How to cite: Animali, L., Corrado, S., Tuccimei, P., Bartoli, M., and Giorcelli, M.: Characterization and use of commercial biochar for water purification in real case scenarios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-326, https://doi.org/10.5194/egusphere-egu24-326, 2024.

Bio-geophysics is a very broad discipline, including a variety of physical monitoring techniques applied to biological processes. As such, it is inherently very challenging and, at the same time, very promising. A variety of scales are being investigated, from the cellular scale to the ecosystem scale. More relevant to the latter scale is the investigation of the plants root zone, where the majority of mass and (latent) energy balance takes place between the soil and biota and, from there, to the atmosphere. The response of the soil-water-vegetation system and of the Earth’s critical zone (from the top of the canopy to the bottom of the shallowest aquifer) to climate and land-use change is crucial for the preservation of essential ecosystem services such as carbon storage, primary productivity, food and materials availability, and water and erosion regulation. In addition, the interaction between atmosphere and land surface is one of the most critical points to be resolved to reduce epistemological uncertainties in atmospheric models, both for numerical weather prediction (NWP) and global and regional climate models (GCMs and RCMs). The use of geophysical techniques in this context provides dense high-resolution spatial information as well as, potentially, high temporal resolution monitoring. Two different viewpoints can be taken in this form of “bio-geophysical” monitoring: on one hand, the physical signals of the biological (e.g. root presence and signals) activity can be directly sought; on the other hand, the effects of biological activity (e.g. root water uptake) can be sensed by the resulting changes of the soil/water system state (especially in terms of moisture content, but also temperature, etc.). Examples of both types of approaches, and links to eco-hydrological modelling, will be presented in this contribution, urging towards a more frequent and more accurate applications of these techniques, particularly for their potential contribution towards a better definition of Land Surface Models, i.e. the bottom, critical, and poorly known boundary condition for atmospheric models.

How to cite: Cassiani, G., Peruzzo, L., Censini, M., Mary, B., and Iván, V.: Non-invasive monitoring of plant root activities in the framework of the Earth’s Critical Zone and soil-plant-atmosphere interactions., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3541, https://doi.org/10.5194/egusphere-egu24-3541, 2024.

This study investigated the influence of long-term irrigation management on plant water use with an emphasis on the development and activity of grapevine root systems in an irrigated vineyard under semi-arid conditions located in the Madrid region (central Spain). The study tested three types of irrigation management, based on the potential evapotranspiration ETp computed with varying crop coefficient Kc (0.2KC, under-irrigated. 0.4KC, control and 0.8KC, over-irrigated). Note that the irrigation water used is considered as highly saline (3890 μS/cm at 20°C).
The interpretation was supported by soil geophysical surveys with electrical resistivity Tomography (ERT), plant physiological traits, and drone-based remote sensing observations. The ERT collected before irrigation showed strong evidence of soil long-term changes, with a gradient of electrical resistivity (ER) increasing with the stress applied, while time lapse ERT before/after the irrigation season showed changes implying deeper root contribution to water uptake in the stressed area. However, uncertainties persisted in interpreting higher ER areas, as it was unclear whether they stemmed from increased soil moisture or were linked to soil salinity caused by soil sodicity.
Insights could be derived from proximal and remote sensing data, revealing patterns consistent with soil responses to the applied irrigation stress. Notably, the higher Normalized Difference Vegetation Index (NDVI), thermal-based actual evapotranspiration rates and stomatal conductance (gs) observed in the over-irrigated area, in contrast to the under-irrigated area, may suggest enhanced plant water accessibility and increased transpiration rates. 
The study paves the way towards the adoption of geophysical methods in combination with remote sensing to control irrigation management particularly in the context of saline water.

How to cite: Peruzzo, L., Mary, B., Burchard Levine, V., Guerra, J., Herrezuelo, M., Lovera, R., Casas, A., Cassiani, G., Nieto, H., and Pena, J.: Identification of long-term irrigation effect on plant water use from geophysical and proximal sensing observations: example of a vineyard, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3610, https://doi.org/10.5194/egusphere-egu24-3610, 2024.

Electromagnetic induction (EMI) allows time-lapse profiling of electrical conductivity (EC). In recent years, progress has been made in the study of the intra-field variability and soil-plant correlations at the scale of a few meters. Yet, some methodological challenges still hinder the possibility to resolve the spatiotemporal complexity at the smaller scales typically associated with irrigation and evapotranspiration (ET) dynamics, and thus central to the agroecosystems and precision agriculture, particularly in orchard farming.

