Protective salt marshes along coasts are in danger across the globe but it's not too late to act, researchers say
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Salt marshes are among coastal habitats endangered by both rising sea levels and urban development.
Preserving and restoring salt marshes is essential not only for wildlife protection and natural flood mitigation, but also for the numerous ecosystem services—such as carbon storage, bird watching and fishing—they provide to urban dwellers.
This is the case a group of Northeastern University scientists is making in a recent study published in the Journal of Environmental Management that predicts how New England salt marshes might look by 2100 due to rising sea levels, using the example of Belle Isle Marsh Reservation, Boston's last remaining salt marsh.
The scientists suggest potential actionable solutions that can help preserve the marsh.
"I don't think it's too late to act," says Jahson Alemu I, who led the study and worked closely with municipalities and communities that border the marsh as a postdoctoral fellow of the Coastal Sustainability Institute, a joint program between the Marine Science Center at Northeastern and the Nature Conservancy, a global environmental nonprofit.
"But with thoughtful planning, like making spaces for marshes to migrate inland as sea levels rise or being mindful with where we build along the coast, these can help preserve these ecosystems for future generations," Alemu says.
Salt marshes are grassy coastal wetlands with deep mud or peat that are flooded and drained by tidal salt water daily.
The study tested a spatio-temporal model at Belle Isle Marsh that measured and described how the marsh will change over time in its ability to store carbon (to fight climate change) and nitrogen (to mitigate harmful algal blooms and oxygen depletion) in the Boston Harbor.
It also examined how the marsh provides suitable habitat for fish nursery and recreational services, such as boardwalks, trail systems and saltmarsh sparrow viewing, for nearby communities.
"Cities like Boston are a biodiversity desert, and the Belle Isle Marsh is the largest green space within the entire city. It's an oasis within an urban desert," Alemu says.
Belle Isle Marsh is a unique research site both within Massachusetts and nationwide, says Randall Hughes, professor of marine environmental sciences, due to its size and its urban setting.
"At the same time, the same plant species and habitats occur from New England along the East Coast all the way through the Gulf of Mexico," she says. "So there's a lot of potential to take what we learn on one site and try and apply it in another for marsh restoration."
While many studies incorporate ecosystem services into risk assessments, they often overlook long-term impacts from rising sea levels and urbanization on these services. This study addresses those gaps by modeling how salt marsh ecosystem services might respond to future climate conditions, offering insights for better adaptation strategies.
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Belle Isle Marsh Reservation supports approximately 266 acres of salt marsh wetland and transitional marsh habitat. The marsh is surrounded by the low-lying, densely developed communities of East Boston, Revere and Winthrop.
Using the Sea Level Affecting Marshes Model, or SLAMM, in collaboration with environmental engineers from Woods Hole Group Inc., the researchers modeled what different habitats might exist in Belle Isle Marsh at different intervals, including in 2030, 2050, 2070 and 2100. The ecosystem services will change in time in this space as well, Alemu says.
"So we'll see some trade-offs, and depending on what we think is important, without intervention, we could lose much more than the benefits that these marshes provide," he says.
The researchers expect high marsh areas to decline dramatically, shrinking by 94% from 2020 levels. This loss will begin after 2030, Hughes says, and accelerate between 2050 and 2100.
Low marsh areas will temporarily expand, peaking by 2070, but will shrink again by century's end. Mudflats will first decline, then expand by 137%, while open water areas will increase significantly due to persistent flooding, replacing marsh habitats.
Habitat shifts will vary across different marsh areas. In the northern region, high marsh will decrease by over 90%, while mudflats and open water will expand. The southeast will see an 85% decline in high marsh, with low marsh expanding until 2070 before retreating. The southwest will experience similar high marsh losses, with a 70% reduction by 2100.
These changes will have mixed effects on ecosystem services the marsh provides overall. The temporary growth of low marsh and mudflats will enhance fish nursery and nitrogen storage services early in the century but reduce carbon storage and wildlife habitats tied to high marsh. By 2100, many benefits will be lost as habitats convert to open water, limiting future provision of ecosystem services.
"That points to the need for a longer time horizon for planning and management because we wouldn't have seen that shift if we hadn't looked out that far," Hughes says.
Managing these challenges will require adaptive strategies. The study suggests potential solutions such as adding sediment to marshes or creating buffer zones that can help marshes migrate and reduce habitat loss.
"That is a technique that has been done in a number of marshes in Rhode Island," Hughes says. "We do have data to suggest that it's effective."
Managed retreat, though difficult, may balance urban development and marsh preservation. Urban planners and coastal managers must prioritize high-elevation marshes for restoration, researchers say, to maintain key services, such as carbon storage and fish habitats.
Boston has a people-centric approach to climate change preparation, Alemu says. Amplifying conversations about the benefits of ecosystem services and the impact of salt marshes on the safety, economy and quality of life of Boston residents can encourage greater investment in preservation and restoration projects. These efforts ultimately represent an investment in the community's future.
"That leaves me with some optimism, because there's an appetite for it," he says.
The Northeastern research contributed to the Belle Isle Marsh climate vulnerability assessment conducted by Woods Hole Group for the town of Winthrop. It informed discussions among stakeholders, including representatives from Winthrop, Boston, Revere, state agencies, the Mystic River Watershed Association and Friends of Belle Isle Marsh.
More information: Jahson B. Alemu I et al, Evaluating ecosystem services in urban salt marshes: Assessing vulnerability to sea-level rise and implications for coastal management, Journal of Environmental Management (2024). DOI: 10.1016/j.jenvman.2024.123065
Journal information: Journal of Environmental Management
Provided by Northeastern University
This story is republished courtesy of Northeastern Global News news.northeastern.edu.