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Title: Solid-Phase Fe Speciation along the Vertical Redox Gradients in Floodplains using XAS and Mössbauer Spectroscopies

Abstract

Properties of Fe minerals are poorly understood in natural soils and sediments with variable redox conditions. In this study, we combined 57Fe Mössbauer and Fe K-edge X-ray absorption spectroscopic techniques to assess solid-phase Fe speciation along the vertical redox gradients of floodplain profiles, which exhibited a succession of oxic, anoxic and suboxic-oxic zones with increasing depth along the vertical profiles. The anoxic conditions at the intermediate horizon (55-80 cm) of the eastern floodplain resulted in extensive depletion of Fe(III)-oxides including both ferrihydrite and goethite, concurrent with a corresponding reduction of phyllosilicates(PS)-Fe(III) to PS-Fe(II). In addition, the anoxic conditions increased the crystallinity of Fe(III)-oxides in this reduced zone, relative to the oxic zones. In the most reduced intermediate sediments at 80-120cm of the western floodplain, the anoxic conditions drove the complete reductive dissolution of Fe(III) oxides, as well as the greatest reduction (48-55%) in PS-Fe(III). In both oxic near-surface horizon and oxic-suboxic gravel aquifers beneath the soil horizons, Fe(III)-oxides were mainly present as ferrihydrite with a less amount of goethite, which preferentially occurred as nanogoethite or Al/Si-substituted goethite. Ferrihydrite with varying crystallinity or impurities such as organic matter, Al or Si, persisted under suboxic-oxic conditions in the floodplain. This study indicatesmore » that vertical redox gradients exert a major control on the quantity and speciation of Fe(III) oxides as well as the oxidation state of structural Fe in PS, which could significantly affect nutrient cycling and carbon (de)stabilization.« less

Authors:
ORCiD logo [1];  [2];  [1];  [1]
  1. Department of Plant and Soil Sciences, Delaware Environmental Institute University of Delaware, Newark, Delaware 19711, United States
  2. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1373835
Report Number(s):
PNNL-SA-123910
Journal ID: ISSN 0013-936X; 44685; KP1704020
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Environmental Science and Technology
Additional Journal Information:
Journal Volume: 51; Journal Issue: 14; Journal ID: ISSN 0013-936X
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Environmental Molecular Sciences Laboratory

Citation Formats

Chen, Chunmei, Kukkadapu, Ravi K., Lazareva, Olesya, and Sparks, Donald L. Solid-Phase Fe Speciation along the Vertical Redox Gradients in Floodplains using XAS and Mössbauer Spectroscopies. United States: N. p., 2017. Web. doi:10.1021/acs.est.7b00700.
Chen, Chunmei, Kukkadapu, Ravi K., Lazareva, Olesya, & Sparks, Donald L. Solid-Phase Fe Speciation along the Vertical Redox Gradients in Floodplains using XAS and Mössbauer Spectroscopies. United States. doi:10.1021/acs.est.7b00700.
Chen, Chunmei, Kukkadapu, Ravi K., Lazareva, Olesya, and Sparks, Donald L. Fri . "Solid-Phase Fe Speciation along the Vertical Redox Gradients in Floodplains using XAS and Mössbauer Spectroscopies". United States. doi:10.1021/acs.est.7b00700.
@article{osti_1373835,
title = {Solid-Phase Fe Speciation along the Vertical Redox Gradients in Floodplains using XAS and Mössbauer Spectroscopies},
author = {Chen, Chunmei and Kukkadapu, Ravi K. and Lazareva, Olesya and Sparks, Donald L.},
abstractNote = {Properties of Fe minerals are poorly understood in natural soils and sediments with variable redox conditions. In this study, we combined 57Fe Mössbauer and Fe K-edge X-ray absorption spectroscopic techniques to assess solid-phase Fe speciation along the vertical redox gradients of floodplain profiles, which exhibited a succession of oxic, anoxic and suboxic-oxic zones with increasing depth along the vertical profiles. The anoxic conditions at the intermediate horizon (55-80 cm) of the eastern floodplain resulted in extensive depletion of Fe(III)-oxides including both ferrihydrite and goethite, concurrent with a corresponding reduction of phyllosilicates(PS)-Fe(III) to PS-Fe(II). In addition, the anoxic conditions increased the crystallinity of Fe(III)-oxides in this reduced zone, relative to the oxic zones. In the most reduced intermediate sediments at 80-120cm of the western floodplain, the anoxic conditions drove the complete reductive dissolution of Fe(III) oxides, as well as the greatest reduction (48-55%) in PS-Fe(III). In both oxic near-surface horizon and oxic-suboxic gravel aquifers beneath the soil horizons, Fe(III)-oxides were mainly present as ferrihydrite with a less amount of goethite, which preferentially occurred as nanogoethite or Al/Si-substituted goethite. Ferrihydrite with varying crystallinity or impurities such as organic matter, Al or Si, persisted under suboxic-oxic conditions in the floodplain. This study indicates that vertical redox gradients exert a major control on the quantity and speciation of Fe(III) oxides as well as the oxidation state of structural Fe in PS, which could significantly affect nutrient cycling and carbon (de)stabilization.},
doi = {10.1021/acs.est.7b00700},
journal = {Environmental Science and Technology},
issn = {0013-936X},
number = 14,
volume = 51,
place = {United States},
year = {2017},
month = {6}
}