Karst aquifers are heterogeneous groundwater systems having both diffuse and concentrated recharge mechanisms. Since their complex recharge, storage, and discharge characteristics, the groundwater divide is generally different from the topographical catchment borders. As a result, karst hydrogeologists are using different methods to obtain more certain recharge areas. Tracer tests are very important and preferred tools to obtain the groundwater recharge areas. An ideal tracer must be detectable in very low concentrations, conservative along the pathways, and cost-effective. In this manner, mineralogical analysis of the suspended particles would be a very good alternative to the isotopic, biochemical, and dye tracers due to the easy collection and cost-efficient analysis methods. In the present study, we collected rock samples from approximately 10 locations surrounding the potential recharge area of the karst aquifer covering all lithological units surrounding the study area. Then, we collected sediment samples at the discharge outlet of the karst spring and suspended particles by filtering the water samples. We analyzed both the sediments and rock samples by the petrographic thin-sections, XRD whole rock, and XRD-clay fraction analysis to compare the minerals between the rock and sediment samples. We obtained Eocene-aged Planktonic Foraminiferal fossils in the spring sediments (in the thin sections), which perfectly fit the Eocene-aged limestone formation in the study area. By overlapping the lithological outcrop of the formation with the isotope-derived recharge elevation, we obtained the locations of two major dolines in the study area. As the final step, we validated our results by conducting dye-tracer tests from these points, and we recovered the tracer dye from the karst springs.

How to cite: Calli, S. S., Celik, M., and Karakas, Z. S.: Combination of Multiple Investigation Methods to Reveal the Recharge Area of a Karst Aquifer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-466, https://doi.org/10.5194/egusphere-egu24-466, 2024.

Discharge in many karst aquifers exhibits distinctive long tails during recession that follow recharge events, a phenomenon often associated with the intricate flow paths that develop due to the underground structure of karst systems. This complexity poses a unique task from the perspective of modeling the flow and discharge patterns. In this study, we propose a novel approach to address long tail discharge during base-flow conditions, by adapting the continuous time random walk (CTRW) framework, known as a robust tool for modeling the long-tailed behavior observed in breakthrough curves of chemical species during transport, under diverse flow conditions. By establishing a theoretical analogy between partially saturated karst flow and chemical transport, we develop and implement a particle tracking (CTRW-PT) model that provides robust fits of three years of data from the Disnergschroef high alpine study site in the Austrian Alps, underscoring the predominance of slow diffusive flow over the rapid conduit flow. The agreement between measured and simulated data not only validates the proposed analogy between partially saturated karst flow and chemical transport but also highlights the utility of the CTRW-PT model, offering valuable insights and enhanced modeling capabilities for future research in this complex field.

How to cite: Elhanati, D., Frank, S., Goeppert, N., and Berkowitz, B.: Application of anomalous transport modeling for karst aquifer discharge response to rainfall, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3029, https://doi.org/10.5194/egusphere-egu24-3029, 2024.

Karst aquifers play a crucial role as water sources globally, with several European countries relying significantly on them for their water supply. Managing these aquifers is challenging due to their subsurface hydraulic heterogeneity. Hydrological modeling has proven valuable, offering insights into the hydraulic dynamics and management of karst water resources. However, characterizing karst drainage attributes at large catchment and regional scales remains challenging, hindering the incorporation of spatial heterogeneity and complexity in large-scale models and leading to unrealistic estimations in karst regions. This study addresses the issue by providing the first regional estimation of karst drainage attribute across Europe, this attribute is herein called Karstification Index (KI). Leveraging a newly developed automated karst spring recession analysis tool, and extensive climatic and physiographic datasets, we applied a regression-based regionalization model to estimate slow and quick flow parameters in karstic landscapes. By estimating KI as the ratio of quick to slow flow parameters, we were able to identify sub-regions with higher and lower degrees of karstification. Our findings highlight the significance of drainage density metrics, particularly in combination with specific climate signals, as predictors of KI. The regionalization model demonstrated high performance, validated by high R² values, especially in well-gauged European catchments. Encouraged by these results, the analysis is being extended to a global scale, marking the first attempt to estimate karstic drainage attributes globally. We believe that this large-scale parameterization of karstification will enhance regional and global karst water resource management. By improving the parameterization and consideration of karst processes in large-scale hydrological models, our research contributes to a more accurate understanding of karst aquifers on a global scale.

