Stepping beyond perfectly mixed conditions in soil hydrological modelling using a Lagrangian approach

Abstract. A recent experiment of Bowers et al. (2020) revealed that diffusive mixing of water isotopes (δ2H, δ18O) over a fully saturated soil sample of a few centimetres in length required several days to equilibrate completely. In this study, we present an approach to simulate such time-delayed diffusive mixing processes on the pore scale beyond instantaneously and perfectly mixed conditions. The diffusive pore mixing (DIPMI) approach is based on a Lagrangian perspective on water particles moving by diffusion over the pore space of a soil volume and carrying concentrations of solutes or isotopes. The idea of DIPMI is to account for the self-diffusion of water particles across a characteristic length scale of the pore space using pore-size-dependent diffusion coefficients. The model parameters can be derived from the soil-specific water retention curve and no further calibration is needed. We test our DIPMI approach by simulating diffusive mixing of water isotopes over the pore space of a saturated soil volume using the experimental data of Bowers et al. (2020). Simulation results show the feasibility of the DIPMI approach to reproduce measured mixing times and concentrations of isotopes at different tensions over the pore space. This result corroborates the finding that diffusive mixing in soils depends on the pore size distribution and the specific soil water retention properties. Additionally, we perform a virtual experiment with the DIPMI approach by simulating mixing and leaching processes of a solute in a vertical, saturated soil column and comparing results against simulations with the common perfect-mixing assumption. Results of this virtual experiment reveal that the frequently observed steep rise and long tailing of breakthrough curves, which are typically associated with non-uniform transport in heterogeneous soils, may also occur in homogeneous media as a result of imperfect subscale mixing in a macroscopically homogeneous soil matrix.

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SOIL PORE SIZE DISTRIBUTION AT DIFFERENT CARBONATE MINERALS CONTENT

IRAQI JOURNAL OF AGRICULTURAL SCIENCES ◽

10.36103/ijas.v47i5.511 ◽

2016 ◽

Vol 47 (5) ◽

Author(s):

Mahdi & Naji

Keyword(s):

Pore Size Distribution ◽

Pore Size ◽

Soil Sample ◽

Size Distribution ◽

Water Retention ◽

Pore Space ◽

Capillary Rise ◽

Water Volume ◽

Carbonate Minerals ◽

Wide Range

Pore space, especially pore size distribution is one of the important properties affecting soil infiltration, hydraulic conductivity, and water retention. To examine the effect of carbonate minerals on pore size distribution, soil material with loam texture was used to prepare nine soil materials containing wide range of carbonate minerals (3.2 - 352 g kg-1). The soil-water retention curve (θ(ψ)) was estimated. Computer program (RETC code) was used to determine the best-fit for experimental data of water potential versus volumetric water content which have nonlinear relationship to determine the parameter of van Genuchten equation [α, n and m with m=1-(1/n)]. The capillary rise equation (young-laplace equation) was used to estimate the effective pore diameter (D). The results show that pore space was affected by carbonate minerals contents. Air pores (> 30 μm) increased 1.4 fold with increasing carbonate minerals at the same time capillary pores filled with water (< 30 μm) decreased by 1.3 folds. The relative of water volume to total soil volume ranged between 0.27 and 0.21 cm3cm-3 for carbonate minerals content 3.2 and 352 g kg-1 respectively. At 10 kPa the amount of water lost increased with increasing carbonate minerals content, where soil sample with 352 g.kg-1 carbonate minerals lost water more than soil sample with 3.2 g.kg-1 carbonate minerals by 42%. The percentage of pores (< 30 μm) ranged from 67% to 79% and the pores (> 30 μm) ranged from 33% to 21%. It can be concluded that high carbonate minerals content in the soil led to change in pore size distribution, where air-filled pores increased and capillary pores filled with water (water holding capacity) decreased at different degree from sample to another.

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INFLUENCE OF SOIL MATRIX ON SOIL-WATER RETENTION CURVE AND HYDRAULIC CHARACTERISTICS

Environmental Engineering and Management Journal ◽

10.30638/eemj.2017.088 ◽

2017 ◽

Vol 16 (4) ◽

pp. 869-877

Author(s):

Vasile Lucian Pavel ◽

Florian Statescu ◽

Dorin Cotiu.ca-Zauca ◽

Gabriela Biali ◽

Paula Cojocaru

Keyword(s):

Soil Water ◽

Water Retention ◽

Water Retention Curve ◽

Hydraulic Characteristics ◽

Soil Water Retention Curve ◽

Soil Water Retention ◽

Soil Matrix ◽

Retention Curve

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Biochars improve aggregate stability, water retention, and pore-space properties of clayey soil

