Salt marsh
Encyclopedia
A salt marsh is an environment in the upper coast
al intertidal zone
between land and salt water
or brackish water
, it is dominated by dense stands of halophytic
(salt-tolerant) plants such as herb
s, grasses
, or low shrub
s. 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 exporting of nutrients to coastal waters. They also provide support to terrestrial animals such as migrating birds as well as providing coastal protection
.
and the leeward side of barrier island
s and spits
. In the tropics
and sub-tropics
they are replaced by mangrove
s; an area that differs to a salt marsh in that instead of herbaceous plant
s, they are dominated by salt-tolerant trees. Most salt marshes have a low topography
with low elevations but a vast wide area, making them hugely popular for human populations.
Salt marshes are located among different landforms based on their physical and geomorphological settings. Such marsh landforms include deltaic
marshes, estuarine, back-barrier, open coast, embayments and drowned-valley
marshes. Deltaic marshes are associated with large river
s where many occur in Southern Europe
such as the Camargue
in the Rhone
delta or the Ebro
delta. They are also highly extensive within the rivers of the Mississippi Delta
. In New Zealand
, most salt marshes occur at the head of estuaries in areas where there is little wave action and high sedimentation. Such marshes are located in Awhitu Regional Park in Auckland, the Manawatu Estuary and the Avon-Heathcote Estuary
in Christchurch. Back-barrier marshes are sensitive to the reshaping of barriers in the landward side of which they have been formed. They are common along much of the eastern coast of the United States
and the Frisian Islands
. Large, shallow coastal embayments can hold salt marshes with examples including Morecambe Bay
and Portsmouth
in Britain
and the Bay of Fundy
in North America
.
Salt marshes are sometime included in lagoons, and the difference is not very marked: e.g. a major part of the Venetian Lagoon
is made up of these sorts of animals and or living organisms belonging to this ecosystem.
Coastal salt marshes can be distinguished from terrestrial habitats by the daily tidal
flow that occurs and continuously floods the area. It is an important process in delivering sediments, nutrients and plant water supply to the marsh. At higher elevations in the upper marsh
zone, there is much less tidal inflow, resulting in lower salinity
levels. Soil salinity in the lower marsh
zone is fairly constant due to everyday annual tidal flow. However, in the upper marsh, variability in salinity is shown as a result of less frequent flooding and climate variations. Rainfall can reduce salinity and evapotranspiration
can increase levels during dry periods. As a result, there are microhabitats populated by different species of flora
and fauna
dependant on their physiological abilities. 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. It has been found that the upper marsh zones limit species through competition and the lack of habitat protection, while lower marsh zones are determined through the ability of plants to tolerate physiological stresses such as salinity, water submergence and low oxygen levels.
The New England
salt marsh is subject to strong tidal influences and shows distinct patterns of zonation. In low marsh areas with high tidal flooding, a monoculture of the smooth cordgrass, Spartina alterniflora
dominate, then heading landwards, zones of the salt hay, Spartina patens
, black rush, Juncus gerardii
and the shrub Iva frutescens are seen respectively. These species all have different tolerances that make the different zones along the marsh best suited for each individual.
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 glasswort
s (Salicornia spp.) and the cordgrass (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
.
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. 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 birds.
The coast is a highly attractive natural feature to humans through its beauty, resources, and accessibility. As of 2002, over half of the world’s population was estimated to being living within 60 km of the coastal shoreline, making our coastlines highly vulnerable to human impacts from daily activities that put pressure on these surrounding natural environments. In the past, salt marshes were perceived as coastal ‘wastelands,’ causing considerable loss and change of these ecosystem
s through land reclamation
for agriculture
, urban development
, salt production
and recreation
. The indirect effects of human activities such as nitrogen loading
also play a major role in the salt marsh area.
were often built to allow for this shift in land change and to provide flood protection further inland. For centuries, livestock
such as sheep and cattle grazed on the highly fertile salt marsh land. Land reclamation for agriculture has resulted in many changes such as shifts in vegetation structure, sedimentation, salinity, water flow, biodiversity
loss and high nutrient inputs. There have been many attempts made to eradicate these problems for example, in New Zealand, the cordgrass Spartina anglica
was introduced from England into the Manawatu River
mouth in 1913 to try and reclaim the estuary land for farming. A shift in structure from bare tidal flat to pastureland resulted from increased sedimentation and the cordgrass extended out into other estuaries around New Zealand. Native plants and animals struggled to survive as non-natives out competed them. Efforts are now being made to remove these cordgrass species, as the damages are slowly being recognised.
