Characteristic Mid-Atlantic Wetland Type - Tidal Wetlands

Tidal wetland at Assateague. Credit: Virginia Dept. of Env'l Quality

Tidal wetlands occur at the land-ocean margin and their hydrology is driven by tides. They can be divided into three segments:

• low marsh, typically submerged at high tide and at the lowest elevation;
• high marsh, at the second-highest elevation and flooded during spring tides but sometimes free from tidal inundation for days at a time; and
• upper border, at the highest elevation and inundated only infrequently during the highest spring tides

The dominant vegetation types in Atlantic coastal wetlands are grasses, such as cordgrass, and wildlife include minnows, mussels, crabs, and snails. Tidal wetlands vary in the salinity gradient they typically experience. Upstream freshwater flows may make a tidal wetland more fresh, whereas limited freshwater flows and greater tidal energy may make them more saline. Characteristic plants and animals vary with the salinity. Salty marshes support particular plant and animal communities adapted to high salinity, whereas brackish (a mix of salt and freshwater) and freshwater marshes typically support a wider range of species.