Environmental Engineering Reference
In-Depth Information
2000
). Note that soil represents approximately 80 % of the carbon stocks in
terrestrial ecosystems, ranging from 50 % in tropical forests to 95 % in tun-
dra (IPCC
2002
). The turnover times of OM, determined through
14
C tracer in
well-drained boreal (Manitoba in Canada), temperate (central Massachusetts in
the USA) and tropical forest soils (eastern Amazonia in Brazil), suggest that the
average age of OM carbon is higher than the average age predicted from CO
2
production by OM decomposition (30, 8, and 3 yr for boreal, temperate, and trop-
ical soil) or from total soil respiration (16, 3, and 1 yr, respectively) (Table
1
)
(IPCC
2001
; Trumbore
2000
). Most of the CO
2
produced during decomposi-
tion is derived from relatively short-lived soil organic matter (SOM) compo-
nents. They do not represent a large fraction of the standing stock of soil organic
matter (Trumbore
2000
). Comparison of the
14
C in soil respiration with soil
organic matter in temperate and boreal forest sites indicates a significant con-
tribution from the decomposition of organic matter fixed >2 yr but <30 yr ago
(Table
1
) (IPCC
2001
). Tropical soil respiration is dominated by C fixed <1 yr
ago (Table
1
) (IPCC
2001
). Monitoring of the
14
C signature of CO
2
emitted from
soils suggests that seasonal and interannual variability in soil respiration are the
key factors in these ecosystems (IPCC
2001
; Trumbore
2000
) (Table
1
).
These findings imply that the soil respiration is very variable in different
ecosystems, with important effects on carbon sequestration and global carbon
dynamics. It is estimated that on a global scale, the soil respiration in terrestrial
ecosystems produces a CO
2
flux of approximately 75
×
10
15
g C yr
−
1
, which
is likely to increase due to changes in the Earth's condition (Schlesinger and
Andrews
2000
).
3.2 Agricultural Activities in Soil
The soil and the related agricultural activities can release significant amounts of
CO
2
, CH
4
and N
2
O to the atmosphere (Mosier et al.
1989
,
1991
,
2004
; Robertson
and Grace
2004
; Ambus and Robertson
2006
; Smith et al.
2008
; Kreileman and
Bouwman
1994
; IPCC
2001
; Raich and Schlesinger
1992
; Aselrnann and Crutzen
1989
; Watson et al.
1992
; Bowden et al.
1993
; Subak et al.
1993
; Zuidema et al.
1994
; Freney
1997
; Tsuruta et al.
1997
; Stevens and Laughlin
1998
; Cole et al.
1997
; Tranvik et al.
2009
). CO
2
is mostly released from agricultural activities
and soil disturbances (IPCC
1996
,
2007a
; Subak et al.
1993
; Bouwman
1990
;
Lal et al.
1999
; Schlesinger
1999
; Izaurralde et al.
2000
). Several processes are
responsible for the production of CO
2
from such activities: (i) CO
2
is produced
during the processing, transport and application of N-containing fertilizers, which
cause the release of around 1.4 mol of CO
2
per mole of N applied (Schlesinger
1999
; Izaurralde et al.
2000
; IPCC
1996
). (ii) Land limes in the form of calcium
carbonate (CaCO
3
) and dolomite [CaMg(CO
3
)
2
] can produce bicarbonate and
CO
2
(Robertson and Grace
2004
; Liu et al.
2010
,
2011
). Note that CaCO
3
and
CaMg(CO
3
)
2
are commonly applied to agricultural soils to counteract soil acidity
