Shoring up Sengekontacket Pond

Living Shoreline project seeks to provide a solution to the salt marsh erosion and excess nitrogen in Senge.


If you’ve been out to Felix Neck in the past year, you may have seen what look to be rolled-up brown rugs along the Sengekontacket pond shoreline. These “rugs” are biodegradable coir logs, made up entirely of coconut fiber and held together by coconut fiber mesh.

These coir logs are an integral part of a Living Shoreline project, an initiative intended to restore the eroding salt marsh by trapping sediment, thus rebuilding the damaged bank. This project is a collaboration between the Oak Bluffs and Edgartown shellfish departments, the Felix Neck Wildlife Sanctuary, the U.S. Environmental Protection Agency (EPA), and the University of Rhode Island (URI) Department of Fisheries, Animals, and Veterinary Sciences.

“It has gotten a lot of attention,” Oak Bluffs shellfish constable David Grunden said. “This might be one of the first [Living Shoreline] projects in Massachusetts. We’re going to learn a lot about this marsh in particular, and it should be applicable to other marshes on the Island and in New England.”

The indicator of success for this project is that the sediment accumulation rate is higher than the erosion rate, meaning that more sediment gets trapped by the coir logs then is eroded from the shoreline. The logs serve to facilitate this process, recreating the habitat in which marshgrasses and other shore-dwelling species thrive.

In late June, Mr. Grunden and EPA zoologist Suzy Ayvazian led eight members of the EPA Atlantic Ecology Division, as well as Friends of Sengekontacket interns Chris Parsons and Justine Cassel, in securing new coir logs.

This project began in early 2014, when Felix Neck director Suzan Bellincampi expressed concern regarding shoreline erosion on Senge’s northeastern banks at a Water Alliance meeting. Mr. Grunden knew that previous Living Shoreline projects have been successful in Delaware Bay, and worked alongside Edgartown shellfish constable Paul Bagnall to propose this project to their respective towns. Both were met with support, and Oak Bluffs and Edgartown appropriated about $10,000 each.

After acquiring funding, Mr. Grunden reached out to the EPA and shared the project details. The EPA joined the study to measure nutrient concentrations, vegetation diversity and density, and fish and invertebrate communities, to determine if the introduced structure will enhance these populations.

The first coir logs were installed in June 2016. At present, the EPA is measuring the effectiveness of the project. In the meantime, the Living Shoreline Project is used to teach Felix Neck visitors about climate change and resilience techniques.

Ms. Bellincampi said, “We’re looking at climate change, and this project is an example of the things that people can do to improve climate resiliency. It’s important to find solutions to address smaller pieces of the puzzle.”

“I would’ve liked to have scaled the project larger, but bearing in mind permits and federal regulations, it’s a good start.” Mr. Bagnall noted. “Ideally you’ll go out there in four to five years and the experimental areas will be overgrown with marsh grasses.”

According to Mr. Grunden, the next step is to add a mixture of sand and shells to the shoreline protected by the coir logs. This will bypass the time-consuming process of waiting for sediment to accumulate naturally. After they’ve added sediment, the involved parties will plant native marsh cordgrass to increase the stability of the shoreline and rebuild the salt marsh ecosystem. The EPA has provided 1,000 Spartina cordgrass plugs, which have since been transplanted into pots at the Martha’s Vineyard Shellfish Group’s greenhouse, and will be planted later this summer, once they’ve matured. After the shoreline has been reinvigorated, the Martha’s Vineyard Shellfish Group will seed ribbed mussels to reintroduce to the experimental sites, in hopes of both rebuilding the ecosystem and reducing excess nitrogen in the pond.


Nitrogen overload

According to Mr. Grunden, excess nitrogen is the main cause of Senge’s increasingly frequent algal blooms, which reduce oxygen levels and the amount of sunlight penetration in deeper water. With less oxygen and less sunlight, every species within the pond suffers. Mr. Grunden speculated that this may have contributed to the loss of eelgrass in the deeper areas of the pond.

The nitrogen coming into Sengekontacket is a result of two main sources; rain and septic systems.

As Mr. Grunden put it, “We can’t do anything about the rain locally, but we can do something about how we treat our own waste.” He went on to say that “most people within the watershed have the state-required Title 5 septic system, which works very well to prevent health risks; however, it does not reduce nutrients to the extent necessary to protect our coastal ponds. There are different ways that we may be able to address this. Additional sewering is probably the most efficient way. Sewering can take between 90 percent and 95 percent of the nitrogen out of the waste stream, but it’s also the most expensive. Right now, the Oak Bluffs waste plant has a limited capacity, so in order for us to add any significant sewering, we would need to expand the plant.”

Another culprit in overwhelming the pond with nitrogen is fertilizer used for lawns. This contributor has been staunched since 2015, when Island communities passed strict regulations.

Mr. Grunden and Mr. Bagnall are also looking to increase water quality by adding filter-feeding shellfish. Along with the annual recreational shellfish stock, both constables are adding 500,000 oysters to Senge annually. Two years of monitoring has shown mixed results.

For the initial two years of oyster propagation, there were nitrogen reductions; however, last year the nitrogen level had risen slightly. Mr. Grunden and Mr. Bagnall agree that it’s difficult to properly attribute this rise, because it can take up to 20 years for nitrogen to travel through septic systems, leaching fields, and finally groundwater systems into Senge. The addition of about 2 million oysters is undoubtedly contributing positively to the pond, and it doesn’t hurt that they’re great to eat as well. “We’ve had really good reviews of the quality of the oysters that we’ve been able to grow in Sengekontacket Pond,” Mr. Grunden said.