Lack of nutrient criteria in Collier's canals leaves gaps in water quality restoration

Collier County’s canals shuttle freshwater toward the area’s estuaries leading to the Gulf, but the state has yet to set a limit on how much nutrient pollution they can contain.

The Florida Department of Environmental Protection identifies 57 different water bodies in the county, 21 of which are impaired since they don’t meet one or more water quality guidelines.

No one knows how much nutrient pollution is too much in Collier's canals. Experts say this could feed red tide in the Gulf, such as the 2018 bloom that devastated Southwest Florida. 

Typically, a guideline for any given pollutant will have an associated maximum limit. For instance, in the western Panhandle, limits for total nitrogen and total phosphorus are set at specific values: 0.06 milligrams per liter and 0.67 mg/L, respectively.

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In South Florida, however, FDEP’s nitrogen and phosphorus limits are vague and based on the natural populations of plants and animals within the canals, creating difficulties meeting standards downstream.

“The far majority of downstream-receiving water bodies are impaired for nutrients,” said Rhonda Watkins, Collier County’s pollution control manager. “They’re not meeting nitrogen and phosphorus criteria, so yeah, we have problems.”

FDEP did not respond to emails about the lack of criteria.

In 2019, the department published a canal study in South Florida monitoring surface water in Broward, Miami-Dade and Collier. Scientists typically look at organisms living within the sediment as indicators of the water quality and then set standards based on those findings.

The problem the study found, however, is that canals here are so highly managed.

“We control everything: water levels, flow, aquatic plants and scrape out the bottom,” Watkins said. “That affects everything that lives there that would have been used for reference.”

The conclusion of the study acknowledges a lack of biological diversity in the canals.

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The department met in mid-May for its triennial review of surface water criteria, and a draft report from that meeting still lacks specific criteria for canals in South Florida.

The guidance for nutrients (total nitrogen and phosphorus) says: “In no case shall nutrient concentrations of a body of water be altered so as to cause an imbalance in natural populations of aquatic flora or fauna.”

The lack of criteria is something the Conservancy of Southwest Florida has been working on for years, said Marisa Carrozzo, the group’s Everglades and water policy manager. Except for phosphorus in the Everglades, FDEP had no set standards for nutrient pollution in the entire state until 2013.

“As a result, there are now numeric standards for almost all water bodies in the state,” Carrozzo said.

The outliers are canal systems and nearly any freshwater that flows in South Florida, just south of Caloosahatchee watershed, she said.

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Nutrients such as total nitrogen and phosphorus occur naturally, but excesses can change vegetation and habitat leading to potential algal blooms.

“There are also indications that if anthropogenically (human-caused) sourced nutrients are going into coastal waters, and if there’s a red tide bloom that moves onshore, it can use those nutrients to proliferate, become more severe and last longer. It’s an equal opportunity feeder,” Carrozzo said.

In 2020, researchers at the University of Florida published a study correlating nitrogen runoff with red tide blooms in Charlotte Harbor.

The water in canals eventually flows out to the coast, Watkins said. The coastal waters have set standards for nutrient pollution, but none of the inland canals that flow into the Gulf do.

Collier County does have a pollution control ordinance in place, so any discharges into canals must meet standards.

“But if there is not a standard, we have no way to regulate or fix it,” Watkins said. “If we have nutrient issues downstream, we can’t say, ‘Stop releasing this amount of nitrogen or phosphorus.’”

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When standards are in place, the county can work with whoever is discharging to get those numbers down.

“Anything from education and outreach, making sure the fertilizer ordinance is being followed correctly and the stormwater management system is being maintained optimally,” Watkins said.

Other preemptive measures are also available, such as rain gardens that soak up nutrients before they reach canals to make sure irrigation is being done properly.

Karl Schneider is an environment reporter. Send tips and comments to kschneider@gannett.com. Follow on Twitter @karlstartswithk