, San Francisco, Amsterdam
, Rotterdam
, Venice
and Tokyo
have all expanded out into areas of salt marsh. The remaining marshes surrounding these urban areas are under immense pressure from the human population as human-induced nitrogen enrichment enters these habitats.
Nitrogen loading through human-use indirectly affects salt marshes causing shifts in vegetation structure and the invasion of non-native species. Human impacts such as sewage, urban run-off, agricultural and industrial wastes are running into the marshes from nearby sources. Salt marshes are nitrogen limited and with an increasing level of nutrients entering the system from anthropogenic effects, the plant species associated with salt marshes are being restructured through change in competition. For example, the New England salt marsh is experiencing a shift in vegetation structure where S. alterniflora is spreading from the lower marsh where it predominately resides up into the upper marsh zone. Additionally, in the same marshes, the reed Phragmites australis
has been invading the area expanding to lower marshes and becoming a dominant species. P. australis is an aggressive halophyte that can invade disturbed areas in large numbers outcompeting native plants. This loss in biodiversity is not only seen in flora assemblages but also in many animals such as insects and birds as their habitat and food resources are altered.
populations. In many locations, particularly in the northeastern United States, residents and local and state agencies dug straight-lined ditches deep into the marsh flats. The end result, however, was a depletion of killifish
habitat. The killifish is a mosquito predator, so the loss of habitat actually led to higher mosquito populations, and adversely affected wading birds that preyed on the killifish. These ditches can still be seen, though with the realization of the impacts on the marshes' health, some places have begun efforts to refill the ditches.
s. Salt marshes are ecologically important providing habitats for native migratory fish and acting as sheltered feeding and nursery grounds. They are now protected by legislation in many countries to look after these ecologically important habitats. In the United States and Europe, they are now accorded to a high level of protection by the Clean Water Act
and the Habitats Directive respectively. With the impacts of this habitat and its importance now realised, a growing interest in restoring salt marshes, through managed retreat
or the reclamation of land has been established. However, many Asia
n countries such as China
are still to recognise the value of marshlands. With their ever-growing populations and intense development along the coast, the value of salt marshes tends to be ignored and the land continues to be reclaimed.
Bakker et al. (1997) suggests two options available for restoring salt marshes. The first is to abandon all human interference and leave the salt marsh to complete its natural development. These types of restoration projects are often unsuccessful as vegetation tends to struggle to revert back to its original structure and the natural tidal cycles are shifted due to land changes. The second option suggested by Bakker et al. (1997) is to restore the destroyed habitat into its natural state either at the original site or as a replacement at a different site. Under natural conditions, recovery can take 2–10 years or even longer depending on the nature and degree of the disturbance and the relative maturity of the marsh involved. Marshes in their pioneer stages of development will recover more rapidly than mature marshes as they are often first to colonize the land. It is important to note, that restoration can often be sped up through the replanting of native vegetation.
This last approach is often the most practised and generally more successful than allowing the area to naturally recover on its own. The salt marshes in the state of Connecticut in the United States have long been an area lost to fill and dredging. As of 1969, the Tidal Wetland Act was introduced that seized this practise, but despite the introduction of the act, the system was still degrading due to alterations in tidal flow. One area in Connecticut is the marshes on Barn Island. These marshes were diked then impounded with salt and brackish marsh during 1946-1966. As a result the marsh shifted to a freshwater state and became dominated by the invasive species P. australis, Typha angustifolia
and T. latifolia
that have little ecological connection to the area. By 1980, a restoration programme was put in place that has now been running for over 20 years. This programme has aimed to reconnect the marshes by returning tidal flow along with the ecological functions and characteristics of the marshes back to their original state. In the case of Barn Island, declines in the invasive species have initiated, re-establishing the tidal-marsh vegetation along with animal species such as fish and insects. This example highlights that considerable time and effort is needed to effectively restore salt marsh systems. Times in marsh recovery can depend on the development stage of the marsh; type and extent of the disturbance; geographical location; and the environmental and physiological stress factors to the marsh-associated flora and fauna.
