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Environmentalists and local public works officials are asking residents to “adopt a storm drain” on their block and keep it free of leaves in order to prevent clogging and protect local water quality.

“Please adopt a storm drain near you and help keep it clear of debris,” urged Lori Wolfe, communications director of the North and South Rivers Watershed Association based in Norwell.

Wolfe said that fallen leaves raked or blown into roadways may block storm drains, causing flooding and degrading water quality. Further, according to WaterSmart, an environmental educational initiative that links the watershed association and 12 South Shore communities, storms such as the recent nor’easter can send excess water flow from streets and sidewalks into local waterways.

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Leaves that end up in storm drains, said Wolfe, who also serves as WaterSmart’s program manager, can affect water quality because “deteriorating leaves add phosphorus to our water bodies, which can pollute our local waters.”

The initiative’s 12 towns are Cohasset, Duxbury, Hanover, Hingham, Hull, Kingston, Marshfield, Norwell, Pembroke, Rockland, Scituate, and Weymouth.

“Leaves clogging a drain can create huge puddles,” said Peter Butkus, Duxbury’s public works director. “When drivers hit them, it can cause problems.”

Heavy rain events may also send “a first flush” of oil or gasoline on pavements into stormwater collection points, Butkus said. Some of those pollutants will end up in the watershed.

The advisory raises the question of what homeowners and others should do with the year’s supply of fallen leaves.

A good alternative, Watersmart suggests, is to “rake leaves into gardens, flower beds, and out of the way areas so that small animals, bees, and butterflies can use them to overwinter. Then in late spring you can compost them, or use them for natural fertilizer or mulch.”

Kristen Nicholson, co-owner of Blue Stem Natives in Norwell, said the new nursery offers some environmentally sensitive ideas on what to do with fallen leaves. While traditional notions of fall lawn and garden care have stressed a fall “garden clean-up,” Nicholsen recommends “leaving the leaves in place as much as possible.”

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Instead of removing fallen leaves as yard waste, the nursery’s blog encourages leaving the leaves and dried perennials for the use of wildlife: “Gently rake any leaves out of the main traffic area into your garden beds, or into a pile in the back corner of your yard. Mowing and using a leaf blower can destroy the cocoons of many over-wintering moths and butterflies, so try to avoid them if you can.”

While acknowledging that homeowners may not always find it practical, or aesthetically pleasing, to “leave the leaves,” Nicholson said, “we recommend leaving whatever falls on your property on your property as the best way to be environmentally friendly.”

Leaving the leaves is especially important, she said, to insects such as fireflies and butterflies.

“People say they remember seeing tons of fireflies,” she said, “but they don’t see them anymore.”

The reason for that absence, Nicholson said, is that what was once the firefly’s habitat is likely now somebody’s backyard. Places where the pupae of fireflies and butterflies used to develop into winged adults are disturbed by raking.

Some butterfly species live as pupae — the inactive stage between caterpillar and adult butterfly or moth, also called the chrysalis — on fallen leaves. With many species, Nicholson said, it’s virtually impossible to distinguish the chrysalis from the dead leaf to which it has been attached.

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“Lots of very interesting butterflies and moths overwinter as a chrysalis attached to tree leaves,” Nicholson said. “Many form chrysalises attached to leaves while the leaves are attached to trees. They wrap up in leaves … or they look like dead leaves.”

She pointed to the Luna moth, a large and “beautiful” species. “It’s so rare to see one. The chrysalis looks exactly like a leaf.”

Among the butterflies that overwinter in the chrysalis state are Swallowtails, Checkered White, Clouded Sulphur, Skippers, along with Elphin and giant Luna moths.

Raking up fallen leaves or mulching them with a lawnmower destroys these overwintering butterflies and moths. “So our propensity to mulch all leaves and remove every speck of fallen leaves from our land is preventing these butterflies and moths from completing their life cycle,” Nicholson said.

She also recommended “gentle raking into flowerbeds” as way to encourage the growth of native plants such as woodland ephemerals like bloodroot and jack-in-the-pulpit, which are “predisposed” to pick their way through up to a foot of leaf coverage.

As for the use of leaf blowers, she recommends moderation. “We don’t need to blow the smithereens out of everything. Gentle raking is the least detrimental.”

For lawns, she recommended leaving a thin layer of leaves on the grass, thin enough so that “you can see some grass working around the leaves.” The leaves will break down over the winter and spring. They won’t harm the grass, she said, and their dissolution will naturally fertilize the lawn.

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As for mulching or composting leaves, Nicholson said, “thin leaves” such as maple, ash, beech, and willows decompose quickly and will be gone by late spring. Thick leaves, such as oak and chestnut, can be raked into piles of 3 feet by 3 feet. They will take two years to break down into compost.

There exists a happy medium between the two approaches, she said. “Leave some of the leaves whole and undisturbed. Also, use a large portion for really valuable compost for your lawn or garden.”

Robert Knox can be contacted at rc.knox2@gmail.com.