This study characterizes the 3D EC variability in an orange orchard in eastern Sicily (Italy). To the best of our knowledge, this is the first 3D investigation capturing both irrigation and ET effects at the meter scale. The characterization successfully distinguishes plant rows and interrows dynamics. The EC in the plant rows increases upwards, from the drier root-water-uptake region to the drip irrigation region above. In the interrows, the EC increases downwards from the drier evaporation-dominated layer to the deeper soil where the irrigation water accumulates without significant ET. The intermediate zones, between the plant rows and interrows, show yet another conductivity profile, homogeneous and relatively conductive. Local effects, such as the plant size, further complicate this conceptual model and add both inter- and intra-row heterogeneity.

While the results confirmed the EMI potential, some methodological challenges were equally important. First, a Geophex GEM-2 and a CMD Mini-Explorer were used, the latter in vertical and horizontal configuration. The choice of instruments and surveys appears now suitable for this field site but it is surely not a priori obvious and/or always possible. We highlight how the use of a single instrument would probably lead to misinterpreting the root water uptake or the evaporation contributions.

Second, the quantitative use of the two instruments required alignment and joint inversion. However, a standard GPS system did not provide a reliable alignment of the surveys. Time-consuming GIS corrections were needed for both intra- and inter-dataset shifts. Third, after GPS alignment, the surveys were interpolated over a common grid to allow the joint inversion. Because of the strong anisotropy of the agroecosystems, this required the careful parametrization of a Kriging algorithm.

Fourth, the individual EMI datasets also differ because of their drift and/or calibration. The lack of convenient alternatives initially motivated an ERT-based calibration, but ultimately two of the twelve datasets were dismissed.

Fifth, noise and instrumental errors required the use of a moving-window median. This common practice poses a trade-off between smoothing and resolution that hinders high-resolution surveys.

Sixth, a sub area of the orchard was investigated at finer resolution. This proved fundamental for the identification of the processes acting at the intermediate zones, between the plant rows and interrows, and other meter-scale details.

Overall, this study presents a state-of-the-art EMI application that focuses on small-scale aspects that were less considered in previous studies. The presented challenges explain the lack of similar studies and should be considered when discussing the EMI convenience and adoption for precision irrigation applications.

How to cite: Cassiani, G., Werban, U., Pohle, M., Consoli, S., Longo-Minnolo, G., Vanella, D., and Peruzzo, L.: EMI surveys under precision irrigation contexts: an orange orchard-case study and methodological challenges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5746, https://doi.org/10.5194/egusphere-egu24-5746, 2024.

Circular economy requires reliable information about the content of old landfills regarding raw materials worth exploiting. Geophysical electrical methods are standard tools for such investigations; however, they require a galvanic contact between electrodes and the ground. Many landfills are covered by a shallow isolating layer consisting of an electrically resistive material (e.g., a PVC layer), which hinders current flow and significantly decreases the resolution and the signal-to-noise ratio (SNR). Low-induction electromagnetic methods have also been suggested for such investigations; yet these methods have a limited depth of investigation. To overcome these limitations, we investigate the applicability of the transient electromagnetic method to characterize an industrial landfill. The investigation is based on a TEM survey to define the positions of two deep boreholes  The combination of borehole and geophysical data aims at identifying the composition and distribution of waste, a prerequisite to evaluate its potential content of raw materials. We conducted TEM measurements in a large industrial landfill (ca. 500 m long, 200 m wide and 20 m deep) sealed by an impermeable PVC layer. The objectives of the TEM survey are: 1) the delineation of the landfill geometry 2) locating possible changes in waste composition and 3) identifying damages in the isolating PVC layer which might result in leachate migration below the landfill. We obtain TEM data with the TEM-FAST 48 instrument in a 12.5 m square single-loop configuration at 81 sounding locations to cover the entire plateau of the landfill. We demonstrate that the TEM signatures are affected by induced polarization effects, which is likely related to the presence of molybdenum and other relevant raw materials. To evaluate this observation, we conducted complementary measurements with the spectral induced polarization method using a large electrode spacing to enhance the SNR. We validated the TEM results using two 40 m deep boreholes that reach from the top of the landfill into the confining clay-rich layer.

