Photo: Dave Burke/SOM.
Floating wetlands along the Chicago River’s Wild Mile.
Here’s an idea whose time has come. Now that we know the role of wetlands in cleaning up pollutants, why not create wetlands where they’re needed most? Having read today’s article, I’m not sure how I feel about the use of phragmites, so often considered an invasive weed. But I’m glad it’s so good at absorbing pollution.
Susan Cosier reports at YaleEnvironment360, “As cities around the world look to rid their waterways of remaining pollution, researchers are installing artificial islands brimming with grasses and sedges. The islands’ surfaces attract wildlife, while the underwater plant roots absorb contaminants and support aquatic life.
“Five small islands roughly the size of backyard swimming pools float next to the concrete riverbank of Bubbly Creek, a stretch of the Chicago River named for the gas that once rose to the surface after stockyards dumped animal waste and byproducts into the waterway. Clumps of short, native grasses and plants, including sedges, swamp milkweed, and queen of the prairie, rise from a gravel-like material spread across each artificial island’s surface.
A few rectangles cut from their middles hold bottomless baskets, structures that will, project designers hope, provide an attachment surface for freshwater mussels that once flourished in the river.
“Three thousand square feet in total, these artificial wetlands are part of an effort to clean up a portion of a river that has long served the interests of industry. This floating wetland project is one of many proliferating around the world as cities increasingly look to green infrastructure to address toxic legacies. …
“Like natural wetlands, floating versions provide a range of ecosystem services. They filter sediment and contaminants from stormwater, and laboratory experiments show that some plants have the ability to lock up some chemicals and metals found in acid mine drainage. These systems take up excess agricultural nutrients that can lead to algal blooms and dead zones, and recent research suggests they could be used to reduce manmade contaminants that persist in the environment. Though it’s difficult to quantify the exact benefits these systems offer, and they have limitations as a tool in remediating polluted waterways, they could provide another option, researchers say.
“Nick Wesley, executive director of Urban Rivers, a nonprofit working with the Shedd Aquarium on the Chicago project, believes floating systems are a natural fit for the urban environment. …. ‘We’re trying to [restore] what the naturalized river would be.’ In many cities, he continues, floating wetlands could provide a low-cost alternative to conventional infrastructure projects because they’re modular and easy to install and to monitor.
“Wesley’s group began, in 2018, with a floating wetlands project on the Chicago River’s North Branch. Called the Wild Mile, the installation aims to improve water quality and has already begun attracting invertebrates, including mollusks and crustaceans. Last month, the group expanded to the shores of Bubbly Creek. Urban Rivers, Shedd employees, and a team of volunteers bolted together polyethylene and metal frames, draped them with matting, dropped them in the water, added plants, and anchored the islands to the river bottom so they stay in place as the roots grow into the water. …
“Floating wetlands ‘are having a bit of a moment,’ says Richard Grosshans, a research scientist with the International Institute for Sustainable Development who works on the floating structures. ‘They function very similarly to a natural wetland: they have the same processes, plants and microorganisms, bacteria and algae.’ …
“Floating wetlands were first tested in retention ponds, the kind often located near developments to hold stormwater, to see if they filtered pollution. ‘The front end of it was, “Will they work? How well do they work? And what plants should we recommend?” ‘ says Sarah White, an environmental toxicologist and horticulturalist at Clemson University who has worked on floating wetlands since 2006. Partnering with researchers at Virginia Tech, White found that the wetland plants she tested not only did well in ponds with lots of nutrient pollution, but the adaptable, resilient plants actually thrived. She did not always choose native plants, opting instead for those that would make the islands more attractive, so that more urban planners would use them.
“In the early 2010s, Chris Walker, a researcher at the University of South Australia, began testing floating wetlands in wastewater, quantifying the pollutants that four species of plants took up in their tissues and improvements to water quality. Two species, twig rush Baumea articulata and the common reed Phragmites australis, showed the highest uptake of nitrogen and phosphorus of any floating wetland research to date. …
“His team also started testing the ability of floating wetlands to filter out emerging contaminants like per- and polyfluoroalkyl substances (PFAS), which are not always filtered by treatment plants and are linked to elevated cholesterol levels, problems with reproductive health, and kidney and testicular cancers. The reed Phragmites australis placed in a floating wetland began absorbing the pollutant into its tissues in less than a month. …
“In Boston, Max Rome, a PhD student at Northeastern University, is attempting to quantify the benefits of wetlands that have been floating since 2020 in the Charles River, another historically degraded waterway. He found that one acre of wetland can absorb the nutrient pollution — usually dumped into the river via stormwater — from seven to 15 acres of dense urban development.
“Rome is also looking into whether floating wetlands can create small pockets of improved water quality or habitat that allow certain native species, like freshwater sponges, to regain a toehold in the river. To do that, he monitored water quality near the wetlands and compared it to other places in the river.
“ ‘The last generation did a really good job of dealing with point source pollution — and it was a huge task,’ he says, referring to the success of the Clean Water Act in reducing effluent from discharge pipes. His generation has a new job, he adds: grappling with ‘ecological restoration of these degraded water bodies at the same time that we do pollution reduction,’ something the wetlands could help address.”
More at YaleEnvironment360, here. Lovely pictures. No firewall.
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