How do nitrates and phosphates contribute to eutrophication in water bodies?

• A. They neutralize acidity in water.
• B. They reduce algal growth by limiting nutrients.
• C. They fuel algal blooms, which upon decay reduce dissolved oxygen.
• D. They directly remove heavy metals.

Answer: (C)

Nitrates and phosphates are nutrients that algae and other aquatic plants need to grow. When these nutrients enter water in excess—often from fertilizer runoff, sewage, or detergents—they fuel rapid algal growth, leading to algal blooms. The major issue isn’t the blooms themselves but what happens after: when the algae die, bacteria decompose the dead material, using up a lot of the dissolved oxygen in the water. This drop in dissolved oxygen makes it hard for fish and other organisms to survive, creating low-oxygen zones or dead zones that are characteristic of eutrophication. So these nutrients drive the process by fueling blooms and then oxygen depletion. They don’t neutralize acidity, they don’t limit growth, and they don’t directly remove heavy metals.