Which process involves the breakdown of organic materials leading to oxygen depletion in water?

The process of eutrophication involves the enrichment of water bodies with nutrients, primarily nitrogen and phosphorus. This nutrient influx often comes from agricultural runoff, sewage, and other sources. When these nutrients are introduced into aquatic ecosystems, they stimulate excessive growth of algae, a phenomenon known as algal bloom.

As the algae proliferate and then die off, the decomposition process begins. Bacteria and other microorganisms break down the organic material from the dead algae. This decomposition requires oxygen, which can lead to significant oxygen depletion in the water. As oxygen levels drop, it creates anoxic or hypoxic conditions, which are detrimental to aquatic life, including fish and other organisms that depend on oxygen for survival.

This process illustrates how eutrophication not only leads to overgrowth of algae but also results in serious ecological consequences due to the consequent decline in oxygen levels in the water.