Abstract:
Natural lakes are fairly large bodies of water occupying inland basins that
are extremely varied in terms of size, shape, depth, water chemistry, and other features.
Surface area of lakes varies from only a few hectares (< 1 km2) to several thousands of
square kilometres. Average depth can range from a few meters to more than a thousand
meters. Lakes can be nearly uniformly round, or they can be irregularly shaped. Natural
lakes are an important part of ecosystems that support a large variety of fauna and flora.
They also assumed significance in the human history, as they could be important sources
of water supply in certain regions. However, their origin and existence on the surface of
the earth are extremely varied and conditioned by the geological processes of the region.
Lakes cover about 1 percent of the continents and contain about 0.02
percent of the world's water. Lakes may be fresh-water, brackish or saline. Most of the
world's large lakes are fresh-water that contain less than one gram per litre of salt. Some
lakes are saline such as Caspian Sea and Aral Sea. Some are hypersaline lakes, such as
the Great Salt Lake of Utah (USA) that contains more than 250 gram per litre of salt. This
value of salinity is much higher than that of the sea water (35 gram per litre). The water
of caldera lakes of volcanic origin can be highly acidic, where as the water in other lakes
can be nearly neutral, or highly alkaline (as in soda lakes). Lakes can be low in nutrients
(oligotrophic), moderately enriched (mesotrophic), or highly enriched (eutrophic).
