Tidal marsh

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Tidal salt marsh at Ella Nore in Chichester, England. Tidal salt marsh at Ella Nore - geograph.org.uk - 1368134.jpg
Tidal salt marsh at Ella Nore in Chichester, England.

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. [1] Tidal marshes experience many overlapping persistent cycles, including diurnal and semi-diurnal tides, day-night temperature fluctuations, spring-neap tides, seasonal vegetation growth and decay, upland runoff, decadal climate variations, and centennial to millennial trends in sea level and climate.


Tidal marshes are formed in areas that are sheltered from waves (such as beside edges of bays), in upper slops of intertidal, and where water is fresh or saline. [2] They are also impacted by transient disturbances such as hurricanes, floods, storms, and upland fires.

The state of tidal marshes can be dependent on both natural and anthropogenic processes. [3] In recent periods, human practices, small and large scale, have caused changes in ecosystems that have had a significant impact on the preservation of tidal marsh ecosystems. [3] Some smaller scale changes include headward (i.e. upstream) erosion [4] and coastal development. Large system changes include pollution and sea level rise (from climate change). These changes are all putting pressure on tidal marshes.


Tidal marshes can be found in two main places: coasts and estuaries. Coastal tidal marshes lie along coasts and estuarine tidal marshes lie inland within the tidal zone. [5] Coastal tidal marshes are found within coastal watersheds and encompass a variety of types including fresh and salt marshes, bottomland hardwood swamps, mangrove swamps, and palustrine wetlands. Estuarine tidal marshes are found in estuaries, areas where freshwater streams flow into brackish areas.

They can be categorized based on salinity level, elevation, and sea level. [1] [6] Tidal marshes are commonly zoned into lower marshes (also called intertidal marshes) and upper/ high marshes, based on their elevation above sea level. [7] A middle marsh zone also exists for freshwater tidal marshes. Location determines the controlling processes, age, disturbance regime, and future persistence of tidal marshes. Tidal marshes are differentiated into freshwater, brackish, and salt according to the salinity of their water. [1] [5] [7]


Freshwater tidal marshes live more inland than saltwater marshes, but their proximity to the coast still allows for daily fluctuations from tides. [8] The inland location allows for a majority of the water content to be from freshwater stream discharge, meaning the salt content is low. [8]

Tidal freshwater marshes are further divided into deltaic and fringing types. [5]

Extensive research has been conducted on deltaic tidal freshwater marshes in the Chesapeake Bay, [9] which were formed as a result of historic deforestation and intensive agriculture. [10]

Freshwater tidal marshes are highly productive and are home to a variety of organisms. There is a variety of vegetation that can reside in freshwater marshes. There is also a vast amount of insects which attract birds, such as wrens and warrens. [8] Aquatic birds, such as ducks and herons, also live in these marshes. Freshwater tidal marshes also serve as spawning grounds for anadromous fish, such as shad and herring. [8] These fish spend most of their lives in saltwater areas, but return back to freshwater during reproduction. [8]

Tidal freshwater marshes are also highly productive, [11] [5] generate a large amount of good quality biomass. [5] [12] They also serve as good waste treatment areas, [11] based on denitrification potential. [5]


Saltwater tidal marshes live on coastlines in areas that are not completely exposed to the open ocean. The volume of water is dependent on the tides. Plant variation throughout marshes can be due to differences in tide exposure and frequency. [7]

Some different types include bottomland hardwood swamps, mangrove swamps, and palustrine wetlands. [13]

Saltwater tidal marshes are correlated with higher decomposition rates and lower denitrification rates. [5]

Island and barrier island

Tidal Marshes also form between a main shoreline and barrier islands. These elongated shifting landforms evolve parallel and in close proximity to the shoreline of a tidal marsh. [14] Many become fully submerged at high tide, and become directly attached to the mainland when at low tide. Barrier island formation includes mechanisms such as offshore bar theory, spit accretion theory, and climate change. [15] [16]

Ecosystem services

Seaside sparrow (Ammospiza maritima). Seaside sparrow (28959673707).jpg
Seaside sparrow (Ammospiza maritima).

Tidal marsh ecosystems provide numerous services, including supplying habitats to support a diverse range of biodiversity. [1] Their areas are spawning grounds and home to "feeder fish" that lie low on the food chain, and serve as crucial rest-stops for migratory birds. Additionally, they provide suitable habitat to various tidal salt marsh specialist bird species, such as the seaside sparrow (Ammospiza maritima) and the willet (Tringa semipalmata) found in tidal marshes in Connecticut, U.S. [17]

Other ecosystem services include their role as significant carbon sinks and shoreline stabilizers. [18] [19] Tidal marshes provide flood protection to upland areas by storing ground water, and lessen the impact of storm surges on nearby shorelines. [1] Tidal marshes located along coastlines also act as intricate filtration systems for watersheds. [20] These areas absorb and trap pollutants from water run-off that travels from higher elevations to open water.

