Ionic liquid extraction unveils previously occluded humic-bound iron in peat soil pore water

Authors

Timothy J. Veverica, Michigan Technological University
Evan S. Kane, Michigan Technological UniversityFollow
Amy Marcarelli, Michigan Technological UniversityFollow
Sarah A. Green, Michigan Technological UniversityFollow

Document Type

Article

Publication Date

6-24-2016

Abstract

Globally, peatland ecosystems store tremendous amounts of C relative to their extent on the landscape, largely owing to saturated soils which limit decomposition. While there is still considerable uncertainty regarding CO₂ production potential below the water table in peatland ecosystems, extracellular Fe reduction has been suggested as a dominant pathway for anaerobic metabolism. However, colorimetric methods commonly used to quantitate Fe and partition between redox species are known to be unreliable in the presence of complex humic substances, which are common in peatland pore water. We evaluated both the standard o-phenanthroline (o-P) Method and an ionic liquid extraction (ILE) Method followed by quantitation with inductively coupled plasma optical emission spectrometry (ICP–OES) to compare total Fe recovery and Fe²⁺/Fe³⁺ ratios in four distinct peatland ecosystems, ranging from rich fen to bog. While total Fe concentrations measured with ILE and o-P were correlated, the ILE method proved to be superior in both total Fe quantitation and in separately quantifying ferric (Fe³⁺) and ferrous (Fe²⁺) iron. In peat pore water, the o-P Method underestimated Fe³⁺ by as much as 100%. A multivariate approach utilizing fluorescence- and ultraviolet (UV)–visable (Vis) spectroscopy identified indices of dissolved organic matter (DOM) humification and redox status that correlated with poor performance of the o-P Method in peat pore water. Where these interferences are present, we suggest that site-specific empirical correction factors for quantitation of total Fe by o-P can be created from ILE of Fe, but recommend ILE for accurate appraisals of iron speciation and redox processes.

Publisher's Statement

© 2016 Soil Science Society of America, Inc. Article deposited in compliance with publisher policies. Publisher's version of record: http://dx.doi.org/10.2136/sssaj2015.10.0377

Publication Title

Soil Science Society of America Journal

Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.

Recommended Citation

Veverica, T. J., Kane, E. S., Marcarelli, A., & Green, S. A. (2016). Ionic liquid extraction unveils previously occluded humic-bound iron in peat soil pore water. Soil Science Society of America Journal, 80(3), 771-782. http://doi.org/10.2136/sssaj2015.10.0377
Retrieved from: https://digitalcommons.mtu.edu/biological-fp/6

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