Which process best explains how fertilizer runoff leads to the formation of dead zones in aquatic ecosystems?

• A. Primary succession, which establishes new communities on bare substrates
• B. Biomagnification, which increases toxin levels in top predators
• C. Denitrification, which converts nitrates into nitrogen gas
• D. Eutrophication, which causes excessive algal growth and subsequent oxygen depletion

Answer: (D)

Verified step by step guidance

1. Understand the concept of eutrophication: Eutrophication is a process where excess nutrients, such as nitrogen and phosphorus from fertilizers, enter aquatic ecosystems, leading to rapid algal growth.
2. Explain how fertilizer runoff contributes to eutrophication: Fertilizer runoff introduces high levels of nutrients into water bodies, which act as a food source for algae, causing their population to grow excessively.
3. Describe the consequences of excessive algal growth: The overgrowth of algae blocks sunlight from reaching underwater plants, disrupting photosynthesis and leading to plant death. Additionally, when algae die, they are decomposed by bacteria, which consume oxygen in the process.
4. Discuss the formation of dead zones: As oxygen levels in the water drop due to bacterial decomposition, aquatic organisms that rely on oxygen, such as fish and invertebrates, cannot survive, leading to areas with little to no life, known as dead zones.
5. Summarize the connection: Fertilizer runoff initiates eutrophication, which ultimately results in oxygen depletion and the formation of dead zones in aquatic ecosystems.