Although much effort has gone into restoring salt marshes worldwide, further research is needed. There are many setbacks and problems associated with marsh restoration that requires careful long-term monitoring. Information on all components of the salt marsh ecosystem should be understood and monitored from sedimentation, nutrient, and tidal influences, to behaviour patterns and tolerances of both flora and fauna species. Once we have a better understanding of these processes and not just locally, but over a global scale, we can then suggest more sound and practical management and restoration efforts that can be used to preserve our valuable marshes and put them back to their original state.
While humans are situated along coastlines, there will always be the possibility of human-induced disturbances despite the number of restoration efforts we plan to implement. Dredging, pipelines for offshore petroleum resources, highway construction, accidental toxic spills or just plain carelessness are examples that will for some time now and into the future be the major influences of salt marsh degradation.
In addition to restoring and managing salt marsh systems based on scientific principles, the opportunity should be taken to educate public audiences of their importance biologically and their purpose as serving as a natural buffer for flood protection. Because salt marshes are often located next to urban areas, they are likely to receive more visitors than remote wetland
s. By physically seeing the marsh, people are more likely to take notice and be more aware of the environment around them. An example of public involvement occurred at the Famosa Slough wetland in San Diego, where a “friends” group worked for over a decade in trying to prevent the area from being developed. Eventually, the 5 hectare site was bought by the City and the group worked together to restore the area. The project involved removing invasive species and replanting with natives, along with public talks to other locals, frequent bird walks and clean-up events.
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...
al intertidal zone
Intertidal zone
The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...
between land and salt water
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
or brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
, it is dominated by dense stands of halophytic
Halophyte
A halophyte is a plant that grows where it is affected by salinity in the root area or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs, and seashores. An example of a halophyte is the salt marsh grass Spartina alterniflora . Relatively few plant species are...
(salt-tolerant) plants such as herb
Herb
Except in botanical usage, an herb is "any plant with leaves, seeds, or flowers used for flavoring, food, medicine, or perfume" or "a part of such a plant as used in cooking"...
s, grasses
Poaceae
The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...
, or low shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
s. These plants are terrestrial in origin and are essential to the stability of the salt marsh
Marsh
In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....
in trapping and binding sediments. Salt marshes play a large role in the aquatic food web and the exporting of nutrients to coastal waters. They also provide support to terrestrial animals such as migrating birds as well as providing coastal protection
Coastal management
In some jurisdictions the terms sea defense and coastal protection are used to mean, respectively, defense against flooding and erosion...
.
Basic information on Salt marsh
Salt marshes occur on low-energy coasts in temperate and high-latitudes. These typically include sheltered environments such as embankments, estuariesEstuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
and the leeward side of barrier island
Barrier island
Barrier islands, a coastal landform and a type of barrier system, are relatively narrow strips of sand that parallel the mainland coast. They usually occur in chains, consisting of anything from a few islands to more than a dozen...
s and spits
Spit (landform)
A spit or sandspit is a deposition landform found off coasts. At one end, spits connect to land, and extend into the sea. A spit is a type of bar or beach that develops where a re-entrant occurs, such as at cove's headlands, by the process of longshore drift...
. In the tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
and sub-tropics
Subtropics
The subtropics are the geographical and climatical zone of the Earth immediately north and south of the tropical zone, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitudes 23.5°N and 23.5°S...
they are replaced by mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
s; an area that differs to a salt marsh in that instead of herbaceous plant
Herbaceous plant
A herbaceous plant is a plant that has leaves and stems that die down at the end of the growing season to the soil level. They have no persistent woody stem above ground...
s, they are dominated by salt-tolerant trees. Most salt marshes have a low topography
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
with low elevations but a vast wide area, making them hugely popular for human populations.
