Brackish marshes develop from

salt marsh A salt marsh or saltmarsh, 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 domin ...

es where a significant freshwater influx dilutes the

seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appr ...

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estu ...

levels of salinity. This commonly happens upstream from salt marshes by

estuaries 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 environmen ...

of coastal rivers or near the mouths of coastal rivers with heavy freshwater discharges in the conditions of low

tidal range Tidal range is the difference in height between high tide and low tide. Tides are the rise and fall of sea levels caused by gravitational forces exerted by the Moon and Sun and the rotation of Earth. Tidal range depends on time and location. ...

Characteristics

The salinity levels in brackish marshes can range from 0.5 ppt to 35 ppt. Marshes are also characterised by low-growing vegetation and bare mud or sand flats. Due to the variations in salinity, brackish marshes create a distinctive

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

where plants from either freshwater or saltwater marshes can co-inhabit. The salinity levels also change with the tides, decreasing at low tide and increasing at high tide as

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

water feeds farther upriver.

Biodiversity

In terms of

biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...

, a brackish marsh serves a unique

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for ...

. Its vegetation is a byproduct of its salinity levels. High salinity serves as an evolutionary barrier for most plants, creating a less diverse number of plant species as an ecosystem moves from fresh to saltwater. Thus, there are only a few colonies of saltwater native plants in freshwater and almost no freshwater plants in saltwater ecosystems. However, in brackish marshes both types of plants are prevalent and are in fact high in plant productivity. Examples include, arrow arum (''

Peltandra virginica ''Peltandra virginica'' is a plant of the arum family known as green arrow arum and tuckahoe. It is widely distributed in wetlands in the eastern United States, as well as in Quebec, Ontario, and Cuba.Whigham, Dennis F., Robert L. Simpson and Ma ...

''), soft rush ''(

Juncus effusus ''Juncus effusus'', with the common names common rush or soft rush, is a perennial herbaceous flowering plant species in the rush family Juncaceae. In North America, the common name soft rush also refers to '' Juncus interior''. Distribution ' ...

)'', cattail ('' Typha''), and sawgrass (''

Cladium ''Cladium'' (fen-sedge, sawgrass or twig-sedge) is a genus of large sedges, with a nearly worldwide distribution in tropical and temperate regions. These are plants characterized by long, narrow (grass-like) leaves having sharp, often serrated ( ...

''). These plants are usually

halophytic A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs and seashores. ...

in order to survive these conditions. For example brackish sites in Georgia, U.S., are dominated by species such as smooth cord grass ( ''Sporobolus'' ''alterniflora)'', big cordgrass (''

Spartina cynosuroides ''Sporobolus cynosuroides'' is a species of grass known by the common names big cordgrass and salt reedgrass. It is native to the East Coast and Gulf Coast of the United States, where it grows in coastal habitat such as marshes, lagoons, and bays ...

)'', and black rush (''

Juncus roemerianus ''Juncus roemerianus'' is a species of flowering plant in the rush family known by the common names black rush, needlerush, and black needlerush. It is native to North America, where its main distribution lies along the coastline of the southeas ...

)''. Other communities are cabbage palm (''

Sabal palmetto ''Sabal palmetto'' (, '' SAY-bəl''), also known as cabbage palm, cabbage palmetto, sabal palm, blue palmetto, Carolina palmetto, common palmetto, Garfield's tree, and swamp cabbage, is one of 15 species of palmetto palm. It is native to the So ...

''), sand cordgrass ('' Spartina bakeri''), black rush (''

''), saltgrass (''

Distichlis spicata ''Distichlis spicata'' is a species of grass known by several common names, including seashore saltgrass, inland saltgrass, and desert saltgrass. This grass is native to the Americas, where it is widespread. It can be found on other continents a ...

'', ''

Paspalum distichum ''Paspalum distichum'' is a species of grass. Common names include knotgrass, water finger-grass, couch paspalum, eternity grass, gingergrass, and Thompson grass. Its native range is obscure because it has long been present on most continents, an ...

''), and mixed halophytes ('' Batis maritima'', ''Salicomia virginica''). Along with salinity, brackish marshes face high physical stress due to

flooding A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrolog ...

and wave currents creating adaptive traits within the plant community. These plant communities also create an environment that provides a nursery for juvenile fish,

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

s, and birds.

Fauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is ''funga''. Flora, fauna, funga and other forms of life are collectively referred to as ''Biota (ecology ...

use the shallow habitat and the turbidity of the water to protect themselves from predators. Similarly the surface of the marsh is covered with vegetation which is used by the

nekton Nekton or necton (from the ) refers to the actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms t ...

species for shelter, leaving enough space to move underneath between the stems. The

trophic levels The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it i ...

within a brackish marsh has been shown to depend on the amount of macro organic matter in the upper level of

soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...

. This macro organic matter is believed to be the food source of detritivore benthic animals that support higher trophic levels. These materials build up as the marsh matures, making age another factor in the biodiversity of a brackish marsh.

Human use and impacts

Brackish marshes are very important for

flood control Flood control methods are used to reduce or prevent the detrimental effects of flood waters."Flood Control", MSN Encarta, 2008 (see below: Further reading). Flood relief methods are used to reduce the effects of flood waters or high water level ...

. However, they are often subject to heavy pollution and

habitat degradation Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...

from land reclamation. For example, the Indian River Lagoon has suffered significant man-made changes since the 1940s. Marshes were often

dredged Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing da ...

or impounded to prevent mosquitoes, however this led to the disruption of connectivity by replacing marshes with open water. These changes prevented fires that allowed invasive species to move into the remaining marshes. Brackish marshes can be restored by human intervention. Studies have found that given that

restoration Restoration is the act of restoring something to its original state and may refer to: * Conservation and restoration of cultural heritage ** Audio restoration ** Film restoration ** Image restoration ** Textile restoration * Restoration ecology ...

is properly carried out, fish do not discriminate between restored or natural marshes.

Conservation and threats

As in most habitats, the greatest threat towards brackish marshes are humans. Traditionally, direct human activities such as dredging and development are the main cause of destruction. Pollution has also been a threat to brackish marshes through chemical run-off. Once degraded, it could take at least 30 to 90 years for restored marsh soil to become equivalent to a natural marsh in terms of

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

and

organic carbon Total organic carbon (TOC) is the amount of carbon found in an organic compound and is often used as a non-specific indicator of water quality or cleanliness of pharmaceutical manufacturing equipment. TOC may also refer to the amount of organic c ...

profile. In some cases, these process could take over 200 years to achieve the wetland soil characteristics of certain communities. For conservation, the key is to restrict human activities. Installing a passive management system could help restore certain species using brackish marshes' role as an ecological nursery. For some areas, periodic livestock

grazing In agriculture, grazing is a method of animal husbandry whereby domestic livestock are allowed outdoors to roam around and consume wild vegetations in order to convert the otherwise indigestible (by human gut) cellulose within grass and other ...

could help create a better habitat for certain species of birds. Brackish marshes are a unique type of wetland and the local circumstances are paramount to consider for either conservation, biodiversity, or restoration.

References

{{Wetlands Coastal geography Salt marshes Marine biology

Characteristics

Biodiversity

Human use and impacts

Conservation and threats

See also

References