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Brackish

Brackish refers to water with a salinity intermediate to that of freshwater and sea water (the latter has a salt concentration of about 3.5%, or 35 parts per thousand). Brackish waters originate by the mixing of sea water and freshwater, and are most common near the coasts of the oceans.

Brackish waters can occur as enclosed systems such as lakes and ponds that receive occasional inputs of oceanic water during severe storms. Brackish waters also occur as coastal estuaries or salt marshes that are more frequently flooded with saline water as a result of tidal cycles. Sometimes, brackish waters can occur far inland, for example, in parts of the prairies of North America where saline ponds and wetlands have variable salt concentrations depending on the diluting effects of recent rains or snowmelt. Two of the most ecologically important types of brackish environments are river estuaries and mangrove swamps. The Baltic Sea is the largest region of brackish water in the world.

The salt concentration of water is highly influential on the transport of ions across cellular membranes, the availability of nutrients in soil, and for other reasons. Most species can tolerate either saltwater or freshwater, but not both. However, organisms that live in brackish habitats must be tolerant of a wide range of salt concentrations (such species are known as euryhaline ). For example, the small fish known as killifish (Fundulus spp.) are common residents of brackish coastal habitats known as estuaries, where within any day the salt concentration in tidal pools and creeks can vary from that typical of freshwater to that of the open ocean. Other fish such as salmon (e.g., Salmo spp.) and eels (Anguilla spp.) move to or from marine waters during their spawning migrations, in the process moving from environments characterized by the salt concentration of full seawater, through brackish, to freshwater. Animals that live in or move through estuaries must be tolerant of the physiological stresses associated with such large and rapid changes in salinity, as must the plants of those habitats, such as the aquatic eelgrass (Zostera spp.) and the cord grass of salt marshes (Spartina spp.).

The environmental conditions of brackish waters are highly stressful for organisms that cannot tolerate such wide swings of salinity. However, for those relatively few species that are tolerant of such difficult environmental conditions, the brackish habitats represent a relatively uncompetitive, ecological opportunity to be exploited.

See also Saltwater.

views updated

Brackish

Brackish refers to water with a salinity intermediate to that of fresh water and sea water (the latter has a salt concentration of about 3.5%, or 35 parts per thousand). Brackish waters originate by the mixing of sea water and freshwater , and are most common near the coasts of the oceans.

Brackish waters can occur as enclosed systems such as lakes and ponds that receive occasional inputs of oceanic water during severe storms. Brackish waters also occur as coastal estuaries or salt marshes that are more frequently flooded with saline water as a result of tidal cycles. Sometimes, brackish waters can occur far inland, for example, in parts of the prairies of North America where saline ponds and wetlands have variable salt concentrations depending on the diluting effects of recent rains or snowmelt.

The salt concentration of water is highly influential on the transport of ions across cellular membranes, the availability of nutrients in soil , and for other reasons. Most species can tolerate either saltywater or freshwater, but not both. However, organisms that live in brackish habitats must be tolerant of a wide range of salt concentrations (such species are known as euryhaline). For example, the small fish known as killifish (Fundulus spp.) are common residents of brackish coastal habitats known as estuaries, where within any day the salt concentration in tidal pools and creeks can vary from that typical of freshwater to that of the open ocean . Other fish such as salmon (e.g., Salmo spp.) and eels (Anguilla spp.) move to or from marine waters during their spawning migrations, in the process moving from environments characterized by the salt concentration of full seawater, through brackish, to freshwater. Animals that live in or move through estuaries must be tolerant of the physiological stresses associated with such large and rapid changes in salinity, as must the plants of those habitats, such as the aquatic eelgrass (Zostera spp.) and the cord grass of salt marshes (Spartina spp.).

The environmental conditions of brackish waters are highly stressful for organisms that cannot tolerate such wide swings of salinity. However, for those relatively few species that are tolerant of such difficult environmental conditions, the environmental conditions of brackish habitats represent a relatively uncompetitive, ecological opportunity to be exploited as a livelihood.

See also Saltwater.

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Brackish

The salinity of brackish water is intermediate between seawater and fresh waters. Brackish water contains too much salt to be drinkable, but not enough salt to be considered seawater. The ocean has an average salinity of 35 parts per thousand (ppt), whereas freshwater contains 0.0650.30 ppt of salts, primarily chloride, sodium, sulfate, magnesium, calcium, and potassium ions. The salt content of brackish water ranges between approximately 0.50 and 17 ppt. Brackish water occurs where freshwater flows into the ocean, or where salts are dissolved from subsoils and percolate into freshwater basins. The gradient between salt and fresh water in estuaries and deltas varies from sharp distinction to gradual mixing, and different levels of vertical and horizontal mixing depend on the influence of tide, current, and rate of freshwater inflow.

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brack·ish / ˈbrakish/ • adj. (of water) slightly salty, as is the mixture of river water and seawater in estuaries. ∎  (of fish or other organisms) living in or requiring such water. ∎  unpleasant or distasteful: the lighting in the movie is brackish. DERIVATIVES: brack·ish·ness n.

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brackish Applied to water that is saline, but less so than sea water. According to the Venice system, brackish waters are classified by the chlorine they contain and divided into zones. The zones, with their percentage chlorinity (mean values at limits) are: euhaline 1.65–2.2; polyhaline 1.0–1.65; meso-haline 0.3–1.0; alpha-mesohaline 0.55–1.0; beta-mesohaline 0.3–0.55; oligohaline 0.03–0.3; fresh water 0.03 or less.

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brackish Applied to water that is saline, but less so than sea water. According to the Venice system brackish waters are classified by the chlorine they contain and divided into zones. The zones, with their percentage chlorinity (mean values at limits), are: euhaline 1.65–2.2; polyhaline 1.0–1.65; mesohaline 0.3–1.0; alpha-mesohaline 0.55–1.0; beta-mesohaline 0.3–0.55; oligohaline 0.03–0.3; fresh water 0.03 or less.

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brackish saltish. XVI. f. †brack salty, brine (XVI) — MLG., MDu. brac (LG., Du. brak), of unkn. orig.; see -ISH1.