CIE iGCSE Co-Ordinated Science B19.2 Conservation Exam Style Questions Paper 2

Eutrophication starts with increased nitrates entering water, usually from fertiliser runoff, which causes producers such as algae to increase rapidly.
This algal bloom blocks light, causing plant death and increased decomposition as decomposers respire aerobically to break down the extra dead matter.
This increased aerobic respiration by decomposers depletes dissolved oxygen, leading to the death of aquatic organisms such as fish.
✅ Answer: (D)