Displays

Preferential fluid flow and chemical transport occur on scales ranging from pores to aquifers and catchments, in both fully and partially water-saturated geological formations. Preferential flows can be considered, in a general sense, manifestations of self-organization that hinders perfect mixing within a system, and leads to faster throughput of water and chemicals. However, unified concepts for the onset, spatiotemporal patterning, and magnitude of such preferential flows are generally difficult to define; and this is compounded by the difficulty – or practical impossibility – of obtaining detailed measurements of the structure and hydraulic functioning of vadose zones, catchments, and aquifers. We propose that conceptualizations and quantitative characterizations of preferential fluid flow and chemical transport in all of these systems can be unified in terms of tools that connect them in a dynamic framework. Here, we discuss key, shared features of fluid flow and chemical transport dynamics in each of these two systems, based on both laboratory and field measurements, and numerical simulations. We show how even well-connected fracture networks can display highly non-uniform preferential paths for fluid and chemicals. We then recognize that this behavior is similar to that of rapid infiltration in soils and the vadose zone, which exhibits strongly localized preferential pathways in root channels, cracks, worm burrows or connected inter-aggregate pore networks. Moreover, both types of domains can display “memory effects”, in terms of the location and functioning of preferential paths even during perturbations in the velocity gradient and/or rates of infiltration. We argue that the ubiquity of unresolved (or uncharacterized) heterogeneity at all spatial and temporal scales necessitates the use of effective medium models that enable an accounting of a wide range of flow and transport behaviors. For chemical transport, we focus on a probabilistic modelling framework that can capture the dynamics in heterogeneous vadose zones and fractured (or otherwise heterogeneous) geological formations. We then demonstrate application of this model to interpret field-scale tracer breakthrough curves (concentration vs. time) in a highly fractured karst formation over length scales of up to more than 7 km.

How to cite: Berkowitz, B.: Preferential fluid flow and chemical transport in saturated fractured porous media and in heterogeneous vadose zones: Two sides of the same coin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3112, https://doi.org/10.5194/egusphere-egu2020-3112, 2020.

Where water goes when it rains, is to a large part controlled by subsurface storage and subsurface flow paths. While these aspects are essential for basic hydrological process understanding, their large spatial and temporal variability makes both systematic studies and extraction of generalizable results challenging.
We investigate systematically how subsurface storage and flow paths change during the temporal evolution of hillslopes. In order to do so we selected 4 moraines of different ages (30, 160, 3000 and 10.000 years) in a glacial foreland in the Swiss Alps. We then studied both soil physical characteristics as well as flow path evolution across this chronosequence by extensive sampling and soil physical laboratory analyses on the one hand and 36 in-situ dye tracer experiments (Brilliant Blue)  on the other hand.
We find that soil physical characteristics change significantly over the millennia. However, vegetational development seems to have a similarly strong effect on flow path evolution. Flow paths evolve from mainly matrix flow at the youngest moraine to increasingly more dominant preferential flow. At the oldest moraine we furthermore find increased subsurface storage, especially in the now strongly developed organic horizon. At intermediate ages preferential flow is less dominated by flow in macropores but is initiated at the soil surface through spatially variable vegetation and microtopography. With this study we provide a first systematic and detailed study of flow path evolution across the first ten millennia of hillslope evolution.

How to cite: Hartmann, A., Semenova, E., Weiler, M., and Blume, T.: Field observations of subsurface flow path evolution over 10 Millennia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17961, https://doi.org/10.5194/egusphere-egu2020-17961, 2020.

This study presents the results of the soil hydraulic characterization performed under three land covers, namely pasture, 9-year-old restored forest, and remnant forest, in the Brazilian Atlantic Forest. Two types of infiltration tests were performed, namely tension (Mini-Disk Infiltrometer, MDI) and ponding (Beerkan) tests. MDI and Beerkan tests provided a complementary information, highlighting a clear increase of the hydraulic conductivity, especially at the remnant forest plots, when moving from near-saturated to saturated conditions. In addition, measuring the unsaturated soil hydraulic conductivity with different water pressure heads also allowed to estimate the macroscopic capillary length in the field. This approach, in conjunction with Beerkan measurements, allowed to generate better estimates of the saturated soil hydraulic conductivity under challenging field conditions, such as soil water repellency (SWR). This research also reports for the first time evidence of SWR in the Atlantic Forest, which affected the early stage of the infiltration process with more frequency in the remnant forest.

How to cite: Lozano-Baez, S. E., Cooper, M., Frosini de Barros Ferraz, S., Ribeiro Rodrigues, R., Castellini, M., and Di Prima, S.: Assessing Water Infiltration and Soil Water Repellency in Brazilian Atlantic Forest Soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22580, https://doi.org/10.5194/egusphere-egu2020-22580, 2020.

Soil aggregation is a dynamic state involving numerous biophysical interactions that cannot be deduced from snapshots of soil aggregate sizes nor the state of bulk soil organic carbon (SOC) alone. Hydrophysical and  biogeochemical functions of soil aggregation are directly linked with dynamic nature of soil aggregation. At the local scale, aggregates are formed and around particulate organic debris and they evolve as undifferentiated biogeochemical hotspots. The rate of evolution varies with the life-stage of each hotspot (the remaining reserve of C and nutrients within the hotspot) as well as the physical environmental conditions (wetness and temperature). Thus, the macroscopic patterns of hotspot (aggregate) distributions reflect the interplay between the spatial/temporal patterns of C inputs and fluctuations of physical environmental conditions. Here, we show a modeling analysis of how these aggregation patterns vary across ranges of climatic and vegetation (root architecture) conditions. We utilize a model that considers the dynamic lifecycle of ensembles of multigenerational aggregates originating from polydisperse C inputs.

