What consequence arises from excess fertilizer runoff increasing nitrates into water?

What consequence arises from excess fertilizer runoff increasing nitrates into water?

• A. Algal blooms and oxygen depletion in aquatic systems
• B. Increased water clarity and oxygen saturation
• C. Reduced nutrient cycling efficiency in soils
• D. Decreased plant growth in terrestrial ecosystems

Answer: (A)

Excess fertilizer runoff raises nutrients, especially nitrates, in water, triggering eutrophication. This nutrient boost fuels rapid growth of algae and other aquatic plants, leading to algal blooms. When these blooms die, their decomposition uses up a lot of dissolved oxygen in the water, causing oxygen depletion and creating dead zones where many aquatic organisms can’t survive. That combination—algal proliferation followed by low oxygen—explains why algal blooms and oxygen depletion in aquatic systems is the expected consequence.

Water becomes muddier rather than clearer during blooms, and oxygen levels drop rather than rise, so the other options don’t fit. The soil-focused idea about reduced nutrient cycling in soils isn’t addressing what happens in the water, and while fertilizer effects on land can be negative, the question targets water ecosystems and the immediate outcomes there.