Natural and Anthropogenic Influences on the Mount Hope Bay Ecosystem
2006 Northeastern Naturalist 13(Special Issue 4):31–46
The Mount Hope Bay Tidal Restriction Atlas:
Identifying Man-made Structures which
Potentially Degrade Coastal Habitats in Mount Hope Bay,
Massachusetts
Stephen B. Barrett1,*, Brian C. Graves2, and Barbara Blumeris3
Abstract - For nearly a decade, Massachusetts resource managers have been systematically
inventorying, assessing and restoring coastal wetlands degraded by
infrastructure crossings such as bridges and culverts, which, unless properly designed
and constructed, restrict tidal flow to upstream areas. These crossings—known as tidal
restrictions—alter the natural flooding and flushing dynamics of coastal estuarine and
wetland habitats, causing damage to salt marshes, eelgrass beds, and other important
shellfish and finfish habitats. The Mount Hope Bay Tidal Restriction Atlas, undertaken
by the Massachusetts Wetlands Restoration Program and the US Army Corps of
Engineers, is the most recent addition to the statewide inventory effort.
The Atlas lists a total of 74 potential tidal restrictions that were initially identified
on maps and aerial photographs, of which 25 sites were documented using rapid field
assessment techniques. Each field-visited site was assessed for severity of restriction
and habitat impacts, potential environmental benefits of restoration, and logistical
feasibility for implementing restoration. Using these factors, sites were prioritized
using a high/medium/low scale. A three-page Site Assessment Report, which includes
data, maps, and photographs, was generated for each field-visited site. The final Atlas
was presented in an interactive digital format to allow users to query its database and
readily move between data fields, maps, and photographs. The Atlas was distributed to
stakeholders as a tool for use in restoration planning and implementation.
Introduction
The Massachusetts Wetlands Restoration Program (MWRP) and the US
Army Corps of Engineers (USACE), New England Division, formed a state/
federal partnership to complete an inventory of tidal restrictions in the Mount
Hope Bay area of Massachusetts under the Corps Planning Assistance to
States Program. Tidal restrictions are manmade structures (e.g., roads,
bridges, dikes/dams, and other barriers) that constrain the natural flood and
ebb flow of salt water through upstream marsh habitats that were historically
inundated by the tide (Massachusetts Wetlands Restoration Program 1999).
The purpose of the inventory was to identify a broad spectrum of tidal
restrictions in the study area that affect coastal habitats, and to investigate a
subgroup of sites with a high potential for ecosystem restoration. It was
1Epsilon Associates, Inc., 3 Clock Tower Place, Suite 250, Maynard, MA 01754.
2Boston Globe, 135 Morrissey Boulevard, Boston, MA 02108. 3US Army Corps of
Engineers, New England District, 696 Virginia Avenue, Concord, MA 01742-2751.
*Corresponding author - sbarrett@epsilonassociates.com.
32 Northeastern Naturalist Vol. 13, Special Issue 4
envisioned that this information would then be used by stakeholders in the
watershed to prioritize and implement restoration projects.
The MWRP established a study area encompassing approximately 64
kilometers of the Mount Hope Bay coastline, including tidally influenced
portions of the Cole, Lee, Palmer, Runnins, and Taunton Rivers. Eight
Massachusetts towns were included in the project area: Berkley, Dighton,
Fall River, Freetown, Rehoboth, Seekonk, Somerset, and Swansea (Fig. 1).
The hydrologic effects of tidal restrictions have caused significant damage
to salt marshes (Burdick et al. 1997). The hydrologic alteration impacts
salt marsh vegetation and the physical and chemical characteristics of marsh
sediments (Portnoy 1999), as well as aquatic organisms and water quality.
Restricted tidal flow: (1) encourages colonization by plant species less
tolerant of salt water than native species (Roman et al. 1984); (2) reduces
utilization of salt marsh by fish species for refuge, forage, nursery, and
spawning habitat (Raposa and Roman 2003, Weinstein et al. 1997); (3) traps
nutrient-enriched waters causing cultural eutrophication (Costa et al. 1999);
and (4) increases peat aeration, leading to subsidence (Portnoy 1999).
Figure 1. Comprehensive inventory of sites.
2006 S.B. Barrett, B.C. Graves, and B. Blumeris 33
Of these impacts, the most visible indicator of salt marsh degradation
from restricted tidal flow is the extensive colonization of salt marsh by
invasive plant species (Tiner 1998). These invasive species, including
common reed (Phragmites australis (Cav.) Trin. Ex Steud) and purple
loosestrife (Lythrum salicaria L.), thrive in disturbed fresh and brackish
areas where they can out-compete the native plant community. Woody
plants, native and exotic, are also able to move onto the marsh where
restrictions can cause the marsh edge to recede or retain freshwater (Buzzards
Bay Project 2002). Other visible signs of restricted tidal flow may
include: back-up or impoundment of water on the upstream side of the
structure, referred to herein as “ponding” (Costa 2000, Montague et al.
