Once a tiny jewel in the Minneapolis chain of parks, Spring Lake has all but disappeared from the public eye. Squeezed between Interstate 394 and a parkway, the little lake is surrounded by a wall of grapevine and buckthorn and, thanks to decades of urban pollution, coated with chartreuse algae.
But recently its fortunes changed. Spring Lake is now home to seven little floating islands built and launched to undo what humans have done to it. Made from recycled plastic bottles and planted with wildflowers, reeds and grasses, the floating islands act like wetlands on steroids and represent a new and startlingly simple technology that’s attracting interest around the world.
“It’s cleaning up water nature’s way,” said Arlys Freeman, president of Midwest Floating Island, the St. Paul company that designs and distributes them. “There is habitat for birds and butterflies, and below that they have habitat for fish.”
Thousands of such islands float on lakes, bays, treatment ponds and rivers from China to Montana. Many environmental experts say they are excited by their potential. But the scientific studies that will show their effectiveness and how best to use them are still underway, said Ted Jattino, of Blue Wing Environmental, an East Coast company that is helping build 18 acres of floating islands in the Baltimore harbor.
“Everybody wants it, but we are waiting for the science,” he said.
Freeman’s grandfather started Bro-Tex, the St. Paul carpet recycling company that owns Midwest Floating Island. The company has launched about 10 projects in the year it’s been in business, including some for loon nesting sites in northern Minnesota lakes.
The Spring Lake project is the company’s largest Twin Cities installation.
The first floating island was supposed to go in the Mississippi River as part of a redesign of the Minneapolis riverfront. But the state government shutdown slowed an approval process already moving at an excruciating pace, said Craig Wilson, of the Minnesota Chapter of the Association of Landscape Architects, one of the partners in the Spring Lake project.
“We needed a new location,” Wilson said.
Blake School, a private academy across the street from Spring Lake, uses the lake to teach environmental science. The Lowry Hill Neighborhood Association considers the polluted little lake its problem. Wilson, who lives nearby, happens to be on the association’s board and persuaded the group to devote US$25,000 to the project.
Today, storm water laced with pollution flows from the highway above into the lake’s 32-foot, spring-fed depths. The city piles salt-laden snow on the other side of I-394, and in spring it melts under the highway and into the lake. Runoff carries phosphorus and nitrogen from yards and gardens.
The lake’s depths are so polluted that the water doesn’t turn over as it would in a healthy lake.
When Freeman first saw Spring Lake, she pulled out her calculator and crunched some numbers. Seven islands, each about 90 feet square, should do it, she said.
International Floating Island, a Montana company, created the technology. Plastic bottles are shredded and for
med into an eight-inch thick mat of fibres, and injected with marine foam to float. Holes are cut into the surface for plants. The mats cost $32 per square foot; plants are extra.
In mid-August, a crew of volunteer landscape architects donned waders and stood in the muck at lake’s edge as they inserted sedges, cardinal flower and other native plants into the holes. The whole surface was covered with peat moss and edged with sod. One by one, the islands were towed by canoe to the middle of the lake and anchored. Over time, the plants’ roots will grow through matting, creating a dense matrix to filter excess nutrients out of the water. But the real cleanup will be done by naturally occurring bacteria that form the familiar green slime on boats, anchor chains and docks. That “biofilm” is expected to coat the island’s bottom and roots, and eventually grow up into the matting itself — a concentrated form of the same process that makes wetlands so vital to clean water.