Salt Marsh Restoration
Salt marshes are coastal wetlands that form transition zones between land and sea. They provide valuable habitat for wildlife, serve as nurseries for fish and shellfish, store floodwaters, and protect our shorelines against damage from storm surges.
Salt marshes act as natural purifiers by filtering pollutants and sediment and by absorbing excess nutrients from streams, rivers, and surface runoff before they can reach coastal waters and drinking water supplies.
Salt marshes are valuable for climate change mitigation because they remove carbon dioxide from the atmosphere and convert it into salt marsh vegetation. Decaying plant matter is stored underground in salt marsh peat, sediments and plant matter that is slow to decay. This carbon removed by coastal wetlands is referred to as blue carbon.
Collectively, these benefits are known as ecosystem services that benefit both humans and plants and animals. The many ecosystem services salt marshes provide makes them critical to the health of our coastal environment and coastal communities.
Subjected to daily tides, the salt marsh environment is constantly changing. Incoming freshwater from rivers, streams and groundwater mixes with tidal saltwater resulting in frequent and rapid changes in salinity, temperature and water depth within the salt marsh system. Salt marshes are characterized by plants and animals that tolerate changes in water temperature, depth, and salinity (ranging from 0-35 parts per thousand, or ppt).
Cape Cod salt marshes provide nesting, feeding and breeding habitat for a variety of animals. Among these are the rare and protected northern harrier, least tern, king rail, river herring, and the Massachusetts-listed diamondback terrapin.
You can find more history on the Cape’s salt marshes in the booklet, Our Cape Cod Salt Marshes by Dorothy Sterling.
What is the status of salt marshes?
Since colonial times, a significant portion of our nation’s salt marshes have been degraded or altered by agriculture, mosquito-ditching, channeling, urban development and other legacies of human activities. On Cape Cod, 36 percent of our historical salt marshes have been lost or severely degraded.
Roads and railroad beds bisect and damage marshes by restricting the tidal flow that nourishes them. Often the culverts and pipes beneath such roads and railroad beds are too small for natural tidal flow to reach the salt marsh. When tidal flow to salt marshes is restricted, these once-saline environments change to a brackish or freshwater condition in which native salt marsh vegetation suffers. Typically, these brackish marshes become colonized by the invasive common reed (Phragmites australis) which forms dense stands 12 feet or higher. As invasive species take over, a major shift in wildlife occurs, and formerly diverse communities of salt marsh inhabitants are replaced by fewer species.
Rising sea level threatens salt marshes with erosion and permanent flooding (inundation). While salt marshes may be able to adapt by migrating landward to higher elevations, when shorelines are hardened with rock walls, roads and development, salt marshes get squeezed out and cannot migrate. Protecting floodplains and uplands adjacent to salt marshes and restoring natural tidal flow that will allow for salt marsh growth is critical for ensuring that our salt marshes continue to survive and provide valuable ecosystem services.
In 2015, APCC produced a report entitled “Inventory of Cape Cod Salt Marshes with the Best Migration Potential.” This report examines the salt marshes damaged by restricted tidal flow and evaluates their potential to migrate inland if they are restored. The report prioritizes potential salt marsh restoration sites according to their potential to migrate inland as sea level rises. The report is intended to serve as a resource to communities, land trusts, and restoration managers and to help prioritize salt marsh restoration projects for climate change adaptation.
Also in 2015, APCC created the Restoration Coordination Center (RCC) to help communities plan and implement ecological restoration projects. APCC’s experience in salt marsh restoration, beginning with the Stony Brook salt marsh and fish passage restoration project in Brewster, along with others, led to the realization that there is a Cape-wide need for central coordination of restoration projects. The RCC was formed to address this need.