1987); increased flow velocity through the restriction opening; and scouring
and slumping of the marsh downstream of the restricting structure
caused by increased flow velocity (Warren 1993).
Tidal restrictions can also exacerbate water quality problems upstream of
the structure due to reduced flushing and mixing. Sources of estuarine
pollution include septic systems, roadways and parking lots, agricultural
fields, and residential lawns. Some pollutants such as excess nutrient loading
(nitrogen and phosphorous) may produce nuisance aquatic plant growth.
Elevated bacterial levels may occur or be more persistent where a bacteria
source exists. Where polluted waters are subject to full tidal flushing, the
diurnal flood and ebb can rapidly dilute contaminants before habitat impacts
are sustained (Kim et al. 2003). Tidal restrictions, however, trap nutrients
upstream and exacerbate eutrophication (Costa et al. 1999). Dense growth
and decomposition of algae deplete oxygen required by marine organisms,
reduce light available to aquatic plants such as eelgrass, and smother benthic
surfaces used by fish for spawning (Valiela et al. 1992).
The removal of tidal restrictions can restore degraded salt marsh and
estuarine habitats by: (1) re-establishing salinity levels that impede encroaching
woody and invasive plants species (Roman et al. 1984, Sinicrope
et al. 1990); (2) flushing stagnant, brackish backwater areas and replenishing
them with low-nutrient marine waters that inhibit the growth of algae
and support healthy aquatic vegetation such as eelgrass (Zostera marina L.)
and fish-spawning habitat utilized by species like winter flounder
(Pseudopleuronectes americanus L.); and (3) improving access to estuarine
habitats used for spawning and foraging by marine fishes.
Mount Hope Bay Study Area
Mount Hope Bay, including the lower Taunton River, is located in the
northeastern section of Narragansett Bay (Fig. 1). Like other estuarine
systems in the northeastern US, Narragansett Bay is a drowned river valley
(Roman et al. 2000). The Taunton River watershed, the second largest
watershed in Massachusetts with an area of 1372.7 square kilometers (Williams
and Wiley 1970), provides the largest contribution of freshwater to the
estuary and regulates seasonal salinity variations. The other rivers in the
34 Northeastern Naturalist Vol. 13, Special Issue 4
project area—Cole, Lee, Palmer, and Runnins—drain a comparatively
smaller area (290 square kilometers) of the Mount Hope Bay watershed
(Wiley et al. 1983).
Salt marsh in Mount Hope Bay
Salt marsh occupies the coastal and estuarine intertidal zone (Nixon
1982) and is generally defined by a low marsh dominated by smooth
cordgrass (Spartina alterniflora Loisel) and a high marsh dominated by
salt marsh hay (Spartina patens (Ait.) Muhl.) (Niering and Warren 1980,
Nixon and Oviatt 1973). The New England-type salt marsh ranging from
Maine to Long Island is distinct from those to the north (Fundy-type) and
to the south (Coastal Plain-type), differing in substrate and vegetation
(Johnson 1925).
The distribution and abundance of salt marsh in Mount Hope Bay, as
elsewhere, is primarily governed by salinity, tidal elevation, substrate characteristics,
and bathymetry. Salt marsh habitat extends upstream in the
Taunton River to about the Berkley Bridge (Massachusetts Department of
Environmental Protection 2003). While salinity in this area is often below
one part per thousand (ppt), particularly during low tides and seasonally high
river flow, the combination of tidal influence and periodically high salinity
(during high tides and low river flows) impedes competition by salt-intolerant
species and thereby supports the salt marsh community. Naturally low
salinity is characteristic of the study area due to its location in the Upper
Narragansett Bay.
Substrate suitability is also important for salt marsh distribution. Salt
marsh colonizes the intertidal zone where it is regularly inundated by tides
(low marsh is flooded daily, high marsh less frequently). Shorelines with
gentle topography, broad areas exposed at low tide, and shelter from wave
energy provide suitable conditions for extensive salt marsh growth. An
example in Massachusetts is Essex Bay, which has 939.3 hectares of salt
marsh and 95.4 kilometers of coastline, a ratio of 9.8 hectares of salt marsh
for each kilometer of shoreline (Chesmore et al. 1973). In comparison,
Mount Hope Bay has little salt marsh relative to the length of its shoreline,
primarily due to the steep topography of the landscape. Mount Hope Bay has
165.9 hectares of salt marsh and 64.4 kilometers of shoreline, a ratio of 2.6
to 1. Approximately 60 percent of the salt marsh in Mount Hope Bay is
located in Broad Cove, the Segreganset River, and Assonet Bay (Curley et
al. 1974). Table 1 lists salt marsh area and shoreline length in representative
estuaries in Massachusetts and demonstrates that salt marsh area is relatively
small in Mount Hope Bay.
