Electrical Resistivity Tomography (ERT) is being increasingly applied to support hydrogeological studies by providing high-resolution images that delineate geological structures, groundwater resources, or soil moisture variability. More recently developed as a monitoring tool, ERT provides time-series data of groundwater content over surface areas of hundreds of square meters, complementing point-based monitoring approaches. ERT systems can be deployed permanently, collecting high-spatial resolution data at varying time frequencies, from days to sub-hourly acquisitions, and delivering near-real-time information. Advances in petrophysical relationships allow changes in electrical resistivity to be converted into calibrated soil moisture models, which feed hydrological models.

In addition to water content, temperature is another critical factor affecting electrical resistivity measurements, with impacts as strong as 2% changes in resistivity per °C in rock or soil materials. Isolating signals caused by hydrological processes in ERT time-series requires assessing subsurface temperature changes and correcting for their effects on resistivity. There is no strong consensus on how to handle these issues in processing ERT monitoring experiments. Sinusoidal 1D models representing seasonal temperature variations are commonly applied to estimate subsurface temperatures. These models define phase lags and damping of air temperature at depths using a damping factor, calibrated with in-situ data from vertical temperature profiles. While simple and independent of measured temperature time-series, these models may introduce biases when air temperature does not follow a sinusoidal seasonal pattern. Alternative approaches include interpolating data from temperature sensors at different depths, or applying heat transfer modelling in 1D, 2D or 3D.

However, a remaining challenge lies in the way the temperature models are being used to correct the resistivity models. Several approaches have been proposed, and in general, resistivity values of each cell of resistivity models is simply corrected using corresponding temperature model values. Such approaches don’t take the ERT data resolution linked with the measurement sequence into account, and the effect this may have on the sensitivity of the measurement to temperature changes. Typically for applications with large or small electrode spacings, or arrays with varying spacings, this approach may introduce relatively large artefacts on the corrected resistivity models. Here, we propose a new correction strategy based on estimating the sensitivity of the ERT dataset to temperature changes via implementing forward modelling onto a temperature corrected homogeneous 1-ohm resistivity model. We compare existing and novel approaches for subsurface temperature modelling and trial our innovative approach on a real ERT dataset acquired in field conditions.

How to cite: Watlet, A., Kaufmann, O., and Gourdol, L.: Temperature correction of electrical resistivity models in time-laspe ERT experiments: towards the integration of model resolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21714, https://doi.org/10.5194/egusphere-egu25-21714, 2025.

Fault zones can play a critical role in controlling small to large scale groundwater flow. Extensive studies have focused on permeability variations along faults in terms of conduit or barrier function for deep groundwater flow. However, little attempt has been made to characterize the hydrologic functions of near-surface fault zones.

When exposed to atmospheric conditions, fault zones are further disturbed by stress relief and chemical weathering, modifying their structure and generally increasing their permeability. Consequently, the fault zone, acting as a near-surface recharge or discharge zone, exerts a non-negligible influence on groundwater flow. However, identifying the hydrological function of such a fault zone remains challenging when relying solely on conventional, often non-integrated, geophysical or hydrological investigation approaches.

This study presents a multiphysics coupled strategy to characterize the groundwater flow regime around near-surface fault zone. The proposed approach is applied to an active reverse fault zone in Kamikita Plain, NE Japan, which extends for 30 km within the recharge zone of the catchment.

The multiphysics approach consists of 5 consecutive steps:

• Electrical Resistivity Tomography (ERT) Survey: A 3.8 km-long profile across the fault zone, with 20 m electrode spacing.
• Self-Potential (SP) survey: Conducted along the ERT profile.
• Rock property characterization: A 160 m deep borehole was drilled in the fault zone and physical properties were measured.
• Groundwater flow simulation of the fault zone: Using hydrogeological data, measured rock properties and a 3D geological model.
• Model evaluation: Post-processing of the groundwater flow simulation to calculate synthetic electrical resistivity and self-potential responses and comparison with observed field data.

