The short version
The Buzzards Bay Coalition and the Buzzards Bay National Estuary Program asked how well salt marshes around the bay can cope with stress and rising seas. With the U.S. Geological Survey and the Woodwell Climate Research Center, they combined on-the-ground measurements at 12 long-term sites with aerial imagery and elevation data. Every site lost marsh between 2001 and 2019, from about 1% to about 20% depending on the site, and the average was about 7%. Marsh surface height and tidal restrictions (such as undersized culverts) were the two factors most closely linked to marsh condition. Room to move inland gives some damaged marshes a chance to persist. The summary is based on the full report.
What the researchers did
The team scored each of 12 marshes on stress, current condition and potential to adapt, using measurements at two scales.
- Field monitoring began in 2019 at 12 sites from Westport to Falmouth. At most sites, crews laid transect lines from a tidal creek up to the woody edge of the marsh and measured about 20 one-square-meter plots, recording bare ground, plant species and surface elevation.
- Three sites (Ocean View Farm, Little Bay North and Little Bay South) were also part of a pilot test of a restoration technique called runnels. Their plots targeted stressed areas, so their numbers may look worse than the marsh as a whole.
- Aerial images from 2001, 2009, 2014 and 2019 were used to measure how much vegetated marsh was lost. A 2018 image analysis by the U.S. Geological Survey gave the ratio of bare to vegetated marsh (UVVR), and airborne laser elevation data from 2013 to 2014 showed how much marsh sits high enough to keep up with sea level rise.
- Nitrogen came from water samples collected by the Coalition's Baywatchers volunteer program (2016 to 2020 averages). Tidal restrictions came from the Buzzards Bay National Estuary Program's atlas of culverts and similar structures.
- The 12 sites cover about 40 acres of the roughly 5,000 acres of salt marsh around Buzzards Bay. The authors say they represent the range of marsh types in the watershed.
What they found
- Loss at every site. Marsh area shrank at all 12 sites between 2001 and 2019. The average loss was about 7%. Herring Brook in Falmouth (18%) and Mattapoisett Neck (23% in the site table) lost the most, while Demarest Lloyd and Little Bay South lost about 1% (Jakuba et al., 2023). Across the sites about 2 acres were lost, which the authors say could mean around 200 acres bay wide if scaled up.
- Near a tipping point. About 9% of the surveyed marsh was bare and about 91% was vegetated. The average ratio of bare to vegetated marsh was 0.17. The authors treat about 0.15 as a threshold above which resilience to sea level rise falls sharply, so Buzzards Bay marshes are near it.
- Height matters most. Marshes with more area above mean high water had less bare ground and more high marsh plants. The authors call surface elevation the most important factor they examined. The sites with the most low-lying marsh were Herring Brook, Little Bay North, Mattapoisett Neck and Wings Neck.
- Restricted tides, more damage. Marshes with full or partial tidal restrictions looked more degraded on average than those without, both in aerial images and in bare ground measured in the plots.
- Room to move inland. Eight of the 12 sites have no hardened barrier (such as a seawall or road) behind them that would block inland migration, and at nine sites more than half the marsh sits high enough to remain marsh until at least 2100. Across the sites, 68% of marsh area is at a resilient elevation.
- A chance for damaged marshes. Ocean View Farm in Dartmouth shows many signs of stress but has protected land behind it. The authors call protecting land next to marshes one of the most promising ways to keep them into the next century. They saw marshes expanding inland in places, but not as fast as marsh was being lost.
- Nitrogen and other pressures. Water near the sites carried 0.4 to 0.9 mg/L of nitrogen, with about 0.5 or less described as more favorable for marsh resilience. At Wings Neck and Patuisset Marsh the authors point to nitrogen from nearby septic systems as a stress. They also note that ditching, wave erosion and crab grazing can add to marsh loss.
What it means for Waquoit Bay today
The 12 sites are around Buzzards Bay, west of the Waquoit Bay watershed. Two of them are in Falmouth (Herring Brook in North Falmouth and Great Sippewissett Marsh), and both drain to Buzzards Bay, not Waquoit. What carries over is how the report reads a marsh: how high it sits, whether tides can flow freely through culverts, and whether undeveloped land lies behind it. Waquoit Bay's marshes have similar settings, including tidal crossings and houses along the edges.
Two local items fit that frame. Mashpee's approval of a larger Red Brook Road culvert was designed in part to let salt marsh move inland (see the Red Brook culvert decision). Research on a different marsh stress is covered in purple marsh crabs and creek widening on Cape Cod. The Buzzards Bay results are from 12 small study areas, so they describe those sites rather than every marsh in either bay.
Read the report
Jakuba, R. W., Besterman, A., Hoffart, L., Costa, J. E., Ganju, N., & Deegan, L. (2023). *Buzzards Bay salt marshes: Vulnerability and adaptation potential*. Buzzards Bay Coalition. https://secure2.convio.net/bbay/site/DocServer/Saltmarsh_Vulnerability_Adaptation_Feb2023.pdf
License: The report shows no open license (© Buzzards Bay Coalition and partners; photos credited to the Buzzards Bay Coalition), so we link to the Coalition's copy rather than host the PDF. This summary is based on the full 36-page report, not only an abstract. The card image is a title card made from the citation.
Drafted with AI assistance from the linked source.
