Q. Zonation in the lake biome?

Precipitation that does not evaporate or penetrate the soil remains on the soil surface resulting in run off which flows down from the mountains in the form of streams and rivers which ultimately discharge into the sea. The downward flow of the river comprises of three phases.

The first phase, when the stream with cold clear water rushes down steep slopes having high dissolved oxygen content. Most organisms which are adapted to cold temperatures and need high amounts of dissolved oxygen are found here. In the second pha se the stream flows over gentle slopes and through wider valleys. Here the temperature of water is warmer and supports a wide variety of cold water and warm water fish that require slightly lower dissolved oxygen. At the point where river discharges into sea, the river may divide into many channels, forming the delta.

Rivers and brookes which are flowing fresh water bodies differ from lakes and ponds in three major aspects:

1. current is the major controlling and limiting factor,

2. land-water interchang e is greater because of the smaller size and depth of moving water systems, and

3. oxygen is always abundant except in case of excessive pollution in river stretches.