Question

In an aquatic ecosystem, what does a high Biological Oxygen Demand (BOD) value indicate about water quality?

• A. High dissolved oxygen and clean water
• B. Low organic pollution in water
• C. High level of organic pollution and poor water quality
• D. High mineral content in water

Hint:

{BOD is directly proportional to water pollution.} Higher BOD → More organic waste → Lower dissolved oxygen → Poor water quality.

Answer 1

The Correct Option is C

Concept: Biological Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen required by microorganisms to decompose organic matter present in water. It is commonly used as an indicator of the level of organic pollution in aquatic ecosystems. When organic wastes such as sewage, agricultural runoff, or industrial effluents enter water bodies, microorganisms break down these substances using dissolved oxygen.

• High BOD → Large amount of organic matter present → Microorganisms consume more oxygen.
• Low BOD → Less organic pollution → Water is relatively clean.

If too much oxygen is consumed during decomposition, aquatic organisms like fish and invertebrates may suffer due to oxygen depletion.
Step 1: Understanding what a high BOD value represents.
A high BOD value means microorganisms require a large amount of oxygen to break down the organic material present in the water.
Step 2: Implication for water quality.
Because oxygen is heavily consumed, less dissolved oxygen remains available for aquatic life. This condition leads to poor water quality and high organic pollution. Therefore, a high BOD indicates polluted water with high organic matter content.