Wetlands: Cleaning Stormwater, Killing Blood-Suckers

Developers most often use “wet ponds” to minimize stormwater runoff pollution at new real-estate developments. Now they may have to start rethinking their options. Research shows that building wetlands does a better job than wet ponds of removing pollutants – and could also help limit mosquito populations.

Researchers from NC State have weighed a range of ecological benefits associated with wet ponds, and compared them to constructed stormwater wetlands – a stormwater treatment technology that is used less often.

A wet pond is a retention basin that receives stormwater runoff and gives pollutants a chance to settle out before the stormwater is discharged. These ponds maintain a permanent pool of water, even in dry weather. Constructed stormwater wetlands are much shallower than wet ponds, and are designed to support a broader array of plant life. That biodiversity turns out to be pretty important.

Previous studies have shown that wetlands generally do a better job than wet ponds when it comes to removing nutrients (a key water quality problem), and that they are comparable at removing other pollutants.

But the new study shows that stormwater wetlands also foster biodiversity. Wetlands support a more diverse variety of plant life, and the researchers found that they host a greater diversity of insect life as well. That bodes well for larger, more charismatic animals. “When you find a more diverse population of insects, that indicates that the habitat is better able to support other wildlife, such as amphibians and waterfowl,” says Trisha Moore, a Ph.D. candidate at NC State who worked on the study.

And, while biodiversity is important in its own right, there are also selfish reasons to support a diverse insect population: it can cut down on mosquitoes. The researchers found higher mosquito larvae populations in waters that had less insect biodiversity. “The greater your insect diversity, the more likely you are to have species that prey on mosquito larvae,” Moore explains. Take that, bloodsuckers!

The researchers will be discussing their findings, including the biodiversity benefits, at two workshops on constructed stormwater wetlands in early June.