Question

Entry of sewage in water caused a spurt in the growth of algae but killed fish due to

• A. Decrease in nutrients
• B. Reduction in light
• C. Depletion of oxygen
• D. All of the above

Answer 1

The correct option is C

Depletion of oxygen

Explanation of correct option:

Depletion of oxygen

1. As the algae die and decompose, the process consumes dissolved oxygen.
2. As a result, there is a decrease in oxygen in water available for fish. Later, they die.

Explanation of incorrect option:

Decrease in nutrients

1. Entry of sewage into the water can cause eutrophication.
2. Sewage water is enriched with nutrients like nitrates and phosphates.
3. Nutrient enrichment.
4. Nutrients present in sewage can cause dense growth of algae.
5. The excess growth of algae that causes the colorations of the water body is known as an algal bloom.

Reduction in light

1. Algal blooms cut off light from submerged plants. The latter died.

Final answer:

Option (C)

Entry of sewage in water caused a spurt in the growth of algae but killed fish due to depletion of oxygen.