Salt marshes are located among different landforms based on their physical and geomorphological settings. Such marsh landforms include deltaic
River delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...
marshes, estuarine, back-barrier, open coast, embayments and drowned-valley
Ria
A ria is a coastal inlet formed by the partial submergence of an unglaciated river valley. It is a drowned river valley that remains open to the sea. Typically, rias have a dendritic, treelike outline although they can be straight and without significant branches. This pattern is inherited from the...
marshes. Deltaic marshes are associated with large river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
s where many occur in Southern Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
such as the Camargue
Camargue
The Camargue is the region located south of Arles, France, between the Mediterranean Sea and the two arms of the Rhône River delta. The eastern arm is called the Grand Rhône; the western one is the Petit Rhône....
in the Rhone
Rhône
Rhone can refer to:* Rhone, one of the major rivers of Europe, running through Switzerland and France* Rhône Glacier, the source of the Rhone River and one of the primary contributors to Lake Geneva in the far eastern end of the canton of Valais in Switzerland...
delta or the Ebro
Ebro
The Ebro or Ebre is one of the most important rivers in the Iberian Peninsula. It is the biggest river by discharge volume in Spain.The Ebro flows through the following cities:*Reinosa in Cantabria.*Miranda de Ebro in Castile and León....
delta. They are also highly extensive within the rivers of the Mississippi Delta
Mississippi Delta
The Mississippi Delta is the distinctive northwest section of the U.S. state of Mississippi that lies between the Mississippi and Yazoo Rivers. The region has been called "The Most Southern Place on Earth" because of its unique racial, cultural, and economic history...
. In New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, most salt marshes occur at the head of estuaries in areas where there is little wave action and high sedimentation. Such marshes are located in Awhitu Regional Park in Auckland, the Manawatu Estuary and the Avon-Heathcote Estuary
Avon Heathcote Estuary
The Avon Heathcote Estuary is the largest semi-enclosed shallow estuary in Canterbury and remains one of New Zealand’s most important coastal wetlands. It is well known as an internationally important habitat for migratory birds, and it is an important recreational playground and educational resource...
in Christchurch. Back-barrier marshes are sensitive to the reshaping of barriers in the landward side of which they have been formed. They are common along much of the eastern coast of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and the Frisian Islands
Frisian Islands
The Frisian Islands, also known as the Wadden Islands or Wadden Sea Islands, form an archipelago at the eastern edge of the North Sea in northwestern Europe, stretching from the north-west of the Netherlands through Germany to the west of Denmark...
. Large, shallow coastal embayments can hold salt marshes with examples including Morecambe Bay
Morecambe Bay
Morecambe Bay is a large bay in northwest England, nearly due east of the Isle of Man and just to the south of the Lake District National Park. It is the largest expanse of intertidal mudflats and sand in the United Kingdom, covering a total area of 310 km².-Natural features:The rivers Leven,...
and Portsmouth
Portsmouth
Portsmouth is the second largest city in the ceremonial county of Hampshire on the south coast of England. Portsmouth is notable for being the United Kingdom's only island city; it is located mainly on Portsea Island...
in Britain
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and the Bay of Fundy
Bay of Fundy
The Bay of Fundy is a bay on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine...
in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
Salt marshes are sometime included in lagoons, and the difference is not very marked: e.g. a major part of the Venetian Lagoon
Venetian Lagoon
The Venetian Lagoon is the enclosed bay of the Adriatic Sea in which the city of Venice is situated. Its name in the Venetian language, Laguna Veneta— cognate of Latin lacus, "lake"— has provided the international name for an enclosed, shallow embayment of saltwater, a lagoon.The Venetian Lagoon...
is made up of these sorts of animals and or living organisms belonging to this ecosystem.
