Salt marsh

An Atlantic coastal salt marsh in Connecticut.

A weed salt marsh in the Marine Park Nature Center in Brooklyn, New York.

A grass salt marsh in the Marine Park Nature Center in Brooklyn, New York.

A walkway for people over a salt marsh.

A salt marsh in the Marine Park Nature Center in Brooklyn, New York, after a snow melt.

A salt marsh is a type of marsh that is a transitional zone between land and salty or brackish water (e.g., sloughs, bays, estuaries). It is dominated by halophytic (salt tolerant) herbaceous plants. Historically, salt marshes have sometimes been treated as "wastelands", along with other wetlands. We now know that salt marshes are one of the most biologically productive habitats on the planet, rivaling tropical rainforests. This is partly due to the daily tidal surges that bring in nutrients, the natural chemical activity of salty (or brackish) water, the tendency of nutrients to settle in roots of the plants there, and the tendency of algae to bloom in the shallow unshaded water. Salt marshes also provide a benefit by protecting against severe weather, such as in the North American Gulf Coast. In the past, substantial areas of saltmarsh have been reclaimed as agricultural land and for urban development, but in the US and Europe they are now accorded a high level of protection by the Clean Water Act and the Habitats Directive respectively. There is growing interest in restoring salt marshes, through a process of managed retreat.

Definition

A marsh is a type of wetland. A wetland is a transitional environment between permanently aquatic and terrestrial environments that shares characteristics of both environments and where water, which covers the soil or is near the surface for substantial parts of the year, is the key factor in determining the nature of the ecosystem and soil. Although wetlands have aspects similar to both wet and and dry environments, they cannot be classified unambiguously as either aquatic or terrestrial (Barbier et al. 1997). In the United States, the four general categories of wetlands, according to the Environmental Protection Agency, are marshes, swamps, bogs, and fens (EPA 2004).

A marsh, or morass, is a type of wetland characterized by being intermittently or continuously flooded with water that is not deep and with predominately soft-stemmed vegetation, such as grasses and sedges, that are adapted to conditions of saturated soil. The water of a marsh can be fresh, brackish, or saline. Like swamps, a marsh generally is considered to be a wetland that does not accumulate substantial peat deposits (NSC 2005).

In North America, marshes usually are regarded as wetlands dominated by soft-stemmed vegetation, while swamps usually are regarded as wetlands dominated by woody vegetation, such as trees and woody bushes (EPA 2004; NSC 2005). However, this distinction does not necessarily apply in other areas; for instance, in Africa swamps may be dominated by papyrus.

Elsewhere, a marsh is distinguished from a swamp by being a wetland with less open water surface and shallower water than a swamp.

There are many types of marshes. Marshes may be freshwater, brackish water, or saltwater, and may be tidal or non-tidal (NSC 2005; EPA 2006). A tidal marsh is a type of marsh that is found along coasts and estuaries of which the flooding characteristics are determined by the tidal movement of the adjacent estuary, sea, or ocean (EPA 2006). A non-tidal marsh lacks the flooding from tidal movement. In North America, non-tidal marshes are the most common and most widely distributed wetlands and are mostly freshwater marshes (EPA 2006). They tend to have highly organic, mineral rich soils of silt, clay, and sand (EPA 2006). According to the salinity of the flooding water, freshwater, brackish and saline tidal marshes are distinguished.

A saltwater marsh has high amounts of salinity and is dominated by halophytic (salt tolerant) herbaceous plants, such as Spartina alterniflora (oyster grass). The National Wetlands Research Center of the U.S. Geological Survey defines a saltwater marsh as having a salinity of 15-18 parts per thousand or greater (NWRC 2007). Below this is brackish marshes, intermediate marshes, and freshwater marshes.

The Natural Resources Conservation Service of the United States Department of Agriculture defines a saltmarsh as a "flat, poorly drained area that is subject to periodic or occasional overflow by salt water, containing water that is brackish to strongly saline, and usually covered with a thick mat of grassy halophytic plants; e.g. a coastal marsh periodically flooded by the sea, or an inland marsh, (or salina) in an arid region and subject to intermittent overflow by salty water" (NRCS 2007). We now know that salt marshes are one of the most biologically productive habitats on the planet, rivaling tropical rain forests.

