Fluvial sediment export from pristine forested headwater catchments in the Congo Basin

Agricultural Land‐Use Increases Carbon Yields in Lowland Streams of the Congo Basin

“…Interestingly, the maximum POC concentration was higher in the Forest site (191 compared to 65 mg L −1 ), perhaps due to the smaller catchment size and thus flashier hydrograph, which is indicated by the higher maximum specific Q (Figure 2). Previous research on the TSS concentrations of the Forest stream showed that sediment concentrations increased with discharge and exhibited clockwise hysteresis, caused by the quick flushing of surface material during the rising limb followed by a depletion of source material during the falling limb (Baumgartner et al., 2022). Both the Ag and Forest streams exhibited similar turbidity increases with discharge (Figure S5 in Supporting Information ), indicating similar sediment mobilization dynamics within the two catchments.…”

“…The short residence time and thus limited potential for decomposition in these low‐order streams, along with the observation that smaller and thus potentially more mobile organic compounds tend to be enriched in N (such as amino acids and microbial necromass; Drake et al., 2019; Wagner et al., 2015), may point to the latter process. Nevertheless, the export of recent C3‐derived OC is typical of lowland forest landscapes that are dominated by C3 vegetation and have low erosion rates (Baumgartner et al., 2022; Mayorga et al., 2005). These results contrast with those from Eastern Congo that showed older and more 13 C enriched DOC in streams draining deforested croplands (Drake et al., 2019).…”

“…Collectively, the C:N and isotopic results indicate that the OC in both streams is primarily composed of topsoil and litter derived from C3 plants (mean δ 13 C values of −30‰) that was recently photosynthesized (high F mod ). The relatively low C:N values for OC observed in the river compared to soil and litter (∼13 and ∼20, respectively; Baumgartner et al., 2022) could have resulted due to either in‐stream decomposition or preferential mobilization of more decomposed (low C:N) material compared to fresher (high C:N) vegetation. The short residence time and thus limited potential for decomposition in these low‐order streams, along with the observation that smaller and thus potentially more mobile organic compounds tend to be enriched in N (such as amino acids and microbial necromass; Drake et al., 2019; Wagner et al., 2015), may point to the latter process.…”

Hydrology drives export and composition of carbon in a pristine tropical river

“…So far, biogeochemical studies have primarily focused on assessing fluxes from the main stem of the Congo River at Kinshasa‐Brazzaville (Coynel et al 2005; Seyler et al 2005; Wang et al 2013; Lambert et al 2016; Spencer et al 2016; Hemingway 2017; Kurek et al 2022). Previous studies have examined transects along Congo mainstem that included outlets of major tributaries (Lambert et al 2016; Borges et al 2019), the Oubangui River (Bouillon et al 2012, 2014), the Kasai River (Borges et al 2019), the Ngoko‐Sangha River (Coynel et al 2005), and smaller rivers of western (Mann et al 2014; Upstill‐Goddard et al 2017; Drake et al 2020 a ) and eastern Congo (Spencer et al 2010; Drake et al 2019; Baumgartner et al 2022). While important, the main‐stem studies are hindered by low temporal resolution and ambiguity arising from the convolution of fluxes and signals from multiple tributaries that drain different land covers.…”