salt marsh

A maritime habitat characterized by grasses, sedges, and other plants that have adapted to continual, periodic flooding. Salt marshes are found primarily throughout the temperate and subarctic regions.

The tide is the dominating characteristic of a salt marsh. The salinity of the tide defines the plants and animals that can survive in the marsh area. The vertical range of the tide determines flooding depths and thus the height of the vegetation, and the tidal cycle controls how often and how long vegetation is submerged. Two areas are delineated by the tide: the low marsh and the high marsh. The low marsh generally floods and drains twice daily with the rise and fall of the tide; the high marsh, which is at a slightly higher elevation, floods less frequently. See also Mangrove.

Salt marshes usually are developed on a sinking coastline, originating as mud flats in the shallow water of sheltered bays, lagoons, and estuaries, or behind sandbars. They are formed where salinity is high, ranging from 20 to 30 parts per thousand of sodium chloride. Proceeding up the estuary, there is a transitional zone where salinity ranges from 20 to less than 5 ppt. In the upper estuary, where river input dominates, the water has only a trace of salt. This varying salinity produces changes in the marsh—in the kinds of species and also in their number. Typically, the fewest species are found in the salt marsh and the greatest number in the fresh-water tidal marsh. See also Estuarine oceanography.

The salt marsh is one of the most productive ecosystems in nature. In addition to the solar energy that drives the photosynthetic process of higher rooted plants and the algae growing on the surface muds, tidal energy repeatedly spreads nutrient-enriched waters over the marsh surface. Some of this enormous supply of live plant material may be consumed by marsh animals, but the most significant values are realized when the vegetation dies and is decomposed by microorganisms to form detritus. Dissolved organic materials are released, providing an essential energy source for bacteria that mediate wetland biogeochemical cycles (carbon, nitrogen, and sulfur cycles). See also Biogeochemistry; Biological productivity.

The salt marsh serves as a sediment sink, a nursery habitat for fishes and crustaceans, a feeding and nesting site for waterfowl and shorebirds, a habitat for numerous unique plants and animals, a nutrient source, a reservoir for storm water, an erosion control mechanism, and a site for esthetic pleasures. Appreciation for the importance of salt marshes has led to federal and state legislation aimed at their protection.

Siltation in estuaries or sheltered bays may create mud flats, many of which become vegetated. It is this vegetation that traps silt particles and, to some extent, consolidates them. As the marsh develops, halophytes, such as marsh samphire and sea aster in Britain, pave the way for less hardy specimens. The marsh becomes part of the coast land.

The salt marshes of tidal estuaries have a very high biological productivity, but in economic terms they are valued as grazing land, potentially reclaimable land for industry, or for waste disposal. In the tropics, it is mangrove swamps which are created by a similar mechanism.

In geography, a marsh, or morass, is a type of wetland which is subject to frequent or continuous flood.^[1] Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, and other herbaceous plants. Woody plants will be low-growing shrubs. A marsh is different from a swamp, which has a greater proportion of open water surface and may be deeper than a marsh. In North America, the term "swamp" is used for wetland dominated by trees rather than grasses and low herbs.

The water of a marsh can be fresh (freshwater marsh), brackish (brackish marsh), or saline (salt marsh).

Coastal marshes may be associated with estuaries, and are also along waterways between coastal barrier islands and the inner coast. The estuarine marsh, or tidal marsh, is often based on soils consisting of sandy bottoms or bay muds. An example is the Tantramar Marsh of eastern Canada.

Marshes are critically important wildlife habitat, often serving as breeding grounds for a wide variety of animal life, particularly including ducks and geese.

Constructed wetlands featuring surface-flow design are usually in the form of a marsh.

Decomposition of plant materials below water often produces marsh gas, which may begin to burn by self-ignition making mysterious lights known locally as Will o' the wisps, Jack-o'-lanterns, or sprites.

See also

Wikimedia Commons has media related to: Marsh

• Aquatic plant
• Bayou
• Biodiversity Action Plan
• Bog
• Fen
• Slough

Reference line notes

1. ^ U.S. Environmental Protection Agency: Characterization of marshes

• Marshes of the Lowcountry (South Carolina) -- Beaufort County Library
• General Information of Ibera Marshes (in English and Spanish)

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