Influence of pore size and geometry on peat unsaturated hydraulic conductivity computed from 3D computed tomography image analysis

Rezanezhad, Fereidoun; Quinton, William L.; Price, Jonathan S.; Elliot, Thomas; Elrick, D. E.; Shook, Kevin

doi:10.1002/hyp.7709

Cited by 78 publications

(77 citation statements)

References 41 publications

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“…As a result, there was the potential for this layer to retain water for capillary rise for Tomenthypnum mosses. However, smaller peat particles and pore sizes with depth, the Tomenthypnum peat pore network may have had less connectivity as water concentrated in crevices and at small angles, thereby increasing the inactive porosity and tortuosity (Rezanezhad et al 2010). This is evident in the K(c m ) relationships with depth as Tomenthypnum K unsat was approximately an order of magnitude lower at matric pressures between 0 and (30 mb at 22.5 cm depth (Fig.…”

Section: Discussionmentioning

confidence: 95%

“…Their shoot morphological structures and community growth forms (general form adapted by colonies of moss shoots) affect the amount and connectivity of water-conducting pores for capillary rise (Voortman et al 2013;McCarter and Price 2014a). Connectivity within moss and peat structures is a function of pore-size distribution, geometry, and tortuosity (Rezanezhad et al 2010), which affect water content and ultimately unsaturated hydraulic conductivity (Price et al 2008). The upward capillary water movement from underlying peat substrates is driven by soil-water pressure gradients within the moss structure caused by atmospheric demand at the canopy surface Rice et al 2001).…”

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confidence: 99%

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Role of morphological structure and layering ofSphagnumandTomenthypnummosses on moss productivity and evaporation rates

Goetz

PriceJonathan

2015

Can. J. Soil. Sci.

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Price, J. S. 2015. Role of morphological structure and layering of Sphagnum and Tomenthypnum mosses on moss productivity and evaporation rates. Can. J. Soil Sci. 95: 109Á124. Morphological structures of peatland mosses control moss water relations and the rate of water loss by drainage and evaporation, thus influencing their physiological functions. While many of these mechanisms are understood for Sphagnum mosses, there is a limited understanding of how these processes operate in Tomenthypnum nitens, a dominant brown moss species in northern rich fens. This study contrasts how different hydrophysical characteristics of Tomenthypnum and Sphagnum species affect capillary water flow that supports evaporation and productivity. Laboratory investigations indicate that volumetric water content (u), gross ecosystem productivity, and evaporation decreased with water ). Despite lower u and a smaller fraction of pores between 66 and 661 mm to retain water within the Tomenthypnum structure (10%) compared with Sphagnum (27%), both mosses had similar fractions of water conducting pore spaces and were able to maintain capillary rise throughout the experiment. While there was a larger difference in the bulk density and porosity of the Tomenthypnum moss compared with its underlying peat than there was in the Sphagnum profile, a layer of partially decomposed moss of intermediate properties was sufficient to provide a connection between the moss and peat under low water table conditions. In trying to characterize the soil-water pressure (c) in near-surface mosses of Tomenthypnum based on measurements of vapour pressure, we found disequilibrium conditions that severely underestimated c (i.e., very large negative pressures). It is this disequilibrium that drives evaporation and draws up capillary water to the moss surface for peatlandÁatmosphere carbon and water transfers.Key words: Peatlands, bryophytes, water retention, hydraulic conductivity, theoretical pore-size distribution, water vapour Goetz, J. D. et Price, J. S. 2015. Influence de la morphologie et de la superposition des couches de mousses de type Sphagnum et Tomenthypnum sur la productivite´de la plante et le taux d'e´vaporation. Can. J. Soil Sci. 95: 109Á124. Dans les tourbie`res, la morphologie des mousses controˆle les relations entre l'eau et la plante, ainsi que la vitesse a`laquelle l'eau disparaıˆt par drainage et e´vaporation, ce qui exerce une influence sur les fonctions physiologiques de la mousse. Quoique beaucoup de ces me´canismes soient bien connus chez les mousses du genre Sphagnum, nos connaissances sont plus limite´es sur ces processus chez Tomenthypnum nitens, une mousse brune qui domine dans les riches marais du nord. Cette e´tude illustre combien les caracte´ristiques hydrophysiques diffe´rentes des espe`ces des genres Tomenthypnum et Sphagnum modifient l'e´coulement capillaire de l'eau, dont de´pendent l'e´vaporation et la productivite´. Les e´tudes en laboratoire indiquent que la masse volumique de l'eau (u), la productivite´brute de l'e´cosyste`me...

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Section: Discussionmentioning

confidence: 95%

mentioning

confidence: 99%

Role of morphological structure and layering ofSphagnumandTomenthypnummosses on moss productivity and evaporation rates

Goetz

PriceJonathan

2015

Can. J. Soil. Sci.

