This is the tale of three lakes, far from each other, located in three diverse climatic set up.
Everyone knows that the lakes are not mere pools of water. They have life in the form of fauna and flora, sometimes microscopic, they have sediments too, the supply of which depends upon the condition of the sediment carrying medium; that is water or air.
B. Sekar, Amlav Bhattacharyya and S.K. Bera of Birbal Sahni Institute of Palaeobotany (BSIP), Lucknow trekked to Tsokar Lake in Ladakh, J&K, Didwana Lake, Rajasthan and Berijam Lake, Palni Hills, Tamilnadu and published their work in the volume of Diamond Jubilee International Conference held at BSIP in November, 2006.
The sediments of these lakes were studied by these experts and lo, they contained tales of the past climates!
Tsokar or the ‘white lake’ of Ladakh is unique, as it is saline and salt deposits on its bank, as water evaporates. That is why the name white lake. Salt extracted from the lake margins is sold in J&K as ‘Rupshu Chang’. The lake is such that a smaller fresh water lake nearby does drain in to it, but water from Tsokar has no outlet. The presence of salts and potash in water has made the water of the lake brackish.
Similarly Didwana Lake in Rajasthan is another salt water lake, a typical example of such type of lakes in arid or semi-arid environment. Didwana Lake is famous amongst zoologists for its Phytoplankton content. (Phyto in Greek means a plant and Plankton means drifting.) In reality these drifting plants are tiny and what one sees of them is only a green patch on the surface of water body. Green color is due to their chlorophyll content. Phyto-planktons are invaluable for us. They are responsible for about 98 percentof oxygen in the Earth’s atmosphere, says the Wikipedia.
Berijam Lake near Kodaikanal in south India was a swamp discovered by the British and Spanish travelers and till about a century ago. It was converted into a beautiful lake with the help of micro-watershed development. The lake water quality is excellent and is used for water supply to the nearby town of Periyakulum.
These lakes located in diverse environmental conditions have revealed many interesting facts. B.Seker and his colleagues plotted radiometric dates obtained from carbon isotopes (14 C) from the sediments of the three lakes against depths. It was found that rate of sedimentation for Tsokar was around 9.5 cm/100 years, for Didwana it came to be 3.9 cm/100 years and for Berijam Lake 2.9 cm/100 years.
The organic contents of these lakes on the other hand were found to be 1-95, 6-18% and 5.5-41.8% respectively for Tsokar, Didwana and Berijam lakes. This shows that the rate of sedimentation in these lakes is indirectly proportional to the influx of organic matter.
These authors attribute the high rate of sedimentation in Tsokar Lake to the dry climate largely in the past 30,000 years (ka). Of course in between there was a period of greater melting of ice due to rise in temperatures, which too was responsible for higher influx of material into the lake.
Compared to Tsokar, Didwana Lake catchments had more congenial climate with stable land conditions all around. However, during 8.1ka to 6.3 ka and 4.6 ka to 2.0 ka landforms were unstable and the climate was dry and arid. That was the time when maximum influx of sediments took place in the lake.
Berijam Lake had the most stable land conditions, thus erosion was less and naturally the lake received less sediment but more organic matter during the last 17.7 ka.
M.D. Kajale and B.C. Deotare of Deccan College, Postgraduate Research Institute, Pune carried out a study of past environments of all the saline lakes in western Rajasthan, including the Didwana Lake too. Analysis of the pollen collected from the depths of the lake bed showed shifts in climatic and vegetational belts during the early Holocene, especially during the period of Indus Valley Culture.
Similarly geo-archaeological studies carried out in the Didwana Lake show a relationship between climatic fluctuations and culture. They also took help of geochemistry and analysis of sediments to work out a detailed history of salinity from 20,000 to 13,000 years before present (BP) and freshwater conditions from 9000 to 6000 years BP.
They found that while the vegetation was lush green with steppe type of vegetation some 18000 years BP, while hypersaline conditions prevailed in Didwana Lake indicating a weak monsoon.
These studies have an impact on the future of such water bodies. Many of them have perished due to climatic vicissitudes and many were fresh water bodies that turned saline due to constant evaporation and lack of replenishment. Such mishaps of the past can be repeated anywhere. If we care for the surface water bodies we must know their history and learn to save them for the posterity.