- A Excess dissolved carbon dioxide gradually entering a freshwater body
- B Excess nutrients (N, P) causing algal blooms, depleting oxygen
- C Oil spills slowly contaminating the surface layer of a water body
- D Heavy metal pollution draining in from nearby industrial runoff sites
Correct answer: B. Excess nutrients (N, P) causing algal blooms, depleting oxygen
Explanation: Eutrophication: excess nutrients (from fertilizer runoff) cause algal blooms. Decomposition depletes O2, killing aquatic life.
Concept context
Ecosystems, food chains, energy flow, nutrient cycles, biodiversity, and conservation.