Buzzards Bay Salt Marshes: Vulnerability and Adaptation Potential

FEBRUARY 2023
BUZZARDS BAY
SALT MARSHES:
Vulnerability
and Adaptation
Potential

• Current conditions – Marsh area at all our study sites
was lost between 2001 and 2019, indicating that
the stressors are overwhelming the marsh’s natural
resilience. The total loss varied, ranging from about
1% to around 20% depending on the site.
• Marsh stressors – Two of the most important stressors
that are impacting Buzzards Bay salt marshes are low
marsh surface elevations that make them susceptible to
drowning with sea level rise and structures that obstruct
natural tidal flow to the marshes.
• Potential to adapt – To adapt to sea level rise, marshes
will need to migrate landward. Eight of our 12 marsh
sites are free from hardened barriers that would prevent
the marsh migrating landward. At nine of the 12 sites,
over 50% of the marsh area is located at an elevation
that is expected to remain marsh until at least 2100.
SUMMARY CONCLUSIONS
Buzzards Bay Coalition
Buzzards Bay National
Estuary Program
PROJECT PARTNERS
Woodwell Climate
Research Center
U.S. Geological Survey
Photo credit for all photographs: Buzzards Bay Coalition

Salt marshes with lush grass meadows teeming with
shorebirds are iconic features of the Buzzards Bay coast
and provide important environmental benefits as well
as opportunities for recreation and aesthetic enjoyment.
These productive coastal wetlands are important because
they protect properties from storm surges, remove
nutrients from the water and carbon from the atmosphere,
and provide critical habitats for fish, shellfish, and birds.
Found where the land meets the sea, salt marshes are
naturally dynamic features that change with rising seas,
waves, ice, and storms. In the past, humans purposely
altered salt marshes by filling them to create buildable
land or digging drainage ditches. These major alterations
harmed marsh structure and health. In recent decades,
however, marshes are degrading because of more diffuse
ABOUT THIS REPORT: and complex pressures such as nutrient pollution, sea level
rise, major storms, and crab overgrazing. As a result, at
many places along the East Coast, marshes have crumbling
banks and large areas where the plants have died, leaving
behind mudflats.
The Buzzards Bay Coalition and the Buzzards Bay National
Estuary Program began field monitoring of salt marshes
around Buzzards Bay in 2019 to document changes (map
below shows sites). We partnered with the U.S. Geological
Survey and the Woodwell Climate Research Center to use
aerial tools to investigate how different characteristics of
the long-term marsh sites and their watersheds affect the
marsh’s current health and likely future. This report brings
together the results of on the ground monitoring with data
from aerial imagery to look at marsh status at 12 long-term
monitoring sites based on existing stressors, current marsh
conditions, and potential for adaptation.
•
•WESTPORT
TOWN FARM
WESTPORT
•
•OCEAN VIEW FARM,
ALLENS POND
DARTMOUTH
•
•DEMAREST LLOYD
DARTMOUTH
•
•LITTLE BAY NORTH
FAIRHAVEN
•
•LITTLE BAY SOUTH
FAIRHAVEN
•
•MATTAPOISETT NECK
MATTAPOISETT
•
•HAMMETTS COVE
MARION
•
•LITTLE HARBOR
BEACH
WAREHAM
•
•WINGS NECK
BOURNE
•
•PATUISSET MARSH
POCASSET
•
•HERRING BROOK
FALMOUTH
•
•GREAT SIPPEWISSETT
MARSH
FALMOUTH
Map shows salt marsh area shaded in green, watershed boundaries in blue, and long-term monitoring sites as colored dots.
Source: Bureau of Geographic Information (MassGIS), Commonwealth of Massachusetts, Executive Office of Technology and
Security Services and Buzzards Bay National Estuary Program. 1

