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Ionic Liquid Extraction Unveils Previously Occluded Humic‐Bound Iron in Peat Soil Pore Water
Author(s) -
Veverica Timothy J.,
Kane Evan S.,
Marcarelli Amy M.,
Green Sarah A.
Publication year - 2016
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2015.10.0377
Subject(s) - peat , chemistry , environmental chemistry , dissolved organic carbon , soil water , ferrous , humus , extraction (chemistry) , organic matter , bog , chromatography , soil science , environmental science , ecology , organic chemistry , biology
Core Ideas Dissolved organic matter character should be evaluated when selecting Fe quantitation methods. The o ‐phenanthroline Method cannot consistently speciate Fe in bogs and fens. Ionic liquid extraction yields superior Fe quantitation over o ‐phenanthroline. 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 CO 2 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 Fe 2+ /Fe 3+ 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 (Fe 3+ ) and ferrous (Fe 2+ ) iron. In peat pore water, the o ‐P Method underestimated Fe 3+ 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.