The eutrophication of water body results in

Eutrophication is the process where a water body becomes excessively enriched with nutrients (especially nitrogen and phosphorus), leading to excessive plant and algal growth.

Understand the eutrophication process: When excess nutrients enter a water body, they promote rapid growth of algae (algal bloom). This dense algal growth covers the surface, blocking sunlight from reaching deeper water.

Consequences of eutrophication: When the algae die, their decomposition by aerobic bacteria consumes large amounts of dissolved oxygen. This leads to:

$$\bullet$$ Depletion of dissolved oxygen (hypoxia or anoxia)

$$\bullet$$ Death of aquatic organisms (fish, invertebrates) that depend on oxygen

$$\bullet$$ Overall loss in biodiversity

Evaluate the options: Option A: Increase in biodiversity — Incorrect; eutrophication kills aquatic organisms due to oxygen depletion.

Option B: Loss in biodiversity — Correct; oxygen depletion causes death of fish and other aquatic life.

Option C: Break down of organic matter — While decomposition does occur, this is part of the process, not the main result of eutrophication.

Option D: Decrease in BOD — Incorrect; BOD actually increases due to the large amount of organic matter from dead algae.

The correct answer is Option B: Loss in biodiversity.