Stressors on Salt Marshes
Changing environmental conditions and human activity
at both small and large scales can stress marsh plants
and soils, altering how these ecosystems “work”.
Sea Level Rise – Due to climate change, sea levels have
been rising over the past century faster than they would
naturally. To persist, salt marshes must build up surface
elevation faster than sea level rises. Marshes increase
surface elevation by: 1) plants producing dense root mats
that build up over time, and 2) stems of marsh plants
trapping sediment particles from flooding tides that
deposit on the marsh surface. If sea level rises faster than
a marsh can increase its elevation, the marsh will begin to
drown. The surface elevation of a marsh determines how
vulnerable it is to drowning from rising sea levels.
Salt marshes with more area sitting at low elevations
are more vulnerable to loss from rapidly rising seas.
What impacts
marsh condition and
future trajectory?
Nitrogen pollution – Excess nitrogen can increase the
amount of marsh grass (like over-fertilizing your lawn),
but it can also cause the underground root network to
become sparse and weak. This destabilizes the marsh and
can lead to marsh banks crumbling into the water. Excess
nitrogen also increases the activity of microorganisms that
break down organic material, which can result in the marsh
losing elevation.
Salt marshes exposed to high nitrogen
concentrations (e.g., from nearby septic systems)
are more vulnerable to marsh loss.
Tidal Restrictions – Many salt marshes are crossed by
highways, roads, and railroads that often have culverts
(pipes or openings) installed to allow tidal water to pass
beneath them. In many cases, these culverts are too small
to allow enough tidal water to pass through to maintain
natural salt marsh conditions.
Tidal restrictions can make marshes more
vulnerable to loss.
Current Conditions
The current health of the marsh reflects how well it is
handling existing pressures.
Vegetated and Unvegetated Areas – Healthy marshes
are covered with dense vegetation that builds up the soil
elevation by creating root mats and peat and by trapping
sediment from flooding tides. When the plant community
becomes stressed by current conditions, vegetation dies
and converts to unvegetated, bare area. Bare areas are
also more susceptible to erosion.
Salt marshes with larger amounts of unvegetated,
bare areas indicate the marsh’s susceptibility
to existing stressors and make the marsh more
vulnerable to marsh loss.
Marsh Loss – Loss of marsh area happens when the edge
of a marsh crumbles into the water, tidal creeks and
ditches expand outward creating mudflats, and interior
areas convert from vegetated marsh to bare mudflats with
standing water.
Marshes have an amazing natural capacity to adapt
to changing environmental conditions. But all things
have limits. With many factors — both historical and
current — stressing marshes, marshes are degrading
across the northeastern United States. These stressors
not only impact a salt marsh’s current condition, but
also its capacity to adapt to changing environmental
conditions. There are many ways to describe aspects
of marshes and their surrounding environment. For
this report, we selected a set of metrics that describe
stress, condition, and potential for adaptation, and that
integrate information about multiple factors. While
not exhaustive, the metrics described below help us
to understand the status of a marsh and how it will
persist into the future.
2

Other Factors
As illustrated above, marshes are complicated. The
exposure to stressors, current conditions of a marsh,
and capacity to adapt to a changing environment are
all dependent on many factors. In addition to those
described above, other factors include the intensity of
mosquito ditching, exposure to wind-driven wave erosion,
and possible impacts from crabs, among others. Intensive
mosquito ditching alters water flow, soils, and vegetation
in marshes, and makes them more vulnerable to loss.
Wind-driven waves can stress the edges of marshes,
causing them to destabilize and erode. And some marsh
crab species eat plants. When crab populations are too
high, plants can be consumed or stressed from herbivory.
Intense burrowing from multiple crab species may also
be a stressor for marshes. Some of these factors are
challenging to quantify and our understanding of their
importance is still developing.
In this report we present a set of metrics describing a
marsh’s stressors, current condition, and potential for
adaptation and apply them to selected sites. These sites
represent about 40 acres of the 5,000 acres of salt marsh
that exists around Buzzards Bay. However, these marshes
represent the diversity of salt marsh ecosystem types and
conditions found throughout the watershed.
The amount of marsh area lost over the past few
decades demonstrates the effect of existing stressors
on the marsh. Marshes showing high amounts of loss
are generally more vulnerable to future losses.
Potential for Adaptation
Salt marsh ecosystems are adapted to thrive in areas
that are periodically flooded by the tides. Within the
marsh, different vegetation “zones” are adapted to
tolerate different amounts of time under water and levels
of saltiness. Each zone has distinct plant species. As
sea level rises and the tides reach further inland, flood-
tolerant grasses and marsh plants will colonize these
places where there is currently forest or fields or other
undeveloped land. If a salt marsh can migrate landward,
the total marsh area may remain the same even if
vegetation is lost at the seaward edge.
Coastal squeeze – Sea walls, roads, or other development
landward of a marsh limit the ability of marsh plants
to colonize new areas. Even where landward areas are
undeveloped, a steep slope may prevent marsh plants
from colonizing the undeveloped area.
Salt marshes with developed areas or steep
slopes on their landward edge have limited
potential for adaptation making them more
vulnerable to marsh loss.
Plant community – If a marsh is covered primarily by
plants that tolerate only a moderate level of seawater
flooding, then as the marsh is flooded more often, the
plant community can transition to plants that tolerate
higher levels of flooding and keep the marsh vegetated.
When a marsh is already dominated by flood-tolerant
species, as sea level rises, there is no additional capacity
for the plant community to adapt. Once flooding exceeds
a threshold, the flood-tolerant plants will die and the
marsh will convert to bare mud flats.
Salt marshes that are already predominantly
covered with very flood-tolerant species have
limited potential for adaptation making them
more vulnerable to marsh loss.
Elevation – While the amount of low elevation areas in a
marsh tells us about its vulnerability to loss from current
stressors, the amount of high elevation areas tells us about
its ability to adapt to rising seas. These higher elevation
areas will persist for longer, and have a better chance of
increasing surface elevation faster than sea level rises.
Salt marshes with a smaller percentage of higher
elevation areas have limited potential for adaptation
making them more vulnerable to marsh loss.
3

