The diffusive tortuosity of fine-grained unlithified sediments

Boudreau, Bernard P.

doi:10.1016/0016-7037(96)00158-5

Cited by 626 publications

(363 citation statements)

References 22 publications

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“…where D mol is the molecular diffusion coefficient, I is the unit tensor, and the multiplier (1−2 ln φ) −1 forms the correction for tortuosity (Boudreau, 1996). The mechanical dispersion tensor D mech is given the classical form (Freeze and Cherry, 1979; …”

Section: Reactive Transport Modelmentioning

confidence: 99%

Quantifying biologically and physically induced flow and tracer dynamics in permeable sediments

et al. 2007

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Abstract. Insight in the biogeochemistry and ecology of sandy sediments crucially depends on a quantitative description of pore water flow and the associated transport of various solutes and particles. We show that widely different problems can be modelled by the same flow and tracer equations. The principal difference between model applications concerns the geometry of the sediment-water interface and the pressure conditions that are specified along this boundary. We illustrate this commonality with four different case studies. These include biologically and physically induced pore water flows, as well as simplified laboratory setups versus more complex field-like conditions: [1] lugworm bio-irrigation in laboratory set-up, [2] interaction of bioirrigation and groundwater seepage on a tidal flat, [3] pore water flow induced by rotational stirring in benthic chambers, and [4] pore water flow induced by unidirectional flow over a ripple sequence. The same two example simulations are performed in all four cases: (a) the time-dependent spreading of an inert tracer in the pore water, and (b) the computation of the steady-state distribution of oxygen in the sediment. Overall, our model comparison indicates that model development for sandy sediments is promising, but within an early stage. Clear challenges remain in terms of model development, model validation, and model implementation.

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Section: Reactive Transport Modelmentioning

confidence: 99%

Quantifying biologically and physically induced flow and tracer dynamics in permeable sediments

et al. 2007

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“…Thereby an almost innumerable amount of empirical expressions was derived (see reviews by Boudreau [25] and Shen and Chen [26]). The fact that no unifying expression could be found indicates that s exp is maybe not a reliable parameter for the description of the microstructure-property relationship.…”

Section: Introductionmentioning

confidence: 99%

The influence of constrictivity on the effective transport properties of porous layers in electrolysis and fuel cells

et al. 2012

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The aim of the present investigation is to define microstructure parameters, which control the effective transport properties in porous materials for energy technology. Recent improvements in 3D-imaging (FIB-nanotomography, synchrotron X-ray tomography) and image analysis (skeletonization and graph analysis, transport simulations) open new possibilities for the study of microstructure effects. In this study, we describe novel procedures for a quantitative analysis of constrictivity, which characterizes the so-called bottleneck effect. In a first experimental part, methodological tests are performed using a porous (La,Sr)CoO 3 material (SOFC cathode). The tests indicate that the proposed procedure for quantitative analysis of constrictivity gives reproducible results even for samples with inhomogeneous microstructures (cracks, gradient of porosity). In the second part, 3D analyses are combined with measurements of ionic conductivity by impedance spectroscopy. The investigations are preformed on membranes of electrolysis cells with porosities between 0.27 and 0.8. Surprisingly, the tortuosities remain nearly constant (1.6) for the entire range of porosity. In contrast, the constrictivities vary strongly and correlate well with the measured transport resistances. Hence, constrictivity represents the dominant microstructure parameter, which controls the effective transport properties in the analysed membrane materials. An empirical relationship is then derived for the calculation of effective transport properties based on phase volume fraction, tortuosity, and constrictivity.

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“…The modelling is based on a coupling between biogeochemical processes [7], interstitial diffusion [2,3] and solid-liquid exchanges. The main originality is the pH determination that is directly calculated from the pore water concentrations of the ionic species and the coupling between biogeochemical processes and solid-liquid exchanges.…”

Section: Discussionmentioning

confidence: 99%

Mobility of trace metals in freshwater sediments by coupling solid-liquid exchanges, biogeochemical reactions and interstitial diffusion

Devallois

Boyer

Boudenne³

et al. 2009

Radioprotection

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Abstract. Sediments may act as a sink for nutrients and trace metals after deposition. It may pose a risk for surface water quality and ecosystem health when environmental changes lead to release nutrients and trace metals stored in these sedimentary stocks. The management of the quality of freshwater systems needs to understand the processes of remobilisation of these stocks. This mobility is dependent on the erosion, on the interstitial diffusion of the mobile phases and on the bioturbation. These mechanisms depend on early diagenetic processes that condition the physical and biogeochemical properties of the sedimentary column. These properties are mainly influenced by the redox transformations resulting from oxidation of the organic matter by the microbial activity. These reactions generate vertical profiles of nutrient and metals concentrations along the sedimentary column. This paper aims to propose a modelling and an experimental protocol to determine vertical profiles of nutrients and trace metals in saturated sedimentary columns of freshwater systems. The modelling approach is based on a coupling between bio-geochemical processes [1], interstitial diffusion [2, 3] and solid-liquid exchanges. The main originality of the model is the pH determination that is directly calculated from the pore water concentrations of the ionic species. As illustration, this paper presents an application to natural sediment cores collected in the Durance Rivers.In freshwater systems, trace metal pollutants are transferred into water and sedimentary columns under dissolved forms and fixed onto solid particles. Accumulated in the sedimentary areas, these latter ones can constitute important stocks of materials and associated pollutants. The mobility of the stocks of pollutants is mainly depending on the erosion, on the interstitial diffusion of the mobile phases (dissolved and colloidal) and on the bioturbation. In this context, this communication presents an analysis of the mobility by interstitial diffusion by comparing experimental results and modelling. This topic involves two main points: 1) Trace metal fractionation between their mobile (dissolved and colloidal) and non mobile (fixed onto the particles) forms; 2) Interstitial diffusion of the mobile phases. The first point is governed by sorption/desorption processes at the particle surfaces. In the sedimentary column, these processes are regulated by physico-chemical parameters as pH, potential redox, concentrations and nature of particles. In sediments, these parameters are mainly influenced by biochemical reactions resulting from the oxidation of the organic matter by the microbial activity: oxic respiration, denitrification, manganese hydroxide and iron hydroxide reduction, sulphate reduction, methanogenesis [4]. In this context, this work proposes a model coupling these biogeochemical reactions to sorption/desorption processes of trace metals and interstitial diffusion. In order to refine and to evaluate this model, an experimental protocol has also been developed to...

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The diffusive tortuosity of fine-grained unlithified sediments

Cited by 626 publications

References 22 publications

Quantifying biologically and physically induced flow and tracer dynamics in permeable sediments

Quantifying biologically and physically induced flow and tracer dynamics in permeable sediments

The influence of constrictivity on the effective transport properties of porous layers in electrolysis and fuel cells

Mobility of trace metals in freshwater sediments by coupling solid-liquid exchanges, biogeochemical reactions and interstitial diffusion

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