Question

A lake near a village suffered heavy mortality of fish within a span of a few days. The possible reasons are
(a) Lot of urea and phosphate fertilizers were used in nearby crops.
(b) The area was sprayed with DDT by an aircraft.
(c) Lake water turned green and stinky.
(d) Phytoplankton population declined reducing photosynthesis.

• A. a, b
• B. a, c
• C. b, c
• D. c, d

Answer 1

Answer: (B)

a, c

The heavy mortality of fishes in the lake within a span of few days is due to Eutrophication.

Eutrophication is the phenomenon of nutrient enrichment of nitrogen and phosphorus in a water body that supports a dense growth of plants and animal life. Due to nutrient enrichment, excess growth of algae occurs which is called algal bloom. When these algae die, their organic matter gets decomposed and this results in the depletion of oxygen leading to death of aquatic animals.

Hence, this indicates that lot of urea and phosphate fertilizers are were used in nearby crops. The lake water could have turned green and stinky due to excess growth of Algae.

Hence, statements a and c are correct.

So, the correct answer is 'a,c'.