Compound-Specific Isotope Analyses of n-Alkane Biomarkers Reveals Source-Dependent and Persistent Priming Effects in Incubated Sediments

The introduction of new bioavailable carbon into natural systems can awaken existing old carbon stocks, not only posing threats to the ecosystem’s health, but also increasing CO₂ fluxes to the atmosphere. The freshly discharged labile organic carbon (OC) can fuel microbial communities to decompose recalcitrant and previously stable native pools, a process known as positive priming effect (PE). While patterns of PE are well investigated in soils and terrestrial systems, it remains insufficiently studied in aquatic environments. In particular, it is not well understood that to what extent and for how long the inputs of labile OC from different origins can trigger distinct PE responses in sediments. Hydrocarbon biomarkers, particularly n-alkanes of different chain lengths, have been wildly used as molecular tracers of different OC sources. In this study, by applying n-alkanes’ stable carbon isotope values and concentrations (C₁₅–C₃₀) in isotopic mass balance equations, we quantified the contributions of fresh labile OC and old sedimentary OC to the remineralized pool and tracked the induced PE and its variation during incubation experiments. Spiking coastal sediments (δ¹³C = −25.26 ± 0.06 ‰) with isotopically distinct marine OC (protein-rich Nannochloropsis phytoplankton, δ¹³C = −43.18 ± 0.31 ‰) and terrestrial OC (polysaccharide-rich C₄ corn leaves, δ¹³C = −13.90 ± 0.09 ‰) across 30 microcosms respectively resulted in 10.3 ± 1.5 % and 30.4 ± 3.6 % stimulation of sedimentary OC decomposition in molecular level that last during the course of incubation (32 days). Moreover, we detected synergistic enhancement of the PE in sediments when receiving 1:1 mixtures of marine and terrestrial OC inputs. These amplified, persistent, and source-specific priming responses of sediments to fresh OC discharges show that the mobilization and degradation of previously stabilized native stocks can potentially turn long-term and major sinks of carbon into sources under different perturbed states, having serious implications during ongoing climatic changes.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Yeganeh Mirzaei, Concordia University and Geotop Research Center (yeganeh.mirzaei@concordia.ca)

Authors:

Yeganeh Mirzaei, Concordia University and Geotop Research Center  (yeganeh.mirzaei@concordia.ca)

Peter Douglas, McGill University and Geotop Research Center  (peter.douglas@mcgill.ca)

Yves Gélinas, Concordia University and Geotop Research Center  (yves.gelinas@concordia.ca)