Ecosystem-scale methane flux in tropical peat swamp forest in Indonesia

Data on ecosystem-scale methane (CH₄ ) fluxes in tropical peatlands are currently lacking in the global CH₄ budget. Although the waterlogged Indonesian peatlands contain the largest share of peat carbon in South-East Asia, ecosystem-scale CH₄ budgets have not yet been reported, although these peatlands have the potential to emit CH₄ . We observed 1-year variations in the ecosystem-scale CH₄ flux in an undrained secondary peat swamp forest in central Kalimantan, Indonesia, using the eddy covariance method. We found that the peat swamp forest switched from being a CH₄ sink during the dry season (as low as -8.9 mg C m^-2  day^-1 ) to a source of CH₄ during the wet season (up to 10.7 mg C m^-2  day^-1 ), and this was dependent on changes in the groundwater level (GWL). The high GWL during the wet season enhanced the anaerobic CH₄ production in the surface layer that had more labile organic matter. However, the CH₄ emission also increased when the GWL dropped during dry spells in the wet season. The annual CH₄ budget in the studied tropical peat swamp forest (0.09-0.17 g C m^-2  year^-1 ) was much lower than that in northern, temperate, and subtropical wetlands. We found that CH₄ fluxes had almost no effect on the global warming gas budget of the peat swamp forest, and values were only a few percent less than the CO₂ fluxes at the same site. In addition, we conducted anaerobic soil incubation experiments to examine the effect of land-use change on CH₄ production. The results indicated much higher CH₄ production potential in undrained forest soil than in drained or drained and burned ex-forest soils. However, although CH₄ production decreased in drained soils relative to undrained soils, conserving pristine peat swamp forests with high GWLs is important to suppress global warming because CO₂ emissions increase in drained peatlands.