Question

Excessive nutrients in a freshwater body cause fish mortality. Give two reasons.

Answer 1

Increase in nutrients in water leads to algal bloom and rapid plant growth which depletes oxygen and leads to fish mortality.

Complete step-by-step answer:
The condition in which the water body has excessive nutrients is called eutrophication also known as dystrophication and is a problem in marine habitats when there is excessive growth of algae causing algal blooms. This rapid growth of algae causes depletion in oxygen levels which affects the other life forms. The reason for this increased growth is the increased availability of limited growth factors required for photosynthesis. Natural eutrophication occurs in lakes and ponds but humans have accelerated the rate of eutrophication. Eutrophication mainly leads to algal blooms and hypoxia. Due to excessive growth of algae and plants oxygen level goes down and when they decompose CO$_2$ levels are increased which lowers the pH of the water and this is called ocean acidification which affects the growth of fish and also inhibits shell formation in bivalves.
1. Eutrophication affects the ecosystem and should be prevented by healthy agricultural practices, no use of fertilizers, and proper waste management.
2. Anthropogenic Eutrophication is caused due to humans. Fertilizers used in plants are washed away with water and accumulate in water bodies. These fertilizers provide many nutrients to algae increasing its growth. Also when soil rich in phosphorus reaches the water body the rate of eutrophication is severely increased.

Note: Eutrophication is the condition of excessive nutrients in a water body. It can be natural or by humans. An increase in nutrients leads to rapid algal and plant growth which depletes oxygen and when these algae and plants die CO$_2$ is released which further decreases the pH and this leads to fish mortality.