Brackish water is water having more salinity than freshwater, but not as much as seawater. It may result from mixing seawater with fresh water together, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak". Certain human activities can produce brackish water, in particular civil engineering projects such as dikes and the flooding of coastal marshland to produce brackish water pools for freshwater prawn farming. Brackish water is also the primary waste product of the salinity gradient power process. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it is damaging to the environment (see article on shrimp farms).
Technically, brackish water contains between 0.5 and 30 grams of salt per litre—more often expressed as 0.5 to 30 parts per thousand (‰), which is a specific gravity of between 1.005 and 1.010. Thus, brackish covers a range of salinity regimes and is not considered a precisely defined condition. It is characteristic of many brackish surface waters that their salinity can vary considerably over space or time.
Brackish water condition commonly occurs when fresh water meets seawater. In fact, the most extensive brackish water habitats worldwide are estuaries, where a river meets the sea.
The River Thames flowing through London is a classic river estuary. The town of Teddington a few miles west of London marks the boundary between the tidal and non-tidal parts of the Thames, although it is still considered a freshwater river about as far east as Battersea insofar as the average salinity is very low and the fish fauna consists predominantly of freshwater species such as roach, dace, carp, perch, and pike. The Thames Estuary becomes brackish between Battersea and Gravesend, and the diversity of freshwater fish species present is smaller, primarily roach and dace; euryhaline marine species such as flounder, European seabass, mullet, and smelt become much more common. Further east, the salinity increases and the freshwater fish species are completely replaced by euryhaline marine ones, until the river reaches Gravesend, at which point conditions become fully marine and the fish fauna resembles that of the adjacent North Sea and includes both euryhaline and stenohaline marine species. A similar pattern of replacement can be observed with the aquatic plants and invertebrates living in the river.
This type of ecological succession from a freshwater to marine ecosystem is typical of river estuaries. River estuaries form important staging points during the migration of anadromous and catadromous fish species, such as salmon, shad, and eels, giving them time to form social groups and to adjust to the changes in salinity. Salmon are anadromous, meaning they live in the sea but ascend rivers to spawn; eels are catadromous, living in rivers and streams, but returning to the sea to breed. Besides the species that migrate through estuaries, there are many other fish that use them as "nursery grounds" for spawning or as places young fish can feed and grow before moving elsewhere. Herring and plaice are two commercially important species that use the Thames Estuary for this purpose.
Estuaries are also commonly used as fishing grounds, and as places for fish farming or ranching. For example, Atlantic salmon farms are often located in estuaries, although this has caused controversy, because in doing so, fish farmers expose migrating wild fish to large numbers of external parasites such as sea lice that escape from the pens the farmed fish are kept in.
Another important brackish water habitat is the mangrove swamp or mangal. Many, though not all, mangrove swamps fringe estuaries and lagoons where the salinity changes with each tide. Among the most specialised residents of mangrove forests are mudskippers, fish that forage for food on land, and archer fish, perch-like fish that "spit" at insects and other small animals living in the trees, knocking them into the water where they can be eaten. Like estuaries, mangrove swamps are extremely important breeding grounds for many fish, with species such as snappers, halfbeaks, and tarpon spawning or maturing among them. Besides fish, numerous other animals use mangroves, including such species as the saltwater crocodile, American crocodile, proboscis monkey, diamondback terrapin, and the crab-eating frog, Fejervarya cancrivora (formerly Rana cancrivora). Mangroves represent important nesting site for numerous birds groups such as herons, storks, spoonbills, ibises, kingfishers, shorebirds and seabirds.
Although often plagued with mosquitoes and other insects that make them unpleasant for humans, mangrove swamps are very important buffer zones between land and sea, and are a natural defense against hurricane and tsunami damage in particular.
Some seas and lakes are brackish. The Baltic Sea is a brackish sea adjoining the North Sea. Originally the confluence of two major river systems prior to the Pleistocene, since then it has been flooded by the North Sea but still receives so much freshwater from the adjacent lands that the water is brackish. Because the salt water coming in from the sea is denser than freshwater, the water in the Baltic is stratified, with salt water at the bottom and freshwater at the top. Limited mixing occurs because of the lack of tides and storms, with the result that the fish fauna at the surface is freshwater in composition while that lower down is more marine. Cod are an example of a species only found in deep water in the Baltic, while pike are confined to the less saline surface waters.
