Brackish water

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

Brackish water is water that is saltier than fresh water, but not as salty as sea water. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur as in brackish fossil aquifers. 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 (ppt or ‰). 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 and/or time.

Water salinity based on dissolved salts in parts per thousand (‰)
Fresh water	Brackish water	Saline water	Brine
< 0.5 ‰	0.5 - 30 ‰	30 - 50 ‰	> 50 ‰

Etymology

The term brackish water derives from the (Middle)Dutch word brakwater, which is the water of a brack. A brack is a small lake created when a storm tide breaks a dike and floods land behind the dike.

Brackish water habitats

The most important brackish water habitats are estuaries, where a river meet the sea. The River Thames flowing through London is one of the most familiar of all river estuaries. The town of Teddington a few miles west of London marks the limit of the tidal part of the Thames, although it is still a freshwater river about as far west as Battersea. In this section, the fish fauna consists predominantly of freshwater species such as roach, dace, carp, perch, and pike. The Thames becomes brackish between Battersea and Gravesend, and the fish fauna comprises a limited selection of freshwater species, particularly roach and dace, as well as euryhaline marine species such as flounder, European seabass, mullet, and smelt. Further east, the salinity increases and the freshwater fish species are completely replaced by 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. A similar pattern of replacement can be observed with the aquatic plants and invertebrates living in the river [http://www.the-river-thames.co.uk/wildlife.htm.

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 and catadromus" target="_blank" >^* fish species, such as salmon 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 used as fishing grounds and as places for fish farming or ranching. Atlantic salmon farms are often located in estuaries, for example, though 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 lagoon 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, magrove 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 specialists as the American crocodile, proboscis monkey, diamondback terrapin, and the crab-eating frog, Rana cancrivora. Although often plagued with mosquitoes and other insects that make them unpleasant places to visit, 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. Orginally the confluence of two major river systems prior to the Pleistocene, since that 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 more dense 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 caviare.

Notable brackish bodies of water

Brackish seas

Baltic Sea (the world’s largest pool of brackish water)
Caspian Sea (world’s largest lake)

Brackish water lakes

Chilka Lake, in Orissa state, India
Pangong Tso in Ladakh, Jammu and Kashmir state, India

Coastal lagoons, marshes, and deltas

Kaliveli Lake, near Pondichery, India
Lagos Lagoon in Lagos, Nigeria
Lake Pontchartrain, north of New Orleans, Louisiana, USA
Pulicat Lake, north of Chennai, India
The Rann of Kutch, on the border of India and Pakistan
Parts of the Rhône Delta, France: An area known as the Camargue

Estuaries

Amazon River, empties so much freshwater into the Atlantic Ocean that it reduces the salinity of the sea for hundreds of miles
Chesapeake Bay, in Virginia and Maryland, USA
The Fleet lagoon, Dorset, England
Hampton Roads, Virginia, USA
Port Royal Sound part of Beaufort County, South Carolina, USA ^*
Lower Hudson River, in New York and New Jersey, USA
Lingding Yang, Guangdong, China
The Thames Estuary in east London

Brackish water aquaria

Keeping brackish water aquaria is a popular specialization within the fishkeeping hobby. Many species of fish traded as freshwater species actually do better in brackish water, for example black mollies, Florida flagfish, and some cichlids such as orange chromides. There are also several popular species traded purely as brackish water fish, including Monodactylus 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.

External links

Brackish Water Aquarium FAQ

Liquid water

Gourt Home::Gourt :: Brackish water

Etymology

Brackish water habitats

Notable brackish bodies of water

Brackish water aquaria

See also

External links