Rhode Island's Coastal Habitats
- Salt Marsh - Anadromous
History | Healthy
vs. Degraded | Salt Marsh Restoration
| Case Study
| Related Links
|Coggeshall Marsh, Prudence Island
Rhode Island salt marshes are found along the shores of salt ponds,
the Narragansett Bay estuary, small embayments (such as Allin's
Cove in Barrington), and estuarine rivers (such as the Narrow River
estuary). Our salt marshes provide nursery grounds and foraging
habitat for hundreds of species of fish, shellfish, birds, and mammals.
Fish of all sizes, from mummichogs to striped
bass, hunt in creeks and ponds. Quahogs
live beneath the surface, while mussels,
crabs, and snails occupy intertidal areas. Many kinds of birds
visit the marsh to feed on the fish and invertebrates: osprey
and herons, ducks of all sorts, and mosquito-eating sparrows that
nest in the marsh. In addition to their habitat value, salt marshes
serve as natural pollution treatment systems by filtering out pollutants
before they reach our coastal waters. The location of salt marshes
between our developed coastal communities and the waters of the
state also provides a buffer during storms and flooding.
Seventy-five percent of commercial fish species depend on estuaries
for their primary habitat, spawning grounds, and nursery areas.
In Rhode Island, the role that salt marshes play in our economy
is evidenced by our 75 million dollar commercial fishery and a recreational
fishery valued at 150 million dollars. The sweeping vistas afforded
by the low lying salt marsh landscape contribute immeasurably to
the beauty and serenity of Rhode Island's coastline, as well as
our tourism and outdoor recreation industry, which is valued at
2 billion dollars on Narragansett Bay alone.
History and Impacts
It is estimated that 60% of Rhode Island's salt marshes have been
filled with mud and sand dredged during navigation projects or waste
material derived from upland sources (Save The Bay 2002). Downtown
Providence was once known as the Great Salt Cove, prior to filling
and conversion to uplands. Marshes can be completely filled or they
can be partially filled, altering the tidal exchange of water, and
impacting vegetation communities that rely on twice-daily flooding.
Often the result of such changes in elevation and flooding is the
invasion by undesirable species such as Phragmites australis
reed). Phragmites is very tolerant of disturbed sites,
and can rapidly overtake such areas.
| Phragmites rapidly invades salt marshes
that have been disturbed or filled.
Courtesy: D. Yozzo, Barry Vittor & Associates
Construction of dikes, roads and rail crossings has resulted in
the degradation of many marshes in Rhode Island. Restriction of
tidal flow by installation of small culverts or drainage pipes under
roads and rail beds leads to changes in salinity and alteration
of the natural vegetation community due to a reduction in duration
and frequency of tidal flooding. Phragmites, which is tolerant
of these altered conditions, especially reduced salinity, often
invades rapidly in areas that have been culverted or diked. Phragmites
out-competes native salt marsh vegetation, and reduces local biodiversity.
Some 1200 of the existing 3700 acres of salt marsh in Narragansett
Bay are impacted by Phragmites and other invasive plant
species (Save The Bay 2002)
Fish communities of salt marshes also suffer from road/rail infrastructure,
as they rely on the natural tidal cycle to maintain populations
in salt marshes. Marsh resident fish species, such as killifish
(Fundulus spp.) spawn in concert with the tidal cycle,
timing their spawning activity to coincide with the highest Spring
tides, due ensure deposition of eggs in the highest portion of the
marsh (Taylor et. al. 1979). When natural tidal cycles are interrupted,
or reduced, killifish spawning success is impaired. Tidal restrictions
can reduce the amount of habitat available for estuarine-dependent
fish that travel up into tidal creeks in search of food.
Mosquito ditching has impacted many marshes in Rhode Island. Mosquito
ditches are very straight, narrow channels that were dug to drain
the upper reaches of salt marshes. Historically, it was believed
that ditching marshes would control populations of mosquitoes that
breed there. It is now known that ditching, in fact, drains standing
water which support populations of mosquito-eating fish (e.g.,
killifish), leading to increases in mosquitoes. These fish are an
important prey item for wading birds (herons and egrets), as well
as larger, predatory fish species. Mosquito ditching alters natural
patterns of groundwater drainage, which alters plant community composition,
and nutrient cycling.
