How do human activities typically disrupt nutrient cycling?

Human activities most commonly disrupt nutrient cycling through nutrient runoff leading to eutrophication. This process occurs when excess nutrients, particularly nitrogen and phosphorus from agricultural fertilizers, sewage, and industrial waste, are washed into waterways. This influx of nutrients stimulates excessive growth of algae, known as algal blooms. While algal blooms can temporarily promote primary production, they can ultimately lead to significant ecological imbalances.

As the algae die and decompose, the decomposition process consumes oxygen in the water, leading to hypoxic conditions or "dead zones" where aquatic life cannot survive. This disruption of aquatic ecosystems illustrates how human activities can derail natural nutrient cycling processes, affecting not only water quality but also the health of the organisms that rely on these ecosystems.

In contrast, enhancing natural decomposition processes and promoting forest growth generally contribute positively to nutrient cycles. Increasing atmospheric nitrogen levels can also impact nutrient dynamics, but it’s often a result of disruption rather than a direct means of disruption. Thus, nutrient runoff’s contribution to eutrophication is the most direct and impactful way that human actions alter the cycling of nutrients in ecosystems.