The Ruki is a pristine blackwater tributary in the Congo Basin draining tropical lowland forest. Daily discharge and fortnightly concentrations, isotopic ratios, and molecular composition of carbon and organic matter were measured for 1 yr (2019–2020). Like the Congo River, discharge peaked from November–January, with a smaller secondary peak in June. Dissolved organic carbon (DOC), inorganic carbon (DIC), carbon dioxide ( p CO 2 ), and methane ( p CH 4 ) concentrations were high (21.3 ± 4.8 mg C L ⁻¹ , 5.8 ± 0.9 mg C L ⁻¹ , 6370 ± 1740 ppm, and 250 ± 100 ppm, respectively) and positively correlated with discharge, indicating transport limitation. Total suspended solids and particulate organic carbon (POC) concentrations were generally low (3.68 ± 1.61 mg L ⁻¹ , 0.88 ± 0.33 mg C L ⁻¹ , respectively) and varied inversely with discharge, indicating source limitation. The Ruki exported a total of 3.25 Tg C yr ⁻¹ , of which DOC, DIC, and POC comprised 76%, 20%, and 3%, respectively. This DOC flux represents ~ 20% of the annual Congo Basin flux from about 5% of its area, highlighting the high yield. Isotopic ratios of DOC and POC indicate modern C3 forest vegetation as a source, except for a few older samples potentially indicating peat inputs. The bulk molecular composition of dissolved organic matter was seasonally consistent; however, a more oxidized and aromatic assemblage occurred at high discharge, corresponding with forest vegetation, while a more aliphatic, nitrogen‐, and sulfur‐enriched assemblage was found during low discharge, corresponding with soil‐derived organic matter. Overall, these results underscore how hydrology controls C concentrations in the Ruki River and how this blackwater river contributes disproportionately to C export per unit area within the Congo Basin hydrosystem.
Drake T. W., Barthel M., Mbongo C. E., Mpambi D. M., Baumgartner S., Botefa C. I., Bauters M., Kurek M. R., Spencer R. G. M., McKenna A. M., Haghipour N., Ekamba G. L., Wabakanghanzi J. N., Eglinton T. I., Van Oost K., Six J.
Hydrology drives export and composition of carbon in a pristine tropical river.
Limnology and Oceanography, 68, (11), 2023, 2476-2491.
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ISSN Print: 0024-3590
ISSN Online: 1939-5590
Digital Object Identifier (DOI): https://doi.org/10.1002/lno.12436
Publikations-ID (Webcode): 54630 Per E-Mail versenden
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