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Restoration Methods

Seagrass - Salt Marsh - Anadromous Fish Habitat

Salt Marsh

Hydrologic Restoration | Invasive Species Removal | Dredged Material Removal | Restoration of Marshes Altered by Mosquito Ditches

Hydrologic Restoration
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.
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 1988).

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.
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 trophic linkages.

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 areas.

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 Mosquito Ditches
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 [Fundulus species]).

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 fishes and decapod crustaceans. Estuaries 23:633-646.

Angradi, T.R., S.M. Hagan, and K.W. Able. 2001. Vegetation type and the intertidal macroinvertebrate fauna of a brackish marsh: Phragmites vs. Spartina. Wetlands 21:75-92.

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.

Barry, D.W., and G.D. Fish. 1995. Biting fly management. Pesticide applicator training manual: Category 7E. University of Maine Cooperative Extension.

Benoit, L.K., and R.A. Askins. 1999. Impact of the spread of Phragmites australis on the distribution of birds in Connecticut tidal marshes. Wetlands 19:194-208.

Broome, S.W., Woodhouse, W.W, Jr., and Seneca, E.D. 1974. Propagation of smooth cordgrass, Spartina alterniflora, from seed in North Carolina. Chesapeake Science 15, 214-21.

Chambers, R.M. 1997. Porewater chemistry of Phragmites and Spartina in a Connecticut tidal marsh. Wetlands 17:360-367.

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.

Rhode Island Public Health Partnership (RIPHP). 1998. Annual Report Web page (http://www.public-health.partner.uri.edu/annual_report/php98b.html). Providence, Rhode Island.

Roman, C.T., W.A. Niering, and R.S. Warren. 1984. Salt marsh vegetation change in response to tidal restriction. Environmental Management 8:141-150.

Rozsa, R. 1988. An overview of wetland restoration projects in Connecticut, pp. 1-11. 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.

Rooth, J.E., and J.C. Stevenson. 2000. Sediment deposition patterns in Phragmites australis communities: Implications for coastal areas threatened by rising sea-level. Wetlands Ecology and Management 8:173-183.

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.

Sinicrope, T.L, P.G. Hine, R.S. Warren, and W.A. Niering. 1990. Restoration of an impounded salt marsh in New England. Estuaries 13:25-30.

Roman, C.T., R.W. Garvine, and J.W. Portnoy. 1995. Hydrologic modeling as a predictive basis for ecological restoration of salt marshes. Environmental Management 19:559-566.

Weinstein, M.P., J.H. Balletto, J.M. Teal, and D.F. Ludwig. 1997. Success criteria and adaptive management for a large-scale wetland restoration project. Wetlands Ecology and Management 4:111-127.

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.

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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