The fault zone is identified by a sharp structural change between conductive and resistive geologic units, which also exhibit a small but shifted SP jump (+20 mV) signal. Our model evaluation process reproduces the entire ERT and SP data.

This newly proposed multiphysics approach offers a robust tool for monitoring groundwater flow in geologically complex regions, with applications in radioactive waste disposal safety, groundwater contamination management, and understanding hydrogeologic processes in tectonically active areas.

Acknowledgements: Main part of this research project has been conducted as the regulatory supporting research funded by the Secretariat of the Nuclear Regulation Authority, Japan.

How to cite: Gresse, M., Miyakoshi, A., Tosaki, Y., Hosono, H., Maeda, S., Mahrous, M., Sato, T., Asahina, D., Komori, S., Tsukamoto, H., Otsubo, M., and Takeda, M.: Characterizing Fault Zone Hydrology Using a Coupled Geophysical and Modeling Approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3049, https://doi.org/10.5194/egusphere-egu25-3049, 2025.

Climate change is rapidly impacting the mountain hydrosphere and cryosphere. Permafrost degradation and decreasing snow accumulation are rapidly altering the hydrological dynamics of headwater catchments with increasing dependence on subsurface water resources. Groundwater and subsurface ice are critical hydrological compartments for the resilience of alpine hydrological systems. While their buffering capacities are known to ensure perennial streamflow during increasingly long warm and dry periods, the limits of these resources are not generally understood. In spite of this growing importance, storage changes of subsurface water, in both solid and liquid form, remain the most uncertain components in alpine hydrological investigations.

Time-lapse gravimetry (TLG) involves the measurement and analysis of temporal variations in acceleration due to gravity (Δg). This hydrogeophysical method is spatially integrative, portable, and non-invasive. Because it is sensitive to all mass distribution changes, TLG is a powerful tool to fill the hydrogeological and cryospheric monitoring void in alpine settings.

Here, we present ongoing investigations of changes in groundwater storage and ground ice at multiple sites in the Swiss Alps and Pre-Alps. At the pre-alpine Röthenbach catchment, we are performing monthly TLG surveys. Preliminary results show significant spatial variability in groundwater storage changes, undetectable by piezometers and wells [see abstract EGU25-11997]. These data are being used to inform the development of a numerical hydrogravimetric data assimilation framework [EGU25-7128]. In the non-glaciated Vallon de Réchy, we have monitored seasonal decreases in groundwater storage across three summer/autumn periods, showing significant spatial and inter-annual variability and informing new conceptual models. Finally, at the Murtèl rock glacier, we recently deployed TLG, coupled with UAV imagery, to measure seasonal thaw in the active layer [EGU25-6793]. The results of this novel application were consistent with point observations and revealed spatially-variable thaw. Additionally, through comparison with a historic (1991) gravimetric survey, we found evidence of long-term permafrost degradation.

Our results, which provide quantitative, and spatially-distributed information on storage changes in groundwater and ground ice, demonstrate the significant potential of TLG for hydrogeology and cryospheric sciences.

How to cite: Halloran, L. J. S., Mohammadi, N., Amschwand, D., Carron, A., Arnoux, M., and Gutierrez, F.: Hydro-gravimetry as a monitoring solution for water and ice storage changes in dynamic alpine environments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3101, https://doi.org/10.5194/egusphere-egu25-3101, 2025.

This research focused on analyzing the hydrological characteristics of the Seolma stream watershed in Paju, Gyeonggi-do, South Korea. The study employed the SWAT model to evaluate various hydrological components, including precipitation, evapotranspiration, runoff, soil moisture, and groundwater recharge. Seolma stream, a small mountainous stream, was assessed for long-term runoff trends using data spanning from 2004 to 2023, which were then compared with observed records. The study also examined whether substituting rainfall observation data with RADAR-based values could enhance the accuracy of the runoff analysis. To address the absence of flow observation data for the period between June 2022 and April 2023, RADAR data and deep learning techniques were utilized to fill in the gaps.

