Types of Regenerated Nitrogen

Of the organic forms, urea and DFAA have received the most attention. Urea is an excretory product of zooplankton and fish. Bacteria also release it during the degradation of some N compounds, such as purines (J0rgensen, 2006). 

Concentrations of urea in marine systems tend to be less than 1 jiM in most systems though in some circumstances much higher concentrations have been observed (e.g., 10 iM in the Resolute Passage, Conover et ah, 1999). DFAAs are produced intraceUularly by phytoplankton and bacteria and are released during such processes as bactivory and grazing. Concentrations of DFAA tend to be lower than urea at less than 0.5 pM (Bronk, 2002). 

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