Invalid Unit Specified
F035 Salt Marsh Formation

The U.S. National
Vegetation Classification
Type Concept Sentence: Salt Marsh is a wetland that has shallow water and levels that usually fluctuate due primarily to tides along the coast or changes in water depth in depressions. Coastal salt marshes are primarily intertidal; that is, they are found in areas at least occasionally inundated by high tide but not flooded during low tide, including estuaries, lagoons, and the lee side of barrier islands. The vegetation comprises emergent shrubs and herbs with at least 10% cover, especially saline or halophytic species. They occur at all latitudes around the globe, but are concentrated in the temperate mid-latitudes (23-70°N and S).
Collapse All::Expand All
Common (Translated Scientific) Name: Salt Marsh Formation
Colloquial Name: Salt Marsh
Hierarchy Level: Formation
Type Concept: Salt Marsh is a wetland that has shallow water and levels that usually fluctuate due primarily to tides along the coast or changes in water depth in depressions. Coastal salt marshes are primarily intertidal; that is, they are found in areas at least occasionally inundated by high tide but not flooded during low tide, including estuaries, lagoons, and the lee side of barrier islands. The vegetation comprises emergent aquatic macrophytes, especially saline or halophytic species, chiefly graminoids such as rushes, reeds, grasses and sedges, and shrubs and other herbaceous species such as broad-leaved emergent macrophytes, floating-leaved and submergent species (aquatic vegetation), and macroscopic algae. The vegetation is usually arranged in distinct zones of parallel patterns in response to gradients of tidal flooding frequency and duration, water chemistry or disturbance, sometimes described simply as "high marsh" (limits of high tide) and "low marsh" (intertidal marsh). Salt marshes have gradients that include barren salt flats at the tidal edge, rushes, and then halophytic herbs and grasses at the outer edge. Daily drawdowns may expose mudflats containing a sparse mix of pioneering herb and grass species. Salt marsh chemistry is dominated by salinity. Salinity levels vary depending on a complex set of factors, including frequency of inundation, rainfall, soil texture, freshwater influence, fossil salt deposits, and other factors. The lower limits of salinity are defined as at least 0.5 ppt, below which it is considered freshwater.
Diagnostic Characteristics: Salt Marsh is a wetland that has shallow water and levels that usually fluctuate due primarily to tides along the coast or changes in water depth in depressions. Coastal tidal salt marshes are found in areas at least occasionally inundated by high tide but not flooded during low tide. The vegetation comprises emergent aquatic macrophytes with at least 10% cover, especially saline or halophytic species, chiefly graminoids such as rushes, reeds, grasses and sedges, and shrubs and other herbaceous species such as broad-leaved emergent macrophytes. They occur at all latitudes around the globe, but are concentrated in the temperate mid-latitudes (23-70°N and S).
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: Further review is needed of the similarities and differences between temperate and tropical salt marshes, as well as subarctic and arctic (polar) salt marshes, all of which are placed in this formation. From an overall physiognomic and ecological perspective, maintaining a single salt marsh formation is desirable. Although they represent a small fraction of the overall salt marsh area, there are extensive tropical salt marshes, often found in association with mangroves; the mangroves occupy the lower, regularly tidally inundated part of the intertidal zone and salt marsh the upper zone above the mangroves. Australia has more than one million hectares of salt marsh and sparsely vegetated high level tidal flats, with a large proportion of this being tropical. More information on potentially distinct floristics and growth forms of tropical salt marshes is needed.
Similar NVC Types:
F006 Mangrove, note: Some mangrove formations may be mixed with salt marshes, but by and large they are physiognomically quite distinct.
F013 Temperate to Polar Freshwater Marsh, Wet Meadow & Shrubland, note: 2.C.5 ~Salt Marsh Formation (F035)$$ contains inland salt marshes that are non-tidal and saline (or haline) and may resemble some brackish freshwater marshes (F013).
Physiognomy and Structure: Salt Marsh vegetation comprises primarily emergent aquatic macrophytes with at least 10% cover, especially saline or halophytic species, chiefly graminoids such as rushes, reeds, grasses and sedges, and shrubs and other herbaceous species such as broad-leaved emergent macrophytes. Floating-leaved and submergent species (aquatic vegetation) and macroscopic algae are present at varying levels of abundance.

In tidal salt marshes, the vegetation is usually arranged in distinct zones of parallel patterns in response to gradients of tidal flooding frequency and duration, water chemistry or disturbance. They are sometimes described simply as "high marsh" (limits of high tide) and "low marsh" (intertidal marsh). These salt marshes have gradients that include barren salt flats at the tidal edge, rushes, and then halophytic herbs and grasses at the outer edge. Daily drawdowns may expose mudflats that contain a sparse mix of pioneering herb and grass species.

