Marshes are transitional areas between land and water. They occur along the intertidal shores of estuaries and sounds. They are subject to rapid changes in salinity, temperature and water depth. Because they have the influence of both sea water and freshwater, the water in marshes is said to be brackish. The main characteristic of a marsh is the tidal influence. Tides control the salinity of the water and soil, the degree of water logging of the soil and it carries sediment into the marsh.
     Salinity is important because certain plants and animals can not survive in water or soil that has a high salinity. Because of this, species diversity is low. The plants that live in a marsh have adaptations that make it possible to live in this changing environment. Salt marsh cordgrass and marsh elder are common plants found in a salt marsh. Marshes serve as a breeding ground for many species of fish and as a habitat for birds, reptiles and amphibians.
     Physical features that you may observe in a salt marsh include tidal creeks and salt pans. Tidal creeks serve as a passageway for water and sediment between the marsh and the adjacent body of water. Salt pans are bare, exposed or water-filled depressions in the marsh. They form because evaporation concentrates salts in the soil and kills the rooted vegetation.
     Salt marshes are most prevalent in the United States along the Eastern Coast from Maine to Florida and in the Gulf of Mexico in Louisiana and Texas.