Journal of Plant Nutrition and Soil Science ◽

10.1002/jpln.201200639 ◽

2013 ◽

Vol 177 (1) ◽

pp. 26-33 ◽

Cited By ~ 143

Author(s):

Fangfang Sun ◽

Shenggao Lu

Keyword(s):

Water Retention ◽

Clayey Soil ◽

Pore Space ◽

Aggregate Stability

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The effects of biochar on soil physical properties and winter wheat growth

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s1755691012000011 ◽

2012 ◽

Vol 103 (1) ◽

pp. 13-18 ◽

Cited By ~ 32

Author(s):

Rachel C. Devereux ◽

Craig J. Sturrock ◽

Sacha J. Mooney

Keyword(s):

Pore Size ◽

Bulk Density ◽

Water Retention ◽

Average Pore Size ◽

Water Repellency ◽

Soil Bulk Density ◽

Average Pore ◽

Wheat Growth ◽

Wetting Ability ◽

X Ray Computed

ABSTRACTBiochar has been reported to improve soil quality and crop yield; however, less is known about its effects on the physical and, in particular, structural properties of soil. This study examines the potential ability of biochar to improve water retention and crop growth through a pot trial using biochar concentrations of 0%, 1·5%, 2·5% and 5% w/w. X-ray computed tomography was used to measure soil structure via pore size characteristics; this showed that pore size is significantly affected by biochar concentration. Increasing biochar is associated with decreasing average pore size, which we hypothesise would impact heavily on hydraulic performance. At the end of the experiment, average pore size had decreased from 0·07 mm2 in the 0% biochar soil to 0·046 mm2 in the 5% biochar soil. Increased biochar concentration also significantly decreases saturated hydraulic conductivity and soil bulk density. It was also observed that increased biochar significantly decreases soil water repellency. Increased water retention was also observed at low matric potentials, where it was shown that increased biochar is able to retain more water as the soil dried out. The application of biochar had little effect on short-term (<10 weeks) wheat growth, but did improve water retention through a change in soil porosity, pore size, bulk density and wetting ability.

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Improving estimation of pore size distribution to predict the soil water retention curve from its particle size distribution

Geoderma ◽

10.1016/j.geoderma.2019.01.011 ◽

2019 ◽

Vol 340 ◽

pp. 206-212 ◽

Cited By ~ 3

Author(s):

Chen-chao Chang ◽

Dong-hui Cheng ◽

Xiao-ying Qiao

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Pore Size Distribution ◽

Pore Size ◽

Size Distribution ◽

Water Retention ◽

Water Retention Curve ◽

Soil Water Retention Curve ◽

Soil Water Retention ◽

Retention Curve

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Using an inverse modelling approach to evaluate the water retention in a simple water harvesting technique

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-6-4265-2009 ◽

2009 ◽

Vol 6 (3) ◽

pp. 4265-4306 ◽

Cited By ~ 4

Author(s):

K. Verbist ◽

W. M. Cornelis ◽

D. Gabriels ◽

K. Alaerts ◽

G. Soto

Keyword(s):

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Water Retention ◽

Measurement Techniques ◽

Inverse Modelling ◽

Model Parameters ◽

Arid Zones ◽

Water Harvesting ◽

Data Set

Abstract. In arid and semi-arid zones runoff harvesting techniques are often applied to increase the water retention and infiltration on steep slopes. Additionally, they act as an erosion control measure to reduce land degradation hazards. Nevertheless, few efforts were observed to quantify the water harvesting processes of these techniques and to evaluate their efficiency. In this study a combination of detailed field measurements and modelling with the HYDRUS-2D software package was used to visualize the effect of an infiltration trench on the soil water content of a bare slope in Northern Chile. Rainfall simulations were combined with high spatial and temporal resolution water content monitoring in order to construct a useful dataset for inverse modelling purposes. Initial estimates of model parameters were provided by detailed infiltration and soil water retention measurements. Four different measurement techniques were used to determine the saturated hydraulic conductivity (Ksat) independently. Tension infiltrometer measurements proved a good estimator of the Ksat value and a proxy for those measured under simulated rainfall, whereas the pressure and constant head well infiltrometer measurements showed larger variability. Six different parameter optimization functions were tested as a combination of soil-water content, water retention and cumulative infiltration data. Infiltration data alone proved insufficient to obtain high model accuracy, due to large scatter on the data set, and water content data were needed to obtain optimized effective parameter sets with small confidence intervals. Correlation between observed soil water content and simulated values was as high as R2=0.93 for ten selected observation points used in the model calibration phase, with overall correlation for the 22 observation points equal to 0.85. Model results indicate that the infiltration trench has a significant effect on soil water storage, especially at the base of the trench.