Saline or brackish non-tidal marshes also have gradients but with fewer zones that include barren salt flats in the center of the marsh, rushes, and then halophytic herbs and grasses at the outer edge. Seasonal drawdowns may expose mudflats that are revegetated by pioneering herb and grass species.

Although the bulk of salt marshes are temperate to polar, there are tropical salt marshes, often found in association with mangroves; the mangroves occupy the lower, regularly tidally inundated part of the intertidal zone and salt marsh the upper zone above the mangroves. Australia has more than one million hectares of salt marsh and sparsely vegetated high level tidal flat, with the greater proportion of this being tropical. Tropical salt marshes are species-poor, and species richness increases with more temperate conditions; for example in Australia, the richest salt marsh floras are found in Tasmania and Victoria.
Floristics:
Dynamics: No Data Available
Environmental Description: A salt marsh is a wetland that has shallow water and levels that usually fluctuate due primarily to tides or drawdowns in seasonal saline basins. Coastal salt marshes are primarily intertidal; that is, they are found in areas at least occasionally inundated by high tide but not flooded during low tide, including estuaries, lagoons, and the lee side of barrier islands. Salt marshes form wherever the accumulation of sediments is equal to or exceeds the rate of land subsidence and where there is adequate protection from high energy waves and storms. Salt marshes are located in estuaries or lower stream reaches, and behind baymouth bars or other sheltered sites. Sediments can either be formed on marine-dominated coastlines from reworked marine sediments or formed in deltaic areas where the main source of mineral sediment is riverine.

Salt marsh chemistry is dominated by salinity. Salinity levels vary depending on a complex of factors, including frequency of inundation, rainfall, soil texture, freshwater influence, fossil salt deposits, and other factors. The lower limits of salinity are defined as at least 0.5 ppt, below which it is considered freshwater, though the oligohaline category (0.5-5 ppt) can be considered transitional freshwater [see Cowardin et al. (1979) for salinity scale]. The concentration of most elements needed for plant growth also varies depending on these factors. A number of studies have shown that salt marshes are especially nitrogen limited. The water in non-tidal saline marshes is high in dissolved salts because water losses through evaporation concentrate sulphates and chlorides of sodium and magnesium. In highly saline non-tidal marshes, vegetation development is severely hampered because salt concentrations are so high as to become toxic to plants (National Wetlands Working Group 1997).
Geographic Range: Salt marshes occur at all latitudes around the globe, but are concentrated in the temperate mid-latitudes (23-70°N and S).

Resolution of the role of climate on salt marshes is needed.
Nations: CA, MX, US
States/Provinces:
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: Moderate
Confidence Level Comments:
Grank: GNR
Greasons:
Concept Lineage:
Predecessors:
Obsolete Names:
Obsolete Parents:
Synonomy: = Salt Marshes (Woodward 2008)
> Tidal Salt Marshes (Mitsch and Gosselink 2000) [Non-tidal inland salt marshes are treated by them under their Freshwater Marsh type.]
Concept Author(s): Hierarchy Revisions Working Group, Federal Geographic Data Committee (Faber-Langendoen et al. 2014)
Author of Description: D. Faber-Langendoen, after National Wetlands Working Group (1997)
Acknowledgements:
Version Date: 17Oct2014
References:
  • Cowardin, L. M., V. Carter, F. C. Golet, and E. T. LaRoe. 1979. Classification of wetlands and deepwater habitats of the United States. FWS/OBS-79/31. USDI Fish & Wildlife Service, Office of Biological Services, Washington, DC. 103 pp.
  • Faber-Langendoen, D., T. Keeler-Wolf, D. Meidinger, C. Josse, A. Weakley, D. Tart, G. Navarro, B. Hoagland, S. Ponomarenko, J.-P. Saucier, G. Fults, and E. Helmer. 2015c. Classification and description of world formation types. General Technical Report RMRS-GTR-000. USDA Forest Service, Rocky Mountain Research Station, Fort Collins, CO.
  • Mitsch, W. J., and J. G. Gosselink. 2000. Wetlands. Third edition. John Wiley & Sons, Inc., New York. 920 pp.
  • National Wetlands Working Group. 1997. Wetlands of Canada. C. D. A. Rubec, editor. Ecological Land Classification Series No. 24. Environment Canada, Ottawa, and Polyscience Publications, Inc., Montreal. 452 pp.
  • Woodward, S. 2008. Grassland biomes. Greenwood Press, Westport, CT.