4
Methods
In this report we present stressors, current conditions,
and potential for adaptation for 12 marshes around
Buzzards Bay. The data presented pertain to our study
sites, so metrics on size and distances describe our study
areas rather than the entirety of the marsh. At each
marsh we provide an overview of the marsh setting as
well as information on the marsh’s resilience against and
vulnerability to future losses. We define resilience as
a marsh’s ability to persist as a marsh ecosystem while
undergoing stress. We define vulnerability as a marsh’s
risk of converting into open water or bare mudflat. This
information is presented in a short paragraph, a table of
metrics, and in figures and maps for each site.
The information presented in this report was collected
at several different scales. On the ground measures were
made at the smallest scale (one-square meter plots).
Aerial and satellite measurements were made at larger
scales (1-10 acres). Collecting information at multiple
scales helps to put the results in context and maximize
the available information.
Marsh-Specific Metrics: At each long-term site, we
established transect lines along which to collect data.
The transects go from a tidal creek or ditch up to where
the vegetation transitions from marsh to woody plants.
The transects are representative of what is happening
across the marsh, but measurements are made at a
limited number of points. At most sites, this resulted in
20 quadrats per site. Three sites were part of a pilot test
for a restoration technique (“runnels”). At these runnel
test sites, sample areas targeted potential restoration
areas where the marsh showed signs of stress. As a
result, the metrics used to quantify current conditions
may look worse than if the sample areas were selected
to target general marsh condition (as they were at other
sites) rather than potential restoration areas. The data are
indicated for runnel test sites with an asterisk.
Bay-Wide Metrics: Airplanes and satellites are able to
collect data and photographs across a large marsh area
at once (collectively referred to as remotely-sensed
data). This information provides an integrated look with
many data points across the marsh. We used metrics
calculated for each marsh site by analyzing aerial images
and remotely-sensed data. Site values were aggregated,
and we present bay-wide estimates based on our 12 marsh
sites. These metrics quantify recent marsh loss, current
vegetation condition, and elevation of all our marsh sites
around Buzzards Bay.
Summer field technician Ryan Kappel measures stem height
at a monitoring quadrat at the Mattapoisett Neck site.

5
Percent Low-Lying – At each site, survey equipment was used to measure marsh
surface elevation along each transect. The percent low-lying was calculated as the
percentage of transect elevations below a point roughly equivalent to the height
of low marsh. Data from 2019-2021 were used. These areas are more vulnerable to
loss with sea level rise. This part of the marsh may be lost within decades.
This metric is presented on each site
page in the “Marsh-Specific Metrics”
tables, and as the area shaded orange
in the figures titled “Vulnerability to
Sea Level Rise.”
2% to 21%
Nitrogen – The concentration of total nitrogen was measured in water samples
collected near the marsh sites. The samples were collected through the Buzzards
Bay Coalition’s Baywatchers Program. Data from 2016–2020 were averaged. Lower
levels of nitrogen in the water (~0.5 mg/L or less) make marshes more resilient.
This metric is presented on each
site page in the “Marsh-Specific
Metric” tables.
0.4 to
0.9 mg/L
Tidal restrictions – Buzzards Bay National Estuary Program (BBNEP) gathered
information on the location and status of tidal restrictions around Buzzards Bay in
2002 and 2009. We used the BBNEP atlas of tidal restrictions to determine when
restrictions were present at a site.
page in the descriptive text.
None to
restricted by
a culvert
METRIC AND METHOD WHERE TO FIND IN REPORT
Stressors
on
Salt
Marshes
Percent Unvegetated – At about 20 locations per site, the area of a one-square
meter plot that was either bare or covered with plants was measured. The percent
unvegetated is the percentage of the plots that were bare without any plants.
Data from 2020 and 2021 were averaged.
page in the “Marsh-Specific Metric”
tables, and as the brown shaded area
in figures titled “Current Conditions.”
1% to 19%
Unvegetated to Vegetated Ratio (UVVR) – The U.S. Geological Survey used
computer software to analyze 2018 aerial images from the National Agricultural
Imagery Program to classify marsh areas as vegetated with plants or as bare
surface or water. The unvegetated to vegetated ratio (UVVR) is a measure of how
much of the overall marsh is covered by bare areas (including water-filled channels,
ponds, and bare mudflats) versus the amount covered with marsh plants. Larger
values indicate more open water, bare areas, and less vegetation. Values above 0.15
indicate higher marsh loss vulnerability. Values below 0.15 indicate greater stability.
This metric is presented using the
data from all sites combined in the
“Results and Conclusions” section.
0.02 to 0.69
Marsh loss – Vegetated marsh areas were measured using GIS tools and aerial
images from 2001, 2009, 2014, and 2019. Marsh loss was calculated by dividing the
slope of the linear regression of the marsh area at the four timepoints with the
marsh area in 2001 and multiplying by 18 for the study period.
This metric is presented in the map
legend of each site page and in the
“Results and Conclusions” section
using the data from all sites combined.
1% to 23%
Current
Conditions
Plant community – We identified marsh plants in the one-square meter plots
and measured their abundance. Plants were classified as low marsh species
(flood-tolerant) or high marsh species (low flood-tolerance). Marshes that are
already predominantly covered with very flood-tolerant species have less
capacity to adapt as sea levels get even higher and are susceptible to converting
to bare mudflats.
tables, and as the pie-chart with high
marsh species in blue and low marsh
species in orange in figures titled
“Potential for Adaptation.”
13 to 63%
High Marsh
37 to 87%
Low Marsh
Percent Above Mean High Water – At each site, survey equipment was used to
measure marsh surface elevation along each transect. The percent of transect
elevations above mean high water (MHW) were calculated. Areas above MHW
are more likely to “keep up” with sea level rise, and persist until at least 2100.
tables, and as the area shaded green
in the figures titled “Vulnerability to
Sea Level Rise.”
36% to 93%
Percent Resilient – The National Ocean Service and U.S. Geologic Survey use laser
instruments (LiDAR) on airplanes to measure ground elevation. Data are from
2013-2014. Percent Resilient was measured as the percentage of vegetated marsh
sitting equal to or above the mean high water (MHW) datum. Areas above MHW
are more likely to “keep up” with sea level and persist until at least 2100.
This metric is presented using the
data from all sites combined in the
“Results and Conclusions” section.
19% to 92%
Potential
for
Adaptation
RANGE*
* Range indicates the highest and lowest value measured from the 12 marshes in this report.