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Obvious and less obvious processes of aggregate formation in soil

10.5194/egusphere-egu21-10597 ◽

2021 ◽

Author(s):

Hans-Jörg Vogel ◽

Maria Balseiro-Romero ◽

Philippe C. Baveye ◽

Alexandra Kravchenko ◽

Wilfred Otten ◽

...

Keyword(s):

Organic Matter ◽

Soil Structure ◽

Solid Phase ◽

Pore Space ◽

Imaging Techniques ◽

Mineral Soil ◽

Aggregate Formation ◽

Conceptual Approach ◽

Soil Matrix ◽

Biophysical Processes

Soil structure, lately referred to as the ''architecture'' is a key to explain and understand all soil functions. The development of sophisticated imaging techniques over the last decades has led to significant progress in the description of this architecture and in particular of the geometry of the hierarchically-branched pore space in which transport of water, gases, solutes and particles occurs and where myriads of organisms live. Moreover, there are sophisticated tools available today to also visualize the spatial structure of the solid phase including mineral grains and organic matter. Hence, we do have access to virtually all components of soil architecture.Unfortunately, it has so far proven very challenging to study the dynamics of soil architecture over time, which is of critical importance for soil as habitat and the turnover of organic matter. Several largely conflicting theories have been proposed to account for this dynamics, especially the formation of aggregates. We review these theories, and we propose a conceptual approach to reconcile them based on a consistent interpretation of experimental observations and by integrating known physical and biogeochemical processes. A key conclusion is that rather than concentrating on aggregate formation in the sense of how particles and organic matter reorganize to form aggregates as distinct functional units we should focus on biophysical processes that produce a porous, heterogeneous organo-mineral soil matrix that breaks into fragments of different size and stability when exposed to mechanical stress.&#160; The unified vision we propose for soil architecture and the mechanisms that determine its temporal evolution, should pave the way towards a better understanding of soil processes and functions.

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Studies on the water retention in arable sandy soil amended with fine size-fractionated sunflower husk biochar

10.5194/egusphere-egu21-15549 ◽

2021 ◽

Author(s):

Łukasz Gluba ◽

Anna Rafalska-Przysucha ◽

Kamil Szewczak ◽

Mateusz Łukowski ◽

Radosław Szlązak ◽

...

Keyword(s):

Particle Size ◽

Bulk Density ◽

Size Distribution ◽

Sandy Soil ◽

Water Retention ◽

Reference Level ◽

Satellite Monitoring ◽

Soil Matrix ◽

Size Fractions ◽

Biochar Amendment

Biochar application has been reported for improving the physical, chemical, and hydrological properties of soil. However, biochar can be produced from different feedstocks and at different conditions having a direct impact on its properties. Furthermore, the overall effect of improvement depends on the type of soil. That makes biochar amendment difficult to optimize and creates the need for extensive studies of this issue for its better understanding. In these studies, we show that water holding capacity (by means of Available Water Content - AWC) can be significantly improved in arable sandy soil using fine-sized biochar particles.For our studies, we have used sunflower husk biochar (pyrolyzed at 650oC). Biochar samples were characterized using an elemental analyzer for C, H, N content studies, mercury porosimeter for porosity and specific pore volumes, and vibratory shaker with a stack of sieves for particle size distribution. The examined biochar was sieved in order to obtain four diameter size fractions: <50 &#181;m, 50&#8211;100 &#181;m, 100&#8211;250 &#181;m and <2000 &#181;m and mixed with arable sandy soil for 0.95, 2.24, 4.76 and 9.52 wt.%. The unamended soil sample served as a reference. At first, we have measured the bulk density of the air-dried samples. After then the pressure plate method was used to determine the water retention curves. The results were fitted using the van Genuchten equation. Finally, the AWC for all the measured samples was calculated from a difference between soil water contents for pF=2.2 and pF=4.2.&#160; The bulk density studies have shown a nonlinear behavior as a function of dose for all fractions of the biochar. The clearest effect is observed for fractions below 100 &#181;m for which the density vs dose characteristics of the samples revealed a maximum for 0.95 wt.% and a decreasing trend for higher biochar contents. The AWC studies shown that the particle size fractions of biochar below 100 &#181;m in diameter cause also the most significant improvement in the water retention, almost doubling the reference level (0.078 m3 m-3) to approximately 0.155 m3 m-3 after biochar amendment. The results are explained by the filling of the free volume in the sandy soil matrix by small biochar particles. That leads to a shift of the pore size distribution to smaller radiuses, which in consequence promotes an increase in AWC.&#160;&#160;The research was conducted under the project&#160; "Water in soil&#160; -&#160; satellite monitoring and improving the retention using biochar" No. BIOSTRATEG3/345940/7/NCBR/2017 which was financed by the Polish National Centre for Research and Development in the framework of &#8220;Environment, agriculture and forestry" -BIOSTRATEG strategic R&D programme.

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