Understanding the Nitrogen Cycle - DrTim's Aquatics

The Nitrogen Cycle

Nitrogen cycle

Forms and Transform of Nitrogen

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1. Forms of nitrogen in Earth's environment
Before plants and animals can make use of nitrogen, the diatomic form of N₂ gas must be "fixed" first, or transformed into usable forms.  So let's discuss the forms of nitrogen first.
 

Compound	Formula	Oxidation State	Phase under normal condition
Nitrate	NO3-	+5	solid salt, ion in solution
Nitrite	NO2-	+3	solid salt, ion in solution
Nitrogen Dioxide	NO2	+4	gas
Ntric Oxide	NO	+2	gas
Nitrous Oxide	N2O	+1	gas
Diatomic Nitrogen Gas	N2	0	gas
Ammonium	NH4+	-3	gas, solid salt, ion in solution
Amines	R-NH2	-3	solid, ion in solution

INSERT: Oxidation-reduction reactions
 

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2. Nitrogen transformation: conversions among different forms of nitrogen

(1) N₂-fixation: N₂ -----> R-NH₂ (or NH₃,NH₄⁺, NO_x)
(2) Nitrification: NH₄⁺ ----> NO₂^- ---->NO₃^-
(3) Assimilation: NO3 (NH₄⁺) ----> R-NH₂
(4) Ammonification: R-NH₂ ----> NH₃ (NH₄⁺)
(5) Denitrification: NO₃^- ----> NO₂^- ----> (NO_x) ----> N₂