Water Quality in Mount Hope Bay
Water quality in Mount Hope Bay is impacted by wastewater treatment
plants and combined sewer overflow discharges in the watershed, highdensity
development in coastal communities, and industrial development
including power generating stations (Curley et al. 1974). Mount Hope Bay
2006 S.B. Barrett, B.C. Graves, and B. Blumeris 35
and its primary tributary rivers (Cole, Lee, Palmer, Runnins, and Taunton)
do not meet state water quality standards for nutrients, organics, and pathogens
(Massachusetts Department of Environmental Protection 2004).
Water quality impairment has degraded estuarine habitats and culturally
important fisheries in Mount Hope Bay as highlighted by commercially
important shellfish species and winter flounder. Harvesting of shellfish,
such as northern quahog (Mercenaria mercenaria L.), soft-shelled clam
(Mya arenaria L.), and eastern oyster (Crassostrea virginica Gmelin), is
restricted due to high bacteria (Germano 1997). Populations of winter
flounder, a commercially important groundfish, have decreased significantly
since the 1970s (Rountree et al. 2003) probably due to over-fishing,
effects from Brayton Point Power Station, and degraded water quality . It is
also possible that high nutrient loading from upstream sources is causing
an over-abundance of green algae (Ulva spp.) which may cover spawning
areas for winter flounder in the lower Lee River (M. Scherer, Marine
Research, Inc., Falmouth, MA, pers. comm.). Green macroalgae have been
found to be dominant in shallow, nutrient-enriched estuaries in southern
Connecticut (Harlin 1995). Some fish species, such as tautog (Tautoga
onitis L.), however, benefit from increased macroalgae in bottom waters
(Dorf and Powell 1997). Cultural eutrophicaton can also degrade eelgrass.
Eelgrass beds, an important habitat for a variety of marine organisms
(Heck and Thoman 1984), are absent from Mount Hope Bay, due in part to
eutrophication (Kopp et al. 1995).
The Mount Hope Bay Tidal Restriction Atlas focused on the potential
impacts of tidal restrictions to salt marsh, intertidal and subtidal flats, and
submerged vegetation such as eelgrass. While the scope of the project did
not allow for a full exploration of the effects of tidal restrictions on water
quality and estuarine habitats, reduced tidal flushing and the documented
water quality impairment of Mount Hope Bay suggest that restrictions have
exacerbated water quality problems.
Table 1. Salt marsh area in Massachusetts estuaries.
Area Shoreline length Ratio of area to
Estuary (hectares) (kilometers) shoreline length
Mount Hope Bay1 165.9 64.4 2.6:1
Plum Island Sound2 3294.1 262.0 12.6:1
Essex Bay3 939.3 95.4 9.8:1
Herring River4 405.9 49.7 8.2:1
Pleasant Bay5 445.6 105.7 4.2:1
Westport River6 405.9 82.6 4.9:1
1Curley et al. 1974
2Buchsbaum and Purinton 2000
3Chesmore et al. 1973
4Curley et al. 1972
5Pleasant Bay Resource Management Alliance 2003
6Fiske et al. 1968
36 Northeastern Naturalist Vol. 13, Special Issue 4
Methods
The geographic scope of the project was limited to the portion of Mount
Hope Bay coastline located within Massachusetts. In addition, the MWRP
established criteria for assessing the landward extent of the survey. For the
Taunton River, the upstream extent of the study area was identified as the
Berkley Bridge, based on known distribution of salt marsh. For other tributary
streams, the upriver extent was established either by a dam, which
prevents further upstream tidal flow (e.g., Cole, Runnins Rivers) or by an
abrupt change in topography and vegetation (e.g., Lee, Palmer Rivers). The
upland boundary of the study area was identified as the area subject to the
one-year storm tidal flood elevation based on mapping by the Federal Emergency
Management Agency (FEMA). Wetland vegetation types illustrated
on Massachusetts Geographic Information System (MassGIS) provided additional
information to verify the upland boundary.
The five steps for developing The Mount Hope Bay Tidal Restriction
Atlas were: (1) initial site identification using a geographic information
system (GIS), (2) stakeholder review of initial site list, (3) field investigations
of a subset of sites, (4) desktop GIS analysis to complete data
collection of field visited sites, and (5) categorization of results.
Initial site identification using GIS
ArcGIS v.8.2 was used as the supporting program for initial site identification.
Existing data, including true color orthophotography, USGS
topographic maps, and 1:5000 scale wetlands and streams maps produced by
MassGIS, were used to complete the analysis.
