HOME

TheInfoList




Salinity () is the saltiness or amount of
salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure fo ...
dissolved in a body of
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
, called
saline water Saline water (more commonly known as salt water) is water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere an ...
(see also
soil salinity 249x249px, Saline incrustation in a PVC irrigation pipe from Brazil Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization. Salts occur naturally within soils and water. Salination can ...
). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ‰). Salinity is an important factor in determining many aspects of the
chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during a with other . ...

chemistry
of natural waters and of
biological Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowl ...

biological
processes within it, and is a thermodynamic state variable that, along with
temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical concept ...

temperature
and
pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

pressure
, governs physical characteristics like the
density The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its per unit . The symbol most often used for density is ''ρ'' (the lower case Greek letter ), although the Latin letter ''D'' can also ...

density
and
heat capacity Heat capacity or thermal capacity is a physical property A physical property is any property Property is a system of rights that gives people legal control of valuable things, and also refers to the valuable things themselves. Depending on t ...
of the water. A
contour line A contour line (also isoline, isopleth, or isarithm) of a function of two variables is a curve In mathematics, a curve (also called a curved line in older texts) is an object similar to a line (geometry), line, but that does not have to b ...
of constant salinity is called an ''isohaline'', or sometimes ''isohale''.


Definitions

Salinity in rivers, lakes, and the ocean is conceptually simple, but technically challenging to define and measure precisely. Conceptually the salinity is the quantity of dissolved salt content of the water. Salts are compounds like
sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salt (chemistry), salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With Molar mass, molar ...
,
magnesium sulfate Magnesium sulfate or magnesium sulphate (in British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial ...

magnesium sulfate
,
potassium nitrate Potassium nitrate is a chemical compound with the chemical formula . It is an ionic salt of potassium ions K+ and nitrate ions NO3−, and is therefore an alkali metal nitrate. It occurs in nature as a mineral, niter (or nitre in the UK). It is a ...

potassium nitrate
, and
sodium bicarbonate Sodium bicarbonate ( IUPAC name: sodium hydrogen carbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation (Na+) and a bicarbonate anion ( HCO3 ...

sodium bicarbonate
which dissolve into ions. The concentration of dissolved chloride ions is sometimes referred to as chlorinity. Operationally, dissolved matter is defined as that which can pass through a very fine filter (historically a filter with a pore size of 0.45 μm, but nowadays usually 0.2 μm). Salinity can be expressed in the form of a mass fraction, i.e. the mass of the dissolved material in a unit mass of solution. Seawater typically has a mass salinity of around 35 g/kg, although lower values are typical near coasts where rivers enter the ocean. Rivers and lakes can have a wide range of salinities, from less than 0.01 g/kg to a few g/kg, although there are many places where higher salinities are found. The
Dead Sea The Dead Sea ( he, יָם הַמֶּלַח lit. Sea of Salt; ar, البحر الميت , lit. ''the Dead Sea'',The first article ''al-'' is unnecessary and usually not used. or Buhayrat, Bahret or Birket Lut, ''lit.'' "Lake/Sea of Lot") is a ...

Dead Sea
has a salinity of more than 200 g/kg. Rainwater before touching the ground typically has a TDS of 20 mg/L or less. Whatever pore size is used in the definition, the resulting salinity value of a given sample of natural water will not vary by more than a few
percent In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities a ...

percent
(%). Physical oceanographers working in the abyssal ocean, however, are often concerned with precision and intercomparability of measurements by different researchers, at different times, to almost five significant digits. A bottled seawater product known as IAPSO Standard Seawater is used by oceanographers to standardize their measurements with enough precision to meet this requirement.


