Arrange these events from fertiliser run-off in the correct order. P. Algae die and aerobic bacteria decompose them; Q. Nitrate and phosphate enter a lake; R. Dissolved oxygen falls and fish die; S. Rapid growth of algae (bloom).

AQ, S, R, P
BS, Q, P, R
CQ, P, S, R
DQ, S, P, R

Answer: D

Nutrient inflow comes first and drives the algal bloom. Dead algae are then decomposed by bacteria which consume oxygen, and the oxygen shortage kills fish.

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