Acknowledgements Research for this paper was carried out under the 2025 KICT Research Program (Development of IWRM-Korea Technical Convergence Platform Based on Digital New Deal) funded by the Ministry of Science and ICT.

How to cite: Choi, G., Yoon, S.-S., Woo, S., Kim, D. P., and Chung, I.-M.: Integrated analysis of hydrological components of the Seolma stream watershed by complementing SWAT model and RADAR-based data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3890, https://doi.org/10.5194/egusphere-egu25-3890, 2025.

The town of Nördlingen is one of the few remaining medieval towns in Germany. In the Middle Ages, Nördlingen was a centre of tanning and dyeing, which shaped hydraulic engineering along the river Eger and thus had a considerable impact on the floodplains close to the town. The DFG funded SPP 2361 ‘On the way to the fluvial anthroposphere’ focusses on investigating such pre-industrial floodplains in Central Europe and their development. Within the sub-project ‘Local Pathways to the Fluvial Anthroposphere at Echaz (Rhine) and Eger (Danube)’, the focus is on the multidisciplinary reconstruction of the land use of the floodplains and the reconstruction of the effects of urban crafts and waste disposal on floodplain pollution. To this end, we use multidisciplinary approaches, including the digitisation of historical maps, the integration of digital terrain models, geophysical investigations and the analysis of sediment cores from the Eger floodplain.

Here, we focus on the results of near-surface geophysical investigations carried out as part of the comprehensive floodplain exploration at the Bleichesee (a former bleaching lake), in which we used (1) electromagnetic induction (EMI) for area-wide mapping and (2) electrical resistivity tomography (ERT) for transect-wise mapping. With this combined approach, we were able to delineate the gravel bodies of the river Eger, which are characterised by a coarse-grained sediments, and identify regions with fine-grained alluvial deposits and anthropogenic backfills. Based on these results, sites were selected for driving core and hand drillings for detailed sediment analysis. In addition, direct push-based investigations can provide high-resolution vertical information on various subsurface properties (electrical conductivity, colour spectrum, hydraulic conductivity, etc.), whereby we focused on colour profiles at the Nördlingen site when investigating the Bleichesee lake. These were logged along a transect at intervals of 25 centimetres and thus provide impressive insights into the deposits and filling of the Bleichesee.

At present, the results of the geophysical measurements and in-situ descriptions by means of driving core and hand drillings as well as the extensive laboratory analyses of the sediment samples are being compiled. The aim is the chronostratigraphic description of the Eger floodplain and its history of pollution. In this respect, geophysical proxies can provide valuable support.

How to cite: Werban, U., Zvara, E., Pohle, M., Bauckholt, M., Pejdanović, S., Nießen, I. O., Werther, L., Kühn, P., and Zielhofer, C.: Geophysical contributions to the multidisciplinary reconstruction of the “Bleichesee” in a floodplain near Nördlingen, Southern Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12844, https://doi.org/10.5194/egusphere-egu25-12844, 2025.

A new sensor for non-invasive soil moisture detection, based on the principle of prepolarized surface-nuclear magnetic resonance (PP-SNMR) (Splith, T., et al., 2024) was tested on a profile covering the transition from mineral to peat soil in the Gnarrenburger Moor in northwest Germany. This prototype has a size of 2.0m by 2.0m and consists of distinct coil systems for prepolarization, stimulation and detection of the NMR response of the protons of the soil water molecules in the Earth’s magnetic field. To provide ground truth for the in-situ measurements, we carried out laboratory NMR experiments using undisturbed soil samples from the PP-SNMR measurement positions at depths between 0.0m to 0.66m. However, the question arises how comparable the relaxation properties of PP-SNMR and laboratory NMR can be, because the latter works at artificial magnetic fields, i.e. at different Larmor frequencies (f_L).

To identify a possible frequency-dependency of the resulting relaxation time distributions (RTD), we used two NMR devices in the laboratory: a single-sided NMR system (PM25, Magritek, f_L =13.2 MHz) and a core scanner (Helios, Vista Clara, f_L =0.5 MHz). The RTDs were calculated using the Matlab-based NUCLEUS-Software (Hiller, T., 2024), which provides confidence intervals for initial amplitude and logarithmic mean relaxation time to allow improved statistical analyses.