How to cite: Olarinoye, T., Weber, N., Gleeson, T., Marx, V., Liu, Y., and Hartmann, A.: Characterisation of drainage dynamics of karst landscapes over Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18008, https://doi.org/10.5194/egusphere-egu24-18008, 2024.

Hydrodynamic understanding of karstic aquifers is a real challenge due to the complexity of their internal structures. However, their societal significance lies in the substantial quantity of groundwater resources they embody. Among these complexities, faults partially control the organization of flows in these systems. The nature of this control can either facilitate rapid flow transfer or act as a barrier, impacting both groundwater quality and quantity. Understanding the behavior of fault zone features is crucial for efficiently management of karstic aquifer resources. However, there is a lack of studies that estimate and simulate flow within fault zones. In this study we estimate the hydraulic properties of the fault zone within carbonate karstic aquifers for flow and transport forecasting purposes based on cross-hole pumping tests simulation and inversion. The flow and transport are modeled using MODFLOW6 and MODPATH7. The inverse modeling approach is based on the Gauss-Levenberg-Marquardt Algorithm (GLMA) and the Iterative Ensemble Smoother (IES) integrated into the PEST++ code. Initially, we applied and validated the approach on a synthetic fault zone and subsequently on a real case studies within karstic carbonate aquifers of interest (Lez aquifer, Montpellier (France)). The inverse modeling approach has proven efficient in exploring hydrodynamic properties and then obtained both flow and transport forecasts with a satisfactory level of uncertainty. These works contribute to a better understanding of the hydrodynamic aspects of fault zones in carbonate environments through an innovative approach specific to its application. This study offers a reproducible method to understand and quantify hydrodynamics in aquifer in general and carbonated aquifer fault zones in particular. This improvement enhances the management strategies for groundwater resources in carbonated aquifers.

How to cite: Aurelie, B., Yohann, C., Victor, C., Rémi, V., and Véronique, L.: Simulation of Carbonated Fault Zones Hydrodynamics and Transport Considering Parametric and Predictive Uncertainty, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19597, https://doi.org/10.5194/egusphere-egu24-19597, 2024.

In the epikarst zone of carbonate areas, numerous fractures have different sizes, shapes, and filling materials. Determining the fractures' horizontal hydraulic conductivity (K_h) simply using slug tests is challenging due to variable flow states (e.g., steady and unsteady). In this study, we characterized fracture features of apertures and soil fillings in terms of 260 fractures of 25 borehole logs at five sites in a karst area of southwest China. The Bouwer and Rice (B & R) solution and a numerical model were used to determine K_h based on the best fitting of observed water head in 105 slug tests. The results comparatively show that Kh from the B & R solution is significantly underestimated. For numerical modeling, the non-linear flow expressed by the Dupuit and Forchheimer equation can improve the water head fitting when the Reynolds number (Re) > 17.27. The optimized K_h ranges 0.014 – 2673 m/d. The mean value of K_h is about 100 times the median value, suggesting that epikarst flow might be controlled by a limited number of larger fractures. Expectedly, K_h exponentially increases with d, but three is a turning point for the fracture aperture d around 10 mm, K_h abruptly decreases due to soil filling. The hydraulic permeability in the naturally full-filling fractures resembles the soil matrix. In contrast, the partial-filling fractures can create preferential pathway with a high K_h around the soil-rock interfaces, allowing preferential flow in fractures. These results fundamentally improve our understanding of water infiltration, retention, and availability for plant uses. 

How to cite: Liu, X.: Estimating fracture characteristics and hydraulic conductivity from slug tests in epikarst of southwest China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2436, https://doi.org/10.5194/egusphere-egu24-2436, 2024.

