Factors Controlling GHG Emissions in Malaysian Tropical Peatland

Abstract:

Southeast Asia peatland undergoing extensive drainage and deforestation for agriculture resulted in intense greenhouse gas (GHG) emissions. Although large areas previously cleared for agriculture have been abandoned, peatland regenerating’s initiative, such as canal’s blocking bringing the groundwater up to the peat surface, reflects evidence of subsequent forest recovery. In this study, we measured GHG emissions from three Malaysian tropical peatland systems: disturbed peatland, (i) oil palm plantation (OP), (ii) recovery forest (RF), and undisturbed peatland, (iii) natural forest (NF) for comparing land-use change. Biweekly temporal measurement of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes were conducted using closed chamber method along with continuously environmental variables from July 2017 to December 2018. One kg peat soil with approximately 10 cm depth was collected for analysing physicochemical properties. Our result shows large emissions of CO₂ and N₂O in disturbed peatland sites (OP and RF) while CH₄ fluxes were reduced. Both cumulative CO₂ and N₂O fluxes in disturbed peatland sites were significantly higher than NF; however, there were no significant differences in both gases emission between OP and RF. Hence, cumulative CO₂ flux demonstrated similar emission trend in OP and RF shows that decomposition rate in both sites was similar resulted from no significant different of their C/N ratio. The cumulative emission of N₂O in OP and RF was almost the same. However, the emission trend was different during mid-annual measurements suggested that the N₂O emissions from OP and recovery PSF were potentially produced from the different reactions of microbial activities; lower groundwater level (GWL) in OP with an average 71±0.21cm depth served an aerobic condition for nitrification while N₂O produced in recovery PSF was likely from denitrification process when the GWL was closed to the surface. Cumulative CH₄ flux was significantly lower in OP compared to both NF and RF, and no significant difference between forested sites. The GWL had a notable influence on the cumulative CH₄ fluxes in both forested sites. The GWL and soil electrical conductivity in NF were noted to be negatively correlated (r² = 0.84), GWL and soil moisture were positively correlated in RF (r² = 0.89).