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Appendix B. Profiles of Some Tidal Wetland Restoration Projects on the Atlantic and Pacific Coasts of the United States
- University of Massachusetts Press
- Chapter
- Additional Information
421 Project types (re-establishment, rehabilitation , and creation) are noted. Some projects involve more than one type of action, such as restoration of a diked tidally restricted marsh that involves dike removal ( re-establishment) and restoration of tidal flow (rehabilitation). Also one of the case studies was restoration brought about by natural forces—storm breaching of dikes and a decision not to repair them. Results are based on published reports and reflect conditions for the reported period; for current findings, contact authors. Case Study 1 Project type: Re-establishment andRehabilitation Location: Hatches Harbor, Cape Cod,Massachusetts Initial condition: 200-acre (80.9 ha) former salt marsh; diked for mosquito control in 1930 with 2-foot (0.6 m) culvert and flap valve installed allowing outflow of water from restricted marsh. In 1987, the flap valve was removed providing limited tidal exchange. Restoration objective: To restore 90 acres (36.4 ha) of salt marsh by increasing tidal exchange; also to provide additional flood storage and protection for adjacent airport. Action taken: In 1997 installed four 7-foot by 3-foot (2.1 m x 0.9 m) box culverts with adjustable tide gates, progressively increased openings from 1999 to 2005 when maximum allowable tidal exchange was achieved. Monitoring commenced in 1997 including pre-restoration site assessment (vegetation, pore-water salinity, nekton, sedimentation, elevation, and fecal coliform; Farris et al. 1998). Results: Tidal regime now equals 57% of neighboring unrestricted marsh; landward retreat of common reed, which is being replaced by smooth cordgrass and salt hay grass depending on elevation; landward expansion of halophytic vegetation and dieback of freshwater species; significant increase in abundance of smooth cordgrass at expense of both common reed and salt hay grass; increased pore-water salinities from fresh to >35 ppt in some places and from fresh to low salinities in uppermost marsh; and increased use by nekton for feeding, nursery grounds, and spawning (Portnoy et al. 2003; Smith et al. 2008, 2009). Case Study 2 Project type: Rehabilitation Location: Potter Pond, Prudence Island, Rhode Island Appendix B Profiles of Some Tidal Wetland Restoration Projects on the Atlantic and Pacific Coasts of the United States 422 Appendix B Initial condition: 5-acre (2.04 ha) tidally restricted estuarine pond with narrow band of salt marsh and 0.6 acre (0.24 ha) back marsh of common reed; tidally restricted since at least the 1930s by two roads with culverts that by 2002 were crushed, providing only a 1.6-inch (4 cm) tide range; pond had oxygen deficits and was often covered with macroalgae. Restoration objective: To improve tidal exchange and restore salt marsh ecology; possibly to eliminate nuisance macroalgae. Action taken: In 2003, replaced two 15-inch (38 cm) diameter culverts with a 50-foot (15.25 m) long, 4.9 foot x 3.9 foot (1.5 m x 1.2 m) aluminum arch culvert between the estuary and the pond, and the culvert to the back marsh with a 2-foot (61 cm) diameter culvert. Results: Tidal range increased from 1.6 inches (4 cm) to 3.9 feet (120 cm), which converted pond to mostly intertidal mudflat with 93% reduction in open water at low tide; mudflat being colonized by smooth cordgrass, which increased its area by 67% and glasswort, which by 2004 occupied 0.7 acres (0.30 ha); 69% decline in common reed cover and the height of remaining reeds was reduced by 2.5 feet (76 cm); salinity of back marsh increased from 1.5 ppt to 26.8 ppt; bird use increased due to creating exposed mudflats, and nekton density decreased largely due to conversion of open water habitat to intertidal habitat (Raposa 2008). Case Study 3 Project type: Re-establishment andRehabilitation Location: Galilee Salt Marsh, Point Judith, Rhode Island Initial condition: Phragmites-dominated wetland where tidal flow was eliminated by road, and some portions of marsh filled with dredged spoil. Restoration objective: Restore tidal flow and salt marsh community, while protecting adjacent low-lying development fromflooding. Action taken: Reconstructed channel, installed two box culverts with self-regulating tide gates, and removed dredge material from the west side of the marsh. Results: Tidal flow restored; salt marsh vegetation recolonizing site; common reed reduced in stature and density; and improved aquatic productivity to about 100 acres (40.5 ha) of degraded marsh; won Coastal America Partnership award in 1999. See www.nae.usace.army.mil/ projects/ri/GalileeSaltMarsh/InfoSheet.pdf and www.nae.usace.army.mil/projects...