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:

The correct answer is D because all three factors contribute to the enrichment of nutrients in seawater, a process known as eutrophication, which triggers harmful algal blooms. 1. Discharge of nutrients from estuaries: Rivers carry agricultural fertilizers, industrial waste, and domestic sewage into estuaries. When these nutrient-rich waters enter the sea, they provide the nitrogen and phosphorus necessary for rapid algal growth. 2. Run-off from the land during the monsoon: Heavy rains wash away fertilizers and organic matter from agricultural fields and urban areas into the ocean. This sudden influx of nutrients during the monsoon season leads to seasonal blooms along the coastline. 3. Upwelling in the seas: This is a natural oceanographic process where deep, cold, and nutrient-rich waters rise to the surface to replace warmer surface water. This enrichment of the upper layers of the ocean often results in massive blooms of phytoplankton and algae. Since all three mechanisms increase the nutrient concentration in surface waters, they are all causative factors for harmful algal blooms.