Data layers were assembled into a single project file and viewed simultaneously
as overlapping layers. Potential restriction sites were initially
identified on orthophotographs and USGS topographical maps where manmade
obstructions were located downstream of the FEMA one-year storm
elevation. Wetland data layers were then overlain to assess wetland types
upstream and downstream of potential restriction sites.
A point shapefile was created in GIS to show the location of all potential
tidal restriction sites in the study area. For each site, a unique site number
was assigned and the following information recorded in a corresponding
data table: town; name of waterbody; proximity to other restriction sites
when “hydrologically connected” (i.e., sites in a series); cumulative area of
affected wetlands; and area of adjacent affected wetlands for sites in a series.
Cumulative affected wetlands are defined as all tidally influenced wetlands
located upstream of the restriction site, including those affected by other
restrictions. Adjacent affected wetlands are defined as only the wetlands
directly upstream of the restriction site.
Once the site information was compiled, an area shapefile was created to
illustrate the spatial extent of wetlands potentially affected by suspected
restriction sites. Wetlands and waterbodies were determined to be tidally
influenced based on hydrologic connection to tidal waterways, topographic
2006 S.B. Barrett, B.C. Graves, and B. Blumeris 37
position relative to adjacent wetlands, and proximity to salt marsh. The
following upgradient wetland types (as defined in the wetlands datalayer)
were determined to be potentially affected by a restriction: open water, salt
marsh, deep marsh, shallow marsh, and shrub swamp. Wooded swamp was
included only in cases where site-specific characteristics (e.g., proximity to
marsh, tidal creeks, and topography) provided compelling evidence that the
wetland was affected by an identified restriction.
Stakeholder review and selection of sites for field investigation
The list of sites identified using GIS was forwarded to local stakeholders
for comment. Stakeholders, including representatives from municipal
conservation commissions, non-profit organizations, and state and federal
agencies, were selected based on their knowledge of the study area and
interest in wetlands restoration. Stakeholders were provided with a summary
cover letter and a series of maps illustrating identified sites, and asked to
provide detailed comments. Follow-up phone calls were made to actively
collect information. Stakeholders provided both confirmatory information
on wetland vegetation, including presence of salt marsh and invasive species,
as well as specific descriptions of the tidal restriction sites, including
relative size and type of restricting structure. Stakeholder comments were
used along with information collected during the initial identification stage
to prioritize sites based on potential restoration benefits. Factors considered
in prioritizing the sites included restricting structure type, proximity to salt
marsh, proximity to tidal waters, and supporting details provided during
stakeholder review. The project team selected 37 sites as the maximum
number that could be investigated in the field based on project funding.
Field investigations
The purpose of the field investigations was to verify the restriction of
tidal flow and to collect information on the restriction site. Criteria used to
evaluate tidal influence included tidal elevation, flow through the restriction,
and presence of salt marsh upstream and downstream of the restriction.
Sites determined to be tidally influenced and potentially restrictive were
further investigated using a rapid assessment technique. A four-page field
inspection form was developed to ensure consistent data collection for each
site. Collected site information included restriction-feature type (e.g., roadway
culvert, bridge, dam) and dimensions, condition of the restriction and its
components, wetland vegetation, waterbody characteristics, tide level, salinity
level and tidal stage, adjacent land uses, and hydrologic evidence (e.g.,
ponding water, flow velocity, scouring). Tide level was measured immediately
upstream and downstream of the restriction opening. Salinity was
measured in the waterway approximately 1.5 m to the side of the structure
opening and 1 m below the surface immediately upstream and downstream
of the restriction using field meter YSI Model 85. Tidal stage was also
recorded at the time of the salinity reading. Digital photographs were taken
of the restriction and adjacent wetlands.
38 Northeastern Naturalist Vol. 13, Special Issue 4
Desktop analysis
Upon completion of the field work, each confirmed tidal restriction site
underwent further computer-based analysis. A one-page analysis sheet was
created to provide a consistent and organized approach to information gathering.
The attributes listed on the sheet and reviewed by GIS included:
ownership type; presence of upstream/downstream restrictions; location
within a designated fish run; total acreage; acreage by wetland type (e.g.,
open water, salt marsh); Massachusetts Natural Heritage and Endangered
Species Program rare species or priority habitat designation; and associated
protected open space.
Categorization of results and distribution to end users
Using the information collected, confirmed tidal restriction sites were
assigned a priority ranking of low, medium, or high in terms of potential
for restoration. Criteria used to prioritize sites included observable impact
indicators (e.g., invasive species, ponding, scouring), potential benefits of
restoration (e.g., reduction in invasive species, increased flushing to water
quality-impaired waters), and feasibility based on practical factors such as
ownership and present uses. Sites that most fully met the criteria were
scored “high” (i.e., high feasibility for restoration), while those that partially
met the criteria were scored “medium,” and those that least met the
criteria were scored “low.”
