Adsorption and Molecular Fractionation of Dissolved Organic Matter on Iron-Bearing Mineral Matrices of Varying Crystallinity

Abstract

Iron (Fe)-bearing mineral phases contribute disproportionately to adsorption of soil organic matter (SOM) due to their elevated chemical reactivity and specific surface area (SSA). However, the spectrum of Fe solid-phase speciation present in oxidation-reduction-active soils challenges analysis of SOM-mineral interactions and may induce differential molecular fractionation of dissolved organic matter (DOM). This work used paired selective dissolution experiments and batch sorption of postextraction residues to (1) quantify the contributions of Fe-bearing minerals of varying crystallinity to DOM sorption, and (2) characterize molecular fractionation using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). A substantial proportion of soil SSA was derived from extracted Fe-bearing phases, and FT-ICR-MS analysis of extracted DOM revealed distinct chemical signatures across Fe-OM associations. Sorbed carbon (C) was highly correlated with Fe concentrations, suggesting that Fe-bearing phases are strong drivers of sorption in these soils. Molecular fractionation was observed across treatments, particularly those dominated by short-range-order (SRO) mineral phases, which preferentially adsorbed aromatic and lignin-like formulas, and higher-crystallinity phases, associated with aliphatic DOM. These findings suggest Fe speciation-mediated complexation acts as a physicochemical filter of DOM moving through the critical zone, an important observation as predicted changes in precipitation may dynamically alter Fe crystallinity and C stability.

Selective Adsorption of Terrestrial Dissolved Organic Matter to Inorganic Surfaces Along a Boreal Inland Water Continuum

“…This is also where WRT and the adsorption treatment diverge in their effect on DOM composition: Whereas unsaturated compounds are generally lost from solution in both processes, even fairly saturated compounds can be adsorbed as long as they have a high O/C (Figures 3c and S3). The observed adsorption of oxygen-rich compounds is in agreement with various other studies, where both highly oxidized aromatics (Coward et al, 2018;Fleury et al, 2017;Galindo & Del Nero, 2014;Lv et al, 2016), and in some cases also oxidized saturated, aliphatic compounds (Galindo & Del Nero, 2014;Avneri-Katz et al, 2017) were preferentially adsorbed. The preferential adsorption of oxygen-rich compounds indicates that the presence of carboxyl and hydroxyl functional groups may be important for adsorptive processes, as these groups allow for ligand exchange with oxide and hydroxide groups at the sorbent's surface (Chassé et al, 2015;Gu et al, 1995;Kaiser, 2003;Kaiser et al, 1997;Kothawala et al, 2012;Lv et al, 2016;Meier et al, 1999;Tipping, 1981b).…”

Molecular Signatures of Three Fulvic Acid Standard Samples as Revealed by Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…In addition, compared with river‐derived FA, the content of protein/peptide‐like and carbohydrate‐like compounds in soil‐derived FA is higher, which may indicate that both labile and refractory constituents are present at soil‐derived FA. The most labile constituents are proteinaceous compounds with varying heteroatom contributions derived from microbial metabolism intermediates or as end products . The higher protein/peptide‐like compounds ratios of ESFA soil result from soil microbial uptake of N‐containing compounds .…”

“…The proportion of lignin‐like compounds in river‐derived FA was nearly 2 times greater than that in soil‐derived FA and the condensed aromatic structure ratios of river‐derived FA was approximately 1/3 of the ratios in soil‐derived FA. Meanwhile, nitrogen and sulfur elements mainly exist in aromatic molecules, which are more easily absorbed by clay minerals and preserved . Hence, soil‐derived FA contains more heteroatoms (especially nitrogen and sulfur atoms).…”

“…The most labile constituents are proteinaceous compounds with varying heteroatom contributions derived from microbial metabolism intermediates or as end products. [24] The higher protein/ peptide-like compounds ratios of ESFA soil result from soil microbial uptake of N-containing compounds. [20a] The ratio of the protein/peptide-like compounds of JFFA soil is smaller than that of ESFA soil although there are many plots in this region of the v-K diagrams, possibly due to the low content and abundant molecular species of this component in JFFA soil.…”

Reactive Iron and Iron‐Bound Organic Carbon in Surface Sediments of the River‐Dominated Bohai Sea (China) Versus the Southern Yellow Sea

“…Enhanced redox cycling of Fe driven by high input of labile marine OC may be the true mechanism given that enhanced redox cycling of Fe oxides tends to selectively stabilize labile and less 13 C‐depleted aliphatic compounds (Adhikari et al, ; Adhikari & Yang, ; Coward et al, ). In the SYS, a unique hydrogeochemical regime of the YSCWM (Figure ) could promote redox cycling of Fe at the oxic‐anoxic interface of the sediments.…”