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Barnstable to experiment with 'floating wetlands' to address freshwater pond algae blooms

Floating Wetland
Kaitlyn Dolan/Kaitlyn Dolan/Chesapeake Bay Pro
An artificial wetland used in Baltimore. The National Aquarium installed the floating wetlands to attract native species and improve water quality. Barnstable is considering installing a similar project. Photo from the Chesapeake Bay Program.

The Town of Barnstable is looking to confront pond pollution with an experimental tool called a floating treatment wetland.

Long Pond in Marstons Mills has been beleaguered by potentially toxic algae blooms, forcing the town periodically to close the pond to recreation.

The idea behind a floating wetland is to grow native species on a buoyant material, while letting the roots submerge. The roots would pull phosphorus out of the water, thereby removing the pollutants.

Amber Unruh with the town's Public Works Department says the town plans to start a pilot program, possibly in the spring, to see how effective the technology is. The hope is create 300-square feet of the wetland and study how much phosphorus is removed from the pond over a number of years.

"These plants would grow biomass shoots on the surface and roots below in the water, and assimilate phosphorous through their roots into their plant biomass," Unruh said. "Later these plants could be harvested, permanently removing phosphorous from the pond.”

Unruh detailed the possibility of the pilot project during a public meeting this week.

Town officials say the pollution problem in Long Pond stems from about 30 private septic systems in the area. The town is encouraging those residents to install special phosphorus-removing technology at their septic systems, but those can cost as much as $30,000.

The town plans to install a sewer collection system in the area, but that could take more than three decades. Barnstable's massive sewer plan is addressing other areas of town first.

Meantime, Unruh and the Public Works Department are exploring other, temporary measures to address pollution at the Marstons Mills freshwater pond. Possibilities include building what are called permeable reactive barriers, which is essentially a barrier installed underground that could capture nutrients before entering the pond. But those can be costly, and cheaper options are still in piloting phases.

Unruh says another option is dumping algaecides into Long Pond, which could wipe out the bad algae. But she says algaecide could also wipe out the good algae, making its use problematic. Other technology, like Solar Bees that circulate the water, she says, won't be effective.

That leaves the floating treatment wetland as the most immediate possible solution.

The next steps for the experimental project is for the DPW to get funding through the Barnstable Town Council.

Sam Houghton left CAI in February, 2023, to become News Editor at the Martha's Vineyard Times.
He worked at CAI since the summer of 2017. Before that, he worked at the Falmouth Enterprise, where he covered local politics.