Saving a salt marsh

Saving a salt marsh

In the summer, Ocean View Farm Reserve in Dartmouth plays host to migratory songbirds, including bobolinks and yellow warblers. Yet Linda Vanderveer, Dartmouth Natural Resources Trust’s land manager, was looking for a lesser-known movement as she walked the nature preserve’s southern boundary in May — a shift with implications for South Coast communities amid intensifying climate change. 

To the north, lush grasses burst forth from Ocean View Farm’s 60 acres of retired farmland. Looking south, a thicket of high-tide bush obscured vegetation growing from sulfur-scented peat in salt marshes at Allens Pond — a 165-acre coastal salt pond system in Dartmouth.

Kneeling on the Ocean View Farm side, Vanderveer gripped a bunch of spindly green stalks, lined with brown flowers. It was black grass, a high-elevation salt marsh plant.

“This shows us an opportunity for hope,” she said.

Dartmouth Natural Resources Trust, which owns Ocean View Farm Reserve, is working with the Massachusetts Audubon Society, Buzzards Bay Coalition, and other partners to help salt marshes at Allens Pond migrate upland into the nature preserve and Mass Audubon’s Allens Pond Wildlife Sanctuary. The effort is meant to protect these coastal wetlands and help them adapt to rising sea levels. 

Salt marshes are made of vegetation that grows on parts of the coastline regularly affected by tides. Just under 5,000 acres of salt marsh are growing around Buzzards Bay. They protect communities during storms, provide habitat for fish and shellfish, and remove large amounts of carbon from the atmosphere. 

Yet the South Coast is losing salt marsh faster than the wetlands can naturally adapt to sea level rise. And coastal development has limited where salt marsh can go. 

Rising seas drown vegetation at the edges of salt marshes as water levels creep higher. Higher tides are also drowning interior vegetation as they wash over low-lying marsh and leave pockets of saltwater pooled on the surface. 

Buzzards Bay may have lost up to 200 acres of salt marsh to sea level rise between 2001 and 2019. Local waters are projected to rise more than a foot over 2000 levels by 2050. That could result in losses of up to a quarter of the bay’s remaining salt marshes. 

“We have to do something to try and save as much as we possibly can,” said Rachel Jakuba, vice president of bay science at Buzzards Bay Coalition.

South Coast conservation groups are working to protect salt marshes by helping them move upland with sea level rise. The marsh migration effort at Allens Pond consists of two separate projects. 

Buzzards Bay Coalition, Dartmouth Natural Resources Trust, and their partners have dug shallow drainage ditches — called runnels — in die-off areas of low-lying salt marsh at Ocean View Farm. These should help them revegetate, and buy the vegetation time to migrate inland. 

Meanwhile, Mass Audubon has constructed runnel networks with its partners on its nearby Allens Pond Wildlife Sanctuary. Mass Audubon is also working with Dartmouth Natural Resources Trust to remove tidal restrictions — like invasive brush and stone berms — from former agricultural fields upland of Allens Pond. That will allow high-elevation marsh to move into the 611-acre wildlife sanctuary and neighboring Ocean View Farm. 

The conservationists know they cannot save all 160 acres of Allens Pond salt marshes amid accelerating sea level rise. But they hope their work can mitigate some losses. They also hope to use it as the template for similar restoration projects across Massachusetts.

“If we can do it here, we can do it elsewhere,” said Mass Audubon senior conservation ecologist Gene Albanese. 

Credit: Kellen Riell / The New Bedford Light

Humans and the marshes

Salt marshes may not drive tourism dollars to coastal Massachusetts like beaches and rental homes do. Yet for year-round residents, their benefits are priceless. 

“They provide a number of really valuable services, things that we as humans don’t always appreciate,” Albanese said. 

Salt marshes hold the coastline together during storms, absorbing floodwater and buffering wave energy. They filter out chemicals and nutrients from stormwater runoff, and provide habitat for 32 state-listed species of “greatest conservation need,” from northern diamond-backed terrapins to saltmarsh sparrows. They also sequester carbon at a rate up to 10 times greater than tropical forests. 

“It’s one of the most productive ecosystems on the planet,” said Massachusetts Department of Fish and Game Commissioner Tom O’Shea.

