Environmental Engineering Reference
In-Depth Information
commonly used, as also are electronic meters in the laboratory. The reason for its
widespread testing is twofold. First, pH reflects a range of
CARBON SEQUESTRATION IN SOILS
new developments
Soil organic matter (SOM) consists of 58 per cent carbon, and we have seen how
important it is in maintaining chemical and biological fertility, water retention, and
aeration in soils, and hence in promoting crop production. Soil carbon is part of the
global carbon cycle, which is very important for global climate because it regulates the
atmospheric content of two important greenhouse gases: carbon dioxide (CO
2
) and
methane (CH
4
). Climate change scientists have suggested that the
sequestration
of
atmospheric CO
2
in SOM could absorb an amount of CO
2
equivalent to the total CO
2
emissions from agriculture, industry and the burning of fossil fuels (the
anthropogenic
CO
2
).
Sequestration
literally means to sequestrate carbon, or remove carbon from
circulation or access, into a store. The carbon cycle, like any other global cycle, consists
of major
pools
or
stores
, with
fluxes
or
flows
between the pools. The pools can act as
sinks
when they sequestrate carbon, or
sources
when they provide carbon. The major
pools in the cycle are the ocean, the atmosphere and the terrestrial biosphere (plants,
animals and soils). The carbon cycle is very complex, and there are still major
uncertainties about it, especially with regard to the loss of CO
2
to a number of as yet
unidentified terrestrial biosphere and ocean sinks. According to calculations of the carbon
cycle, sources of carbon in the atmosphere are 1ยท1 gigatonnes (Gt) greater than the sinks,
indicating that there are as yet unidentified carbon sinks (1 gigatonne = 1 billion tonnes =
10
9
tonnes). Table 1 shows the major carbon sinks on Earth.
Table 1 Major sinks or stores of carbon on Earth
Carbon pool
Size (gigatonnes of carbon)
Atmosphere
720
Ocean
38,400
Rock carbonates
>60,000,000
Kerogens
15,000,000
Living biomass
600
Soil
1500
Peat
250
Coal
3510
Oil
230
Natural gas
140
Terrestrial ecosystems exchange CO
2
rapidly with the atmosphere. CO
2
is removed by
plants from the atmosphere through photosynthesis
It is returned to the atmosphere by
