What is a consequence of excessive fertilization in aquatic ecosystems?

Excessive fertilization in aquatic ecosystems leads to increased nutrient runoff, particularly nitrogen and phosphorus, which promotes the overgrowth of algae, commonly referred to as algal blooms. These blooms can significantly reduce oxygen levels in the water when they die and decompose, as the decomposition process consumes large amounts of dissolved oxygen. This reduction in oxygen levels can result in hypoxic conditions, which can be detrimental to fish and other aquatic life, leading to fish kills and a decline in overall ecosystem health.

In contrast, improved water quality, enhanced biodiversity, and increased water clarity are more often associated with balanced nutrient levels, where aquatic ecosystems can maintain their natural processes and support a diverse range of species. Thus, the consequence of excessive fertilization primarily manifests as reduced oxygen levels, causing severe impacts on aquatic ecosystems.