How to cite: Aigner, L. and Flores Orozco, A.: Characterization of an urban landfill with the transient electromagnetic and spectral induced polarization methods to quantify raw materials and map leakages, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6124, https://doi.org/10.5194/egusphere-egu24-6124, 2024.

Removing Cr from contaminated (ground)water is often attempted via active remediation using easily deployable permeable reactive (barrier) materials, such as iron oxide mineral coatings. In particular, magnetite has been shown to be a highly effective and low-cost option for removing redox-active Cr from solution. Magnetite not only binds Cr, but it also reduces Cr(VI) to the less toxic and immobile Cr(III). Monitoring the extent of Cr retention in remediation schemes, however, relies on down-flow concentration sampling. Consequently, detectable levels of Cr must exit remediation barriers in order to detect the decreasing remediation efficiency of reactive materials with the progression of immobilization. Spectral induced polarization (SIP), a non-invasive geophysical technique sensitive to sorption-induced changes in the surface charging properties of mineral surfaces in porous media, offers a potentially powerful monitoring alternative to detect changes in remediation efficiency in situ without the need for down-flow monitoring and contamination hazard. Here, we apply SIP, as a proxy to monitor the extent of Cr retention in a flow-through column experiment, packed with magnetite-coated sand. We observed a rapid increase in polarization upon Cr(VI) adsorption on magnetite coated sand, followed by a strong continuous decrease. Our joint reactive transport modeling and post-column geochemical measurements highlighted a drop in the remaining sorption capacity of the coated sand, thereby linking the reduced sorption capacity to the drop in SIP signal. The excellent agreement between concentration breakthrough curves, our model and SIP measurements suggests that SIP signals can be used as an early warning tool to detect the approaching saturation of reactive materials deployed in remediation schemes.

How to cite: Rahmani, A., Franz, M., Bär, F., Backes, C., M. Byrne, J., and Mellage, A.: Sensing Cr(VI) retention with spectral induced polarization (SIP) in a magnetite-coated sand pack, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7971, https://doi.org/10.5194/egusphere-egu24-7971, 2024.

This study introduces a straightforward and cost-effective Bio-Electrochemical System (BES) design that can be easily retrofitted into a borehole. The design uses standard bailers and Granular Activated Carbon (GAC) to create electrodes. These electrodes are connected across redox environments in nested boreholes. The  electrodes were installed in pre-existing boreholes surrounding a groundwater plume at a gasworks site. The BES at the plume fringe had the highest electrical response and showed variations in the bacterial and archaeal taxa between the anode and cathode electrodes. The other BES configurations in the plume center and uncontaminated groundwater showed little to no electrical response, suggesting minimal microbial activity. This approach enables rapid decision-making to effectively monitor degradation at groundwater plumes. 

How to cite: Doherty, R., Kirmizakis, P., Cunningham, M., and Kumaresan, D.: Bio-Electrochemical Systems to Monitor Biodegradation around Groundwater Plumes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11508, https://doi.org/10.5194/egusphere-egu24-11508, 2024.

The Seewinkel National Park in Burgenland (Austria) encompasses the largest inland soda lakes in central Europe. The shallow aquifer in the soda lakes is confined by an impermeable clay-rich layer, which is nourished with salts through capillary upward transport during the summer periods. Sinking groundwater levels are responsible for a decline in the upward transport and a decrease in salt content within the impermeable unit, threatening the ecological state of the lakes and their rich and unique biosphere. Yet, the extension of the hydraulic barrier, its salt content, and changes within the system accompanying seasonal temperature variations are still open to debate due to the lack of subsurface information with high spatial and temporal coverage. Here, we propose the application of geophysical methods to complement existing drill core data. Our research aims at reconstructing the architecture of the lakes, particularly the geometry and composition of the impermeable layer with a higher spatial and temporal resolution. We applied electromagnetic induction (EMI) for contactless rapid mapping of the lateral extent of the impermeable layer, assumed to have higher electrical conductivity due to its clay and salt content, and solving for the mean features in the shallow aquifer. To resolve vertical variations of the electrical conductivity with high resolution, we applied electrical resistivity tomography (ERT) at selected locations.  The initial independent inversion results from EMI and ERT, inherently ambiguous, showed discrepancies in the thickness of the impermeable layer. To permit an adequate interpretation of the geophysical data and harness the strengths of both methods, we employed numerical simulations, including ERT data to constrain EMI inversion and vice versa, as well as borehole electrode data, which allowed us to resolve for a subsurface electrical conductivity model able to explain both EMI and ERT data. Our results permit us to understand the characteristics of the impermeable layer and to develop a suitable technique to apply EMI and ERT to investigate other lakes in the national park.

