- Salt Marsh - Anadromous
Hydrologic Restoration | Invasive
Species Removal | Dredged Material Removal
| Restoration of Marshes Altered by Mosquito Ditches
Reestablishment of tidal hydrodynamics is a critical first step
in the restoration process. Tidal restriction due to dikes, levees,
and poorly designed water-control structures leads to a substantial
reduction in porewater salinity, lowering of the water table, and
a relative drop in marsh surface elevation (Roman et al. 1984, Rozsa
1988). All of these conditions favor the establishment of Phragmites.
In southern New England, Spartina marshes which have historically
been subjected to extensive diking and ditching have experienced
rapid and widespread Phragmites invasion.
|Re-designed culverts with self-regulating
tide gates at Galilee Salt marsh restoration site.
Courtesy: D. Yozzo, Barry Vittor & Associates
Hydrologic restoration of southern New England marshes began in
the late 1970s. Breaching of existing dikes, and modifications
to tide gates and other water control structures in order to recreate
historic tidal flushing regimes has resulted in the reestablishment
of native salt marsh vegetation at many restoration sites along
the southern New England coast, such as the Sachuest Salt Marsh. Re-introduction of tidal flooding
can result in a substantial decrease in Phragmites height
and vigor within one growing season. Vegetation change is most apparent
in lower intertidal areas and along creeks and ditches, where tidal
inundation is greatest, as seen with the Little Mussachuck Creek Marsh restoration. However, restoration of an entire marsh
is gradual, and may take decades following reestablishment of tidal
hydrodynamics (Sinicrope et al. 1990; Roman et al. 1984, 1995; Rozsa
In other areas, where the degree of tidal flooding is sufficient,
or where removal of water control structures or dikes is not feasible,
restoration may focus primarily on removal of Phragmites
and replanting with native intertidal vegetation.
Invasive Species Removal
|Phragmites invasion of upper intertidal marsh.
Courtesy: D. Yozzo, Barry Vittor & Associates
Ecologists are only now beginning to understand the ecological
consequences of Phragmites expansion in tidal marshes.
Accumulation of inorganic sediments and organic biomass associated
with the rapid growth of Phragmites increases marsh elevation
and decreases tidal flooding (Windham and Lathrop 1999, Rooth and
Stevenson 2000). Reduced tidal exchange limits production of fishery
species that use marsh surface and tidal creek habitats as a predation
refuge, forage site, and spawning area (Weinstein and Balleto 1999).
Benthic invertebrates may be impacted due to reduction in flooding
depth and duration and or litter quality (Able and Hagan 2000, Angradi
et al. 2001). Phragmites marshes are generally considered
to be low-quality foraging and nesting habitat for birds and wildlife;
however some species (e.g., red-winged blackbird) are known
to use Phragmites extensively as nesting habitat (Benoit
and Askins 1999). Restoration of intertidal wetlands through eradication
of Phragmites and revegetation with native, non-invasive
plant species should net an overall improvement in habitat quality
for fishery and wildlife species, and maintain marsh-open water
In addition to maintaining natural ecological processes and trophic
dynamics, removal of Phragmites should contribute to the
maintenance of biodiversity throughout Rhode Island's coastal zone.
Although salt marshes are generally species-poor, elimination of
the vast, monotypic stands of Phragmites will provide a
modest increase in regional plant species diversity, as seen at Allen Harbor. Maintenance
of characteristic invertebrate, fish, and wildlife communities will
also contribute to improvement of and maintenance of biodiversity
within Rhode Island's coastal habitats.
Most salt marsh restoration projects completed to date in Rhode
Island have relied on the elimination of Phragmites through
an increase in flooding with saline tidewaters. The gradual accumulation
of sulfides (an important component of seawater) in flooded marsh
soils inhibits the ability of Phragmites to take up nutrients.
Eventually, the Phragmites stands lose vigor and height,
and die back (Chambers 1997). This process can take up to several
years. It is also possible to eradicate Phragmites using
herbicides, burning, and manual harvesting. These techniques have
been used extensively in other area (e.g., New Jersey),
where restoration of tidal hydrology is not possible, or in combination
with hydrologic restoration techniques in order to accelerate the
process of ecosystem restoration. These techniques
are expensive and difficult to implement, and in the case of herbicide
application, multiple applications over several growing seasons
may be necessary to maintain a Phragmites-free plant community.
Harvesting is labor intensive, and the cuttings must be disposed
of in such a way as to prevent spreading of seeds and rhizomes
to other locations. Burning of Phragmites has been conducted
in a few instances, but is not advised in marshes adjacent to residential
Dredged Material Removal
Many salt marshes in Rhode Island have been impacted by the deposition
of fill, either dredged mud and sand derived from historic navigation
projects, or various types of structural fill derived from various
industrial activities. This was the case in Allin's Cove and Common Fence Point. These fill activities have persisted for
centuries. Originally this was considered a beneficial practice,
as "marsh wastelands" were converted to usable, "fast-land."
