Which nutrient is most commonly responsible for eutrophication?

• A. Phosphorus
• B. Calcium
• C. Potassium
• D. Sodium

Answer: (A)

Eutrophication happens when a water body receives more nutrients than it can process, leading to rapid algal growth, then oxygen depletion as those organisms decompose. In most freshwater systems, phosphorus is the nutrient that limits primary production, so when phosphorus enters water from sources like wastewater, detergents, or fertilizer runoff, it strongly promotes algal blooms. Those blooms can shade and kill other aquatic life, and their decay uses up dissolved oxygen, creating hypoxic conditions. Calcium, potassium, and sodium are essential ions for organisms, but they don’t typically limit algae growth or drive the blooms that cause eutrophication. So phosphorus is the nutrient most commonly linked to eutrophication.