Theoretical Constraints on Fe Reduction Rates in Upland Soils as a Function of Hydroclimatic Conditions

Salvatore Calabrese, Diego Barcellos, Aaron Thompson, Amilcare Porporato

Research output: Contribution to journalArticlepeer-review

Abstract

Periods of high soil wetness promote anaerobic processes such as iron (Fe) reduction within soil microsites, with implications for organic matter decomposition, the fate of pollutants, and nutrient cycling. Here we discuss potential Fe reduction rates emerging from an interplay between the timescales of the internal reactions (Fe oxidation and reduction) and external forcings (length of oxic vs. anoxic conditions), and under no organic substrate and microbial population limitations. We compute the upper bound on Fe reduction and the theoretical maximum reduction rate, which would be reached under “resonant conditions,” whereby the timescales of external forcings match the internal timescales of the redox reactions. The variability of soil oxygen is then linked to rainfall frequency and intensity through soil moisture dynamics, allowing us to determine the hydroclimatic conditions that generate oxic/anoxic cycles that most favor Fe reduction. These predictions are applied to an aseasonal tropical (Luquillo, Puerto Rico, USA) and a seasonal subtropical (Calhoun, SC, USA) humid forests. We show that the tropical site maintains a high potential for Fe reduction throughout the year, due to rapid and frequent transitions between predicted oxic and anoxic microsite conditions, with a potential to reduce up to 1,800 mmol kg1 soil of Fe per year, while a less humid and seasonal climate in the subtropical site limits maximum reduction rates to 60 mmol kg−1 year−1. This analysis paves the way for a global identification of hot spots of potential Fe reduction using readily available hydroclimatic observations.

Original languageEnglish (US)
Article numbere2020JG005894
JournalJournal of Geophysical Research: Biogeosciences
Volume125
Issue number12
DOIs
StatePublished - Dec 2020

All Science Journal Classification (ASJC) codes

  • Soil Science
  • Forestry
  • Water Science and Technology
  • Palaeontology
  • Atmospheric Science
  • Aquatic Science
  • Ecology

Keywords

  • carbon cycle
  • iron redox model
  • iron reduction
  • soil iron redox
  • soil moisture control

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