UGC NET Questions (Paper – 1)

Eutrophication occurs when excess nutrients, particularly nitrates and phosphates, enter water bodies from sewage or fertilisers. These nutrients stimulate rapid growth of algae and aquatic plants. When the biomass dies and decomposes, bacteria consume large amounts of oxygen, leading to hypoxic conditions that can kill fish and other organisms. Thus, algal blooms followed by oxygen decline and fish kills are characteristic.

Option A:
Option A is incorrect because eutrophication initially increases, not eliminates, algal growth.

Option B:
Option B is correct as it captures the sequence of nutrient enrichment, algal proliferation and oxygen depletion.

Option C:
Option C is incorrect; lakes do not suddenly become deserts, though they can become choked with vegetation and lose biodiversity.

Option D:
Option D is incorrect because crystal-clear water usually indicates low nutrient levels (oligotrophic conditions), the opposite of eutrophication.

Eutrophication occurs when excess nutrients, especially nitrates and phosphates, enter a water body. These nutrients stimulate dense growth of algae and aquatic plants, creating algal blooms. When the algae die and decompose, oxygen in the water is depleted, often leading to fish mortality. Thus, algal blooms followed by fish kills are characteristic signs of eutrophication.

Option A:
Option A is incorrect because eutrophication produces excessive algae, not their sudden disappearance. Clear water usually indicates low nutrient levels.

Option B:
Option B is correct as it clearly links nutrient enrichment, algal growth and oxygen depletion. This sequence is widely documented in polluted lakes and reservoirs.

Option C:
Option C is incorrect since crystal-clear water with low biological activity suggests oligotrophic conditions, not eutrophication. Such lakes are nutrient-poor, not nutrient-rich.

Option D:
Option D is incorrect; lakes do not rapidly become deserts due to eutrophication. They may become choked with plants and lose fish, but water remains present.

Eutrophication occurs when excess nutrients, mainly nitrates and phosphates from agricultural runoff and sewage, enter a water body. This nutrient enrichment stimulates excessive growth of algae, forming algal blooms. When these organisms die and decompose, they consume dissolved oxygen, leading to hypoxic conditions that can kill fish and other aquatic organisms. Therefore, eutrophication is best described by nutrient enrichment leading to algal growth and oxygen depletion, as in option C.

Option A:
Option A is the opposite of eutrophication and describes oligotrophic conditions, where nutrient levels are low and water is often clear. Eutrophication is associated with high nutrient loads and turbid water, not decreased nutrient content.

Option B:
Option B is incorrect because warming of water is related to climate change and thermal pollution, not specifically to eutrophication. Although temperature can influence algal growth, eutrophication is fundamentally about nutrient enrichment.

Option C:
Option C correctly combines nutrient enrichment, algal blooms and oxygen depletion, which are the key features of eutrophication. It explains why eutrophication is harmful to aquatic ecosystems and contributes to fish kills and biodiversity loss.

Option D:
Option D is incorrect since conversion to saline water is typically due to seawater intrusion or evaporation in closed basins, not eutrophication. Salinity changes are a different type of water quality issue.