COS 99-5 - Vulnerability of organo-mineral controls on C bioavailability at the terrestrial-aquatic interface

Wednesday, August 9, 2017: 2:50 PM
B117, Oregon Convention Center
A. Peyton Smith1, Malak M. Tfaily2, Kenton Rod1 and Ryan Renslow1, (1)Pacific Northwest National Laboratory, Richland, WA, (2)Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland, WA

Sorption of organic matter (OM) to mineral surfaces is a primary process governing its persistence by rendering it unavailable for microbial degradation. How climate change-induced shifts in temperature and moisture influence the bioavailability of previously-bound OM remains highly uncertain. We used a short-term laboratory incubation to test the combined effects of temperature (4˚ vs 20˚C) and moisture (50 vs 100% water-filled pore space, WFPS) on microbial respiration, biomass and community composition in capillary fringe-sediments (Nisqually River, Mt. Rainier, WA) maintained under different mineralogical conditions (illite amended vs un-amended). We also measured changes in the molecular composition of soluble-OM using high-resolution, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). We hypothesized that OM in clay-amended sediments would be less vulnerable to changes in moisture and temperature than OM in un-amended, natural sediments as the OM would be protected from decomposition via mineral sorption. We also hypothesized that increased temperature, more than a change in moisture content, would alter mineral-OM interactions in clay-amended sediments resulting in more transformations of OM at 20˚C than at 4˚C.


At 4˚C, CO2-C was more sensitive to changes in moisture content in clay-amended sediments, with the highest CO2-C emitted from clay-amended sediments held at 50% WFPS compared to sediments under saturated conditions at 4˚C. At 20˚C, unexpectedly more CO2-C was emitted from un-amended, saturated sediments (100% WFPS), compared to clay-amended sediments maintained at 50 and 100% WFPS. This may be due to an increased abundance of microaerophilic organisms. Cumulative CO2-C was positively correlated with many FT-ICR-MS metrics, such as the nominal oxidation state of carbon (NOSC, p = 0.0004), aromaticity (AI, p = 0.0004) and the double-bond equivalent (DBE, p < 0.0001), suggesting that complex forms of OM are thermodynamically available for microbial degradation. We also observed increases in NOSC, AI and DBE, but only in clay-amended sediments maintained at 50% WFPS. In addition, decreases in lipid-, lignin- and tannin-like compounds were mostly observed in clay-amended sediments maintained at 50% WFPS, compared to un-amended sediments under saturation. Our results, contrary to our hypotheses, show that OM transformations were most vulnerable in clay-amended sediments compared to un-amended, natural sediments and that moisture content, rather than temperature, was more important for transformations in OM composition.