Overland Park’s ‘floating wetland’ looks to have potential in fighting algae in South Lake Park

Floating wetlands
The floating wetlands at South Lake Park are taking up nutrients and reducing algal blooms.

After nine months of testing out the floating wetland aimed at reducing toxic algal blooms at South Lake Park, Overland Park city staff brought it in last week to see if it’s working. Turns out, it is working so well that they hope to expand the program in the near future.

Ian Fannin-Hughes, a water quality specialist with Overland Park public works, said city staff brought in the floating wetland — a manmade island with native Kansas wetland plants growing on it — to shore on June 14 to observe it, see how well the plants were growing on it and see if any invasive plants or weeds had sprouted.

Floating wetlands
City staff in September 2018 planted native Kansas wetland plants on the manmade island in South Lake, including blue flag irises, sweet flag flowers, soft rushes and sedge.

The island needs to be significantly larger to see a reduction, he said. But they found that the wetland can be maintained easily with little material and will survive in the climate.

“It’s taking up nutrients and it’s reducing algae but it’s not doing it on a scale that we can tell right now,” he said.

When staff brought the wetland to shore, they lifted it out of the water and measured the root systems. While they were working, children at the youth fishing derby got a close-up look at the wetland project.

“Most of the roots are dipping down into the water probably about a foot to two feet — pretty good for what we expected — which means that there’s a lot of nutrients in the water and that the plants are really thriving in that situation,” Fannin-Hughes said. “When we observed it, we were excited to see that all the plants were doing well, that nothing was eating it.”

The water quality project is aimed at improving the lake’s appearance and limiting the amount of harmful algal blooms that occur in the lake.

“They’re out there to soak up the nutrients and ideally reduce phosphorus to a level that would minimize the amount of algae that’s out there and the occurrence of toxic algal blooms,” he said. “Harmful algal blooms have been in this lake for at least 10 years that we know of, and they continue to expand in their duration and their toxicity as we’re getting warmer weather, we’re getting longer periods of drought-like conditions that exacerbate the algae in the lake. It’s important that we reduce this public safety problem at the lake.”

A close-up look at the plants on the floating wetlands. Photo courtesy of Ian Fannin-Hughes

Reducing the toxic algal blooms also improve the water quality downstream, as water flows from the lake into Indian Creek and, eventually, the Blue and Missouri rivers, he added.

The native plants on the floating wetland include blue flag irises, sweet flag flowers, soft rushes and sedge.

“None of the plants looked stressed. None of the plants really seemed to be out of their element,” Fannin-Hughes said. “They’re native wetland species, so they will occur here naturally, but being out in the middle of the lake on top of a buoyant structure isn’t quite a natural habitat. But it mimics it close enough that really all the plants did really well.”

The program is working so well that they hope to expand the wetland by 10 times its size.

The 75 square foot wetland can reduce about three pounds of phosphorus a year. Fannin-Hughes said calculations show that they must reduce up to 120 pounds of phosphorus per year to eliminate algae in the lake.

To reduce the amount of harmful algal blooms, they must shoot for a goal of reducing 60 pounds of phosphorus per year, which means they need a floating wetland to be 1,000 to 1,500 square feet.