WEST PALM BEACH — Increases both in the number and frequency of water samplings from Lake Okeechobee are helping the South Florida Water Management District (SFWMD) track and learn about “blooms” of algae and cyanobacteria (commonly called blue-green algae) in Lake Okeechobee.
During the July 9 meeting of the SFWMD Governing Board, Lawrence Glenn provided an ecological update for July.
He said there is a little more algae potential this year than in 2019.
He said water samples are now taken every two weeks. The sampling taken June 23 and 24 had 32 samples, and had four samples with elevated levels of toxins. Two levels of concern were L004 (about 6 miles west of the Port Mayaca Lock) with 800 micrograms per liter and LZ40 (near the center of the lake) with 290 micrograms per liter. Levels under 8 micrograms per liter are considered safe for human recreational contact by the Environmental Protection Agency.
“We sent crews out a week later,” Glenn continued. At L004, the June 30 sampling found toxin levels had dropped to 1.3 micrograms per liter. At LZ40, toxin levels had dropped to 99 micrograms per liter.
There is still a lot to be learned about why microcystin is produced by cyanobacteria and when microcystin is released, he explained.
Glenn said many factors may influence reproduction of blue-green algae.
Spikes in the load of phosphorus and nitrogen to the lake may be what are providing the nutrient source for these algae blooms to proliferate, he said.
He said Dr. Barry Rosen has found nitrogen load is a critical factor for the development of toxins in cyanobacteria.
There is a theory that rains can disrupt the blooms, he said. A large bloom can also go through a nutrient load pretty quickly, he said, and may die off when it runs out of available nitrogen. (Some cyanobacteria can fix nitrogen from the air, but the June bloom was dominated by Microcystis aeruginosa, which is not a nitrogen fixer.)
Glenn said since last year, SFWMD went from six stations to 32 and went from sampling once a month to twice a month.
“We’re getting a lot more data on conditions in the lake,” he said.
He said there are no blooms near the outlets to the Caloosahatchee River and the St. Lucie Canal.
Glenn said the U.S. Army Corps of Engineers had some constraints on flow in the Kissimmee River last month in order to keep the work area dry for the portion of the river that is being restored.
Lake Okeechobee has been hovering right around 12.2 to 12.3 feet above sea level, he said. The marshes around the edge of the lake dried up when the lake fell below 12 feet earlier this year. Now that water is flowing back into the marshes, “we are seeing good response around the littoral fringe.
If the lake continues to rise slowly, it will continue to refill the marshes, he said.
“From a lake ecology standpoint, we want that gradual ascension,” he explained. If the water level rises faster than the submerged aquatic vegetation (SAV) can grow, it can endanger the SAV.
A survey of the SAV will be conducted in August and September, he said. The SAV provides the natural filter for the lake.