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Frustrated by misfires in two recent, ambitious and expensive municipal plans to address water quality problems in Mill Pond, residents of pondfront neighborhoods have proposed a new, less costly, idea for tamping down the number of nutrients that flow into the pond.

Water Mill residents and a North Carolina botanist on Monday pitched an idea of creating a floating island of vegetation along the pond’s northeastern shoreline, where plumes of 
polluted storm water flow into the pond. The plants, woven into floating foam platforms, would sprout roots into the lake water and sop up nutrients before they have a chance to feed the choking algae blooms that have plagued the pond for decades.

On Monday, botanist Rob Crook of Floating Islands International, told members of the Southampton Town Trustees that a 200 to 300-foot long by 10-foot wide floating island, effectively an artificial ribbon of wetlands vegetation, could potentially capture all of the nutrients being carried into Mill Pond by runoff from Deerfield Road.

The floating vegetation, which Mr. Crook recommended be planted with locally indigenous grasses, would cost approximately $90,000 and could be expected to last for at least 10 years and possibly 20 to 30 years if maintained right.

“It does take time, they’re not magic,” Mr. Crook said. “You have to work with them and manage them like any other tool. It’s a capital investment.”

Planted through holes in the foam floats, the roots of the plants would soak up nutrients from the water and feed them into the fronds of the plants above water. Each year the fronds, laden with nutrients, would be trimmed and carted away and could be used as fertilizers elsewhere.

Plants’ fondness for nutrients like phosphorous and nitrogen has been the root, so to speak, of the problems in Mill Pond for many years. High levels of nutrients carried into the pond in groundwater tainted with fertilizers from centuries of farming in its watershed and rainwater runoff from fields and roadways along Deerfield Road feed algae blooms that stain the pond’s waters a pea soup green in summer. Mr. Crook noted that this week, even with water temperatures still relatively cold, algea blooms had already started popping up in Mill Pond.

The pond has been the focus of two recent municipal attempts to treat or stanch the impacts of nutrients in the ponds waters. Last spring the town and the Town Trustees conducted a mineral treatment of the pond intended to sap phosphorous from the water column. The effort’s success has been hotly debated in the year since, it’s less dramatic than expected results blamed on unusually high rainfalls in both the spring and fall following the application. A second application of the mineral, known as Phoslock, has been put off by the town for at least a year while it awaits more detailed assessments of the effects the experiment had.

This summer the town had been planning to embark on a two-phased stormwater runoff abatement project. The first phase, which will establish more concentrated drainage of runoff alongside the roadway, is due to begin this month, but the second phase, a more ambitious effort to capture runoff and reduce the amount of nutrients it carries to the pond, has been shelved because of logistical concerns about its cost effectiveness.

Mr. Crook said that a barrier of carefully designed vegetation islands anchored off the outflow of the roadway’s drainage into the pond, could strain out the nutrients before they have time to disperse into the pond’s main body and feed alge blooms.

Floating vegetation islands have been used around the U.S. and overseas to address nutrient loads in water bodies.

The typical scale for a floating island to have an impact on water quality is usually 5-percent of a water body’s size, which would be more than foura acres in 92-acre Mill Pond, but by siting the island at the northeastern corner of the pond, near Muller’s Corner on Deerfield Road, Mr. Crook said he thought a much smaller island could be effective.

Steve Abramson, who has led a variety of efforts by residents from around the pond to find innovative ways to address its water quality problems, said he hoped the town and the Trustees would be able to find a way to foot the cost of the project in the wake of the cancellation of the other two projects.

“The other thing is to cap the [nutrient] input at its source,” Mr. Abramson said. “This is one natural way to cap it. It looks like it woudl be able to capture all of that nutrient matter, and more.”

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