Distinguishing Biotic and Abiotic Iron Oxidation at Low Temperatures

Brian St Clair, Justin Pottenger, Randall Debes, Kurt Hanselmann, Everett Shock

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


The rates of microbial and abiotic iron oxidation were determined in a variety of cold (T = 9-12 °C), circumneutral (pH = 5.5-9.0) environments in the Swiss Alps. These habitats include iron-bicarbonate springs, iron-arsenic-bicarbonate springs, and alpine lakes. Rates of microbial iron oxidation were measured up to a pH of 7.4, with only abiotic processes detected at higher pH values. Iron oxidizing bacteria (FeOB) were responsible for 39-89% of the net oxidation rate at locations where biological iron oxidation was detected. Members of putative iron oxidizing genera, especially Gallionella, are abundant in systems where biological iron oxidation was measured. Geochemical sampling suites accompanying each experiment include field data (temperature, pH, conductivity, dissolved oxygen, and redox sensitive solutes), solute concentrations, and sediment composition. Dissolved inorganic carbon concentrations indicate that bicarbonate and carbonate are typically the most abundant anions in these systems. Speciation calculations reveal that ferrous iron typically exists as FeCO3(aq), FeHCO3+, FeSO4(aq), or Fe2+ in these systems. The abundance of ferrous carbonate and bicarbonate species appears to lead to a dramatic increase in the abiotic rate of reaction compared to the rate expected from chemical oxidation in dilute solution. This approach, integrating geochemistry, rates, and community composition, reveals locations and geochemical conditions that permit microbial iron oxidation and locations where the abiotic rate is too fast for the biotic process to compete.

Original languageEnglish (US)
Pages (from-to)905-921
Number of pages17
JournalACS Earth and Space Chemistry
Issue number6
StatePublished - Jun 20 2019


  • Gallionella
  • chemical speciation
  • iron oxidizing bacteria
  • iron redox cycling
  • metal bicarbonates
  • metal carbonates
  • rate experiments

ASJC Scopus subject areas

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


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