OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What initiates the process of eutrophication?

1. Excessive rainfall into lakes

2. Runoff of non-organic fertilizers containing nitrates

3. Overfishing in nearby waters

4. Deforestation in surrounding areas

The correct answer is: Runoff of non-organic fertilizers containing nitrates

Eutrophication is primarily initiated by the runoff of nutrients, particularly nitrates and phosphates, into aquatic systems such as lakes and rivers. Non-organic fertilizers are rich in these nutrients, and when they are applied to agricultural fields, they can be washed away by rain or irrigation, leading to increased concentrations of nitrates in the water. This nutrient overload stimulates the growth of algae and aquatic plants, often resulting in algal blooms. As the algae die and decompose, a further depletion of oxygen occurs in the water, which can lead to dead zones where aquatic life cannot survive. This process can significantly disrupt aquatic ecosystems and negatively impact biodiversity. Therefore, the runoff of non-organic fertilizers containing nitrates is a key factor in initiating eutrophication.