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“…Dimitrov et al, 2010;Sulman et al, 2012;Wu and Blodau, 2013;Mezbahuddin et al, 2016). However, the investigation of the WRC of organic soils has revealed bimodal pore-size distributions which have been found for different but limited pressure head ranges (Rezanezhad et al, , 2010(Rezanezhad et al, , 2016Quinton et al, 2008Quinton et al, , 2009Kettridge and Binley, 2011), and have so far rarely been expressed in terms of effective SHP over the full pressure head range. Weber et al (2017a) applied the highly sensitive method of inverse modelling evaporation experiments performed on Sphagnum moss and peat over a wide moisture range to parameterize SHP.…”

Section: Introductionmentioning

confidence: 99%

A pore-size classification for peat bogs derived from unsaturated hydraulic properties

Weber

Iden

Durner

2017

Hydrol. Earth Syst. Sci.

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Abstract. In ombrotrophic peatlands, the moisture content of the acrotelm (vadoze zone) controls oxygen diffusion rates, redox state, and the turnover of organic matter. Thus, variably saturated flow processes determine whether peatlands act as sinks or sources of atmospheric carbon, and modelling these processes is crucial to assess effects of changed environmental conditions on the future development of these ecosystems. We show that the Richards equation can be used to accurately describe the moisture dynamics under evaporative conditions in variably saturated peat soil, encompassing the transition from the topmost living moss layer to the decomposed peat as part of the vadose zone. Soil hydraulic properties (SHP) were identified by inverse simulation of evaporation experiments on samples from the entire acrotelm. To obtain consistent descriptions of the observations, the traditional van GenuchtenMualem model was extended to account for non-capillary water storage and flow. We found that the SHP of the uppermost moss layer reflect a pore-size distribution (PSD) that combines three distinct pore systems of the Sphagnum moss. For deeper samples, acrotelm pedogenesis changes the shape of the SHP due to the collapse of inter-plant pores and an infill with smaller particles. This leads to gradually more homogeneous and bi-modal PSDs with increasing depth, which in turn can serve as a proxy for increasing state of pedogenesis in peatlands. From this, we derive a nomenclature and size classification for the pore spaces of Sphagnum mosses and define inter-, intra-, and inner-plant pore spaces, with effective pore diameters of > 300, 300-30, and 30-10 µm, respectively.

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“…Notwithstanding the progress in describing the evaporation process in 3D porous media, to our knowledge there has been no experimental work that attempted to deduce directly the structure of 3D drying fronts in porous media and the scaling characteristics of the liquid-and air-phase distributions during the process. For example, the fractal dimension D f of 3D fronts has been typically estimated by the box-counting method applied to 2D images [24,25], and using the relation between D f for 2D cuts from 3D systems. Reporting new results on these aspects is one main objective of this paper.…”

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confidence: 99%

Structure of drying fronts in three-dimensional porous media

Shokri

Sahimi

2012

Phys. Rev. E

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Evaporation in a three-dimensional (3D) porous medium, a sand column saturated by water, was studied using synchrotron x-ray tomography. Three-dimensional images of the medium with a resolution of 7 µm were obtained during the evaporation. The entire column was scanned seven times, resulting in nearly 10 4 2D cross sections and illustrating the spatial distribution of air, liquid and solid phases at the pore scale. The results were analyzed in order to gain new insights and better understanding of the characteristics of the drying front that was formed when the liquid-filled pores were invaded by air, as well as the structure of the liquid phase as it was dried. The analysis indicates that the liquid phase has a self-similar fractal structure, with its fractal dimension D f in all the cross sections being a function of the water content or saturation. In addition, D f for the 3D liquid structure, as well as its density correlation function, were computed using the 3D images. A crossover length scale ξ was identified that separates the fractal regime from the compact geometry. For length scales r > ξ, the density correlation function approaches asymptotically the water content of the porous medium. The drying front is shown to be rough and multi-affine, rather than self-affine. Its properties were also computed using the 3D images. The rougness characteristics agree with those for imbibition in porous media, but not with those of fracture surfaces and crack lines. PACS number(s):

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Influence of pore size and geometry on peat unsaturated hydraulic conductivity computed from 3D computed tomography image analysis

Cited by 78 publications

References 41 publications

Role of morphological structure and layering ofSphagnumandTomenthypnummosses on moss productivity and evaporation rates

Role of morphological structure and layering ofSphagnumandTomenthypnummosses on moss productivity and evaporation rates

A pore-size classification for peat bogs derived from unsaturated hydraulic properties

Structure of drying fronts in three-dimensional porous media

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