Spatiotemporal variability of CO ₂ , N ₂ O and CH ₄ 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 the biosphere and atmosphere. Despite having 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 16 months from automated and manual fast-box soil chambers are combined to characterize spatiotemporal variability in soil greenhouse gas fluxes from a lowland tropical forest in Yangambi in the Congo Basin. Based on subdaily continuous measurements for CO2, a total emission of 15.3 ± 4.4 MgCha-1yr-1 was calculated, with the 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 kgCha-1yr-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 kgNha-1yr-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, although less so for CO2. Higher spatial variability was assessed through the manual measurements compared to the automated measurements. Overall, the tropical forest soil acted as a major source of CO2 and N2O and a minor sink of CH4.