Composition

Measurement and definition difficulties arise because natural waters contain a complex mixture of many different elements from different sources (not all from dissolved salts) in different molecular forms. The chemical properties of some of these forms depend on temperature and pressure. Many of these forms are difficult to measure with high accuracy, and in any case complete chemical analysis is not practical when analyzing multiple samples. Different practical definitions of salinity result from different attempts to account for these problems, to different levels of precision, while still remaining reasonably easy to use. For practical reasons salinity is usually related to the sum of masses of a subset of these dissolved chemical constituents (so-called ''solution salinity''), rather than to the unknown mass of salts that gave rise to this composition (an exception is when
artificial seawater Artificial seawater ( abbreviated ASW) is a mixture of dissolved mineral salts (and sometimes vitamin A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an Nutrient#Essential nutrients, ...
is created). For many purposes this sum can be limited to a set of eight major ions in natural waters, although for seawater at highest precision an additional seven minor ions are also included. The major ions dominate the inorganic composition of most (but by no means all) natural waters. Exceptions include some s and waters from some
hydrothermal spring A hot spring, hydrothermal spring, or geothermal spring is a spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of w ...
s. The concentrations of dissolved gases like
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
and
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
are not usually included in descriptions of salinity. However,
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
gas, which when dissolved is partially converted into
carbonates In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity, crystalline min ...
and
bicarbonates In inorganic chemistry, bicarbonate (International Union of Pure and Applied Chemistry, IUPAC-recommended nomenclature: hydrogen carbonate) is an intermediate form in the deprotonation of carbonic acid. It is a Polyatomic ion, polyatomic anion w ...
, is often included.
Silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

Silicon
in the form of
silicic acid Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more t ...

silicic acid
, which usually appears as a neutral molecule in the range of most natural waters, may also be included for some purposes (e.g., when salinity/density relationships are being investigated).


Seawater

The term 'salinity' is, for oceanographers, usually associated with one of a set of specific measurement techniques. As the dominant techniques evolve, so do different descriptions of salinity. Salinities were largely measured using
titration Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis Analytical chemistry studies and uses instruments and methods used to separate, identify, and quantify matter. In pr ...

titration
-based techniques before the 1980s. Titration with
silver nitrate Silver nitrate is an inorganic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, be ...

silver nitrate
could be used to determine the concentration of
halide A halide is a binary phase, of which one part is a halogen atom and the other part is an chemical element, element or radical (chemistry), radical that is less electronegative (or more electropositive) than the halogen, to make a, e.g., fluoride, ...
ions (mainly
chlorine Chlorine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemica ...

chlorine
and
bromine Bromine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elemen ...

bromine
) to give a
chlorinity File:IAPSO Standard Seawater.jpg, upInternational Association for the Physical Sciences of the Oceans (IAPSO) standard seawater. Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (se ...
. The chlorinity was then multiplied by a factor to account for all other constituents. The resulting 'Knudsen salinities' are expressed in units of
parts per thousand In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable explanations and predictio ...
(ppt or ). The use of
electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current An electric current is a stream of charged particle In p ...
measurements to estimate the ionic content of seawater led to the development of the scale called the ''practical salinity scale 1978'' (PSS-78).Unesco (1981). The Practical Salinity Scale 1978 and the International Equation of State of Seawater 1980. ''Tech. Pap. Mar. Sci.'', 36Unesco (1981)
Background papers and supporting data on the Practical Salinity Scale 1978
''Tech. Pap. Mar. Sci.'', 37
Salinities measured using PSS-78 do not have units. The suffix psu or PSU (denoting ''practical salinity unit'') is sometimes added to PSS-78 measurement values. The addition of PSU as a unit after the value is "formally incorrect and strongly discouraged". In 2010 a new standard for the properties of seawater called the ''thermodynamic equation of seawater 2010'' ( TEOS-10) was introduced, advocating absolute salinity as a replacement for practical salinity, and
conservative temperature Conservative temperature (Θ) is a thermodynamic property of seawater. It is proportional to the potential enthalpy and is recommended as a replacement for potential temperature as it more accurately represents the heat content. Motivation The ...
as a replacement for
potential temperature The potential temperature of a parcel of fluid at pressure P is the temperature that the parcel would attain if adiabatically brought to a standard reference pressure P_, usually . The potential temperature is denoted \theta and, for a gas well-ap ...
. This standard includes a new scale called the ''reference composition salinity scale''. Absolute salinities on this scale are expressed as a mass fraction, in grams per kilogram of solution. Salinities on this scale are determined by combining electrical conductivity measurements with other information that can account for regional changes in the composition of seawater. They can also be determined by making direct density measurements. A sample of seawater from most locations with a chlorinity of 19.37 ppt will have a Knudsen salinity of 35.00 ppt, a PSS-78 practical salinity of about 35.0, and a TEOS-10 absolute salinity of about 35.2 g/kg. The electrical conductivity of this water at a temperature of 15 °C is 42.9 mS/cm.


