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Climate ChangeHow Floating Wetlands Are Helping to Clean Up Urban Waters

How Floating Wetlands Are Helping to Clean Up Urban Waters

Five small islands roughly the dimensions of backyard swimming pools float next to the concrete riverbank of Bubbly Creek, a stretch of the Chicago River named for the gas that after 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 couple of rectangles cut from their middles hold bottomless baskets, structures that may, project designers hope, provide an attachment surface for freshwater mussels that after flourished within the river.

Three thousand square feet in total, these artificial wetlands are a part of an effort to wash up a portion of a river that has long served the interests of industry. This floating wetland project is one among many proliferating world wide as cities increasingly look to green infrastructure to handle toxic legacies. In the USA, researchers are conducting experiments in Boston and Baltimore in addition to in Chicago, each team sharing best practices with the opposite to maximise the ecological advantages of their systems. The Canadian government and native municipalities are allotting more funding for revolutionary projects. Floating wetlands are also multiplying in the UK, and studies to quantify additional advantages proceed in Australia and Brazil.

Floating wetlands filter contaminants and take up excess agricultural nutrients that may result in algal blooms and dead zones.

Like natural wetlands, floating versions provide a spread of ecosystem services. They filter sediment and contaminants from stormwater, and laboratory experiments show that some plants have the flexibility to lock up some chemicals and metals present in acid mine drainage. These systems take up excess agricultural nutrients that may result in algal blooms and dead zones, and up to date research suggests they could possibly be used to scale back manmade contaminants that persist within the environment. Though it’s difficult to quantify the precise advantages these systems offer, they usually have limitations as a tool in remediating polluted waterways, they may provide an alternative choice, 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. Many urbanized river systems, he says, have the identical “steel sheet pile wall, some rough-wrap riprap on the perimeters. We’re attempting to [restore] what the naturalized river could be.” In lots of cities, he continues, floating wetlands could provide a low-cost alternative to standard infrastructure projects because they’re modular and straightforward to put in and to observe.

Wesley’s group began, in 2018, with a floating wetlands project on the Chicago River’s North Branch. Called the Wild Mile, the installation goals to enhance 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 within the water, added plants, and anchored the islands to the river bottom so that they stay in place because the roots grow into the water. The plants will grow for years to return, a part of a “riverponic” system, as Wesley calls it, that requires no soil or other substrate for support.

A floating wetland in Baltimore’s Inner Harbor installed by the National Aquarium.
National Aquarium

Floating wetlands “are having a little 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’ve the identical processes, plants and microorganisms, bacteria and algae, [which] naturally break down toxins. They take up nutrients and supply habitat. It’s type of common sense to those of us who work with these kinds of systems.”

Floating wetlands were first tested in retention ponds, the type often situated near developments to carry stormwater, to see in the event that 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 a lot of nutrient pollution, however the adaptable, resilient plants actually thrived. She didn’t at all times select native plants, opting as an alternative for those that may make the islands more attractive, in order that more urban planners would use them.

Within the early 2010s, Chris Walker, a researcher on the University of South Australia, began testing floating wetlands in wastewater, quantifying the pollutants that 4 species of plants took up of their tissues and enhancements to water quality. Two species, twig rush Baumea articulata and the common reed Phragmites australis, showed the very best uptake of nitrogen and phosphorus of any floating wetland research up to now. “That creates an actual opportunity for [the] everlasting removal of sequestered nutrients,” says Walker, who can also be the principal scientist for a floating wetland company called Clarity Aquatic.

One acre of floating wetland can absorb the nutrient pollution from seven to fifteen acres of urban development, one researcher found.

His team also began testing the flexibility of floating wetlands to filter out emerging contaminants like per- and polyfluoroalkyl substances (PFAS), which aren’t at all times filtered by treatment plants and are linked to elevated levels of cholesterol, 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 lower than a month.

Islands anchored in cities are giving scientists a chance to review environments which have long been ignored. In Chicago, Austin Happel, a research biologist on the Shedd Aquarium, is starting a study on fish near the floating wetlands in Bubbly Creek. Starting within the spring, he’ll use acoustic telemetry to tag fish captured near the wetland and monitor where they go. By the next yr, he should have the opportunity to see in the event that they use the floating wetlands as a buffet or as a spot to cover from predators.

In Boston, Max Rome, a PhD student at Northeastern University, is attempting to quantify the advantages of wetlands which were floating since 2020 within the Charles River, one other historically degraded waterway. He found that one acre of wetland can absorb the nutrient pollution — normally dumped into the river via stormwater — from seven to fifteen acres of dense urban development.

Rome can also be 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 within the river. To try this, he monitored water quality near the wetlands and compared it to other places within the river.