In systems where surface water and groundwater interact, management of the water resource often involves conflicting objectives between water supply and baseflow maintenance. Balancing such objectives requires understanding of the role of groundwater in integrated water systems to inform the design of an efficient strategy to minimise abstraction impacts. This study first develops a reduced-complexity, processed-based groundwater model within the water systems integration modelling framework (WSIMOD). This model is applied to the Lea catchment, UK, as a case study and evaluated against monitored groundwater level and river flow data. A flux tracking approach is developed to reveal the origins of both river baseflow at a critical assessment point and abstracted groundwater across the systems. The insights obtained are used to design two strategies for groundwater abstraction reduction. Results show that the model has good performance in simulating the groundwater and river flow dynamics. Three aquifer bodies that contribute the most to the river baseflow in the dry season at the assessment point are identified; contributions being 17%, 15%, and 5%. The spatial distribution of abstracted groundwater originating from these aquifer bodies is illustrated. Compared to the default equal-ratio reduction, the strategy prioritising abstraction reduction in these three aquifer bodies increases a similar amount of baseflow (13%) by reducing much less abstraction (23%). The other strategy, which further decreases abstraction in the adjacent aquifer bodies, increases more baseflow (16%) with a similar abstraction reduction (30%). Both strategies can more efficiently improve the baseflow. The flux tracking approach can be further implemented to trace water from other origins, including runoff, stormwater, and wastewater, to enable coordinated management for better systems-level performance.

How to cite: Liu, L., Bianchi, M., Jackson, C., and Mijic, A.: Flux tracking of groundwater via integrated modelling for abstraction management, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5158, https://doi.org/10.5194/egusphere-egu24-5158, 2024.

Bedding plane partitions are an important geological medium to guide cave passages during the early stages of karstification in limestone formations. However, how stress load affects karst genesis processes along the large rough fractures remains poorly understood. Here, we develop a novel coupled hydro-mechanical-chemical (HMC) model to improve the understanding of this complicated process. This model considers a two-way mechanical-chemical coupling where dissolution perturbs the contact-stress distribution, in return impacting the fracture dissolutional enlargement. A non-linear correlation between the local fracture stiffness and contact stress is further incorporated. We study a two-dimensional horizontal fracture surface embedded in a three-dimensional rock block subjected to vertical stress loading. Simulation results show that dissolution causes local stress reduction (mechanical weakening), simultaneously accompanied by stress concentration at its fringe. The competition between dissolution-induced aperture enlargement and compaction-induced closure significantly retards the dissolution evolution. Without mechanical effect, linear dissolution fingering exhibits. As the applied stress increases, the secondary karstic conduits become more pronounced and a ramiform dissolution fingering featuring branching and winding is induced. Our results also provide important implications for understanding other engineering applications such as geothermal development and carbonate acidification.

How to cite: Jiang, C., Wang, X., and Jourde, H.: Stress-induced ramiform karstic conduits along a bedding plane: insights from a coupled hydro-mechanical-chemical (HMC) model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9657, https://doi.org/10.5194/egusphere-egu24-9657, 2024.

This study focuses on the role of karst aquifers in the Mediterranean Basin as a buffered storage of freshwater, especially considering the anticipated increase in drought periods due to climate change. Climate change underscores the need for innovative groundwater management approaches to maximize the storage capacity of these aquifers. This study emphasizes the importance of enhancing aquifer recharge during normal or high rainfall to mitigate the impacts of droughts. Notably, many karst aquifers in this region, which developed extensively during the lower base levels of the Messinian Salinity Crisis, exhibit a dual-domain flow pattern. This pattern consists of a slower flow through the rock matrix and a faster flow through conduits. Despite the rapid drainage of these mature karst systems, some, particularly those in the Mediterranean, are limited in their outflow to the sea by marine clay deposits, as highlighted by Bakalowicz (2015, Environmental Earth Sciences). These systems have shown a significant capacity for storage over several years.

In our study, we applied dual-permeability flow modeling to evaluate the storage potential of the Western Mountain Aquifer in Israel and the West Bank. The model utilizes the volume-averaged Richards' equation and integrates a term to account for the characteristic preferential infiltration in karst aquifers, even under nearly dry conditions. The model includes phreatic and vadose zone flows to comprehensively assess the storage capacities of the aquifer comprehensively. The results indicate that despite its advanced karst development, the Western Mountain Aquifer possesses a notable long-term storage capability. This is attributed to its extensive vadose zone and the restricted outflow, which is constrained by surrounding and overlying low-permeability formations (such as the Talme-Yafe, Negba, Daliya, and Menuha Formations, composed mainly of chalk and marl). The study explores various infiltration sites for managed aquifer recharge and considers current and future climatic conditions based on the RCP4.5 climate change scenario.

