Structure and composition of natural ferrihydrite nano-colloids in anoxic groundwater

Maya Engel, Vincent Noël, Samuel Pierce, Libor Kovarik, Ravi K. Kukkadapu, Juan S.Lezama Pacheco, Odeta Qafoku, J. Ray Runyon, Jon Chorover, Weijiang Zhou, John Cliff, Kristin Boye, John R. Bargar

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Fe-rich mobile colloids play vital yet poorly understood roles in the biogeochemical cycling of Fe in groundwater by influencing organic matter (OM) preservation and fluxes of Fe, OM, and other essential (micro-)nutrients. Yet, few studies have provided molecular detail on the structures and compositions of Fe-rich mobile colloids and factors controlling their persistence in natural groundwater. Here, we provide comprehensive new information on the sizes, molecular structures, and compositions of Fe-rich mobile colloids that accounted for up to 72% of aqueous Fe in anoxic groundwater from a redox-active floodplain. The mobile colloids are multi-phase assemblages consisting of Si-coated ferrihydrite nanoparticles and Fe(II)-OM complexes. Ferrihydrite nanoparticles persisted under both oxic and anoxic conditions, which we attribute to passivation by Si and OM. These findings suggest that mobile Fe-rich colloids generated in floodplains can persist during transport through redox-variable soils and could be discharged to surface waters. These results shed new light on their potential to transport Fe, OM, and nutrients across terrestrial-aquatic interfaces.

Original languageEnglish (US)
Article number119990
JournalWater research
StatePublished - Jun 30 2023


  • Electron microscopy
  • Fe mineral
  • Mössbauer spectroscopy
  • Oxidation–reduction

ASJC Scopus subject areas

  • Environmental Engineering
  • Civil and Structural Engineering
  • Ecological Modeling
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution


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