Only within the last few decades have coastal resource managers
been able to realize the benefits and functions of salt marshes
and enact legislation to protect them from land reclamation activities.
To restore marshes which have been impacted by fill, the historic
intertidal elevations must be reestablished with earth-moving equipment.
Elevation criteria to be used in recontouring projects can be obtained
by surveying nearby reference marshes located in similar geomorphic
and landscape settings. This is critical to achieving the proper
tidal flooding characteristics for the desired vegetation community
type (e.g., Spartina alterniflora low marsh).
Following the removal of dredged material or upland fill, new soils
can be placed on the site and graded to the proper elevations. Soil
organic matter content and grain size should match that of reference
marshes. In cases where organic matter content of new soil is low,
restoration practitioners can add organic matter (usually terrestrial
vegetation mulch) to enhance soil quality. However, this additional
step can be expensive and time-consuming. Fortunately, Spartina
spp. is well-adapted to sandy, low-nutrient soils, and is relatively
easy to propagate upon properly prepared restoration sites (Broome
et al. 1974; Woodhouse et al. 1974; Seneca et al. 1975, 1976; Barko
et al. 1977; Garbisch 1977; Garbisch et al. 1975).
Restoration of Marshes Altered by
Many salt marshes in Rhode Island have been impacted by the excavation
of mosquito ditches. These straight, narrow channels were designed
to drain the upper reaches of salt marshes in the belief that this
would eliminate breeding habitat for salt marsh mosquitoes, thereby
reducing the prevalence of mosquitoes and mosquito borne diseases.
Coastal managers now know that this approach was poorly conceived;
draining the high marshes eliminated vast amount of habitat for
marsh resident fishes which prey upon mosquito larvae (mostly killifish
Open-water marsh management (OWMM) is a habitat restoration and
mosquito control technique which is specifically intended to recreate
the natural flow patterns in ditched marshes (Barry and Fish 1995).
Under an OWMM program, existing drainage ditches are abandoned or
plugged, and natural tidal creeks are reconnected to newly excavated
ponds in the upper intertidal marsh. This allows fish which prey
on mosquito larvae to reestablish populations in areas which were
previously inaccessible to them (e.g., pools and creeks
in high marsh areas). OWMM has been successfully implemented in
many ditched marshes throughout the Northeast, notably in Connecticut.
In Rhode Island, OWMM techniques have been implemented in several
locations, notably at Mosquito Beach on Block Island, and as a component
of the restoration plan at Sachuest Point, in Middletown, Rhode Island. Department of Environmental Management (DEM)
has allocated funding to monitor the success of OWMM in reducing
mosquito populations at these sites (RIPHP 1998).
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Able, K.W., and S.M. Hagan. 2000. Effects of common reed (Phragmites
australis) invasion on marsh surface macrofauna: Response of
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Angradi, T.R., S.M. Hagan, and K.W. Able. 2001. Vegetation type
and the intertidal macroinvertebrate fauna of a brackish marsh:
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R.N. Gordon. 1977. Establishment and growth of selected freshwater
and coastal marsh plants in relation to characteristics of dredged
sediments. Technical Report D-77-2, U.S. Army Engineer Waterways
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australis on the distribution of birds in Connecticut tidal
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Broome, S.W., Woodhouse, W.W, Jr., and Seneca, E.D. 1974. Propagation
of smooth cordgrass, Spartina alterniflora, from seed in
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Chambers, R.M. 1997. Porewater chemistry of Phragmites
and Spartina in a Connecticut tidal marsh. Wetlands
Garbisch, E.W., Jr. 1977. Recent and planned marsh establishment
work throughout the contiguous United States: A survey and basic
guidelines. Contract Report D-77-3, U.S. Army Engineer Waterways
Experiment Station, Vicksburg, Mississippi.
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of the Fourth Wetlands Conference: Wetlands Creation and Restoration, November 15, 1986. Report No. 34, Connecticut Institute of Water Resources. University of Connecticut, Storrs, Connecticut.
Rooth, J.E., and J.C. Stevenson. 2000. Sediment deposition patterns
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Restoration of an impounded salt marsh in New England. Estuaries
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marshes. Environmental Management 19:559-566.
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Windham, L. and R. G. Lathrop. 1999. Effects of Phragmites
australis (Common Reed) invasion on aboveground biomass and
soil properties in brackish tidal marsh of the Mullica River, New
Jersey. Estuaries 22:927-935.
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of Spartina alterniflora for substrate stabilization and
salt marsh development. Technical Memorandum 46, U.S. Army Corps
of Engineers, Coastal Engineering Research Center, Fort Belvoir,
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