All data generated for each site were compiled into individual three-page
site-assessment reports. Site-assessment reports were formatted in Adobe
and linked to a database-supporting searchable data fields with site
attributes, aerial photography with superimposed GIS data layers, and representative
photographs taken at the site (Figs. 2, 3, and 4). The final Atlas
included site-assessment reports for the field-visited sites as well as a
spreadsheet of data collected during the initial stage of the project. The Atlas
was presented in an interactive digital format to provide users with a practical
means for reviewing the data. It was distributed to local stakeholders on
a compact disk and made available on internet webpages. Examples of the
representative site assessment reports can be viewed at
www.epsilonassociates.com.
Results and Discussion
Seventy-three sites were identified through the initial GIS-based identification
step (Fig. 1). A 74th site was added following stakeholder input.
Of the 74 sites, 37 were selected for field investigation. Of these 37,
twelve were determined in the field not to be tidally influenced, and
therefore no further data were collected. For the remaining 25 sites, data
were collected in the field and from the desktop, and a site-assessment
report was generated. Priority designations for the 25 sites where restrictions
were found included 11 low-, 12 medium-, and 2 high-priority sites.
2006 S.B. Barrett, B.C. Graves, and B. Blumeris 39
Tidal restrictions in the Mount Hope Bay study area can be broadly
categorized as bridges/fill, undersized culverts, and dams/impoundments
(Table 2). These structures support active or abandoned highways, roads,
cartpaths, railroad lines, and stonewalls. Other components of restrictions
included dikes, berms, tide gates, and fill material.
Bridges
Fourteen of the tidal restrictions investigated in the field were bridges
with adjacent fill and causeways. The majority of these crossings were road
bridges, and the remainder were abandoned railroad bridges. In two
instances, the railroad bridges have been removed, with the causeway fill
left in place, restricting tidal flow. As a group, these restrictions appear to be
relatively minor in that they permit sufficient water to pass so that no
differences in tidal height and/or salinity were found on either side of the
restriction. However, the structures often exhibit hydrologic indicators of
restricted flow (such as ponding, increased flow velocity, and scouring).
These restrictions, where significant length of fill has been placed in a tidal
tributary, also exhibit channel widths much larger than the widths of structure
openings. While visible indicators of water quality impairment such as
algal blooms were generally not observable during winter field work,
blooms have been observed during the growing season, and these barriers
likely exacerbate nutrient and pathogen enrichment. The removal or modification
of these tidal restrictions for increased tidal flushing would be
expected to improve upstream water quality and estuarine habitats. Examples
of restoration actions include the addition of culverts or small
bridges to open up discrete areas along the filled causeway. The feasibility
for removing such restrictions varies widely. Where the restricting structure
is no longer in use (e.g., abandoned railroad beds), removal of the structure
could be an option. Where the restriction is part of an active roadway,
reasonable improvements are dependent on scheduled repairs and extent of
work necessary to alleviate the restriction.
Table 2. Types of tidal restriction identified in the study area.
Restriction type Number identified
Bridges 14
Roadway bridges 6
Roadway causeways 3
Railroad bridges 1
Railroad causeways 3
Stone wall 1
Culverts 8
Arched culverts 2
Single conventional culverts 4
Multiple (grouped) conventional culverts 1
Culverts with tide gates 1
Dams 3
Dams 2
Dikes 1
40 Northeastern Naturalist Vol. 13, Special Issue 4
Figure 3. Site assessment
report example: site photographs.
Figure 2. Site assessment report example: site overview.
2006 S.B. Barrett, B.C. Graves, and B. Blumeris 41
Culverts
While bridges were the most common restricting structure in Mount
Hope Bay, undersized culverts and their impacts on New England salt
marsh have been the focus of past research (Burdick et al. 1997, Sinicrope
et al. 1990, Warren et al. 2002) and inventory work (Buzzards Bay Project
2002, Cape Cod Commission 2001, MWRP 1999). Eight such sites were
identified in the study area during the field investigations. The culverts
observed in the field included a range of configurations from 23-centimeter
diameter round culverts to 61-centimeter box culverts. Most restrictions
consisted of a single culvert, but in one case a system of six parallel
Figure 4. Site assessment report example: site data.
42 Northeastern Naturalist Vol. 13, Special Issue 4
culverts was identified. Varying culvert sizes designed to accommodate
different amounts of stream flow also affected the potential for tidal restriction.
For example, larger arch culverts located near major tributaries
pass significantly more water and therefore are similar in characteristics to
bridges rather than the undersized culverts studied elsewhere in New England
(Burdick et al. 1997, Sinicrope et al. 1990, Warren et al. 2002).
