What does eutrophication result in when it occurs in water bodies?

Eutrophication is the process through which water bodies become enriched with nutrients, particularly nitrogen and phosphorus. This nutrient enrichment often leads to explosive growth of algae, commonly referred to as algal blooms. When these blooms die and decompose, the decomposition process consumes a substantial amount of dissolved oxygen in the water, resulting in oxygen depletion.

This reduction in oxygen levels can become critical and harm aquatic life, as many fish and other organisms rely on dissolved oxygen for survival. Hence, excessive plant growth, which is a hallmark of eutrophication, directly correlates with the depletion of oxygen in the water body. This phenomenon is why the choice stating excessive plant growth and oxygen depletion is identified as the correct answer. It highlights the detrimental impacts of eutrophication on aquatic ecosystems.

The other options do not accurately represent the effects of eutrophication. For instance, increased aquatic diversity would typically not occur due to the conditions created by eutrophication; instead, it usually leads to a decline in biodiversity as oxygen levels fall. Enhanced water clarity would be contradictory, as algal blooms often create turbid conditions. Finally, decreased levels of pollutants is misleading, as the process relates to nutrient enrichment rather than a reduction in pollutants.