text: Estimates of lake metabolism typically rely on the measurement of dissolved oxygen or carbon dioxide, or measurements of a carbon or oxygen tracer to estimate production and consumption of organic carbon. Oxygen is produced and carbon dioxide consumed through photosynthesis and oxygen is consumed and carbon dioxide produced through respiration.  Here, organic matter is symbolized by glucose, though the chemical species produced and respired through these reactions vary widely. 
  Photosynthesis: 
  Respiration: 
  Photosynthesis and oxygen production only occurs in the presence of light, while the consumption of oxygen via respiration occurs in both the presence and absence of light. Lake metabolism terms include:
  * GPP - gross primary production (e.g. total photosynthesis)
  * R - total respiration 
  * - heterotrophic respiration 
  * - autotrophic respiration 
  * NEP - net ecosystem production = GPP - R
  * NPP - net primary production = GPP -