It is widely acknowledged that tropical peatlands play an important role in the global carbon balance. Carbon stocks and fluxes have been the focus of growing research attention as the greenhouse gas emissions from peatlands, as well as their potential to act as carbon sinks, have gained international prominence in forums such as the COP talks and IPCC reports.
Tropical peatlands are formed by an accumulation of partially decayed vegetation under waterlogged conditions, where oxygen deficiency limits decomposition of organic materials.
Peatland drainage accelerates degradation of peat soil by lowering the water table and thereby increasing the thickness of the oxidative peat layer. The drainage and conversion of natural peatlands increases fire frequency, haze air pollution and carbon emissions.
Nonetheless, rapid human population growth in Southeast Asia has led to increasing drainage of natural peatland ecosystems for conversion to agricultural use. Peatland drainage lowers the water table, thereby increasing the thickness of the peat layer that is exposed to oxidation. Drying leads to shrinkage of organic materials, resulting in compression of peat layers. The combination of oxidation, shrinkage and compaction causes subsidence of the soil surface.
Due to these chemical and physical processes of peatland degradation, Indonesian Government Regulation No. 57 (2016) on protection and management of peatland stipulates that peatland is considered damaged if the water table is more than 40 cm below the ground surface.
Studies on the impact of drainage on peat soil began in the early 2000s, in response to the extensive drainage and conversion of natural peatland that occurred during this period.
Studies on the effect of drainage on peat soils are needed in order to develop restoration strategies, improve conservation management, and mitigate fires and carbon emissions.
- The 0–40-cm interval sits above the water level throughout most of the year. At this level, chemical and physical processes such as oxidation, shrinkage and compaction are expected to be more prevalent due to changes in hydrological conditions.
- The second depth interval, 40–80 cm, is the region in which the water level fluctuates during the year and thus it is temporarily saturated, especially in the rainy season.
- The third interval, > 80-cm depth, is the region that is expected to be water-saturated during most of the year; an exception is drained peatland during El Ñino years, where the water level may fall by more than 1 m.
Based on the scientific literature, the depth of 80 cm is an average water level in the field, especially in drained peatland or in managed perennial vegetation. For example, research conducted in Southeast Asia’s oil palm and acacia plantations recorded an average water level between 68 and 91 cm below the surface. This is because Acacia established in peatland requires water levels between 70 and 90 cm below the surface to support productivity.
In recent years, a new peatland management approach, ‘eko-hidro,’ has been promoted by several industry actors and academics. It proposes that water levels in plantations are managed at between 50 and 80 cm below the peat surface to minimise subsidence and reduce carbon emissions.
For a recent review of studies into tropical peat soils under different land uses, please see the full paper: Kunarso, A., Bonner, M.T.L., Blanch, E.W. et al. Differences in Tropical Peat Soil Physical and Chemical Properties Under Different Land Uses: A Systematic Review and Meta-analysis. J Soil Sci Plant Nutr (2022). https://doi.org/10.1007/s42729-022-01008-2