There are 45,000 acres of salt marshes statewide. Yet salt marshes have been declining across Massachusetts, as a consequence of human activity. 

These impacts date back to the 17th century, when colonial farmers started ditching marshes and building stone embankments to alter tidal flow and improve hay yields for cattle. And into the mid-20th century, Massachusetts communities filled marshes to develop the coastline. The state has perhaps roughly half as much salt marsh as it had when the United States was founded.

The Massachusetts Legislature slowed this loss by passing laws protecting coastal wetlands, including the Jones Act in 1963 and the Wetlands Protection Act in 1972. 

Yet a new problem has emerged for local salt marshes, one that cannot be solved with regulation alone: sea level rise. 

“In my eyes, it’s the biggest threat,” Jakuba said. 

Since the 1970s, global temperatures have risen roughly one degree Fahrenheit. Sea levels have gone up several inches in southern New England. These trends are accelerating as humans put more carbon into the atmosphere, stressing Buzzards Bay salt marshes.

Staff from the Massachusetts Audubon Society, Save the Bay, and the National Oceanic and Atmospheric Administration look at salt marsh die-off areas at Allens Pond Wildlife Sanctuary in May 2024. Credit: Gene Albanese / Massachusetts Audubon Society

Salt marsh consists of low-marsh and high-marsh plants. “Low-marsh” vegetation grows close to the water and floods frequently with the tides. “High-marsh” vegetation grows farther upland, and floods only in the highest tides. No marsh can survive being in saltwater all of the time. When it is, the vegetation dies off, leaving mud behind. 

Higher tides can leave saltwater trapped on the surface of a marsh. That creates vegetation dieback areas, which expand over time. This problem has been made worse by legacy agricultural ditching around Buzzards Bay, which caused parts of marshes to sink. 

Jakuba said a few Buzzards Bay salt marshes are suffering from edge loss, while dieback areas have appeared in salt marshes across the region. 

Salt marshes can naturally adapt to sea level rise. They do this by slowly building up sediment from coastal waves and accumulating peat as dead plant matter decays. These processes create a gentle slope in the topography, which allows marsh vegetation to expand upland.

Yet many parts of the Buzzards Bay coastline lack the gentle slope needed to facilitate salt marsh migration that can keep pace with sea level rise. And those that do have it are largely developed with buildings, roads and parking lots. 

This means the salt marshes of Buzzards Bay — which are mostly low-lying — are especially vulnerable to rising seas. From 2001 to 2019, there were 10 Buzzards Bay Coalition test sites that registered losses of salt marsh area, ranging from roughly 1% to 20%. By 2100, the Coalition estimates, up to 32% of Buzzards Bay marsh could be lost to sea level rise. 

The gently sloping coast around Allens Pond, and the amount of protected upland area, make it one of the few spots in Buzzards Bay where human-assisted marsh migration can be implemented. And accelerating sea level rise means these conservation groups feel urgency to do it.

“If we wait for any more time, any more decades, we’re just going to lose these systems that we depend on,” Albanese said. 

Moving the marsh

Making a salt marsh move inland may sound daunting. Yet “it is not rocket science,” Albanese says. “It’s really a two-pronged approach.” 

The first step is restoring dieback areas in low marsh. Buzzards Bay Coalition and Dartmouth Natural Resources Trust are doing that at Ocean View Farm, using a technique known as runneling. 

Runneling is the process of digging shallow channels that connect flooded portions of low marsh to natural drainage features on the surface, like streams. This helps drain saltwater from marsh die-off areas, allowing vegetation to rebound.

Buzzards Bay Coalition vice president for bay science Rachel Jakuba (left) and Save the Bay intern Malarie Pittsley dig runnels on salt marshes at at Ocean View Farm in the fall of 2020. Credit: Rachel Jakuba / Buzzards Bay Coalition

In 2020, Buzzards Bay Coalition designed networks of runnels for marsh die-off areas at Ocean View Farm and Little Bay Conservation Area in Fairhaven, with the Woodwell Climate Research Center and Save the Bay. These groups then dug these runnels at 10 test sites: five at Ocean View, and five at Little Bay. 

The groups have been evaluating revegetation and standing water levels at the runneled sites against control sites since 2021. They are analyzing their first three years of data, Jakuba said, and hope to publish a research article this year. 

