Pond Cut Scheduled for Weekend:
The current elevation of Edgartown Great Pond is ~4 feet above sea level. Pond cuts are possible when EGP is ≥ 3.5 feet above sea level. Shellfish Constable, Paul Bagnall, announced Monday afternoon at the meeting of the Edgartown Board of Selectmen that the Town of Edgartown has scheduled an opening of Edgartown Great Pond for this Saturday, February 27th 2021, weather permitting. Mr. Bagnall also explained if the weather is not favorable on Saturday, there are contingency plans in place to open the pond each of the following days this week, as equipment is standing by. As of Friday afternoon Mr. Bagnall indicated that Sunday’s weather is looking favorable.
Cuts & Dredging – Essential Management Activities
Two of the most essential management activities are pond openings or “cuts” that infuse the pond with clean, cool, salty, and oxygenated seawater, and dredging that enhances the effectiveness of openings, allowing seawater to flush all coves and corners of Edgartown Great Pond.
Balancing the Needs of an Ecosystem
Balancing the needs of an ecosystem is no small feat. We want to commend the Town for scientifically informed proactive management of Edgartown Great Pond as demonstrated this offseason through the coordination of dredging operations and responsive pond opening planning to mitigate the rising pond elevation.
Beginning in early 2021, Ed Handy led the work of the Edgartown dredge crew and they not only dredged the traditional area in the pond north of “the cut”, but they also opened up the southeast corner of the pond that leads to the sluiceway. Removing the sand from Edgartown Great Pond (EGP) improves the circulation and flushing of the pond and also brings the added benefit of beach renourishment. The harvested sand (a.k.a. dredge spoil) is being used by the Town to rebuild some of the Right Fork dune that was decimated in a recent storm. The swift restoration response was led by Town Conservation Agent, Jane Varkonda, who worked with state regulatory agencies to make the emergency action possible.
The dredge needs a high elevation pond for launch and operation, so dredging activities needed to be completed prior to a pond opening. Today, Friday February 26th, the Town dredge moved to Wilson’s Landing to await haul-out by crane.
Timing of Pond Openings Critical to Pond Health
Each time the elevation of EGP has exceeded 4 feet in the late winter, we have seen a subsequent algal bloom the following summer. When EGP exceeds 4 feet above sea level, the traditional edge of the pond is breached and the wider lens of the pond covers a greater surface area, bringing pond water into contact with nutrient (nitrogen/phosphorus) enriched groundwater. When the pond is cut and the level drops, the mixed ground and pond water brings those elevated nutrients back to the pond, catalyzing the growth of algae during the summer. Extreme high-water events can feed contaminated groundwater back into the pond for up to 5 years.
Data and past experience indicate that damage to both the pond ecosystem and property around the pond will occur if the elevation of EGP exceeds 4 feet above sea level. In March of 2018, EGP rose to >5 feet above sea level and the pond had its first macro algal bloom in a decade. As the pressures of climate change increase, the margin for error in the execution of management activities decreases. Data-driven management is essential the continued health of Edgartown Great Pond’s ecosystem.