Smaller culverts were identified, and several of these sites included upstream
salt marshes extensively colonized by invasive plant species. At
some sites, the most noticeable indicators of a tidal restriction—differences
in tidal height and salinity between the upstream and downstream
openings—were recorded. A tide gate observed at one of the culvert sites
provided undisputable evidence of tidal flow restriction. While many factors,
such as potential flooding impacts on upstream private property, must
be evaluated before enlarging an undersized culvert, these sites are among
the most promising to remediate, as the solution requires replacing the
existing culvert with a larger one (Roman et al. 1995). Accurately predicting
hydraulic design is essential for selecting the appropriately sized replacement
culvert (Sinicrope et al. 1990).
Dams
While restrictions caused by roads and railroads are mostly unintended
consequences of development, dams and impoundments have been constructed
for the primary purpose of impounding water for various uses. Three such
structures were identified in the study area: a farm pond, a former hydroelectric
dam (known as the Mobil Dam), and a golf course irrigation pond.
Restoration feasibility is dependent, in part, on the utility and value of
the structure to its owner. If the structure is no longer serving its intended
use, then there is an opportunity to remove or modify it. An example in the
study area is the Mobil Dam, which measures 2.5 meters in height, on the
Runnins River. Built for hydropower, it is no longer used for its original
purpose. However, a thorough evaluation of the value of the existing
impounded habitat compared to the restored tidal habitat is needed. Environmental
factors also affect feasibility such as the potential impact of
mobilizing contaminated sediment that may have collected behind the dam.
Where impoundments continue to provide value to the owner, restoration
requires the consideration of multiple factors that balance restoration benefits
and the current uses. While the two irrigation ponds identified above
continue to provide water for their existing owners—a country club and a
farmer—creative solutions may be available.
Conclusions
The Mount Hope Bay Tidal Restriction Atlas is different from other atlases
completed in Massachusetts in two important ways. First, the majority of
identified tidal restrictions in the study area are affecting tidal exchange in
estuaries rather than in salt marshes. Second, salinity levels in upper Mount
2006 S.B. Barrett, B.C. Graves, and B. Blumeris 43
Hope Bay are naturally low, which has implications for restoring the salt
marshes that are restricted. These factors presented challenges for assessing
tidal restrictions and the potential benefits of their removal.
The unique characteristics of Mount Hope Bay with its relatively small
area of salt marsh were first recognized after the project had begun. The
initial site identification confirmed a considerable number of bridges and
filled causeways, but few marshes. The field program was modeled after
other tidal restriction assessments, which focused on rapid field assessment
based on visible evidence of impact (e.g., vegetation, tidal height and salinity
disparities, ponding, scouring). While at least one of these indicators was
present at each of our sites, vegetation and salinity change were often not
visually perceptible at bridge/fill sites, the most common restriction type
found. Assessments of bridge/fill sites that are based solely on these factors
would have resulted in a conclusion that such restriction sites do not cause
habitat impacts. However, extensive fill in a natural channel to support
causeways and bridges suggests that tidal flow patterns and water exchange
upstream of the crossing may be impacted. Water sampling conducted by
state agencies and local groups demonstrates that nutrients and pathogen
levels in most upstream areas are elevated. Targeted water-quality sampling
upstream and downstream of restriction sites could provide evidence of
water-quality impacts of restrictions, but this was beyond the scope of the
project. Instead, potential impacts of restrictions were inferred based on
published pathogen data, past observations of macroalgal growth during the
growing season, and known effects of structures on limiting tidal exchange.
The initial site identification located many undersized culverts; however,
field work showed that many were located above tidal influence, due
to steep topography. For undersized culverts that were confirmed, two
factors suggest that enlarging these culverts may not have a significant
positive effect on upstream marshes in Mount Hope Bay. First, natural
salinity is generally lower than 10 ppt due to the location of these sites in
the upper estuary. As a consequence, an increase in salinity to 20 ppt
(necessary to prevent growth of invasive species such as common reed
[Tiner 1998]) will not occur. Second, the marshes upstream of the culverts
in Mount Hope Bay are often small ( 0.5 hectare) due to the steep shoreline
topography. While the identified culverts appeared to be undersized,
they seemed to pass sufficient tidal water to flood the upstream marsh due
to the small area which required flooding.
Despite the challenges presented by the broadened scope, The Mount
Hope Bay Tidal Restriction Atlas attained several fundamental achievements.
First, it compiled a comprehensive inventory of potential tidal
restriction sites in Mount Hope Bay using GIS and aerial photographs.
