Limnology (2+1)

Unit 1- Limnology- An introduction

1.3.1. Ponds, lakes, streams, river
Ponds:
Ponds are defined as small, shallow, inland standing water bodies, where rooted plants can grow over most of the bottom. Ponds are mainly of three general classes, they are :
i. Those which represent the pond stage in the extinction of previously existing lakes
ii. Those whose basins have never been large or deep (not preceded by a lake) but or for some special reason, have persisted in the pond stage and
iii. Those whose basins are the results of man’s activities (excavations, quarries, impoundments, etc.)
Natural process alone are constantly forming new pond basins (cut-offs from streams solution basins, beach ponds, and many others), some of which are never more than temporary ponds from the beginning; others qualifying as permanent ponds at least for a period in their existence.

Classification of ponds
With respect to seasonal duration, ponds are divided into two general classes
a. Permanent – those which contain some water the year round and
b. Temporary – those in which the basin contains water at certain times or seasons and becomes dry at others.
Those which occur for a limited period in spring are called Vernal ponds
Those which contain water in spring, dry up during summer, and again contain water in the autumn are called Vernal autumnal ponds and
Those which contain some water throughout the open season but freeze to the bottom in winter have been called Aestival ponds.

Other classifications of ponds are as follows
Natural ponds
These are perennial shallow water bodies. When a stream shifts its position it leaves behind an isolated body of standing water which forms the "Ox-Bow" pond. In limestone regions where depressions are formed due to the solution of the underlying strata, the water gets accumulated either by flood water or rainfall and natural ponds are formed. Sometimes the last remnant of a lake whose basin has become filled progressively by sedimentation in course of time is transformed into a pond.
Artificial pond
Most of the fish ponds are semi artificial ponds. Some are constructed by erecting dams across a stream or basin and their water level can be regulated by inflow and drainage where pisciculture is practiced. Fish pond is a shallow body of water that can be drained completely. It is often supplied by running water, but also by spring, ground or rain water.
Pools or Temporary Ponds
They occur in depressions in the ground either at the margin of glaciers where they fill with melt water or in the vicinity of river bed, after the floods have receded. The water thus collected usually is very shallow and measures maximum to a few feet only. Also prolonged rainfall may form temporary small pools. All these pools dry up in some part of the year, and as such organisms in these habitats must be able to survive in a dormant stage during dry periods and be able to move in and out of the pools.
General Characteristics of ponds
• Ponds are small, shallow standing water bodies.
• They have calm water
• Have more vegetation
• Growth of plants can also found at the bottom
• They have outlet streams
• The movement of water is minimum
• They have slight wave action
• The average depth of water is 8 – 10 feet
• The temperature of the pond more or less changes with that of atmosphere
• Light penetrates up to the bottom