The Caspian Sea is the world's largest lake and contains brackish water with a salinity about one-third that of normal seawater. The Caspian is famous for its peculiar animal fauna, including one of the few non-marine seals (the Caspian seal) and the great sturgeons, a major source of caviar.
The Hudson Bay is a brackish marginal sea of the Arctic ocean, it remains brackish due its limited connections to the open ocean, very high levels freshwater surface runoff input from the large Hudson Bay drainage basin, and low rate of evaporation due to being completely covered in ice for over half the year.
In the Black Sea the surface water is brackish with an average salinity of about 17-18 parts per thousand compared to 30 to 40 for the oceans. The deep, anoxic water of the Black Sea originates from warm, salty water of the Mediterranean.
Lake Texoma, a reservoir on the border between the U.S. states of Texas and Oklahoma, is a rare example of a brackish lake that is neither part of an endorheic basin nor a direct arm of the ocean, though its salinity is considerably lower than that of the other bodies of water mentioned here. The reservoir was created by the damming of the Red River of the South, which (along with several of its tributaries) receives large amounts of salt from natural seepage from buried deposits in the upstream region. The salinity is high enough that striped bass, a fish normally found only in salt water, has self-sustaining populations in the lake.
A brackish marsh may occur where a freshwater flow enters a salt marsh.
Brackish water lakes
Coastal lagoons, marshes, and deltas
Indonesia produced 490000 tons of shrimp in 2004, which was 8% of the world production for the year. In 1999, 507.513 ha of Indonesia was occupied by aquaculture, 60% of which being brackish water ponds, 28% being integrated rice-fish farming, and 12% being freshwater ponds.Inland waters include rivers, lakes, swamps, reservoirs or dams, fields and ponds. Aquaculture can be divided into two types namely brackish water fisheries and freshwater fisheries. Indonesian brackish water fisheries in the north coast of Java do a lot, the east coast of Aceh, Riau, North Sumatra and South Sumatra.Ariidae
The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones. The family includes about 143 species.Bayou
In usage in the United States, a bayou () is a body of water typically found in a flat, low-lying area, and can be either an extremely slow-moving stream or river (often with a poorly defined shoreline), or a marshy lake or wetland. The term bayou can also refer to a creek whose current reverses daily due to tides and which contains brackish water highly conducive to fish life and plankton. Bayous are sometimes paved to help prevent flooding. Bayous are commonly found in the Gulf Coast region of the southern United States, notably the Mississippi River Delta, with the states of Louisiana and Texas being famous for them. A bayou is frequently an anabranch or minor braid of a braided channel that is moving much more slowly than the mainstem, often becoming boggy and stagnant. Though fauna varies by region, many bayous are home to crawfish, certain species of shrimp, other shellfish, catfish, frogs, toads, American alligators, American crocodiles, herons, turtles, spoonbills, snakes, leeches, and many other species.Brackish-water aquarium
A brackish-water aquarium is an aquarium where the water is brackish (semi-salty). The range of "saltiness" varies greatly, from near freshwater to near marine and is often referred to as specific gravity (SG) or salinity. Brackish water aquaria is a popular specialization within the fishkeeping hobby. Many species of fish traded as freshwater species are actually true brackish species, for example mollies, Florida flagfish, and some cichlids such as chromides and black-chin tilapia. There are also several popular species traded purely as brackish water fish, including monos spp, scats, archerfish, and various species of pufferfish, goby, flatfish, and gar. Generally, aquarists need to maintain a specific gravity of around 1.005 to 1.010 depending on the species being kept, but practically all brackish water fish tolerate variations in salinity well, and some aquarists maintain that regularly fluctuating the salinity in the aquarium actually keeps the fish healthy and free of parasites.Brine
Brine is a high-concentration solution of salt (usually sodium chloride) in water. In different contexts, brine may refer to salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of solutions used for brining foods) up to about 26% (a typical saturated solution, depending on temperature). Lower levels of concentration are called by different names: fresh water, brackish water, and saline water.
