Read the following passage and answer the given questions. Lakes are crucial…
2025
Read the following passage and answer the given questions.
Lakes are crucial freshwater reserves that support aquatic life, agriculture, and human needs. Their long-term health depends greatly on internal chemical processes. Two significant ones are phosphorus reactions and the chloride + water reaction. Phosphorus, though essential for growth, becomes harmful when it enters lakes in excess through fertilizers, detergents, or untreated sewage. These phosphorus reactions trigger algal blooms that block sunlight and reduce oxygen. As algae decompose, oxygen levels in the lake lower, suffocating fish and disrupting biodiversity. Since phosphorus can remain trapped in sediments for years, its negative effects often persist long after the external supply is reduced. The chloride + water reaction influences lakes differently. Chloride, introduced through road salts, mining, or industrial effluents, steadily raises salinity. This alters water density and circulation, stressing species adapted to freshwater. Over time, plant diversity declines, fish populations shrink, and the water often acquires a taste unsuitable for drinking or irrigation.
Lake water naturally contains several elements vital for ecological balance. Oxygen is essential for aquatic organisms, calcium supports shell-forming species like mollusks, while sodium and magnesium maintain mineral stability. When levels of elements such as chloride or phosphorus rise unnaturally, however, the lake’s chemistry shifts in ways that damage both ecosystems and human use. Monitoring these chemical reactions helps prevent major damage. Tracking phosphorus levels makes it possible to predict algal blooms, while chloride studies guide alternatives to road salt, such as sand or organic compounds. Establishing buffer zones around farms and improving wastewater treatment can also reduce nutrient flow into lakes. Yet, implementing such measures often demands high costs or changes in established practices. Farmers may resist reducing fertilizer use, while cities in snowy regions rely heavily on road salts for safety. Balancing ecological preservation with economic and practical needs remains a challenge. If ignored, these reactions can leave lakes unsuitable for consumption, raising the risk of dehydration in communities dependent on them. Protecting the chemical balance of lakes is therefore vital not only for biodiversity but also for ensuring safe and reliable freshwater for human survival.
Why the effects of phosphorus on lake ecosystems are difficult to reverse?
- A.
Phosphorus is continually supplied by natural sources like aquatic plants.
- B.
Phosphorus boosts oxygen production, which leads to microbial overgrowth.
- C.
Phosphorus reactions are neutralized quickly, masking their long-term impact.
- D.
Even after external inputs are reduced, phosphorus trapped in sediments continues to affect the ecosystem.
- E.
Chloride intensifies phosphorous effects.
Attempted by 3 students.
Show answer & explanation
Correct answer: D
Ans.(d) Sol. The passage states: “Since phosphorus can remain trapped in sediments for years, its negative effects often persist long after the external supply is reduced.” This clearly supports option (d). Other choices either misrepresent the passage (a, b, c) or add unrelated information (e).
(a) Incorrect – The passage does not mention continual supply by natural plants.
(b) Incorrect – Phosphorus reduces oxygen (via algal decomposition), it does not boost oxygen.
(c) Incorrect – Effects are not neutralized quickly; they persist. (d) Correct – Matches the passage: trapped phosphorus in sediments continues long-term impact.
(e) Incorrect – Passage does not state chloride intensifies phosphorus effects.