Q. What is limnetic zone?

The open water zone is called the limnetic zone. This represents the zone or depth of the water upto which sunlight can penetrate. Phytoplankton along with algal forms, various zooplankton species and fish abound in this zone. The deep water zone lying below the limnetic zone is called profundal zone. It is relatively cool and dark, having low dissolved oxygen content and is inhabited by fish which can tolerate such stressful conditions. The bottom of the lake is inhabited by bacteria, fungi, blood worms and other decomposers which live on dead plants, organic matter including remains of animals and their metabolic wastes.

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.