Spatiotemporal variability of CO2, N2O and CH4 fluxes from a semi-deciduous tropical forest soil in the Congo basin

Abstract. Tropical forests play an important role in the greenhouse gas exchange between biosphere and atmosphere. Despite holding the second largest tropical forest globally, the Congo basin is generally understudied and ground based greenhouse gas flux data are lacking. In this study, high frequency measurements spanning of sixteen months from automated and manual soil chambers are combined, to characterize spatio-temporal variability in soil greenhouse gas fluxes from a lowland tropical forest in Yangambi, in the Congo Basin. Based on sub-daily continuous measurements, for CO2, a total emission of 15.3 ± 4.4 Mg C ha-1 yr-1 was calculated, with highest fluxes at the start of the wetter periods and a decline in emissions during drier periods. For CH4, the total uptake was -3.9 ± 5.2 kg C ha-1 yr-1. Over the whole period the soil acted as a sink however sporadic emission events were also observed. For N2O an emission of 3.6 ± 4.1 kg N ha-1 yr-1 was calculated, which is higher than most previously reported tropical forest estimates. N2O emissions decreased substantially during drier periods and emission pulses were detected after rain events. High spatial and temporal variability was observed for both CH4 and N2O, but less for CO2. Higher spatial variability was assessed by the manual compared to the automated measurements. Overall, the tropical forest soil acted as a major source for CO2 and N2O and a minor sink for CH4.