With reference to Eutrophication, which of the following statements is/are correct? 1) It decreases dissolved oxygen in water. 2) It is a phenomenon of nutrient enrichment of a water body. Select the correct answer from the codes given below:

Both statements are correct, so the answer is C. Eutrophication is the enrichment of a water body with nutrients, mainly nitrogen and phosphorus, from sewage, detergents and fertilizer runoff. That is statement 2, and it is the cause.

The effect is statement 1. Nutrient enrichment triggers algal blooms. When the algae die, decomposing bacteria consume them and use up dissolved oxygen. Dense algae also block sunlight, so submerged plants die and add to the decay load. The result is hypoxia, fish kills and, in severe cases, anaerobic conditions.

• Option A is wrong because statement 2 correctly describes eutrophication.
• Option B is wrong because statement 1 is a documented effect.
• Option D is wrong because both statements hold.

Mains angle: eutrophication links to the Ganga pollution debate, lake restoration under the National Lake Conservation Plan, and the Wetlands (Conservation and Management) Rules, 2017, which is useful for GS-III environment answers.

Trap: aspirants often treat eutrophication as only a nutrient problem and forget the oxygen depletion that follows, or they assume low oxygen always means toxicity rather than decomposition.