These are factors that control the transformations within a biogeochemical cycle. The number of important factors for a particular transformation can be large; some common ones include temperature, pH, light intensity, compound concentration, identity and concentration of biota, moisture content, etc. Biological, physical, and chemical factors can be significantly influenced by human activities, such as industrial activities (e.g., mining, smokestack emissions, effluents discharged to water bodies), agricultural activities (e.g., plowing, planting, application of agrichemicals), construction, sewage treatment, etc. Mediating factors can change the concentration and chemical form of compounds within a sphere in the absence of a change of inputs. For example the concentration of NO₃^- in a river can increase if sufficient oxygen is available to transform reduced forms of nitrogen into NO₃^-. (for more details, see Human Influences)

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