Floating Wetland Repurposes Invasive Japanese Knotweed for Ecological Healing

Roger Williams Park’s Polo Lake is in poor shape: excess phosphorus and nitrogen cause toxic blue-green algae (cyanobacteria) blooms which rob the water of oxygen and make it inhospitable to aquatic life. People (and pets) are warned not to ingest or even touch the water. The same is true for Mashapaug Pond which drains into Roger Williams Park. In turn, the Park’s water empties into the Pawtuxet River and ultimately, Narragansett Bay.  One solution is to dump a load of chemicals in the lake, but that stop-gap measure needs to be continually repeated and creates its own set of problems.

Map courtesy of the Roger Williams Park Conservancy

“Floating Wetland,” installed on June 15, takes a more inventive and sustainable approach to healing Polo Lake. First and foremost, it’s a nature-based solution to poor water quality, but it’s also an experiment, an environmental model, a teaching tool, and a piece of living art. The project was conceived and installed by the six-person Below and Above Collective in partnership with the Providence Stormwater Innovation Center (the latter employs green infrastructure to ameliorate the poor quality of RWP’s water bodies).

Uniting ecology and design, the floating wetland is fashioned from hollow, dried stalks of the highly invasive Japanese knotweed plant which were harvested by collective members and volunteers. The stalks form a series of pontoons that are now home to over two dozen native aquatic plants. The plants’ roots lie below the surface and remediate the water, absorbing phosphorus. “It’s a nature-based solution to cleaning water and cycling nutrients” says collective member Alexandra Ionescu.

Holly Ewald with highly invasive knotweed.  Photo: Tim Lehnert

Japanese knotweed is an ideal choice for the raft as cutting down the prolific pest represents a gain for the local environment. Collective member Max Fertik, who did his RISD master’s thesis on knotweed, advocated for its use on the project. It’s a herbaceous perennial, which means it dies back in winter but then pops back up in spring. During its growing season, the knotweed “is very soft and has a lot of cellulose. People make paper out of it,” says botanist Hope Leeson, another Below and Above member. “As the stalks age, the cells build up the outside layer of lignin, which is more tree-like. We want stalks made of dried lignin.”

The plant, which can grow over ten feet tall and is native to East Asia, is found throughout the Northeast. Fallopia japonica is no newcomer to these shores; it arrived via a clone of a specimen in London’s Kew Gardens that was installed in Boston’s Emerald Necklace as an ornamental in the late 1800s. Bad move. “They have a giant underground tuber like a yam which can be as big as six feet,” says Leeson.

The knotweed was felled in March, and then left to dry and cut to size. It was important to ensure that no live seeds remained to germinate. In its desiccated, hollow state the plant looks like bamboo and is similarly strong and buoyant, perfect for constructing a lightweight raft.

Knotweed ready for use photo: Tim Lehnert

The plants that grow on and around the knotweed structure make an attractive home for insects, and much tinier organisms, and can provide shelter and food for aquatic animals including frogs, turtles, and muskrats. “By placing a floating wetland you generate biodiversity and ecological healing through the food web,” says Ionescu.

A bamboo scaffolding was erected above the plant-embedded raft. “It creates a visual presentation for the wetland and provides an area for birds” says Matt Muller who, along with Augie Lehrecke, is behind the structure’s design and engineering. The two, who run the design firm Pneuhaus, note that the bamboo’s pyramid shape comprises “a tetrahedron on the outside and an octahedron on the inside. They’re both very stable.”

The Floating Wetland is almost entirely organic (the only non-plant-based material is repurposed steel mesh used to lash the knotweed). Moreover the wetland is dynamic: seasons change, and plants, animals and microorganisms grow and die. Water temperature and composition are always in flux. Collective members hope to glean valuable information about pond ecology from the project.

