Water transports organic matter through soils, where mineral-organic associations form to retain dissolved organic matter (“DOM”), influencing terrestrial carbon cycling, nutrient availability for plant growth, and other soil organic matter functions. We combined Fourier transform ion cyclotron resonance mass spectrometry with novel data analysis techniques to examine the role of sorptive fractionation in the associations between Fe(III)-montmorillonite and DOM from composted biosolids (“anthropogenic DOM”). To examine the influence of DOM composition on sorption and sorptive fractionation, we used resin-based separation to produce DOM subsamples with different molecular compositions and chemical properties. A large proportion (45 to 64%) of the initial carbon in every DOM solution sorbed to the Fe(III)-montmorillonite. However, when the compositions of the initial solutions were compared to the sorbed organic matter, the computed changes in composition were lower (10 to 32%). In fact, non-selective sorption was more important than selective sorption in every sample, except for the hydrophilic neutral (HiN) fraction, where high nitrogen content and acidic conditions appeared to enhance sorptive fractionation. The results from this study demonstrate that the importance of sorptive fractionation varies with DOM composition and other factors, and that non-selective sorption can contribute substantially to the formation of mineral-organic associations.
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Acknowledgments: This research was supported by research grants from the U.S. National Science Foundation (grant nos. 1451508 and 1512670), the Israel Science Foundation (grant no. 102/14) and the United States—Israel Binational Agricultural Research and Development Fund (grant nos. US-4551-12 and US-4656-13). The National High Magnetic Field Laboratory is supported by the National Science Foundation Division of Materials Research through DMR-1157490, Florida State University, and the State of Florida.
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- Dissolved organic carbon
- Dissolved organic nitrogen
- FT-ICR MS
- Sewage sludge
- Soil organic matter