How to cite: Ghezzehei, T. and Or, D.: Root architecture and hydrologic fluctuations explain spatiotemporal soil aggregation patterns, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21957, https://doi.org/10.5194/egusphere-egu2020-21957, 2020.

The WormEx I Experiment was launched on 9 March 2016 to investigate the effects of biopores and earthworms holes on soil-water constitutive laws.
Particularly, changes in the soil hydraulic conductivity, in the soil sorptivity and in the macroscopic capillary length were evaluated in different soil conditions, by means of infiltrometric tests performed in a shallow anthropogenic soil of the Central Italian Alps (Cividate Camuno, Italy).
About 50 field infiltration tests were performed by means of a tension infiltrometer (TI) and by means of a small single ring infiltrometer, in view of applying the simplified BEST method (Beerkan Estimation of Soil Transfer parameters).
The worms presence was accounted for by counting worms' castings in 1 m² experimental plots, and it was considered a proxy of the biogenic activity.
Various meteorological conditions and various conditions of the presence of worms' castings were sampled during a period of three years.
Obtained results highlight how soil hydrological properties change depending on the biopores presence.

As a result, the hydraulic conductivity greatly increased in presence of soil biopores, both in ponding and in near-saturation conditions.
Conductivity at saturation increased on average by 45% (TI method), between great and small presence of earthworms' holes.
Considering soil conditions that stimulate the biological activity (e.g. the previous days precipitation and the great water content at the beginning of the infiltration tests), the conductivity at saturation increased more, i.e. by 85% (TI) and by 105% (BEST) on average.
The increase is even more relevant passing from adverse conditions (low castings number and small initial soil-water content) to optimal conditions (high castings number and great initial soil-water content).
In these cases average increments are more than 200% (TI).

Also the hydraulic conductivity of the nearly saturated soil, with pressure potential ranging between -5 cm and  0 cm, meaningfully increased in case of biopores presence.
The greatest (relative) increase of the soil hydraulic conductivity was observed in most of the cases at a pressure potential of -2 cm.

Sorptivity meaningfully increased from low to high wormholes number (45% at saturation) and from optimal to adverse conditions (114% at saturation).
As for the hydraulic conductivity, this increase was even greater nearby ponding conditions.
Field-tests results changed greatly depending on time and space: great standard deviations were observed for both hydraulic conductivity and sorptivity at all the values of pressure potential.

The macroscopic capillary length λ_c, which provides concise information about the soil attitude to diffusion, determined by numerically evaluating the subtended area to the experimental hydraulic-conductivity curve, also evidenced the presence of earthworms' burrows, ranging from 16.9 mm to  11.6 mm in optimal and adverse conditions respectively.

How to cite: Pezzotti, D., Peli, M., Ranzi, R., and Barontini, S.: The WormEx I Experiment: Effects of biopores and earthworm holes on soil hydraulic conductivity, sorptivity and macroscopic capillary length, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19338, https://doi.org/10.5194/egusphere-egu2020-19338, 2020.

In an endeavour to describe quantitatively the water flow and solute transport in soils and other heterogeneous porous media, various different approaches have been introduced in the past decades, including double porosity, double permeability and other multiple-continua approaches. Recently, a promising methodology to identify experimentally the pore structure of porous media has been proposed, where a discrete distribution of effective pore radii is established based on saturated flow experiments with non-Newtonian (shear-thinning) fluids, as described by Abou Najm and Atallah (2016) and in other works. In this particular concept, the porous media is idealised as a bundle of capillaries with only a reasonably small number of distinct values of their radii. This allows to identify the pore radii and the contributions of the corresponding pore groups to the total flow by performing and evaluating a reasonable number of flow experiments.

In an attempt to understand better the relation of the effective discrete pore radii distribution concept (with a given number of distinct pore radii allowed) to the structure of the porous media, we perform numerical experiments with other idealised geometries of the pore space. The saturated flow experiments with shear-thinning fluids are simulated by finite element method and then, based on the resulting flow, the discrete pore radii distributions are established and compared with the original geometry. For simplicity, we stick to one-dimensional models analogous to Poiseuille or Hagen-Poiseuille flow. The idea is to examine pore size distributions that are continuous rather than discrete, while keeping the advantage of a perfectly controlled and comprehensible idealised geometry. This in-silico approach may later serve as a supporting tool for studying various aspects of the addressed experimental methodology, e.g., in taking into account realistic non-Newtonian rheology, proposing an optimal set of experiments, or contemplating links with solute transport models.

How to cite: Lanzendörfer, M.: Numerical experiments with idealised pore space geometries and shear-thinning fluids., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16647, https://doi.org/10.5194/egusphere-egu2020-16647, 2020.

