Research shows urea causes blue-green algae bloom under certain conditions in Lake O system
Scientists are trying to better understand what forms of nutrients fuel cyanobacteria blooms, and at least one test points to urea.
Researchers from the U.S. Geological Survey, Nova Southeastern University and – as an extension – Florida Gulf Coast University, were given a $2.4 million, three-year grant from the U.S. Army Corps of Engineers to map out the genetics of microscopic organisms living in Lake Okeechobee and around water control structures in the Caloosahatchee and St. Lucie rivers.
A second phase of the project focuses on how Caloosahatchee water responds to various forms of nutrients in hopes of seeing which ones are capable of fueling a bloom.
"It tells us urea is a super food for algae," said Barry Rosen, an FGCU professor and one of the nation's top experts when it comes to identifying toxin strains of bacteria, "if it's available for cyanobacteria, if it's the right concentration. If it were urea it could be coming from septic tanks. But we don't know that."
Scientists from USGS and both universities placed large plastic containers called mesocosms at places like the W.P. Franklin Lock and Dam in Alva.
Various forms of nitrogen and phosphate were exposed to river water. Urea was added to some of the mesocosms in the river, and the growth of cyanobacteria, relative to the other forms of nitrogen, exploded.
Where does the urea come from?
Urea is the main nitrogen-containing substance in the urine of animals, but it's is also used heavily in fertilizers as a source of nitrogen.
"Ammonia and nitrate didn't look all that different than others, so we added urea and at least visually the urea seemed to be a big stimulate," Rosen said. "That's unwrapped candy to these organisms. They took advantage of the urea dose."
Joe Lopez is a researcher and professor at Nova Southeastern University and has been working on the project with Rosen, who applied for the grant several years ago while working for the USGS.
Rosen's work isn't part of the grant but he is still acting as a liaison for the project.
"It worked in terms of just what we could see in terms of physical growth and noticeably significant growth last month," Lopez said. "(But) urea is a common substance in the environment."
But there are many unanswered questions, like: Would that particular concentration of urea ever exist in the historic Everglades water network?
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"Whether it could get that dose in nature, we don't know," Lopez said. "It’s a fertilizer and it’s been linked to blooms from the past."
The historic Everglades is a 16-county region that stretches from just south of Orlando to Florida Bay and includes Lee and Collier counties.
Some giant changes to natural systems
Speculators blasted and dredged miles of canals in the upper Caloosahatchee and St. Lucie to connect them to Lake Okeechobee in order to help drain the Everglades for farming and development.
Combined with flow ways to the south, the rivers are used as a flood plain to release water when the Army Corps determines levels are too high.
The Caloosahatchee River now needs water from the lake during very dry times to establish balanced salinity levels in the river's estuary.
But sometimes water from the lake is tainted with cyanobacteria, which can produce toxins that threaten public and domestic animal health and can cause fish kills.
The project started in 2019, but bloom conditions haven't been extensive the past two summers.
This year was different as a bloom sprang up on the lake and in the upper Caloosahatchee River earlier this year.
"We’re not sure what’s causing the blooms this year but the last couple of years we’ve been monitoring they haven’t been this big," Lopez said. "But we were surprised to see a much larger bloom and that was happening before the rain even started."
Some organisms can absorb nitrogen from the atmosphere and may be able to transmit that nitrogen to the cyanobacteria, or blue-green algae.
That's one theory.
"This is all exploratory," Lopez said. "Hopefully it’s going to establish a baseline and we can add to this monitoring in the future. The communities are complex. They’re interacting. We’re trying to monitor what happens over time under different conditions."
Calusa Waterkeeper John Cassani said he thinks the urea is a sign that farming is impacting the river and estuary.
"I think urea is put in that category of organic nitrogen, which I think the dominant form and is mostly an agriculture contributor," Casani said. "The genetic markers are really powerful stuff in terms of segregating species and finding what's there. Some of the important things there are the ratio of nitrogen to phosphorus and perhaps iron in the water."
Rosen said he expects several papers will eventually be published about this research.
"We’re trying to see what factors might contribute to the bloom," Rosen said. "It’s going to most likely be multi-factorial. You’re not going to be able to point to one specific cause and say ‘this is causing the bloom and we can stop it.’"
Connect with this reporter: @ChadEugene on Twitter.