et al. (2013) N 2 O emission are higher in drained peatlands where fertilizers and
manure are used. However, continuous measurement, especially in peatlands used
for agriculture with nitrogen inputs, is needed to provide adequate information on
N 2 O emission (Couwenberg et al. 2009; Hooijer et al. 2010).
The difference in magnitude of GHGs emission can be caused by a “trade-off”
effect (for instance, reducing emission of one gas increases emission of other gas at
the same time). GHGs emission in peatlands is affected by biogeochemical processes
that cause a redox potential effect, which among others occurs due to change in
groundwater level (GWL). Therefore, understanding the process of GHGs emission
that occurs on peatlands is important in order to better control the impact of resulted
GHGs emission.
Tropical peat tends to have a higher lignin content compared to subtropical peat.
Decomposition process of lignin will produce organic acids that will affect the
chemical mechanism in peat and is highly dependent on the state of reduction–
oxidation (redox). An increase in CO 2 flux with a decrease in GWL is caused by the
oxidation process in peat decomposition which is triggered by increased aeration.
When GWL is low, most organic matter decomposes aerobically to CO 2 (Itoh et al.
2017), thereby increasing CO 2 emissions gradually (Wang et al. 2018) and limiting
CH 4 production. Therefore CH 4 soil flux shows the opposite relationship that
increasing GWL will increase CH 4 production (Ishikura et al. 2019). A higher
GWL will improve anaerobic conditions which results in relatively large production
of CH 4 in peat and limits aerobic CH 4 oxidation (Sakabe et al. 2018). Variations in
soil redox conditions that are driven by GWL fluctuations play an important role in
influencing both quantity and quality of the organic substrate used by methanogenic
archaea for CH 4 production (Winton et al. 2017). This condition results in higher
CH 4 emission in undrained peat swamp forest compared to forests that have drainage
or are disturbed on tropical peatlands (Ishikura et al. 2019; Deshmukh et al. 2020).
15.3 Current Methodology for Estimating Peatlands’
GHGs Emission
General guidelines for estimating GHGs emission caused by activities on forests and
peatlands are available in the IPCC Guidelines (IPCC 2003, 2006, 2019) and
especially in the IPCC Wetlands Supplement 2013 (IPCC 2014). As previously
explained, activities on forests and peatlands that cause peat disturbances will result
in CO 2 emission due to loss of carbon stored in the aboveground biomass, belowground biomass, litter, woody debris, and peat/soil pools as well as other non-CO 2
emissions due to fires, biological oxidation, and peat decomposition.
GHGs emission released from the aboveground biomass, belowground biomass,
litter, and woody debris carbon pools in the forests (including peat swamp forests) as
well as other GHGs emission produced in the combustion process have been clearly
explained and the default values of emission factors are provided in the IPCC
448
H. Krisnawati et al.
manure are used. However, continuous measurement, especially in peatlands used
for agriculture with nitrogen inputs, is needed to provide adequate information on
N 2 O emission (Couwenberg et al. 2009; Hooijer et al. 2010).
The difference in magnitude of GHGs emission can be caused by a “trade-off”
effect (for instance, reducing emission of one gas increases emission of other gas at
the same time). GHGs emission in peatlands is affected by biogeochemical processes
that cause a redox potential effect, which among others occurs due to change in
groundwater level (GWL). Therefore, understanding the process of GHGs emission
that occurs on peatlands is important in order to better control the impact of resulted
GHGs emission.
Tropical peat tends to have a higher lignin content compared to subtropical peat.
Decomposition process of lignin will produce organic acids that will affect the
chemical mechanism in peat and is highly dependent on the state of reduction–
oxidation (redox). An increase in CO 2 flux with a decrease in GWL is caused by the
oxidation process in peat decomposition which is triggered by increased aeration.
When GWL is low, most organic matter decomposes aerobically to CO 2 (Itoh et al.
2017), thereby increasing CO 2 emissions gradually (Wang et al. 2018) and limiting
CH 4 production. Therefore CH 4 soil flux shows the opposite relationship that
increasing GWL will increase CH 4 production (Ishikura et al. 2019). A higher
GWL will improve anaerobic conditions which results in relatively large production
of CH 4 in peat and limits aerobic CH 4 oxidation (Sakabe et al. 2018). Variations in
soil redox conditions that are driven by GWL fluctuations play an important role in
influencing both quantity and quality of the organic substrate used by methanogenic
archaea for CH 4 production (Winton et al. 2017). This condition results in higher
CH 4 emission in undrained peat swamp forest compared to forests that have drainage
or are disturbed on tropical peatlands (Ishikura et al. 2019; Deshmukh et al. 2020).
15.3 Current Methodology for Estimating Peatlands’
GHGs Emission
General guidelines for estimating GHGs emission caused by activities on forests and
peatlands are available in the IPCC Guidelines (IPCC 2003, 2006, 2019) and
especially in the IPCC Wetlands Supplement 2013 (IPCC 2014). As previously
explained, activities on forests and peatlands that cause peat disturbances will result
in CO 2 emission due to loss of carbon stored in the aboveground biomass, belowground biomass, litter, woody debris, and peat/soil pools as well as other non-CO 2
emissions due to fires, biological oxidation, and peat decomposition.
GHGs emission released from the aboveground biomass, belowground biomass,
litter, and woody debris carbon pools in the forests (including peat swamp forests) as
well as other GHGs emission produced in the combustion process have been clearly
explained and the default values of emission factors are provided in the IPCC
448
H. Krisnawati et al.