Preferential flow paths in soils play a major role for transport processes of heat, gas, water, and solutes and are important adsorption sites. For mass-exchange processes and water storage in soils, small-scaled soil properties, like the spatial distribution of adsorption sites and their accessibility, and the permeability are crucial. Interfaces between macropores (i.e., earthworm burrows, cracks, and root channels) and the soil matrix control the mass exchange. Water and solute transfer through the interface between bio-pores, aggregate or crack surfaces and the matrix was traced at the scale of small soil blocks (≤45 mm edge length) with Fluorescein (i.e., a reactive, fluorescent dye). The objectives were to visualize and quantify hydraulic transport, and sorption characteristics of earthworm-, root- and shrinkage-induced interfaces. Batch experiments were performed to calibrate the Na-Fluorescein tracer concentration versus fluorescence-intensity relationship and to derive parameters for two kinetic sorption models (i.e., Freundlich vs. Langmuir). Fluorescence imaging in the laboratory of small soil blocks was applied with a self-constructed spraying device, and with the help of the calibration, small-scaled dye-concentration maps were derived. Time- and interface-dependent positions of the wetting fronts in vertical direction were estimated with the help of the cumulative infiltration. Assuming equilibrated conditions between Na-Fluorescein in solution (calculated by multiplying the locale dye-concentration and the local water content) and Na-Fluorescein sorbed to soil, the total mass transfers as a function of macropore-type and spraying time were determined. The results of the mass transfer for water and reactive solutes were characteristic for the soil structure type and depending on the composition of the macropore-matrix interface. Differences were explained by alterations in soil structure and chemical composition of the coatings. Results suggest relations between mass exchange and observable soil properties. This can be helpful for improving the numerical simulation of macropore-matrix mass transfer and inverse simulations of small-scaled hydraulic, transport, and sorption characteristics of macropore walls.

How to cite: Haas, C., Ellerbrock, R., and Gerke, H. H.: Macropore-matrix mass transfer: reactive solute transport as quantified with Fluorescence imaging, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14230, https://doi.org/10.5194/egusphere-egu2020-14230, 2020.

Recharge estimation in fractured-porous aquifers is an essential tool for proper water management and assessment of vulnerability. As opposed to diffuse infiltration, often encountered in consolidated and unconsolidated porous media, the infiltration dynamics in the unsaturated zone of fractured-porous media and karst aquifers often exhibit a rapid, gravity-driven flow component along preferential flow paths such as fractures, fracture networks, faults and fault zones. The partitioning into two hydraulically contrasting domains commonly leads to a breakdown of classical volume-effective flow equations employed in many FD or FEM modeling approaches which only consider the capillarity of the medium. Even in the presence of a porous matrix, preferential pathways along fractures have been shown to sustain flow percolation under equilibrium and non-equilibrium conditions. In order to properly capture the flow physics, various components have to be considered such as static and dynamic contact angles, surface tension, free-surface (multi-phase) interface dynamics, dynamic switching of flow modes (between droplets, rivulets, films) and associated formation of singularities in the case of merging or snapping flow. Here we study the process of vertical infiltration and partitioning at a single fracture intersection into a horizontal and vertical flow component. Via parallelized Smoothed Particle Hydrodynamics simulations we demonstrate how flow is first channeled into the horizontal fracture and then transitions into a Washburn-type inflow when pressure conditions are met and a connection to the next vertical flow path is established. We further proceed to capture this process with an analytical approach and finally demonstrate how to obtain a process-based transfer function to upscale this process to arbitrary fracture geometries and fracture cascades.

How to cite: Kordilla, J., Dentz, M., and Tartakovsky, A.: Partitioning of preferential flows in fracture networks: Smoothed Particle Dynamics simulations and analytical modeling of infiltration dynamics , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22595, https://doi.org/10.5194/egusphere-egu2020-22595, 2020.

Infiltration processes in fractured consolidated aquifer systems often exhibit complex gravity-driven flow features and hence tend to develop preferential flow paths along fracture network which contribute to rapid mass fluxes. This behavior is often difficult to model with classical methods such as the Richards equation, as a variety of interacting flow modes, ranging from free-surface flows over droplet and and rivulet flows, control the mass partitioning processes at fracture intersections and within fractures. Here we demonstrate with two different types of laboratory experiments how the complexity of such flows affects the discharge behavior: (1) In order to isolate the mass partitioning process at fracture intersections we use custom-made acrylic cubes to establish a set of vertical fractures (free-surface, bounded by one side only) intersected by horizontal fractures. In order to control the prevailing flow mode we use a multichannel dispenser and set flowrates to critical thresholds for each regime. We then calculate normalized horizontal fracture inflow rates and delineate classical Washburn-type behavior in order to obtain an analytical transfer function for the given system and extended fracture cascades. (2) In order to study the effect of a porous matrix adjacent to the fractures we carried out quasi-2D laboratory experiments of infiltration into complex fracture networks using Seeberger sandstone slices. The system allows to study both the onset of preferential fracture flow dynamics as well as the porous matrix imbibition under dynamics conditions. To study the effect of geometry on discharge dynamics we modify fracture apertures as well as fracture offsets, i.e., the geometry of the fracture intersections. Results show that, despite the complex internal flow dynamics, clear scaling patterns can be observed and the geometrical characteristics are imprinted into the outflow behavior.

