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Evidence linking calcium to increased organo-mineral association in soils


Rowley, Mike C; Grand, Stephanie; Spangenberg, Jorge E; Verrecchia, Eric P (2021). Evidence linking calcium to increased organo-mineral association in soils. Biogeochemistry, 153:223-241.

Abstract

Geochemical indicators are emerging as important predictors of soil organic carbon (SOC) dynamics, but evidence concerning the role of calcium (Ca) is scarce. This study investigates the role of Ca prevalence in SOC accumulation by comparing otherwise similar sites with (CaCO$_{3}$-bearing) or without carbonates (CaCO$_{3}$-free). We measured the SOC content and indicators of organic matter quality (C stable isotope composition, expressed as δ$^{13}$C values, and thermal stability) in bulk soil samples. We then used sequential sonication and density fractionation (DF) to separate two occluded pools from free and mineral-associated SOC. The SOC content, mass, and δ$^{13}$C values were determined in all the fractions. X-ray photoelectron spectroscopy was used to investigate the surface chemistry of selected fractions. Our hypothesis was that occlusion would be more prevalent at the CaCO$_{3}$-bearing site due to the influence of Ca on aggregation, inhibiting oxidative transformation, and preserving lower δ$^{13}$C values. Bulk SOC content was twice as high in the CaCO$_{3}$-bearing profiles, which also had lower bulk δ$^{13}$C values, and more occluded SOC. Yet, contrary to our hypothesis, occlusion only accounted for a small proportion of total SOC (< 10%). Instead, it was the heavy fraction (HF), containing mineral-associated organic C, which accounted for the majority of total SOC and for the lower bulk δ$^{13}$C values. Overall, an increased Ca prevalence was associated with a near-doubling of mineral-associated SOC content. Future investigations should now aim to isolate Ca-mediated complexation processes that increase organo-mineral association and preserve organic matter with lower δ$^{13}$C values.

Abstract

Geochemical indicators are emerging as important predictors of soil organic carbon (SOC) dynamics, but evidence concerning the role of calcium (Ca) is scarce. This study investigates the role of Ca prevalence in SOC accumulation by comparing otherwise similar sites with (CaCO$_{3}$-bearing) or without carbonates (CaCO$_{3}$-free). We measured the SOC content and indicators of organic matter quality (C stable isotope composition, expressed as δ$^{13}$C values, and thermal stability) in bulk soil samples. We then used sequential sonication and density fractionation (DF) to separate two occluded pools from free and mineral-associated SOC. The SOC content, mass, and δ$^{13}$C values were determined in all the fractions. X-ray photoelectron spectroscopy was used to investigate the surface chemistry of selected fractions. Our hypothesis was that occlusion would be more prevalent at the CaCO$_{3}$-bearing site due to the influence of Ca on aggregation, inhibiting oxidative transformation, and preserving lower δ$^{13}$C values. Bulk SOC content was twice as high in the CaCO$_{3}$-bearing profiles, which also had lower bulk δ$^{13}$C values, and more occluded SOC. Yet, contrary to our hypothesis, occlusion only accounted for a small proportion of total SOC (< 10%). Instead, it was the heavy fraction (HF), containing mineral-associated organic C, which accounted for the majority of total SOC and for the lower bulk δ$^{13}$C values. Overall, an increased Ca prevalence was associated with a near-doubling of mineral-associated SOC content. Future investigations should now aim to isolate Ca-mediated complexation processes that increase organo-mineral association and preserve organic matter with lower δ$^{13}$C values.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Geography
Dewey Decimal Classification:910 Geography & travel
Scopus Subject Areas:Physical Sciences > Environmental Chemistry
Physical Sciences > Water Science and Technology
Physical Sciences > Earth-Surface Processes
Uncontrolled Keywords:Earth-Surface Processes, Water Science and Technology, Environmental Chemistry
Language:English
Date:4 April 2021
Deposited On:20 Sep 2023 11:58
Last Modified:29 Jun 2024 01:38
Publisher:Springer
ISSN:0168-2563
OA Status:Hybrid
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1007/s10533-021-00779-7
Project Information:
  • : FunderCanton de Vaud
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  • : FunderUniversite de lausanne
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  • : FunderSwiss National Science Foundation
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  • : FunderUniversité de Lausanne
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  • Content: Published Version
  • Language: English
  • Licence: Creative Commons: Attribution 4.0 International (CC BY 4.0)