Physics of Viscous Bridges in Soil Biological Hotspots

Benard, Pascal; Schepers, Judith; Crosta, Margherita; Zarebanadkouki, Mohsen; Carminati, Andrea

doi:10.1029/2021wr030052

Cited by 13 publications

(19 citation statements)

References 39 publications

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“…The high concentration of Ca-bacterial alginate hydrogel over the composite materials generates low Reynolds numbers (Re < 0.02; viscous forces domain over intertial forces), meaning that all treatments had a Darcy´s flow regime (i.e., laminar flow) [ 47 , 48 ]. Furthermore, for all treatments Oh >> 1, meaning that viscosity dominates over the inertial forces and fluid surface tension, leading to the formation of thicker filaments that hold the soil media matrix together ( Figure 6 D–F) [ 36 ]. The filaments act like the root mucilage ligands between soil particles, which could avoid the root-soil air gaps that are generated by drought.…”

Section: Discussionmentioning

confidence: 99%

“…The incorporation of Ca-bacterial alginate hydrogel in the different soil media changed the biophysical composition of soil particles at the microstructural level. Due to the high viscosity (µ) levels of Ca-bacterial alginate hydrogel (~0.501 Pa s), the viscous forces overpass inertial forces and fluid surface tension, which can alter the forces that holds water at macro and micropore levels in agricultural soils [ 36 ]. The effect of high µ creates embolized Ca-bacterial alginate hydrogel channels (CHG; Figure 6 D).…”

Section: Discussionmentioning

confidence: 99%

“…To verify the flow regime, we estimated the Reynolds number for each treatment as [ 12 ]

where ρ is the density of the fluid (kg m −3 ), v is the flow speed (m s −1 ), D p is the diameter of particles of the growing media (mm) and μ is the dynamic viscosity of the fluid (Pa·s). Finally, to evaluate the relevance of the viscous forces versus surface tension of the Ca-bacterial alginate hydrogel filaments and its effects on the different composite materials, the Ohnesorge number was used [ 35 , 36 ]

where

is the dynamic viscosity of the fluid (Pa·s),

is the density of the fluid (kg m −3 ),

is the surface tension of water (N m −1 ) and L belongs to the length scale of filaments of Ca-bacterial alginate hydrogel between soil particle surfaces (m).…”

Section: Methodsmentioning

confidence: 99%

“…where ρ is the density of the fluid (kg m −3 ), v is the flow speed (m s −1 ), D p is the diameter of particles of the growing media (mm) and µ is the dynamic viscosity of the fluid (Pa•s). Finally, to evaluate the relevance of the viscous forces versus surface tension of the Cabacterial alginate hydrogel filaments and its effects on the different composite materials, the Ohnesorge number was used [35,36]…”

Section: Hydraulic Conductivity Testmentioning

confidence: 99%

See 3 more Smart Citations

Bacterial Alginate-Based Hydrogel Reduces Hydro-Mechanical Soil-Related Problems in Agriculture Facing Climate Change

et al. 2022

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Agricultural systems are facing the negative impacts of erosion and water scarcity, directly impacting the hydro-mechanical behavior of soil aggregation. Several technologies have been proposed to reduce hydro-mechanical soil-related problems in agriculture. Biopolymer-based hydrogels have been reported to be a great tool to tackle these problems in soils. In this study, we investigated the hydro-mechanical behavior of different soils media treated with Ca-bacterial alginate hydrogel. We used an unconfined uniaxial compression test, aggregate stability test and hydraulic conductivity measurements to investigate the mechanical and hydraulic behavior of treated soils media. Our results from unconfined uniaxial compression test showed that yield stress (i.e., strength) increased in treated soils with higher kaolinite and water content (i.e., HCM3), compared with untreated coarse quartz sand (i.e., CM1). Furthermore, we found that temperature is an important factor in the gelation capacity of our hydrogel. At room temperature, HCM3 displayed the higher aggregate stability, almost 5.5-fold compared with treated coarse quartz sand (HCM1), while this differential response was not sustained at warm temperature. In general, the addition of different quantities of kaolinite decreased the saturated hydraulic conductivity for all treatments. Finally, bright field microscopy imaging represents the soil media matrix between sand and clay particles with Ca-bacterial alginate hydrogel that modify the hydro-mechanical behavior of different soils media. The results of this study could be helpful for the soil-related problems in agriculture facing the negative effects of climate change.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…To verify the flow regime, we estimated the Reynolds number for each treatment as [ 12 ]

where

is the dynamic viscosity of the fluid (Pa·s),

is the density of the fluid (kg m −3 ),

is the surface tension of water (N m −1 ) and L belongs to the length scale of filaments of Ca-bacterial alginate hydrogel between soil particle surfaces (m).…”

