Water transports organic matter through soils, where mineral-organic associations form to\nretain dissolved organic matter (ââ?¬Å?DOMââ?¬Â), influencing terrestrial carbon cycling, nutrient availability\nfor plant growth, and other soil organic matter functions. We combined Fourier transform ion\ncyclotron resonance mass spectrometry with novel data analysis techniques to examine the role of\nsorptive fractionation in the associations between Fe(III)-montmorillonite and DOM from composted\nbiosolids (ââ?¬Å?anthropogenic DOMââ?¬Â). To examine the influence of DOM composition on sorption and\nsorptive fractionation, we used resin-based separation to produce DOM subsamples with different\nmolecular compositions and chemical properties. A large proportion (45 to 64%) of the initial carbon\nin every DOM solution sorbed to the Fe(III)-montmorillonite. However, when the compositions of the\ninitial solutions were compared to the sorbed organic matter, the computed changes in composition\nwere lower (10 to 32%). In fact, non-selective sorption was more important than selective sorption in\nevery sample, except for the hydrophilic neutral (HiN) fraction, where high nitrogen content and\nacidic conditions appeared to enhance sorptive fractionation. The results from this study demonstrate\nthat the importance of sorptive fractionation varies with DOM composition and other factors, and that\nnon-selective sorption can contribute substantially to the formation of mineral-organic associations.
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