Question

Eutrophication of water bodies leading to killing of fishes is mainly due to non availability of
A. Oxygen
B. Food
C. Light
D. Essential minerals

Answer 1

Hint:Water bloom is caused by rapid increase in the population of algae causing the water body to change its colour. It is caused by a type of bacteria called cyanobacteria.

Complete Answer:
Eutrophication is marked by excess plant and algal growth due to increased abundance of one or more growth factors, such as sunshine, carbon dioxide and nitrogen fertilizers. The growth of algae is encouraged by the high levels of nutrients in water (most commonly phosphorus and nitrogen) that may come from fertilisers, manures, municipal runoff or animal waste entering the water sources.Algae boom or water bloom is a sudden rise in the abundance of algae in the marine environment. The colours seen are green, yellowish-brown or red. Bright green blooms can also occur. They are the product of blue-green algae, which are actually bacteria (cyanobacteria).

The more algae and plants grow excess plants in the water die. This dead organic matter becomes a food for the bacteria that breaks it down. With more food present, the amount of bacteria increases and dissolved oxygen is used up in the water. As the dissolved oxygen content is decreased, many fish and aquatic insects cannot survive leading to death of aquatic animals. Eutrophication can also cause the water quality to deteriorate.

Thus, the correct answer is option A i.eOxygen.

Note:Eutrophication is a gradual phenomenon that the lake goes through for hundreds to thousands of years due to the addition of sediments. Natural eutrophication is often referred to as ageing of the lake. Human activities, however, are accelerating the process of eutrophication.