Which sequence correctly describes the full process of eutrophication?

Which sequence correctly describes the full process of eutrophication?

• A. Algal bloom → nutrients → blocks sunlight → plants die → bacteria decompose → BOD increases → oxygen drops → fish die
• B. Nutrients → algae bloom → blocks sunlight → plants die → bacteria decompose → BOD increases → oxygen drops → fish die
• C. Nutrients → bacteria decompose → BOD increases → algae bloom → oxygen drops → fish die → blocks sunlight
• D. Algal bloom → bacteria decompose → fish die → nutrients → BOD increases

Answer: (B)

Eutrophication starts when excess nutrients enter a water body, fueling rapid algal growth. As nutrients drive an algal bloom, more algae accumulate on the surface, shading the water and blocking sunlight. This reduced light harms submerged aquatic plants, causing them to die. The dead plant material and algae then become food for bacteria, whose break-down of this organic matter raises the Biological Oxygen Demand (BOD)—the amount of oxygen bacteria need to decompose the material. With more oxygen being used, dissolved oxygen in the water drops, creating low-oxygen conditions that lead to fish kills. So the sequence that matches this progression is: nutrients → algae bloom → blocks sunlight → plants die → bacteria decompose → BOD increases → oxygen drops → fish die. The other sequences either skip the initial nutrient trigger, place decomposition before there’s enough organic matter, or mix the steps in a way that doesn’t reflect how oxygen is consumed during decomposition.

Eutrophication starts when excess nutrients enter a water body, fueling rapid algal growth. As nutrients drive an algal bloom, more algae accumulate on the surface, shading the water and blocking sunlight. This reduced light harms submerged aquatic plants, causing them to die. The dead plant material and algae then become food for bacteria, whose break-down of this organic matter raises the Biological Oxygen Demand (BOD)—the amount of oxygen bacteria need to decompose the material. With more oxygen being used, dissolved oxygen in the water drops, creating low-oxygen conditions that lead to fish kills.

So the sequence that matches this progression is: nutrients → algae bloom → blocks sunlight → plants die → bacteria decompose → BOD increases → oxygen drops → fish die. The other sequences either skip the initial nutrient trigger, place decomposition before there’s enough organic matter, or mix the steps in a way that doesn’t reflect how oxygen is consumed during decomposition.