Controls on the carbon balance of tropical peatlands

The carbon balance of tropical peatlands was investigated using measurements of gaseous fluxes of carbon dioxide (CO2) and methane (CH4) at several land-use types, including nondrained forest (NDF), drained forest (DF), drained regenerating forest (DRF) after clear cutting and agricultural land (AL) in Central Kalimantan, Indonesia. Soil greenhouse gas fluxes depended on land-use, water level (WL), microtopography, temperature and vegetation physiology, among which WL was the strongest driver. All sites were CH4 sources on an annual basis and the emissions were higher in sites providing fresh litter deposition and water logged conditions. Soil CO2 flux increased exponentially with soil temperature (T-s) even within an amplitude of 4-5 degrees C. In the NDF soil CO2 flux sharply decreased when WLs rose above -0.2 and 0.1 m for hollows and hummocks, respectively. The sharp decrease suggests that the contribution of surface soil respiration (RS) to total soil CO2 flux is large. In the DF soil CO2 flux increased as WL decreased below -0.7 m probably because the fast aerobic decomposition continued in lower peat. Such an increase in CO2 flux at low WLs was also found at the stand level of the DF. Soil CO2 flux showed diurnal variation with a peak in the daytime, which would be caused by the circadian rhythm of root respiration. Among the land-use types, annual soil CO2 flux was the largest in the DRF and the smallest in the AL. Overall, the global warming potential (GWP) of CO2 emissions in these land-use types was much larger than that of CH4 fluxes.