How to cite: Noffz, T., Rüdiger, F., Dentz, M., and Kordilla, J.: Analogue laboratory experiments of preferential flow dynamics in porous fractured media: Importance of fracture intersections and porous matrix imbibition processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22593, https://doi.org/10.5194/egusphere-egu2020-22593, 2020.

Saline water evaporation from a single meniscus plays an important role in determining the general dynamics of evaporation from porous media filled with saline water, which is relevant to several processes such as soil salinization, land-atmosphere interaction and soil moisture-precipitation interactions. Fundamental understanding of the mechanisms controlling solute transport and deposition in single capillary tubes is a necessary step to describe saline water evaporation and solute precipitation in complex porous media (Norouzi Rad et al., 2013; Shokri-Kuehni et al., 2017a; Shokri-Kuehni et al., 2017b). Within this context, we utilized dual energy imaging using synchrotron X-ray micro-tomography (Shokri-Kuehni et al., 2018) to investigate solute transport and deposition during evaporation from single capillary tubes of square and circular cross sections with lateral dimension of 1 mm and 3 mm (two sizes per cross section which resulted in four capillary tubes in total). The capillary tubes were filled with CaI2 solution of 5% concentration (by weight) and were placed under similar evaporative conditions. All boundaries were closed except top which was exposed to air for evaporation. The drying capillary tubes were scanned approximately once every hour for nearly 20 hrs. The recorded images enabled us to quantify solute concentration with a high spatial and temporal resolution throughout the capillary tubes with different sizes and cross sections and delineate the key transport mechanisms controlling solute transport and preferential deposition during evaporation. Our findings clearly show the contribution and impact of corner flow observed in square capillary tubes on the spatio-temporal distribution of solute, the evaporative mass losses and the velocity of the receding meniscus. The obtained results extend the fundamental understanding required for describing the transport mechanisms controlling saline water evaporation from porous media.

References

Norouzi Rad, M., N. Shokri, M. Sahimi (2013), Phys. Rev. E, 88, 032404.

Shokri-Kuehni, S.M.S., T. Vetter, C. Webb, N. Shokri (2017a), Geophys. Res. Lett., 44, 5504–5510.

Shokri-Kuehni, S.M.S., M. Norouzirad, C. Webb, N. Shokri (2017b), Adv. Water Resour., 105, 154-161.

Shokri-Kuehni, S.M.S., M. Bergstad, M. Sahimi, C. Webb, N. Shokri (2018b), Sci. Rep., 10, 10731, London: Nature Publishing Group.

How to cite: Shokri, N., Shokri-Kuehni, S. M. S., and Shojaei, M. J.: Dynamics of solute transport in capillary tubes delineated by dual energy imaging , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10737, https://doi.org/10.5194/egusphere-egu2020-10737, 2020.

X-ray computational tomography (CT) is becoming more and more popular research tool in geosciences. Estimation of the saturated conductivity of the porous media based on X-ray CT images is an example of its application. In case of simulations for the pore media, which are approximated by the very complicated meshes, problems might arise when mesh does not follow the shape of pore-space ideally, which may happen due to limitations imposed (e.g. due to some technical constraints) on minimum mesh cell size which usually is bigger than CT scan resolution used for determination of the pore space. If this is the case, the mesh can’t be generated properly in the narrow regions of the pore-space.

The work tries to quantify the impact of the limited mesh quality on estimation of the saturated conductivity coefficient. Four mesh generation parameters, resulting in different sizes of the minimum mesh cell size, were compared. For comparison five different pore media (three sandpacks prepared from different sand fractions and two types of sandstones) were used, all of them were used in two repetitions which resulted in 10 studied samples in total. First samples were X-ray CT scanned with resolution 2um. Than images were thresholded to obtain information about pore-space. In the next step, for all of 10 3D images of pore-space, mesh was generated in four repetitions differing with minimum mesh cell size: 2.56, 3.41, 5.12 and 10.25 times greater than voxel size used for CT scanning.

Saturated conductivity was simulated based on prepared meshes using finite volume based solver of the Navier-Stokes equations. Estimated for each sample saturated conductivity differed from 12% for coarse media to 200% for fine grain media for different numerical meshes representing with different accuracy pore space geometry.

Based on samples studied, one may conclude that for optimal results of saturated conductivity numerical estimation, the smallest numerical mesh’s cell size should be of the level of pore media CT scan resolution.  

Acknowledgments:

This work was partially supported by a grant from the Polish National Centre for Research and Development within the contract no.: PL-TW/IV/5/2017.

How to cite: Lamorski, K., Gackiewicz, B., Sławiński, C., Hsu, S.-Y., and Chang, L.-C.: Numerical modelling based saturation conductivity estimation uncertainty – influence of the quality of the pore space geometry representation based on X-ray CT images, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19695, https://doi.org/10.5194/egusphere-egu2020-19695, 2020.

The measurement of the water potential is important to characterize solute transport in soil and water uptake by plants. Many researchers have characterized the matric potential and its impact on evaporation from porous media. However, only few studies have been carried out to characterize the effect of the osmotic potential. In this study, we investigated the simultaneous influences of the osmotic and matric potentials on the evaporation from soil. Our hypothesis was that both potential components affect the two stages of evaporation and that the osmotic potential in direct vicinity of the soil surface is a controlling variable. To meet our objective, we performed evaporation experiments on columns filled with pure quartz sand and natural soil materials with different textures, under climate-controlled laboratory conditions. The soils were initially saturated with different concentrations of saline solutions and evaporation from each column was measured daily. Our results show that the osmotic potential reduced the amount of evaporated water from the investigated porous media. The amount of reduction due to the osmotic potential is compared with model calculations that consider the total water potential at the soil surface.

