Oysters in St. Lucie Estuary starting to see reprieve from freshwater runoff discharges
Max Chesnes
The monthly update from state water managers on the health of the St. Lucie Estuary came with a point of good news Thursday: For the first time since August, oysters are finally getting some reprieve from the recent deluge of rainfall runoff.
The salinity range for adult oysters surpassed 10 parts per thousand this week, or the minimum range needed for oysters to thrive, said Lawrence Glenn, director of the South Florida Water Management District's water resources division.
Anything less than that, and oyster growth can be slowed. The brackish estuary needs the perfect balance for oysters to survive, and too little or too much saltwater can be "detrimental" to the animal, Glenn told TCPalm.
That's good news for the beleaguered St. Lucie. Oysters are one of nature's best filters, removing pollutants at a rate of 50 gallons per day, for one adult oyster.
For comparison, seawater just offshore of Martin County measures at about 35 ppt, according to Glenn. Adult oysters start dying when water is below 10 ppt for 28 days.
"If it goes below that, obviously the oyster will start to become stressed," said Loraé Simpson, director of scientific research and conservation at the Stuart-based Florida Oceanographic Society.
"Depending on the amount of time that you have salinity below that, it can eventually lead to mortality," Simpson said.
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Freshwater releases slowing?
It's been exactly two months since the U.S. Army Corps of Engineers began releasing local basin runoff in the C-44 Canal through the St. Lucie Lock and Dam and into the St. Lucie River.
Last week, the Corps was releasing a weekly average rate of 35 million gallons per day of rainfall runoff into the river, Col. James Booth, commander of the Corps' Jacksonville District, told TCPalm during a weekly media call Friday.
That compares to mid-September, when more local rainfall meant water was released at an average rate of 206 million gallons daily, according to Corps data.
Smaller freshwater releases gives the oysters a chance to bounce back.
"We're finally creeping back into the good range for adult oysters," Glenn said during a SFWMD governing board meeting.
Despite that, researchers at Florida Oceanographic are having a hard time finding oysters above 3 inches, the minimum size allowed to harvest for studying, Simpson said.
A 3-inch oyster is usually about 2-3 years old, Simpson said.
"They're not surviving long enough," Simpson said. "Where did all of our entire population go? They've died, somehow, some way."
Cattle leases, LOSOM updates
Aside from the update on oyster salinity, state water managers Thursday also extended the lease of 557 acres of uplands in St. Lucie County for cattle grazing to Garry Webb.
The land falls in the area where the C-23/C-24 South Reservoir will be built, with construction targeted to begin around 2024, according to the District.
The north and south reservoirs together will store over 4 billion gallons of rainfall runoff annually that now drains from an 827-square-mile watershed in western St. Lucie County into the North Fork of the river, polluting it with nutrients, bacteria, herbicides, pesticides and more.
The cattle grazing agreement with the SFWMD, now extended for another five years, calls for six acres of land for every one cow, according to the District. The approximate annual revenue is $10,300.
Water managers also approved additional work on the pump stations for C-44 Reservoir Stormwater Treatment Area Project. The approval includes the replacement of wiring and changes to vacuum piping — small steps that will ultimately lead to the final operation of a pump station that will draw water otherwise heading into the river.
The new playbook for managing Lake Okeechobee for roughly the next decade — dubbed the Lake Okeechobee System Operating Manual, or LOSOM — also got several mentions during Thursday's board meeting.
On Wednesday, the Corps released new model data guiding them toward a final decision in November. The agency will host a meeting to discuss the data Oct. 26, and will announce a final optimized plan Nov. 2.
"That's the important part: We've got these next few years - we don't know what the climate's going to be, we don't know what the weather's going to be, but we've got to have the manual words right in order to give the water managers the ability to make the right decisions," said SFWMD Executive Director Drew Bartlett.
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Max Chesnes is a TCPalm environment reporter focusing on issues facing the Indian River Lagoon, St. Lucie River and Lake Okeechobee. You can keep up with Max on Twitter @MaxChesnes, email him at max.chesnes@tcpalm.com and give him a call at 772-978-2224.