Tidal flooding and vegetation zonation
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
flow that occurs and continuously floods the area. It is an important process in delivering sediments, nutrients and plant water supply to the marsh. At higher elevations in the upper marsh
High marsh
High marsh is a tidal marsh zone located above the Mean Highwater Mark which, in contrast to the low marsh zone, is inundated infrequently during periods of extreme high tide and storm surge associated with coastal storms...
zone, there is much less tidal inflow, resulting in lower salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
levels. Soil salinity in the lower marsh
Low marsh
Low marsh is a tidal marsh zone. It is characterized as being flooded daily....
zone is fairly constant due to everyday annual tidal flow. However, in the upper marsh, variability in salinity is shown as a result of less frequent flooding and climate variations. Rainfall can reduce salinity and evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...
can increase levels during dry periods. As a result, there are microhabitats populated by different species of flora
Flora
Flora is the plant life occurring in a particular region or time, generally the naturally occurring or indigenous—native plant life. The corresponding term for animals is fauna.-Etymology:...
and fauna
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
dependant on their physiological abilities. 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
Submersion
Submersion may refer to:*Being underwater or going underwater: see scuba diving or submarine or :wikt:submerge.*Submersion , in the mathematical sense.*Submersion , an episode of the television series Stargate Atlantis....
, and a certain amount of water movement, while plants further inland in the marsh can sometimes experience dry, low-nutrient conditions. It has been found that the upper marsh zones limit species through competition and the lack of habitat protection, while lower marsh zones are determined through the ability of plants to tolerate physiological stresses such as salinity, water submergence and low oxygen levels.
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...
salt marsh is subject to strong tidal influences and shows distinct patterns of zonation. In low marsh areas with high tidal flooding, a monoculture of the smooth cordgrass, Spartina alterniflora
Spartina alterniflora
Spartina alterniflora is a perennial deciduous grass which is found in intertidal wetlands, especially estuarine salt marshes. It grows 1-1.5 m tall, and has smooth, hollow stems which bear leaves up to 20-60 cm long and 1.5 cm wide at their base, which are sharply tapered and bend down...
dominate, then heading landwards, zones of the salt hay, Spartina patens
Spartina patens
Spartina patens , also known as salt marsh hay, is a species of cordgrass native to the Atlantic coast of the Americas, from Newfoundland south along the eastern United States to the Caribbean and northeast Mexico...
, black rush, Juncus gerardii
Juncus gerardii
Juncus gerardii, commonly known as blackgrass, black needle rush or saltmarsh rush, is a member of the family Juncaceae.-Site:...
and the shrub Iva frutescens are seen respectively. These species all have different tolerances that make the different zones along the marsh best suited for each individual.
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 glasswort
Glasswort
Salicornia is a genus of succulent, halophyte plants that grow in salt marshes, on beaches, and among mangroves. Salicornia species are native to North America, Europe, South Africa, and South Asia...
s (Salicornia spp.) and the cordgrass (Spartina spp.), which have worldwide distribution. They are often the first plants to take hold in a mudflat
Mudflat
Mudflats or mud flats, also known as tidal flats, are coastal wetlands that form when mud is deposited by tides or rivers. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of...
and begin its ecological succession
Ecological succession
Ecological succession, is the phenomenon or process by which a community progressively transforms itself until a stable community is formed. It is a fundamental concept in ecology, and refers to more or less predictable and orderly changes in the composition or structure of an ecological community...
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
Plantago is a genus of about 200 species of small, inconspicuous plants commonly called plantains. They share this name with the very dissimilar plantain, a kind of banana. Most are herbaceous plants, though a few are subshrubs growing to 60 cm tall. The leaves are sessile, but have a narrow...
(Plantago spp.), and varied sedges
Cyperaceae
Cyperaceae are a family of monocotyledonous graminoid flowering plants known as sedges, which superficially resemble grasses or rushes. The family is large, with some 5,500 species described in about 109 genera. These species are widely distributed, with the centers of diversity for the group...
and rushes
Juncaceae
Juncaceae, the rush family, are a monocotyledonous family of flowering plants. There are eight genera and about 400 species. Members of the Juncaceae are slow-growing, rhizomatous, herbaceous plants, and they may superficially resemble grasses. They often grow on infertile soils in a wide range...
grow once the mud has been vegetated by the pioneer species
Pioneer species
Pioneer species are species which colonize previously uncolonized land, usually leading to ecological succession. They are the first organisms to start the chain of events leading to a livable biosphere or ecosystem...
