Salt lakes



Salt lakes/Soda lakes

Definition

Salt lakes are naturally occurring highly alkaline aquatic bodies, widely spread throughout the world. Salt lakes are ecosystem with extremely high pH (up to 11) and salinity (up to saturation) due to the presence of high concentrations of sodium carbonate.

Salt lakes, located in Kenya and Tanzania (Bogoria, Magadi, Natron), in Egypt (Wadi Natrun), and California (Mono Lake) are good example of typical salt lakes. Another area abundant in saline alkaline lakes is Central Asia (south Siberia and north-east China). Here the lakes are much smaller, more shallow, and water regimen is unstable due to freezing winter period which cause fluctuations of the water salinity and temperature.

There are so many salt lakes and salt deserts around the world. Some of them are listed below.

         
source: https://d-nb.info/968508480/34


Formation of Salt Lakes

One of the theory suggest that rocks are made up of high amount of sodium carbonate washed out by ground water and accumulated at lake basin. Other theory suggests that water enter into the aquatic body during rain or surface run off and amount leave behind by evaporation leads to formation of salt lake. Geochemistry of the regions is another reason for the origin of salt lakes.
Concentration of the ions present in ground water through evaporation favor the formation of carbonate.
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- ↔ 2H+ + CO32-
Carbon                Carbonic               Bicarbonate            Carbonate
Di oxide               acid

Carbonate ions further form sodium and potassium carbonate and accumulate in the basin.

Microorganisms present in salt lakes

Environment of these lakes are extremely alkaline. In such extreme conditions only those living being can survive which are tolerant for such conditions e.g archaebacteria. Salt lakes provide favourable environment for growth of organotrophic, halophilic (Halorhodospira), alkaliphilic bacteria (natronococcus sp.) sulphur oxidising bacteria (Thioalkalivibrio, and Thioalkalimicrobium) and cynobacteria. Less alkaline lakes support the growth of cynobacteria while highly alkaline lakes support growth of both cynobacteria and alkaliphilic bacteria.

Lake Natron is a good example of salt lake as it is a highly alkaline in nature, situated in south Nairobi, Kenya. The colour of the lake is vivid red due to presence of red colour pigment containing Spirulina (cyanobacteria). 

Satellite image of lake Natron, credit: March 1989. (Credit: NASA Discovery Mission)
Survival in alkaline environment
Microorganisms face many challenges to survive in extremely alkaline conditions, to combat such difficulties bacteria developed certain adaptations which help them to grow in alkaline environment.
a) Internal pH maintenance by active and passive regulation mechanism. Check out the link below for more information
https://www.researchgate.net/publication/278705829_Adaptive_Mechanisms_of_Extreme_Alkaliphiles
b) Evolution of pH stable enzymes, which are used for industrial purpose also. For more information click the link below:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC98975/
c) Alkaliphilic bacteria compensate for reversal of the pH gradient by having a high membrane potential. Check out the link below.
https://atlasofscience.org/how-alkaliphiles-produce-energy-to-sustain-their-life-under-extremely-low-concentration-of-proton/
Other living beings
Flamingos are most prominent living being present in dry land of salt lakes. Lake natron, lake bogoria and lake magadi have good number of flamingos. These dry areas provide perfect breeding ground to flamingos for their nest, and cynobateria present in lake become food source for them. Brine shrimps and brine flies also make their habitat in salt lakes as they are tolerant to alkaline conditions and feed on the algae. Salt lakes also form fresh water wetlands at shores and become a home for other wetland birds, tilapia fish and algae.

Panoramic view of lake Bogoria, Image Credit: By Fred Barasa, Anthony Ochieng and Maaike Manten

Some of the salt lakes are so caustic in nature, when birds and animals fall in there, their body turned to stone (calcified) due to carbonates present in water. It has been said that Egyptians used this water for mummification as it is a fantastic type of preservative.



The body of a flamingo on Lake Natron, Image Credit: Nick Brandt 2013 Courtesy of Hasted Kraeutler Gallery, NY

  Image Credit: Nick Brandt 2013 Courtesy of Hasted Kraeutler Gallery, NY

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