Question

Which of the following statements is not correct regarding algal blooms?
A. Algal blooms are formed by blue-green algae.
B. Growth of Eichhornia crassipes causes coloration of water during algal blooms.
C. Increased growth of algae causes depletion of \[{{O}_{2}}\] in the water.
D. Algal blooms cause deterioration of water quality and fish mortality.

Answer 1

Hint: Algae consists of various unicellular and multicellular organisms that consist of cyanobacteria and seaweed. The overgrowth or accumulation of algae on the freshwater or marine water body is termed as an algal bloom. It is usually identified by discoloration of the water body. Algal blooms cause eutrophication like water hyacinth overgrowth.

Complete answer: Algae are a diverse group of photosynthetic organisms. Algae include both macroscopic multicellular organisms like seaweed and microscopic unicellular organisms like cyanobacteria. The algal blooms are overpopulation of algae grown over the surface of freshwater or marine water. These algal blooms usually form mat-like structures that cover the whole water body.
Algal blooms generally impart coloration to the water bodies in which they grow. The photosynthetic pigments present in them are responsible for this coloration. Excessive growth of algae-like blue-green algae leads to the production of the green color of the water. The algal blooms lead to eutrophication. This means that the overgrowth of algae consumes all of the oxygen presents inside the water body. Also, the algal coverings or mats inhibit oxygen diffusion from the atmosphere into the water body. This depletes the oxygen levels in the water ecosystem that results in deterioration in the quality of water as marine life suffers and becomes dead or decayed. Therefore, options A, C, and D are correct statements about the algal blooms.
Eichhornia crassipes or water hyacinth is an aquatic plant. Some of the species of water hyacinth are invasive and thus grow rapidly covering the surface of water bodies. These species compete with aquatic life resulting in deterioration of transparency of water and oxygen levels of water. It is not an algal bloom.
Hence, the right answer is option B.

Note: The reason for the occurrence of algal blooms is the presence of nutritive substances like nitrogen and phosphorus in water bodies. This is due to the run-offs from the fields that carry fertilizers in them. This causes eutrophication and hence pollutes and deteriorates the water bodies.