Salinity
Salinity is the
saltiness of a body of
water. Water is defined as saline if it contains 3 to 5% salt by volume. The ocean is naturally saline at ~3.5% salt (see
sea water). Some inland salt lakes (
seas) are even saltier. The technical term for ocean saltiness is
halinity, from the fact that
halides (
chloride, specifically) are the most abundant
anion in the mix of dissolved solids. In
oceanography, it has been traditional to express salinity as concentration in parts per thousand (ppt or
o/oo), which is grams salt per liter of water. After 1978, oceanographers defined salinity as the
electrical conductivity ratio of a sea water to a standard KCl solution. Ratios have no units.
The salt content of most lakes, rivers, and streams is so small that these waters are termed
fresh or even
sweet water. Salt is difficult to remove from water, and salt content is a factor in water
potability. Salinity is an ecological factor of considerable import, influencing the types of organisms that live in a body of water. As well, salinity influences the kinds of
plants that will grow either in a water body, or on land fed by a water (or by a
groundwater). A plant adapted to a saline conditions is called a
halophyte (for
salt loving). See also
biosalinity. Animals and bacteria that can live in very salty conditions are classified as
extremophiles.
Systems of classification of water bodies based upon salinity
Marine waters are those of the ocean, another term for which is
euhaline seas. The salinity range for euhaline seas is 30 to 35
o/oo.
brackish seas or waters have salinity in the range of 0.5 to 29
o/oo; and
metahaline seas from 36 to 40
o/oo. These waters are all grouped as
homoiohaline because their salinity is derived from the ocean (
thalassic) and essentially invariant, in contrast to poikilohaline environments in which the salinity variation is biologically significant (Dahl, 1956).
Poikilohaline waters may range anywhere from 0.5
o/oo to greater than 300
o/oo. 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 variable salinity. The following table, modified from Por (1972) follows the "Venice system" (1959):
\n\n | THALASSIC SERIES | \n
\n\n| >300 o/oo | \n-------------------- | \n
\n\n | \n hyperhaline | \n
\n\n| 60 - 80 o/oo | \n-------------------- | \n
\n\n | \n metahaline | \n
\n\n| 40 o/oo | \n-------------------- | \n
\n\n | \n mixoeuhaline | \n
\n\n| 30 o/oo | \n-------------------- | \n
\n\n | \n polyhaline | \n
\n\n| 18 o/oo | \n-------------------- | \n
\n\n | \n mesohaline | \n
\n\n| 5 o/oo | \n-------------------- | \n
\n\n | \n oligohaline | \n
\n\n| 0.5 o/oo | \n-------------------- | \n
\n
\nHighly saline water is referred to as
brine.
References
- Dahl, E. 1956. Ecological salinity boundaries in poikilohaline waters. Oikos, 7(I): 1–21.\n*Por, F. D. 1972. Hydrobiological notes on the high-salinity waters of the Sinai Peninsula. Mar. Biol., 14(2): 111–119.\n*Venice system. 1959. Final resolution of the symposium on the classification of brackish waters. Archo Oceanogr. Limnol., 11 (suppl): 243–248.
Category:Oceanography\nCategory:Ecology