Natural ponds are the best when it comes to removing rainwater
In the summer, the Sunshine State experiences daily storms, and with the rain, you have to manage flooding in some areas. Florida is swimming in 76,000 stormwater retention basins.
Although stormwater detention ponds are designed to control flooding, they are not as effective at removing nitrogen as natural ponds. Nitrogen is a pollutant that can leach downstream into lakes, rivers and other bodies of water, new research from the University of Florida shows.
Stormwater control measures must be implemented in new residential areas to respond to changes in stormwater runoff.
Stormwater retention basins are usually constructed before houses are built, as they must be in place before any potential hydrological or environmental impacts on downstream waters can occur. However, sometimes houses and settlements are built around naturally formed ponds.
Despite the large number of stormwater retention ponds, scientists say the internal processes within them are not yet sufficiently understood. That’s why Audrey Goeckner led the new study. Goeckner will earn her doctorate this summer in the UF/IFAS College of Agricultural and Life Sciences.
As part of her dissertation, Goeckner conducted this research under the supervision of AJ Reisinger, an assistant professor of soil, water and ecosystem sciences at UF/IFAS.
Scientists conducted the study in Melrose (natural ponds) and Bradenton (stormwater ponds), but they said their findings are likely applicable to all of Florida.
They measured the amount of dinitrogen gas dissolved in 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 nitrogen cycle processes: denitrification and nitrogen fixation.
Denitrification is the permanent removal of nitrogen from the system and improves water quality. Nitrogen fixation is an introduction of nitrogen from the atmosphere into the system and because it is a new nitrogen input, it has a negative impact on water quality.
Scientists found that the natural ponds they studied remove rather than produce nitrogen because they support denitrification rather than nitrogen fixation. In contrast, stormwater ponds equally remove or add nitrogen by supporting either net denitrification or nitrogen fixation.
“This is important because stormwater basins are designed to remove nutrients from runoff,” Reisinger said. “But when researchers compare the nitrogen content of water entering stormwater basins (stormwater runoff) and leaving the water (runoff), they find that stormwater basins often don’t remove as much nitrogen as we expect.”
The new research supports the concept that stormwater detention basins should be viewed as ecosystems that support a range of processes that alter matter cycles. They are not just inactive water basins where stormwater sediment settles, Goeckner said.
“Stormwater detention basins are one of the most widely used stormwater control measures,” she said. “If water managers are interested in targeted nitrogen removal, this work should prompt them to evaluate their effectiveness or consider alternative stormwater control ecosystems.”
