High marsh is a

tidal marsh A tidal marsh (also known as a type of "tidal wetland") is a marsh found along rivers, coasts and estuaries which floods and drains by the tidal movement of the adjacent estuary, sea or ocean.

zone located above the

Mean Highwater Mark A chart datum is the water surface serving as origin (or coordinate surface) of depths displayed on a nautical chart and for reporting and predicting tide heights. A chart datum is generally derived from some tidal phase, in which case it is als ...

(MHW) which, in contrast to the low marsh zone, is inundated infrequently during periods of extreme high tide and storm surge associated with coastal storms. This zone is impacted by spring

tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

, which is a bi-monthly lunar occurrence where the high marsh experiences higher inundation levels. The high marsh is the intermittent zone between the low marsh and the uplands, an entirely terrestrial area rarely flooded during events of extreme tidal action caused by severe coastal storms. The high marsh is distinguished from the low marsh by its sandy soil and higher elevation. The elevation of the high marsh allows this zone to be covered by the high tide for no more than an hour a day. With the soil exposed to air for long periods of time, evaporation occurs, leading to high salinity levels, up to four times that of sea water. Areas of extremely high salinity prohibit plant growth altogether. These barren sandy areas are known as "salt pans". Some

cordgrass ''Spartina'' is a genus of plants in the grass family, frequently found in coastal salt marshes. Species in this genus are commonly known as cordgrass or cord-grass, and are native to the coasts of the Atlantic Ocean in western and southern Eu ...

plants do survive here, but are stunted and do not reach their full size. The high marsh depends on regular tidal activity and inundation to deposit sediments.

Sediment deposition Deposition is the geological process in which sediments, soil and rocks are added to a landform or landmass. Wind, ice, water, and gravity transport previously weathered surface material, which, at the loss of enough kinetic energy in the fluid ...

facilitates mineral and

organic matter Organic matter, organic material or natural organic matter is the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come fro ...

buildup and sediment accretion. The minerals and organic matter promote vegetation growth and the sediment accretion promotes heightened elevation growth.Tiner, R.W. 2013. Tidal wetlands primer: an introduction to their ecology, natural history, status, and conservation. University of Massachusetts Press, Amherst and Boston. 508 pp. The high marsh is also important to many habitat specialists such as the

Saltmarsh Sparrow The saltmarsh sparrow (''Ammospiza caudacuta'') is a small New World sparrow found in salt marshes along the Atlantic coast of the United States. At one time, this bird and the Nelson's sparrow (''Ammospiza nelsoni'') were thought to be a single ...

Black Rail The black rail (''Laterallus jamaicensis'') is a mouse-sized member of the rail family Rallidae that occurs in both North and South America. Taxonomy The black rail was Species description, formally described in 1789 by the German naturalist J ...

, American Black Duck, saltmarsh spike-grass, and salt-hay. These specialists rely on the high marsh ecosystem to provide for their biological needs to ensure stable productivity and abundance. Among these biological needs are foraging, mating, nesting, incubation, and brooding. The

Clean Water Act of 1972 The Clean Water Act (CWA) is the primary federal law in the United States governing water pollution. Its objective is to restore and maintain the chemical, physical, and biological integrity of the nation's waters; recognizing the primary respo ...

was the first act to protect these ecosystems but, due to the absence of protection, many wetlands were converted into farmland and residential land.

Marsh Prevalence Worldwide

Saltmarshes are found in at least 99 countries, as mapped by scientists Mcowen et al. in 2017.Mcowen, Chris; Weatherdon, Lauren; Bochove, Jan-Willem; Sullivan, Emma; Blyth, Simon; Zockler, Christoph; Stanwell-Smith, Damon; Kingston, Naomi; Martin, Corinne (21 March 2017). "A global map of saltmarshes". ''Biodiversity Data Journal''. 5 (5): e11764.

ISSN An International Standard Serial Number (ISSN) is an eight-digit to uniquely identify a periodical publication (periodical), such as a magazine. The ISSN is especially helpful in distinguishing between serials with the same title. ISSNs a ...

1314-2828. PMC5515097.

PMID PubMed is an openly accessible, free database which includes primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine (NLM) at the National Institutes of ...