Within their individual confidence intervals, the T₂ RTDs measured in the laboratory are in agreement to each other and also to the RTDs of T₂* measured in the field for relaxation times >6 ms, which corresponds to the effective dead time of the PP-SNMR prototype. Correspondingly, the PP-SNMR moisture content from soil regions with significant amount of micropores with T₂(*)<6 ms is underestimated, whereas the water content estimates from the two laboratory NMR instruments agree within their individual confidence intervals. Due to the lower magnetic field, the signal-to-noise ratio of the core scanner is strongly reduced compared to the single-sided device and leads thus to a higher uncertainty.

A reduction of the effective PP-SNMR dead time would be desirable to detect also the micropores of the soil. Apart from that, laboratory NMR and PP-SNMR provide comparable results, at least for the T₂(*) relaxation, and we conclude that laboratory NMR studies can support PP-SNMR field campaigns. However, this observation does not hold for the T₁ relaxation behavior, for which a strong frequency dispersion, at least for weakly decomposed peat soils, is evident. Our future studies aim on the relationship between NMR relaxation time distribution and the water retention properties of peat soils.

Acknowledgements

This research is funded by the German Research Foundation (CO 1738/1-1).

References

Hiller, T. (2024), ThoHiller/nmr-nucleus: Version v.0.2.1 (v.0.2.1). Zenodo. https://doi.org/10.5281/zenodo.10647253.

Splith,T., Hiller, T, Costabel, S., Müller-Petke, M., (2024), Soil moisture measurements with compact prepolarization surface NMR sensors, MRPM, 2024.

How to cite: Costabel, S., Beisembina, G. T., Splith, T., Hiller, T., and Müller-Petke, M.: Laboratory NMR relaxometry provides ground truth for prepolarized surface NMR measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18804, https://doi.org/10.5194/egusphere-egu25-18804, 2025.

Finding effective methods for locating groundwater resources and ensuring safe drinking water is more crucial than ever, especially in the face of climate change and growing population pressures. Electromagnetic imaging techniques can significantly enhance our understanding of groundwater assessment, contamination detection, and overall management strategies. We discuss both time-domain and frequency-domain electromagnetic methods, emphasising the computational techniques used to analyse the electromagnetic data, along with several notable case studies that illustrate their effectiveness.

With the increasing availability of open-source software frameworks, more researchers are now able to analyse their data using sophisticated computational tools. Our contribution highlights the open-source software options for assessing electromagnetic data, focusing on the challenges presented by groundwater imaging, particularly due to the variations in spatial and temporal scales. We review various hydrological studies along with their corresponding electromagnetic surveying methods and the computational techniques employed. Moreover, we explore the potential benefits of advanced computational approaches, such as three-dimensional modelling and machine learning, when integrated with numerical groundwater modelling for enhanced imaging of groundwater systems. Although there are obstacles related to complexity and resource demands, our results indicate that the integration of these advanced techniques can improve the assessment and interpretation of geophysical and hydrological data, leading to a more effective understanding and management of groundwater resources.

How to cite: Rulff, P., Deleersnyder, W., Castillo-Reyes, O., Carrizo Mascarell, M., and King, J.: An evaluation of computational methods in electromagnetic geophysics and their potential for groundwater system imaging, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5895, https://doi.org/10.5194/egusphere-egu25-5895, 2025.

Saltwater intrusion (SWI) and submarine groundwater discharge (SGD) are critical processes influencing coastal aquifer dynamics. A transition zone formed where fresh and saline groundwater mixed at the coastline. However, the position of the interface shifts due to cyclic tides and varying freshwater discharge rates. Understanding characteristics of the fresh-saltwater interface is crucial to analyze the development of groundwater salinity in land subsided coastal areas.