.
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. 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 birds.
Human impacts
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
s through land reclamation
Land reclamation
Land reclamation, usually known as reclamation, is the process to create new land from sea or riverbeds. The land reclaimed is known as reclamation ground or landfill.- Habitation :...
for agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
, urban development
Urban planning
Urban planning incorporates areas such as economics, design, ecology, sociology, geography, law, political science, and statistics to guide and ensure the orderly development of settlements and communities....
, salt production
Salt evaporation pond
Salt evaporation ponds, also called salterns or salt pans, are shallow artificial ponds designed to produce salts from sea water or other brines. The seawater or brine is fed into large ponds and water is drawn out through natural evaporation which allows the salt to be subsequently harvested...
and recreation
Recreation
Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasure and are considered to be "fun"...
. The indirect effects of human activities such as nitrogen loading
Eutrophication
Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...
also play a major role in the salt marsh area.
Land reclamation
Reclamation of land for agriculture by converting marshland to upland was historically a common practice. DikesLevee
A levee, levée, dike , embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels...
were often built to allow for this shift in land change and to provide flood protection further inland. For centuries, livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...
such as sheep and cattle grazed on the highly fertile salt marsh land. Land reclamation for agriculture has resulted in many changes such as shifts in vegetation structure, sedimentation, salinity, water flow, biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
loss and high nutrient inputs. There have been many attempts made to eradicate these problems for example, in New Zealand, the cordgrass Spartina anglica
Spartina anglica
Spartina anglica is a species of cordgrass that originated in southern England in about 1870. It is an allotetraploid species derived from the hybrid Spartina × townsendii, which arose when the European native cordgrass Spartina maritima hybridised with the introduced American Spartina...
was introduced from England into the Manawatu River
Manawatu River
The Manawatu River is a major river of the southern North Island of New Zealand.The river has its headwaters to the northwest of Norsewood in the Ruahine Ranges of southern Hawke's Bay. It flows initially eastward before turning south-west near Ormondville, flowing 40 km before turning...
mouth in 1913 to try and reclaim the estuary land for farming. A shift in structure from bare tidal flat to pastureland resulted from increased sedimentation and the cordgrass extended out into other estuaries around New Zealand. Native plants and animals struggled to survive as non-natives out competed them. Efforts are now being made to remove these cordgrass species, as the damages are slowly being recognised.
Nitrogen loading
Following the period of marshland conversion for agriculture, these areas were later transformed into urban, residential and industrial land. Major cities such as BostonBoston
Boston is the capital of and largest city in Massachusetts, and is one of the oldest cities in the United States. The largest city in New England, Boston is regarded as the unofficial "Capital of New England" for its economic and cultural impact on the entire New England region. The city proper had...
, San Francisco, Amsterdam
Amsterdam
Amsterdam is the largest city and the capital of the Netherlands. The current position of Amsterdam as capital city of the Kingdom of the Netherlands is governed by the constitution of August 24, 1815 and its successors. Amsterdam has a population of 783,364 within city limits, an urban population...
, Rotterdam
Rotterdam
Rotterdam is the second-largest city in the Netherlands and one of the largest ports in the world. Starting as a dam on the Rotte river, Rotterdam has grown into a major international commercial centre...
, Venice
Venice
Venice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...
and Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...
have all expanded out into areas of salt marsh. The remaining marshes surrounding these urban areas are under immense pressure from the human population as human-induced nitrogen enrichment enters these habitats.