How to cite: Salman, A., Joshi, D., Naseri, M., and Durner, W.: Evaporation from porous media as influenced by osmotic potential, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9693, https://doi.org/10.5194/egusphere-egu2020-9693, 2020.

The understanding of hydrological processes requires the investigation of preferential flows. In particular, the infiltration compartment is strongly affected by preferential flows. Recently, Lassabatere et al. (2014) proposed a model for the analytical modelling of the infiltration impacted by preferential flow. These authors extended the model developed by Haverkamp et al. (1994) for single permeability soils to the case of dual permeability soils. However, this model remains implicit, requiring an inversion procedure for the quantification of the bulk cumulative infiltration. Such an implicit feature prevents from direct computation and may annoy any fellow who wants a direct and simple computation procedure. In this paper, we develop two approximate expansions for both transient and steady states. For that, we use the expansions proposed by Haverkamp et al. (1994) for single permeability systems. These expansions are written for each compartment of the dual permeability soils, i.e. the matrix and the fast-flow regions and are combined for the computation of the bulk infiltration. After formulation of these expansions, these are assessed in terms of their capability to accurately reproduce the complete implicit model. Their validity time intervals are also determined and discussed. The main limitation for the use of these expansions results from the fact that the time intervals that define the transient and steady states are contrasted between the matrix and the fast-flow regions. However, some domain of validity can be defined allowing the use of these approximate expansions.

Haverkamp, R., Ross, P. J., Smettem, K. R. J. and Parlange, J. Y.: 3-Dimensional analysis of infiltration from the disc infiltrometer .2. Physically-based infiltration equation, Water Resour. Res., 30(11), 2931–2935, 1994.

Lassabatere, L., Angulo-Jaramillo, R., Soria-Ugalde, J. M., Simunek, J. and Haverkamp, R.: Numerical evaluation of a set of analytical infiltration equations, Water Resour. Res., 45, W12415, doi:doi:10.1029/2009WR007941, 2009.

How to cite: Lassabatere, L., Di prima, S., Iovino, M., Bagarello, V., and Angulo-Jaramillo, R.: Approximate expansions for water infiltration into dual permeability soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5172, https://doi.org/10.5194/egusphere-egu2020-5172, 2020.

Preferential flow is more the rule than the exception, in particular during water infiltration experiments. In this study, we demonstrate the potential of GPR monitoring to detect preferential flows during water infiltration. We monitored time-lapse ground penetrating radar (GPR) surveys in the vicinity of single-ring infiltration experiments and created a three-dimensional (3D) representation of infiltrated water below the devices. For that purpose, radargrams were constructed from GPR transects conducted over two grids (1 m × 1 m) before and after the infiltration tests. The obtained signal was represented in 3D and a threshold was chosen to part the domain into wetted and non-wetted zones, allowing the determination of the infiltration bulb. That methodology was used to detect the infiltration below the devices and clearly pointed at nonuniform flows in correspondence with the heterogeneous soil structures. The protocol presented in this study represents a practical and valuable tool for detecting preferential flows at the scale of a single ring infiltration experiment.

How to cite: Di Prima, S., Winiarski, T., Angulo-Jaramillo, R., Stewart, R. D., Castellini, M., Abou Najm, M. R., Ventrella, D., Pirastru, M., Giadrossich, F., and Lassabatere, L.: Ground-penetrating radar surveys for the detection of preferential flow into soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4177, https://doi.org/10.5194/egusphere-egu2020-4177, 2020.

Cardoon (Cynara cardunculus L.) is a promising energy crop for marginal areas in Mediterranean environment. Temporary intercropping with cover crops can provide multiple services such as weed suppression, additional and diversified biomass production and soil physical quality (SPQ) improvement.

A number of studies have demonstrated that the Beerkan estimation of soil transfer parameters (BEST) method appears promising for assessing SPQ in agricultural soils, given that it allows the entire determination of the water retention and hydraulic conductivity curves, and the derivation of both static and dynamic SPQ indicators in the field. However, BEST is suitable only for single-permeability (SP) soils. Lassabatere et al. (2019) designed a method for the hydraulic characterization of dual-permeability (DP) soils named BEST-2K to address the case of the soils prone to preferential flow. DP models are increasingly adopted in soil science to take better account of water flow dynamics in heterogeneous soils. Moreover, recent investigations suggested that a comprehensive assessment of SPQ of agricultural soils also involving DP approaches may substantially improve our capacity to evaluate the effect of specific management practices on key “domain-oriented” processes. Indeed, DP models assume that soil encompass two domains, including the matrix and the fast-flow domain that respectively host the smallest and the largest pores. While in the matrix domain the intra-aggregate pores constitutes the primary source of plant-available water and nitrous oxides, in the fast-flow domain the inter-aggregate pores are the primary region for root-essential air, carbon dioxide generation and nutrient leaching losses (Reynolds, 2017).

