From the Coastal Systems Program, UMass Dartmouth School for Marine Science and Technology, for the Town of Barnstable · February 3, 2026 · By Ed Eichner, Jen Benson and Micheline Labrie
Barnstable’s test of floating wetlands in Long Pond, Marstons Mills, ended with the plants taking up only a few grams of phosphorus, the nutrient that feeds the pond’s algae, according to a February 3, 2026 technical memo from UMass Dartmouth’s School for Marine Science and Technology (SMAST) to the town’s Department of Public Works. On April 24, 2024, the town anchored ten plastic rafts, about 455 square feet in all, in the pond’s shallow north end, where most of the groundwater and its nutrients come in, and planted them with 500 plugs of seven native wetland plants. SMAST’s 2022 plan for the pond had traced its phosphorus mainly to septic systems. The rafts spent the winter in a sheltered cove and were harvested and removed on October 22, 2025. Over the first season the plants took up a net 6.87 grams of phosphorus; in the second, 1.94 grams, much of it in blue vervain, a wildflower that seeded itself on the rafts. The 2024 total was 0.065% of the phosphorus in the pond’s water, and town sampling found no significant change in phosphorus or clarity.
To reach the pond’s phosphorus target at the 2024 rate, SMAST estimated the town would need 9.7 acres of rafts, about a fifth of the pond, at roughly $25.6 million for materials plus about $509,000 for plants every other year. Long Pond’s rate was about a tenth of what a pilot in Baltimore, Boston and Chicago measured, partly because the pond carries far less phosphorus than the Charles River. The memo suggests choosing plants by season and harvesting earlier if the town keeps going, and SMAST offered to help the town weigh next steps. Sewers for the area are planned for Phase 3 of Barnstable’s wastewater plan, 21 to 30 years out. Floating wetlands were proposed for Waquoit Bay and Santuit Pond at CPWB’s 2021 Annual Meeting, and Long Pond is the closest field test of the idea so far, though it measured phosphorus in a freshwater pond rather than the nitrogen that harms the Bay.
This is CPWB’s summary of a technical memo prepared for the Town of Barnstable. The full memo is published by the Town of Barnstable.
Drafted with AI assistance from the linked source.
