UF scientists to probe downstream ecological impacts of stormwater ponds

Posted 3/17/21

Although ponds do help water quality, research has shown that ponds aren’t as good at removing nutrients

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UF scientists to probe downstream ecological impacts of stormwater ponds

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GAINESVILLE — Florida teems with rain. Depending on where you live, you might get 40 to 60 inches annually. That rain must go somewhere. Enter Florida’s 76,000 stormwater ponds. When it rains, the water runs off the land, bringing chemicals, grass clippings, lawn debris and more from the landscape into these ponds.

Yet little to no research analyzes downstream ecological impacts from those ponds. Stormwater ponds were originally designed to reduce downstream flooding and are expected to provide water quality benefits by preventing things like sediments or nutrients from entering natural water bodies.

Although ponds do help water quality, research has shown that ponds aren’t as good at removing nutrients such as phosphorus and nitrogen as they were originally designed. Nutrients not removed by the ponds might go from the stormwater pond – which collects the rain and debris – to nearby bodies of water.

A University of Florida scientist will embark on a study this summer, using Manatee County as his lab. But his results will apply to much of Florida, including Tampa Bay and Biscayne Bay.

“We think ponds are pretty good - but not great - at removing nutrients from stormwater runoff,” said AJ Reisinger, a UF/IFAS assistant professor of soil water sciences. “But we know that only from measuring activities in the ponds themselves. We have very little information related to how stormwater ponds affect nutrient cycling and ecological processes of natural water bodies downstream of stormwater ponds.”

“Stormwater ponds are meant to protect the quality of downstream natural water bodies but aren’t designed or constructed to have good water quality themselves,” he said

Reisinger gave the background for his upcoming research project at the UF/IFAS Urban Landscape Summit last week.

Because ponds are designed to protect downstream ecosystems, it’s important to know what’s happening within ponds themselves, Reisinger said.

“To really get at whether or not the ponds work, we need to assess those downstream ecosystems,” he said. His new research will serve as a precursor to other studies that will provide recommendations on how to improve stormwater ponds themselves. “Once we identify whether natural water bodies are influenced by stormwater ponds, we will be able to design research and management recommendations for the ponds so we can reduce their impacts further. Our upcoming research will identify the problem, allowing future projects to work toward finding the solution.”

Reisinger will study wet stormwater ponds, not to be confused with dry ponds. Wet ponds are permanently flooded and look like what you would think a natural pond would look like. Dry ponds look like dug-out holes in the land that fill up with water when it rains but then drain out within two to three days later.

Developers often install wet stormwater ponds to capture runoff from urban landscapes and reduce flood risks.

“You can think of a stormwater pond sort of like a wastewater treatment plant - albeit getting stormwater runoff instead of wastewater - the chemistry of the pond effluent is probably different than what is in the natural river into which that pond discharges,” Reisinger said. “But we don’t know anything about how these pond discharges alter processes in streams or rivers that receive them.”

Rivers can take up and retain nutrients before they are discharged even further downstream into sensitive water bodies like Tampa Bay or Biscayne Bay. Ponds might increase or decrease the ability of the rivers they feed into to remove nutrients.

“We’re going to try and find that out by looking at changes in nutrient and energy cycling in the Braden River as it flows from its headwaters in an undeveloped area through developed communities with hundreds to thousands of ponds,” Reisinger said. “We’ll look at changes in ecological processes affecting nutrients in the river above and below these ponds. Results will tell us more about how well ponds are actually protecting downstream water quality and the ability of those downstream waters to protect themselves.”

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