Which process describes how excess nutrients lead to algal blooms and oxygen depletion?

• A. Eutrophication.
• B. Leaching.
• C. Sedimentation.
• D. Evaporation.

Answer: (A)

Excess nutrients in water bodies stimulate rapid growth of algae and other algae-like organisms, causing algal blooms. When these blooms explode, they block sunlight and, as the organisms die and decompose, microbes consume a lot of dissolved oxygen. That drop in oxygen leads to oxygen depletion, which can create dead zones where aquatic life struggles to survive. This chain of events is what eutrophication describes: nutrient pollution driving bloom formation and subsequent oxygen shortages.

Leaching describes nutrients moving through soil into groundwater, not the rapid in-water growth and oxygen decline. Sedimentation is the settling of suspended particles, which affects clarity and sediment buildup rather than nutrient-driven blooms. Evaporation is the transformation of water into vapor, unrelated to nutrient enrichment and its ecological effects. So the process that best fits the scenario is eutrophication.