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:

All three factors drive harmful algal blooms (HABs), so the answer is D. The core concept is eutrophication, or nutrient enrichment of coastal water. Phytoplankton need nitrogen and phosphorus, and when these arrive in excess, some species multiply rapidly and a few produce toxins.

• Statement 1 (correct): Estuaries and rivers carry fertilizer runoff, sewage and industrial effluent to the sea, adding nutrients directly to coastal waters.
• Statement 2 (correct): Monsoon run-off washes nutrients from farmlands and cities into the sea, creating a seasonal pulse that can trigger blooms.
• Statement 3 (correct): Upwelling brings cold, nutrient-rich water from depth to the surface. Along the west coast, upwelling during the southwest monsoon is a known trigger.

Mains link: this connects to coastal pollution, the Coastal Regulation Zone notifications under the Environment (Protection) Act, 1986, and fisheries management.

Trap: Many candidates reject statement 3 because upwelling is a natural process, not a human one. The question asks for causative factors, not only anthropogenic ones.