Lakes and rivers

Limnologist Limnology ( ; from Greek λίμνη, ''limne'', "lake" and λόγος, ''logos'', "knowledge") is the study of inland aquatic ecosystems An aquatic ecosystem is an ecosystem An ecosystem is a community (ecology), community of living organ ...
s and chemists often define salinity in terms of mass of salt per unit volume, expressed in units of mg per litre or g per litre. It is implied, although often not stated, that this value applies accurately only at some reference temperature. Values presented in this way are typically accurate to the order of 1%. Limnologists also use
electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current An electric current is a stream of charged particle In p ...
, or "reference conductivity", as a proxy for salinity. This measurement may be corrected for temperature effects, and is usually expressed in units of μS/cm. A river or lake water with a salinity of around 70 mg/L will typically have a specific conductivity at 25 °C of between 80 and 130 μS/cm. The actual ratio depends on the ions present. The actual conductivity usually changes by about 2% per degree Celsius, so the measured conductivity at 5 °C might only be in the range of 50–80 μS/cm. Direct density measurements are also used to estimate salinities, particularly in highly
saline lake A salt lake or saline lake is a landlocked body of water (Lysefjord) in Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål (, ; literally "book tongue") is an official wr ...
s. Sometimes density at a specific temperature is used as a proxy for salinity. At other times an empirical salinity/density relationship developed for a particular body of water is used to estimate the salinity of samples from a measured density.


Classification of water bodies based upon salinity

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 constant). The table on the right, modified from Por (1972), follows the "Venice system" (1959). In contrast to homoiohaline environments are certain ''poikilohaline'' environments (which may also be ''thalassic'') in which the salinity variation is biologically significant. ''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 Brine is a high-concentration solution of salt (NaCl) in water (H2O). 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 food ...

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 Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
s that will grow either in a water body, or on land fed by a water (or by a
groundwater Groundwater is the water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known form ...

groundwater
). A plant adapted to saline conditions is called a
halophyte A halophyte is a salt-tolerant plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular r ...
. A halophyte which is tolerant to residual sodium carbonate salinity are called
glasswort The glassworts are various succulent, annual halophytic 250px, '' Spartina alterniflora'' (cordgrass), a halophyte.">cordgrass.html" ;"title="Spartina alterniflora'' (cordgrass">Spartina alterniflora'' (cordgrass), a halophyte. A halophyte is ...

glasswort
or
saltwortSaltwort is a common name for various genera of flowering plants that thrive in salty environments, typically in coastal salt marshes and seashores. Including various matter such as: :*'' Salsola'' and related genera within subfamily '' Salsoloidea ...
or
barilla ''Barilla'' refers to several species of salt-tolerant ( halophyte) plants that, until the 19th Century, were the primary source of soda ash and hence of sodium carbonate Sodium carbonate, , (also known as washing soda, soda ash and soda crys ...
plants. Organisms (mostly bacteria) that can live in very salty conditions are classified as
extremophile An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochem ...
s, or
halophile The halophiles, named after the Greek word for "salt-loving", are extremophiles that thrive in high salt concentrations. While most halophiles are classified into the domain Archaea, there are also bacterial halophiles and some Eukaryote, eukaryotic ...
s specifically. An organism that can withstand a wide range of salinities is
euryhaline Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct relat ...
. Salt is expensive to remove from water, and salt content is an important factor in water use (such as ). Increases in salinity have been observed in lakes and rivers in the United States, due to common
road salt Sodium chloride , commonly known as salt (although sea salt Sea salt is salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined ...
and other salt de-icers in runoff. The degree of salinity in oceans is a driver of the , where density changes due to both salinity changes and temperature changes at the surface of the ocean produce changes in buoyancy, which cause the sinking and rising of water masses. Changes in the salinity of the oceans are thought to contribute to global changes in carbon dioxide as more saline waters are less soluble to carbon dioxide. In addition, during glacial periods, the
hydrography Hydrography is the branch of applied sciences which deals with the measurement and description of the physical features of ocean The ocean (also the sea The sea, connected as the world ocean or simply the ocean The ocean (a ...
is such that a possible cause of reduced circulation is the production of stratified oceans. In such cases, it is more difficult to subduct water through the thermohaline circulation.


