Overview
  Biogeochemical Cycles
    Glossary
  Spheres of B. Cycles
  Nitrogen Properties
  Simple Nitrogen Cycle
  Human Influences
  Spheres of the N Cycle
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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.

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