Question

Arrange the steps of eutrophication in the order in which they occur.

• A. Influx of N & P
• B. Algal bloom
• C. Decrease in $O_2$
• D. Death of fish
• E. Bacterial growth

Answer 1

When nitrogen and phosphorus present in fertilisers used in farms runoff and enters the water body, it leads to an increase in algal growth (algal bloom) which utilise the dissolved oxygen.

When these algae die, bacteria start decomposing them hence utilising more oxygen. While the fish move away from this hypoxic (low oxygen condition) environment, the depletion in oxygen levels leads to death of shellfish in the water leading to collapse of water ecosystem (dead zone). This process is called eutrophication.