Salinity
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[[Image:Wiki plot 04.png|thumb|right|Annual mean sea surface '''salinity''' for the [[World Ocean]]. Data from the [[World Ocean Atlas]] [http://www.nodc.noaa.gov/OC5/WOA01/ 2001].]]
'''Salinity''' is the [[salt]]iness or dissolved salt content of a body of [[water]]. ''Salinity'' in [[Australian English]] and [[North American English]] may also refer to the salt in [[soil]] (see [[soil salination]]).
==Definitions==
{| style="margin-left:auto; margin-right:auto;"
|-
! style="background:#B8E0F6" colspan="4" | Water salinity
|-
! style="background:#87CEFA" | [[Fresh water]]
! style="background:#87CEFA" | [[Brackish water]]
! style="background:#87CEFA" | [[Saline water]]
! style="background:#87CEFA" | [[Brine]]
|-
! style="background:#00BFFF" | < 0.05 %
! style="background:#00BFFF" | 0.05 - 3 %
! style="background:#00BFFF" | 3 - 5 %
! style="background:#00BFFF" | > 5 %
|-
! style="background:#00BFFF" | < 500 ppm
! style="background:#00BFFF" | 500 - 30 000 ppm
! style="background:#00BFFF" | 30 000 - 50 000 ppm
! style="background:#00BFFF" | > 50 000 ppm
|}
The technical term for saltiness in the ocean is ''salinity'', from the fact that [[halide]]s - [[chloride]] specifically - are the most abundant [[anions]] in the mix of dissolved elements. In [[oceanography]], it has been traditional to express salinity not as percent, but as parts per thousand (ppt or [[permille|‰]]), which is approximately grams of salt per liter of solution. Other disciplines use chemical analyses of solutions, and thus salinity is frequently reported in mg/L or ppm (parts per million). Prior to 1978, salinity or halinity was expressed as ‰ usually based on the [[electrical conductivity]] ratio of the sample to "Copenhagen water", an artificial sea water manufactured to serve as a world "standard"<ref>Lewis, E.L. (1980). The Practical Salinity Scale 1978 and its antecedents. ''IEEE J. Ocean. Eng.'', OE-5(1): 3-8.</ref>. In 1978, oceanographers redefined salinity in the '''Practical Salinity Scale''' ('''[[PSS]]''') as the conductivity ratio of a sea water sample to a standard KCl solution<ref>Unesco (1981a). The Practical Salinity Scale 1978 and the International Equation of State of Seawater 1980. ''Tech. Pap. Mar. Sci.'', 36: 25 pp.</ref><ref>Unesco (1981b). Background papers and supporting data on the Practical Salinity Scale 1978. ''Tech. Pap. Mar. Sci.'', 37: 144 pp.</ref>. Ratios have no units, so it is not the case that a salinity of 35 exactly equals 35 grams of salt per litre of solution<ref>Unesco (1985). The International System of Units (SI) in Oceanography. ''Tech. Pap. Mar. Sci.'', 45: 124 pp.</ref>.
These seemingly esoteric approaches to measuring and reporting salt concentrations may appear to obscure their practical use; but it must be remembered that salinity is the sum weight of many different elements within a given volume of water. It has always been the case that to get a precise salinity as a concentration and convert this to an amount of substance (sodium chloride, for instance) required knowing much more about the sample and the measurement than just the weight of the solids upon evaporation (one method of determining "salinity"). For example, volume is influenced by water temperature; and the composition of the salts is not a constant (although generally very much the same throughout the world ocean). Saline waters from inland seas can have a composition that differs from that of the ocean. For the latter reason, these waters are termed '''saline''' as differentiated from ocean waters, where the term '''haline''' applies (although is not universally used).
[[Contour line]]s of constant salinity are called '''isohale'''s.
