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When green isn't the goal

Lincoln’s Drumlin Farm paints new landscaping system as path to cleaner waterways

By Denise Taylor
Globe Correspondent / July 19, 2009

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Midnight the Pony doesn’t look like your usual environmental culprit - what with his cute furry ears and big brown eyes. But on a recent weekday, as unsuspecting young visitors to Drumlin Farm in Lincoln admired the grazing “horsey,’’ proof of his crime lay at a pond just a few hundred yards away on the Massachusetts Audubon Society property.

The pond is choking under a mat of bright green duckweed, and Midnight, Mia the Goat, a few cows, and some equally harmless-looking sheep are the guilty parties - at least indirectly.

“The problem is storm water,’’ and the animal manure that it carries, explained the director of the Drumlin Farm Wildlife Sanctuary, Christy Foote-Smith. “As storm runoff washes over the paddocks and pastures, pollutants - especially nitrogen and phosphorus - flow directly into the pond, which leads to algal overgrowth in the summer and murky water, because there are higher levels of suspended solids in the water.’’

Roughly three-quarters of Massachusetts ponds are similarly contaminated by storm-water runoff carrying agricultural and lawn chemicals, pet waste, road residue, or other pollutants. So when Drumlin staff members came across a cutting-edge remedy with features that developers, farmers, and individual residents can replicate, they seized on it as a teaching opportunity.

Last month, the farm on South Great Road in Lincoln unveiled its new low-impact, low-cost system, which primarily uses landscaping to filter pollutants from runoff.

“Because this pond is in a public area, it can, and it should, be a little gem that can sparkle and be an example of what a pond can be if you take care to eliminate pollutants and manage the incoming storm water,’’ Foote-Smith said, noting that the educational farm operation and sanctuary draws more than 100,000 visitors annually.

Drumlin’s efforts to reclaim the pond are two-pronged. With volunteer help, and a grant from the state Department of Environmental Protection, the farm’s staff is working to return the similarly contaminated wetland area bordering the pond to a more pristine state, while the new storm-water filtering system will block further contamination.

All it took was a group of 50 students from the Middlesex School in Concord to get started. In 2007, the students and their teachers spent a morning pulling invasive plants from a 20-foot-wide strip of dense overgrowth beside the pond. Like duckweed, nonnative plants such as buckthorn and bittersweet feed on the excess nitrogen and phosphorus from manure carried by storm water into the wetland area.

“Before the students came, you could not see the pond from the poultry house. It was completely hidden,’’ said Foote-Smith. “But they came and pulled and sawed and lopped away that outer edge, and when they were done it was like a miracle to actually be able to see the pond again.’’

Contractors completed the task by pulling stumps and regrading the cleared area, and more volunteers turn out several times a year to pull new invasive growth. Mass Audubon estimates that more than 250 hours have been devoted to the effort, and that volunteers will be needed for several more years.

“The invasives keep coming back because the seed stock is in the soil,’’ said Foote-Smith. “But eventually, once we get the invasives really under control, we’ll plant a mix of native grasses in that area.’’

Meanwhile, the new storm-water system is in place, but, were it not for the signs explaining it, few would likely notice the system of ditches and depressions planted with native plants.

“We’re using techniques called best management practices (or BMPs) for low-impact development (or LID), and that’s a lot of acronyms,’’ Foote-Smith said. “But basically it means you’re using natural materials and natural landscaping techniques instead of hard structures like tanks and pumps to remove pollutants and then infiltrate the water into the ground.’’

Drumlin’s system first intercepts the storm-water runoff at its main source, the Big Red Barn (Midnight’s home) that sits uphill from the pond. When it rains, a narrow drain called a linear inlet grate catches surface water and runoff from the barn’s roof and feeds it into a concrete chamber buried under a grassy mound. Called a water quality inlet, the chamber traps solids, the first step in treating the storm water.

Next, the inlet channels the water into a swale (or ditch) planted with water-hardy native plants such as sweet flag and cardinal flower. Pollutants that make it through the inlet are taken up by the plants, and thus kept out of the pond.

