Natural ponds are better than stormwater ponds at removing nutrients.

Summer brings daily storms to the Sunshine State, and with the rain comes flood control in some neighborhoods. Florida is inundated with 76,000 stormwater ponds.

Designed to control flooding, stormwater ponds are not as effective as natural ponds at removing nitrogen, a pollutant that can wash downstream into lakes, rivers and other bodies of water, new research from the University of Florida shows.

New neighborhoods must use stormwater control measures to manage any changes in stormwater runoff.

Stormwater ponds are often installed before homes because they need to be in place before potential hydrologic or ecological impacts occur on downstream waters. But sometimes homes and developments are built around natural ponds.

Despite the prevalence of stormwater ponds, scientists say the internal processes within them are poorly studied.

That’s why Audrey Goeckner led the new study. Goeckner will earn her Ph.D. in the UF/IFAS College of Agricultural and Life Sciences this summer.

As part of her dissertation, Goeckner conducted this research under the supervision of A.J. Reisinger, UF/IFAS assistant professor of soil, water and ecosystem sciences.

The scientists conducted the study in Melrose (natural ponds) and Bradenton (stormwater ponds), but said their findings are likely applicable throughout Florida.

They measured the amount of dissolved dinitrogen gas in the ponds. Dinitrogen makes up 80% of the atmosphere and the amount dissolved in a pond can be used to understand the balance of two competing processes in the nitrogen cycle: denitrification and nitrogen fixation.

Denitrification is the permanent removal of nitrogen from the system and benefits water quality. Nitrogen fixation is an input of nitrogen into the system from the atmosphere and, as it is a new input of nitrogen, it negatively affects water quality.

The scientists found that the natural ponds they studied were more likely to remove nitrogen than produce it, by favoring denitrification rather than nitrogen fixation. In contrast, stormwater ponds were equally likely to remove or introduce nitrogen, by favoring net denitrification or nitrogen fixation.

“This is important because stormwater ponds are expected to remove nutrients from runoff,” Reisinger said. “But when researchers compared the nitrogen in the water entering stormwater ponds (stormwater runoff) to that leaving them (discharge), stormwater ponds often don’t remove as much nitrogen as we expected.”

The new research supports the concept that stormwater ponds should be recognized as ecosystems that support a variety of processes that alter elemental cycles. They are not simply inert water reservoirs where stormwater sediments settle, Goeckner said.

“Stormwater ponds are one of the most widely used stormwater control measures,” he said. “If water managers are interested in targeting nitrogen removal, this work should prompt them to evaluate their effectiveness or consider alternative stormwater control ecosystems.”