Question

If fertilisers are added to fresh water then

• A. Plants will die
• B. Overall animal population will increase
• C. Eutrophication will occur
• D. Fish population will decrease

Answer 1

The correct option is D Fish population will decrease

The streams draining the fertilisers into the lake introduce nutrients such as nitrogen and phosphorus, which encourage the growth of algae. As the lake's fertility increases, algal bloom occurs. Algal bloom causes the deterioration of water quality and dead remains begin to be deposited on the lake bottom. After the death of such organisms, the bacterial degradation of their biomass consumes the oxygen in the water, thereby creating the state of hypoxia (deficiency in the amount of oxygen reaching tissue) that leads to the death of aquatic plants and animals like fishes.

Thus, the correct answer is option D.