Question

Assertion:
Cultural eutrophication is nutrient enrichment of water bodies due to human activities like passage of sewage, industrial effluents, etc.

Reason:
The prime contaminants from sewage and industrial effluents are nitrates and phosphates, which act as plant nutrients and overstimulate the growth of algae.
a. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
b. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
d. Both Assertion and Reason are incorrect

Answer 1

Human beings have been deteriorating and damaging the water-bodies around the world by disposing into them all kinds of waste generated from factories and other places . We always think and believe that water can take away everything not taking into consideration the fact that the water bodies are our lifeline as well as that of all other living organisms and are essential to all. Due to such activities of humans that are throwing waste in water , the ponds, lakes, streams, rivers, estuaries and oceans are becoming polluted in several parts of the world.

Complete answer:
Eutrophication:- It is excessive growth of algae, plants and animals in water bodies due to the nutrient enrichment particularly with nitrogen and phosphorus. Eutrophication is both natural and accelerated.

Cultural or Accelerated Eutrophication
- It is caused by human activities like effluents that are dissolving substances from the industries and homes, run-off of fertilizer that is chemicals -rich agriculture fields.
- During the past century, lakes and oceans also in many parts of the earth have been severely eutrophied by sewage damaging particles and agricultural and industrial wastes.
- The prime contaminants that damage the water are nitrates and phosphates, which act as plant nutrients. They cause excessive growth of algae, causing unsightly scum also called as foaming substance and unpleasant odours, and robbing the water of dissolved oxygen vital to other aquatic life.
- At the same time other pollutants that are contamination substances flowing into a lake may poison whole populations of fish, and also cause death of them whose decomposing remains further deplete the water's dissolved oxygen content. In such a fashion, a lake can literally choke to death.

Hence, the correct answer is option (B).

Note: It is defined as the natural ageing due to nutrient enrichment of the water body. It is a slow process which may not be seen in human lifetime. A young water body has cold, clear water where there is no nutrient enrichment. Runoff and streams draining into it gradually add nutrients, especially nitrogen and phosphorus, which encourage growth of aquatic organisms.