Molecular Nature of Mineral-Organic Associations within Redox-Active Mountainous Floodplain Sediments

Cam G. Anderson, Genevieve M. Goebel, Malak M. Tfaily, Patricia M. Fox, Peter S. Nico, Scott Fendorf, Marco Keiluweit

Research output: Contribution to journalArticlepeer-review


Floodplains are critical terrestrial-aquatic interfaces that act as hotspots of organic carbon (OC) cycling, regulating ecosystem carbon storage as well as export to riverine systems. Within floodplain sediments, regular flooding and textural gradients interact to create dynamic redox conditions. While anaerobic protection of OC upon burial is a well-recognized carbon storage mechanism in redox-active floodplain sediments, the impact of protective mineral-organic associations is relatively unknown. Here we determined the quantitative importance and chemical composition of mineral-organic associations along well-defined redox gradients emerging from textural variations and depth within meander sediments of the subalpine East River watershed (Gothic, CO). We characterized mineral-organic associations using a combination of sequential extractions, physical fractionation, and high-resolution mass spectrometry. Across the meander, we found that mineral-associated OC constitutes a significant fraction of total OC, and that extractable iron (Fe) and aluminum (Al) phases as well as high-density isolates were strongly correlated with total OC content, suggesting that mineral-organic associations are quantitatively important for floodplain sediment OC protection. Our mass spectrometry results showed OC associated with increasingly ordered Fe and Al phases are relatively enriched in low-molecular weight, oxidized, aromatic compounds. Surprisingly, however, total OC content showed weak or no correlation with indicators of anaerobic protection, such as relatively bioavailable OC pools (water-extractable and particulate OC) or the molecular weight and oxidation state of OC. Overall, this work highlights that protection of OC bound to reactive mineral phases─in addition to anaerobic protection─can play a quantitatively important role in controlling soil carbon storage in redox-active floodplain sediments.

Original languageEnglish (US)
Pages (from-to)1623-1634
Number of pages12
JournalACS Earth and Space Chemistry
Issue number9
StatePublished - Sep 21 2023


  • Climate change
  • Floodplains
  • Mineral-organic associations
  • Redox gradients
  • Soil organic carbon

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Atmospheric Science
  • Space and Planetary Science


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