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Quantitative imaging of the 3-D distribution of cation adsorption sites in undisturbed soil

Keck, Hannes and Strobel, Bjarne and Gustafsson, Jon Petter and Koestel, John (2017). Quantitative imaging of the 3-D distribution of cation adsorption sites in undisturbed soil. Soil. 3, 177-189
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Abstract

Several studies have shown that the distribution of cation adsorption sites (CASs) is patchy at a millimetre to centimetre scale. Often, larger concentrations of CASs in biopores or aggregate coatings have been reported in the literature. This heterogeneity has implications on the accessibility of CASs and may influence the performance of soil system models that assume a spatially homogeneous distribution of CASs. In this study, we present a new method to quantify the abundance and 3-D distribution of CASs in undisturbed soil that allows for investigating CAS densities with distance to the soil macropores. We used X-ray imaging with Ba2+ as a contrast agent. Ba2+ has a high adsorption affinity to CASs and is widely used as an index cation to measure the cation exchange capacity (CEC). Eight soil cores (approx. 10 cm3 ) were sampled from three locations with contrasting texture and organic matter contents. The CASs of our samples were saturated with Ba2+ in the laboratory using BaCl2 (0.3 mol L−1). Afterwards, KCl (0.1 mol L−1) was used to rinse out Ba2+ ions that were not bound to CASs. Before and after this process the samples were scanned using an industrial X-ray scanner. Ba2+ bound to CASs was then visualized in 3-D by the difference image technique. The resulting difference images were interpreted as depicting the Ba2+ bound to CASs only. The X-ray image-derived CEC correlated significantly with results of the commonly used ammonium acetate method to determine CEC in well-mixed samples. The CEC of organic-matter-rich samples seemed to be systematically overestimated and in the case of the clay-rich samples with less organic matter the CEC seemed to be systematically underestimated. The results showed that the distribution of the CASs varied spatially within most of our samples down to a millimetre scale. There was no systematic relation between the location of CASs and the soil macropore structure. We are convinced that the approach proposed here will strongly aid the development of more realistic soil system models.

Authors/Creators:Keck, Hannes and Strobel, Bjarne and Gustafsson, Jon Petter and Koestel, John
Title:Quantitative imaging of the 3-D distribution of cation adsorption sites in undisturbed soil
Series/Journal:Soil (BIB20118321)
Year of publishing :2017
Volume:3
Page range:177-189
Number of Pages:12
Publisher:Copernicus Publications, European Geosciences Union
ISSN:2199-3971
Language:English
Additional Information:Data are now available using https://doi.org/10.5281/zenodo.1020068.
Publication Type:Journal article
Refereed:Yes
Article category:Scientific peer reviewed
Version:Published version
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Soil Science
(A) Swedish standard research categories 2011 > 1 Natural sciences > 105 Earth and Related Environmental Sciences > Environmental Sciences (social aspects to be 507)
(A) Swedish standard research categories 2011 > 1 Natural sciences > 105 Earth and Related Environmental Sciences > Geosciences, Multidisciplinary
Agrovoc terms:soil chemistry, adsorption, image analysis
Keywords:cation adsorption sites (CASs), adsorption, soil systems
URN:NBN:urn:nbn:se:slu:epsilon-e-4483
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-4483
Additional ID:
Type of IDID
DOI10.5194/soil-3-177-2017
ID Code:14679
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
Department:(NL, NJ) > Dept. of Soil and Environment
(S) > Dept. of Soil and Environment
Deposited By: SLUpub Connector
Deposited On:14 Nov 2017 09:32
Metadata Last Modified:14 Nov 2017 09:32

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