Marsh Vegetation
Within a salt marsh, different plant species are adapted to
tolerate certain levels of flooding by seawater with the tides.
The areas of marsh that are flooded daily by the tides are
known as the low marsh. The primary low marsh plant adapted
to this frequent flooding is Spartina alterniflora (smooth
cordgrass). High marsh areas are only flooded when the
tides are particularly high — such as the highest high tides
each month or from storm surge. Plants that occur in the
high marsh include Spartina patens (salt marsh hay), Juncus
gerardii (saltmarsh rush), Distichlis spicata (saltgrass), and
Iva frutescens (high tide bush), which is the least tolerant of
flooding. The images to the right show examples of the most
common species observed at our marsh sites.
6
LOW MARSH
LOW MARSH SPECIES
Spartina alterniflora (FIGURE A)
HIGH MARSH SPECIES
Spartina patens (FIGURE B)
High Tide Bush (FIGURE C)
Saltmarsh rush (FIGURE D)
Saltgrass (FIGURE E)
HIGH MARSH
UPLAND

WESTPORT TOWN FARM
WESTPORT
830 Drift Rd. Westport, MA 02790
Owner: Town of Westport
The Westport Town Farm site is a large marsh and is located on the upper part of the East Branch
of the Westport River. There are no restrictions to the flow of seawater to the marsh. Behind the
marsh are large hayfields and conservation land. Over 90% of the study area sits at a relatively high
elevation, there is a large proportion of high marsh species, and the current vegetation coverage is
99%. These characteristics will help the marsh’s resilience to current and future stressors. A factor
that contributes to the marsh’s vulnerability is that the marsh is flooded by water with some of the
highest nitrogen concentrations across our study sites. For details on the metrics presented below,
see the Methods section (pages 4-5).
Westport Town Farm
800 ft
N
➤
➤
N
CURRENT CONDITIONS
1% Unvegetated
VULNERABILITY TO SEA LEVEL RISE
2% Low-Lying
POTENTIAL FOR ADAPTATION
50% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Percent Low-Lying 2%
Nitrogen Pollution
0.8
mg/L estuary
Current Conditions
Percent Unvegetated 1%
Potential For Adaptation
Plant Community
50% High Marsh
50% Low Marsh
Percent Above MHW 93%
MARSH-SPECIFIC METRICS
93% above MHW
2% low-lying
8
Site map showing transects where on the ground
measurements were made. Created with Google Earth.

