," said Brian Lapointe, a Harbor Branch researcher and co-author of the study.

Citing a report by Tetra Tech, an environmental consulting firm, Lapointe's study states the amount of nitrogen sold in fertilizer along the lagoon dropped 45,896 pounds between fiscal year 2013-14 and 2014-15. 

"There may be less nitrogen in the water from fertilizer," Lapointe said, "but the effect isn't evident. That's because the nitrogen we're finding in the lagoon isn't the type you find in fertilizers, but it is the type that feeds algae blooms."

Algae blooms, Lapointe said, are bolstered by ammonia, "the reactive forms of nitrogen. To support an algae bloom, that's what you want."

That echoes a statement by Edie Widder, founder and lead scientist at Ocean Research & Conservation Association, who said ammonia "is like a Big Mac" to algae blooms.

More: ORCA: Ammonia like a 'Big Mac' for algae blooms in lagoon, St. Lucie River

The dominant source of ammonia in the lagoon, Lapointe said, is sewage.

Even with fertilizer bans, sewage runoff has caused an increase in nitrogen levels in the northern lagoon, especially in Brevard County, Lapointe said.

"Looking at all the data in the northern lagoon," Lapointe said, "we concluded that wastewater, in the form of septic leakage and antiquated sewage treatment facilities, is the big problem."

Ed Phlips, an algae expert at the University of Florida, agreed all kinds of algae "feed" on ammonia — and the brown algae that blooms in the northern lagoon "feeds" almost exclusively on it.

But other algae species, Phlips said, including the blue-green algae that blanketed the St. Lucie River in 2016, grow on the nitrogen found in fertilizer.

"Keeping all kinds of nutrients out of the lagoon is always a good thing," he said.

"I think we need to focus on pollution in the lagoon as a whole, and not get hung up on one thing, whether it's septic tanks or fertilizer," said Alexis Peralta, Indian River County's stormwater educator and fertilizer enforcement officer.

"We need to keep all the nutrients out," Peralta said, "and I think that in the four years our ordinance has been in place, we've made a real impact."

Citing sewage

Lapointe has reached similar conclusions about the impact of sewage in the lagoon before.

In a study published in the December issue of the journal "Harmful Algae," he stated septic tank runoff was a major contributor to the toxic blue-green algae blooms that festered in the St. Lucie River during the summer of 2016.

Like other scientists, Lapointe agreed the bloom was caused by algae in the water discharged from Lake Okeechobee to the river.

More: Scientists agree: Lake O discharges, not septic systems, caused algae bloom

"But once the algae in the lake water got to the (St. Lucie) estuary, it exploded because of all the nitrogen, particularly ammonia, from septic systems," Lapointe said.

Lagoon symposium

Restoration will be the theme of the Indian River Lagoon Symposium on Thursday and Friday at Harbor Branch Oceanographic Institute at Fort Pierce.

Thursday will be geared toward scientists, as dozens of researchers will give  presentations on their work to study and preserve the lagoon.

How wonky will it be? One presentation is titled "Integrating Flow: Cytometric and Molecular Tools to Characterize Bloom Dynamics of Nano- and Picplanktonic Algae in the Indian River Lagoon."

Friday's sessions are open to the public, with numerous organizations giving presentations and leading discussions about their work in the lagoon and how they need the public's help.

A group from the University of Central Florida will conduct a focus group to learn about public perceptions of the lagoon as part of a larger National Science Foundation project on lagoon restoration.

If you go

• What: Indian River Lagoon Symposium
• When: 8:45 a.m. to 1 p.m. Friday
• Where: Harbor Branch Oceanographic Institute, 5600 N. U.S. 1, Fort Pierce 
• Registration:Online 
• Information: Jill Sunderland at 772-242-2506