Limnology

Unit 2- Lakes

2.1.1 Lakes
Lakes origin
Lake is defined as a large body of standing water occupying a basin which does not have any connection with sea. Approximately 1% of water is found in lakes, but the renewal time is much more rapid than the ocean.
Classification of lakes on the basis of their origin
1.Tectonic lakes
These are formed in basins created by movements of the earth’s crust by different processes.

2.Crater lakes (Volcanic lakes)
In many cases when a volcano becomes extinct, its hollow interior is filled with water by precipitation or by percolation. They are near circular or sometimes elliptical in outline. eg, Crater lake in Oregon (USA).

3.Glacial lakes
Most common lakes are originated due to erosion and deposition associated with glacial ice movements eg. Finger lakes of New York.

4.Basal rock dissolution lake
These are formed by the slow dissolving of soluble rock (Calcium carbonate) by water eg, clear lake in California and Deep lake Florida (USA).

5.Oxbow lakes
An oxbow is a crescent-shaped lake lying alongside of meandering streams or rivers in the floor of a valley. The oxbow lake is created over time as erosion and deposits of soil change the river's course. On the inside of the loop, the river travels more slowly leading to deposition of silt. Water on the outside edges tends to flow faster, which erodes the banks making the meander even wider. When the streams bend and are cut off from the main stream flow, an oxbow lake results. Such lakes may be entirely cut off and become totally lentic or a little flow may persist seasonally at floods. eg, Dal and Woolar lakes of Kashmir.

6.Fluvial lakes
These lakes are formed by river activity.

7.Aeolian lakes
These are formed by the wind activity in arid regions which may erode with broken rocks or redistribute sand which are generally temporary.

8.Shoreline lakes
Created by irregularities or inundation along the coastline of large lakes which usually a result of long shore currents.

9.Reservoir lakes
These are man made lakes formed by the construction of dams across the streams eg, Thungabhadra reservoir in South India, Bhakra-Nangal reservoir in north western part of India (Anthropogenic lakes).

10.Bog lakes
Bogs are best developed in the north temperate glaciated region when precipitation is abundant throughout the year, atmospheric humidity is great. Soil temperature is low, evaporation is reduced, and run-off water is minimum having abundant growth of plants. A typical bog lake is defined as an area of open water surrounded either wholly or by part of true margins. Possessing peat deposits about the margins or in the bottom usually with a false bottom of very finely divided flocculent vegetable matter.

11.Salt lakes
There are many salt lakes throughout the world, much as saline lake waters as freshwater lakes. When climate change become drier or geological events change drainage basins, the annual flows into lake may be greatly reduced. The lake may seem to have a significant outflow and become a terminal or sink lake. The salts from the flowing stream are concentrated by evaporation and are no longer flushed out through outflow eventually the lake may dry completely. In dry climates the lakes gradually become salty.
Lake Bonneville and Lahontau of south western United States, the Great Salt Lake, Utah and lake Walker and Pyramid in Wiveda are other examples.
Salt lakes also found in areas of drier climates such as Australia, South America, East Africa, Antarctica, Russia and dry northern side of Himalayas, South and North East America.