Land‐use controls on carbon biogeochemistry in lowland streams of the Congo Basin. (11th January 2020)

• Record Type: Journal Article
• Authors: Drake, Travis W.; Podgorski, David C.; Dinga, Bienvenu; Chanton, Jeffrey P.; Six, Johan; Spencer, Robert G. M.
• Is Part Of: Global change biology. Volume 26:Number 3(2020)
• Page Start: 1374
• Page End: 1389
• Publication Date: 2020-01-11
• Subjects: African lowland forest -- carbon biogeochemistry -- carbon cycle -- Congo Basin -- dissolved inorganic carbon -- dissolved organic matter -- land‐use change -- tropical deforestation; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.14889
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: The flux and composition of carbon (C) from land to rivers represents a critical component of the global C cycle as well as a powerful integrator of landscape‐level processes. In the Congo Basin, an expansive network of streams and rivers transport and cycle terrigenous C sourced from the largest swathe of pristine tropical forest on Earth. Increasing rates of deforestation and conversion to agriculture in the Basin are altering the current regime of terrestrial‐to‐aquatic biogeochemical cycling of C. To investigate the role of deforestation on dissolved organic and inorganic C (DOC and DIC, respectively) biogeochemistry in the Congo Basin, six lowland streams that drain catchments of varying forest proportion (12%–77%) were sampled monthly for 1 year. Annual mean concentrations of DOC exhibited an asymptotic response to forest loss, while DIC concentrations increased continuously with forest loss. The isotopic signature of DIC became significantly more enriched with deforestation, indicating a shift in source and processes controlling DIC production. The composition of dissolved organic matter (DOM), as revealed by ultra‐high‐resolution mass spectrometry, indicated that deforested catchments export relatively more aliphatic and heteroatomic DOM sourced from microbial biomass in soils. The DOM compositional results imply that DOM from the deforested sites is more biolabile than DOM from the forest, consistent with the corresponding elevated stream CO2 concentrations. In short, forest loss results in significant and comprehensive shifts in the C biogeochemistry of the associated streams. It is apparent that land‐use conversion has the potential to dramatically affect the C cycle in the Congo Basin by reducing the downstream flux of stable, vascular‐plant derived DOC while increasing the transfer of biolabile soil C to the atmosphere. Abstract : This study documents the perturbation of the carbon cycle by agricultural deforestation within the dominant forest type of the Congo Basin. Forest loss resulted in significant and comprehensive shifts in the biogeochemistry of dissolved organic and inorganic carbon found in streams, suggesting that deforestation reduces the aquatic export of stable, vascular‐plant derived organic carbon while relatively increasing the transfer of biolabile soil carbon to the atmosphere.