How to cite: Bresinsky, L., Kordilla, J., Livshitz, Y., and Sauter, M.: Optimizing Water Storage in a Mediterranean Karst Aquifer: A Comprehensive Vadose and Phreatic Modeling Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9697, https://doi.org/10.5194/egusphere-egu24-9697, 2024.

Apulia is one of the most interesting karst lands in the Mediterranean area, hosting a variety of distinctive surficial and underground landforms. Among these, polje, a wide and flat depression of tectono-karstic origin, represents one of the most typical epigean landforms in karst. The “Canale di Pirro” polje, located in the central part of Apulia (SE Italy), is the largest in the region (Pisano et al., 2020), bounded on both sides by tectonically-controlled ridges, with an overall length of some 12km and a remarkable underground system of caves, among which there is the deepest of Apulia, where the water table is reached at -264 m from the ground (Parise & Benedetto, 2018). As a karst land, within the polje the water rapidly infiltrates into the ground, making difficult its accumulation at the surface, with the exception of the period of heavy rainfall, when wide sectors of Canale di Pirro become temporary lakes which require several hours to days to be absorbed underground. In ancient documents and maps, with particular regard to historical cartography, the Canale di Pirro polje was drawn as being crossed by a long river, nowadays missing, called Cana (from this river, it seems that the same toponym of the polje took its name). The first written testimonies concern in particular a parchment dating back from the twelfth century; the more recent document we found, still showing the presence of the river, instead, is an ancient map of the nineteenth century. Considering the time span in which Cana River is still represented in historical writings and maps, it is possible to identify its existence between 1195 and 1840, and to hypothesize a presumed coincidance with the Little Ice Age, a climate interval characterized by a long cooling period, especially in the northern hemisphere. In this work, we present a series of historical documents about the existence of the Cana River, collected through literature research, in order to evaluate all the possible causes that led to the river disappearance over the centuries.

References

Parise M. & Benedetto L. (2018). Surface landforms and speleological investigation for a better understanding of karst hydrogeological processes: a history of research in southeastern Italy. In: Parise M., Gabrovsek F., Kaufmann G. & Ravbar N. (Eds.), Advances in Karst Research: Theory, Fieldwork and Applications. Geological Society, London, Special Publications, 466, p. 137-153, https://doi.org/10.1144/SP466.25.

Pisano, L., Zumpano, V., Liso, I. S., & Parise, M. (2020). Geomorphological and structural characterization of the ‘Canale di Pirro’ polje, Apulia (Southern Italy). Journal of Maps, 16(2), 479-487, https://doi.org/10.1080/17445647.2020.1778550.

How to cite: Cofano, V., D'Ettorre, U. S., Liso, I. S., Capolongo, D., and Parise, M.: An ancient river disappears in a Mediterranean karst land: the old history of Cana River (Apulia, Southern Italy) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2828, https://doi.org/10.5194/egusphere-egu24-2828, 2024.

Research on groundwater residence times is essential for evaluating groundwater abstraction rates and aquifer vulnerabilities, and hence, for sustainable water resources management. Naturally occurring radionuclides are suitable tools for related investigations. While the applicability of several long-lived radionuclides for the investigation of long-term processes has been demonstrated frequently, tracer-based approaches for studying residence times of less than one year have not been fully exploited. That is due to the rather small number of applicable radionuclides that show adequately short half-lives. A promising approach for investigating sub-yearly residence times applies radioactive Sulphur (³⁵S). Radio-Sulphur is naturally produced by high-energy cosmic radiation in the upper atmosphere from where it is transferred with precipitation to the groundwater. As soon as the meteoric water enters the subsurface its ³⁵S activity concentration decreases with an 87.4-day half-life. This makes ³⁵S suitable for investigating sub-yearly groundwater residence times. However, the low ³⁵S activities in natural waters require sulphate pre-concentration for ³⁵S detection by means of liquid scintillation counting. This is done by sulphate extraction from large water samples with anion-exchange resins or/and precipitation as BaSO₄. The resulting samples are usually associated with background interferences and quenching. The presented experiments aim at (i) optimizing the sample preparation procedure by simplifying the pre-concentration of sulphate to make it applicable for field sampling and at (ii) reducing quench and background during measurement. We will discuss the different sample preparation methods and lessons learned for the detection and quantification of ³⁵S pre-concentrated from natural water samples that contain a wide range of SO₄²⁻ concentrations.

