Nitrogen Dynamics

Nitrogen Fixation
Transformation of N 2
to form NH 3
, NH 4+
, organic N
• Triple bond in N 2 requires a great deal of energy to break
Fixation requires heat or enzymatic catalysis
• Heat
– Lightning, Forest Fires
• High temperatures break N 2 bonds and combine N with O
• ~10
Teragrams N/yr (1 Tg = 10 12
g)
12 g)
• Biotic
– Nitrogen-fixing bacteria, cyanobacteria
• Use nitrogenase enzyme to cleave N 2 bond, combine with H 2 to
form ammonia (NH 3 )
• Nitrogenase enzyme contains two metalloproteins: : Mo/Fe and Fe
• ~130 Tg/yr (non-anthropogenic, non-agricultural)
• Industrial
– Fertilizer manufacture, agricultural legume cultivation, biomass burning,
land draining and clearing