How to cite: Hettegger, A., Flores Orozco, A., Roser, N., and Cimadom, A.: Geophysical investigation of the Soda Lakes at the Seewinkel National Park (Austria) through electromagnetic and electrical methods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11986, https://doi.org/10.5194/egusphere-egu24-11986, 2024.

Biochar as a carbon-negative product from organic waste increases porosity and water availability when deployed and mixed with soil, as one of many benefits for agrivolatics projects. Biochar can mitigate climate change by locking away carbon in concrete and during steel production, supporting food security and a circular economy, producing composites for water treatment and nutrient availability, and restoring soils affected by sodicity or contaminants. However, the utilization of biochar in combined farming and large-scale solar PV projects (i.e., agrivoltaics) provides more opportunities such as credits for carbon dioxide removal (CDR) and increased land-use efficiency. This project at a 7-megawatt solar PV (14-hectare) mixed-use farm at Deakin University in Australia aims to evaluate how biochar could contribute to agrivoltaics, particularly its influence on soil moisture, nutrient availability, and pasture productivity. This presentation focuses on part of the datasets, with initial results for water availability in the soil and pasture for sheep grazing. We applied biochar into a hand-dug trench along the drip line of PV panels, with several reference sampling sites (0.6m deep holes) beyond the pasture that is shaded by the panels. The trench was 0.6 m deep and 0.3 m wide, with 0.1 m of drainage sand at the base, a 0.3 m thick layer of mixed straw-biochar followed by 0.1 m of biochar particles, and 0.1m of soil and grass. Pasture treatments of liquid biochar and fertilisers followed installation. Soil moisture sensors were installed in the trench and sampling sites at 0.1, 0.3, and 0.5 m below ground level, and volumetric soil water content (V-SWC %) was recorded every 15 minutes. The initial results showed that the biochar trench in the mid-depth zone (~0.3m below the ground) can retain ~45% soil moisture after initial rainfall events. The maximum value of V-SWC in the bottom zone of the biochar trench was 47%. Similarly, V-SWC trends at other sites indicated that the middle and bottom zones can hold water for a period of time after rainfall occurs and values were up to 20%. Ongoing analysis will include variations of soil carbon and nitrate and the chemistry of leachate water that is collected from piezometers that were installed in the sand base of the trenches for mini-monitoring. The findings of this project will be useful for wide-scale applications of biochar on agrivoltaics or farming projects in environments sensitive to water balance. Biochar in soils can act as a sponge to store more water, slow down water flows in rivers, and increase groundwater recharge to shallow aquifers. This could ensure local catchments are more resilient to dry periods while benefiting ecosystems, and production of renewable energy and farmland.  

How to cite: Zhou, Z., Timms, W., Adhikari, S., and Joseph, S.: Multiple benefits of biochar in agrivoltaics including rainfall harvesting and water balance , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13784, https://doi.org/10.5194/egusphere-egu24-13784, 2024.

Bio-remediation of soil contaminated by petroleum hydrocarbon is a highly complex process, requiring coupled interactions and synergistic effects between physical, chemical and biological phenomena. Monitoring and improving the bio-remediation of such system remains a formidable challenge. Our approach involves the development of a comprehensive mathematical and numerical model that couples two-phase flow, bio-reactive transport, and the dynamic of bacterial populations, with the aim of investigating the mechanisms governing pollutant and nutrient transport, bacterial activities and bio-degradation within porous media. Important processes including the effect of biofilm growth on the permeability of the porous media and the interaction between the biofilm matrix and the fluid system, are taken into account. Numerical simulations were carried out to evaluate the effect of biomass accumulation and nutrients availability on the bio-degradation rate, providing new insights into optimizing in-situ bio-remediation processes for effective cleanup. Additionally, key issues such as controlling contaminant mobility and estimating efficiency criteria will be addressed as well.

How to cite: Eddaoui, N. and Soulaine, C.: Enhancing Bioremediation: Insights from a Numerical Modeling Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17693, https://doi.org/10.5194/egusphere-egu24-17693, 2024.