How to cite: Kamau, S., Mostafa Amghar, E., Bibby, R., Copia, L., Coulson, L., Damatto, S., Harjung, A., Kopitz, J., Kralik, M., McGuire, B., Schubert, M., and Terzer-Wassmuth, S.: Conclusions from an IAEA Meeting on the sample preparation and measurement of radio sulfur in natural water samples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20334, https://doi.org/10.5194/egusphere-egu24-20334, 2024.

Alluvial aquifers have a significant potential for pumping large quantities of groundwater, essential for meeting drinking water needs. Abstracted water typically consists of a mix of regional groundwater and freshly infiltrated river water. A good understanding of surface water – groundwater interactions in these types of systems is required for managing both qualitative and quantitative aspects of riverbank filtration or river renaturations. Tracers are important tools in these contexts, as they provide crucial information on travel times and mixing ratios.

We present data from a comprehensive multi-tracer approach obtained in a field experiment conducted in a pre-alpine valley in central Switzerland. Over several months, river works were undertaken in an infiltrating river in the proximity of an important field of groundwater wells used for drinking water production. We investigated the impact of these river modifications on surface water - groundwater dynamics by monitoring the natural concentrations of (noble) gases with multiple potable mass spectrometers (miniRuedi, Gasometrix) and radon detectors (Rad7, Durridge). Additionally, we injected different noble gas species as artificial tracers both in the river and in groundwater and gained valuable insights into the evolving dynamics of the system.

The combination of these different tracers provided insights that could not have been obtained by a single tracer. Our results demonstrate that during and immediately after restoration works the infiltration of river water increases temporarily and provide insights about the time it takes for a riverbed to recover after restoration works and for river-groundwater interactions to reach a new dynamic equilibrium.

How to cite: Blanc, T., Currle, F., Peel, M., Brennwald, M. S., Tomonaga, Y., Schilling, O. S., Hunkeler, D., Kipfer, R., and Brunner, P.: Use of dissolved gases as tracers to study the impacts of floods and river works on Surface water – Groundwater interactions., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18189, https://doi.org/10.5194/egusphere-egu24-18189, 2024.

Groundwater, as the key strategic reserve in times of drought, is sensitive to climate change, especially unconfined, shallow aquifers. Frequent and prolonged drought provides an urgent impetus to improve understanding of groundwater dynamics and its residence times in drought-sensitive areas where water and food security are threatened. The Demnitzer Mill Creek catchment is a long-term environmental observatory typical lowland of North German Plain where streams are dominated by groundwater, however its groundwater recharge and dynamics remain poorly constrained. We applied water table observations, isotopic (δ¹⁸O, δ²H, ³H), hydrogeochemical, and geophysical investigations to characterize the spatial and temporal patterns of groundwater recharge in a shallow, unconfined aquifer system. Long-term groundwater levels showed a declining trend since 2011, which accelerated after 2018 resulting in increasingly intermittent seasonal streamflow. Geophysical surveys and groundwater monitoring indicated that shallow water tables (typically <3 m deep) in low to moderate permeability surficial deposits are generally recharged during winter, leading to higher groundwater – surface water connectivity in riparian alluvial aquifers, which is the first order control on streamflow generation. This was supported by similar geochemical characteristics of groundwater and streamflow. Water stable isotopes indicated a high damping in groundwater with a bias towards winter precipitation and direct recharge. Although ³H dating showed that the age of shallow groundwater was young (~5 years) and generally similar to streamflow, estimates had high uncertainty and some deeper groundwater was free of ³H. Such multiple approaches help understand changes in groundwater recharge and dynamics during droughts and contribute to the development of sustainable land and water management strategies for groundwater systems that are sensitive to climate change.

How to cite: Ying, Z., Tetzlaff, D., Freymueller, J., Comte, J.-C., Goldhammer, T., Schmidt, A., and Soulsby, C.: Using contrasting tracers to characterize groundwater dynamics under a prolonged drought in the lowland catchments in the North German Plain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-602, https://doi.org/10.5194/egusphere-egu24-602, 2024.

