Question

The graph shows the change in a fish population over several years. During this same time, artificial fertilizer was used nearby.
What probably caused the fish population to change in the way shown?

A. Too much oxygen
B. An algal bloom
C. A gene mutation
D. Too little nitrogen

Answer 1

Answer: B. An algal bloom

Explanation:

• Fertilizers manufactured from petrol or natural gas are called artificial fertilizers and they consist of a wide variety of nutrients like nitrates, magnesium, phosphorous and potassium.

• Normally, in the water bodies, the number of algae is very less due to less amount of nutrients present in it. However, when these artificial fertilizers reach the water bodies, they release their nutrients quickly which causes a spurt in the growth of algae known as algal bloom.

• When the algae die, its decomposition by the microbes causes a decrease in the dissolved oxygen concentration in water and leads to the death of fishes.

Answer 2

B. An algal bloom

the process involved here is called eutrophication that causes a growth in algae.