Researchers are focusing on high nitrogen levels in one stormwater lake and a fish kill.

ST. PETERSBURG – After initial testing in and around a retention pond known as Riviera Bay Lake, independent biologists from Arcadis have discovered a potential cause.

“There’s a significant nutrient impact on this stormwater lake,” interim water resources director John Palenchar said. “A lot of nitrogen was seen in the analytical results that came back from this lake.”

Arcadis biologists say potential sources of the increased nitrogen could be from runoff containing fertilizers which create the neighborhood’s landscaping up to the lake shore, as well animal waste. They also point to a cold-weather snap that occurred the first week of January, which produced an inversion event. Inversion events occur when the surface water temperature drops dramatically and is replaced with a bottom layer of water, containing lower levels of oxygen. That led to a substantial fish kill in the lake – primarily of tilapia. Tilapia are mainly freshwater fish, known for an inability to survive in cooler waters, and inhabit shallow streams, ponds, rivers and lakes and less commonly found living in brackish water -and are a food source of pelicans.

“It was very likely some sort of pathogen within the freshwater fish that may have caused this,” Palenchar said. While studies continue to further pinpoint the problem, including tests on samples obtained along Coffee Pot Bayou, Palenchar said he is confident that Florida Fish and Wildlife Conservation Commission-initiated necropsies and future Arcadis findings will help chart a course of action to remedy the situation, including aerating dissolved oxygen in the lake.

“Being able to put in a fountain or a pump could actually alleviate that,” he said. “We are asking Arcadis to look at any best management practices or improvements that can be done to improve water quality.”

City officials hired Arcadis U.S., based in Melbourne, in mid-January to work with the city and the FWC to gather clues into what was causing pelicans to be sick and to die.

The latest findings from Arcadis are available at stpete.org.

St. Petersburg | Pelicans | Dead Pelicans | Arcadis | Riviera Bay | TB Reporter

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