Geoscience Reference
In-Depth Information
Figure 10-6.
Basic scheme for carbon storage and transformations in wetlands. Carbon movements may take place
as gases in air, dissolved in water, or as particulate matter. Adapted from Charman, D. 2002. Peatlands and
Environmental Change. J. Wiley & Sons, London and New York, 301 p, Fig. 5.2.
coal and is the main source for sulfur dioxide
released upon burning coal (see section 10.3.1).
Carbon held in air, biomass, and suri cial
water has relatively short residence time
-
days
to decades, whereas soils and peat may retain
carbon for centuries or millennia. Deeper carbon
reservoirs include methane clathrates in seal oor
sediment and permafrost, deep ocean water,
fossil fuels, and carbonate sediments (see Fig. 8-
24). Residence time in these carbon pools ranges
from centuries to hundreds of millions of years.
Carbon is taken into wetlands primarily via
plant photosynthesis in the aerobic zone and
lost mainly by organic decay and decomposition
in both the aerobic and anaerobic zones (Fig.
10-6). The boundary between these zones often
l uctuates on a seasonal basis as the water table
rises and falls. The conversion of organic matter
into carbon dioxide is accomplished by respira-
tion in the aerobic zone. In the anaerobic zone,
fermentation produces acids, alcohols and
carbon dioxide, and methane is derived from
Archaea
bacteria (methanogens).
10.2 Carbon cycle
10.2.1 Carbon reservoirs
Carbon is the chemical basis for life and exists
in gases, is dissolved in water, and forms solid
organic compounds and inorganic minerals
essentially everywhere on Earth. Published
values for global soil and peat carbon storage
vary widely, but most estimates are around
1500 Gt
1
for total soil carbon, of which about
500 Gt are peat carbon (Adams 1999; Roulet
2000). Thus peat carbon represents about one-
third of soil carbon. In comparison, atmospheric
carbon is about 750 Gt, carbon stored in the
world's land vegetation is in the range of 500-
1000 Gt, and ocean surface water has some 700-
1000 Gt carbon (Adams 1999). Based on these
approximate values, it is apparent that wetlands,
particularly peatlands, are major storage points
for carbon as well as sources and sinks for
greenhouse gases (CO
2
and CH
4
).
10.2.2 Carbon balance
The accumulation or release of carbon in peat-
lands and other types of wetlands depends on
the balance between productivity and decay.
Wetlands are, for the most part, among the
most productive ecosystems in the world,
1
Gigatons of carbon (1 Gt
=
=
1 billion tons
1
=
×
10
15
g).
Petagram
1