Catchment transit times are often inferred by assuming a transit time distribution (TTD) or a SAS function and calibrating their parameters against measured tracer data. In the presence of high-resolution tracer data, machine learning tools may offer a promising avenue for advancing TTD estimation by leveraging data-driven approaches, integrating diverse data sources, and improving accuracy, scalability, and adaptability. Here, we lump together ideas coming from Large Languages Models, survival analysis and sum of squares techniques to introduce a novel data-driven model for estimating TTDs. Our model is influenced by SAS-based approaches; however, unlike previous studies, we avoid imposing strong parametric assumptions on the SAS function. We showcase the performance of our model against a benchmark of eight virtual datasets that differ in precipitation amounts, seasonality and runoff flashiness. We find that machine learning methods may effectively predict solute concentration in streamflow yet struggle to accurately estimate the true TTDs. However, when the appropriate inductive bias is incorporated, numerous key aspects of TTDs, such as the young water fraction and the average TTDs, can be estimated robustly. We also identify settings where the estimation task is more challenging for our model. This analysis, based on reproducible virtual benchmarks, provides a first overview of machine learning capabilities in estimating TTDs and inspires future TTD model inter-comparisons.

How to cite: Benettin, P., Duchemin, Q., Zanoni, M. G., Rinaldo, A., and Kirchner, J.: Data-driven approaches to infer transit time distributions from high-resolution tracer data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12200, https://doi.org/10.5194/egusphere-egu24-12200, 2024.

Groundwater from karst aquifers is a major source of drinking water worldwide. These complex aquifer systems are exceptionally vulnerable to pollution and may be impacted by multiple contamination sources. Consequently, water contaminated with pollutants, such as microbial and chemical, from different sources can reach water sources used for human supplies (i.e. karst springs, boreholes, and wells that are being used for domestic purposes and/or irrigation).

In rural and suburban areas, human wastewater effluent (from on-site domestic wastewater treatment systems - DWTSs) and agricultural sources are generally considered among the most significant threats to groundwater quality. This is particularly of concern in Ireland given that more than one third of the population (>500,000 homes) use DWTSs. However, significant knowledge gaps exist with respect to linking contaminants with the origins of pollution and quantifying different pollution impacts on groundwater quality in karst environments.

The domestic wastewater is primarily discharged from toilets, washing machines, showers, and dishwashers, therefore, a wide range of contaminants (including source-specific contaminants) eventually reach the environment even after on-site wastewater treatment processes. We evaluated a range of chemical contamination fingerprinting techniques in terms of their ability to determine human wastewater pollution impacts on karst aquifers. Springs provide appropriate natural locations for monitoring pollutant concentrations in karst aquifer systems as they provide an integrated picture of contaminant transport through a karst conduit network, compared to wells and boreholes which are not necessarily directly connected to the most transmissive parts of the aquifer. Hence, nine separate karst springs in the West of Ireland (of varying catchment sizes) were studied and monitored over a 14-month period.

The results demonstrate how fluorescent whitening compounds (FWCs; well-known indicators of human contamination since their origin is mostly from laundry detergents), microplastic particles, and faecal sterols and stanols can be used together to cover different detectability chances, and provide useful information about DWTSs pollution impacts on karst springs. This study also provides an important benchmark for microplastic contamination in low-lying karst aquifer systems. Furthermore, a link between changes in FWCs signals and microplastic concentration changes in karst groundwater has been found, which indicates that the majority of microplastic particles originated from human wastewater sources. Unsurprisingly, the highest detection rates of FWCs and high concentrations of microplastic particles were found in karst catchments with very high densities of DWTSs and high percentages of DWTSs in the catchment that are within 200 m of at least one karst feature (such as swallow hole), indicating a direct pathway into the underlying aquifer. Moreover, the results suggest that while total sterol content in collected groundwater samples was generally low, faecal sterols and stanols can still be used as chemical faecal markers at karst springs.

How to cite: Vucinic, L., O'Connell, D., Dubber, D., Behan, P., Crowley, Q., Coxon, C., and Gill, L.: Understanding the impacts of human wastewater effluent pollution on karst springs using chemical contamination fingerprinting techniques, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11063, https://doi.org/10.5194/egusphere-egu24-11063, 2024.

