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Florida reservoir leak puts ecosystems at risk

Researchers fear that draining the pond is creating ‘perfect recipe’ for ecological harm

by Giuliana Viglione, special to C&EN
April 6, 2021


An aerial photo shows three large wastewater ponds
Credit: Associated Press
After one of the holding ponds at the Piney Point plant sprung a leak, crews began draining the pond to reduce the risk of nearby flooding.

Florida governor Ron DeSantis declared a state of emergency April 3 as wastewater from Piney Point, an old phosphate-processing plant, threatened to breach its holding pond.

The state began pumping water out of the pond to reduce the risk of flooding should the leaks detected in the reservoir’s lining cause failure of the pond walls. Although the reservoir’s levels are now low enough that the risk of catastrophic flooding has passed, according to the Florida Department of Environmental Protection (DEP) workers continue to pump more than 35 million gallons of water per day into Tampa Bay. This large discharge has raised concerns among many scientists that conditions are ripe for harmful algal blooms and long-term ecological damage to the bay.

The three wastewater ponds at Piney Point are filled with a combination of stormwater runoff, water used to process phosphate at the now-defunct plant, and seawater and material dredged from the nearby Port Manatee, says Matthew Pasek, a geochemist at the University of South Florida. The leaking pond is the least hazardous of the three, likely because of greater dilution of the contents with seawater or because of other water treatments at that pond.

Pasek notes that such holding ponds are common in the region, which produces about 70% of the US phosphate supply. The ponds also hold phosphogypsum, a form of calcium sulfate that is a side product of the process that turns calcium phosphate ore into ammonium phosphate. These so-called gypsum stacks also contain radioactive elements and other trace amounts of material contained in the original ore. But while the stacks themselves are slightly radioactive, much of the material is insoluble in water. “It’s not something you really need to worry about,” Pasek says.

The DEP says that the holding pond water entering the bay meets the standards for marine discharge except for nitrogen and phosphate levels and pH; data that Pasek have reviewed show that the phosphorus and nitrogen concentrations at the site are about 100,000 times as high as the natural concentrations of Tampa Bay. Of these three breaches of standards, the nitrogen concentrations are the most concerning, says Sarina Ergas, an environmental engineer at the University of South Florida, because “nitrogen tends to be the nutrient that fuels the growth of algae.”

In addition to producing toxins harmful to both humans and wildlife, decomposing algal blooms can draw down oxygen levels in the water, leading to mass die-offs of fish, seagrasses, and other important marine life. Such blooms are relatively common in Florida and elsewhere around the Gulf Coast because of high nutrient concentrations in fertilizer-laden runoff, says Justyna Hampel, a biogeochemist at the University of Southern Mississippi. The developing situation is “a perfect recipe for a harmful algal bloom,” she says.

The DEP and several of the surrounding counties are collecting daily water samples in the bay and analyzing them for nutrient content, chlorophyll, and water clarity, all of which are important indicators that could help reveal the formation of a bloom, says Marcus Beck, a program scientist at the Tampa Bay Estuary Program.

Although researchers have analyzed very few of the water samples so far, preliminary analysis of water collected at the discharge site shows ammonia concentrations that are 100-fold higher than the baseline data, Beck says, raising concern that ecological harm is a matter of when—not if—it occurs. “We’re kind of just in a waiting game,” he says. “We don’t know when these impacts are going to be manifested.”


This article was updated on April 8, 2021, to reflect changes to the situation at Piney Point since the story originally posted. The state is still pumping water out of the reservoir, but the evacuation notice has been lifted, and the immediate risk of catastrophic flooding has passed.


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