Question

Which of the following can be the reason(s) for increase in BOD in water bodies?

• A. When fertilizers enter into water, it helps algae to bloom.
• B. When fertilizers enter into water, it starts to react with dissolved oxygen.
• C. When algae die, large organic matter gets released.
• D. When bacteria starts decomposing the dead organic matter.

Answer 1

Answer: (A), (C), (D)

The correct options are
A When fertilizers enter into water, it helps algae to bloom.
C When algae die, large organic matter gets released.
D When bacteria starts decomposing the dead organic matter.

Algae cover the water surface depriving under water plants of sunlight. When algae die, large amount of organic matter gets released. Bacteria starts decomposing this dead organic matter. Because decomposition requires more oxygen, the increased bacterial activity further drives down the level of dissolved oxygen and biological oxygen demand gets increased. Agricultural chemical fertilizers like phosphates and nitrates, run-off due to rain and enter water. It fertilizes algae and other aquatic plants boosting their growth. The biological oxygen demand(BOD) increases with increase in aquatic organisms.