Floating wetlands on Serpentine Lake in London's Hyde Park.

Floating wetlands on Serpentine Lake in London’s Hyde Park.
Royal Parks

“The last generation did a extremely good job of coping with point source pollution — and it was an enormous task,” he says, referring to the success of the Clean Water Act in reducing effluent from discharge pipes. His generation has a latest job, he adds: grappling with “ecological restoration of those degraded water bodies at the identical time that we do pollution reduction,” something the wetlands could help address.

Despite the advantages of floating wetlands, obstacles to widespread adoption remain. They require time and energy to put in and monitor, they usually could potentially cause flooding in the event that they change into unmoored and interfere with water flow. A city would also need a whole bunch of floating wetlands to wash up probably the most polluted stretches of waterways and manage the contaminants that proceed to flow into them.

One other potential drawback is the specter of invasive plants colonizing a floating wetland, which might then require maintenance. One species that effectively sucked up PFAS within the Australian study, for instance, is an aggressive invader already colonizing wetlands across the U.S. As well as, if the goal of a floating wetland is to permanently remove phosphorous and nitrogen from an ecosystem, managers might have to remove and compost plants so that they don’t release the nutrients back into the environment once they go dormant, though ongoing research suggests that biofilms that form on plant roots and on the underside of wetlands could proceed to remove nutrients even after plants begin to senesce. Plants that remove PFAS would likely must be incinerated.

The National Aquarium in Baltimore is planning to expand its 400-square-foot floating wetland to 10,000 square feet by 2024.

Still, say researchers, floating wetlands do profit the environment. “I believe we’re just on the lookout for yet one more tool in our toolbox to assist manage water quality,” says Clemson’s White. “This offers us one other place within the landscape where we will even have a technology that may do it.”

The varieties of places that could possibly be improved by these projects are growing more varied. The National Aquarium in Baltimore was the primary place within the U.S. to check floating wetlands in a tidal system, and today 400 square feet planted in saltmeadow hay and smooth cordgrass float in the town’s Inner Harbor. The project has been so successful at lowering levels of nutrients and bacteria and at making a refuge for wildlife — including American eels, gizzard shad, and ghost anemones — that the aquarium now plans to expand the islands to 10,000 square feet in 2024, says Charmaine Dahlenburg, the aquarium’s director of field conservation.

The Harbor islands are the National Aquarium’s fourth attempt at making a thriving wetland system, demonstrating how difficult it could possibly be to tailor a floating wetland to a selected location. When the aquarium first installed wetlands in 2010, geese invaded them and ate the plants. The same problem occurred with a second version two years later. The third attempt fared higher, because of fencing that excluded geese, however the fourth iteration — which contains a channel that stops algal blooms from killing plants — fared the perfect.

A rendering of a cross-section of a floating wetland installed in Baltimore.

A rendering of a cross-section of a floating wetland installed in Baltimore.
National Aquarium

National Aquarium researchers investigating how the floating wetlands help mitigate such blooms found that microscopic organisms on plant roots and on the underside of the wetlands help move nitrogen from the water and thru the food chain — from barnacle to crab to fish. There are ecosystem advantages above the waterline, too: Night herons and otters visit the islands, finding refuge within the grasses. Research on fish, birds, and mammals interested in floating wetlands is just not well developed, but these structures clearly provide habitat in places where buildings, bulkheads, and riprap have replaced natural wetlands.

The quantity of contamination that plants can remove from aquatic environments is dependent upon the quantity and form of pollution, the plant species used, and the dimensions of the floating wetlands. But some scientists, including Dahlenburg and Rome, are hoping that as research accumulates, government agencies will think about using such projects to mitigate contamination and wetland development.

In three Boston-area watersheds, a latest regulation under the Clean Water Act would require certain industrial, industrial, and institutional properties with a number of acres of impervious surface to scale back nutrient and bacterial pollution in stormwater running off their properties, something never mandated before. Britain recently announced a requirement for homes and water firms to scale back water pollution. Floating wetlands that do which are already growing in London, and plans for other locations are within the works.

Regulations like these could compel cities to take a more aggressive approach to green stormwater infrastructure. “As that begins to occur,” says Rome, “the role that will be played by floating treatment wetlands goes to return into focus.”

The growing use of the buoyant, lush gardens — in cities that range from Australia to Europe to North America — show how even small wetland islands could make a difference. “Our little postage stamp of a wetland isn’t going to unravel every little thing,” says Dahlenburg, of the Baltimore project. “What we’re attempting to create is that this model urban waterfront. We wish other cities to know that there are methods to include natural habitat, to bring back the ecosystem services that were lost because of commercial development.”


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