Abstract Humic tropical lakes and wetlands are globally important sources of atmospheric greenhouse gases (GHGs). However, mechanistic insight into GHG cycling in such systems remains limited—especially in understudied central Africa. To address this, here we measured high‐, falling‐, and low‐water seasonal concentrations and isotopic compositions of the major dissolved GHGs , , and in Africa's largest humic lake: Mai Ndombe, Democratic Republic of Congo. We find that the water column is weakly to non‐stratified and is highly supersaturated with respect to atmospheric equilibrium for all GHGs across all seasons, sampling stations, and water depths. Additionally, all GHG concentrations increase steadily with increasing water depth, reflecting atmospheric gas exchange due to physical mixing in the upper water column as well as biological processes. Extrapolating these results—combined with field measurements such as temperature and wind speed—we estimate that Lake Mai Ndombe emits 375 ± 32 Gg C yr −1 as , 623 ± 136 Mg C yr −1 as , and 223 20 Mg N yr −1 as ( propagated Monte Carlo uncertainty). Furthermore, carbon‐isotope signals suggest that is largely sourced from respiration of bioavailable organic carbon, whereas reflects sedimentary methanogenesis followed by aerobic methanotrophy in the water column. Finally, bulk and position‐specific isotopic compositions reveal a nitrogen cycle dominated by sedimentary denitrification, with near‐quantitative reduction to prior to upward diffusion into the water column and eventual outgassing. Combined, these observations reveal that carbon inputs, total water depth, and/or dissolved oxygen saturation are the major drivers of the flux and composition of GHGs emitted from Lake Mai Ndombe and potentially other tropical humic lakes.
Barthel et al. (Sun,) studied this question.