Dissolved organic carbon lability and stable isotope shifts duringmicrobial decomposition in a tropical river system

[摘要] A significant amount of carbon is transported to the ocean as dissolvedorganic carbon (DOC) in rivers. During transport, it can be transformedthrough microbial consumption and photochemical oxidation. In darkincubation experiments with water from the Tana River, Kenya, we examinedthe consumption of DOC through microbial decomposition and the associatedchange in its carbon stable isotope composition (δ¹³C). In 15of the 18 incubations, DOC concentrations decreased significantly by 10 to60 %, with most of the decomposition taking place within the first24–48 h. After 8 days, the remaining DOC was up to 3 ‰ moredepleted in ¹³C compared with the initial pool, and the change inδ¹³C correlated strongly with the fraction of DOC remaining. We hypothesizethat the shift in δ¹³C is consistent with greater microbiallability of DOC originating from herbaceous C₄ vegetation than DOC derivedfrom woody C₃ vegetation in the semi-arid lower Tana. The resultscomplement earlier findings that the stable isotope concentration of riverineDOC does not necessarily reflect the proportion of C₃ and C₄-derived DOCin the catchment: besides spatial distribution patterns of different vegetation types,processing within the river can further influence the δ¹³C of riverine OC.

[学科分类] 地球化学与岩石