Question

When $P{O_4}$ and $N{O_3}$ is more in the water of a lake it causes
A. Growth of bacteria
B. Growth of fishes
C. Death of algae
D. Algal bloom

Answer 1

Eutrophication is the excessive growth of algae in water due to the increased concentrations of fertilizers in the soil. The fertilizers are made up of compounds of phosphates and nitrates.

Complete step by step answer: Eutrophication is the excessive growth of algae, along with some plants and animals in the water bodies. This is due to nutrient enrichment particularly, the salts of nitrogen and phosphorus. In eutrophication, the nutrient content of the lake increases gradually. This is due to the surface runoff, and various types of streams, rivers, and other water bodies draining into it. This process can be slow and gradual and it is known as natural eutrophication. When it is fast and caused by man-made activities, it is known as cultural or accelerated eutrophication. Due to the eutrophication, the temperature of the lake or the water body increases. Due to this, the water body becomes inhabitable. The increased content of nitrogen and phosphorus accelerates the growth of the algae. This process is known as an algal bloom. This is because these nutrients are needed by the algae and plants for their growth. Thus, when $P{O_4}$ and $N{O_3}$ are more in the water of a lake it causes algal blooms.
Hence, the correct answer is option (D).

Note: Eutrophication is very harmful to aquatic water systems. This is because the algae growing on the water deprives the aquatic flora and fauna of oxygen. Moreover, the algae compete with them for the resources. Due to this the aquatic flora and fauna slowly deplete and they gradually die and finish. This process is called the death of the lake. This causes unsightly scum on the surface of the lake and a very foul and unpleasant odor.