Sunset Lake gets a new lease on life
Of all the Martha's Vineyard tidal ponds, Sunset Lake, adjacent to Oak Bluffs Harbor, is one of the smallest, but like the others, it is vulnerable to circulation problems and eutrophication. Over the last 60 years, I've watched the lake slowly filling in.
In the 1950s, my brothers and I used to sail toy boats and dig quahogs in Sunset Lake. It was easily accessible and the water was clean enough to support a healthy community of blue crabs, clams and scallops. Today it is harder to get to the water with all the marsh along the edges, but it is still a refuge for ducks and other migratory birds. I haven't seen clams or crabs in years, and floating algae has become a nuisance.
In the mid 1800s, the Sunset Lake area was the south section of Squash Meadow Pond. Like Sengekontacket and Menemsha Ponds, Squash Meadow developed over the last several thousand years as a drowned valley tidal estuary caused by rising sea level. Over time, sand eroded from nearby headlands formed barrier sand spits enclosing the ponds. These sand barriers were periodically breached by storms, leaving ephemeral inlets to the open ocean that were later stabilized with stone jetties. The mix of freshwater and seawater allowed a diverse community of organisms to develop. In the larger ponds, shellfishing continues to be an important component of Vineyard life and channel maintenance is a high priority to assure the health of the shellfish beds.
In the late 1860s, an extension of New York Avenue, called Lake Avenue, was built on fill across Squash Meadow Pond creating Sunset Lake (then sometimes called Meadow Lake or Jordon) and Lake Anthony (later called Oak Bluffs Harbor after the jetties were built around 1900).
In the early to mid 1800s, Sunset Lake extended over 1,000 feet farther south to a street aptly named Swamp Way on modern maps. This is evidenced by a circa 1875 lithograph of Cottage City showing a much larger Sunset Lake. The Google air photo shows the approximate location of the south end of Sunset Lake that is now peat deposits and a dense thicket of invasive trees and shrubs.
Fill for Greenleaf Avenue and School Street cut across this area that was once open all the way to Nantucket Sound. The cut-off ponds, now marshes, drain into Sunset Lake through small culverts. With tidal circulation virtually arrested by the fill, it is no wonder that marshland rapidly encroached into the south end of Sunset Lake. Today, the last section of Sunset Lake shows signs of accelerated eutrophication, including cloudy water and marsh grasses thriving on once sandy shores of Squash Meadow Pond.
An extensive floating mat of algae observed in the summer and fall 2009 attests to Sunset Lakes deteriorated condition. As an estuary, Sunset Lake is not only a nursery ground for a variety of marine species, but it also plays an important role in improving the water quality of Vineyard coastal waters. Tidal ponds and wetlands act as filters for runoff from the land that sometimes carry harmful bacteria, nutrients and other pollutants. We know that nutrient loading and poor circulation can result in high levels of phosphorus, anaerobic sediments and a rapid expansion of marshland into the basin.
An informal walk around Sunset Lake this summer showed no point-sources of pollution like a broken sewer that might have caused the algal bloom. Serious ponding on Greenleaf Avenue after rainfalls may be indicative of a blocked storm sewer and might be worth investigating. An examination of the concrete culvert connecting Oak Bluffs Harbor to Sunset Lake showed the channel nearly filled with cobbles and large boulders; the tidal flow through the culvert was minimal. I talked to a number of folks including Todd Alexander, Oak Bluffs Harbormaster, who agreed to look into the matter. I understand that he contacted the Oak Bluffs Conservation Commission and, with their approval, he arranged for removal of the debris from the channel.
Several days ago I learned from Mr. Alexander of the successful clearing of the channel debris, including large boulders, that blocked the culvert. It is a mystery as to where the large boulders came from. Waves and currents in Sunset Lake are too small to move stones that size. The good news is that circulation, and hopefully water quality, will improve greatly thanks to Todd Alexander's efforts.
Charles W. Shabica is a long-time seasonal resident of Oak Bluffs and Emeritus Professor at Northeastern Illinois University. He is President of Shabica & Associates, Inc. Coastal Scientists and Engineers. Dynamics of the Martha's Vineyard coastline has been a compelling research interest of his for more than 50 years.