Section: Methodsmentioning

confidence: 99%

Section: Hydraulic Conductivity Testmentioning

confidence: 99%

See 2 more Smart Citations

Bacterial Alginate-Based Hydrogel Reduces Hydro-Mechanical Soil-Related Problems in Agriculture Facing Climate Change

et al. 2022

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“…Surface tension determines the spatial configuration of the capillary bridge formed by water between two soil particles and the work needed to stretch the gas-liquid interface (Benard et al 2021). Surface tension opposes to the stretching of the liquid bridge, which shrinks during drying and eventually breaks up as drying progresses (Benard et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Effect of changing chemical environment on physical properties of maize root mucilage

et al. 2022

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Aims High viscosity, low surface tension and hydrophobicity are specific properties of maize root mucilage which contribute to modulate the spatial configuration of the liquid phase in soil pores. Several processes in the rhizosphere, in particularly nutrient absorption, root exudation and microbial activity, may cause strong temporal variations in the chemistry of the soil solution of the rhizosphere. Although the physical properties of maize root mucilage have been repeatedly measured in the last years, their variation upon a changing chemical environment and understanding of the chemical mechanisms governing these properties remain unexplored. Methods We investigated how flow and surface properties of maize root mucilage varied by changes in pH, calcium chloride (CaCl2) and lecithin concentrations. Results The physical properties of mucilage can strongly vary depending on the environmental conditions. Low surface tension of maize root mucilage at pH7 was increased by addition of calcium. Upon pH change and lecithin addition, hydrophobic mucilage turned hydrophilic. High Ca concentration above 0.83 mmol Ca (g dry mucilage)−1, the addition of 167 μg lecithin (g dry mucilage)−1 and a pH rise to 9 decreased the viscosity of mucilage. Conclusion Such variations strongly suggest that the role of mucilage in hydraulic processes in the rhizosphere depends on changes of solutes concentration and composition, which themselves vary according to plant growth and soil water content. It seems that mucilage can best serve as a hydraulic bridge only under certain chemical environments, whose spatio-temporal occurrence in the changing rhizosphere remains to be defined.

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Pore‐scale simulation of mucilage drainage

Jahromi

Knott

Janakiram

et al. 2022

Vadose Zone Journal

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Compared with bulk soil, rhizosphere has different properties because of the existence of root mucilage, which affects physical, chemical, and microbial processes. The slow response of rhizosphere to changes in water potential buffers water content changes and leads the rhizosphere to be wetter than bulk soil during drying. By affecting connectivity of the liquid and gas phases, mucilage can also influence solute transport and gas diffusion. Overview of the literature and previous models shows the lack of a model that describes the connectivity between different phases in the rhizosphere pore space during wetting and drying processes. A major challenge is that mucilage shows a complex behavior, which at low concentrations is more like a liquid, whereas at higher concentration, dry mucilage becomes a solid. In between, a viscoelastic state is observed where mucilage can be considered as a hydrogel. In this study a three‐dimensional pore‐scale model based on the lattice spring method is introduced and used to simulate drying of mucilage between two soil particles. The model is capable of reproducing spider‐web‐like structures that are specific for mucilage. This three‐dimensional mucilage drying model is qualitatively validated via environmental scanning electron microscopy (ESEM) images of dry mucilage between glass beads. The proposed model may provide us with a new perspective on hydrodynamic processes within the pore space of the rhizosphere. In addition, the model may help to better understand further important processes that strongly depend on rhizosphere hydraulic dynamics, such as solute transport, connectivity of the liquid phase, root penetration resistance, rhizosheath formation, and microbial activity.

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Physics of Viscous Bridges in Soil Biological Hotspots

Cited by 13 publications

References 39 publications

Bacterial Alginate-Based Hydrogel Reduces Hydro-Mechanical Soil-Related Problems in Agriculture Facing Climate Change

Bacterial Alginate-Based Hydrogel Reduces Hydro-Mechanical Soil-Related Problems in Agriculture Facing Climate Change

Effect of changing chemical environment on physical properties of maize root mucilage

Pore‐scale simulation of mucilage drainage

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