Researchers Testing Floating Treatment Wetlands' Winter Survivability

Researchers Testing Floating Treatment Wetlands' Winter Survivability

Alexa Davis, (right) graduate student with the School of Natural Resources, and Tiffany Messer, assistant professor and water quality engineer at the University of Nebraska-Lincoln, in the Messer Laboratory surrounded by floating wetland experiments.

The grasses are dormant, their brown leaves poking the sky as they float in one of the now-frigid lily ponds in Lincoln, Nebraska's Sunken Gardens — the 1.5-acre public garden at 27th Street and Capital Parkway. During the summer season, the garden contains 30,000 living plants, bright bursts of color layered on the pocket of land where koi fish swim merrily in their ponds.

It is here Alexa Davis, graduate student with the University of Nebraska-Lincoln's School of Natural Resources, first anchored her living, floating treatment wetland — a collection of 12 Nebraska native wetland sedges and milkweed planted in holes in a buoyant rubber mat, the roots hanging down into the shallow water.

She set out to discover two things: whether the floating treatment wetland would reduce excess nutrients, such as nitrogen, from the water; and whether the plants can survive Nebraska’s harsh winter.

To answer the first, Davis collected and tested water samples from the middle of the two koi ponds (one a control site) and from the base of the fountain that feeds water into the two ponds. She needed metrics for temperature, as well as the water’s acidity, salinity and oxygen levels, and wanted to know what levels of E. coli, nitrogen and phosphorus were present.

After placing her floating wetland in the pond, she tested for those same variables weekly for the next four weeks.

Early results suggested a reduction in nitrogen levels, but also brought up a number of new questions that will still need answers. Would older plants do better? How many more plants would it take to get a drastic reduction in nutrients? If the researchers sample the water more often, can they gain better insight into potential nutrient removal?

And while those questions will wait for a future project and another student, Davis is still waiting to answer part two of her research as cold and snow and ice fall on Lincoln: Will the plants survive?

Whether they do could have long-lasting implications and cost-savings for Midwestern states wanting to reduce nutrients from entering — and potentially contaminating — local streams and rivers.

“Whether they survive will provide us guidance on maintenance practices when we do full-scale projects,” says Tiffany Messer, University of Nebraska-Lincoln assistant professor and water quality engineer and Davis’ adviser on the project. “In the Southeast (United States), people just leave the floating wetlands year-round. But they don’t have freezing ponds. This is our pilot study.”

Survival means floating wetlands could be planned, installed and forgotten about until the plants or mats need replacing decades down the road. But if the plants die, costs will increase as it becomes necessary to remove the floating plants each fall, store them, and then re-install them each spring. And those may be costs that cities, counties or states are not be willing to pay.

As of late December, the researchers were still hopeful. The plants were still alive. “Looking sad, but still alive,” Davis says with a hint of humor in her voice. The hope is that when this spring comes around, the sedges and milkweed will bounce back, shooting their green leaves into the sky and sucking nutrients from the ponds again.

Only time will tell.


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.