A riverine case study shows nutrient runoff increasing eutrophication. Which sequence describes the ecological impacts from runoff to hypoxic zones?

A riverine case study shows nutrient runoff increasing eutrophication. Which sequence describes the ecological impacts from runoff to hypoxic zones?

• A. Runoff adds nutrients (N, P) → algal blooms → die-off and decomposition consume oxygen → reduced dissolved oxygen → hypoxic zones → species loss and degraded habitat.
• B. Runoff reduces nutrients → clearer water → more sunlight → more fish.
• C. Runoff has no effect on oxygen levels.
• D. Runoff immediately causes fish kills without algae involvement.

Answer: (A)