Brine naturally occurs on the Earth's surface (salt lakes), crust, and within brine pools on ocean bottom. High-concentration brine lakes typically emerge due to evaporation of ground saline water on high ambient temperatures. Brine is used for food processing and cooking (pickling and brining), for de-icing of roads and other structures, and in a number of technological processes. It is also a by-product of many industrial processes, such as desalination, and may pose an environmental risk due to its corrosive and toxic effects, so it requires wastewater treatment for proper disposal.Common roach
The roach (Rutilus rutilus), also known as the common roach, is a fresh and brackish water fish of the Cyprinidae family, native to most of Europe and western Asia. Fishes called roach can be any species of the genera Rutilus and Hesperoleucus, depending on locality. The plural of the term is also roach.Eastern Coastal Plains
The Eastern Coastal Plains is a wide stretch of landmass of India, lying between the Eastern Ghats and the Bay of Bengal. It is wider and leveled than the Western Coastal Plains and stretches from Tamil Nadu in the south to West Bengal in the north through Andhra Pradesh and Odisha. Chilka Lake is a brackish water lake along the eastern coastal plain. It lies in the state of Odisha and stretches to the south of the Mahanadi Delta.Deltas of many of India's rivers form a major portion of these plains. The Mahanadi, Godavari, Kaveri and Krishna rivers drain these plains. The region receives both the Northeast & Southwest monsoon rains with its annual rainfall averaging between 1,000 and 3,000 mm (39 and 118 in). The width of the plains varies between 100 and 120 km (62 to 80 miles).
It is locally known as Utkal Plains in the Northern part between Kangsabati and Rushikulya Rivers, Northern Circars in the Central part between Rushikulya and Krishna Rivers and, as Coromandel Coast in the Southern part from the south of river Krishna till the Southern tip of Mainland India at Cape Comorin where it merges .Euryhaline
Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly (Poecilia sphenops) which can live in fresh water, brackish water, or salt water. The green crab (Carcinus maenas) is an example of a euryhaline invertebrate that can live in salt and brackish water. Euryhaline organisms are commonly found in habitats such as estuaries and tide pools where the salinity changes regularly. However, some organisms are euryhaline because their life cycle involves migration between freshwater and marine environments, as is the case with salmon and eels.
The opposite of euryhaline organisms are stenohaline ones, which can only survive within a narrow range of salinities. Most freshwater organisms are stenohaline, and will die in seawater, and similarly most marine organisms are stenohaline, and cannot live in fresh water.Fresh water
Fresh water (or freshwater) is any naturally occurring water except seawater and brackish water. Fresh water includes water in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams, and even underground water called groundwater. Fresh water is generally characterized by having low concentrations of dissolved salts and other total dissolved solids. Though the term specifically excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs.
Fresh water is not the same as potable water (or drinking water). Much of the earth's fresh water (on the surface and groundwater) is unsuitable for drinking without some treatment. Fresh water can easily become polluted by human activities or due to naturally occurring processes, such as erosion.
Water is critical to the survival of all living organisms. Some organisms can thrive on salt water, but the great majority of higher plants and most mammals need fresh water to live.Freshwater bivalve
Freshwater bivalves are one kind of freshwater molluscs, along with freshwater snails. They are bivalves which live in freshwater, as opposed to saltwater, the main habitat type for bivalves.
The majority of species of bivalve molluscs live in the sea, but in addition, a number of different families live in freshwater (and in some cases also in brackish water). These families belong to two different evolutionary lineages (freshwater mussels and freshwater clams), and the two groups are not closely related.
Freshwater bivalves live in many types of habitat, ranging from small ditches and ponds, to lakes, canals, rivers, and swamps.
Species in the two groups vary greatly in size. Some of the pea clams (Pisidium species) have an adult size of only 3 mm. In contrast, one of the largest species of freshwater bivalves is the swan mussel, in the family Unionidae; it can grow to a length of 20 cm, and usually lives in lakes or slow rivers.
