Inputs, Outputs, and Storage
Inputs and outputs refer to the transfer of the elemental compounds
among the physical spheres (atmosphere, biosphere, geosphere, and hydrosphere) or geographical
entities (e.g., watershed, aquifer, wetland), including the identity of elemental compound(s) and
magnitude of the transfers. Inputs and outputs within a sphere or geographical entity are not necessarily
balanced, and spheres can become enriched or depleted with respect to chemical elements. For
example, nitrogen and other nutrients become depleted in most agricultural soils unless fertilizers are
applied. Storage of an element refers to the accumulation of the element within a sphere when inputs
exceed outputs. This stored material is still available for biogeochemical cycling, and variations in
inputs, outputs, and/or mediating
factors will influence the amount in storage.
