Greenhouse gas emissions from ditches in oil palm plantations on tropical peatlands in Malaysia

Tropical peatlands, which store 20% of global peat carbon, are increasingly threatened by conversion to alternative land-uses such as oil palm plantations, pulp wood plantations, crop growth or other economic activities. This transformation involves peatland drainage, which lowers water tables, exposes peat to oxygen, and alters greenhouse gas (GHG) emissions: increasing carbon dioxide (CO₂) and nitrous oxide (N₂O) fluxes while reducing methane (CH₄) emissions from soils. However, drainage ditches created in the process may become significant sources of CH₄ due to anoxic conditions. This study quantified GHG fluxes from drainage ditches in Sarawak, Malaysia, through spatial sampling conducted during the daytime in the transitional period between the drier and wetter seasons using portable trace gas analyzers. Median fluxes were 0.19 g CH₄ m^-2 d^-1, 17.1 g CO₂ m^-2 d^-1, and - 0.12 mg N₂O m^-2 d^-1. Physical water parameters such as pH, oxygen concentration, temperature, and oxidation-reduction potential were found to be significant drivers of GHG fluxes. The median emissions from ditches in one hectare of land were 5.84 kg CO₂ ha^-1 d^-1, 2.78 kg CH₄ as CO₂ eq ha^-1 d^-1, and - 0.001 kg N₂O as CO₂ eq ha^-1 d^-1. These findings underscore the role of drainage ditches as CH₄ sources in tropical peatland agriculture, highlighting the need for further research into GHG management in these modified landscapes.