A draft report of the long-awaited Massachusetts Estuaries Project study of Sengekontacket Pond sketches a profile of a coastal pond that is at once troubling and hopeful.
Although the vast pond that spans the towns of Oak Bluffs and Edgartown has undergone significant ecological changes with increased development in the past half century, including a drastic decline in eelgrass beds, specific steps could be taken that would restore the pond to nearly its original state, the report finds.
A joint venture of the Massachusetts Department of Environmental Protection and the University of Massachusetts at Dartmouth aided by the efforts of dozens of volunteers from Oak Bluffs, Edgartown and the Martha’s Vineyard Commission — the study, along with reports on Edgartown Great Pond (completed in 2007) and Farm Pond (also in draft form), is just one of many under way in Southeastern Massachusetts by the Massachusetts Estuaries Project. In total, the project aims to identify sources of nutrient loading in 89 estuary systems in the region to give town planners a baseline of data on the ecosystems in their jurisdiction.
To kayakers and recreational boaters, Sengekontacket is an almost pristine place, undisturbed by human activity. But to the families and commercial shellfishermen who have seen it closed in recent years due to concerns over bacterial contamination, and to the researchers who have documented its decreased capacity for nitrogen absorption, the degradation of the complex ecosystem is already painfully understood.
Eutrophication, a term long used by ecologists to describe the negative effects of excess nutrients — such as nitrogen and phosphorus — on marine ecosystems, has entered the Vineyard lexicon in recent years as the impact of decades of development has been observed in the Island’s coastal ponds. The estuaries draft report estimates that 58 per cent of the excess nitrogen in the Sengekontacket watershed comes from Title V septic systems leaching nitrogen-rich wastewater to the pond mainly through groundwater. The ensuing bloom and decomposition of algae can rob the water column of oxygen, with devastating effects on marine life.
“Short-duration oxygen depletions can significantly affect communities even if they are relatively rare on an annual basis,” the draft study says.
A comparison of eelgrass bed surveys of Sengekontacket from 1951 with more recent surveys carried out in 1998 and 2006 paints a bleak picture. A once-lush expanse of the underwater flowering plant has declined to a few small patches in corners of the compromised pond shallow enough to allow adequate light penetration and less vulnerable to oxygen depletion.
Even in areas where eelgrass does exist, it is often heavily coated with epiphytes, organisms that serve as an indicator of nutrient-loading and which can crowd out species like bay scallops. And the vast majority of the main basin of Sengekontacket has fallen victim to the familiar suite of symptoms of a nutrient-overloaded pond: episodes of oxygen depletion and accumulations of algae that stifle eelgrass beds and the overall health of the saltwater pond.
“Given the significant loss of eelgrass beds, the Sengekontacket pond system is clearly impaired by nutrient overloading,” the report says.
And the future prospects for development outlined in the report are stark: under current zoning 554 more houses and 139 guest houses could be built around the pond and in its watershed.
The problems in Sengekontacket are not uniform, the draft study shows. The middle portion of the pond, adjacent to the main inlet at the Big Bridge (which provides 85 per cent of the total flow into and out of the pond), is the healthiest and supports the greatest diversity of marine life, from quahaugs and bay scallops to skittering blue claw crabs. A little farther north, at the end of the pond abutting the Farm Neck Golf Course, mollusks and crustaceans still thrive but are accompanied by nitrogen-tolerant species of segmented worms. An estimated nine per cent of the nitrogen loading in the pond watershed can traced to lawn fertilizer, especially golf course fertilizer. Three golf courses lie in the pond watershed: Edgartown, Farm Neck and the Vineyard Golf Club. Precise numbers on fertilizer use were not available from Farm Neck and Edgartown, the two courses that lie closest to the pond. The more distant Vineyard Golf Club is an organic course and its numbers were available. The remainder of the study applied estimates based on fertilizer use at other golf clubs.
As with the Farm Pond study, released in draft form early this month, the draft Sengekontacket report suggests that major improvements to water quality could be achieved with more flushing.
Trapp’s Pond, located on the extreme Edgartown end of the pond system and separated by a narrow culvert, is in the worst shape, primarily due to poor flushing, the report finds. Major’s Cove, situated in the upper middle of the pond, is also threatened for similar reasons, although not as extreme as at Trapp’s Pond.
“Trapp’s Pond is significantly tidally restricted, increasing the sensitivity of this basin to nitrogen loading,” the report says.
Illustrating the point, 66 per cent of the fauna in Trapp’s Pond is made up of amphipods, small shrimp-like organisms which are indicative of an ecosystem in transition.
“[Amphipods] were among the first groups to colonize the sediments of Boston Harbor as it recovered,” the report says.
Widening culverts would do much to alleviate nitrogen loading throughout Sengekontacket, the report says. And it concludes that a responsible solution could include addressing Trapp’s Pond as well as addressing the human contributions of nitrogen in the watershed, particularly in areas such as Major’s Cove, which remains closed to shellfishing out of fears of bacterial contamination from septic systems.
One thing is certain: continued unchecked development around Sengekontacket could spell disaster for the pond.
“Large portions of the Sengekontacket Pond watershed are not connected to any municipal sewerage system,” the report says. “As existing and probably increasing levels of nutrients impact the coastal embayments of the town of Oak Bluffs and Edgartown, water quality degradation will accelerate, with further harm to invaluable environmental resources of the towns and the Island on the whole.”