HS8.3.1

The fate and transport of metallic nanoparticles (NPs) in the soil has been a major concern over the last decade due to the increasing use of NPs in many industries and their appearance in the environment. However, the study of NP fate and transport traditionally relies on intensive sample collection ana chemical analysis. In this work we use spectral induced polarization (SIP) to monitor the transport of metallic NPs in soils. In SIP, an alternating current in wide range of frequencies is injected, and the phase and amplitude difference between the injected and induced potential are measured. Our experimental setup involves flow-through columns packed with different types of soil, through which a suspension of NPs with different ionic compositions is passed. Electrical potentials are recorded at three locations along the column. The analyzed SIP measurements allow not only non-invasive, non-destructive monitoring of the NP’s progression through the soil but also deduction of the NPs’ fate and transport patterns through combination with elemental analysis. The sensitivity of SIP to the presence of the NPs is high and was found to be correlated to their progression in the soil even in low and environmentally relevant NP concentrations (<5mg/L).  Our results indicate that SIP is a promising method for monitoring of NPs in the soil and with further research may serve as an easy and efficient alternative to the standard methods that involve extensive water and soil sampling.

How to cite: Ben Moshe, S. and Furman, A.: Monitoring nanoparticle progression and fate in the soil using spectral induced polarization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-195, https://doi.org/10.5194/egusphere-egu22-195, 2022.

Stony soils are soils with a considerable volume of rock fragments (RF). They influence the soil hydraulic properties (SHP), including the water retention curve (WRC) and hydraulic conductivity curve (HCC). However, because of the challenges in the measurement and modeling of SHP in stony soils, RF are normally neglected in hydrological and land surface modeling.

In the present study, we measured SHP of stony soils with volumetric RF contents up to 50 % (v/v) in the laboratory using the simplified evaporation method. Afterward, we applied Hydrus 2D/3D software to create virtual stony soils with impermeable RF up to 37.3 % (v/v) in three spatial dimensions, 3D. The evaporation and multistep unit gradient experiments were simulated for the virtual stony soils, and inverse modeling in 1D was applied to identify their effective SHP. The identified effective SHP by measurement and inverse modeling were used to evaluate the available scaling models of hydraulic conductivity, such as the simple scaling model based on only the volume of RF (Ravina and Magier, 1984), and the most recent model, GEM, proposed by Naseri et al. (2020).

From the lab experiments, we successfully identified SHP of these stony soils for pressure heads from near saturation to -1000 cm. We also found that scaling the WRC of the background soil based on the volume of rock fragments gave reasonable effective SHP for low RF content, but was not appropriate for the highly stony soils. A higher reduction in conductivity was visible compared to the predicted values by the model of Ravina and Magier. Furthermore, comparison of the evaluated scaling models displayed a better performance of the GEM model especially when volume of RF in soil was low.

References:

Naseri, M., Peters, A., Durner, W. and Iden, S.C., 2020. Effective hydraulic conductivity of stony soils: General effective medium theory. Advances in Water Resources, 146, p.103765. DOI: 103765doi.org/10.1016/j.advwatres.2020.103765.

Ravina, I. and Magier, J., 1984. Hydraulic conductivity and water retention of clay soils containing coarse fragments. Soil Science Society of America Journal, 48(4), pp.736-740. DOI: 10.2136/sssaj1984.03615995004800040008x.

How to cite: Naseri, M., Iden, S. C., and Durner, W.: Effective Hydraulic Properties of Stony Soils: Simulation, Laboratory Experiment and Modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-644, https://doi.org/10.5194/egusphere-egu22-644, 2022.

Cosmic-Ray Neutron Sensing (CRNS) is a modern technique for non-invasive soil moisture estimation at the field scale. It closes the scale gap between point-scale observations (e.g. soil sampling, in-situ sensors) and coarse-scale satellite-derived estimates. While CRNS has a large horizontal footprint with a radius of roughly 150 m around the instrument, the average vertical measurement depth is only about 30 cm. Thus, extrapolating the CRNS-derived soil moisture to greater soil depths such as the entire root zone can be highly beneficial for hydrological applications such as landscape water balancing or irrigation management. To this end, previous studies have used, for instance, additional in-situ sensors and time-stability approaches or calibrated exponential filters against reference measurements in deeper soil depths.

However, additional permanent in-situ sensors and reference measurements in greater depths are not always available or feasible. Against this background, we use the physically-based soil moisture analytical relationship (SMAR) which can be used without calibration against reference measurements. We estimate the required model parameters from soil characteristics (e.g. porosity, water content at field capacity and wilting point) as well as from the CRNS soil moisture time series itself.

