With reference to Eutrophication, which of the following statement(s) is/are correct ?
1. It decreases dissolved oxygen of water.
2. It is a phenomenon of nutrient enrichment of a water body.
Select t

Question

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

UnlockIAS · Accepted Answer

Correct — C, Both 1 and 2. Eutrophication is the process by which a water body becomes over-enriched with nutrients — chiefly nitrogen and phosphorus from fertiliser run-off, sewage and detergents (statement 2 is the very definition of eutrophication, correct). This nutrient loading triggers explosive growth of algae and aquatic plants (an algal bloom); when that biomass dies, its decomposition by aerobic bacteria consumes large amounts of dissolved oxygen, while the surface bloom also blocks sunlight and gas exchange. The result is oxygen-depleted (hypoxic) water and fish kills — so statement 1 (it decreases dissolved oxygen) is also correct. Both are true, hence (c).

Why the other options are wrong — (a) Incomplete — statement 2 (nutrient enrichment of a water body) is the very definition of eutrophication and is also correct.  (b) Incomplete — statement 1 is also correct: decomposition of the algal bloom consumes dissolved oxygen, lowering it.  (d) Wrong — both statements accurately describe eutrophication.

Concept: Eutrophication is nutrient (nitrogen and phosphorus) enrichment of a water body. The chain of effects is: excess nutrients from run-off/sewage → algal bloom → the bloom dies → aerobic bacteria decompose it, raising biochemical oxygen demand (BOD) → dissolved oxygen falls (hypoxia) → aquatic life, especially fish, dies. Human-accelerated eutrophication is called 'cultural eutrophication'.

State PCS 2020 Q75 — Environment & Ecology PYQ with Answer

State PCS 2020 Q75 — Environment & Ecology PYQ with Answer