How does fertilizer runoff contribute to the occurrence of algal blooms in aquatic ecosystems?

• A. Fertilizer runoff increases the amount of dissolved oxygen, which inhibits algal growth.
• B. Fertilizer runoff decreases water temperature, making conditions ideal for algae.
• C. Fertilizer runoff increases nutrient levels, especially nitrogen and phosphorus, which promote rapid algal growth.
• D. Fertilizer runoff introduces toxic chemicals that directly kill algae, preventing blooms.

Answer: (C)

Verified step by step guidance

1. Understand the concept of fertilizer runoff: Fertilizer runoff occurs when excess fertilizers used in agriculture or landscaping are washed into nearby water bodies by rain or irrigation. These fertilizers often contain nutrients like nitrogen and phosphorus.
2. Recognize the role of nutrients in aquatic ecosystems: Nitrogen and phosphorus are essential nutrients for plant and algal growth. When these nutrients are introduced into aquatic ecosystems in large quantities, they can disrupt the natural balance of the ecosystem.
3. Explain how nutrient enrichment leads to algal blooms: Excess nitrogen and phosphorus act as a food source for algae, promoting their rapid growth. This phenomenon is known as eutrophication, which often results in algal blooms.
4. Discuss the consequences of algal blooms: Algal blooms can deplete oxygen levels in the water as algae die and decompose, leading to hypoxic conditions that harm aquatic life. Additionally, some algal blooms produce toxins that can be harmful to both aquatic organisms and humans.
5. Clarify why the correct answer is 'Fertilizer runoff increases nutrient levels, especially nitrogen and phosphorus, which promote rapid algal growth': This option accurately describes the process by which fertilizer runoff contributes to algal blooms, emphasizing the role of nutrient enrichment in promoting algal growth.