Question

What is the significance of dissolved oxygen to the aquatic organisms? How it gets depleted?

Answer 1

Dissolved oxygen is used by the plants and animals that live in water for respiration. It is also used for the decomposition of dead plants and animals in water. Any change that would reduce the amount of this dissolved oxygen would adversely affect these aquatic organisms. The dissolved oxygen gets depleted in the following ways:

(i)Change in the pH : More acidic is water less it has dissolved oxygen.

(ii) Change in the temperature: More is the temperature of the water, less dissolved oxygen it has. Because solubility of gases decreases with the rise in temperature.

(iii) Fertilisers and pesticides : More amount of fertilisers in any water body will lead to the growth of more algae which on decomposition will use more of dissolved oxygen, thus decreasing its amount in water. More amount of pesticides will cause death of algae which will reduce the dissolved oxygen content.