Lake Tashmoo Management

Lake Tashmoo Targeted Watershed Management Plan

In 2017 the Massachusetts Estuary Project (MEP) completed their assessment of water quality in Lake Tashmoo and established a Total Maximum Daily Load (TMDL) for nitrogen. Achieving this TMDL will require the elimination of approximately 32% of the nitrogen load currently feeding into the pond.

Tisbury has been a leader in the implementation of best available nitrogen removal septic technologies. (See the section, Nitrogen Mitigation, on our website under Current Issues, and the article about new Massachusetts Department of Environmental Protection Title 5 Septic Requirements in our winter 2022-2023 newsletter.) However, the cost to property owners for replacing their septic system is an obstacle to rapid progress. While the targeted management plan for Tashmoo may not be limited to nitrogen removing septics, having the plan enables to town to seek state funds to help property owners pay for installation of enhanced septics. A Huge Benefit!

The expectation is that the management plan will be available by Summer 2023, in time for a fall submission to the state for funding help. TWI will keep you informed on progress.

Further Protecting the Lake Tashmoo Environment

As we noted in the Summer 2021 Newsletter water quality and quality of life on Lake Tashmoo is threatened by too many boats, too much nitrogen, and too much bacteria.

In recent years Lake Tashmoo has experienced a dramatic increase in visiting boaters from across the Sound. For the past several years, to protect valuable eelgrass beds, much of the pond has been closed to anchoring, confining these day-tripper recreational boats to a small area near the western flats inside the channel on the right. TWI believes that this activity by recreational boaters will only increase, and in 2021 met with Town officials to discuss taking action.

In March 2023 TWI supported the decision of the Tisbury Select Board to place a moratorium on anchoring in the lake. The move came in response to concerns about the negative impacts of dozens of recreation boats anchoring in eelgrass beds in the northwest section of the lake. We all know that setting, dragging and lifting anchors uproots and kills eelgrass which, in turn, degrades the abundant marine life that eelgrass supports. While the town is contemplating a guest mooring program (with limited moorings in non-eelgrass areas), the moratorium that’s now in place provides the lake with a respite from one of the multiple negative impacts on its ecosystem and will give the eelgrass a chance to grow back.

However, as we stressed to the Select Board, boat anchors are just one immediate threat to Lake Tashmoo and its eelgrass. Far more pernicious is the nitrogen that steadily flows into Lake Tashmoo from septic systems, lawn fertilizer and geese feces in the lake’s watershed. Excessive amounts of nitrogen kill eelgrass beds, which are essential for carbon sequestration and as a habitat for marine life, including shellfish.

TWI has supported action to tackle these threats on multiple fronts.

First and foremost, TWI has supported Tisbury’s decision in 2023 (above) to create a state-approved Targeted Watershed Management Plan (TWMP) for Lake Tashmoo that will seek to reduce the amount of nitrogen feeding into the estuary to the state-established Total Maximum Daily Load (TMDL). This 20-year plan will offer a range of solutions to maintain the ecological balance of the lake, including but not limited to many initiatives TWI has supported:

Completion of the State Road sewer project, to alleviate nitrogen flow from septic systems;
Stormwater improvements to areas such as West Spring Street and Lake Street, where effluent with high bacteria levels is carried without treatment into the lake;
Enforcement of Island-wide regulations that reduce the use of harmful fertilizers that boost nitrogen levels;
Installation of nitrogen-reducting septic systems for any new home construction and replacement of existing systems, to minimize leaching of nitrogen into the lake from existing Title V septic systems;
Regular dredging of the channel at the Tashmoo opening to create better flushing of the lake and continued access for boaters.

TWI will continue to monitor, support and engage with these initiatives that aim to help Lake Tashmoo flourish and we will keep you apprised of developments as they occur.

Protecting Our Eelgrass

Eelgrass (Zostera marina L.) is a “seagrass” that grows in temperate waters, often forming extensive underwater meadows. Eelgrass beds are highly productive communities, acting as a nursery, habitat, and feeding ground for many fish, waterfowl, and invertebrates.

Eelgrass also absorbs carbon dioxide and methane—both climate-warming greenhouse gases—and stores them in its root system. By one scientific estimate, an acre of seagrass can sequester 740 pounds of carbon per year, about the same amount emitted by a car traveling 3,860 miles.

An excellent spotlight article on the importance of eelgrass, with a focus on the Cape Cod National Seashore, has been published by the National Park Service. The article notes that “nearly 30% of global seagrass habitat has vanished since the 1800’s alone. The most pervasive negative impacts include pollution, sewage runoff, watershed development, and boat traffic”

At the 2015 TWI Annual Meeting, Phil Colarusso, an EPA marine biologist, presented an informative talk titled, “Eelgrass: Not Just for Eels Anymore.” In his presentation, linked here, Mr. Colarusso reviewed the natural history, ecology, threats to, and restoration efforts for eelgrass.

In April 2016, Sheri Caseau, Martha’s Vineyard Commission Water Resource Planner, and Danielle Ewart, Tisbury Shellfish Constable, presented a talk, “Eelgrass in Tisbury,” at a Tisbury Selectmen (now Select Board) meeting. Among the “Things We Can Do” recommendations in that talk were use of conservation moorings (see below) and establishing rules prohibiting anchoring in eelgrass. At that same meeting, the Selectmen created an ad hoc Eelgrass Advisory Committee. A summary of the August 2016 report from this committee to the Selectmen, recommending a trial of a “no anchoring in eelgrass” position, was published in August 2016 in a Vineyard Gazette article, also linked here. Also see the summary article in the Winter 2016 TWI Newsletter.

Despite clear evidence that anchoring in eelgrass and careless boating can significantly harm these valuable but fragile plants, issues still persist worldwide, as evidenced by this December 2022 article in the Tampa Bay (FL) Times.

Historical eelgrass beds in Tashmoo have slowly disappeared, threatened by the combined threats of poor water quality, the anchoring of pleasure and commercial boats, and the use of heavy chain moorings, which scrape the seafloor and kill the eelgrass. The sensitivity of eelgrass to pollution makes it an ideal indicator species for spotting changes in water quality.

All of these factors make it critically important to protect remaining eelgrass in Tashmoo and to look for ways to restore beds that have been lost over time. In 2021 the Massachusetts Division or Marine Fisheries carried out an eelgrass survey of a portion of Lake Tashmoo. Click here to see a report from this survey, now available on the Town website.

An alternative to heavy chain moorings that damage vital eelgrass beds is the use of conservation moorings, which don’t have a chain lying on the seafloor. For several years TWI has championed the use of conservation moorings. Two years ago, the Buzzards Bay Coalition in partnership with the town of Falmouth organized an effort to replace 41 conventional boat moorings in West Falmouth Harbor with conservation moorings. An article describing this project can be found on the website of the Buzzard’s Bay Coalition.

Seagrass Studies

Matthew Long’s lab at the Woods Hole Oceanographic Institute is actively doing research to find ways to overcome the water quality issues and at the same time reduce the nitrogen loads that cause seagrass-smothering algal blooms. Over time, his lab also wants to find the best places to plant new seeds to help bring populations back. Click here is see a brief summary of his work.