As CRNS for soil moisture estimation is developing rapidly, new transfer functions from observed neutron intensities to surface soil moisture have been introduced. We investigate the influence of using both the standard transfer function and the recently introduced universal transport solution (UTS) on the depth-extrapolated soil moisture time series. These depth-extrapolated soil moisture time series are then evaluated against soil moisture reference time series from in-situ soil moisture sensors down to 450 cm depth.

How to cite: Rasche, D., Blume, T., and Güntner, A.: Extrapolating field-scale near-surface soil moisture information from Cosmic Ray Neutron Sensing to greater depth, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3721, https://doi.org/10.5194/egusphere-egu22-3721, 2022.

In recent years, models for the unsaturated hydraulic conductivity have emerged that separate the soil hydraulic conductivity to constituting conductivities of water held in soil pores by capillary forces and of water adsorbed in films on the surface of soil grains. Some models include an equivalent hydraulic conductivity that accounts for diffusive movement of water vapor. The bulk soil hydraulic conductivity for a particular matric potential is the sum of these constituting conductivities.

The additivity attribute of the constituting conductivities relies on implicit assumptions regarding the configuration of the three domains: capillary water, water adsorbed in films, and the gas phase. These assumptions are not met in natural soils, and so alternatives to straight-forward addition are examined.

This examination unfortunately shows that any type of averaging of the constituting hydraulic conductivities leads to a non-monotonic hydraulic conductivity curve if the capillary water content reaches zero at a distinct matric potential above oven dryness. In fact, a correct expression for the hydraulic conductivity based on physically sound configurations of the domains can be shown to be realistically unattainable, leaving us without many alternatives for the additive model.

This being the case, an additive conductivity model and one alternative that is also unconditionally monotonic are introduced for a recently described parameterization of the soil water sigmoidal retention curve with a distinct air-entry value and a logarithmic dry branch terminating at a finite matric potential.

How to cite: de Rooij, G. H.: The difficulty of finding conceptually correct yet practically feasible unsaturated hydraulic conductivity curves., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6499, https://doi.org/10.5194/egusphere-egu22-6499, 2022.

The agricultural production in coastal environments is challenging. In the low-lying farmlands along the Venice Lagoon, Italy, saltwater intrusion that naturally occurs in coastal environments is exacerbated by land subsidence, seawater encroachment along the main watercourses, peat oxidation, and peat-driven salinity. Sea level rise expected in the next decades will intensify seawater contamination, enhancing the threats for crop productions. In this context, mitigation strategies are fundamental to avoid the loss of agricultural land. To this end, a test of freshwater recharge through a ~200-m long buried drain was conducted in an experimental field located at the southern margin of the Venice Lagoon. The soil is mainly silt-loam with the presence of acidic peat and sandy drifts. The drain was installed in 2021 at 1.5 m depth along a sandy paleochannel crossing the area in southwest to northeast direction. It supplies the Morto Channel freshwater to the farmland taking advantage of the high hydraulic conductivity of the sandy soil and the 2-m elevation difference between the channel water level and the farmland surface. The drain was tested at the end of the 2021 maize growing season, from August, 2^nd until September, 7^th. Five monitoring stations were installed and equipped with a 2.5 m deep piezometer to monitor depth to the water table and electrical conductivity (EC_w) and TEROS 12 (METER Group, Inc., Pullman, WA, USA) soil moisture, electrical conductivity (EC_b), and temperature sensors installed at four depths (0.1, 0.3, 0.5, and 0.7 m). Three of those stations were placed along the paleochannel (S1, S2, S3), while S4 and S5 were placed outside about 30 m away. Moreover, six additional piezometers were placed at 5, 10, and 20 m from both sides of S2 station to monitor the lateral spread of freshwater supply. Stations S1 and S2 were also equipped with electrical resistivity tomography (ERT) lines crossing the recharging infrastructure. The ERT lines were 14.4 m long, electrode spacing was 0.3 m and the resistivity electrode array was dipole-dipole, obtaining a maximum depth of investigation equal to approx 2.5 m. Data were collected on five dates, two before (7/12 and 7/30) and three after the drain opening (8/10, 8/20, and 9/7). The freshwater supplied to the farmland caused an increase of resistivity at both S1 and S2, with higher resistivity differences between dates at S1, suggesting a certain effectiveness of the implemented recharge solution. The EC_w measurements carried out in the piezometers show a highly variable response during the test, however EC_w increased after drain closure at all piezometers. On the contrary, the effects on soil water content and EC_b was negligible. The effectiveness of the strategy will be tested more deeply during the 2022 maize growing season by monitoring the effects of freshwater supply on plant stress and final crop yield.