Freshwater pearl mussels are economically important as a source of freshwater pearls and mother of pearl.Green chromide
The green chromide (Etroplus suratensis) is a species of Cichlid fish from freshwater and brackish water in southern India and Sri Lanka. Other common names include pearlspot cichlid, banded pearlspot, and striped chromide. In Kerala in India it is known locally as the Karimeen. In Goa the fish is known as Kalundar
In Sri Lanka this fish is known as Koraliya
This fish is native to Sri Lanka and coastal regions of India. Many species have been introduced in various parts of the world, including Singapore, where it occurs in estuaries.The adult is oval in shape with a short snout. It is gray-green in color with dark barring and a dark spot at the base of the pectoral fin. It commonly reaches 20 centimetres (7.9 in) in length, and the maximum length is twice that.This species lives in brackish water habitat types, such as river deltas. It eats mainly aquatic plants, but it consumes the occasional mollusk, diatoms, and other animal matter. This species engages in attentive parental care in which several adults care for each brood.In Sri Lanka local name for this fish is Koraliya (කොරළියා). In 2010 this species was named the official state fish of Kerala. The following year was declared "The Year of the Karimeen". Karimeen Pollichatthu, a fried dish, is a delicacy served in restaurants. It is familiar to tourists, but because it is very expensive it is not easily accessible to poor folks. Production of the species for food is expected to increase in the near future.They are closely related to the Paretroplus fishes from Madagascar.Etroplus suratensis and E. maculatus form the main species and the former is dominant among Pearl spots in reservoirs of India. They mainly feed
on detritus and occupy the same niche as that of Oreochromis mossambicus. These fishes are very popular food fishes but their biomass is very low in reservoirs compared to other cichlids.Hydrobiidae
Hydrobiidae, commonly known as mud snails, is a large cosmopolitan family of very small freshwater and brackish water snails with an operculum; they are in the order Littorinimorpha.List of brackish aquarium fish species
This is a list of commonly seen fish that can be kept in a brackish water aquarium.List of brackish aquarium plant species
Aquatic plants are used to give the aquarium a natural appearance, oxygenate the water, and provide habitat for fish, especially fry (babies) and for invertebrates. Some aquarium fish and invertebrates also eat live plants. Hobby aquarists use aquatic plants for aquascaping.
Brackish plants are known to occur in brackish water.Neritidae
Neritidae, common name the nerites, is a taxonomic family of small- to medium-sized saltwater and freshwater snails which have a gill and a distinctive operculum.
The family Neritidae includes marine genera such as Nerita, marine and freshwater genera such as Neritina, and freshwater and brackish water genera such as Theodoxus.
The common name "nerite" as well as the family name Neritidae and the genus name Nerita, are derived from the name of Nerites, who was a sea god in Greek mythology.Northern river shark
The northern river shark or New Guinea river shark (Glyphis garricki) is a species of requiem shark, in the family Carcharhinidae, found in scattered tidal rivers and associated coastal waters in northern Australia and in Papua New Guinea. This species inhabits areas with poor visibility, soft bottoms, and large tides, with immature sharks ranging into fresh and brackish water. It is similar to other river sharks in having a stocky grey body with a high back, tiny eyes, and broad fins. It measures up to 2.5 m (8.2 ft) long.
Northern river sharks are likely piscivorous. This species is viviparous, with females bearing litters of 9 young possibly every other year before the wet season. Very rare and facing threats from commercial and recreational fishing, and perhaps also habitat degradation, this species has been assessed as critically endangered by the International Union for Conservation of Nature.Rissooidea
Rissooidea, originally named Rissoacea by Gray, 1847, is a taxonomic superfamily of small and minute marine snails, belonging to the clade Littorinimorpha.With their phylogenetic analysis of rissooidean and cingulopsoidean families, Criscione F. & Ponder W.F. (2013) have created the superfamily Truncatelloidea containing many families previously included in the superfamily Rissooidea. They have shown that Rissooidea was not monophyletic, encompassing two major clades, i.e. Risooidea s.s. and Truncatelloidea. The freshwater, brackish water, and semi-terrestrial families and genera were brought under Truncatelloidea.Terrapin
A terrapin is one of several small species of turtle living in fresh or brackish water. Terrapins do not form a taxonomic unit and may not be related. Many belong to the families Geoemydidae and Emydidae.
The name "terrapin" is derived from torope, a word in the Native American Algonquian language that referred to the species, Malaclemys terrapin. It appears that it became part of common usage during the colonial era of North America and was carried back to Great Britain. Since then, it has been used in common names for testudines in the English language.Yoldia Sea
Yoldia Sea is a name given by geologists to a variable brackish-water stage in the Baltic Sea basin that prevailed after the Baltic ice lake was drained to sea level during the Weichsel glaciation. Dates for the Yoldia sea are obtained mainly by radiocarbon dating material from ancient sediments and shore lines and from clay-varve chronology.
They tend to vary by as much as a thousand years, but a good estimate is 10,300 – 9500 radiocarbon years BP, equivalent to ca 11,700-10,700 calendar years BP. The sea ended gradually when isostatic rise of Scandinavia closed or nearly closed its effluents, altering the balance between saline and fresh water. The Yoldia Sea became Ancylus Lake. The Yoldia Sea stage had three phases of which only the middle phase had brackish water.
The name of the sea is adapted from the obsolete name of the bivalve, Portlandia arctica (previously known as Yoldia arctica), found around Stockholm. This bivalve requires cold saline water.
It characterizes the middle phase of the Yoldia Sea, during which saline water poured into the Baltic, before the acceleration of glacial melting.