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Cities turn to innovative 'green infrastructure'

From Seattle to Sweden, city and regional governments are using roof gardens, specially designed wetlands, and other forms of 'green infrastructure' to rein in pollution – and to save money.

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The concept of green infrastructure is hardly new. New York City has long preserved watersheds in the Catskills Mountains and Hudson Valley for the city’s drinking water supplies. Since the 1990s, in order to comply with federal regulations, New York City has committed $1.5 billion dollars for protection of the forests that blanket much of the Catskills rather than build and operate a water filtration and purification plant costing $10 billion.

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“We’re at a tipping point,” says Katherine Baer of American Rivers, which is working with communities to implement green infrastructure. “We’re going to see a lot more of these practices that protect, restore, or replicate natural functions, as cities grapple not only with water quality, but with livability and climate adaptation.”

Seattle is one of the early adopters of this new approach, which can begin with preserving existing wetlands critical to cleaning water and storing runoff. Seattle also asks residents, for example, to install “rain gardens” — native plants in special soil mixes designed to hold water and allow it to percolate into the ground. “They are a lot like sponges to keep water from flowing onto streets and sidewalks” with silt and pollutants, says Baer. Seattle homeowners are eligible for reimbursement for their rain garden costs, which average $3,000 to $4,000. Seattleites also are being urged to disconnect their downspouts from storm drains and to re-direct the water from their roofs for gardens or lawns, or to store it in cisterns or rain barrels.

The Puget Sound city of Coupeville, Wash., is experimenting with the use of trees and other plants to clean water — known as phyto-remediation — to scrub runoff from a large parking lot and housing development. The water flows first through a bio-swale, which is essentially a drainage ditch with gently sloping sides and rip rap and vegetation that catches silt and sediment. The water flows to a depression, 250 feet by 35 feet, planted densely with poplar and willow trees designed to capture and hold thousands of gallons of runoff a day.

“Every drop of water passes within an inch of the roots and the root zone reactor cleans it,” said Lou Licht, president of Ecolotree, the company that installed the system. Thanks to a dense community of microbes that live around their roots — the so-called root zone reactor — trees neutralize the nastiest waste coming off streets, including ammonia, nitrates, and the copper from brake linings. Once the roots work their magic, the water is released for irrigation.

Copper, it turns out, is a big problem in the Puget Sound region. As people brake their cars, fine copper dust is emitted and washes into streams. In some streams, 90 percent of coho salmon returning to spawn have been wiped out, in part because of high copper levels from brakes and other sources; the copper can harm a salmon’s sense of smell, interfering with its ability to navigate back to natal streams or detect predators. But, says Licht, copper is an essential nutrient for trees, whose roots and hummus can absorb large quantities of the element.

Green roofs, long used in Europe, are another tool being rapidly adopted in North America. Toronto is the first city in North America to require green roofs on new commercial construction.

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