Here, we present the laboratory experiment of In-well Electrical Resistivity Tomography (ERT) under controlled saltwater intrusion tests. This approach leads to a straightforward detection of fresh-saltwater interface incorporating the temporal dynamics of real systems. Unlike conventional ERT, it offers higher resolution imaging at greater depths and captures more accurate subsurface data, particularly around the fresh-saltwater interface. To establish our research in investigating the local groundwater salinization distribution using in-well ERT, Numerical experiments were initially conducted using COMSOL to determine the minimum electrode spacing that would not significantly impact the results.     These simulations helped identify the optimal spacing required to maintain the accuracy and reliability of the measurements, given the limited space available in the laboratory. Based on the findings from these numerical experiments, a laboratory-scale setup was designed and implemented in a vertical direction within a cylinder tank.

In the present study, a clear interface was observed and measured, through density flow, mounted observation tubes, dyeing and a series of operations. Preliminary results show a strong correlation between the measured resistance values and the actual interface changes. Additionally, the numerical experiments simulated real well conditions, including the thickness of the internal reinforced mud cake, and incorporated a detailed electrode structure (ring structure). This work provides valuable insights through laboratory results coupled with model simulations, which are essential for the future real-site application at the lower reach of Nabaki River, Chiba, Japan—a typical tidal river system in a below-sea-level land subsided area.

How to cite: Li, J., Tsai, C. S., Liu, J., and Tokunaga, T.: Applying In-well ERT to characterize and monitor fresh-saltwater interface in coastal aquifer：A Laboratory and Numerical Study, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8183, https://doi.org/10.5194/egusphere-egu25-8183, 2025.

Altiplano salt flats in northern Chile are areas of high hydrological and ecological importance, due to the availability of water in extremely arid environments. Groundwater dynamics in these areas are complex, largely because of density driven flow. The Salar de Huasco (20.2°S; 68.8°W; 4,164 m a.s.l.) is a salt flat located in an endorheic basin in the Chilean altiplano, which has little anthropogenic disturbance. The main surface water expressions in the basin are a shallow saline lagoon with an area of ∼2 km², and the Collacagua river that infiltrates ∼8 km north of the lagoon. The salt flat counts with two monitoring stations, with meteorological, soil and groundwater sensors. Amongst other geophysical methods, electrical resistivity tomography (ERT) data have been acquired on the salt flat during austral spring. Six 160m ERT profiles were measured using a Schlumberger array, in the study area. Two profiles were measured outside the salt flat, where the Collacagua river completely reinfiltrates. Two other profiles were measured inside the salt flat, near one of the monitoring sites; and the last two were measured along its edge, at the second monitoring site. The profiles were inverted using pyGIMLi, an open-source python library. The inversion models revealed three main geo-electrical units: a resistive unit (∼600 Ωm), interpreted as dry sediment or ignimbrite, an intermediate unit (∼100 Ωm), corresponding to freshwater-saturated sediment, and a rather conductive unit (∼40 Ωm), associated with sediment saturated in water with higher salinity, or sediments with a smaller grain size saturated with freshwater. The preliminary interpretation of the models indicates a groundwater depth between 0 and 10 m, and a brine-freshwater mixing zone reaching a minimum depth of 20 m in the northernmost monitoring station. The spatial distribution of these structures supports a conceptual model of an upwelling of freshwater pushed from beneath by a denser saline wedge, never considered at the study site. The ERT profiles allow to distinguish vertical and horizontal variations in electrical resistivity, aiding to further understand and characterize the groundwater systems in this salt flat. If confirmed by complementary measurements and analyses, this upwelling groundwater flow could be significant in maintaining superficial ecosystems. 

How to cite: Farah, B., Yáñez, G., Peña-Echeverría, A., Leray, S., and Suarez, F.: Geophysical insights into the shallow groundwater system of the Salar de Huasco, northern Chile, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10130, https://doi.org/10.5194/egusphere-egu25-10130, 2025.

