Brackish water

"Brackish" redirects here. For the Kittie song, seeSpit (album).

Brackish water,sometimes termedbrack water,is water occurring in a natural environment that has moresalinitythanfreshwater,but not as much asseawater.It may result from mi xing seawater (salt water) and fresh water together, as inestuaries,or it may occur in brackishfossil aquifers.The word comes from the Middle Dutch rootbrak.Certain human activities can produce brackish water, in particularcivil engineeringprojects such as dikes and the flooding of coastalmarshlandto produce brackish water pools forfreshwater prawn farming.Brackish water is also the primary waste product of thesalinity gradient powerprocess. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it is damaging to the environment (see article onshrimp farms).

Technically, brackish water contains between 0.5 and 30 grams ofsaltper litre—more often expressed as 0.5 to 30parts per thousand(‰), which is aspecific gravityof between 1.0004 and 1.0226. Thus,brackishcovers a range ofsalinity regimesand 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. Water with a salt concentration greater than 30‰ is consideredsaline.Seethe salinity tablefrom theWikipedia salinity article.

Brackish water habitats

Estuaries

A brackish water fish:Monodactylus argenteus

Brackish water condition commonly occurs when fresh water meets seawater. In fact, the most extensive brackish water habitats worldwide areestuaries,where a river meets the sea.

TheRiver Thamesflowing throughLondonis a classic river estuary. The town ofTeddingtona few miles west of London marks the boundary between thetidaland non-tidal parts of the Thames, although it is still considered a freshwater river about as far east asBatterseainsofar as the average salinity is very low and the fish fauna consists predominantly of freshwater species such asroach,dace,carp,perch,andpike.TheThames Estuarybecomes brackish between Battersea andGravesend,and the diversity of freshwater fish species present is smaller, primarily roach and dace;euryhalinemarine species such asflounder,European seabass,mullet,andsmeltbecome 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 adjacentNorth Seaand includes both euryhaline andstenohalinemarine species. A similar pattern of replacement can be observed with the aquatic plants and invertebrates living in the river.

This type ofecological successionfrom freshwater to marineecosystemis typical of river estuaries. River estuaries form important staging points during the migration ofanadromous and catadromousfish species, such assalmon,shadandeels,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.Herringandplaiceare 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 salmonfarms are often located in estuaries, although this has caused controversy, because in doing so, fish farmers expose migrating wild fish to large numbers of externalparasitessuch assea licethat escape from the pens the farmed fish are kept in.

Mangroves

Main article:Mangrove

Another important brackish water habitat is themangrove swampormangal.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 aremudskippers,fish that forage for food on land, andarcher 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 assnappers,halfbeaks,andtarponspawning or maturing among them. Besides fish, numerous other animals use mangroves, including such species as thesaltwater crocodile,American crocodile,proboscis monkey,diamondback terrapin,and thecrab-eating frog,Fejervarya cancrivora(formerlyRana cancrivora). Mangroves represent important nesting sites for numerous birds groups such as herons, storks, spoonbills, ibises, kingfishers, shorebirds and seabirds.

Although often plagued withmosquitoesand 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.

TheSundarbansandBhitarkanika Mangrovesare two of the large mangrove forests in the world, both on the coast of theBay of Bengal.

Brackish seas and lakes

See also:Salt lake

Some seas and lakes are brackish. TheBaltic Seais a brackish sea adjoining theNorth Sea.Originally theEridanosriver system prior to thePleistocene,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. Asseawateris denser, the water in the Baltic is stratified, with seawater at the bottom and freshwater at the top. Limited mi xing 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.Codare an example of a species only found in deep water in the Baltic, whilepikeare confined to the less saline surface waters.

TheCaspian Seais 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 (theCaspian seal) and the greatsturgeons,a major source ofcaviar.

Hudson Bayis a brackishmarginal seaof theArctic Ocean,it remains brackish due its limited connections to the open ocean, very high levels freshwatersurface runoffinput from the largeHudson Bay drainage basin,and low rate of evaporation due to being completely covered in ice for over half the year.

In theBlack Seathe 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,anoxicwater of the Black Sea originates from warm, salty water of theMediterranean.

Lake Texoma,a reservoir on the border between the U.S. states ofTexasandOklahoma,is a rare example of a brackish lake that is neither part of anendorheic basinnor 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 theRed 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 thatstriped bass,a fish normally found only in salt water, has self-sustaining populations in the lake.

Brackish marsh

Main article:Brackish marsh

Other brackish bodies of water

• Anchialine pool– Landlocked body of water with underground connection to the seaPages displaying short descriptions of redirect targets

Human uses

Brackish water is being used by humans in many different sectors. It is commonly used as cooling water for power generation and in a variety of ways in the mining, oil, and gas industries. Oncedesalinatedit can also be used for agriculture, livestock, and municipal uses.Brackish water can be treated usingreverse osmosis,electrodialysis,and other filtration processes.

See also

• List of brackish bodies of water
• Biosalinity– Use of salty water for irrigation
• Brackish-water aquarium– aquarium with brackish waterPages displaying wikidata descriptions as a fallback
• Desalination– Removal of salts from water
• Halocline– Stratification of a body of water due to salinity differences

Further reading

• Moustakas, A. & I. Karakassis. How diverse is aquatic biodiversity research?, Aquatic Ecology,39,367-375