This study aims to determine the in-situ coordination environment and oxidation state of Fe present in redox stratified peat cores using Fe L-edge XANES studies together with EXAFS to develop a molecular level understanding of the redox transformations between Fe and natural organic matter. Chemical extractions reveal that residual Fe dominates in the deepest suboxic regions whereas the amorphous fraction dominates in the intermediate anoxic regions. XANES spectra of anoxic soils resembled those of Fe(III)-organic complexes with O donor atoms (citrate, acetate) indicating that Fe-OM complexation can stabilize Fe(III) under anoxic conditions where Fe(II) would typically exist. Fe(II) was found to be stable on the surface soils and had spectral features similar to that of Fe(II)-organic complexes with N donor atoms (amino acids) indicating Fe(II) stabilization under oxic conditions where Fe(III) would typically exist. Spectral features of siderite in oxic soils and ferrihydrite in the anoxic soils are also observed.

Iron speciation in redox stratified peat soils

243rd National Meeting (2012)

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