Despite significant advancements and numerous applications in the study of the critical zone, seismic methods remain underutilized for exploring the vadose zone compared to hydrogeophysical approaches dominated by electrical and electromagnetic methods. These latter methods are often preferred due to their sensitivity to water content and salinity. However, seismic techniques offer a valuable complement through their sensitivity to mechanical properties essential for characterizing subsurface heterogeneity, as well as key hydraulic parameters such as porosity, permeability, and saturation. This is particularly relevant in clay-rich environments, where clays tend to obscure saturation contrasts for electrical and electromagnetic methods. The aim here is not to pit these approaches against each other but to highlight their complementarity, as recently demonstrated in studies that also underscored the efficiency of electrical methods in terms of implementation and interpretation. While the combination of seismic refraction tomography (SRT) and surface-wave dispersion analysis (MASW) produces useful images for identifying significant saturation contrasts, it remains limited in detecting subtle spatial or temporal variations. These limitations are especially pronounced in time-lapse experiments, which in addition are often complex and resource-intensive to implement. Current inversion techniques struggle to represent continuous saturation variations between the surface and the water table, and interpretations frequently adopt a binary perspective, distinguishing only between partially and fully saturated zones. A promising alternative lies in the use of recently developed rock physics models capable of simulating the impact of saturation variations on seismic-wave velocities. Recent studies have shown that surface-wave dispersion is particularly sensitive to these variations, providing insights into the influence of hydrological and hydrogeological dynamics on passive seismic results. Although this approach is rapidly advancing in environmental seismology, it remains relatively underexplored in hydrogeophysics and agrogeophysics. Through examples obtained at a study site, we illustrate how passive seismic methods could enable precise monitoring of hydrological and mechanical properties. We also show that simple neural networks can effectively extrapolate water table maps from 2D seismic velocity data obtained through hybrid approaches, using a limited number of spatial piezometric observations. Finally, we test how high-density surface-wave dispersion monitoring data, combined with artificial intelligence algorithms (inspired by neural machine translation and speech recognition architectures), can deliver precise petrophysical and hydrogeological descriptions.

How to cite: Bodet, L., Cunha Teixeira, J., Rivière, A., Solazzi, S. G., Gesret, A., Sanchez Gonzalez, R., and Dangeard, M.: Combination of Active and Passive Seismic Methods with Artificial Intelligence for Hydrogeophysical Monitoring of the Vadose Zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12834, https://doi.org/10.5194/egusphere-egu25-12834, 2025.

Time domain induced polarization (TDIP) has emerged as a highly effective tool for characterizing soil and groundwater contamination. Numerous studies have focused on the objective of enhancing accuracy of TDIP results. However, the acquisition of high quality TDIP data has received less attention than it deserved. In this study, three data acquisition methods were evaluated across seven distinct sites, with a particular focus on the controlling factors that influence data quality. This study addresses the questions about how to select a reliable TDIP acquisition method. The results demonstrate that there are significant differences in the raw data obtained through different acquisition methods, with the inverted results derived from these datasets exhibiting varying discrepancy. The data quality associated with the dual cables utilizing non-polarizable electrodes layout (Dual-CL-NP) is markedly superior, thereby ensuring the reliability of the results. Furthermore, apparent resistivity and measured voltage are identified as the key factors on data quality. The threshold values for selecting the acquisition method are determined. The Dual-CL-NP method should be utilized when the averaged apparent resistivity is less than 7.9 Ω·m. Consequently, a guideline for TDIP data acquisition is proposed, which addresses the limitations associated with TDIP data quality and facilitates its advancement.

How to cite: Meng, J., Mao, D., Zhai, K., Liu, S., Ma, X., Zhao, R., and Rahman, K.: Time domain induced polarization data acquisition at contaminated sites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8401, https://doi.org/10.5194/egusphere-egu25-8401, 2025.