We investigated the effects of temporary intercropping with cover crops belonging to different functional groups on SPQ. In October 2019, an experimental trial intercropping Cynara cardunculus cv Bianco Avorio with four different cover types (3 cover crops: Vicia villosa Roth. cv Haymaker Plus, Eruca sativa L. cv Nemat and Camelina sativa (L.) Crantz. cv Italia and spontaneous weeds) was set up at the Ottava experimental station of the University of Sassari (Sardinia, IT).

The new BEST-2K method was used for assessing SPQ of the different intercropping systems. At this aim, we carried out multi-tension infiltration experiments in order to selectively activate only the matrix or the whole pore network, and for the characterization of the water retention and hydraulic conductivity functions of matrix and fast-flow domains. Then, we used these functions to determine SPQ indicators for the two domains. A zero-point scenario (1 month after sowing) has been already drawn. The field measurements will be repeated in summer after the harvest of the above-ground biomass of both cardoon and cover crops.

References

Lassabatere, L., Di Prima, S., Bouarafa, S., Iovino, M., Bagarello, V., Angulo-Jaramillo, R., 2019. BEST-2K Method for Characterizing Dual-Permeability Unsaturated Soils with Ponded and Tension Infiltrometers. Vadose Zone Journal 18. https://doi.org/10.2136/vzj2018.06.0124

Reynolds, W.D., 2017. Use of bimodal hydraulic property relationships to characterize soil physical quality. Geoderma 294, 38–49. https://doi.org/10.1016/j.geoderma.2017.01.035

How to cite: Giannini, V., Di Prima, S., Mula, L., Marrosu, R., Pirastru, M., Lassabatere, L., Angulo-Jaramillo, R., and Roggero, P. P.: Assessing the effects of cardoon intercropping with different cover crops on soil physical quality with BEST-2K method and automatic infiltrometers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7919, https://doi.org/10.5194/egusphere-egu2020-7919, 2020.

In natural systems, preferential flow is the rule rather than the exception. Non-uniform and preferential flows significantly impact mass transport, and by this way most of geochemical processes and pollutant dispersion in the environment. Laboratory columns are experimental devices used for the monitoring of solute transfer through porous. In particular, several studies used such experimental devices for characterizing mass transfer through heterogeneous systems and macropored systems. However, the design of these devices and its impacts on the experimental results has never been investigated in depth so far. In particular, the edge effect is rarely questioned and the transfer is always hypothesized to correspond to a fully developed flow (i.e., flow in an equivalent infinite system). In this study, we question this hypothesis both experimentally and numerically for the case of a macropored system. Tracer elutions, magnetic resonance imaging (MRI), and modeling using multiphysics approaches (Comsol) are conducted to demonstrate that flow is affected by edge effects close to the inlet and the outlet of the column, and that the presence of filters (used to prevent particles from exiting the system and clogging the outlet) do impact the flow and transfer breakthrough. Consequently, these edge effects should be considered when analyzing the results and concluding on the involved processes, in particular for the case of soils and systems with macropores.

How to cite: Raimbault, J., Lassabatere, L., Peyneau, P.-E., Courtier-Murias, D., and Béchet, B.: Is breakthrough of solute impacted by the edges of the columns in the case of macropored systems?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8220, https://doi.org/10.5194/egusphere-egu2020-8220, 2020.

The transfer of water and solutes between soil matrix and macropores controls preferential flow. Mass transfer depends on soil structural geometry and on properties of biopore walls and crack coatings that can differ from those of the matrix with respect to texture, organic matter, bulk density, and porosity. Agrochemicals and other solutes can react during transport along macropores, which has yet not been well-considered. The objective of this study was to study the specific effects of sorption on the reduction of mass exchange due to the effects of sorption at the macropore-matrix interface. Field and lab percolation experiments under unsaturated flow conditions were carried out with intact soil columns to simulate movement of bromide as a conservative and Brilliant Blue, iodide, and Na-Fluorescein as a reactive tracer. Sorption properties were determined separately for the biopore walls and crack coatings. The results suggest that preferential transport of reactive solutes depends even more strongly on the geometry and properties at flow paths surface than conservative solutes. If these properties can be determined, mass transfer coefficients in two-domain models can be related to soil structure and management.

How to cite: Gerke, H. H., Dusek, J., Leue, M., Beck-Broichsitter, S., Sobotkova, M., Dohnal, M., Vogel, T., Snehota, M., Cislerova, M., Ellerbrock, R. H., and Haas, C.: Soil macropore-matrix mass exchange tracer experiments that account for sorption at macropore walls, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17727, https://doi.org/10.5194/egusphere-egu2020-17727, 2020.

Flow heterogeneity strongly impacts mass transport. In particular, the presence of water fractionation into mobile and immobile water fractions may affect pollutant sorption to soil particles. Indeed, before sorbing, the pollutants need to diffuse from mobile water to immobile water fractions. In a previous study, we investigated the possibility of stop-flow experiments for the detection of physical and chemical non-equilibria. A sensitivity analysis proved that it was possible to detect the two types of non-equilibria. The effect of parameters related to physical  (mobile water fraction and solute exchange rate)  and chemical (chemical kinetics) non-equilibria were varied and related impacts on the shape of the breakthrough curves were characterized for stop-flow experiments. However, the feasibility of inverting procedures was not investigated at all. In particular, the estimation of these parameters by fitting the model to real experimental data (with noise) may be feasible but may also bring some uncertainty with biased and non-unique estimates. In this study, using both numerically generated data and experimental data, we characterize the estimate uncertainty and equifinality. This study will help in optimizing the inverting procedure for the design of more robust and less biased estimates and the quantification of physical and chemical non-equilibria parameters.

