Which of the following are common causes of eutrophication?

• A. Plastic debris
• B. Heavy metals
• C. Fertilizers, Sewage, Animal Waste (Nitrogen and Phosphorus)
• D. Saltwater intrusion

Answer: (C)

Eutrophication happens when a water body receives too many nutrients, especially nitrogen and phosphorus, which fuel rapid growth of algae and aquatic plants. The most important sources of these nutrients are fertilizers used on crops and lawns, sewage, and animal waste that run off into streams, rivers, and lakes. When these nutrients wash into water, algal blooms can explode, and as the algae die, their decomposition uses up dissolved oxygen, creating dead zones where aquatic life struggles to survive.

Plastic debris can harm ecosystems in other ways, but it doesn’t add nutrient loads to water to trigger algal blooms. Heavy metals are toxic pollutants rather than nutrient contributors, and saltwater intrusion changes salinity rather than delivering the nutrients that drive eutrophication. So the nutrient-rich inputs from fertilizers, sewage, and animal waste are the primary causes of eutrophication.