Second, the project provided the restoration community with a database of
useful information about restriction sites in Mount Hope Bay. The Atlas has
a user-friendly format with searchable data fields, GIS data layers, and site
photographs in digital form. Third, the project has increased the attention of
44 Northeastern Naturalist Vol. 13, Special Issue 4
State restoration planners on other estuarine habitats that may be impacted
by tidal restrictions. While additional research is required to demonstrate the
extent of water-quality impacts and degradation of other estuarine habitats,
the problem of eutrophication is documented in past reports (Massachusetts
Department of Environmental Protection 2004), and the Atlas has identified
the restriction sites for future investigation. Finally, the Atlas has provided
restoration advocates with a baseline tool for future environmental restoration
planning in Mount Hope Bay.
Acknowledgments
We wish to thank Deb Walker of Battelle Ocean Sciences and Hunt Durey of
Massachusetts Coastal Zone Management for their technical assistance during the
project’s implementation; Lori Parham of the Cobb County (GA) Planning Office
(formerly of Epsilon Associates) for GIS support; and Bill Hubbard of the US Army
Corps of Engineers New England District and Sam Mygatt and Les Smith of Epsilon
Associates for editorial assistance in reviewing this manuscript.
Literature Cited
Buchsbaum, R., T. Purinton, and B. Magnuson (Eds.). 2000. The Marine Resources
of the Parker River–Plum Island Sound Estuary: An Update After 30 Years.
Massachusetts Coastal Zone Management, Boston, MA. 159 pp.
Burdick, D.M., M. Dionne, R.M. Boumans, and F.T. Short. 1997. Ecological responses
to tidal restorations of two northern New England salt marshes. Wetland
Ecology and Management 4(2):129–144.
Buzzards Bay Project. 2002. Atlas of Tidally Restricted Salt Marshes in the Buzzards
Bay Watershed. Marion, MA. 182 pp.
Cape Cod Commission. 2001. Cape Cod Atlas of Tidally Restricted Salt Marshes.
Barnstable, MA. 268 pp.
Chesmore, A., D. Brown, and R. Anderson. 1973. A study of the marine resources of
Essex Bay. Massachusetts Department of Natural Resources, Division of Marine
Fisheries, Boston, MA. Monograph Series Number 13. 38 pp.
Costa, J. 2000. Potential habitat restoration in the East Branch of the Westport River
by removal of obstructions to tidal flushing at the Hix Bridge. Buzzards Bay
Project. Marion, MA. 10 pp.
Costa, J., B. Howes, D. Janik, D. Aubrey, E. Gunn, and A. Giblin. 1999. Managing
anthropogenic nitrogen inputs to coastal embayments: Technical basis and evaluation
of a management strategy adopted for Buzzards Bay. Buzzards Bay Project
Technical Report, Draft Final, September 24, 1999. Marion, MA. 9 pp.
Curley, J.R., R.P. Lawton, D. Whittaker, and J.M. Hickey. 1972. A study of the
marine resources of Wellfleet Harbor. Massachusetts Department of Natural
Resources, Division of Marine Fisheries, Boston, MA. Monograph Series Number
12. 37 pp.
Curley, J.R., R.P. Lawton, D.L. Chadwick, K. Reback, and J.M. Hickey, 1974. A study
of the marine resources of the Taunton River and Mount Hope Bay. Massachusetts
Division of Marine Fisheries. Boston, MA. Monograph Series No. l5. 37 pp.
2006 S.B. Barrett, B.C. Graves, and B. Blumeris 45
Dorf, B.A., and J.C. Powell. 1997. Distribution, abundance, and habitat characteristics
of juvenile tautog (Tautoga onitis, family labridae) in Narragansett Bay, RI,
1988–1992. Estuaries 20:3:589–600.
Fiske, J., J. Curley, and R. Lawton. 1968. A study of the marine resources of the
Westport River. Monograph Series Number 7. Massachusetts Department of
Natural Resources, Division of Marine Fisheries, Boston, MA. 52 pp.
Germano, F. 1997. Sanitary Survey Report of Mt Hope Bay (MHB:1) in the Towns
of Swansea and Somerset and the City of Fall River. Massachusetts Division of
Marine Fisheries, Pocasset, MA. 44 pp.
Harlin, M. 1995. Changes in major plant groups following nutrient enrichment. Pp.
173–187, In A.J. McComb (Ed.). Eutrophic Shallow Estuaries and Lagoons.
CRC Press, Inc., Boca Raton, fl.
Heck, Jr., K.L., and T.A. Thoman. 1984. The nursery role of seagrass meadows in the
upper and lower reaches of the Chesapeake Bay. Estuaries 7(1):70–92.
Johnson, D. 1925. The New England–Acadian Shoreline. Hafner Publishing Company.
New York, NY. 608 pp.
Kim, H.-S., J.C. Swanson, and J. Patel. 2003. Flushing analysis of the Acushnet River.
