Coastal Wetlands Salt Marshes

COASTAL SALT MARSH

Coastal salt marsh, also termed tidal salt marsh, is the dominant, mostly herbaceous vegetation of seacoast mudflats, especially outside the tropics and subtropics, including around estuaries of all sizes, coastal plain, and deltas, and characterizing vegetation along huge bays, inlets, and fjords in subpolar and polar zones. For just the United States, salt marsh extends,interrupted only by beaches, from New Jersey to northern Florida along the Atlantic Ocean, rimming the Gulf of Mexico, and at scattered, nonrocky stretches from Washington to San Diego. These are incredibly productive biological systems, and are major feeding and nesting grounds of birds. In tropical and subtropical latitudes, coastal salt marsh is instead mangal, i.e., mangrove vegetation.
Likemangal, salt marsh is populated by halophytes, plants that can live under saline conditions. In the lowest portion of a typical marsh (lower marsh), especially one that is open to the sea, plants generally are flooded twice each day at high tide. These areas require plants to be able to withstand regular inundation by saltwater. Higher there may be an upper marsh zone, where inundation may not beas often, for example, less than one time per day. If inundation is uncommon and evaporation is intense, of if a marsh is closed from direct contact with seawater, a different type of halophytic vegetation may occur, such as salt flat succulent. High evaporation in dry coastal locations may produce muddy salt flats so toxic that no plants will grow there, at soil salt concentrations exceeding onehundred parts per thousand, i.e., three times that of ocean water. At the other end of the scale, river discharge of large volumes of freshwater into the upper salt marsh may have make some zones weakly brackish, supporting yet a different set of wetland plants.




General Properties of the Salt Marsh Environment.

1. Soil is very fine-grain clay mixed with humus, carried to the estuaryand coastline from freshwater rivers and land.
2. Most of the water for plant growth comes from seawater in the lower salt marsh, but the upper marsh is often heavily influenced either by abundant freshwater from the land drainage and flooding or the occasional catastrophic storms that floods the entire marsh with seawater.
3. When tides carry water into the coastal salt marsh, the wateris layered, with the heavier water moving below and the freshwater on the surface.
4. Rain may have little impact on salt marsh vegetation, when it is inundated.
5. Zones of a salt marsh that are regularly inundated by tides tend to have lower salinity in the soil than zones in which the rate of evaporation is very high. Consequently, salt marshes in semiarid and arid regions can haveextremely high salinity.
6. During the rainy season, with flooding and runoff from the land coupled with heavy rainfall, soil salinity can drop significantly due to the extra leaching that occurs.
[pic]
Salt Marsh
by Geoff Wilson
February 2005
Salt Marshes are one of our nation's most important natural resources. These seas of grass are inundated by salt water twice daily, and provide nurseryhabitat for almost 90% of our coastal fish species.
The area comprising a salt marsh is neither ocean nor land. The tidal currents that dictate all of the natural biorhythms flood the salt marsh 730 times each year. As the waters recede, the enriched waters provide as much as 54% of the soluble and particulate nutrients to the surrounding coastal waters.
[pic]
Salt marshes are the mostproductive natural habitats on the face of the earth. The nutrients exchanged between the salt marshes and the open ocean nourishes the coastal waters for a distance of nearly three miles out to sea. It is in this way that these two separate ecosystems complement each other. The effect of the nourishing waters starts with the nutrients available for the production of phyto-plankton, and is transferred...