Finally, farther downhill, a larger depression, called a bioretention area, also catches water and uses native plants to take up pollutants. Below the surface of the planted area, six feet of natural materials such as filter fabric, sand, gravel, and mulch also clean the water as it seeps into the groundwater.

In total, the system is expected to remove 3.9 pounds of phosphorus, 2.24 pounds of nitrogen, and 250 pounds of suspended solids from the storm water flowing into the pond each year. But to the untrained eye, the entire project appears as if Drumlin simply invested in some attractive landscaping.

“The beauty of this whole system is that it looks like the natural landscape while it naturally filters out pollution and replenishes the groundwater,’’ said Lucy Edmondson, a Department of Environmental Protection official who attended a recent ribbon cutting for the Drumlin project.

The state already requires that developments bordering wetlands include storm-water management features, but there are regulations being drafted for a new program that would establish broader regulations. The proposal is expected to be ready for public review this summer.

“Storm water is the final frontier when it comes to clean water,’’ said Edmondson. “About three-quarters of our lakes and streams are polluted, and many lack enough water in the summer, and part of the reason for that is storm water. It both damages water quality and quantity.’’

The Horsley Witten Group, a regional environmental consulting firm that designed Drumlin’s system, is among the proponents of low-impact development for storm-water control. They also designed the bioretention features, vegetated buffers, and sand filters that were installed in 2007 at Hammond Pond in Newton, which receives runoff from 8 acres of paved and solid surfaces surrounding the Mall at Chestnut Hill.

“The University of New Hampshire Stormwater Center has been testing low-impact development features, and bioretention is the best-performing pollutant treatment system they’ve tested,’’ said Scott Horsley, president of the consulting firm. “They’re getting removal rates of nutrients, metals, and hydrocarbons in the 90 percent range.’’

Restoration of Drumlin’s pond will nonetheless take time. “They should see some benefits immediately,’’ said Horsley. “For bacteria, you’ll see a very quick response in a matter of weeks or months. . . . For solids, which cause turbidity and cloudiness in the water, you’ll see that improve very quickly as well, probably the first season. Other pollutants like metals or nutrients will take a period of years, because some of these things are already in the pond.’’

Drumlin naturalist Tia Pinney looks forward to the improvement. “It’s hard to run ponding programs when you have to dig through this,’’ she said, waving toward the carpet of duckweed floating atop the pond. “This also prohibits sunlight from getting through, so nothing can grow beneath it that needs light.’’

Pinney noted that the pond does support plenty of creatures, including turtles, salamanders, and frogs. But seasonal low oxygen levels in the pond, due to the duckweed overgrowth, impacts other aquatic life, she said.

“Mostly it’s fish that can’t survive with low dissolved oxygen levels in the water,’’ said Pinney. “They respire underwater and can’t survive if the levels get too low. Sue Flint, of the Organization for the Assabet River, has talked about how with the water chestnut that’s on the rivers, she’s actually seen the fish come up and start gulping for air.

“But we don’t have fish in this pond. Here it’s your dragonflies and damselflies that are somewhat more sensitive, as well as stone flies and crane flies. They are all in here at various times, but you don’t find them all of the time. I think if we could reduce the amount of duckweed and open this up a little bit, then we would have more.’’

Drumlin is planning a series of storm-water system workshops for public officials, farmers, gardeners, and other interested parties. More informally, visitors to the Mass Audubon sanctuary can survey Drumlin’s project for features of interest.

Horsley noted that a rain barrel can be purchased for as little as $75, and a simple vegetated swale can be installed by a property owner for “next to no cost.’’ More involved features start in the low thousands of dollars, he said.

Meanwhile, Foote-Smith is looking forward to the day when visitors to Drumlin will be as likely to gaze into the clear waters of the pond and spot a turtle or a frog as they are to squeal “look at the horsey.’’

“So many people see this one pond,’’ she said. “So this is a great opportunity to get rid of one major source of pollution in one pond. It’s a start.’’