2.4 Urgent Need for a Stock-Based Water Management
System
The ideal eco-management of tropical peatland is close to that of native tropical
peatland in achieving water cycling and water reservoir maintenance. That is, in
undisturbed conditions, these peatlands serve as an overall long-term carbon sink
because the high GWL provides saturated conditions with low redox potentials
(Dommain et al. 2015; Cobb et al. 2017; Hodgkins et al. 2018). In modern economic
based-management of tropical peatland, almost all programs and projects intend to
drain water in peatlands, which causes serious issues in peatlands: (1) peat degradation by fire and microorganism oxidation, (2) loss of biodiversity, and (3) environmental pollution such as haze by fire and water by chemical application (Fig. 2.2
bottom).
In native tropical peatland (Fig. 2.2 top), a high rate of rainfall (precipitation) is
one of the first steps to generate a tropical peatland. O 2 solubilization is very poor in
water, and high groundwater levels (GWLs) prevent decomposition of organic
matter by microorganisms, leading to low CO 2 emission, for which organic matter
increasingly accumulates under high GWL conditions. As water is supplied mainly
in the form of rainfall, nutrient supply from outside environments (river, sea, and
atmosphere) is extremely poor. Nutrients are stored mainly in trees (i.e., vegetation)
with cycling and N 2 fixation in the rhizosphere. Thus, in nutrient-poor ecosystems,
GHG emissions are low because of minimal microorganism activity.
In developed tropical peatland (Fig. 2.2 bottom), it is assumed that water is the
most serious limiting factor, and drains (i.e., ditches, canals) are often constructed for
water drainage. Then, as plantation crops require large amounts of nutrients, heavy
amounts of chemical fertilizer are applied, which cause environmental pollution by
leaching and activation of microorganisms in peatland. The activated microorganisms decompose (1) peat (CO 2 emission) and nitrogen fertilizer (N 2 O) in the air layer
(aerobic) and (2) peat (CH 4 emission) in the deep aquatic layer (anaerobic) of
peatland. With heavy drainage, the water stock and water cycle rate decrease
drastically, and peatland fires occur more frequently.
An essential element of the tropical peatland ecosystem is a water statute; it is
clarified as Stock-based Water Management [irrigation system] and Drainage-based
Water Management [drainage system]. The principle of eco-management of tropical
peatland includes (1) how to establish Stock-based Water Management and (2) how
to reform Drainage-based Water Management into Stock-based Water Management.
Under climate change, El Niño events become more severe and frequent in the
tropical zone, especially in peatlands in Southeast Asia. Land use conversion and
peatland drainage practices may have an impact on the climate, in which case, the
water stock system becomes urgent. However, it is difficult to maintain a water stock
in a Drainage-based Water Management system, even if the canal or drain is blocked
in the dry season. The basic design of water management should be changed to
Stock-based Water Management on a large scale.
2 Principles of Eco-Management in a Large-Scale Ecosystem of Tropical Peatland
71
System
The ideal eco-management of tropical peatland is close to that of native tropical
peatland in achieving water cycling and water reservoir maintenance. That is, in
undisturbed conditions, these peatlands serve as an overall long-term carbon sink
because the high GWL provides saturated conditions with low redox potentials
(Dommain et al. 2015; Cobb et al. 2017; Hodgkins et al. 2018). In modern economic
based-management of tropical peatland, almost all programs and projects intend to
drain water in peatlands, which causes serious issues in peatlands: (1) peat degradation by fire and microorganism oxidation, (2) loss of biodiversity, and (3) environmental pollution such as haze by fire and water by chemical application (Fig. 2.2
bottom).
In native tropical peatland (Fig. 2.2 top), a high rate of rainfall (precipitation) is
one of the first steps to generate a tropical peatland. O 2 solubilization is very poor in
water, and high groundwater levels (GWLs) prevent decomposition of organic
matter by microorganisms, leading to low CO 2 emission, for which organic matter
increasingly accumulates under high GWL conditions. As water is supplied mainly
in the form of rainfall, nutrient supply from outside environments (river, sea, and
atmosphere) is extremely poor. Nutrients are stored mainly in trees (i.e., vegetation)
with cycling and N 2 fixation in the rhizosphere. Thus, in nutrient-poor ecosystems,
GHG emissions are low because of minimal microorganism activity.
In developed tropical peatland (Fig. 2.2 bottom), it is assumed that water is the
most serious limiting factor, and drains (i.e., ditches, canals) are often constructed for
water drainage. Then, as plantation crops require large amounts of nutrients, heavy
amounts of chemical fertilizer are applied, which cause environmental pollution by
leaching and activation of microorganisms in peatland. The activated microorganisms decompose (1) peat (CO 2 emission) and nitrogen fertilizer (N 2 O) in the air layer
(aerobic) and (2) peat (CH 4 emission) in the deep aquatic layer (anaerobic) of
peatland. With heavy drainage, the water stock and water cycle rate decrease
drastically, and peatland fires occur more frequently.
An essential element of the tropical peatland ecosystem is a water statute; it is
clarified as Stock-based Water Management [irrigation system] and Drainage-based
Water Management [drainage system]. The principle of eco-management of tropical
peatland includes (1) how to establish Stock-based Water Management and (2) how
to reform Drainage-based Water Management into Stock-based Water Management.
Under climate change, El Niño events become more severe and frequent in the
tropical zone, especially in peatlands in Southeast Asia. Land use conversion and
peatland drainage practices may have an impact on the climate, in which case, the
water stock system becomes urgent. However, it is difficult to maintain a water stock
in a Drainage-based Water Management system, even if the canal or drain is blocked
in the dry season. The basic design of water management should be changed to
Stock-based Water Management on a large scale.
2 Principles of Eco-Management in a Large-Scale Ecosystem of Tropical Peatland
71