Which cycle is heavily impacted by human activities such as the use of fertilizers?

The phosphorus cycle is significantly influenced by human activities, particularly through the use of fertilizers. In agriculture, phosphorus is added to soils in the form of synthetic fertilizers to enhance plant growth. While phosphorus is an essential nutrient for plants and is often found in fertilizers, its excessive use can lead to runoff into waterways during rain events. This runoff can result in eutrophication, where nutrient overloads cause algal blooms, which deplete oxygen in the water and disrupt aquatic ecosystems.

Additionally, phosphorus does not have a gaseous phase like carbon or nitrogen, meaning it tends to accumulate in soils and waterways. The disruption caused by human inputs into the phosphorus cycle can lead to long-term ecological imbalances, affecting both land and aquatic systems. Understanding this cycle's sensitivity to human influence highlights the broader impacts of agricultural practices on the environment.