How to cite: Zhou, L., Lassabatere, L., and Hanna, K.: Inverting stop-flow leaching experiments and detection of physical and chemical non-equilibria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22395, https://doi.org/10.5194/egusphere-egu2020-22395, 2020.

Freshly deposited tailings define finely crushed rock rarely altered by weathering processes. In modelling water flow and solute transport for saturated and unsaturated conditions in deposited tailings, the hydraulic parameters are essential required parameters. It has been proposed that these parameters vary as the materials evolve through weathering processes which transform minerals and hence chemical and physical properties. Several methods, destructive and non-destructive, have been used to determine the change of these parameters. The evaporation method as a non-destructive method, for deriving hydraulic parameters of porous media can be employed to monitor the overall changes in the pores as the properties of the porous matrix changes. In order to test this hypothesis, 25% of pyrite, 25% of dolomite, 35% of quartz and 15% of chlorite, reflecting typical acid producing, acid neutralising and inert minerals were mixed to form artificial tailings. The mineral admixture was mixed at a water content of 10% and allowed to equilibrate for two weeks before the start of the experiment. The mineral admixture was packed to a bulk density of 1.4 g/cm³. The hydraulic parameters for the near saturation state were measured using the simultaneous measurement of water content and water potential as a consequence of evaporation. The mineral admixture was subjected to 9 drying and wetting cycles over a period of 9 months. The hydraulic parameters were estimated using RETC and HYDRUS 1D. After 9 months of drying and wetting, there was a slight change in the bulk density of the material. This change had an overall effect on the subsequent hydraulic parameters. This study implies that feedback effects should be considered in modelling ageing of mine tailings.

How to cite: Akesseh, R., Edraki, M., and Baumgartl, T.: Examining saturated and unsaturated hydraulic parameter changes as a result of geochemical reactions in tailings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6213, https://doi.org/10.5194/egusphere-egu2020-6213, 2020.

Numerical modelling is a tool allowing the prediction of water flow and water balance based on material properties and time dependent input information at defined boundaries. Long time series are often required for a well informed assessment of the performance of a site. It has been shown that covers as a preferred option constructed in semi-arid and arid climates on mine sites to manage water flows and to prevent deep drainage have a characteristic bi-modal pore system largely caused by a large fraction of coarse rocks. Bi-modal water retention curves have been established for such covers which have proven to describe the response to precipitation with higher accuracy. Meteorological data as input information are in many cases only available on a daily basis if time series over decades are used for modelling. For a bi-modal pore system with often very high values for saturated hydraulic conductivity, a daily time-step may be to large to capture numerically the response in water flow. The objective of the presented work is the comparison of modelled deep drainage data for a specific cover design where hourly data are compared with daily input data. The latter were aggregated from the hourly information.

The results from the numerical modelling showed that for environments with high intensity rainfall events the calculated amount of deep drainage was by up to 10% smaller for the aggregated daily input data compared to the hourly data.

The presentation will inform which rainfall events contributed primarily to the difference in the water balance parameters and to which extent a generalisation can be made on the choice or requirement to choose an appropriate time step for specific climatic conditions.

How to cite: Baumgartl, T. and Shaygan, M.: The effect of the choice of time resolution on the prediction of deep drainage rates in rocky covers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20305, https://doi.org/10.5194/egusphere-egu2020-20305, 2020.

A key risk to reclamation covers over oil sands shale overburden is salinization of the cover soil due to salt transport from the underlying shale. The objective of this study was to evaluate controls on salt ingress based on observations and modelling of the transport of a conservative chemical species, chloride (Cl-), and a produced species, sulphate (SO42-) within reclamation profiles at the South Bison Hills overburden dump located north of Fort McMurray, Alberta, Canada.  The SO42- is produced as a result of pyrite oxidation.  Previously developed water dynamics models, including a fully coupled water and heat transfer model (CM) and a modified CM model (CM-EI) to account for enhanced snow melt infiltration, were coupled with an advective-dispersive transport model to simulate the observed Cl- profiles and concomitantly constrain the solute transport parameters.  This transport model was then used to simulate SO42- migration to evaluate the impact of pyrite oxidation (i.e. depth and SO42- production rate) on the evolving SO42- profiles.  It was found that the observed SO42- distributions could be simulated using an initially low rate of SO42- production (0.1 g SO42- m-2 d-1) in the first 5 years while macropore development as a result of freeze/thaw and wet/dry cycling was occurring, followed by a higher rate (0.62 g SO42- m-2 d-1) once this soil structure evolution was complete.  These average rates were applied over a shale depth of 0.75 m, consistent with field observations of oxygen ingress.  Mass balance estimates using measured available pyrite suggest that at these rates oxidation could continue for approximately 93 years.  Inclusion of enhanced snow melt (CM-EI model) results in higher rates of both net percolation and evapotranspiration (ET). The increased net percolation enables more rapid flushing of the produced SO42- deeper into the profile; however, the increased ET also draws produced SO42- into the cover soils. It is therefore likely that short-term soil salinization of the base of the covers is exacerbated by increased snowmelt infiltration, while in the long run salinity levels will drop due to increased net percolation.   

