Rivers supply clay, and the sea supplies nutrients by tidal effects; however, the
area influenced by these effects is too small. The peat dome structure prevents the
supply of water and nutrients from reaching the inside of the peatland. The peat
dome is an almost-flat structure with a height of 10 m at the top of the dome with
10 km distance from ridge to top (10 m/10 km inclination); however, no water flows
from the bottom to the top of the peat dome. Thus, as the water supply in the dometype peatland depends on only rainfall, the nutrient supply is also extremely limited
over the long term.
The pH of rain is acidic (5.6) because of CO 2 solubilization. The low pH rain
leaches nutrients in the same way as an acid reagent. Under these conditions, Na
+
and K
+ are leached quickly (Fig. 1.12).
Figure 1.12 shows the very intersecting mechanisms of peat accumulation (peat
dome formation). Plants grow well on the river side and in tidally affected areas
because of the rich nutrient supply, and biomass production is high; however, the
peat is shallow because of the high activity of microorganisms and small animals
under nutrient-rich conditions, and little organic matter accumulates. In contrast, at
the top of the peat dome, as nutrients are always leaching, plant growth is poor;
however, activity by microorganisms and small animals is also low under nutrientpoor conditions, and organic matter decomposes slowly and accumulates gradually.
This nutrient balance pattern is the main reason for peat dome formation. In other
words, if there are large rivers in flat plains and heavy rain in the rainy season causes
flooding, peat accumulation will be restricted because of the provided clay and
nutrients, which accelerate CO 2 emissions near the surface (aerobic) and CH 4
emissions in deep peat (anaerobic). These conditions form cuvette-type peatlands.
1.5.2.1 Oxygen
As oxygen solubility in water is extremely low, plant roots cannot absorb nutrients
because the nutrient absorption process depends on the energy supplied by O 2 and
depends on respiration (Fig. 1.13). Additionally, nodulation and N 2 fixation by
legume plants strongly depend on the oxygen supply.
Therefore, aeration is an important aspect of water culture systems; for instance,
rice crops are adapted to aquatic conditions. Because nutrient absorption depends on
active absorption mechanisms, oxygen is essential to produce the energy in the roots
that is required for the absorption of nutrients.
Redox Potential (Eh) The redox potential (Eh) of the peat surface clearly responds
to inundation of the peat surface, and Eh shows large fluctuations according to the
water level (Fig. 1.14). A case study in Lahei district, Central Kalimantan, Indonesia,
showed that a high mound (>ca. 40 cm in relative elevation) was never inundated,
and the surface of the mound was constantly oxic (Eh ¼ ca. 600 mV vs. NHE;
Haraguchi and Yabe 2002). The Eh on the surface peat of the inundated peat was
<400 mV, and the Eh of the constantly inundated, low-elevation site was approximately 0 mV, implying anoxic conditions on the peat surface. The vertical profile of
1 Basic Information About Tropical Peatland Ecosystems
21
area influenced by these effects is too small. The peat dome structure prevents the
supply of water and nutrients from reaching the inside of the peatland. The peat
dome is an almost-flat structure with a height of 10 m at the top of the dome with
10 km distance from ridge to top (10 m/10 km inclination); however, no water flows
from the bottom to the top of the peat dome. Thus, as the water supply in the dometype peatland depends on only rainfall, the nutrient supply is also extremely limited
over the long term.
The pH of rain is acidic (5.6) because of CO 2 solubilization. The low pH rain
leaches nutrients in the same way as an acid reagent. Under these conditions, Na
+
and K
+ are leached quickly (Fig. 1.12).
Figure 1.12 shows the very intersecting mechanisms of peat accumulation (peat
dome formation). Plants grow well on the river side and in tidally affected areas
because of the rich nutrient supply, and biomass production is high; however, the
peat is shallow because of the high activity of microorganisms and small animals
under nutrient-rich conditions, and little organic matter accumulates. In contrast, at
the top of the peat dome, as nutrients are always leaching, plant growth is poor;
however, activity by microorganisms and small animals is also low under nutrientpoor conditions, and organic matter decomposes slowly and accumulates gradually.
This nutrient balance pattern is the main reason for peat dome formation. In other
words, if there are large rivers in flat plains and heavy rain in the rainy season causes
flooding, peat accumulation will be restricted because of the provided clay and
nutrients, which accelerate CO 2 emissions near the surface (aerobic) and CH 4
emissions in deep peat (anaerobic). These conditions form cuvette-type peatlands.
1.5.2.1 Oxygen
As oxygen solubility in water is extremely low, plant roots cannot absorb nutrients
because the nutrient absorption process depends on the energy supplied by O 2 and
depends on respiration (Fig. 1.13). Additionally, nodulation and N 2 fixation by
legume plants strongly depend on the oxygen supply.
Therefore, aeration is an important aspect of water culture systems; for instance,
rice crops are adapted to aquatic conditions. Because nutrient absorption depends on
active absorption mechanisms, oxygen is essential to produce the energy in the roots
that is required for the absorption of nutrients.
Redox Potential (Eh) The redox potential (Eh) of the peat surface clearly responds
to inundation of the peat surface, and Eh shows large fluctuations according to the
water level (Fig. 1.14). A case study in Lahei district, Central Kalimantan, Indonesia,
showed that a high mound (>ca. 40 cm in relative elevation) was never inundated,
and the surface of the mound was constantly oxic (Eh ¼ ca. 600 mV vs. NHE;
Haraguchi and Yabe 2002). The Eh on the surface peat of the inundated peat was
<400 mV, and the Eh of the constantly inundated, low-elevation site was approximately 0 mV, implying anoxic conditions on the peat surface. The vertical profile of
1 Basic Information About Tropical Peatland Ecosystems
21