Conditions required

Salt marshes develop on depositional coasts, bays, and estuaries where tidal action is relatively gentle and erosion no more than intermittent and light enough to allow vegetation to take hold. They are common on low-energy coasts such as estuaries, enclosed bays, and the land sides of barrier islands and strips.

Vegetation

Plant species diversity is relatively low, since the flora must be tolerant of salt, complete or partial submersion, and anoxic mud substrate. The most common salt marsh plants are glassworts (Salicornia spp.) and the cord grasses (Spartina spp.), which have worldwide distribution. They are often the first plants to take hold in a mudflat and begin its ecological succession into a salt marsh. Their shoots lift the main flow of the tide above the mud surface while their roots spread into the substrate and stabilize the sticky mud and carry oxygen into it so that other plants can establish themselves as well. Plants such as sea lavenders (Limonium spp.), plantains (Plantago spp.), and varied sedges and rushes grow once the mud has been vegetated by the pioneer species.

The flora of a salt marsh is differentiated into levels according to the plants' individual tolerance of salinity and water table levels. Vegetation found at the water must be able to survive high salt concentrations, periodical submersion, and a certain amount of water movement, while plants further inland in the marsh can sometimes experience dry, low-nutrient conditions.

Salt marshes are quite photosynthetically active and are extremely productive habitats. They serve as depositories for a large amount of organic matter, and are full of decomposition, which feeds a broad food chain of organisms from bacteria to mammals. Interestingly (in such a biologically productive biome), many of the halophytic plants such as cordgrass are not grazed at all by higher animals, but die off and decompose, to become food for micro-organisms, which in turn become food for fish and in turn birds.

In wintertime the saltmarsh looks more open than in summer. More space is seen between reeds as snow falls between them. The water partly freezes, which makes it look rather spectacular.

Marais salants

In warmer climates, salt can be produced by solar energy so that the French equivalent of the salt marsh, the marais salant has come to be envisaged primarily as an industrial plant, though classified as a form of agriculture, known in French as saliculture. For this aspect of the salt marsh, see Salt evaporation pond.

Wetland dieback

In the summer and fall of 2002, Dr. Scott Warren at Connecticut College and Ron Rozsa of the Connecticut Department of Environmental Protection, noticed the sudden (within one year) disappearance of emergent vegetation at several south shore Cape Cod wetlands connected to Nantucket Sound. The vegetation loss could not be explained by any typical New England causes of vegetation loss such as ice, wrack or herbivory (e.g., geese or muskrat).[1]

Four years later, the cause is still unknown, but there are 17 suspected dieback marshes on Cape Cod, and a few other possible sites are on the North and South Shore, according to the Wetland Restoration Program of the Massachusetts Office of Coastal Zone Management.

In Louisiana, 300,000 acres (1200 km²) turned brown around the year 2000. In 2002, researchers noticed that about 2,000 acres (8 km²) of salt marsh in Georgia turned to mud, similar to what is happening in New England. But as of mid-2006, the Louisiana and Georgia marshes are growing back — or at least not getting worse — while marshes on the Cape do not seem to be recovering naturally. [2]

Importance

Marshes are vital wildlife habitats, often serving as breeding grounds for a wide variety of animal life. Salt marshes rival tropical rain forests in productivity.

Tidal marshes slow erosion along the shoreline, buffer stormy seas, and remove pollutants before they enter oceans and estuaries (EPA 2006).

See also

Bayou Biodiversity Action Plan Body of water Bog Fen ground plane

Mangrove swamp Marsh Mesopotamian Marshes Seagrass Swamp

External links

• Geography resource for schools
• Salt Marsh Nature Center located in the Marine Park section of Brooklyn, New York, USA
• Marine Nature Study Area operated by the Town of Hempstead: Dept. of Conservation & Waterways, located in Oceanside, New York, USA

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

• Salt_marsh  ^history

The history of this article since it was imported to New World Encyclopedia:

• History of "Salt marsh"

Note: Some restrictions may apply to use of individual images which are separately licensed.