600 ft N
➤
➤
N
9
Site map with marsh area in different years
shown by shaded regions. Blue, pink, and
orange shading indicate areas that were
previously vegetated marsh but were bare
in 2019. Created with Google Earth.
2001
2009
2014
2019
STUDY AREA:
4.5 ACRES
LOST FROM 2001–2019:
1%

OCEAN VIEW FARM, ALLENS POND
DARTMOUTH
DNRT Ocean View Farm Reserve: Allen Neck Rd. and Barneys Joy Rd. Dartmouth, MA 02748
Owner: Dartmouth Natural Resources Trust (DNRT), conservation restriction held by the Buzzards Bay Coalition
The Ocean View Farm site is located on the northern shores of Allens Pond, which is a salt pond
behind a barrier beach. The flow of seawater to the marsh is restricted by the natural tidal inlet of
Allens Pond that closes intermittently, though the inlet is managed to prevent closure for more than
a few months. The site is adjacent to retired farm fields that are now managed to provide grassland
habitat for birds. The large extent of marsh within Allens Pond, and absence of any restrictions to
migration support the resilience of this marsh. In fact, the Dartmouth Natural Resources Trust is
looking to actively facilitate marsh migration into the former farm fields. However, almost 16% of the
study area along our transects is bare, and only 47% of the marsh is sitting above mean high water.
These factors contribute to the marsh’s vulnerability. For details on the metrics presented below,
see the Methods section (pages 4-5).
Ocean View Farm
800 ft
N
➤
➤
N
10
CURRENT CONDITIONS
16% Unvegetated
5% Low-Lying
27% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Percent Low-Lying 5%*
Nitrogen Pollution
0.9
mg/L estuary
Current Conditions
Percent Unvegetated 16%*
Plant Community
27% High Marsh
73% Low Marsh*
Percent Above MHW 47%*
47% above MHW
5% low-lying
*Runnel test site. On the ground measurements
were collected using a modified sampling design.
See methods for details.

600 ft N
➤
➤
N
11
2001
2009
2014
2019
STUDY AREA:
5.7 ACRES
6%

DEMAREST LLOYD
DARTMOUTH
115 Barneys Joy Rd. Dartmouth, MA 02748
Owner: Demarest Lloyd State Park
The Demarest Lloyd site is located near the mouth of the Slocums River, along the banks of a tidal
creek. Seawater flows to the marsh freely, without any tidal restriction. The marsh is adjacent to
a recreational area that includes some forested land, picnic areas, and a large parking lot. A large
portion of this site sits at relatively high elevation, and the current vegetation coverage is
99% — these two characteristics increase the marsh’s resilience to future stressors. Two
factors that contribute to the marsh’s vulnerability are that low marsh species dominate the
plant community (65%) and that the marsh is flooded by water with relatively high nitrogen
concentrations. As a well-loved public destination, another pressure on this site is a large number
of people walking through the marsh. Low marsh plant species are damaged when they are
stepped on, increasing their vulnerability to other pressures. For details on the metrics presented
below, see the Methods section (pages 4-5).
Demarest Lloyd
800 ft
CURRENT CONDITIONS
1% Unvegetated
7% Low-Lying
35% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Nitrogen Pollution
0.6
mg/L estuary
Current Conditions
Plant Community
35% High Marsh
65% Low Marsh
68% above MHW
7% low-lying
12

600 ft N
➤
➤
N
13
2001
2009
2014
2019
STUDY AREA:
2.2 ACRES
1%

LITTLE BAY NORTH
FAIRHAVEN
12 Little Bay Rd. Fairhaven, MA 02719
Owner: Town of Fairhaven
Little Bay North marsh is located where the Nasketucket River opens into the inner part of Little Bay.
The marsh is exposed to a large, open embayment, with a protected forest upland found adjacent
to the marsh. A paved walking trail provides access to this marsh and a small fishing pier. The flow
of seawater to the marsh is unrestricted, and there are no impediments to upland marsh migration.
The high elevation at this marsh contributes to its resilience. Resilience is further enhanced by the
prevalence of high marsh plants. However, the marsh’s vulnerability is increased by the fact that the
marsh is exposed to open water and high wind, increasing the risk of erosion from waves. For details
on the metrics presented below, see the Methods section (pages 4-5).
Little Bay North
800 ft
N
➤
➤
N
CURRENT CONDITIONS
9% Unvegetated
14% Low-Lying
52% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Nitrogen Pollution
0.6
mg/L estuary
Current Conditions
Plant Community
52% High Marsh
48% Low Marsh*
76% above MHW
14% low-lying
14

