What effect does the addition of fertilizer have on aquatic ecosystems downstream?

What effect does the addition of fertilizer have on aquatic ecosystems downstream?

• A. Decrease in water temperature
• B. No change
• C. Increase in dissolved oxygen
• D. Increase in biological oxygen demand

Answer: (D)

When fertilizer enters a waterway, it brings extra nutrients like nitrogen and phosphorus that fuel plant and algal growth. This quick, abundant growth increases the amount of organic matter in the water. As that organic material decomposes, microbes consume dissolved oxygen, raising the biological oxygen demand. With more oxygen being used up to break down this material, the dissolved oxygen available for fish and other aquatic life drops, leading to stressed or dead zones downstream. Fertilizer doesn’t directly lower water temperature and doesn’t cause no change or higher dissolved oxygen overall, so the most accurate effect is an increase in biological oxygen demand.

When fertilizer enters a waterway, it brings extra nutrients like nitrogen and phosphorus that fuel plant and algal growth. This quick, abundant growth increases the amount of organic matter in the water. As that organic material decomposes, microbes consume dissolved oxygen, raising the biological oxygen demand. With more oxygen being used up to break down this material, the dissolved oxygen available for fish and other aquatic life drops, leading to stressed or dead zones downstream. Fertilizer doesn’t directly lower water temperature and doesn’t cause no change or higher dissolved oxygen overall, so the most accurate effect is an increase in biological oxygen demand.