1.3.4 Two Different Peatland Formation Processes
There are two general processes of tropical peatland formation: (1) the dome
formation process, which occurs between two large rivers and is found on island
ridges in the maritime continent of Southeast Asia and (2) the Cuvette Centraledepression formation process, which occurs around a large river and is found in the
central Congo Basin and the Amazon Basin. Dome-type peatlands are assumed to
develop in three phases: phase 1 is mangrove vegetation with sea water (sea
nutrients); phase 2 is mosaic vegetation with fresh water from rain (no nutrients)
and rivers (clays) and sea water from tidal bores (sea nutrients); and phase 3 is a peat
swamp forest with water only from rain (no nutrients). The Cuvette Centrale
depression-type peatland is assumed to have only one phase, which is similar to
phase 2 of the dome formation-type peatland. In the Cuvette Centrale depressiontype peatland, as water floods from rivers in the rainy season, clay and nutrients are
supplied in small amounts. Then, the river side of the peatland becomes slightly
nutrient rich, and microorganism activity increases, causing oxygen deficiency and
low redox potential and finally resulting in higher CH 4 emissions. To confirm these
two peat formation models, it is necessary to study CH 4 emissions and redox
potential along transects from the ridge to the center (top) of peatlands.
The three most important factors influencing methane production in peatlands and
wetlands are anoxia, temperature, and substrate availability (Valentine et al. 1994;
Wania et al. 2010; Whalen 2005). However, in tropical peatlands, changes in
temperature and substrate availability (woody material) are minimal, and anoxia
may influence CH 4 emissions. Anoxia is linked to water saturation because O 2
solubility in water is too low. Methanogenesis by methanogenic bacteria occurs
only under strictly anaerobic conditions. However, the redox potential in peatlands is
still high, approximately 0 mV in dome-type peatlands in Southeast Asia; nutrient
levels are extremely low in peat and peat water, microorganism activity is low, and
oxygen consumption is also low. Thus, in nutrient-poor peatlands, the redox potential is still too high for methanogenesis, even with a high water table. Unfortunately,
this important point (factor) is missing in CH 4 emissions estimations, such as in the
three most important factors influencing methane production mentioned above.
Thus, it is still difficult to discuss the CH 4 emissions process and to develop a
CH 4 emissions model for peatlands.
The global methane (CH 4 ) budget was reported in “The Global Methane Budget
2000–2017” (Saunois et al. 2020). The latitudinal distribution of atmospheric-based
CH 4 emissions indicates a predominance of tropical emissions (~ 65% of the global
budget, <30
N) compared to those at midlatitudes (~30%, 30
N to 60
N) and high
northern latitudes (~4%, 60
N to 90
N). The largest wetland areas in WAD2M
(Wetland Area Dynamics for Methane Modeling) are in Amazonia, the Congo
Basin, and the western Siberian lowlands. Due to the large wetland areas and high
temperatures, CH 4 emissions from tropical wetlands are very high compared with
those from other natural methane sources. The highest methane emissions from
1 Basic Information About Tropical Peatland Ecosystems
15
There are two general processes of tropical peatland formation: (1) the dome
formation process, which occurs between two large rivers and is found on island
ridges in the maritime continent of Southeast Asia and (2) the Cuvette Centraledepression formation process, which occurs around a large river and is found in the
central Congo Basin and the Amazon Basin. Dome-type peatlands are assumed to
develop in three phases: phase 1 is mangrove vegetation with sea water (sea
nutrients); phase 2 is mosaic vegetation with fresh water from rain (no nutrients)
and rivers (clays) and sea water from tidal bores (sea nutrients); and phase 3 is a peat
swamp forest with water only from rain (no nutrients). The Cuvette Centrale
depression-type peatland is assumed to have only one phase, which is similar to
phase 2 of the dome formation-type peatland. In the Cuvette Centrale depressiontype peatland, as water floods from rivers in the rainy season, clay and nutrients are
supplied in small amounts. Then, the river side of the peatland becomes slightly
nutrient rich, and microorganism activity increases, causing oxygen deficiency and
low redox potential and finally resulting in higher CH 4 emissions. To confirm these
two peat formation models, it is necessary to study CH 4 emissions and redox
potential along transects from the ridge to the center (top) of peatlands.
The three most important factors influencing methane production in peatlands and
wetlands are anoxia, temperature, and substrate availability (Valentine et al. 1994;
Wania et al. 2010; Whalen 2005). However, in tropical peatlands, changes in
temperature and substrate availability (woody material) are minimal, and anoxia
may influence CH 4 emissions. Anoxia is linked to water saturation because O 2
solubility in water is too low. Methanogenesis by methanogenic bacteria occurs
only under strictly anaerobic conditions. However, the redox potential in peatlands is
still high, approximately 0 mV in dome-type peatlands in Southeast Asia; nutrient
levels are extremely low in peat and peat water, microorganism activity is low, and
oxygen consumption is also low. Thus, in nutrient-poor peatlands, the redox potential is still too high for methanogenesis, even with a high water table. Unfortunately,
this important point (factor) is missing in CH 4 emissions estimations, such as in the
three most important factors influencing methane production mentioned above.
Thus, it is still difficult to discuss the CH 4 emissions process and to develop a
CH 4 emissions model for peatlands.
The global methane (CH 4 ) budget was reported in “The Global Methane Budget
2000–2017” (Saunois et al. 2020). The latitudinal distribution of atmospheric-based
CH 4 emissions indicates a predominance of tropical emissions (~ 65% of the global
budget, <30
N) compared to those at midlatitudes (~30%, 30
N to 60
N) and high
northern latitudes (~4%, 60
N to 90
N). The largest wetland areas in WAD2M
(Wetland Area Dynamics for Methane Modeling) are in Amazonia, the Congo
Basin, and the western Siberian lowlands. Due to the large wetland areas and high
temperatures, CH 4 emissions from tropical wetlands are very high compared with
those from other natural methane sources. The highest methane emissions from
1 Basic Information About Tropical Peatland Ecosystems
15