What defines eutrophication?

Eutrophication is defined as the process where water bodies, such as lakes and rivers, become enriched with excessive amounts of nutrients, particularly nitrogen and phosphorus. This nutrient overload often comes from sources like agricultural runoff, wastewater discharge, and urban runoff. The result of this increased nutrient richness is a significant increase in algae growth, commonly referred to as algal blooms.

These blooms can obstruct sunlight from reaching other aquatic plants and lead to a decline in water quality. As algae die and decompose, the process consumes oxygen from the water, leading to hypoxic or anoxic conditions that can harm or kill aquatic life. The definition effectively encompasses this chain of events, emphasizing the role of nutrient over-enrichment in the biological productivity of water bodies.

The other options, while related to different environmental issues, do not accurately capture the essence of eutrophication. High sediment levels, low oxygen levels due to pollution, and rapid cooling in winter are important environmental concerns, but they do not define the specific process of nutrient enrichment that characterizes eutrophication.