How to cite: Zancanaro, E., Ilaria, P., Pietro, T., and Francesco, M.: A strategy to mitigate soil and water salinity in a coastal farmland at the southern margin of the Venice Lagoon: preliminary results from a 2021 recharge test, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7543, https://doi.org/10.5194/egusphere-egu22-7543, 2022.

The origins of the Richard’s equation date back more than a century but it is still the most commonly used model to describe variably saturated soil water movement. It requires the specification of the characteristic relationships between soil water content, tensiometric pressure and hydraulic conductivity, which can be subsumed as soil hydraulic models. Numerous soil hydraulic models and variants thereof have been developed to mimic the behaviour of natural soils, including hysteresis, macro-pore flow, and dynamic non-equilibrium flow. Despite the progress being made, it is often difficult to accurately simulate retention data derived from undisturbed field soils.

This work presents a benchmark inverse modelling study for 1D soil water movement and field retention data from a wetting-drying cycle using state-of-the-art soil hydraulic models. The main aim is to test the ability of the different models to reproduce the field data. The soil hydraulic models tested are, among others, the van Genuchten-Mualem model (VGM, 1976, 1980), VGM with hysteresis (Kool and Parker, 1987), Brooks-Corey (1966), Dual porosity (Durner, 1994) and the non-equilibrium flow model by Diamantopoulus (2015).

In our study, we used an implementation of the Richards equation with the highly efficient and numerically stable Methods-of-Line scheme. Best-fit estimates and parameter posterior distributions were derived using the Markov-Chain Monte Carlo sampling algorithm DREAM_ZS and time series of soil water content and tensiometric pressure. The field data shows clear signs of non-equilibrium flow. It originates from an intensively studied, inverted-lysimeter site with Pumice soils under grass from the central part of the North Island of New Zealand.

Results demonstrate that none of the models was able to accurately mimic soil water content and tensiometric pressure data simultaneously at all times. Model deficiencies were identified particularly for the two wetting events, where all models underestimated soil water content while tensiometric pressure matched the data closely. We hypothesise that at least part of the discrepancies relate to an oversimplification of the hydraulic conductivity function for non-equilibrium flow.

This study is limited to a single data set and by several assumptions that are commonly made in inverse parameter estimation studies. The better assessment and implementation of measurement error (structures) might alleviate (or mask) some of the discrepancies between model simulations and data. However, this is apparently not the solution to the problem. Dynamic non-equilibrium flow has been observed in natural soils in several well-conducted field experiments. Our results are just one example that demonstrates the need to improve soil hydraulic modelling by revisiting the physics of fundamental processes in natural soils. 

How to cite: Wöhling, T. and Mietrach, R.: Richard’s equation revisited – the challenge to reconstruct non-equilibrium field retention data with soil hydraulic models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7865, https://doi.org/10.5194/egusphere-egu22-7865, 2022.

This contribution illustrates the GEOframe Soil Plant Atmosphere Continuum Estimator (GEOSPACE). It is the ecohydrological model of the GEOframe system and it wants to simulate the soil-vegetation-atmosphere interactions to study and analyze the complex processes that occur in the Earth Critical Zone (CZ). The CZ is defined as the “heterogeneous, near surface environment in which complex interactions involving rock, soil, water, air, and living organism regulate the natural habitat and determine the availability of life-sustaining resources”.

GEOSPACE is a coupled model in which the three major components are WHETGEO, GEO-ET and BrokerGEO. WHETGEO, Water Heat and Transport in GEOframe, (Tubini N. and Rigon R., 2021), solves the conservative form of Richardson-Richards equation using the Newton-Casulli-Zanolli algorithm (Casulli V. and Zanolli P., 2010) that guarantees the convergence at any time step, and the proper transition from unsaturated condition to saturated one. Besides it deals seamlessly the surface water ponding. WHETGEO also implements the numerical solution shown in Casulli and Zanolli (2005) to solve the advection-dispersion equation and describe the solute transport. GEO-ET, EvapoTranspiration in GEOframe, computes evapotranspiration according to three different formulations, the Priestley-Taylor model, Penman FAO model and GEOframe-Prospero model (Bottazzi, 2020), by considering Jarvis model (Macfarlane et al., 2004) and Ball-Berry-Leuning model (Lin et al., 2015) to compute environmental and water stress factors. BrokerGEO is the coupler component that allow the exchange of data between the other two components in memory and considers the root water uptake for the computation of the actual evapotranspiration. The GEOSPACE model was tested with the lysimeter of the “Spike II” experiment (Nehemy et al., 2019; Benettin et al., 2021) of the Ecole Polytechnic Federal de Lausanne. The analysis we carried out with GEOSPACE concern the flux partitioning of precipitation and irrigation water into evaporation and transpiration; the soil water and groundwater storage; the transport of water stable isotopes through the soil. In this research we present them and show how GEOSPACE can be used to test hypotheses on the links between the plant water status and its isotopic signatures.

