Thompson Island Salt Marsh Restoration Project

June 23, 2007, BOSTON, MA

After 3 years of study and environmental permitting, Thompson Island Outward Bound Education Center completed construction on a small salt marsh/brackish pond on the easterly shore of the island. Check out the construction photos of this project.

The construction was completed by SumCo Eco-Contracting of Hamilton, Massachusetts. The salt marsh restoration project was funded by grants from the National Fish and Wildlife Foundation (NFWF), the Commonwealth of Massachusetts, Office of Environmental Affairs, Coastal Zone Management (CZM), Wetlands Restoration Program and the Corporate Wetlands Restoration Partnership. The Five Star NOAA Partnership Grant from the NFWF include the following partners: Thompson Island Education Center, MA CZM, Corporate Wetlands Restoration Partnership (with funding from Capaccio Environmental Engineering and the Gillette Company), MA Department of Conservation and Recreation, The National Park Service and the Island Alliance.

U.S. Army Corp of Engineers Permit: NAE-2006-587.

The Salt Marsh Restoration project is located on the easterly shore of Thompson Island, one of the Boston Harbor islands. Thompson Island is approximately 240 acres in size and contains a diverse assemblage of woodlands, meadows, beaches, and salt marshes. The island was initially developed in the 1600s and has since hosted farms, schools, hospitals, shops, and industrial operations. The island is owned and operated by Thompson Island Outward Bound Education Center.

Of the island’s two salt marshes, one is in pristine condition. The other salt marsh, however, is degraded and is the focus of this restoration effort. USGS topographic maps from 1903 and 1946 depict the area as salt marsh. Currently the degraded marsh is impounded by debris and rubble clogging the outlet. At some point a structure was built across the tidal channel, presumably to power a mill and/or to create a fresh or brackish pond. The remnants of the structure – bricks, concrete, rebar, wood timbers, etc. – remain in the channel. As a result, the former salt marsh is cut off from tidal flow. Preliminary hydrologic assessment work performed by WRP in September 2003 shows essentially no tidal influence within the impoundment. Freshwater drains from the pond, but no seawater enters. Lack of tidal flushing has resulted in a stagnant waterbody. The invasive plant common reed, Phragmites australis, has taken advantage of the fresher conditions and colonized the edges of the marsh. Study of recent aerial photos indicates that common reed is increasing and spreading toward the center of the marsh. In the summer, the pond experiences severe algal blooms and is covered by a thick green mat. Because of poor water quality and lack of physical access, the site is under utilized by marine fish species.

To address these problems, Thompson Island Outward Bound proposes to restore tidal flushing to the former salt marsh. This will involve first removing the material clogging the tidal channel. The channel will be dredged to the depth of its natural bottom. Freshwater will drain more effectively from the marsh and it will be flooded with seawater during most high tides.

The improved tidal flow will allow freshwater drainage of the marsh and seawater to flood the marsh during most high tides. Stands of monotypic common reed are expected to die back and be replaced by native salt marsh grasses, such as Spartina alterniflora and Spartina patens. Areas that are currently inundated with freshwater, will be exposed at low tide, providing exceptional feeding habitat for late summer migrating shorebirds. The restored hydrologic connection to Boston Harbor will allow fish to pass into the marsh, providing important nursery and feeding habitat for species such as striped bass and winter flounder.

The partnerships that helped to bring this project to completion... Thank you to:

• Thompson Island Outward Bound Education Center
• National Fish and Wildlife Foundation

• NOAA
• Commonwealth of Massachusetts, Executive Office of Environmental Affairs, Coastal Zone Management, Massachusetts Wetlands Restoration Program
• Corporate Wetlands Restoration Partnership and grants from Capaccio Environmental Engineering and the Gillette Company
• Massachusetts Audubon
• Northern Ecological Associates, Inc.
• University of Massachusetts Boston, Department of Archeology
• Boston Harbor Islands National Park Area and the Island Alliance
• Massachusetts Department of Conservation and Recreation
• Green Corp

Learn about Salt Marsh Restoration Curriculum for your school!