Polluted runoff from adjacent uplands can degrade salt marshes.
Runoff from roads and other paved surfaces, and nutrient-rich runoff
from fertilized lawns, agricultural areas, and septic systems can
degrade marshes by encouraging growth of Phragmites and
other invasive species. Forested buffer zones between populated
areas and salt marshes have diminished as population growth in coastal
areas increases. Approximately 58% of Narragansett Bay's marshes
are impacted by polluted runoff. Some 30% of the Bay's marshes
have inadequate or non-existent buffer zones (Save The Bay, 2002).
Healthy vs. Degraded Salt Marshes
|An example healthy marsh with a vast meadow
of Spartina, upland buffer, and no road crossings
Courtesy: Coastal Resources Mangement Council
Healthy Salt Marsh
The typical vegetation of a salt marsh (smooth
cordgrass and salt
hay grasses) are a beautiful green in the summer and interspersed
with purple sea
lavender. Fiddler crabs can be seen scurrying along the intertidal
mudflats at lower tides and fish dart through the tide pools and
ditches. Sharp tailed sparrows and red winged blackbirds nest in
tidal marshes. A great
egret or a glossy
ibis can be seen circling the marsh, while black ducks slowly
wade through the marsh. The healthy salt marsh offers more than
just a picture of beauty and wildlife; it is actively enhancing
water quality by filtering sediments, nutrients, heavy metals, and
other toxins from upland runoff. This benefit helps keep our state's
waters clean and available for swimming and other recreational activities.
In addition to the filtering processes, salt marshes are also intercepting
waters during storms that could cause expensive, damaging flooding
of residential and commercial properties.
|An example degraded marsh that has a large
stand of Phragmites and hydrologic restriction
Courtesy: Save The Bay
Degraded Salt Marsh
Today many of us would be surprised to learn how extensively
salt marshes and other wetland types used to occur in Rhode Island.
For instance, Providence was one area where salt marshes were prevalent
and have since been filled in to make way for population centers.
Obviously, areas such as these cannot be reclaimed as salt marsh
habitats. But there are other sites in our watersheds where tidal
flows have been restricted, invasive plants are taking over, and
sedimentation is changing the hydrology of the marsh. These types
of impacts to a salt marsh result in lower biodiversity, a decrease
in flood abatement and erosion benefits, and provide potential mosquito
Salt Marsh Restoration
As early as the 1950s, studies had shown that changes to the tidal
flushing, or hydrology, of a salt marsh would degrade its quality
as habitat, and that the restoration of historic hydrology could
restore the habitat value of the marsh. In New England, where many
salt marshes have been hydrologically altered by road and dike construction,
dredged material disposal, and ditching, salt marshes have been
a major focus of coastal habitat restoration efforts. Looking back
on these projects after a decade or more, many of them have been
very successful. The science and technology of salt marsh restoration
are becoming fairly well established.
Salt marshes are complexes of specialized plants and animals living
in a low-energy, intertidal environment. Hydrology, the precise
way in which the marsh is flooded by the tide, dictates which species
can survive in any particular part of the marsh, and therefore defines
the entire marsh ecosystem.
Low marsh is flooded by nearly every tide. The dominant vegetation
in a New England low marsh is usually smooth
mussels and fiddler
crabs are some of the more common animals. High marsh is flooded
only by the highest high tides. In New England, the dominant high
marsh vegetation is generally salt
hay grass, black grass, or spike
grass. Common animals include deer and a wide variety of birds,
The simplest form of salt marsh restoration involves re-establishing
historic hydrology where it has been lost (see Restoration Methods for more details). In New England, roads
and railways have often been built through marshes. Many times,
culverts were placed in the tide creeks at the road crossings. The
culverts may have been too small to begin with, or may have collapsed
over time. The resulting tidal restrictions prevent most tides from
reaching the marsh inland of the road. The marsh becomes a brackish,
rather than tidal system; Phragmites,
replaces the salt marsh vegetation; and the marsh
habitat becomes severely degraded. In these instances, the installation
of a culvert or culverts large enough to allow the full tidal range
to return may be all that is needed to restore the marsh. The salinity
of the tides will kill the Phragmites, and salt marsh vegetation
and fauna will return over a number of years. Two completed projects in Rhode Island that primarily involved hydrologic restoration are highlighted on this Web site: the Little Mussachuck Creek Restoration and the Sachuest Salt Marsh Restoration.
