Eh within a mound was consistently oxic (400–600 mV) from the top to 50 cm
below the mound surface. The oxic conditions of peat mounds are maintained even
below the groundwater table by oxygen transport through the aerenchyma of aerial
root systems.
A case study in Lahei district, Central Kalimantan, Indonesia, showed that the
Eh7 (redox potential corrected at pH ¼ 7) value in peat pore water in a peat dome of
a pristine peat swamp forest was almost constant (ca. 200–400 mV vs. NHE) from
the surface to the bottom of the peat (max. 8 m in depth) with minimum
(ca. 50–200 mV) at approximately 2 m depth (Haraguchi et al. 2000). Eh7 showed
a decreasing tendency from the top to the bottom of the peat layer; however, Eh7
showed an increasing tendency from 2 m depth to the peat bottom because of the
oxygen supply from groundwater flow at the mineral horizon under peat in combination with the low oxygen consumption within the peat layer. Because of the
limited information about groundwater flows in peat swamp forests, it is difficult
to conclude whether the profile of Eh in Lahei is typical. However, the vertical
distribution of Eh in the pristine peat layer was >0 mV, implying the low methane
emissions potential of pristine peat swamp forests. The Eh of the peat surface was
>300 mV and was sometimes accompanied by a high concentration of nitrate
(10–170 mg L
À1 ) within 1 m from the peat surface; thus, surface peat has some
potential for nitrous oxide emissions even in pristine peat swamp forests.
Greenhouse Gas (GHG) Issues Related to Nutrients
Oxygen is an essential limiting factor under high water conditions because oxygen
only slightly dissolves in water. For instance, the redox potential in air and dried
peatland (the upper zone of the water table) is +600 mV, while it is 0 mV in water
and wet peatland (the lower zone of the water table) (Fig. 1.15).
Methane (CH 4 ) emissions from native tropical peatlands are low because microbial activity is extremely low under low-nutrient conditions, and the redox potential
in water and in water-saturated peatland is 0 mV even at 10-m peat depth (Haraguchi
and Yabe 2002). CO 2 emissions mainly occur from highly dried peatlands to which a
large amount of O 2 is supplied from the atmosphere. In addition, once chemical
fertilizers are applied to a dried peatland, the microorganism activity level increases,
and O 2 is rapidly consumed by respiration. Under these, the redox potential can
reach À300 mV in the water table zone, leading to CH 4 emissions. Moreover, N 2 O
emissions are accelerated in the upper peatlands, with +300 mV redox potential.
In conclusion, the GHG emissions from native tropical peatlands with high
groundwater can be explained by Eh (approximately 0 mV) and nutrients
(Fig. 1.15, left).
1. CO 2 emissions are low because of the low Eh (approximately 0 mV) and the
insufficient oxygen and nutrients to support microorganism activity,
2. CH 4 emissions are also low because the Eh (approximately 0 mV) is too high for
methanogenesis, and
1 Basic Information About Tropical Peatland Ecosystems
23
below the mound surface. The oxic conditions of peat mounds are maintained even
below the groundwater table by oxygen transport through the aerenchyma of aerial
root systems.
A case study in Lahei district, Central Kalimantan, Indonesia, showed that the
Eh7 (redox potential corrected at pH ¼ 7) value in peat pore water in a peat dome of
a pristine peat swamp forest was almost constant (ca. 200–400 mV vs. NHE) from
the surface to the bottom of the peat (max. 8 m in depth) with minimum
(ca. 50–200 mV) at approximately 2 m depth (Haraguchi et al. 2000). Eh7 showed
a decreasing tendency from the top to the bottom of the peat layer; however, Eh7
showed an increasing tendency from 2 m depth to the peat bottom because of the
oxygen supply from groundwater flow at the mineral horizon under peat in combination with the low oxygen consumption within the peat layer. Because of the
limited information about groundwater flows in peat swamp forests, it is difficult
to conclude whether the profile of Eh in Lahei is typical. However, the vertical
distribution of Eh in the pristine peat layer was >0 mV, implying the low methane
emissions potential of pristine peat swamp forests. The Eh of the peat surface was
>300 mV and was sometimes accompanied by a high concentration of nitrate
(10–170 mg L
À1 ) within 1 m from the peat surface; thus, surface peat has some
potential for nitrous oxide emissions even in pristine peat swamp forests.
Greenhouse Gas (GHG) Issues Related to Nutrients
Oxygen is an essential limiting factor under high water conditions because oxygen
only slightly dissolves in water. For instance, the redox potential in air and dried
peatland (the upper zone of the water table) is +600 mV, while it is 0 mV in water
and wet peatland (the lower zone of the water table) (Fig. 1.15).
Methane (CH 4 ) emissions from native tropical peatlands are low because microbial activity is extremely low under low-nutrient conditions, and the redox potential
in water and in water-saturated peatland is 0 mV even at 10-m peat depth (Haraguchi
and Yabe 2002). CO 2 emissions mainly occur from highly dried peatlands to which a
large amount of O 2 is supplied from the atmosphere. In addition, once chemical
fertilizers are applied to a dried peatland, the microorganism activity level increases,
and O 2 is rapidly consumed by respiration. Under these, the redox potential can
reach À300 mV in the water table zone, leading to CH 4 emissions. Moreover, N 2 O
emissions are accelerated in the upper peatlands, with +300 mV redox potential.
In conclusion, the GHG emissions from native tropical peatlands with high
groundwater can be explained by Eh (approximately 0 mV) and nutrients
(Fig. 1.15, left).
1. CO 2 emissions are low because of the low Eh (approximately 0 mV) and the
insufficient oxygen and nutrients to support microorganism activity,
2. CH 4 emissions are also low because the Eh (approximately 0 mV) is too high for
methanogenesis, and
1 Basic Information About Tropical Peatland Ecosystems
23