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Chemical Oceanography, 4th Edition
(decay) of plants in a nearly fixed stoichiometric ratio. The decomposition of organic
matter and the associated release of nutrients proceed by aerobic respiration in the
presence of oxygen. Denitrification occurs when oxygen is depleted, by sulfate reduction when nitrate and nitrite are depleted, and by fermentation when sulfate is depleted.
Richards (1965) developed stoichiometric models for these processes using a C:N:P ratio
of 106:16:1, the Redfield ratios for average plankton material for the world ocean.
In an aerobic environment, O 2 is the electron acceptor; aerobic respiration occurs according to
(CH 2 O) 106 (NH 3 ) 16 H 3 PO 4 + 138O 2 → 106CO 2 + 122H 2 O + 16HNO 3 + H 3 PO 4 (10.63)
After the oxygen is depleted, denitrification occurs, with NO 3
– being the electron acceptor.
The denitrification can be described by
SiO 2 (µM)
0
100
200
300
400
500
600
H
2 S (µM)
0
20
40
60
80
100
Pre-clearcut
Post-clearcut
Figure 10.38
H 2 S concentration as a function of silicate.
Temperature (°C)
2.0
2.5
3.0
3.5
4.0
Observation Number
0
20
40
60
80
100
120
140
Fe(II) (µM)
–0.02
0.00
0.02
0.04
0.06
Fe(II)
Temp.
Figure 10.37
Temperature and Fe(II) over a vent system.