Effect of multivalent cations, temperature, and aging on SOM thermal properties

Diehl, Dörte; Schwarz, Jette; Goebel, Marc‐Oliver; Woche, Susanne K.; Schneckenburger, Tatjana; Krüger, Jaane; Shchegolikhina, Anastasia; Marschner, Bernd; Lang, Friederike; Thiele‐Bruhn, Sören; Bachmann, Jörg; Schaumann, Gabriele E.

doi:10.1007/s10973-014-3989-7

Cited by 10 publications

(9 citation statements)

References 42 publications

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“…By this procedure, we aimed to remove as many as possible cations from the sample. The resin was used in a number of studies before (Kunhi Mouvenchery et al, 2013;Schaumann et al, 2013b;Diehl et al, 2014a;2014b). In preliminary experiments on a peat (Kunhi Mouvenchery et al, 2013), no relevant release of organic carbon from the resin was observed.…”

Section: Removal Of Cations Originally Present In the Soil Sample Andmentioning

confidence: 99%

“…These models address monodentate and bidentate sites (e.g., Kinniburgh et al, 1996) and ligand exchange-surface complexation of DOM with iron and aluminium oxides (McKnight et al, 1992). The ability of SOM to form cross-linked structures, will strongly determine its ability to store nutrients and its flexibility to react on environmental conditions (Diehl et al, 2014b).…”

Section: Introductionmentioning

confidence: 99%

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Considerations on cross‐linking by bivalent cations in soil organic matter with low exchange capacity

Schaumann

Mouvenchery

2018

J. Plant Nutr. Soil Sci.

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A soil's cation exchange capacity (CEC) is expected to be relatively inert against changes in cation loading. In this study, we treated a soil sample originating from the organic layer of a forest soil with various bivalent cations after removing the native cations. Sorption isotherms and cation exchange capacity were determined, the latter using the BaCl2 method. Sorption showed Langmuir characteristics, with the maximum coverage (Qmax) increasing in the order Ba2+ < Ca2+ < Mg2+, but being clearly smaller than the initial load of native exchangeable cations. The Langmuir coefficient, kMe, depended oppositely to the order obtained for Qmax. CEC increased upon cation treatment and it varied by a factor of almost two. The unexpected variation of CEC was explained by the low cation exchange capacity of the organic matter such that not all functional groups are close enough to be bridged and the second charge of a bivalent cation is not neutralized by the organic functional group. The Langmuir sorption type, and Qmax being smaller than the content of sorption sites and being largest for Mg, suggested that only a part of the sites can be cross‐linked and at least part of the cross‐links are formed by hydrated cations. Thermodynamic considerations allowed reconstruction of two contrasting processes during CEC determination by Ba2+: Case A: the disruption of cross‐links, which increases with the cationic strength and the cation load before CEC determination, but does not require structural re‐orientation in the SOM matrix, and Case B: the formation of new cross‐links during CEC determination, depending only on the content of unoccupied sites before CEC determination and requiring structural re‐organization of the matrix and thus a minimum matrix flexibility. The use of bivalent cations for CEC determination may thus result in an overestimation of CEC for organic matter with low CEC. This has, however, promising potential when comparing CEC determined with monovalent cations and bivalent cations. Using a set of bivalent cations, may allow probing distribution of distances between functional groups in the organic matter and even characterize the matrix rigidity of the cation‐cross‐linked network.

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Section: Removal Of Cations Originally Present In the Soil Sample Andmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Considerations on cross‐linking by bivalent cations in soil organic matter with low exchange capacity

Schaumann

Mouvenchery

2018

J. Plant Nutr. Soil Sci.

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“…Sapric histosol, an organic soil with a high organic matter content and negligible mineral content, was collected from Totes Moor, which is located ∼30 km northwest of Hannover, Germany, consisting of peat bog and fen areas. As this soil has already been subjected to a large number of studies, ,,,,− it appeared as a good model for understanding the relationship between WaMB and SOM. The soil was collected from a profile above a drainage channel from a stronger decomposed layer (>30 cm), underlying an upper fibric histosol (peat) layer (0–30 cm) with a lower degree of humification .…”

Section: Experimental Sectionmentioning

confidence: 99%

“…To follow the kinetics of water uptake and change in WaMBrelated DSC parameters, the soils exposed to p/p 0 = 0.32 and 0.76 were sampled several times during their equilibration. Previous results, for example, 10,24,30,34,36,37,40 showed that under constant relative vapor pressure and temperature, some parameters, such as the WaMB transition temperature (T*), change after 4 weeks, but to a much lower extent in comparison to first few days during which the water content changes rapidly. Therefore, it is assumed that the system was in a quasi-stationary state when the data were acquired.…”

Section: ■ Introductionmentioning

confidence: 99%

Formation of Water Molecule Bridges Governs Water Sorption Mechanisms in Soil Organic Matter

