Given below are two statements :
Statement I : The nutrient deficient water bodies lead to eutrophic

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Question

Given below are two statements :
Statement I : The nutrient deficient water bodies lead to eutrophication
Statement II : Eutrophication leads to decrease in the level of oxygen in the water bodies.
In the light of the above statements, choose the correct answer from the options given below:
(1) Both Statement I and Statement II are true
(2) Both Statement I and Statement II are false
(3) Statement I is correct but Statement II is false
(4) Statement I is incorrect but Statement II is true

Accepted Answer

Correct Answer: D — Statement I is incorrect but Statement II is trueStep-by-step Solution:Statement I (INCORRECT): Eutrophication is caused by excess nutrients (nutrient enrichment), NOT by nutrient deficiency. When water bodies receive excess nutrients — especially nitrogen (nitrates, ammonium) and phosphorus (phosphates) — from agricultural runoff, sewage discharge, and industrial effluents, algal blooms (explosive growth of algae and cyanobacteria) occur. The term 'eutrophication' literally means 'well-nourished.' So the statement is wrong — it should say 'nutrient-enriched' not 'nutrient-deficient.'Statement II (CORRECT): Eutrophication does lead to a decrease in dissolved oxygen (DO) levels in the water body. This happens in two ways: (a) Dense algal blooms block sunlight, reducing photosynthesis by submerged plants → less O₂ production. (b) When the algae die, bacteria decompose the dead organic matter aerobically, consuming large amounts of dissolved oxygen → Biochemical Oxygen Demand (BOD) increases → DO decreases drastically → fish and other aquatic organisms die (fish kills).Key Concepts:Eutrophication: Process by which a water body becomes progressively enriched with nutrients (N, P), leading to excessive plant/algal growth → depletion of oxygen → death of aquatic life.Causes: Agricultural runoff (fertilisers), sewage, industrial discharge, animal waste. Key pollutants: nitrates (NO₃⁻) and phosphates (PO₄³⁻).Effects: Algal bloom → death of algae → bacterial decomposition → increased BOD → decreased DO → fish deaths → ecosystem collapse.BOD (Biochemical Oxygen Demand): Amount of O₂ required by bacteria to decompose organic matter in water. High BOD = highly polluted water.Prevention: Reduce fertiliser use, treat sewage before discharge, control agricultural runoff.

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