Prelims 2011 · archive
MediumThere 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:
Answer & explanation
Answer: (d) 1, 2 and 3
Harmful algal blooms in Indian seas are driven by extra nutrients in the water. Estuaries and monsoon run-off from land bring these nutrients in, and upwelling lifts nutrient-rich deep water to the surface. All three factors are therefore causes, so the answer is (d).
- ✓ 1. Estuaries collect nutrients from their river catchments and discharge them into coastal waters. In the Mandovi–Zuari estuarine complex of Goa, rising nutrient loading has been linked to the growth of harmful algal flora. The nutrient-rich estuarine water that reaches the coastal sea can feed blooms there.
- ✓ 2. Monsoon rain washes nutrients off the land into rivers, estuaries and the sea. A study on the Goa coast links nutrient loading during monsoonal run-off directly to the growth of harmful algal flora.
- ✓ 3. Upwelling brings cool, nutrient-rich subsurface water to the surface. Off the southwest coast, upwelled water during the Southwest Monsoon has fuelled exceptionally high phytoplankton stock. Upwelling along the Dakshina Kannada coast has been associated with HABs on the southwest coast of India.
- ✗ (a) '1 only' wrongly leaves out monsoon run-off and upwelling. Both supply nutrients that feed blooms in Indian coastal waters.
- ✗ (b) '1 and 2 only' ignores upwelling. Upwelling is a natural nutrient pump along the Indian west coast, especially during the Southwest Monsoon.
Remember · Algal blooms need nutrients. In India these come from estuarine discharge, monsoon land run-off and coastal upwelling, so all three act as causes.
Sources
- Spatiotemporal Distribution of Harmful Algal Flora in the Tropical Estuarine Complex of Goa, India (PMC) ↗ “there has been an increase in nutrient loading specially during monsoonal runoff which is responsible for the growth of harmful algal flora.”
- Perceived Intensification in Harmful Algal Blooms Is a Wave of Cumulative Threat to the Aquatic Ecosystems (PMC) ↗ “Some studies in India were conducted along Dakshina Kannada coast and reported the occurrence of upwelling from March to October in that region, which was associated with HABs on the southwest coast of India”
- Upwelling and Alappuzha Mud Bank plankton, southwest coast of India (PMC) ↗ “The upwelled water persisting throughout the Southwest Monsoon period was found to have fuelled the exceptionally high phytoplankton stock in the entire study area”
Question: UPSC Civil Services (Preliminary) 2011, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·