Kučerík

Ondruch

Mouvenchery³

et al. 2018

Langmuir

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Adsorption is the main mechanism of capturing water in soil organic matter (SOM) under arid conditions. This process is governed by hydrophilic sites, which are gradually bridged via water molecule bridges (WaMB). Until now, the link between WaMB and other types of water molecules occurring in SOM during sorption has not been systematically investigated. In this work, we compared the formation and stability of WaMB simultaneously with the total water content, strength of water binding, and kinetics of water sorption in a vacuum-dried model SOM (sapric histosol) exposed to different relative water pressures. The same parameters were then determined in SOM exposed to reduced relative pressures. The adsorption resulted in an adsorption isotherm with a Langmuir-like part below a relative pressure of 0.5 and a Brunauer-Emmett-Teller-like isotherm at higher relative pressures. The WaMB formation was observed at a relative pressure of 0.32, which represented the pressure at which Langmuir-like part reached a plateau. The binding energy showed a linear decrease with an increasing pressure; the slope increased at a relative pressure of 0.46. Reduction of relative pressures above 0.46 showed that the water content remained constant, but the binding energy was lowered. In contrast, below a relative pressure of 0.46, the water content decreased, but the binding energy was not changed. The results indicate that in SOM exposed to different relative pressures, water exists in three types: first, it is strongly bound to primary sorption sites (Langmuir-like), second, it occurs in the form of WaMB water, which bridges functional groups and where predominates water-water interactions, and third, it occurs in the form of phase water, which is located in larger pores similar to the pure water phase. The latter either surrounds the WaMB and destabilizes it or, for higher water content, links individual WaMB and successively reduces their stabilizing effect. Formation of phase water leads to swelling processes including plasticizing effects and potential volume changes of SOM. Accordingly, the results suggest that at lower water relative pressures WaMB stabilizes the SOM structure, whereas at higher water relative pressures, it influences the formation of phase water and thereby the total water content in SOM.

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“…It is well known that charge and size of cations ( Dudev and Lim , ; Xu et al, ; Kalinichev and Kirkpatrick , ) are important for the interaction of cations with NOM (natural organic matter). CaB have implications on structural organisation of SOM ( e.g ., Aquino et al, ; Gildemeister et al, ), SOM thermal stability ( Diehl et al, ), and sorptive and other interfacial properties ( Diehl et al, ). However, classical theories of cation binding in humic acids ( e.g ., Tipping , ; Kretzschmar et al, ; Ghabbour et al, ) partly fail to explain the dynamics observed in solid SOM ( Kunhi Mouvenchery et al, ).…”

Section: Introductionmentioning

confidence: 99%

Cation binding in a soil with low exchange capacity: Implication for the structural rigidity of soil organic matter

Mouvenchery

Schaumann

2017

J. Plant Nutr. Soil Sci.

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Two previous studies suggested that part of the cation sorption sites in soil organic matter with low exchange capacity have to be considered as “lonely”, i.e., too far from each other to allow direct cross‐linking by bivalent cations. The objective of this contribution was to understand the mechanisms controlling structural rigidity and physicochemical aging of the SOM (soil organic matter) and the role of water molecule bridges (WaMB) therein. For this, we evaluated the matrix rigidity of an organic surface layer of a Haplic Podzol on a quantitative basis, by assessing WaMB transition temperature (T*) directly after treatment with bivalent cations (Mg2+, Ca2+, or Ba2+) and after eight weeks of aging. Cation loading as well as cation type influenced matrix rigidity. Ba2+ induced the most rigid matrix and Mg2+ the weakest, which is in line with their binding strength in terms of Langmuir coefficient. The matrix rigidity increased with the cross‐linking activity, which is the product of loading and Langmuir constant of the respective cation. The aging process, however, was slowed down by the initial matrix rigidity, and the rigidity of the aged matrix decreased with increasing Langmuir constant. The degree of aging increased with increasing hydration enthalpy of the cation and decreased with increasing cation loading. Thus, directly after cation treatment, direct cross‐links by multivalent cations were most relevant, but WaMB increasingly gained influence on the matrix rigidity during aging. The untreated sample revealed a considerable number of WaMB, resulting in a fairly rigid and strongly cross‐linked matrix which, however, flexibly reacts on external influences like change in cation concentration or relative humidity. With these findings, the ideas on the relevance of indirect CaB‐WaMB associations between distant sorption sites for the rigidity and flexibility of the OM matrix as proposed in previous studies were confirmed on a mechanistic basis in this study.

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Effect of multivalent cations, temperature, and aging on SOM thermal properties

Cited by 10 publications

References 42 publications

Considerations on cross‐linking by bivalent cations in soil organic matter with low exchange capacity

Considerations on cross‐linking by bivalent cations in soil organic matter with low exchange capacity

Formation of Water Molecule Bridges Governs Water Sorption Mechanisms in Soil Organic Matter

Cation binding in a soil with low exchange capacity: Implication for the structural rigidity of soil organic matter

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