Anthropogenic threats

Historically, the global loss of tidal marshes can be attributed to the implementation of tidal restrictions and other draining activities. [21] [22] [23] Tidal restrictions methods include diking, tide gates, and impoundments, which were implemented on coastal lands internationally in favour of creating agricultural land, as exemplified with large-scale diking that has occurred in Atlantic Canada and the U.S. (e.g. in The Bay of Fundy). [21] [24] [25]

Historical changes (due to anthropogenic activity) to tidal marshes have a lasting impact on them today. Tidal marshes have experienced the Gold Rush which filled some marshes with sediment due to erosion. [26] Logging has also damaged tidal marshes due to their decomposition and filling of marshes. [27] Tidal marshes sensitivity to anthropogenic activity have created long lasting affects.

Currently, rising sea levels is one of the leading threats to tidal marshes caused by global warming and climate change. [28] [29] Pollution due to urbanization also continues to endanger tidal marsh ecosystems. [1]


Restoration of tidal marshes through the removal of tidal restrictions to re-establish degraded ecosystem services have been underway internationally for decades. [21] Deliberate and natural restoration practices have occurred in the U.S., United Kingdom, Europe, and Canada. [21] [22] Research shows that tidal marsh restoration can be evaluated through various factors, such as vegetation, biogeochemical responses (e.g. salinity, sediment deposition, pH, and carbon sequestration), hydrologic responses, and wildlife community responses. [18] [21] [22]

See also

Related Research Articles

<span class="mw-page-title-main">Estuary</span> Partially enclosed coastal body of brackish water

An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environments and are an example of an ecotone. Estuaries are subject both to marine influences such as tides, waves, and the influx of saline water, and to fluvial influences such as flows of freshwater and sediment. The mixing of seawater and freshwater provides high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world.

<span class="mw-page-title-main">Lagoon</span> Shallow body of water separated from a larger one by a narrow landform

A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

<span class="mw-page-title-main">Wetland</span> Land area that is permanently, or seasonally saturated with water

Wetlands, or simply a wetland, is a distinct ecosystem that is flooded or saturated by water, either permanently or seasonally. Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The primary factor that distinguishes wetlands from terrestrial land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique anoxic hydric soils. Wetlands are considered among the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal species. Methods for assessing wetland functions, wetland ecological health, and general wetland condition have been developed for many regions of the world. These methods have contributed to wetland conservation partly by raising public awareness of the functions some wetlands provide. Constructed wetlands are designed and built to treat municipal and industrial wastewater as well as to divert stormwater runoff. Constructed wetlands may also play a role in water-sensitive urban design.

<span class="mw-page-title-main">River delta</span> Silt deposition landform at the mouth of a river

A river delta is a landform shaped like a triangle, created by the deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs when a river enters an ocean, sea, estuary, lake, reservoir, or another river that cannot carry away the supplied sediment. It is so named because its triangle shape resembles the Greek letter Delta. The size and shape of a delta are controlled by the balance between watershed processes that supply sediment, and receiving basin processes that redistribute, sequester, and export that sediment. The size, geometry, and location of the receiving basin also plays an important role in delta evolution.

<span class="mw-page-title-main">Marsh</span> Low-lying and seasonally waterlogged land

A marsh is - according to ecological definitions - a wetland that is dominated by herbaceous rather than woody plant species. More in general, the word can be used for any low-lying and seasonally waterlogged terrain. In Europe and in agricultural literature low-lying meadows that require draining and embanked polderlands are also referred to as marshes or marshland.

<span class="mw-page-title-main">Salt marsh</span> Coastal ecosystem between land and open saltwater that is regularly flooded

A salt marsh, saltmarsh or salting, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated by dense stands of salt-tolerant plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh in trapping and binding sediments. Salt marshes play a large role in the aquatic food web and the delivery of nutrients to coastal waters. They also support terrestrial animals and provide coastal protection.

<span class="mw-page-title-main">Coos Bay</span>

Coos Bay is an estuary where the Coos River enters the Pacific Ocean, the estuary is approximately 12 miles long and up to two miles wide. It is the largest estuary completely within Oregon state lines. The Coos Bay watershed covers an area of about 600 square miles and is located in northern Coos County, Oregon in the United States. The Coos River, which begins in the Oregon Coast Range, enters the bay from the east. From Coos River, the bay forms a sharp loop northward before arching back to the south and out to the Pacific Ocean. Haynes Inlet enters the top of this loop. South Slough branches off from the bay directly before its entrance into the Pacific Ocean. The bay was formed when sea levels rose over 20,000 years ago at the end of the Last Glacial Maximum, flooding the mouth of the Coos River. Coos Bay is Oregon's most important coastal industrial center and international shipping port, with close ties to San Francisco, the Columbia River, Puget Sound and other major ports of the Pacific rim.