See also

*Desalination for economic purposes **
Desalination Desalination is a process that takes away mineral components from saline water Saline water (more commonly known as salt water) is water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odor ...
of water **Desalination of soil:
soil salinity control Soil salinity control relates to controlling the problem of soil salinity Soil salinity is the salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a ...
**
Sodium adsorption ratioThe Sodium adsorption ratio (SAR) is an irrigation water quality parameter used in the management of sodium-affected soils. It is an indicator of the suitability of water for use in agricultural irrigation Irrigation is the artificial process o ...
* Measuring salinity **
Salinometer A salinometer is a device designed to measure the salinity Salinity () is the saltiness or amount of salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound w ...
* Salinity by biologic context ** In organisms generally, with particular emphasis on human health ***
Electrolyte An electrolyte is a medium containing ions that is electrically conducting Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that quantifies how strongly it resis ...

Electrolyte
s ***
Fluid balance Fluid balance is an aspect of the homeostasis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecula ...
***
Hypernatremia Hypernatremia, also spelled hypernatraemia, is a high concentration of sodium in the Serum (blood), blood. Early symptoms may include a strong feeling of thirst, weakness, nausea, and anorexia (symptom), loss of appetite. Severe symptoms include de ...
***
Hyponatremia Hyponatremia is a low sodium concentration in the Serum (blood), blood. It is generally defined as a sodium concentration of less than 135 mmol/L (135 mEq/L), with severe hyponatremia being below 120 mEq/L. Symptoms can be absent, mild or severe. ...
*** Salt poisoning ** In plants *** ''Arabidopsis thaliana'' responses to salinity ** In fish *** Stenohaline fish *** Euryhaline fish *Salinity by geologic context **
Fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in ...

Fresh water
**
Seawater Seawater, or salt water, is water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for al ...

Seawater
**
Soil salinity Soil salinity is the salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure th ...
**
Thermohaline circulation Thermohaline circulation (THC) is a part of the large-scale Ocean current, ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from ''wikt:thermo-, t ...

Thermohaline circulation
** Paleosalinity **
CORA dataset CORA (standing for Coriolis Ocean database ReAnalysis) is a global oceanographic temperature and salinity dataset produced and maintained by the French institute IFREMER. Most of those data are real-time data coming from different types of platforms ...
data on salinity of global oceans *General cases of solute concentration **
Osmotic concentration Osmotic concentration, formerly known as osmolarity, is the measure of solute upMaking a table salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), sa ...
**
Tonicity Tonicity is a measure of the effective osmotic pressure gradient; the water potential Water potential is the potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, ...

Tonicity


References


Further reading

*
MIT page of seawater properties, with Matlab, EES and Excel VBA library routinesEquations and algorithms to calculate fundamental properties of sea water.History of the salinity determinationPractical Salinity Scale 1978.Salinity calculatorLewis, E. L. 1982. The practical salinity scale of 1978 and its antecedents. Marine Geodesy. 5(4):350–357.Equations and algorithms to calculate salinity of inland waters
{{Authority control Chemical oceanography Aquatic ecology Oceanography Coastal geography Water quality indicators Articles containing video clips