Large variation in carbon dioxide emissions from tropical peat swamp forests due to disturbances

The huge carbon stock of tropical peat swamp forest (PSF) in Southeast Asia has been threatened by environmental disturbances due to quasi-periodic El Ni & ntilde;o-Southern Oscillation (ENSO) droughts, biomass and peat burning, smoke haze, drainage, and deforestation. Carbon dioxide (CO2) emissions from such disturbances have not been well quantified because of insufficient field data. Therefore, we quantified the ecosystem-scale CO2 balance and examine the disturbance effects from a long-term field experiment for 12-15 years at three PSF sites with different degrees of degradation in Indonesia. Here, we show a drastic change of an undrained PSF from a CO2 sink to a source owing to the transient groundwater lowering by the droughts, a significant decrease in ecosystem photosynthesis due to the radiation attenuation by smoke haze in drought years, and long-lasting CO2 emissions through enhanced peat decomposition by drainage. The impact on CO2 emissions was greater from drainage than drought-induced disturbances. Reductions in groundwater level due to El Ni & ntilde;o-induced drought events changed an undrained tropical peat swamp forest from a carbon dioxide sink to a source with cumulative impacts of drainage and smoke haze further enhancing long term emissions, suggest long-term field experiments in Indonesia.