Oyster Pond is a 62-acre shallow coastal salt pond comprised of a series of kettle ponds that were flooded by rising sea levels at the end of the last glacial period. In its geologic past, the pond was both a bay and an estuary. The pond drains into Vineyard Sound via a culvert under Surf Drive into a small, shallow marsh we affectionately call the “Lagoon” and then into Trunk River and out to the Sound.
The Wampanoag, also known as the People of the First Light, were the first to live in this area. There are scant relics of their time on Oyster Pond. Maize pollen was found in pond sediment core samples taken by Dr. Jeff Donnelly. This is evidence that corn was growing on the shores of the pond by the late 1400s. By 1665 rye pollen starting appearing in the cores, an indication that Europeans started farming in the area.
A “midden” was uncovered during the construction of the Treetop condominiums in early 1978. Middens are “trash dumps” of shells, bones, and other debris. This midden contained a mixture of mollusk shells (oysters, soft clams, and bay scallops) animal bones, Native tools (chisel, arrowheads, a bearing for a bow and an adze) and European origin artifacts (pieces of clay pipe, handmade nails, steel knife blades, piece of blue and white china and cheap earthenware pottery). Unfortunately, due to the disturbance, it was impossible to know if the contents of the midden were stratified over time or mixed at the time of disposal.
Historically, the number and location of Oyster Pond’s connections to Vineyard Sound has changed and fluctuated over time, depending on the ferocity of winter nor’easters and hurricanes. Geological evidence shows there were up to three outlets at one time. Once the railroad to Woods Hole was completed in 1872, the outlet of Oyster Pond was fixed to Trunk River. Sometimes during extreme weather events, such as hurricanes, water from the sound will wash over into the pond.
In 1990, the culvert through which Oyster Pond drained into the lagoon collapsed. It was replaced by a larger culvert, which unfortunately allowed much more salt water into the pond than before. Salinity levels skyrocketed from 5 ppt up to 30 ppt. It was so high, barnacles were growing on the Treetops’ dock. The high salinity levels caused a precipitous drop in the fish populations, water column stratification and a massive growth of aquatic plants.
A weir was installed in 1998 to control the amount of saltwater entering the pond. It is designed to maintain the salinity levels at between 2 – 4 ppt (parts per thousand). By comparison, the salinity of Vineyard Sound is 32 ppt.
One of OPET’s biggest management issues is keeping the pond’s connection to the Sound via the Trunk River open and flowing. Storms are a constant challenge as they bring in fine sands and dead eel grass that clog both the river and the Lagoon. The connection between these three water bodies is a delicate balancing act that requires constant monitoring to ensure there is sufficient flow out of the pond to maintain safe and open passage for the pond’s resident herring population, prevent algal blooms in the lagoon, avoid flooding basements, and maintain targeted salinity levels between 2 to 4 ppt.
The “headwaters” of Oyster Pond and the only surface freshwater source to the pond comes from the aptly named Mosquito Creek. It drains from a wetland system in Zinn Park. It empties into the pond via a culvert under Ransom Road.