‘The cut’ is half the battle 

Efforts are underway to further mitigate the increasing nitrogen levels in the Great Ponds.

Efforts are underway to mitigate and reduce increasing nitrogen levels in Edgartown Great Pond. — Abigail Rosen

Increasing nitrogen deposits into the Island’s estuaries, ponds, and coastwater have prompted more vigorous conservation efforts among various Vineyard organizations aiming to effectively mitigate the increase. 

A recent study by the Great Pond Foundation (GPF) and the Marine Biological Laboratory (MBL) has reported that the source of “over half of the nitrogen in Edgartown Great Pond, Tisbury Great Pond, and Crackatuxet Pond” has been identified as wastewater runoff. 

Edgartown shellfish constable Rob Morrison told The Times that nitrogen loading has been a “major issue” for all Island estuaries, and causes detrimental and detectable effects on the local ecosystems.

With increasing nitrogen levels, algal blooms occur, leaving the ponds susceptible to an overgrowth of undesirable microscopic algae or cyanobacteria, which in turn hinders the ability of necessary plant life — such as eelgrass — to thrive, particularly by blocking its access to sunlight. With this, as in any functional ecosystem, the disruption of one key organism, such as eelgrass growth, can wreak havoc on the surrounding environment. 

The health and vitality of the Island’s eelgrass is vital to the health and vitality of the Island’s ponds and waterways. And with increasing human-created nitrogen loading, those waters are at risk. 

Although it has been undeniably concluded that the increased nitrogen levels are indeed linked to wastewater, exact sources from either specific residential areas or locations of groundwater seepage have not yet been identified. Regarding Edgartown Great Pond, the years-long study conducted by GPF and MBL has allowed scientists to hone in on the highest wastewater nitrogen concentrations using — Emily Reddington, executive director of the Great Pond Foundation, simplified it for The Times — methods similar to that of a heat map of dots. 

Reddington noted that the studies, conducted by MBL scientist Dr. Javier Lloret, have shown that in consideration of the high concentration of nitrogen, Edgartown Great Pond “shouldn’t be as healthy as it is.” Much of the reason it is? The “cut.”

Through effective dredging, “the tidal flushing that’s made when the barrier beach is opened,” said Reddington, “makes it all the way up to the heads of the cove,” and prevents a stagnant, high concentration of nitrogen. 

Morrison said the beach barrier is typically opened three to five times a year, and “you have to wait for certain determining factors to have a successful cut.” These factors include pond height, weather conditions, wave height on South Beach, prevailing winds, and tide cycle — all determinants being naturally occurring, and while it has been monumental in the health of the pond, cannot be the relied-upon solution. This makes updating wastewater management plans, and creating more efficient sewer systems, all the more important. As the Island’s population increases, so does the nitrogen. “More people moving to the coast, more nitrogen is going into these ecosystems,” said Morrison.

Plans are in place for when precise locations and sources of the nitrogen wastewater have been traced, but “the mitigating and decreasing,” said Reddington, “has to be a community-wide effort.”

In a similar sentiment, Morrison said, “there are things that can be done; I think we’re moving in the right direction.”