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Transport of chloride and deuterated water in peat: The role of anion exclusion, diffusion, and anion adsorption in a dual porosity organic media.

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Title: Transport of chloride and deuterated water in peat: The role of anion exclusion, diffusion, and anion adsorption in a dual porosity organic media.
Authors: McCarter, C.P.R.1 (AUTHOR) colin.mccarter@utoronto.ca, Rezanezhad, F.1 (AUTHOR), Gharedaghloo, B.1 (AUTHOR), Price, J.S.1 (AUTHOR), Van Cappellen, P.1 (AUTHOR)
Source: Journal of Contaminant Hydrology. Aug2019, Vol. 225, p103497-103497. 1p.
Subjects: Peat, Porosity, Adsorption (Chemistry), Diffusion, Peat soils
Abstract: The dual-porosity structure of peat and the extremely high organic matter content give rise to a complex medium that typically generates prolonged tailing and early 50% concentration breakthrough in the breakthrough curves (BTCs) of chloride (Cl−) and other anions. Untangling whether these observations are due to rate-limited (physical) diffusion into inactive pores, (chemical) adsorption or anion exclusion remains a critical question in peat hydrogeochemistry. This study aimed to elucidate whether Cl− is truly conservative in peat, as usually assumed, and whether the prolonged tailing and early 50% concentration breakthrough of Cl− observed is due to diffusion, adsorption, anion exclusion or a combination of all three. The mobile-immobile (MiM) dual-porosity model was fit to BTCs of Cl− and deuterated water measured on undisturbed cores of the same peat soils, and equilibrium Cl− adsorption batch experiments were conducted. Adsorption of Cl− to undecomposed and decomposed peat samples in batch experiments followed Freundlich isotherms but did not exhibit any trends with the degree of peat decomposition and sorption became negligible below aqueous Cl− concentrations of ~310 mg L−1. The dispersivity determined by fitting the Cl− BTCs whether assuming adsorption or no adsorption were significantly different than determined by the deuterated water (p <.0001). However, no statistical differences in dispersivity (p =.27) or immobile water content (p =.97) was observed between deuterated water and Cl− when accounting for anion exclusion. A higher degree of decomposition significantly increased anion exclusion (p <.0001) but did not influence the diffusion of either tracer into the immobile porosity. Contrary to previous assumptions, Cl− is not truly conservative in peat due to anion exclusion, and adsorption at higher aqueous concentrations, but the overall effect of anion exclusion on transport is likely minimal. • Chloride is not, strictly speaking, a conservative tracer. • Chloride sorbs to peat, but the extent of binding is low and highly variable. • Anion exclusion was observed but it did not appreciably affect chloride breakthrough. • Chloride diffusion into immobile porosity is not governed by degree of decomposition. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Contaminant Hydrology is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Transport of chloride and deuterated water in peat: The role of anion exclusion, diffusion, and anion adsorption in a dual porosity organic media.
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  Data: &lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22McCarter%2C+C%2EP%2ER%2E%22&quot;&gt;McCarter, C.P.R.&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;i&gt; colin.mccarter@utoronto.ca&lt;/i&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Rezanezhad%2C+F%2E%22&quot;&gt;Rezanezhad, F.&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Gharedaghloo%2C+B%2E%22&quot;&gt;Gharedaghloo, B.&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Price%2C+J%2ES%2E%22&quot;&gt;Price, J.S.&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Van+Cappellen%2C+P%2E%22&quot;&gt;Van Cappellen, P.&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)
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  Data: &lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Peat%22&quot;&gt;Peat&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Porosity%22&quot;&gt;Porosity&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Adsorption+%28Chemistry%29%22&quot;&gt;Adsorption (Chemistry)&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Diffusion%22&quot;&gt;Diffusion&lt;/searchLink&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Peat+soils%22&quot;&gt;Peat soils&lt;/searchLink&gt;
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  Label: Abstract
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  Data: The dual-porosity structure of peat and the extremely high organic matter content give rise to a complex medium that typically generates prolonged tailing and early 50% concentration breakthrough in the breakthrough curves (BTCs) of chloride (Cl−) and other anions. Untangling whether these observations are due to rate-limited (physical) diffusion into inactive pores, (chemical) adsorption or anion exclusion remains a critical question in peat hydrogeochemistry. This study aimed to elucidate whether Cl− is truly conservative in peat, as usually assumed, and whether the prolonged tailing and early 50% concentration breakthrough of Cl− observed is due to diffusion, adsorption, anion exclusion or a combination of all three. The mobile-immobile (MiM) dual-porosity model was fit to BTCs of Cl− and deuterated water measured on undisturbed cores of the same peat soils, and equilibrium Cl− adsorption batch experiments were conducted. Adsorption of Cl− to undecomposed and decomposed peat samples in batch experiments followed Freundlich isotherms but did not exhibit any trends with the degree of peat decomposition and sorption became negligible below aqueous Cl− concentrations of ~310 mg L−1. The dispersivity determined by fitting the Cl− BTCs whether assuming adsorption or no adsorption were significantly different than determined by the deuterated water (p &lt;.0001). However, no statistical differences in dispersivity (p =.27) or immobile water content (p =.97) was observed between deuterated water and Cl− when accounting for anion exclusion. A higher degree of decomposition significantly increased anion exclusion (p &lt;.0001) but did not influence the diffusion of either tracer into the immobile porosity. Contrary to previous assumptions, Cl− is not truly conservative in peat due to anion exclusion, and adsorption at higher aqueous concentrations, but the overall effect of anion exclusion on transport is likely minimal. • Chloride is not, strictly speaking, a conservative tracer. • Chloride sorbs to peat, but the extent of binding is low and highly variable. • Anion exclusion was observed but it did not appreciably affect chloride breakthrough. • Chloride diffusion into immobile porosity is not governed by degree of decomposition. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  Data: &lt;i&gt;Copyright of Journal of Contaminant Hydrology is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder&#39;s express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.&lt;/i&gt; (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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      – Type: doi
        Value: 10.1016/j.jconhyd.2019.103497
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      – Code: eng
        Text: English
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      Pagination:
        PageCount: 1
        StartPage: 103497
    Subjects:
      – SubjectFull: Peat
        Type: general
      – SubjectFull: Porosity
        Type: general
      – SubjectFull: Adsorption (Chemistry)
        Type: general
      – SubjectFull: Diffusion
        Type: general
      – SubjectFull: Peat soils
        Type: general
    Titles:
      – TitleFull: Transport of chloride and deuterated water in peat: The role of anion exclusion, diffusion, and anion adsorption in a dual porosity organic media.
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            NameFull: McCarter, C.P.R.
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            NameFull: Rezanezhad, F.
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            NameFull: Price, J.S.
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            NameFull: Van Cappellen, P.
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              M: 08
              Text: Aug2019
              Type: published
              Y: 2019
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