What term describes the buildup of chemical nutrients to harmful levels in an ecosystem?

The term that describes the buildup of chemical nutrients to harmful levels in an ecosystem is eutrophication. This process typically occurs when excess nutrients, particularly nitrogen and phosphorus, enter water bodies, often through runoff from agricultural lands, fertilizers, or sewage. These nutrients lead to an overgrowth of algae, known as algal blooms, which can create low-oxygen conditions in the water as they decay. This depletion of oxygen can harm aquatic life, disrupt ecosystems, and lead to the overall degradation of water quality.

The other terms listed pertain to related concepts but do not specifically describe the nutrient buildup scenario. Bioaccumulation refers to the gradual accumulation of substances, such as pesticides or heavy metals, in an organism over time, while biomagnification is the increase in concentration of these substances in organisms as you move up the food chain. Decomposition involves the breakdown of organic matter by decomposers but does not relate directly to nutrient buildup in the sense of causing harmful levels within an ecosystem.