What are the main nutrients that cause eutrophication?

• A. Carbon dioxide and methane
• B. Nitrates and phosphates
• C. Chlorine and fluoride
• D. Sodium and potassium salts

Answer: (B)

Eutrophication is driven by excess nutrients in water, especially nitrogen and phosphorus. When nitrates (a form of nitrogen) and phosphates enter aquatic systems from fertilizer runoff, sewage, and cleaning detergents, they fuel rapid growth of algae and aquatic plants. This lush growth can block sunlight and, when the blooms die and decompose, microbial activity uses up a lot of oxygen, leading to low-oxygen zones that harm fish and aquatic life.

Other options don’t fit because carbon dioxide and methane are greenhouse gases and not the nutrients that trigger algal blooms; chlorine and fluoride are disinfectants; and sodium and potassium salts are minerals that don’t drive the nutrient-driven algal overgrowth seen in eutrophication. The key drivers are nitrates and phosphates.