What process leads to eutrophication in water bodies?

Eutrophication is primarily caused by the over-enrichment of nutrients, particularly nitrogen and phosphorus, in aquatic environments. This excess nutrient input often originates from agricultural runoff, wastewater discharge, and other human activities.

When these nutrients enter water bodies, they promote rapid algal blooms, a proliferation of algae that can cover the water's surface. While initially this might seem beneficial, as it can increase productivity in the ecosystem, the subsequent decomposition of these algae depletes oxygen in the water as microorganisms break them down. This decrease in oxygen can lead to hypoxic conditions or "dead zones," where aquatic life cannot survive, resulting in decreased biodiversity and detrimental effects on the ecosystem.

In contrast, under-enrichment of nutrients would not lead to eutrophication, nor would excessive filtration of water or increased oxygen levels contribute to this phenomenon. Instead, eutrophication is directly linked to the imbalance caused by excessive nutrient concentrations in aquatic systems.