ASA Report 01-123. Applied Science Associates, Narragansett, RI. 138 pp.
Kopp, B, A. Doherty, and S. Nixon. 1995. A Guide to Site Selection for Eelgrass
Restoration Projects in Narragansett, Rhode Island. Rhode Island Aqua Fund
Program. 128 pp.
Massachusetts Department of Environmental Protection. 2003. MassGIS Wetlands
Datalayer. Wetlands Conservancy Program, Boston, MA.
Massachusetts Department of Environmental Protection. 2004. 303(d) Report of
State Waters. Boston, MA. 123 pp.
Massachusetts Wetlands Restoration Program. 1999. Atlas of Tidally Restricted
Marshes—North Shore of Massachusetts. Boston, MA. 120 pp.
Montague, C., A. Zale, and H. Percival. 1987. Ecological effects of coastal marsh
impoundments: A review. Environmental Management 11:743–756.
Niering, W.A., and R.S. Warren. 1980. Vegetation patterns and processes in New
England salt marshes. BioScience 30:301–307.
Nixon, S.W. 1982. The Ecology of New England High Salt Marshes: A Community
Profile. FWS/OBS-81/55. Washington, DC.
Nixon. S.W., and C.A. Oviatt. 1973. Ecology of a New England salt marsh. Ecological
Monographs 43(4):463–498.
Pleasant Bay Resource Management Alliance. 2003. Pleasant Bay Resource Management
Plan. Orleans, MA. Available at: http://www.pleasantbay.org. 67 pp.
Portnoy, J. 1999. Salt marsh diking and restoration: Biogeochemical implications of
altered wetland hydrology. Environmental Management 24(1):111–120.
Raposa, K.B., and C.T. Roman. 2003. Using gradients in tidal restriction to evaluate
nekton community responses to salt marsh restoration. Estuaries 26(1):98–105.
Roman, C.T., W. Niering, and R.S. Warren. 1984. Salt marsh vegetation change in
response to tidal restrictions. Environmental Management 8(2):141–149.
Roman, C.T., R. Garvine, and J. Portnoy. 1995. Hydrologic modeling as a predictive
basis for ecological restoration of salt marshes. Environmental Management
19(4):559.
Roman, C.T., N. Jaworski, F.T. Short, S. Findlay, and R.S. Warren. 2000. Estuaries
of the northeastern United States: Habitat and land-use signatures. Estuaries
23(6):743–764.
46 Northeastern Naturalist Vol. 13, Special Issue 4
Rountree, R., D. Borkman, W. Brown, Y. Fan, L. Goodman, B. Howes, B.
Rothschild, M. Sundermeyer, and J. Turner. 2003. Framework for formulating
the Mount Hope Bay Natural Laboratory: A synthesis and summary. School for
Marine Science and Technology, University of Massachusetts at Dartmouth,
Dartmouth, MA.. Final Draft. May 22, 2003. 300 pp.
Sinicrope, T., P. Hine, R. Warren, and W. Niering. 1990. Restoration of an impounded
salt marsh in New England. Estuaries 13(1):25–30.
Tiner, R. 1998. Managing Common Reed (Phragmites australis) in Massachusetts:
An introduction to the species and control techniques. US Fish and Wildlife
Service, Hadley, MA. 56 pp.
Valiela, I., K. Foreman, M. LaMontagne, D. Hersh, J. Costa, P. Peckol, B. DeMeo-
Andreson, C. D’Avanzo, M. Babione, C.H. Sham, J. Brawley, and K. Lajtha.
1992. Couplings of watersheds and coastal waters: Sources and consequences of
nutrient enrichment in Waquoit Bay, Massachusetts. Estuaries 15:443–457.
Warren, L., 1993, Scour at bridges. Open-File Report 93-480, US Geological Survey,
Marlboro, MA. 2 pp.
Warren, R.S., P.E. Fell, R. Rozsa, A.H. Brawley, A.C. Orsted, E.T. Olson, V.
Swamy, and W.A. Niering. 2002. Salt marsh restoration in Connecticut: 20 years
of science and management. Restoration Ecology 10(3):497–513.
Weinstein, M., J. Balletto, J. Teal, and D. Ludwig. 1997. Success criteria and
adaptive management for a large-scale wetland restoration project. Wetlands
Ecology and Management 4:111–127.
Wiley, R.E., J.R. Williams, and G.D. Tasker. 1983, Narragansett Bay and Rhode
Island Sound. USGS Basin Report, HD-25. US Geological Survey, Marlboro,
MA. 42 pp.
Williams, J.R., and R.E. Willey. 1970. Taunton River Basin. USGS Basin Report
HD-12. US Geological Survey, Marlboro, MA. 102 pp.