Salt marshes are coastal wetlands that form transition zones between land and sea. They provide habitat for wildlife, serve as nurseries for fish and shellfish, store floodwaters, and protect our shorelines against storm surge damage. Salt marshes also 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.
Subjected to the daily rise and fall of the sea, 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 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.
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% of our historical salt marshes have been lost or severely degraded.
Roads and railroad tracks bisect and damage marshes by restricting the tidal flow that nourishes them. When tidal flow is restricted, these once-saline environments change to a brackish or freshwater condition in which native salt marsh vegetation suffers. Typically, these 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.