Low N${}_2$O and variable CH${}_4$ fluxes from tropical forest soils of the Congo Basin

Globally, tropical forests are assumed to be an important source of atmospheric nitrous oxide (N${}_2$O) and sink for methane (CH${}_4$). Yet, although the Congo Basin comprises the second largest tropical forest and is considered the most pristine large basin left on Earth, in situ N${}_2$O and CH${}_4$ flux measurements are scarce. Here, we provide multi-year data derived from on-ground soil flux (n = 1558) and riverine dissolved gas concentration (n = 332) measurements spanning montane, swamp, and lowland forests. Each forest type core monitoring site was sampled at least for one hydrological year between 2016 - 2020 at a frequency of 7-14 days. We estimate a terrestrial CH${}_4$ uptake (in kg CH${}_4$-C ha${}^{-1}$ yr${}^{-1}$) for montane (−4.28) and lowland forests (−3.52) and a massive CH${}_4$ release from swamp forests (non-inundated 2.68; inundated 341). All investigated forest types were a N${}_2$O source (except for inundated swamp forest) with 0.93, 1.56, 3.5, and −0.19 kg N${}_2$O-N ha${}^{-1}$ yr${}^{-1}$ for montane, lowland, non-inundated swamp, and inundated swamp forests, respectively.