<span class="mw-page-title-main">Tidal creek</span> Inlet or estuary that is affected by ebb and flow of ocean tides

A tidal creek or tidal channel is a narrow inlet or estuary that is affected by the ebb and flow of ocean tides. Thus, it has variable salinity and electrical conductivity over the tidal cycle, and flushes salts from inland soils. Tidal creeks are characterized by slow water velocity, resulting in buildup of fine, organic sediment in wetlands. Creeks may often be a dry to muddy channel with little or no flow at low tide, but with significant depth of water at high tide. Due to the temporal variability of water quality parameters within the tidally influenced zone, there are unique biota associated with tidal creeks which are often specialised to such zones. Nutrients and organic matter are delivered downstream to habitats normally lacking these, while the creeks also provide access to inland habitat for salt-water organisms.

<span class="mw-page-title-main">Aquatic ecosystem</span> Ecosystem in a body of water

An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic ; lotic ; and wetlands.

<span class="mw-page-title-main">Wetlands of Louisiana</span>

The wetlands of Louisiana are water-saturated coastal and swamp regions of southern Louisiana, often called 'Bayou'.

A tidal river is a river whose flow and level are caused by tides. A section of a larger river affected by the tides is a tidal reach, but it may sometimes be considered a tidal river if it had been given a separate and another title name.

<span class="mw-page-title-main">Marine ecosystem</span> Ecosystem in saltwater environment

Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply and 90% of habitable space on Earth. Seawater has an average salinity of 35 parts per thousand of water. Actual salinity varies among different marine ecosystems. Marine ecosystems can be divided into many zones depending upon water depth and shoreline features. The oceanic zone is the vast open part of the ocean where animals such as whales, sharks, and tuna live. The benthic zone consists of substrates below water where many invertebrates live. The intertidal zone is the area between high and low tides. Other near-shore (neritic) zones can include mudflats, seagrass meadows, mangroves, rocky intertidal systems, salt marshes, coral reefs, lagoons. In the deep water, hydrothermal vents may occur where chemosynthetic sulfur bacteria form the base of the food web.

<span class="mw-page-title-main">Brackish marsh</span> Marsh with brackish level of salinity

Brackish marshes develop from salt marshes where a significant freshwater influx dilutes the seawater to brackish levels of salinity. This commonly happens upstream from salt marshes by estuaries of coastal rivers or near the mouths of coastal rivers with heavy freshwater discharges in the conditions of low tidal ranges.

<span class="mw-page-title-main">High marsh</span>

High marsh is a tidal marsh zone located above the Mean Highwater Mark (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, 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 plants do survive here, but are stunted and do not reach their full size.

Low marsh is a tidal marsh zone located below the Mean Highwater Mark (MHM). Based on elevation, frequency of submersion, soil characteristics, vegetation, microbial community, and other metrics, salt marshes can be divided to into three distinct areas: low marsh, middle marsh/high marsh, and the upland zone. Low marsh is characterized as being flooded daily with each high tide, while remaining exposed during low tides.

Estuary freshwater inflow is the freshwater that flows into an estuary. Other types of environmental flows include instream flow, the freshwater water flowing in rivers or streams, and estuary outflow, the outflow from an estuary to the ocean.

<span class="mw-page-title-main">Coastal erosion in Louisiana</span> Overview of costal erosion in Louisiana

Coastal erosion in Louisiana is the process of steady depletion of wetlands along the state's coastline in marshes, swamps, and barrier islands, particularly affecting the alluvial basin surrounding the mouth of the Mississippi River. In the last century, Southeast Louisiana has lost a large portion of its wetlands and is expected to lose more in the coming years, with some estimates claiming wetland losses equivalent to up to one football field per hour. One consequence of coastal erosion is an increased vulnerability to hurricane storm surges, which affects the New Orleans metropolitan area and other communities in the region. The state has outlined a comprehensive master plan for coastal restoration and has begun to implement various restoration projects such as fresh water diversions, but certain zones will have to be prioritized and targeted for restoration efforts, as it is unlikely that all depleted wetlands can be rehabilitated.

<span class="mw-page-title-main">Climate change in Virginia</span> Climate change in the US state of Virginia

Climate change in Virginia encompasses the effects of climate change, attributed to man-made increases in atmospheric carbon dioxide, in the U.S. state of Virginia.

The marsh organ is a collection of plastic pipes attached to a wooden framework that is placed in marshes to measure the effects of inundation time and flood frequency on the productivity of marsh vegetation. The information is used for scientific research purposes.

An anchialine system is a landlocked body of water with a subterranean connection to the ocean. Depending on its formation, these systems can exist in one of two primary forms: pools or caves. The primary differentiating characteristics between pools and caves is the availability of light; cave systems are generally aphotic while pools are euphotic. The difference in light availability has a large influence on the biology of a given system. Anchialine systems are a feature of coastal aquifers which are density stratified, with water near the surface being fresh or brackish, and saline water intruding from the coast at depth. Depending on the site, it is sometimes possible to access the deeper saline water directly in the anchialine pool, or sometimes it may be accessible by cave diving.


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