“We don’t know the amount of phosphorus that each individual planting triangle bed can absorb and uptake,” notes Ionescu. “It varies depending on the context, and the amount of phosphorus entering the pond.” A complete analysis would be very expensive, but a start is being made as Marcelo Alexandre, Environmental Geochemistry Facility Manager and Research Scientist in Brown University’s Department of Earth, Environmental & Planetary Sciences, is testing the plants’ roots over the course of the summer to get a preliminary idea of how effective the plants’ roots are in capturing excess phosphorous. “Each plant has a unique phosphorus uptake rate and pattern,” says Ionescu. Given that there are 26 different plants on board, it’s complicated.

During the Floating Wetland’s launch, collective members and volunteers stocked it with plants and then anchored it in the lake. Narragansett Indian tribal elder Lorén Spears delivered a land acknowledgement. Funding for the wetland comes from the Stormwater Innovation Center, UPP Arts, Rhode Island Wild Plant Society, the Narragansett Bay Estuary Program, and the Providence Parks Department provides key logistical support. The structure will remain at Polo Lake until December 2025.

Preparing the floating wetland for launch. Photo credit: Beatrice Steinert

Floating Wetland team members have been working on the project in one form or another for several years and it is also a tool for teaching about local ecology; collective members Holly Ewald and Max Fertik are using the Providence wetland in a summer program for students from New Urban Arts.

The wetland is a model of a low-tech, organic solution to the local and regional problem of degraded fresh water. Ultimately, the project, or some version of it, would need to be replicated on a much larger scale for it to deliver results beyond the single-pond level. Augie Lehrecke thinks it’s possible and sees the design as enabling the creation of a “bunch of islands that could grow over time.”

The following is a rundown of the Below and Above Collective members, a veritable pond ecology super group!

Alexandra Ionescu is an ecological artist-researcher and Associate Director of Regenerative Projects for Biodiversity For a Livable Climate. She is a 2024 Creature Conserve Curatorial Fellow, and has master’s degrees in Nature-Culture-Sustainability Studies (RISD) and Biomimicry (Arizona State University). After graduating, she worked at Floating Island International where her interest in floating wetlands was cultivated. Alexandra is also interested in Miyawaki forests (dense urban pocket forests), among other ecological initiatives.

Augie Lehrecke and Matt Muller were tasked with designing the physical structure of the wetland so that it is both functional and works aesthetically. The RISD grads run Pneuhaus, an art and design studio based in Rumford. Their large-scale, inflatable kinetic sculptures have been installed at numerous venues around the U.S. and abroad.

Holly Ewald is an artist, educator, and organizer. She was a Community Fellow in Brown’s Public Humanities program, and has a long-standing interest in the intersection of art, the natural world and public spaces and their histories. She founded and served as director of the Urban Pond Procession (UPP) which used art, science, history and activism to bring ecological healing to Providence’s Mashapaug Pond.

Hope Leeson is a botanist, artist and wetlands and native-plant expert who is part-time faculty at RISD. She serves as botanist for the Rhode Island Natural History Survey and has worked as a consultant and contractor for numerous environmental and conservation organizations including the U.S. Fish and Wildlife Service and the Nature Conservancy.

Max Fertik is an artist, designer, and writer. He received a master’s in industrial design from RISD in 2023 and his thesis “POSTINDUSTRIAL PLAYBOOK++” employed Japanese knotweed. The abstract noted, “By making knotweed objects at three different scales, (silverware, table and raft), and discussing the xenophobic language around invasive species, this project investigates resilience and local resourcefulness within a post-industrial future.”

 

Tim Lehnert lives in Cranston with his family. His short plays have been performed by theaters around the U.S. (and by Providence’s Wilbury Theatre) and he has published short fiction for adults and kids. He is the author of the book Rhode Island 101 and has written journalism, essays and humor pieces appearing in the Boston Globe Magazine, Rhode Island Monthly, the Providence Journal and elsewhere. His bread-and-butter work includes writing immigration petitions for “scientists of extraordinary ability,” and occasionally serving as a “standard patient actor” for the Rhode Island Nursing Education Center.