Prelims · Environment & ecology · 40 questions

Pollution & waste

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Prelims 2018 · Q13

Easy

Which of the following has/have shrunk immensely/dried up in the recent past due to human activities?

1.Aral Sea
2.Black Sea
3.Lake Baikal

Select the correct answer using the code given below:

Answer & explanation

Answer: (a) 1 only

Only the Aral Sea fits. From the 1960s the Soviet Union diverted its feeder rivers, the Amu Darya and Syr Darya, to irrigate cotton, and the lake that was once the world's fourth largest broke into small remnants. The Black Sea and Lake Baikal have not shrunk in this way.

✓ 1. Irrigation diversions starved the Aral Sea (on the Kazakhstan–Uzbekistan border) of inflow; satellite images show it was already a fraction of its 1960 extent by 2000.
✗ 2. The Black Sea, a large inland sea linked to the Mediterranean through the Bosporus, faces pollution problems but has not dried up.
✗ 3. Lake Baikal in Siberia, the world's deepest lake, still holds its vast volume of fresh water; it has not shrunk immensely.

Remember · Aral Sea: once the world's fourth-largest lake, fed by the Amu Darya and Syr Darya; shrank drastically after Soviet-era irrigation diversions from the 1960s.

Sources

World of Change: Shrinking Aral Sea, NASA Earth Observatory ↗ “In the 1960s, the Soviet Union undertook a major water diversion project on the arid plains of Kazakhstan, Uzbekistan, and Turkmenistan. … The lake they made, the Aral Sea , was once the fourth largest in the world. Although irrigation made the desert bloom, it devastated the Aral Sea.”

Question and answer: UPSC's official GS Paper I (2018, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

Prelims 2018 · Q81

Medium

Which of the following is/are the possible consequence/s of heavy sand mining in riverbeds?

1.Decreased salinity in the river
2.Pollution of groundwater
3.Lowering of the water-table

Select the correct answer using the code given below:

Answer & explanation

Answer: (b) 2 and 3 only

Heavy sand mining harms groundwater in two ways: it can pollute it and it can pull the water-table down. It does not lower river salinity; near the coast it makes salt-water intrusion more likely.

✗ 1. Removing sand deepens the channel and weakens natural barriers, so salt water can enter aquifers; UNEP lists 'salination of aquifers' as a result of sand extraction. Salinity goes up, not down.
✓ 2. The sand layer filters water that seeps into the ground. The MoEFCC guidelines say mining can pollute groundwater by thinning this filter material, especially over recharge fissures.
✓ 3. Mining lowers the riverbed and river level, and groundwater in the adjoining flood plain drains towards it, so the water-table falls. The guidelines record this as a listed effect.

Remember · Heavy riverbed sand mining lowers the water-table, weakens the sand filter that protects groundwater, and raises salt intrusion risk near the coast.