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Title: Thermodynamically controlled preservation of organic carbon in floodplains

Organic matter decomposition in soils and terrestrial sediments has a prominent role in the global carbon cycle. Carbon stocks in anoxic environments, such as wetlands and the subsurface of floodplains, are large and presumed to decompose slowly. The degree of microbial respiration in anoxic environments is typically thought to depend on the energetics of available terminal electron acceptors such as nitrate or sulfate; microbes couple the reduction of these compounds to the oxidation of organic carbon. But, it is also possible that the energetics of the organic carbon itself can determine whether it is decomposed. We examined water-soluble organic carbon by Fourier-transform ion-cyclotron-resonance mass spectrometry to compare the chemical composition and average nominal oxidation state of carbon—a metric reflecting whether microbial oxidation of organic matter is thermodynamically favourable—in anoxic (sulfidic) and oxic (non-sulfidic) floodplain sediments. We also observed distinct minima in the average nominal oxidation state of water-soluble carbon in sediments exhibiting anoxic, sulfate-reducing conditions, suggesting preservation of carbon compounds with nominal oxidation states below the threshold that makes microbial sulfate reduction thermodynamically favourable. Finally, we show that thermodynamic limitations constitute an important complement to other mechanisms of carbon preservation, such as enzymatic restrictions and mineral association, within anaerobic environments.
 [1] ;  [2] ;  [3] ;  [2] ;  [4] ;  [2] ;  [5]
  1. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource; Stanford Univ., CA (United States). Earth System Science Dept.
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Science Lab.
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Climate and Ecosystem Sciences Division
  5. Stanford Univ., CA (United States). Earth System Science Dept.
Publication Date:
Grant/Contract Number:
AC02-76SF00515; FG02-13ER65542; AC02-05CH11231
Accepted Manuscript
Journal Name:
Nature Geoscience
Additional Journal Information:
Journal Volume: 10; Journal Issue: 6; Journal ID: ISSN 1752-0894
Nature Publishing Group
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
58 GEOSCIENCES; carbon cycle; freshwater ecology
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1368457