You may not think Lake Okeechobee would affect water quality in the Tampa Bay region. But when that freshwater is released to prevent flooding, it can make red tide blooms worse off the coast of Sarasota, around 100 miles away.
That's according to a peer-reviewed study in The Florida Scientist. It looked at the impact of nitrogen-rich water that flows west — from the lake, down the Caloosahatchee River and into Estero Bay and Charlotte Harbor.
"The tons of nitrogen that you're putting in 30 days before and 30 days after a red tide bloom starts correlates with how long the red tide bloom lasts. It's a really strong correlation," said Steve Suau, a water engineer and co-author of the study.
"What we're basically saying is humans aren't causing red tides, but we can cause them to be worse," said lead author Dave Tomasko, director of the Sarasota Bay Estuary Program.
He said reducing the amount of water released from Lake Okeechobee could shorten red tide outbreaks on the southwest coast.
"To fix this problem you have to go after the flows. There is not a magic wastewater treatment plant upgrade or stormwater retrofit that is going to fix this" Tomasko said. "We have to work up above the lake, in the lake and below the lake to reduce the flows enough to get this under control."
Water from Lake Okeechobee and surrounding areas is heavy in nitrogen due to industrial activity, agricultural runoff and septic tanks.
"Nitrogen is food for red tide. That's what it likes. And so what's out there 30 days before it starts is like just a bank of food," said Suau.
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The study looked at five river basins: Joshua Creek, Peace River, Horse Creek, Myakka River and the Caloosahatchee.
The statistically significant relationship was only present in the Caloosahatchee, suggesting a direct link over the past 16 years to the amount of water sent from Lake Okeechobee into the Caloosahatchee River that flows toward the Gulf of Mexico.
"That's one of the cool findings. You can explain the red tide duration almost as well just looking at water flow as looking at nutrient loads," said Tomasko.
The more nitrogen-heavy water released toward Sarasota, the longer the red tide events lasted.
"There's nothing natural about our watershed and the nutrient loads coming off of Tampa Bay, Sarasota Bay, Lemon Bay, Charlotte Harbor; they're like two to four times what they used to be," said Tomasko.
"So if humans contribute excess nitrogen, and we know they do, and if red tide organisms can use nitrogen from all sources, then we should be making it worse. And we've known that for a couple years now," he added.
The latest findings show that "77 percent of the variability and the duration of red tides, as we defined them, is explained by variation in the nitrogen load that comes out in that first 60-day period," added Tomasko.
The research could be used to help water managers assess whether the impact of a project to reduce pollution would do enough to shorten red tide outbreaks.
"If you have a project, and everyone's really happy about it, but it only reduces nutrient loads by, you know, 5 percent, it might not make much of a difference," said Tomasko.
"But if you have a project that can do, like 20 percent, now we can basically say, 'Well, that'll shave a couple of weeks off the next red tide, on average.'"
Tomasko said he's optimistic that a number of projects already underway to improve Lake Okeechobee and the Everglades will help reduce red tide outbreaks.
Suau said the study stopped short of issuing recommendations, "because everybody has their own opinion."
And his?
"My opinion is the state buys out Big Sugar and restores the Everglades, (and) lets Lake Okeechobee flow back into the Everglades," said Suau.