500 ft
N
➤
➤
N
15
2001
2009
2014
2019
STUDY AREA:
4.7 ACRES
5%

Little Bay South
800 ft
N
➤
➤
N
CURRENT CONDITIONS
11% Unvegetated
5% Low-Lying
37% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Nitrogen Pollution
0.6
mg/L estuary
Current Conditions
Plant Community
37% High Marsh
63% Low Marsh*
76% above MHW
5% low-lying
LITTLE BAY SOUTH
FAIRHAVEN
Near 10 Edgewater St. Fairhaven, MA 02719
Owner: Town of Fairhaven
The Little Bay South marsh site is found just south of Little Bay North, open to the inner part of
Little Bay and seaward of a small area of undeveloped land and neighboring residential buildings.
A paved road bisects this marsh, but does not create a barrier to migration. At this marsh, resilience
is promoted by an unrestricted flow of seawater, and only a small percentage of low-lying elevation.
However, vulnerability is increased by a high density of historical ditches which are eroding and
expanding today, especially in the areas closest to the water beyond our study area. The marsh
is also exposed to wind-driven waves which can contribute to erosion. For details on the metrics
presented below, see the Methods section (pages 4-5).
16

600 ft
N
➤
➤
N
17
2001
2009
2014
2019
STUDY AREA:
4.8 ACRES
1%

MATTAPOISETT NECK
MATTAPOISETT
70 Mattapoisett Neck Rd. Mattapoisett, MA 02739
Owner: Town of Mattapoisett
The Mattapoisett Neck site lies within a large marsh in the upper part of Mattapoisett Harbor, near
the mouth of the Mattapoisett River. The flow of seawater to the marsh is restricted by a culvert
running beneath a road. There are several houses behind the marsh, limiting space for migration.
A factor that supports the resilience of this marsh is that 88% of the survey area is covered with
vegetation. However, low marsh species make up 87% of the vegetation surveyed which is the
greatest amount at any of our sites and contributes to the marsh’s vulnerability. A large percentage
of the marsh is also found at low-lying elevations, and the ditches have significantly eroded
and expanded. These factors contribute to the marsh’s vulnerability. For details on the metrics
Mattapoisett Neck
800 ft
N
N
CURRENT CONDITIONS
12% Unvegetated
14% Low-Lying
13% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Nitrogen Pollution
0.4
mg/L estuary
Current Conditions
Plant Community
13% High Marsh
87% Low Marsh
44% above MHW
14% low-lying
18

600 ft
N
➤
➤
N
19
2001
2009
2014
2019
STUDY AREA:
1.3 ACRES
23%

HAMMETT COVE
MARION
18 Creek Rd. Marion, MA 02738
Owner: Town of Marion
The Hammett Cove site is open to the upper part of Hammett Cove. The site is small, and
lies just seaward of a small undeveloped upland area. Hammett Cove is found in an open
embayment, where the flow of seawater to the marsh is unrestricted. This site’s resilience is
enhanced by the plant community, with the highest proportion of high marsh species of any
of our sites. A factor contributing to this marsh’s vulnerability is that it is relatively narrow,
extending only about 30 yards from upland boundary to open water. For details on the metrics
Hammetts Cove
800 ft
CURRENT CONDITIONS
11% Unvegetated
6% Low-Lying
63% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Nitrogen Pollution
0.6
mg/L estuary
Current Conditions
Plant Community
63% High Marsh
37% Low Marsh
89% above MHW
6% low-lying
20

600 ft N
➤
➤
N
21
2001
2009
2014
2019
STUDY AREA:
1.3 ACRES
6%

LITTLE HARBOR BEACH
WAREHAM
32 Little Harbor Rd. Wareham, MA 02571
Owner: Town of Wareham
The Little Harbor Beach site is located on the back side of a barrier beach. Directly behind the
marsh is a large parking lot for the beach, which is very popular. The flow of seawater to the
marsh is unrestricted. Two factors that support the resilience of this marsh are that it sits at a high
elevation and a high percentage (93%) of the survey area is vegetated. The beach parking lot built
next to the marsh limits the potential for this marsh to migrate with rising sea level — this contributes
to the marsh’s vulnerability. For details on the metrics presented below, see the Methods section
(pages 4-5).
Little Harbor Beach
800 ft
CURRENT CONDITIONS
7% Unvegetated
5% Low-Lying
43% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Nitrogen Pollution
0.6
mg/L estuary
Current Conditions
Plant Community
43% High Marsh
57% Low Marsh
80% above MHW
5% low-lying
22

600 ft N
➤
➤
N
23
2001
2009
2014
2019
STUDY AREA:
1.9 ACRES
5%

WINGS NECK
BOURNE
3 Harbor Dr. Pocasset, MA 02559
Owner: Town of Bourne
The Wings Neck site is found along the inner part of Pocasset Harbor. A road was built over the
marsh so the flow of seawater to the northern half of the site is restricted by the road and culvert.
The marsh is surrounded by residential areas. A factor that supports the resilience of this marsh is
that 91% of the study area is covered with vegetation. However, a large proportion of the marsh is
low-lying, and the marsh is surrounded by homes which contribute nitrogen to the marsh system
via septic fields. These factors contribute to the marsh’s vulnerability. For details on the metrics
Wings Neck
800 ft
N
➤
➤
N
CURRENT CONDITIONS
9% Unvegetated
12% Low-Lying
38% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Nitrogen Pollution
0.4
mg/L estuary
Current Conditions
Plant Community
38% High Marsh
62% Low Marsh
76% above MHW
12% low-lying
24

