A tidal marsh is a type of marsh that is found along rivers, coasts and estuaries of which the flooding characteristics are determined by the tidal movement of the adjacent estuary, sea or ocean. Tidal wetlands experience many overlapping persistent cycles, including day-night temperature fluctuations, diurnal tides, semi-diurnal tides, spring-neap tides, seasonal vegetation growth and decay, decadal El Niño-Southern Oscillation climate variations, and centennial to millennial trends in sea level and climate. They are also impacted by transient disturbances such as hurricanes, floods, storms, and upland fires.
According to the salinity of the flooding water, tidal marshes are differentiated into freshwater, brackish and saline varieties. They may also be classified into coastal marshes and estuarine marshes on the basis of their landscape position. From landscape position one can infer a lot about the origin, controlling processes, age, disturbance regime, and future of a tidal marsh. Tidal freshwater marshes are further divided into deltaic and fringing types. Extensive research has been conducted on deltaic tidal freshwater marshes in Chesapeake Bay, which saw many form as a result of historic deforestation and intensive agriculture.
Internally, individual marshes of each salinity level are commonly zoned into lower marshes (also called intertidal marshes) and upper or high marshes, based on their elevation with respect to the sea level. In tidal freshwater marshes there can also be a middle marsh zone.
Coastal wetlands are found within coastal watersheds and encompass a variety of types including fresh and salt marshes, bottomland hardwood and mangrove swamps, and palustrine wetlands.  These areas provide vast benefits to the ecosystem. They serve as flood protection to upland areas by storing ground water. Additionally, shoreline erosion is impeded by the ability of wetland plants to counter wave impaction. Coastal wetlands act as intricate filtration systems for watersheds.  As water run-off travels from higher elevations to open water, the coastal wetland areas absorb and trap pollutants. These areas also provide habitat to many creatures and serve as rest-stops for migratory birds.
Island and Barrier Island
Tidal Marshes can contain island off their shore called barrier islands. These cigar shaped islands form parallel and close to the shoreline of a tidal marsh. The islands fully exposed during low tide look like a hill, and during a high tide being fully surrounded by water look like an island. Formation of barrier islands have been explained in many ways by history’s scientific minds, some mechanisms of barrier island formation are offshore bar theory, spit accretion theory, and formation can even be due to climate change. Contrary to what one might think the presence of saline resistant plants does not affect the erosion rates of tidal marsh islands, rather the contributing factor to erosion rates is the soil type of the island.
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