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 nutrient inputs to lakes,rivers or coastal waters become very high,stimulating dense algal blooms. When these algae die and decompose, they consume dissolved oxygen, often causing fish kills and ecological imbalance. The stem describes this nutrient enrichment and algal growth process,so eutrophication is the correct term. It is a key water quality problem linked to fertiliser use and sewage.

Option A:
Sedimentation involves deposition of suspended soil particles in water bodies,which can reduce depth and alter habitats. It does not directly involve nutrient driven algal growth or oxygen depletion,so it is not the phenomenon described.

Option B:
Eutrophication is especially common in stagnant or slow moving waters that receive agricultural runoff and untreated sewage. It dramatically changes aquatic food webs and can produce harmful algal toxins. These characteristics fit the events outlined in the question.

Option C:
Thermal pollution refers to increases in water temperature due to discharge of heated effluents,often from power plants. While it affects dissolved oxygen levels,it is not primarily caused by nutrient enrichment,so it does not match the stem.

Option D:
Acidification means lowering of pH in water or soil due to acid inputs,such as acid rain or carbon dioxide absorption. It affects organisms differently from eutrophication and is not chiefly associated with nutrient overloading and algal blooms.