Nitrogen loading through human-use indirectly affects salt marshes causing shifts in vegetation structure and the invasion of non-native species. Human impacts such as sewage, urban run-off, agricultural and industrial wastes are running into the marshes from nearby sources. Salt marshes are nitrogen limited and with an increasing level of nutrients entering the system from anthropogenic effects, the plant species associated with salt marshes are being restructured through change in competition. For example, the New England salt marsh is experiencing a shift in vegetation structure where S. alterniflora is spreading from the lower marsh where it predominately resides up into the upper marsh zone. Additionally, in the same marshes, the reed Phragmites australis
Phragmites
Phragmites, the Common reed, is a large perennial grass found in wetlands throughout temperate and tropical regions of the world. Phragmites australis is sometimes regarded as the sole species of the genus Phragmites, though some botanists divide Phragmites australis into three or four species...
has been invading the area expanding to lower marshes and becoming a dominant species. P. australis is an aggressive halophyte that can invade disturbed areas in large numbers outcompeting native plants. This loss in biodiversity is not only seen in flora assemblages but also in many animals such as insects and birds as their habitat and food resources are altered.
Mosquito Control
Earlier in the 20th century, it was believed that draining the salt marshes would help mitigate mosquitoMosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
populations. In many locations, particularly in the northeastern United States, residents and local and state agencies dug straight-lined ditches deep into the marsh flats. The end result, however, was a depletion of killifish
Killifish
A killifish is any of various oviparous cyprinodontiform fish . Altogether, there are some 1270 different species of killifish, the biggest family being Rivulidae, containing more than 320 species...
habitat. The killifish is a mosquito predator, so the loss of habitat actually led to higher mosquito populations, and adversely affected wading birds that preyed on the killifish. These ditches can still be seen, though with the realization of the impacts on the marshes' health, some places have begun efforts to refill the ditches.
Restoration and management
The perception of bay salt marshes as a coastal ‘wasteland’ has since changed, acknowledging that they are one of the most biologically productive habitats on earth, rivalling tropical rainforestTropical rainforest
A tropical rainforest is an ecosystem type that occurs roughly within the latitudes 28 degrees north or south of the equator . This ecosystem experiences high average temperatures and a significant amount of rainfall...
s. Salt marshes are ecologically important providing habitats for native migratory fish and acting as sheltered feeding and nursery grounds. They are now protected by legislation in many countries to look after these ecologically important habitats. In the United States and Europe, they are now accorded to a high level of protection by the Clean Water Act
Clean Water Act
The Clean Water Act is the primary federal law in the United States governing water pollution. Commonly abbreviated as the CWA, the act established the goals of eliminating releases of high amounts of toxic substances into water, eliminating additional water pollution by 1985, and ensuring that...
and the Habitats Directive respectively. With the impacts of this habitat and its importance now realised, a growing interest in restoring salt marshes, through managed retreat
Managed retreat
In the context of coastal erosion, managed retreat allows an area that was not previously exposed to flooding by the sea to become flooded by removing coastal protection...
or the reclamation of land has been established. However, many Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
n countries such as China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
are still to recognise the value of marshlands. With their ever-growing populations and intense development along the coast, the value of salt marshes tends to be ignored and the land continues to be reclaimed.
Bakker et al. (1997) suggests two options available for restoring salt marshes. The first is to abandon all human interference and leave the salt marsh to complete its natural development. These types of restoration projects are often unsuccessful as vegetation tends to struggle to revert back to its original structure and the natural tidal cycles are shifted due to land changes. The second option suggested by Bakker et al. (1997) is to restore the destroyed habitat into its natural state either at the original site or as a replacement at a different site. Under natural conditions, recovery can take 2–10 years or even longer depending on the nature and degree of the disturbance and the relative maturity of the marsh involved. Marshes in their pioneer stages of development will recover more rapidly than mature marshes as they are often first to colonize the land. It is important to note, that restoration can often be sped up through the replanting of native vegetation.
