Plastic powers a lake cleanup

Spring Lake in Minneapolis is getting a cleansing thanks to floating wetlands that are a mix of nature and recycling.

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Seven floating islands made from recycled plastic bottles and filled with aquatic plants were set loose on Spring Lake this week.

Photo: Richard Sennott, Star Tribune

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Once a tiny jewel in the Minneapolis chain of parks, Spring Lake has all but disappeared from the public eye. Squeezed between Kenwood Parkway and Interstate 394, the little lake is surrounded by a wall of grapevine and buckthorn and, thanks to decades of urban pollution, coated in a thick layer of chartreuse algae.

But this week 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, and 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.

Interest in Minnesota is equally strong, said Freeman, whose grandfather started Bro-Tex, the St. Paul carpet recycling company that owns Midwest Floating Island. The company has launched about 10 projects in the one year it's been in business, including some for loon nesting sites in northern Minnesota lakes.

The project in Spring Lake is the company's largest Twin Cities installation, said Freeman -- and it happened by chance.

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, who is with 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. "And nobody cares about Spring Lake."

Except for Blake School, the private academy across the street, which uses Spring Lake to teach environmental science, and the local Lowry Hill Neighborhood Association, which considers the polluted little lake its problem. Wilson, who lives nearby, also happens to be on the board of the association and persuaded the group to devote $25,000 to the project.

Time takes its toll

Spring Lake happens to be a perfect test site for the islands. The lake and 2 surrounding acres were acquired by the Minneapolis Park and Recreation Board in 1893 as a wildlife refuge. At the time, the lake was much larger and cleaner. But lawns, streets, highways and industrial lots grew up around it. Today, storm water laced with pollution flows from the highway above down into the lake's 32-foot, spring-fed depths. The city piles salt-laden snow on the other side of I-394; in springtime it melts under the highway and into the lake. Runoff from the hill on the south side 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, and there is an urban myth that a railroad car rests at the bottom.

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.

How it works

The technology was created by International Floating Island, a company in Montana. Plastic bottles are shredded and formed into a wiry mat of fibers, 8 inches thick, and injected with marine foam so the whole structure floats. Holes are cut into the surface for plants. The mats cost $32 per square foot; plants are extra.

Starting Monday afternoon, a crew of volunteer landscape architects donned waders and hats, and stood in the muck at the edge of the lake 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. A low green fence staked around the perimeter would keep off the pesky Canada geese that consider the islands a perfect resting place. One by one, the islands were towed by canoe to the middle of the lake and secured with anchors.

Over time, the plants' roots will grow through matting, creating a dense matrix below that filters 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" will coat the bottom of the island and the roots, and eventually grow up into the matting itself -- a concentrated form of the same process that makes wetlands so vital to clean water.

A year from now the plants will be several feet high. A sign on the bike path that runs on the east side of the lake next to the Parade Ice Garden will explain the islands to passersby.

The plastic islands themselves will last 200 to 300 years -- plenty of time to do the job.

Josephine Marcotty • 612-673-7394

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