UPSC Prelims 2011 · Question 17 of 100

UPSC Prelims 2011 question on Harmful Algal Blooms

There is a concern over the increase in harmful algal blooms in the seawaters of India. What could be the causative factors for this phenomenon?

1. Discharge of nutrients from the estuaries.

2. Run-off from the land during the monsoon.

3. Upwelling in the seas.

Select the correct answer from the codes given below:

  1. 1 only
  2. 1 and 2 only
  3. 2 and 3 only
  4. 1, 2 and 3
Show answer

Answer: D. 1, 2 and 3

Verdict

Correct Answer: 1, 2 and 3

Analysis

All three factors — nutrient discharge from estuaries, monsoon run-off, and oceanic upwelling — enrich Indian seawaters with nitrogen and phosphorus, promoting rapid algal growth called Harmful Algal Blooms (HABs).

Statement by statement

1. Discharge of nutrients from estuaries — Correct
Estuaries receive river water carrying sewage, industrial effluents, urban waste, and organic matter. These contain nitrates and phosphates, which act like fertilisers for phytoplankton and cause eutrophication near coastal waters.

2. Run-off from land during monsoon — Correct
During monsoons, rainwater washes agricultural fertilisers, animal waste, soil nutrients, and organic matter into rivers and seas. This seasonal nutrient loading is a major trigger for algal blooms, especially along India’s coastal regions.

3. Upwelling in the seas — Correct
Upwelling brings cold, nutrient-rich deep water to the sunlit surface. In the Arabian Sea, monsoon winds cause strong upwelling, supplying nutrients that support large algal blooms.

Extra UPSC Info
HABs can create hypoxic/dead zones by reducing dissolved oxygen, causing fish deaths.
Some algae, especially dinoflagellates, release toxins that may enter the food chain through shellfish.
Large blooms may cause water discolouration, commonly called red tides.
HAB monitoring is done using remote sensing satellites such as MODIS-Aqua.
Climate change can intensify blooms by warming surface waters and increasing water-column stability.
Final Takeaway

HABs in Indian waters are caused by both human-induced nutrient pollution and natural oceanic processes like upwelling. Therefore, all three statements are correct.

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