Typha angustifolia
Typha angustifolia L., , is a perennial herbaceous plant of genus Typha. This cattail is an "obligate wetland" species that is commonly found in the northern hemisphere in brackish locations...
and T. latifolia
Typha latifolia
Typha latifolia is a perennial herbaceous plant in the genus Typha. It is found as a native plant species in North and South America, Europe, Eurasia, and Africa...
that have little ecological connection to the area. By 1980, a restoration programme was put in place that has now been running for over 20 years. This programme has aimed to reconnect the marshes by returning tidal flow along with the ecological functions and characteristics of the marshes back to their original state. In the case of Barn Island, declines in the invasive species have initiated, re-establishing the tidal-marsh vegetation along with animal species such as fish and insects. This example highlights that considerable time and effort is needed to effectively restore salt marsh systems. Times in marsh recovery can depend on the development stage of the marsh; type and extent of the disturbance; geographical location; and the environmental and physiological stress factors to the marsh-associated flora and fauna.
Although much effort has gone into restoring salt marshes worldwide, further research is needed. There are many setbacks and problems associated with marsh restoration that requires careful long-term monitoring. Information on all components of the salt marsh ecosystem should be understood and monitored from sedimentation, nutrient, and tidal influences, to behaviour patterns and tolerances of both flora and fauna species. Once we have a better understanding of these processes and not just locally, but over a global scale, we can then suggest more sound and practical management and restoration efforts that can be used to preserve our valuable marshes and put them back to their original state.
While humans are situated along coastlines, there will always be the possibility of human-induced disturbances despite the number of restoration efforts we plan to implement. Dredging, pipelines for offshore petroleum resources, highway construction, accidental toxic spills or just plain carelessness are examples that will for some time now and into the future be the major influences of salt marsh degradation.
In addition to restoring and managing salt marsh systems based on scientific principles, the opportunity should be taken to educate public audiences of their importance biologically and their purpose as serving as a natural buffer for flood protection. Because salt marshes are often located next to urban areas, they are likely to receive more visitors than remote wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....
s. By physically seeing the marsh, people are more likely to take notice and be more aware of the environment around them. An example of public involvement occurred at the Famosa Slough wetland in San Diego, where a “friends” group worked for over a decade in trying to prevent the area from being developed. Eventually, the 5 hectare site was bought by the City and the group worked together to restore the area. The project involved removing invasive species and replanting with natives, along with public talks to other locals, frequent bird walks and clean-up events.
See also
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Marsh In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss.... Mesopotamian Marshes The Mesopotamian Marshes are a wetland area located in southern Iraq and partially in southwestern Iran. Historically the marshlands, mainly composed of the separate but adjacent Central, Hawizeh and Hammar Marshes, used to be the largest wetland ecosystem of Western Eurasia... Outwelling Outwelling is a hypothesized process by which coastal salt marshes and mangroves, “hot spots” of production, produce an excess amount of carbon each year and “outwell” these organic nutrients and detritus into the surrounding coastal embayment or ocean, thus increasing the productivity of local... Seagrass Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:... Swamp A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp... Tidal marsh 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 . According to the salinity of the flooding water, freshwater, brackish and saline tidal marshes are... Brackish marsh Brackish marshes develop by salt marshes where a significant freshwater influx dilute the seawater to brackish levels of salinity. This commonly happens upstream salt marshes by estuaries of coastal rivers or near the mouths of coastal rivers with heavy freshwater discharges in the conditions of... Freshwater marsh A freshwater marsh is a marsh that contains fresh water. They are usually found near the mouths of rivers and are present in areas with low drainage. The Florida Everglades, the largest freshwater marsh in the United States, are an example of this type of marsh.... |
Further reading
External links
- Friends of Famosa Slough
- Geography resource for schools
- Johnson, CY (2006). Cause sought as marshes turn into barren flats. The Boston Globe.
- Marine Nature Study Area operated by the Town of Hempstead: Dept. of Conservation & Waterways, located in Oceanside, New York, USA
- New England Sudden Wetland Dieback
- Salt Marsh Nature Center located in the Marine ParkMarine ParkMarine Park is a neighborhood located in the New York City borough of Brooklyn, that lies between Mill Basin and Gerritsen Beach. The neighborhood is mostly squared off in area by Gerritsen Avenue, Flatbush Avenue, Avenue U and Kings Highway. It partly surrounds the eponymous park. The neighborhood...
section of Brooklyn, New York, USA