Q. 22

A fresh water pon

Answer :

Eutrophication is the natural aging of a lake by biological enrichment of its water.

(a) Status of eutrophication in the pond of algae:

The excessive growth of free-floating algae caused by nutrient enrichment of water bodies through various means is called algal bloom. The nutrients act as food for algae hence support the growth of algae. Due to the algal bloom, the water body is green in colour.

Algae cover the surface of water, blocking sunlight and depleting oxygen in the water. The reduction of oxygen concentration in water causes the death of many aquatic organisms, this result in a disfunctioning ecosystem.

(b) Status of eutrophication in the pond of BOD:

During the decomposition of algae the oxygen-demanding bacteria are increasing in the ecosystem, which in turn increases the biological oxygen demand (BOD) of the ecosystem.

The amount of dissolved oxygen needed by biological organisms for the decomposition of organic compounds in a given amount of water is known as BOD.

A higher BOD indicates a lower level of dissolved oxygen.

Thus lower level of oxygen causes in the water bodies results in death of many fishes due to suffocation. When many fishes die the number of oxygen-demanding decomposers increases even more.

This is how eutrophication happens in the pond with BOD.

(c) Status of eutrophication in the pond of large animals:

Ponds have many primary producers. Animals usually consume primary producers. These types of animals are known as Primary consumers. These primary consumers are consumed larger fishes and animals they are called high-level consumers.

When the surface of ponds is covered by algal bloom, it blocks the sunlight from reaching other primary producers that live below the surface of the water. Due to this there is decrease in primary producers, thereby creating a problem for primary consumers. This in turn will result in food deficit for higher-level consumers and due to lack of food they may die.

Many large fishes start dying due to deficiency of oxygen in the water bodies. The deficiency of oxygen may result due to death of algae. When the algae die, they sink to the bottom of the water and start decomposing. And this in turn uses up the dissolved oxygen from the water leading to oxygen deficiency.

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