RAS question
Biological Oxygen Demand (BOD) indicates:
Correct answer: (D) Amount of oxygen required by microorganisms to decompose organic matter.
Biological Oxygen Demand indicates the amount of dissolved oxygen required by microorganisms to decompose organic matter in water.
Explanation
Biological Oxygen Demand, or BOD, is a water-quality measure of how much oxygen microorganisms consume while decomposing organic matter in stream water. BOD is linked to oxygen requirement during microbial decomposition, not to oxygen already present in water. The EPA source also notes that BOD directly affects dissolved oxygen in rivers and streams; when BOD is higher, oxygen is depleted faster, leaving less oxygen available for aquatic life. Higher BOD points to greater organic pollution, while clean water typically has BOD below 1 mg/L.
Why the other options are wrong
- (A) Dissolved Oxygen is the amount of oxygen already dissolved in water, whereas BOD measures oxygen consumed or required during decomposition.
- (B) Oxygen produced by aquatic plants comes from photosynthesis; BOD is about microorganisms using oxygen while breaking down organic matter.
- (C) Atmospheric oxygen content is a property of the air, while BOD is a water-quality indicator for streams and other water bodies.
Concept
Water-pollution indicators include BOD and dissolved oxygen as distinct measures. RAS often uses BOD because it connects basic ecology, organic pollution and aquatic-life stress in one measurable parameter.