Eutrophication is driven by nutrient enrichment leading to algal blooms and oxygen depletion; which nutrients are key drivers?

• A. Lead and arsenic
• B. Nitrates and phosphates
• C. Mercury and cadmium
• D. Nitrates only

Answer: (B)

Eutrophication happens when waterways receive excess nutrients that fuel rapid algae growth, and that boom-stay-bust cycle eventually steals oxygen from the water as the blooms die and decompose. The nutrients that most drive this process are nitrates, which supply nitrogen, and phosphates, which supply phosphorus. Both elements are essential for algae to grow and reproduce, and when they enter rivers, lakes, or coastal areas in high amounts—often from fertilizers, wastewater, and detergents—they trigger dense algal blooms. As these blooms die, microbial decomposition uses up dissolved oxygen, creating low-oxygen conditions that can harm aquatic life and lead to dead zones. The other options miss the point: heavy metals like lead, arsenic, mercury, and cadmium are pollutants that can harm organisms, but they don’t provide the nutrient enrichment that causes bloom-driven oxygen depletion; and relying on nitrates alone ignores phosphorus, which is also a key nutrient for many freshwater algal systems.