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Design Considerations

Seagrass - Salt Marsh - Anadromous Fish Habitat

Salt Marsh

A number of geomorphic, hydrologic, and biotic factors should be considered during the design phase of a salt marsh restoration project. Consideration of nearby seed sources (wind or waterborne) and adequate excavation depths (to eliminate regrowth from buried rhizomes and runners) are critical factors to consider in the elimination of invasive plant species. Care must be taken to ensure that replacement soils do not contain seed banks or rhizome material. Revegetation with desired intertidal vegetation (e.g., Spartina alterniflora) should follow established techniques for propagation and planting, such as those developed by the U.S. Army Corps of Engineer's (USACE) Dredged Material Research Program (DMRP; Broome et al. 1974; Woodhouse et al. 1974; Seneca et al. 1975, 1976; Barko et al. 1977; Garbisch 1977; Garbisch et al. 1975). Local or regional sources of donor plantings or seedlings are preferable for use in revegetation efforts and are available from commercial nurseries in the northeast (Broome et al 1974, Seneca et al. 1985).

Tidal channel morphology and the natural dendritic patterns of creeks and channels are important considerations in designing a salt marsh. Tidal creeks and ponds provide "edge" habitat, which is important in maintaining adequate drainage, facilitating nutrient exchange between groundwater and surface waters. Tidal creeks are the pathways for predatory fish to gain access to abundant forage resources within the marsh. Depositional edges of tidal creeks provide access points for smaller finfish and crustaceans, which move on and off the flooded marsh surface to forage and avoid predators (Minello et al. 1994). Channel size and sinuosity can be matched to that observed in reference wetlands. A GIS application can be a powerful tool in identifying appropriate reference areas, and in determining the appropriate amount of edge to be incorporated into a restoration project design. The Salt Marsh Site Selection Tool in development for Rhode Island can be used to identify reference areas.

Potential Obstacles to Restoration | Equipment Sources and Contacts

Potential Obstacles to Restoration
Phragmites is notoriously persistent and resistant to many eradication techniques. Tidal flushing, mowing, prescribed burning, and application of chemical herbicides have all been attempted at various locations in the northeast, often with less than desirable results. Manual cutting, although labor intensive, has been effective in removing Phragmites in conjunction with herbicide application. The herbicide Rodeo, in combination with an organic surfactant has been used successfully to eradicate Phragmites in southern New Jersey. In many cases, burning invigorates existing stands by removing standing dead biomass. Burning in conjunction with herbicide applications appears to be more successful than prescribed burns alone in controlling Phragmites.

Often the most successful attempts involve multiple control strategies, such as repeated harvesting, with burning to remove accumulated litter. Chemical control typically requires multiple applications over several growing seasons and careful monitoring in order to identify and control reinvasion.

Typha, a freshwater invasive species.
Typha, a freshwater invasive species.
Courtesy: U.S. Army Corps of Engineers

Sometimes, the duration of tidal flooding necessary for Phragmites control can also result in elimination of desirable salt marsh vegetation. For example, in a restored marsh in Stonington, CT, Phragmites coverage increased following reintroduction of tidal flooding (Sinicrope et al. 1990). This was attributed to the elimination of a freshwater invasive species, Typha, which reduced competition, allowing Phragmites to expand aggressively. Ideally, reestablishment of tidal hydrodynamics should be gradual and controlled, in order to avoid subsidence and permanent flooding.

Many intertidal wetlands in the northeast contain contaminated sediments. Toxic constituents of note include heavy metals, Polychlorinated Biphenyls (PCB), Polycyclic Aromatic Hydrocarbons (PAH), and dioxin. Excavation and removal or disposal of these sediments in an environmentally acceptable and economically feasible manner requires careful planning and coordination. Disposal of contaminated sediments can be very expensive, and suitable land or water-based repositories are scarce in the Northeast. Large-scale sediment decontamination technologies are currently unavailable or so expensive as to be cost-prohibitive. Clean substrates are needed to cap contaminated areas. Sources of clean soil with suitable grain size and organic matter content need to be identified, and an economically feasible means of obtaining such material would need to be determined prior to project implementation.

Some animals are known to be highly destructive in their grazing to recently established salt marsh plants. Snow geese, which graze on the soft shoots and rhizomes of smooth cordgrass (Spartina alterniflora), can decimate large areas of newly established marsh within days. On a much smaller spatial scale, muskrat burrowing and feeding activity can also damage newly restored salt marshes. Fences, and grids of narrow stakes, which prevent birds from landing in the vicinity of a newly planted or restored area, are often used to prevent snow geese and other animals from disturbing a newly restored site.

Restoration practitioners must be sure that a project does not conflict with existing land uses such as industrial or commercial facilities in the area, parks and recreational facilities, or existing residential developments. Ideally, these issues are to be resolved in the reconnaissance and planning phase, long before project construction takes place. Hydrologic restoration projects are particularly subject to landowner concerns about increased flooding of adjacent coastal properties (Steinke 1988).

Equipment Sources and Contacts
There are a variety of sources and professional contacts to assist restoration practitioners in gathering information and forming partnerships. Salt marsh plantings can be obtained from local and regional nurseries that specialize in products for wetland restoration and creation projects. Several comprehensive literature reviews and guidebooks are available from various agencies and other organizations involved in salt marsh restoration.

Local experts can be accessed at federal and state environmental resource agencies, non-profit organizations, and at academic research institutions. Many of these include the National Marine Fisheries Service Restoration Center, Narragansett Bay National Estuarine Research Reserve, DEM Narragansett Bay Estuary Program, Coastal Resources Management Council, Save The Bay, and the University of Rhode Island. Contacts for these groups and others are available from this Web site.

Many companies specialize in the manufacture and sale of environmental monitoring equipment used in conducting restoration and data collection in salt marshes. Supplies and equipment includes marsh plants, seine nets, tide gauges, sediment sampling tools, and water quality monitoring supplies.

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References

Barko, J.W., R.M. Smart, C.R. Lee, M.C. Landin, T.C. Sturgis, and 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 Experiment Station, Vicksburg, Mississippi.

Broome, S.W., E.D. Seneca, and W.W. Woodhouse, Jr. 1988. Tidal salt marsh restoration. Aquatic Botany 32:1-22.

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.

Garbisch, E.W., Jr., P.B. Woller, and R.J. McCallum. 1975. Salt marsh establishment and development. Technical Memorandum 52, U.S. Army Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, Virginia.

Minello, T.J., R.J. Zimmerman and R. Medina. 1994. The importance of edge for natant macrofauna in a created salt marsh. Wetlands 14:184-198.

Seneca, E.D., W.W. Woodhouse, Jr., and S.W. Broome. 1975. Salt-water marsh creation. pp. 427-437 in: L.E. Cronin, (Ed.), Estuarine Research Volume II: Geology and Engineering, Academic Press, New York, New York.

Seneca, E.D., S.W. Broome, W.W. Woodhouse, Jr., L.M. Cammen, and J.T. Lyon, III. 1976. Establishing Spartina alterniflora marsh in North Carolina. Environmental Conservation 3:185-188.

Steinke, T.J. 1988. Restoration of degraded salt marshes in Pine Creek, Fairfield, Connecticut, pp. 19-33. In: M.W. Lefor and W.C. Kennard, (eds.), Proceedings 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.

Woodhouse, W.W., Jr., E.D. Seneca, and S.W. Broome. 1974. Propagation 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, Virginia.

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Project Partner web pages - RIHRT, CRMC, NBEP, STB

This site was created through a partnership of the:

Coastal Resources Management Council
Narragansett Bay Estuary Program
Save The Bay®