Nuclear Magnetic Resonance Analysis of Changes in Dissolved Organic Matter Composition with Successive Layering on Clay Mineral Surfaces

Perry Mitchell,Myrna Simpson,Ronald Soong,André Simpson

doi:10.3390/soils2010008

Perry Mitchell, Myrna Simpson + Show 2 more

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https://doi.org/10.3390/soils2010008

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Journal: Soil Systems	Publication Date: Feb 9, 2018
Citations: 27	License type: CC BY 4.0

Affiliation: University of Toronto, The Scarborough Hospital

Abstract

Dissolved organic matter (DOM) chemistry and the potential for organic matter (OM) to self-associate with other OM components are important aspects of understanding the mechanisms of DOM sorption to clay surfaces. To investigate this further, we sorbed DOM isolated from peat humic acid onto either kaolinite, montmorillonite and gibbsite via ten sequential batch equilibration sorption experiments. Dissolved organic carbon (DOC) sorption to all minerals increased consistently, suggesting that sorption occurred via mineral-OM interactions at the beginning of the experiment. After six successive DOM loadings, the concentration of DOC sorbed by kaolinite and gibbsite began to plateau, likely due to the saturation of mineral surface sorption sites. Solution-state nuclear magnetic resonance (NMR) analysis of unbound DOM showed that kaolinite and montmorillonite sorbed aliphatic, protein and lignin components initially and primarily aliphatic and aromatic constituents in later sorption experiments, whereas gibbsite sorbed mostly aliphatic compounds during all DOM loadings. Analysis of the organo-clay complexes using 1H high resolution–magic angle spinning (HR-MAS) NMR confirmed the preferential sorption of aromatic and aliphatic components to all three minerals. Overall, these results suggest that OM-OM interactions may be important mechanisms of DOM sorption to clay mineral surfaces.

Highlights

Soil organic matter (OM) is a critical component of the global carbon cycle [1], but the environmental factors contributing to soil OM stabilization and persistence are difficult to characterize because of its molecular complexity, variation with environmental controls such as climate and vegetation, and interactions with other soil components such as minerals and biota [2]
This is consistent with the higher specific surface area (SSA) of montmorillonite compared to the other two minerals (Table 1), and with previous studies which suggested that Dissolved organic carbon (DOC) sorption to minerals increases with increasing mineral SSA [18,21,22,48]
Kaolinite and gibbsite initially sorbed a similar concentration of DOC, but from loading five onward gibbsite sorbed a higher concentration of DOC than kaolinite

Summary

Introduction

Soil organic matter (OM) is a critical component of the global carbon cycle [1], but the environmental factors contributing to soil OM stabilization and persistence are difficult to characterize because of its molecular complexity, variation with environmental controls such as climate and vegetation, and interactions with other soil components such as minerals and biota [2] Among these interactions, organo-mineral associations, which occur via hydrophobic, van der Waals and electrostatic interactions, cation bridging and ligand exchange are believed to protect OM from degradation and contribute to the accumulation and preservation of soil OM [3,4,5,6]. It is unclear whether mineral properties such as SSA and CEC continue to control DOM sorption with increasing OM layering [19,20,21,22], which may limit the amount of OM that can be sequestered by organo-mineral associations [23]

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