How to cite: Huang, M., Ireson, A., and Barbour, L.: Effects of snow melt infiltration and geochemical oxidation on the distribution of sulphate in reclaimed oil sands shale overburden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1548, https://doi.org/10.5194/egusphere-egu2020-1548, 2020.

Preferential flow pathways (PFPs) are key contributors for the ecological status of the hydrosphere in high mountain environments, as the precipitation will transfer to PFPs with rapid solute transport from soil to groundwater. This particularly refers to nutrient allocation from soils to groundwater and surface waters.

To understand the effects of the pedogenesis and forest types on the soil PFPs, the soil preferential flow was studied by in situ dye tracing image analysis and elemental chemical analysis at the Hailuogou glacier chronosequence, Gongga Mountain on the eastern Tibetan Plateau. A soil chronosequence and a vegetation primary succession following the retreat of the Hailuogou glacier has been forming since ~1890. Three sites representing different exposure age (45, 85 and 125 years) in the Hailuogou glacier retreat area chronosequence and two sites typical forest lands (deciduous broadleaf forest and coniferous forest) were selected to carry out a brilliant blue dyeing experiment to visualize the distribution of water infiltration in soil.

The tracer-infiltration patterns were parameterized by dye coverage (DC), preferential flow fraction (PF), length index (L_i) and the variation coefficient of DC in the PFPs (C_V). Furthermore, the distribution of PFPs, transported solute of soil PFPs was analyzed including Hailuogou glacier chronosequence and vegetation succession.

According to the comparison of PFPs parameters, soil PFPs at the 125-year-old site extremely more developed than that at the younger site due to the fracture development between rock and soil on the process of soil development. The soil PFPs under broadleaf forest is more pronounced than that in coniferous forest soils, largely depending on the different root system.

In general, PFPs in Gongga Mountain were important contributors to the potential translocation of bioavailable inorganic P (PBPi) and organic P translocation to the hydrosphere. The elements transported with PFPs could be divided into three categories, reactive, conservative, and both reacted and conservative elements for the concentration of the elements remain in the PFPs. The results indicated that Mg and Al are the reactive elements, while Na, K, Ca and Mn are the conservative elements in the PFPs. Iron is both reacted and conservative element in the PFPs. Zn, Na, K, Mg, PBPi, had a significant correlation with the variation coefficient of DC in the PFPs (C_V).

The results highlight the effects of the pedogenesis and forest types on the distribution of PFPs and solute transfer. Preferential flow contributes largely to elements flow at the Hailuogou glacier chronosequence and vegetation succession, Gongga Mountain.

The financial support of this work was obtained from National Natural Science Foundation of China (Grant No. 41272220) and Natural Scientifc Foundation for Young Scientists of Guangxi Zhuang Autonomous Region of China (Grant No. 2017GXNSFBA198162). The first author was financially supported by the Sino-German (CSC-DAAD) Postdoc Scholarship Program funded by China Scholarship Council (CSC) and Deutscher Akademischer Austausch Dienst (DAAD).

How to cite: Liang, J.-H., Wu, Y.-H., and Guggenberger, G.: Distribution of preferential flow pathways and solute transfer along the Hailuogou Glacier Chronosequence on the Eastern Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19059, https://doi.org/10.5194/egusphere-egu2020-19059, 2020.

Soil water repellency is a common feature of dry soils under permanent vegetation and drought conditions. Soil-water hydrology is markedly affected by soil-water repellency as it hinders infiltration, leading to enhanced surface runoff and soil erosion. Although this phenomenon was primarily ascribed to sandy soils, it has been observed in loam, clay, and peat soils in dry and humid regions. One detrimental effect of soil water repellency on plants is the reduction of soil water availability that stems from the non-uniform water retention and flow in preferential pathways (gravity-induced fingers) with relatively dry soil volume among these paths. It was recently discovered that prolonged irrigation with treated wastewater, a widely used alternative in Israel and other Mediterranean countries due to the limited freshwater, triggers soil water repellency which invariably resulted in preferential flow development in the field. Due to climate change events, the use of treated wastewater for irrigation as a means of freshwater conservation is expected to widen, including in countries that are not considered dry.

While a vast amount of research has been devoted to characterizing the preferential flow in water repellent soils, the effect of this flow regime on the spatial distribution of salt and fertilizers in the root zone was barely investigated. Results from a commercial citrus orchard irrigated with treated wastewater that includes the spatial and temporal distribution of preferential flow in the soil profile measured by ERT will be demonstrated. The associated spatial distribution of salinity, nitrate, phosphate, and SAR in the soil profile will be shown as well.  We investigated the efficacy of two nonionic surfactants application to remediate hydrophobic sandy soils both in the laboratory and field. The effect of the surfactant application to the water repellent soils in the orchards on the spatial distribution of soil moisture and the associated agrochemicals will be presented and discussed.

How to cite: Ogunmokun, F. A. and Wallach, R.: Induced uneven spatial distribution of agrochemicals due to preferential flow in water repellent soils and its remediation by surfactant , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2974, https://doi.org/10.5194/egusphere-egu2020-2974, 2020.