The data shows “regrowth and revegetation wherever we have been able to drain the water off of these areas,” Jakuba said. 

The project — funded by roughly $600,000 in grants over four years — is the first scientific study on runneling ever conducted in Buzzards Bay. 

Runnels are not a permanent solution for salt marsh loss. They require regular maintenance. Sea level rise will eventually swallow sections of the marsh they lie on. 

Still, Jakuba said, they will buy time for the marshes to build up peat and migrate upland. 

Mass Audubon designed, dug and started monitoring runnels across 33 acres of low marsh at its Allens Pond Wildlife Sanctuary with Save the Bay in 2022 and 2023, as part of their separate $150,000 grant-funded project.

Albanese’s team — along with Dartmouth Natural Resources Trust — has been also working to get “high marsh” vegetation at Allens Pond into Allens Pond Wildlife Sanctuary and Ocean View Farm. 

“We just have to undo agricultural practices for the last couple hundred years,” Albanese said. 

Volunteers with the Massachusetts Audubon Society and Dartmouth Natural Resources Trust clear invasive brush at Ocean View Farm Reserve in Dartmouth in 2021. Credit: Gene Albanese / Massachusetts Audubon Society

Stone embankments from cattle operations have sunk into the marsh, blocking paths to migrate. And invasive brush species like honeysuckle outcompete high marsh plants and cut off tidal flow.

These challenges have not deterred Albanese, Vanderveer, and their teams. In 2022 and 2023, Mass Audubon removed invasive brush and stone debris from eight acres surrounding Allens Pond salt marsh. It also cleared out brush and debris from three acres of Ocean View Farm in 2021, with Dartmouth Natural Resources Trust and volunteers. 

And in 2022, Mass Audubon seeded high-marsh plants and flowers on eight acres of upland area bordering Allens Pond salt marsh — including five acres of Ocean View’s southern field.

Putting these additional seeds in the ground, says Albanese, will increase the likelihood of a successful movement inland. 

The partners are reporting encouraging results. High marsh plants are moving into Ocean View Farm, and uplands at Allens Pond Wildlife Sanctuary. 

Albanese and his team have been hosting workshops to share the techniques they are using to help the marsh migrate. 

“In order for us to have the change that’s necessary on a mass scale, it’s going to take people at all levels to make that happen,” Albanese said. 

Scaling up

While the initial grants for salt marsh work at Ocean View may be spent, the work is not over.

“None of this is going to be one and done,” said Wenley Ferguson, director of restoration at Save the Bay in Rhode Island, a partner on both Allens Pond projects.  “We’re going to have to be continually managing these lands.”

Buzzards Bay Coalition is continuing to monitor and maintain their runnels at Ocean View. And Mass Audubon received another $465,000 grant for salt marsh restoration across the South Coast in late 2023. A chunk will go to continued invasive and debris removal at Allens Pond and Ocean View Farm. 

The new work period started this spring, with a focus on eliminating Phragmites australis, an invasive reed.

Albanese feels good about the work these conservation groups are doing at Allens Pond. The challenge will be scaling it up, and finding money for it. 

Massachusetts’ complex permitting process for salt marsh restoration has also slowed projects down, Jakuba said, especially those involving runneling. 

Runnels have helped salt marshes migrate in New York and Rhode Island. Yet the practice is new to Massachusetts environmental regulators, who are concerned that runnels may contribute to coastal erosion and loss of salt marsh. The permitting process takes an estimated 18 months.

Most salt marsh restoration is funded through short-term grants, so this timeline makes it hard for practitioners to complete impactful projects, Jakuba said. 

State officials say they understand the urgency and challenge of salt marsh restoration. 

They say the state will “soon” release guidelines to help conservation groups navigate the existing permitting process. They are working on wetlands regulations that “will streamline ecological restoration projects … and increase resiliency.”

The state is also looking into creating a “blue carbon” market that would incentivize salt marsh restoration projects, and is developing a statewide dataset of potential salt marsh migration corridors. 

State leaders and conservationists say now is the time to preserve as much marsh as possible for future generations. 

“Five or 10 years could really make a big difference,” Albanese said. “We can’t wait on this at all.”

Email environmental reporter Adam Goldstein at [email protected].

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