Origins, seasonality, and fluxes of organic matter in the Congo River. Issue 7 (28th July 2016)

• Record Type: Journal Article
• Authors: Spencer, Robert G. M.; Hernes, Peter J.; Dinga, Bienvenu; Wabakanghanzi, Jose N.; Drake, Travis W.; Six, Johan
• Is Part Of: Global biogeochemical cycles. Volume 30:Issue 7(2016:Jul.)
• Page Start: 1105
• Page End: 1121
• Publication Date: 2016-07-28
• Subjects: organic matter -- organic carbon -- Congo River -- land‐ocean -- lignin -- Atlantic Ocean; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1002/2016GB005427
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: The Congo River in central Africa represents a major source of organic matter (OM) to the Atlantic Ocean. This study examined elemental (%OC, %N, and C:N), stable isotopic ( δ 13 C and δ 15 N), and biomarker composition (lignin phenols) of particulate OM (POM) and dissolved OM (DOM) across the seasonal hydrograph. Even though the Congo exhibits an extremely stable intra‐annual discharge regime, seasonal variability in OM composition was evident. DOM appears predominantly derived from vascular plant inputs with greater relative contribution during the rising limb and peak in discharge associated with the major November–December discharge maximum. Generally, POM appears to be sourced from soil‐derived mineral‐associated OM (low C:N, low Λ8, and higher (Ad:Al)v ) but the relative proportion of fresh vascular plant material (higher C:N, higher Λ8, and lower (Ad:Al)v ) increases with higher discharge. During the study period (September 2009 to November 2010) the Congo exported 29.21 Tg yr −1 of total suspended sediment (TSS), 1.96 Tg yr −1 of particulate organic carbon (POC), and 12.48 Tg yr −1 of dissolved organic carbon. The Congo exports an order of magnitude lower TSS load in comparison to other major riverine sources of TSS (e.g., Ganges and Brahmaputra), but due to its OM‐rich character it actually exports a comparable amount of POC. The Congo is also 2.5 times more efficient at exporting dissolved lignin per unit volume compared to the Amazon. Including Congo dissolved lignin data in residence time calculations for lignin in the Atlantic Ocean results in an approximately 10% reduction from the existing estimate, suggesting that this material is more reactive than previously thought. Key Points: Seasonal variability in OM composition is apparent in an extremely stable discharge regime The Congo is 2.5 times more efficient at exporting dissolved lignin per unit volume in comparison to the Amazon Congo River dissolved lignin fluxes decrease residence time estimates for the terrigenous biomarker lignin in the Atlantic Ocean