== Systems of classification of water bodies based upon salinity ==
<!--Before changing this cumbersome title, please ensure you modify the pages Hypersaline, Burgsvik beds, and anything else linking directly to this section-->
{| align=right
|-its true
|
| bgcolor=lightgrey align=center|'''THALASSIC SERIES'''
|-
| width=85px align=right bgcolor=lightgrey| >300
| align=center|--------------------
|-
|
| width=170px bgcolor=lightgrey align=center|hyperhaline
|-
| align=right bgcolor=lightgrey| 60 - 80
| align=center|--------------------
|-
|
| bgcolor=lightgrey align=center|metahaline
|-
| align=right bgcolor=lightgrey| 40
| align=center|--------------------
|-
|
| bgcolor=lightgrey align=center|mixoeuhaline
|-
| align=right bgcolor=lightgrey| 30
| align=center|--------------------
|-
|
| bgcolor=lightgrey align=center|polyhaline
|-
| align=right bgcolor=lightgrey| 18
| align=center|--------------------
|-
|
| bgcolor=lightgrey align=center|mesohaline
|-
| align=right bgcolor=lightgrey| 5
| align=center|--------------------
|-
|
| bgcolor=lightgrey align=center|oligohaline
|-
| align=right bgcolor=lightgrey| 0.5
| align=center|--------------------
|}
Marine waters are those of the ocean, another term for which is '''euhaline seas'''. The salinity of euhaline seas is 30 to 35. '''Brackish seas''' or waters have salinity in the range of 0.5 to 29 and '''metahaline seas''' from 36 to 40. These waters are all regarded as '''thalassic''' because their salinity is derived from the ocean and defined as '''homoiohaline''' if salinity does not vary much over time (essentially invariant). The table on the right, modified from Por (1972)<ref>Por, F. D. (1972). Hydrobiological notes on the high-salinity waters of the Sinai Peninsula. ''Mar. Biol.'', 14(2): 111–119.</ref>, follows the "Venice system" (1959)<ref>Venice system (1959). The final resolution of the symposium on the classification of brackish waters. ''Archo Oceanogr. Limnol.'', 11 (suppl): 243–248.</ref>.
In contrast to homoiohaline environments are certain '''poikilohaline''' environments (which may also be ''thallassic'') in which the salinity variation is biologically significant<ref>Dahl, E. (1956). Ecological salinity boundaries in poikilohaline waters. ''Oikos'', 7(I): 1–21.</ref>. ''Poikilohaline'' water salinities may range anywhere from 0.5 to greater than 300. The important characteristic is that these waters tend to vary in salinity over some biologically meaningful range seasonally or on some other roughly comparable time scale. Put simply, these are bodies of water with quite variable salinity.
Highly saline water, from which salts crystallize (or are about to), is referred to as [[brine]].
==Environmental considerations==
Salinity is an ecological factor of considerable importance, influencing the types of organisms that live in a body of water. As well, salinity influences the kinds of [[plant]]s that will grow either in a water body, or on land fed by a water (or by a [[groundwater]]). A plant adapted to saline conditions is called a [[halophyte]]. Organisms (mostly bacteria) that can live in very salty conditions are classified as [[extremophile]]s, [[halophile]]s specifically. An organism that can withstand a wide range of salinities is [[euryhaline]].
Salt is difficult to remove from water, and salt content is an important factor in water use (such as [[drinking water|potability]]).
==See also==
* [[Salinity control]]
* [[Desalination]]
* [[Fresh water]]
* [[Seawater]]
* [[Soil salination]]
* [[Stenohaline|Stenohaline fish]]
* [[Euryhaline|Euryhaline fish]]
==References==
<references/>
* Mantyla, A.W. 1987. Standard Seawater Comparisons updated. ''J. Phys. Ocean.'', 17: 543-548.
[[Category:Chemical oceanography]]
[[Category:Aquatic ecology]]
[[Category:Oceanography]]
[[Category:Coastal geography]]
[[Category:Water quality indicators]]
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