Lake Okeechobee discharges may prolong red tide outbreaks in Sarasota, study finds

You might not think that Lake Okeechobee would affect water quality in the Tampa Bay area. But when that fresh water is released to prevent flooding, it can make red tide worse off the coast of Sarasota, about 100 miles away.

That’s according to a peer-reviewed study study in The Florida Scientist. The study looked at the impact of nitrogen-rich water flowing west — out of the lake, down the Caloosahatchee River and into Estero Bay and Charlotte Harbor.

“The tons of nitrogen that you add 30 days before and 30 days after the start of a red tide bloom correlates with the duration of the red tide bloom. It is a very strong correlation,” said Steve Suau, water engineer and co-author of the study.

“What we’re basically saying is that humans aren’t causing red tides, but we can make them worse,” said lead author Dave Tomasko, director of the River Estuary Program. Sarasota Bay.

He said reducing the amount of water released from Lake Okeechobee could shorten red tide outbreaks on the Southwest Coast.

“To solve this problem, you have to address the flows. There is no magic wastewater treatment plant upgrade or stormwater modernization that will solve this problem,” Tomasko said. “We need to work above the lake, in the lake and below the lake to reduce flows enough to get the situation under control.”

The water in Lake Okeechobee and surrounding areas is rich in nitrogen due to industrial activity, agricultural runoff and septic tanks.

“Nitrogen is the food of the red tide. That’s what it likes. And so what exists 30 days before the red tide starts is like a simple food bank,” Suau said.

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The study focused on five river basins: Joshua Creek, Peace River, Horse Creek, Myakka River and 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 as it flows to the Gulf of Mexico.

“That’s one of the interesting findings. You can explain the duration of red tide almost as well by just looking at water flow as you can at nutrient loads,” Tomasko said.

The more nitrogen-laden water was released toward Sarasota, the longer red tide events lasted.

“There is nothing natural about our watershed and the nutrient loads from Tampa Bay, Sarasota Bay, Lemon Bay and Charlotte Harbor are two to four times what they used to be.” , Tomasko said.

“So if humans are bringing in excess nitrogen, and we know they are, and if red tide organisms can use nitrogen from all sources, then we should make the situation worse. And we know that for a few years now,” he added.

The latest findings show that “77 percent of the variability and duration of red tides, as we have defined them, is explained by the variation in the nitrogen load that comes out during this first 60-day period ” Tomasko added.

The research could be used to help water managers assess whether the impact of a project aimed at reducing pollution would be enough to shorten red tide outbreaks.

“If you have a project and everyone is really happy with it, but it only reduces nutrient loads by, you know, 5 percent, it might not make much difference,” said Tomasko.

“But if you have a project that can reach 20 percent, we can now say, ‘Well, that will reduce the next red tide by a few weeks, on average.’”

Tomasko said he is 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 did not make recommendations, “because everyone has their own opinion.”

And his?

“My opinion is that the state buy out Big Sugar and restore the Everglades, (and) let Lake Okeechobee flow back into the Everglades,” Suau said.