In other cases, the marsh itself may have been filled, often as
a disposal site for marine sediments dredged from navigational channels.
In these instances, it is not enough merely to restore hydrology
because the surface of the marsh is too high to allow the tide to
flood it. In these instances, marsh elevations must be re-established
in order to restore a salt marsh ecosystem. These types of restoration
projects tend to be more difficult and expensive as more construction
is required, and the logistics of earth-moving in a marsh can be
challenging. Nevertheless, some very successful projects of this
type have been accomplished, such as the Galilee
Salt Marsh Restoration in Narragansett, and the Allen Harbor Restoration in North Kingstown, Rhode Island.
Salt Marsh Restoration Case Study: Galilee
|Galilee Bird Sanctuary
The Galilee Bird Sanctuary is a 130-acre salt marsh owned by the
state of Rhode Island. The sanctuary is located east of the port
of Galilee and is bounded by the Galilee Escape Road to the north
and Sand Hill Cove Road to the south. During the l950s, dredged
material from the Port of Galilee was deposited in parts of the
marsh, filling in a tidal channel and significantly altering the
natural tidal action.
During Hurricane Carol in 1954, coastal flooding in the area was
so severe that local residents were trapped, unable to evacuate
their homes. As a result, in 1956 the state built the Galilee Escape
Road, which greatly improved public safety in Galilee but caused
additional harm to the salt marsh by further restricting tidal flushing.
These changes transformed the marsh into a dense thicket of Phragmites
with very little habitat value for birds, fish, or shellfish.
In 1991, the R.I. Department of Environmental Management (DEM),
which manages the marsh as a wildlife refuge, began a project to
restore the ecological productivity of the marsh by reestablishing
tidal flushing. DEM's Division of Fish and Wildlife organized a
partnership of federal, state, and non-governmental agencies; developed
a restoration plan; oversaw construction; and monitored the recovery
of the salt marsh. The team regraded the marsh, cut new tidal channels,
and installed large culverts under the Galilee Escape Road to allow
the tide to return to the marsh. The culverts are outfitted with
self-regulating tide gates that allow normal tides in and out of
the marsh, but prevent extreme tides from flooding coastal homes.
|Tide gates at Galilee
Since the completion of construction in 1997, the ecology of the
marsh has begun to return. Fish and wildlife have responded to the
restoration in dramatic fashion, as finfish recolonized the tidal
creeks within days following opening of the tide gates. Waterfowl,
including the American
black duck, use the restored marsh extensively for nesting,
feeding, and resting during migration. In total, approximately 84
acres of salt marsh habitats and 14 acres of tidal creeks and ponds
were restored. Project partners included the U.S. Army Corps of
Engineers, DEM Mosquito Abatement, the University of Rhode Island,
R.I. Coastal Resources Management Council, R.I. Department of Transportation,
Ducks Unlimited, and U.S. Fish and Wildlife Service.
- Save The Bay's Web page on Salt Marsh Restoration
- Coastlines June 1997 - Setting
the Stage for Salt Marsh Restoration in Narragansett Bay
- Galilee Salt Marsh virtual tour - Discovery
of Rhode Island Coastal Environments
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Save The Bay. 2002. Restoration projects throughout the Narragansett
Bay watershed. (http://www.savebay.org/bayissues/restoreprojects.htm).
Save The Bay, Inc., People for Narragansett Bay. 2001. Save The
Bay Web site: What is Habitat Restoration? (http://www.savebay.org/).
Taylor M.H., G.J. Leach, L. DiMichele, W.M. Levitan, and W.F. Jacob.
1979. Lunar spawning cycle in the mummichog, Fundulus heteroclitus
(Pisces: Cyprinodontidae). Copeia 1979:291-297.
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This site was created through a partnership
Coastal Resources Management Council
Narragansett Bay Estuary Program
Save The Bay®