600 ft N
➤
➤
N
25
2001
2009
2014
2019
STUDY AREA:
8.1 ACRES
2%

PATUISSET MARSH
POCASSET
176 Circuit Ave. Pocasset, MA 02559
Owner: Town of Bourne
The Patuisset Marsh site is located behind a barrier beach and upland areas in upper Pocasset
Harbor. The flow of seawater to the marsh is partially restricted by a road culvert on the northwest
side. Directly behind the marsh is a small conservation area that is ringed by residential buildings.
A factor that supports the resilience of this marsh is that 94% of the transects are covered with
vegetation. However, the high density of residential buildings with septic fields surrounding the
marsh adds nitrogen to the system, and the marsh beyond our transect area shows substantial
degradation and loss — these factors contribute to the marsh’s vulnerability. For details on the
metrics presented below, see the Methods section (pages 4-5).
Patuisset
800 ft
N
➤
➤
N
CURRENT CONDITIONS
6% Unvegetated
4% Low-Lying
32% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Nitrogen Pollution
0.4
mg/L estuary
Current Conditions
Plant Community
32% High Marsh
68% Low Marsh
69% above MHW
4% low-lying
26

600 ft N
➤
➤
N
27
2001
2009
2014
2019
STUDY AREA:
3 ACRES
6%

HERRING BROOK
FALMOUTH
301 Quaker Rd. North Falmouth, MA 02556
Owner: Town of Falmouth
Herring Brook Marsh is our smallest marsh site. It is located on a tidal creek behind a recreational
beach, parking lot, road, and bridge. The flow of seawater to the marsh is partially restricted by a
bridge and man-made channel. It is our only site with no historical ditching. The lack of ditching
contributes to its resilience. However, multiple factors contribute to this site’s vulnerability. This
marsh has the lowest vegetation cover of all of the marshes and a high percentage of low-lying area.
Tidal restrictions and development adjacent to the marsh limit its capacity to adapt to future sea
level rise. It experienced consistent edge loss over time and lost the second highest percentage of
marsh area of any of our sites. For details on the metrics presented below, see the Methods section
(pages 4-5).
Herring Brook
800 ft
CURRENT CONDITIONS
19% Unvegetated
21% Low-Lying
31% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Nitrogen Pollution
0.7
mg/L estuary
Current Conditions
Plant Community
31% High Marsh
69% Low Marsh
36% above MHW
21% low-lying
28

600 ft N
➤
➤
N
29
2001
2009
2014
2019
STUDY AREA:
0.9 ACRES
18%

GREAT SIPPEWISSETT MARSH
FALMOUTH
Near 410 W. Falmouth Hwy. Falmouth, MA 02540
Owner: Salt Pond Areas Bird Sanctuaries, Inc.
The Great Sippewissett Marsh is a large marsh. It sits in a protected location behind a barrier
beach and is bordered by wooded areas and a raised bike path. The flow of seawater to the marsh
is unrestricted, and a creek adds freshwater to the system. This marsh is one of our most highly
vegetated sites with 99% cover of vegetation. It also sits at a high elevation. These characteristics
contribute to this marsh’s resilience. However, the nearby raised bike path would restrict marsh
expansion and adaptation to sea level rise, adding to its vulnerability. Despite a relatively high
proportion of high marsh species, the marsh study area is still dominated by low marsh species,
contributing to this site’s vulnerability to future sea level rise. For details on the metrics presented
below, see the Methods section (pages 4-5).
Great Sippewissett
800 ft
N
➤
➤
N
30
CURRENT CONDITIONS
1% Unvegetated
2% Low-Lying
41% High Marsh
Plant Type
High Marsh
Low Marsh
Stressors
Nitrogen Pollution
0.5*
mg/L estuary
Current Conditions
Plant Community
41% High Marsh
59% Low Marsh
89% above MHW
2% low-lying
*Nitrogen value from nearby Little Sippewissett
Marsh because no data available for Great
Sippewissett Marsh.

