Glacial recession is occurring at unprecedented rates resulting in increased sediment accumulations in some riverine ecosystems. Increased sediment deposition has implications for ecosystem stability (e.g. floods and river paths) and environmental services (e.g. carbon sequestration). Soils and sediments have an enormous potential to retain carbon (C), predominantly due to sorption to mineral surfaces. However, C persistence may be sensitive to climate-change induced changes in temperature and moisture. We coupled ultrahigh resolution organic matter classification (Fourier Transform Ion Cyclotron Resonance Mass Spectrometry, FTICR MS) with bacterial characterization (16S rRNA sequencing) and CO2 respiration measurements to test the combined effects of temperature (4˚ vs 20˚C) and moisture (50 vs 100% water-filled pore space) on C turnover in sediments maintained under different mineralogical conditions (illite-amended vs non-amended).
Results/Conclusions
Here we show that the inhibition of CO2 emissions from the combined effect of increased moisture content and illite is reflected in the turnover of key molecular signatures, such as the nominal oxidation state of C, often irrespective of temperature. Shifts in bacterial communities from a coupled moisture-mineral interaction were, however, temperature-dependent. Yet organic matter turnover was driven more by moisture content than temperature or illite. Our results reveal that microbial access to C is governed by both mineral sorption and thermodynamics (i.e. O2 availability) and that C in water-saturated sediments is thermodynamically unfavorable for microbial consumption.