Geoscience Reference
In-Depth Information
In other words, when green rusts are present, denitrification will happen
only after some iron compounds have been reduced (Trolard and Bourrié
1999).
12.3.3 Denitrification/Nitrification
In
denitrification
, the transformation of
NO
3
-
to
N
2
is not direct
and the intermediate products, in sequence, are:
NO
2
-
,
NO
,
N
2
O
(Fig. 12.8, right half).
NH
3
Organic N
Heterotrophic
nitrification
Assimilation
(or fixation)
Ammonification
Volatilization
N
2
NH
4
+
Symbiotic fixation
Ammonium
Anaerobic
dissimilative
ammonification:
nitrogen acts as
electron acceptor
but is not
incorporated
Dinitrogen
oxide or
nitrous
oxide or
nitrogen
protoxide
gas
N
2
Nitritation
NO
(
)
Assimilation
Nitrogen
monoxide or
nitric oxide
gas
NO
2
-
(
)
Nitrite
ion in
solution
Assimi-
lation
Nitratation
(
)
Sequence of
reactions in
denitrification
NO
3
-
Nitrate
ion in solution
(
)
Fig. 12.8
Nitrifi cation and denitrifi cation.
At each stage of denitrification, electrons are consumed, that is,
reduction occurs (cf. Table 12.5), the electrons being provided mainly
by organic matter that gets oxidized.