600 ft N
➤
➤
N
31
2001
2009
2014
2019
STUDY AREA:
5.1 ACRES
5%

What factors lead to the different patterns of loss and
vegetation we see in Buzzards Bay?
There is a large range of conditions observed at the
different study sites around Buzzards Bay. This reflects
the fact that marshes are complex with many factors
affecting their vulnerability to stressors and resilience
against loss.
A variety of stressors can impact marsh health.
Of the factors we examined, marsh surface elevation
and tidal restrictions were the two factors most closely
linked to marsh health.
Elevation: Surface elevations appear to be the most
important factor for marshes.
• Marshes with high percentages of elevations above
mean high water had lower amounts of bare area and
a higher proportion of high marsh species. Our sites
with the highest percentages above mean high water
are Great Sippewissett, Hammetts Cove, and Westport
Town Farm.
• Low-lying elevations are vulnerable to loss in the
next few decades. The amount of these low-lying
elevations at each marsh indicates how much will
likely be lost soon. Of our sites, those with the highest
percentages of low-lying area are Herring Brook, Little
Bay North, Mattapoisett Neck, and Wings Neck.
Tidal Restrictions: Marshes with tidal restrictions, even
partial tidal restrictions, appear more degraded on
average than marshes without restrictions. Sites with
tidal restrictions have both higher UVVR values in
aerial imagery analysis, and higher percent bare area
measured on the ground.
Are there some silver linings for marshes in poor
condition today?
Marshes with low elevations, high rates of recent loss, and
poor vegetation condition today are likely to experience
greater marsh loss, but may persist if they are able to migrate
landward. One example is Ocean View Farm. Ocean View
Farm shows many signs of stress and vulnerability, but has
significant protected areas to migrate into. Land protection
of areas adjacent to marshes is one of the most promising
methods to help conserve marshes into the next century. We
have observed evidence of marshes expanding landward at
some locations. We did not quantify landward expansion as a
part of this report, but based on our observations it appears
to be occurring at a slower rate than marsh loss.
All marshes around Buzzards Bay are vulnerable to loss
due to accelerated sea level rise, and other factors such
as tidal restrictions exacerbate the problem. Large losses
have already occurred in some places including our Herring
Brook and Mattapoisett Neck study sites.
How are marshes doing around Buzzards Bay?
Around the bay about 9% of surveyed areas within
marsh complexes were bare, while about 91% were
covered with marsh plants. The bare areas represent
expanding ditches and creeks, patches of bare and
shallow water areas on the marsh, and unvegetated
banks at the water’s edge. Of our sites, Herring Brook
and Ocean View Farm had the largest percentage of
unvegetated areas, whereas Westport Town Farm,
Demarest Lloyd, and Great Sippewissett had the lowest
percentages of unvegetated areas.
Between 2001 and 2019, our marsh sites lost area
where vegetation died leaving behind bare soil and
open water, where pieces of the marsh-edge broke
off into creeks and embayments, and where ditches
expanded. Around Buzzards Bay our marsh sites lost
about 7% of their area on average, but there was a
wide range across sites. Two sites (Demarest Lloyd
and Little Bay South) were quite stable with about 1%
loss between 2001 and 2019, but two sites had losses
of about 20% each (Herring Brook and Mattapoisett
Neck). Though our study area at Little Bay South was
stable, just outside the area there has been visibly
dramatic loss. Across all our sites, a total of about 2
acres of marsh loss was observed. If we scale these
observations to all the marshes in Buzzards Bay, it
suggests a possible loss of around 200 acres bay wide.
The ratio of unvegetated to vegetated areas within
marsh sites provides an indicator for marsh resilience
to change. Values of ~0.15 represent a tipping
point, above which marsh resilience to sea level rise
decreases sharply. Around Buzzards Bay, the average
UVVR was 0.17. This value suggests Buzzards Bay
marshes are near this tipping point.
Around Buzzards Bay, 68% of our marsh areas are
sitting at a resilient elevation based on analysis of
aerial imagery and remotely sensed elevation data.
These areas are likely to survive until at least 2100.
RESULTS AND CONCLUSIONS:
32

ACKNOWLEDGEMENTS
We greatly appreciate the support of landowners who provided access for collecting on the ground
information. Support for this project was provided by a Southeast New England Program (SNEP)
Watershed Grant funded by the U.S. Environmental Protection Agency (EPA), by EPA Cooperative
Agreements to the Massachusetts Executive Office of Energy and Environmental Affairs, Buzzards
Bay National Estuary Program, and by the Rose Family and Fleetwing Foundations. This research
was also funded by the U.S. Geological Survey (USGS) Northeast Climate Adaptation Science Center
(NE CASC). The contents do not necessarily reflect the views and policies of EPA.
Suggested Citation
Jakuba, R. W., Besterman, A., Hoffart, L., Costa, J. E., Ganju, N., Deegan, L. (2023)
Buzzards Bay Salt Marshes: Vulnerability and Adaptation Potential. 32pp.

114 Front Street • New Bedford, Massachusetts 02740
(508) 999-6363
info@savebuzzardsbay.org
www.savebuzzardsbay.org

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