Environmental Engineering Reference
In-Depth Information
Global Sinks and Sources of Methane
a
TABLE 12.2
Methane flux
Percentage
(10
12
g CH
4
year
1
)
Sources and sinks
of total
Sources
Natural wetlands (microbial)
115
21
Freshwaters (microbial)
5
1
Termites (microbial)
20
4
Oceans and geological (microbial and abiotic)
20
4
Human activities (burning, landfills, gas and
230
43
coal mining)
Rice paddies (microbial)
60
11
Grazing animals (microbial)
85
16
Total sources
535
Sinks
Reaction with OH and loss in atmosphere
475
89
Soil microbes
30
6
Increase in atmosphere
30
6
a
Modified from Schlesinger (1997).
With potential energy
Oxic processes
Oxidation
Remineralization
Heterotrophy
As
si
m
ilation
As
si
mil
atio
n
Oxidized inorganic
Organic
compound
Reduced inorganic
compound
compound
Reduction
Putrifaction or fermentation
Anoxic processes
With potential energy
FIGURE 12.5
Diagram of a hypothetical nutrient cycle. This will be the general format used
to represent nutrient cycles. Oxic processes are above the center line and anoxic processes are
below. Those that move on the center line are required, independent of O
2
concentration. In-
organic forms are listed from left to right, from reduced to oxidized. Thus, transformations
are generally occurring with potential energy if they move from left to right in the top half
of the diagram or from right to left in the bottom half of the diagram.
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