Probing the oxidation–reduction properties of terrestrially and microbially derived dissolved organic matter

• Published in: Geochimica et cosmochimica acta Vol. 71; no. 12; pp. 3003 - 3015
• Main Authors: Fimmen, Ryan L., Cory, Rose M., Chin, Yu-Ping, Trouts, Tamara D., McKnight, Diane M.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.06.2007
• Subjects: Freshwater; USA, Alaska, North Slope, Toolik L; USA, Great Dismal Swamp
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/j.gca.2007.04.009

Dissolved organic matter (DOM) has been shown to be an integral component in biogeochemical electron transfer reactions due to its demonstrated ability to facilitate redox reactions. While the role of DOM as a facilitator of electron transfer processes has been demonstrated, greater knowledge would lead to better understanding of the structural components responsible for redox behavior, such as quinones and nitrogen and sulfur (N/S) functional groups. This investigation uses direct scan voltammetry (DSV) coupled with fluorescence and NMR spectroscopy as well as thermochemolysis gas chromatography mass spectrometry (GC–MS) and X-ray photoelectron spectroscopy (XPS) to elucidate the organic moieties responsible for facilitating electron transfer reactions. We contrast electrochemical properties and structural details of three organic matter isolates from diverse sources; Great Dismal Swamp DOM (terrestrially derived, highly aromatic), Pony Lake DOM (microbially derived, highly aliphatic) and Toolik Lake (terrestrially derived, photochemically and microbially altered) with juglone (a redox-active model quinone). Aromatic and phenolic constituents were detected (by 13C NMR) and recovered (by thermochemolysis GC–MS) from all three fulvic acid samples, highlighting the ubiquity of these compounds and suggesting that the quinone–phenol redox couple is not limited to DOM derived from lignin precursors. The range of hydroxy-benzene and benzoic acid derivatives may explain the lack of a single pair of well-defined oxidation and reduction peaks in the DSV scans. The presence of a wide-range of hydroxylated benzoic acid isomers and other redox-active aromatic residues implies that native DOM possesses overlapping redox potentials analogous to their characteristic range of p K a values.