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Saline Lakes

The largest, highest & lowest lakes of the world!

January 05, 2006                                      

What value of salt concentration demarcates fresh from saline water?

The term salinity needs careful definition to avoid confusion with the oceanographic definition: for limnologists, salinity is the sum total of ions! A conventional value, now widely accepted, and with atleast some physico-chemical and biological basis, is 3 g/L or 3 o/oo. This salinity is near, i) the calcite branch point, ii) the low points between modes when the frequency distribution of salinity of all lakes over 100 sq.km area is plotted logarithmically, iii) the salinity at which most humans first begin to taste salt, and iv) the salinity below which biota typical of higher salinities are not found and above which the freshwater biota begins quickly to disappear or not extend.

• Salt lakes are a good deal more varied in many physico-chemical features than freshwater lakes. Salinities are between 3 and >300 g/L (not <1-3 g/L as in freshwater lakes); salinity may vary widely on a seasonal (<50 - >300 g/L) or secular basis or, as in freshwater lakes, scarcely at all; and major ions may show a variety of patterns of dominance (most freshwater lakes are dominated by the divalent cations and bicarbonate).
• Most saline lakes are also defined by endorheic drainage basins, so that most slat lakes represent the termini of inland drainage basins in which there is a balance between inputs and outputs. Since all inflows contain significant concentrations of salts and evaporating water none, salts accumulate in the lake itself.. Coastal marine embayments, although saline and often lake-like, are not the termini of inland drainage basins and have many physico-chemical and biological features closer to marine (thalassic) than inland (athalassic) environments. A few inland salt lakes, mostly in temperate areas, are not within endorheic basins; their high salinities derive from underground or local salt sources, often associated with mining. On the other hand, solar salt ponds drawing water from the sea, and in which this water is progressively concentrated, do have many similarities to salt lakes.
• Salt lakes may contain water permanently, intermittently or episodically; water levels may be constant or fluctuate widely on a seasonal or secular basis, often in accord with salinity fluctuations; and they range from deep to shallow, small to extremely large, round to dendritic in shape.

The global importance of salt lakes

One should note that 70 percent of all inland salt water is held in the Caspian Sea. But in this regard, note that about 40 percent of global freshwater is held in Lake Baikal and the Great Lakes of North America. Notwithstanding, many of the world's largest lakes are saline (Table-2).

Major values and threats

Economically, salt lakes are important as a source of minerals (especially halite, but including also uranium, zeolites, lithium, borax and many other minerals), water (by diversion of inflows), fish, biochemical products (e.g. glycerol and β-carotene from Dunaliella, protein from Spirulina), and foodstuffs for aquaculture (especially Artemia cysts). Many are of cultural significance (e.g. the Dead Sea). A large number has high aesthetic values both as naturally attractive environments (e.g. Mono Lake, California), and as habitats for certain biota (notably flamingos).

• Threats: Perhaps threats to salt lakes are even greater than to freshwater lakes because of a general perception that salt lakes are less valuable than other sorts of inland water. Best known examples of severely damaged slat lakes are undeniably the Dead Sea, the Aral Sea, and Mono Lake. In each case, levels have dropped tens of metres and salinity risen by many g/L in the relatively recent past. For the Aral Sea, the total effects have been catastrophic to the local human population, agricultural production, and the environment in general.
• Not the least of threats are those likely from global climatic change, given the sensitivity of salt lakes to climatic events, and increased levels of UVB radiation, given that many salt lakes are shallow, already exposed to high levels of solar irradiation, and have fewer refuges from light than many freshwater lakes.
• Pollution of salt lakes is yet another anthropogenic activity of widespread importance, as is the ad hoc spread of exotic biota, especially Artemia.

The global distribution of salt lakes

Salt lakes are widespread, occur on all continents, and are often present not far from centres of population. They are not abundant in very dry areas though, in true deserts where annual precipitation is <25 mm, but they are otherwise widespread in drylands. Within each continent, they are also widely dispersed and extensive.

References:

• Williams, W.D. 1996. The largest, highest and lowest lakes of the world: Saline lakes. Peter Kilham Memorial Lecture, Sao Paulo, 1995. Verh. Internat. Verein. Limnol. 26:61-79.

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