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The biogeochemistry of carbon across a gradient of streams and rivers within the Congo Basin
Author(s) -
Mann P. J.,
Spencer R. G. M.,
Dinga B. J.,
Poulsen J. R.,
Hernes P. J.,
Fiske G.,
Salter M. E.,
Wang Z. A.,
Hoering K. A.,
Six J.,
Holmes R. M.
Publication year - 2014
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2013jg002442
Subject(s) - dissolved organic carbon , environmental science , hydrology (agriculture) , swamp , drainage basin , water quality , biogeochemistry , ecology , geology , oceanography , geography , geotechnical engineering , cartography , biology
Dissolved organic carbon (DOC) and inorganic carbon (DIC, p CO 2 ), lignin biomarkers, and theoptical properties of dissolved organic matter (DOM) were measured in a gradient of streams and rivers within the Congo Basin, with the aim of examining how vegetation cover and hydrology influences the composition and concentration of fluvial carbon (C). Three sampling campaigns (February 2010, November 2010, and August 2011) spanning 56 sites are compared by subbasin watershed land cover type (savannah, tropical forest, and swamp) and hydrologic regime (high, intermediate, and low). Land cover properties predominately controlled the amount and quality of DOC, chromophoric DOM (CDOM) and lignin phenol concentrations (∑ 8 ) exported in streams and rivers throughout the Congo Basin. Higher DIC concentrations and changing DOM composition (lower molecular weight, less aromatic C) during periods of low hydrologic flow indicated shifting rapid overland supply pathways in wet conditions to deeper groundwater inputs during drier periods. Lower DOC concentrations in forest and swamp subbasins were apparent with increasing catchment area, indicating enhanced DOC loss with extended water residence time. Surface water p CO 2 in savannah and tropical forest catchments ranged between 2,600 and 11,922 µatm, with swamp regions exhibiting extremely high p CO 2 (10,598–15,802 µatm), highlighting their potential as significant pathways for water‐air efflux. Our data suggest that the quantity and quality of DOM exported to streams and rivers are largely driven by terrestrial ecosystem structure and that anthropogenic land use or climate change may impact fluvial C composition and reactivity, with ramifications for regional C budgets and future climate scenarios.