Nuclear magnetic resonance (NMR) reveals pore water properties due to its unique sensitivity to water, making it a powerful tool in hydrogeological studies. By measuring the magnetization and relaxation time of hydrogen atoms, NMR enables estimation of water content, pore size distribution, irreducible and free water content, and hydraulic conductivity in geologic media. However, interpreting NMR data in the vadose zone remains challenging. While established relationships between NMR signals, pore structure, and physiochemical properties are reliable under saturated conditions, they often fail or yield significant errors in unsaturated environments due to the complex pore structure and solid-liquid-vapor interactions within vadose zone’s pore spaces. A key challenge in unsaturated NMR data interpretation is the pore coupling effect, where protons diffuse across multiple pore environments before relaxing. This phenomenon can distort NMR relaxation time distributions, resulting in averaged representations of pore networks rather than individual pore environments, leading to misinterpretation of NMR data. In this study, we investigate the impact of pore coupling on NMR signals using experimental and numerical methods. Using glass bead samples of different sizes (0.05-0.1 and 0.4-0.6 mm diameters) under different saturation states, we measure the NMR T₂ and T₂-store-T₂ measurements to quantify pore coupling phenomena. Our T₂-store-T₂ data show that the decreased saturation weakens the influence of pore coupling on NMR relaxation. We further scan our samples using micro X-ray computed tomography (µCT) to establish 3D structures with detailed structural characteristics and solid-water-air interfaces. We develop a numerical simulation framework incorporating geometric models derived from µCT scans, acquired using HECTOR at the Center of X-ray Tomography (UGCT) with the EXCITE network, to simulate the NMR T₂ and T₂-store-T₂ responses. This framework enables investigation of how various pore network structures and water distribution patterns influence NMR relaxation under different saturations, providing theoretical support for our experimental observations. Our findings enhance the understanding of NMR response in unsaturated porous media with the presence of pore coupling, providing improved interpretation strategies for NMR vadose zone characterization.

How to cite: Zhou, J. and Zhang, C.: Pore network connectivity affecting the NMR relaxation in unsaturated porous media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-300, https://doi.org/10.5194/egusphere-egu25-300, 2025.

Environmental magnetism uses rock and mineral magnetic methods to study changes of magnetic minerals influenced by various environmental processes. The field is well-established and has significantly contributed to our understanding of past and present environmental changes on Earth, including those driven by land use. Magnetic methods are used to identify ferromagnetic minerals, which serve as tracers for anthropogenic pollutants. Besides being non-destructive, these methods are fast and cost-effective when compared to chemical analyses. The magnetic properties of contaminated soils can provide information about the transformations of the environment affected by the degradation of organic matter, enriching our knowledge of the spatial and temporal evolution of the pollutant and the impacted area. In this work we present the environmental magnetism study conducted in the São Paulo Critical Zone Observatory (CZO) seed site, an endeavor to understand anthropogenic effects on groundwater, soils, and vegetation in a tropical megacity that has experienced diverse urban transformations over time. The multidisciplinary team of São Paulo CZO’ scientists approached the following main questions: (1) How are soils, water and vegetation resources in a tropical megacity responding to natural and anthropogenic drivers? and (2) How can a critical zone observatory in an urban environment advance the understanding of the critical zone response to natural and anthropogenic drivers? We hypothesize that CZOs can more effectively identify and monitor biogeochemical processes in urban environments, where land is heavily degraded. This study allowed a better understanding of the architecture and dynamic of the urbanization impacted CZ, revealed by magnetic signatures that indicated Fe-bearing minerals transformations driven by changes in redox conditions. Our results also reveal striking differences between the analyzed soils that can be linked to anthropogenic activities. More specifically, magnetic properties identified one important soil interface, which show mineral phases and grain size transformations of Fe-bearing mineral at depth. Characterizing the architecture and dynamic processes of the subsurface in urbanized areas provides a comprehensive understanding of how human-induced changes impact the natural environment.

How to cite: Ustra, A., Dantas, L. R., Imbernon, R., do Carmo, J. A., Hirata, R., and Pioker, F.: On the Contributions of Environmental Magnetism for Exploring the Critical Zone: A Case Study in an Urban Environment of a Tropical Megacity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10342, https://doi.org/10.5194/egusphere-egu25-10342, 2025.