GEOSPACE is developed in Java using the Object-Oriented programming paradigm and it is completely open source, available on the GEOframe GitHub website. The code organization and its functionalities besides solving the hydrological issues are designed according to principle of open science to be inspectable and verified by third parties.

How to cite: D'Amato, C., Tubini, N., Benettin, P., Rinaldo, A., and Rigon, R.: The GEOframe Soil Plant Atmosphere Continuum Estimator (GEOSPACE) to investigate the vadose zone processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9284, https://doi.org/10.5194/egusphere-egu22-9284, 2022.

Water drop penetration time (WDPT), i.e. the time it takes for a water drop to be absorbed by the soil, is widely used as a measure of soil water repellency. Despite its popularity, little is known about the processes that govern WDPT and how WDPT is related to other soil hydraulic properties such as sorptivity. To shed some light on the physics of the WDPT, we measured apparent contact angles of sessile water drops on water repellent sand using a goniometer and compared apparent with effective contact angles of the same sand. Results showed that WDPT can be related to sorptivity by means of apparent and effective contact angles.

How to cite: Berli, M., Shillito, R., Inouye, S., Nikolich, G., and Etyemezian, V.: Water Drop Penetration Time Revisited, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10743, https://doi.org/10.5194/egusphere-egu22-10743, 2022.

A new monitoring network was setup to adequatly assess the hydryogelogical condtions within the vadose zone in Malta. The installation of the monitoring equipment allows for the measurement of water content along the vadose zone from distinct points and along varying. Data on water content variation with time and depth was collected throughout the rainy season of 2021 and 2022 from two sites within this network. The lithology of both sites consists of alternate bands of carbonate sediments with varying levels of porosity. The data generated from these two sites allowed for the continuous tracking of water percolation within the vadose zone and therefore enabled the evaluation of water flow velocities. It was observed that the intensity and frequency of occurence of rain events controls the initiation and downward propagation of wetting fronts along the carbonate litholgical sequence within the vadose zone. The initiated wetting fronts exhibited significant variations in the velocity of the draininage process as a result of the varying lithological sequence. The velocity of the drainage process and the variations in water storage content within the vadose zone were utlised to calculate the rate of groundwater recharge for these two sites.

How to cite: Schembri, M., Sapiano, M., Mamo, J., Debattista, H., and Dahan, O.: Insights on vadose zone hydrologeology within a carbonate setting: Preliminary results based on a new vadose zone monitoring system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12503, https://doi.org/10.5194/egusphere-egu22-12503, 2022.

A thorough understanding of preferential finger flow through the vadose zone is critical to deepen our knowledge on the processes of infiltration, runoff, erosion, plant growth, and contaminant transport. The paths formed during this fingered flow can be “remembered” by the soil matrix during future infiltration, even after periods of desaturation.

It has been shown many times that the traditional porous media equation, Richards’ equation, is incapable of capturing this phenomenon [1]. However, recent studies demonstrate the process can be described by combining a non-equilibrium, relaxation version of Richards’ equation [2] with Preisach hysteresis (applied to the pressure-saturation relationship). In this work, the authors build upon their previously published one-dimensional work [3]. The first part of this study is to present a numerical scheme for the two-dimensional non-equilibrium Richards’ equation using operator splitting methods. The second part is a comparison to previously published experimental results that demonstrates the ability of the model to capture realistic fingering behaviour.

[1] Nieber, J., et al. “Non-equilibrium model for gravity-driven fingering in water repellent soils: Formulation and 2D simulations.” Soil water repellency: occurrence, consequences and amelioration (2003): 245-258.

[2] G C Sander et al 2008 J. Phys.: Conf. Ser. 138 012023

[3] Roche, Warren & Murphy, K. & Flynn, Denis. (2021). Modelling preferential flow through unsaturated porous media with the Preisach model and an extended Richards Equation to capture hysteresis and relaxation behaviour. Journal of Physics: Conference Series. 1730. 012002. 10.1088/1742-6596/1730/1/012002.

How to cite: Roche, W., Flynn, D., and Murphy, K.: Numerical Simulations for Preferential Finger Flow Using a Two-Dimensional Non-Equilibrium Richards’ Equation with Preisach Hysteresis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13224, https://doi.org/10.5194/egusphere-egu22-13224, 2022.