What is a key impact of excess nitrogen in ecosystems?

Excess nitrogen in ecosystems primarily leads to eutrophication in water bodies. When nitrogen from fertilizers, sewage, or other sources enters aquatic environments, it acts as a nutrient that stimulates excessive growth of algae, known as algal blooms. These blooms can significantly deplete oxygen levels in the water as they die and decompose, leading to hypoxic conditions that are harmful to aquatic life. This process disrupts the balance of the ecosystem, resulting in reduced biodiversity, fish kills, and changes in species composition.

In contrast, while increased biodiversity and heightened carbon capture may appear beneficial, they are generally not direct outcomes of excess nitrogen. Decreased soil fertility is also misleading in this context; instead, excess nitrogen can initially enhance soil fertility but ultimately contribute to environmental degradation. Therefore, the most accurate and significant impact of excess nitrogen in ecosystems is the process of eutrophication.