Barrier islands are among the most beautiful and precious features of our coastline. A barrier island is defined as a long, offshore, dune-covered deposit of sand lying roughly parallel to and separated from the mainland by a shallow sound (lagoon) and/or salt marsh; barrier islands are separated from each other by tidal inlets. Our present barrier islands have evolved over thousands of years and are a wonderful example of a delicate but balanced system in a constantly changing environment.
Intertidal mud flats are located along the edges of the salt marsh. This harsh habitat is covered by water at flood (high) tide and exposed to the scorching sun at ebb (low) tide. It consists of a soggy substrate (soil) made up of clay and silt that is deposited during slack tide. Slack tide is the brief period between flood tide and ebb tide during which the water is not flowing in or out but is still. Only the upper layers of this muddy substrate contain oxygen. The deeper layers contain decaying organic matter that gives off a hydrogen sulfide gas that causes a rotten egg smell.
Georgia’s coastal marshlands encompass approximately 378,000 acres in a four to six mile band behind the barrier islands. Thriving in the waters of the estuaries, these marshes have been identified as one of the most extensive and productive marshland systems in the United States. There are nearly 400,000 acres of coastal marshlands in Georgia which represent a considerable portion of all remaining marshlands along the entire eastern coast of the United States.
The sound is the deeper portion of the estuary located between the mud flats and marshes of the mainland and barrier island. The temperature and salinity of the sound varies with the amount of fresh water entering from rivers or rainfall and from mixing with salt water during incoming tides. An increase in rainfall will quickly decrease the salinity and most times the temperature of the water. The substrate or soil type at the bottom of the sound is a direct result of the deposition of mud and sand from the freshwater streams of the drainage basin that empties into the sound. The grain and particle size of this bottom substrate determine the type, distribution and abundance of the organisms that live there.