Select the correct statements about Eutrophication. I. It is a general term describing a process in which nutrients accumulate in…

Question

Select the correct statements about Eutrophication.

I. It is a general term describing a process in which nutrients accumulate in a body of water, resulting in increased growth of organisms.

II. It leads to an increase in levels of dissolved oxygen, favoring fish growth.

1. A. I only (Correct answer)
2. B. II only
3. C. Both I and II
4. D. Neither I nor II

Correct Answer

Option A — I only

Detailed Solution & Explanation

The correct answer is I only.

Key Points

• Statement I is correct. Eutrophication is the process by which a water body becomes progressively enriched with nutrients — chiefly nitrogen and phosphorus — leading to excessive growth of algae and aquatic plants.
• Statement II is incorrect. Eutrophication reduces dissolved oxygen rather than increasing it, and therefore harms fish rather than favouring them.

Additional Information

• How oxygen is lost — the sequence that makes statement II wrong:
  • Nutrient enrichment triggers an algal bloom that forms a dense mat on the surface.
  • The mat blocks sunlight, killing submerged plants that would otherwise release oxygen.
  • When the algae die, decomposer bacteria multiply and consume large volumes of dissolved oxygen while breaking down the biomass.
  • The water becomes hypoxic or anoxic, producing fish kills and "dead zones".
• Main sources of nutrients: agricultural run-off carrying fertiliser, untreated sewage, and detergents containing phosphates.
• Related terms:
  • Oligotrophic — nutrient-poor, clear, oxygen-rich water.
  • Eutrophic — nutrient-rich, turbid, oxygen-poor water.
  • Cultural eutrophication — the accelerated form caused by human activity, as distinct from the natural process that takes centuries.
• Harmful Algal Blooms (HABs) may also release cyanotoxins that poison livestock and contaminate drinking water.