28765720. Similarly, in 43 countries/territories there are 5,495,089 mapped hectares of saltmarsh. The coterminous United States has many estimates for original wetland content, spanning from 211 to 217 million acres total.Dahl, Thomas E. (1990). "Wetlands Loss Since the Revolution" (PDF). ''National Wetlands Newsletter''. Alaska has the highest amount of wetlands, with an estimated 165 million acres originally. The

U.S. Department of Interior The United States Department of the Interior (DOI) is an executive department of the U.S. federal government responsible for the management and conservation of most federal lands and natural resources. It also administers programs relating ...

and the U.S. Fish and Wildlife Service estimate that colonial United States had approximately 392 million acres, with 221 million in the 48 states, 170 million acres in Alaska, and 59,000 acres in Hawaii.Dahl, T.E. 1990.Wetland losses in the United States 1780s to 1980’s. U.S. Department of the Interior, Fish and Wildlife Service. Washington. D.C. 13pp. https://www.fws.gov/wetlands/documents/Wetlands-Losses-in-the-United-States-1780s-to-1980s.pdf Thomas Dahl reports in ''Wetlands'' that from 1780 to 1980 there was a “53-percent loss from the original etlandacreage total." Further, United States wetlands experienced a net loss of approximately 60,000 acres per year spanning from 1998 to 2004. This increased to 80,000 acres per year between 2004 and 2009.

High Marsh Loss Cause

The high marsh is one of the most threatened features of

wetland A wetland is a distinct semi-aquatic ecosystem whose groundcovers are flooded or saturated in water, either permanently, for years or decades, or only seasonally. Flooding results in oxygen-poor ( anoxic) processes taking place, especially ...

s. On average, the United States' coastal areas support high per capita communities. Due to this, these areas face the pressure of development and

overdevelopment In international economics, overdevelopment refers to a way of seeing global inequality and pollution that focuses on the negative consequences of overconsumption, excessive consumption. It is the opposite extreme to underdevelopment. In mainstre ...

. The

United States Fish and Wildlife Service The United States Fish and Wildlife Service (USFWS or FWS) is a List of federal agencies in the United States, U.S. federal government agency within the United States Department of the Interior which oversees the management of fish, wildlife, ...

(FWS) summarizes data from the

Cape Cod National Seashore The Cape Cod National Seashore (CCNS) encompasses on Cape Cod, in Massachusetts. CCNS was created on August 7, 1961, by President John F. Kennedy, when he signed a bill enacting the legislation he first co-sponsored as a Senator a few years pr ...

(CCNS) and states that “there has been a documented shift in the high marsh to low marsh boundary by 100 m (328 ft) upslope between 1984 and 2000 in the ‘Gut’ at Wellfleet, and a loss of 46 percent of the high marsh between 1947 and 2005."U.S. Fish and Wildlife Service. 2020. Report on the current conditions for the saltmarsh sparrow. U.S. Fish and Wildlife Service, Northeast Region, Charlestown, RI. 106 pp. https://fws.gov/northeast/saltmarsh-sparrow/PDF/20200821-Current-Conditions-Report_SALS-Final.pdf This high marsh loss is evident throughout the United States. Overall, the high marsh is particularly vulnerable to the impacts of climate change and anthropogenic actions, as follows.

Nutrient Overload and Contamination

This coastal development near marshes may increase the

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

and

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

concentration leached into waterways, particularly from sewage treatment and systems. Further, due to farmlands, lawns, and golf courses, nitrogen concentrations may also be increased. When the high marsh plants are exposed to a higher concentration of nitrogen and phosphorus, the underground biomass decreases and the aboveground increases, making the ecosystem susceptible to widening and

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

. These higher nutrient concentrations may also lead to

eutrophication Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...

and

fish kill The term fish kill, known also as fish die-off, refers to a localized mass mortality event, mass die-off of fish populations which may also be associated with more generalized mortality of aquatic life.University of Florida. Gainesville, FL (200 ...

s.Deegan, L.A., J.L. Bowen, D. Drake, J.W. Fleeger, C.T. Friedrichs, K.A. Galvan, J.E. Hobbie, C. Hopkinson, D.S. Johnson, J.M. Johnson, L.E. LeMay, E. Miller, B.J. Peterson, C. Picard, S. Sheldon, M. Sutherland, J. Vallino and R.S. Warren. 2007. Susceptibility of salt marshes to nutrient enrichment and predator removal. Ecological Applications 17(5) Supplement: Nutrient Enrichment and Estuarine Eutrophication S42–S63.

Infrastructure

Certain tidal restricting infrastructure—such as roadways,

dikes Dyke or dike may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), formations of magma or sediment that cut through and across the layering of adjacent rocks * Dike (mythology), ''Dikē'', the Greek goddess ...

, and

floodgate Floodgates, also called stop gates, are adjustable gates used to control water flow in flood barriers, reservoir, river, stream, or levee systems. They may be designed to set spillway crest heights in dams, to adjust flow rates in sluices and ...

s—disrupt the natural tidal flow. These restrictions prevent the sediment accretion and nutrient deposition that the high marsh relies on for elevation growth and vegetation health.

Marsh Prevalence Worldwide

High Marsh Loss Cause

Nutrient Overload and Contamination

Infrastructure

References

See also