The residence time of a spring located in central Mexico has been affected by seismic activity. The region is influenced by the interaction of five tectonic plates - Cocos, North American, Pacific, Rivera, and Caribbean - with convergent, divergent, and transform boundaries, leading to frequent earthquakes.

The spring, known as the name “Agua Hedionda”, has therapeutic properties due to sulfate concentrations exceeding 1 g/L that contributes significantly to the local economy. However, the earthquake of magnitude 7.1 in 2017 had a substantial impact, particularly on the flow quantity and sulfate concentrations, evidencing the vulnerability of the spring and, consequently, the community's economy.

To comprehend the vulnerability and changes in the spring, data of tracers (O-18, H-2, H-3, C-14), major ions and flow measurements were collected in 2022.Then, these data were compared with pre- and post-earthquake information.

Tracers facilitated the estimation of residence time for water reaching the spring, indicating a regional flow after the earthquake and an intermediate flow before and currently. The chemical and isotopic data suggest a mixing of flows.

Tectonic movements imply that the spring received water with a longer residence time compared to its original state. The combined analysis of these data in tectonically active areas offers valuable insights into changes in residence times, thereby understanding variations and the vulnerability of groundwater resources.

How to cite: Sierra Garcia, B. A., Olea-Olea, S., and Medina Ortega, P.: Changes in the residence time of a spring in a tectonic active zone of central Mexico, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4793, https://doi.org/10.5194/egusphere-egu24-4793, 2024.

Thermal springs are natural discharge points that can offer valuable information on groundwater circulation. The use of tracers to determine residence times can help us understand complex hydrogeochemical processes despite limited data availability.

The present work aims to determine groundwater chemistry composition of two thermal springs located in east-central Mexico as well as understand some of the processes that may impact residence time estimation.

Tritium and carbon-14 tracers indicated a significant component of pre-modern water. Major ions data collected showed both springs have concentrations of HCO₃^- greater than 1,000 mg/l and temperatures around 41 °C. Saturation indices showed water-rock interaction with geological formations present in the area, such as limestone sequence ‘El Doctor’, that could influence groundwater residence time. Isotope data (δ¹⁸O) was used to determine a recharge elevation ranging from 2900 to 3000 meters above sea level. Additionally, SiO₂ geothermometers were also applied to quantify circulation depth and reservoir temperature.

Analysis of hydrochemical composition, residence times, and any other information obtained from tracers, such as tritium and C-14, allows us to gain a better understanding of how groundwater systems work, along with a more accurate interpretation of results.

How to cite: Ramírez González, L., Escolero, O., Olea-Olea, S., and Medina-Ortega, P.: Understanding groundwater chemistry and residence times of two thermal springs in east-central Mexico., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6376, https://doi.org/10.5194/egusphere-egu24-6376, 2024.

The characteristics of groundwater flow and solute transport in karst aquifers differ considerably from those in intergranular and fissured aquifers. To understand how they function, appropriately adapted hydrogeological research techniques and analyses are required. In this study, a binary karst aquifer in the recharge area of the Malenščica and Unica springs, which covers an area of about 820 km² in southwestern Slovenia, was selected as the study area. A monitoring network was set up to obtain data on precipitation and discharge at the two springs, two sinking streams and two water-active caves in their catchment over a period of two hydrological years. First, a classical approach of correlation and spectral analysis of these time series data was applied to determine and compare the flow characteristics and storage capacity of selected springs and their recharge areas. The allogenic and autogenic recharges were considered separately as input functions and the results of the analysis were compared. Although these widely used methods provided a good characterization of the studied karst system, the interpretation can be ambiguous due to the interference of the two input components. To avoid this problem, an innovative method of partial cross-correlation analysis was used, which has previously only been applied to separate the influence of different precipitation stations in karst. Here, its application was extended to the evaluation of the influence of allogenic recharge. By controlling the input parameters precipitation and discharge of one of the sinking streams, it was possible to determine the contribution of the other sinking stream to the observed spring. The differences in the recharge characteristics of the Unica and Malenščica springs were revealed, and the ability of this innovative approach to provide additional insights into the functioning of binary karst aquifers was confirmed.

Key words: karst aquifer, autogenic and allogenic recharge, time series analysis, partial cross-correlation, Slovenia.

How to cite: Kogovšek, B., Jemcov, I., and Petrič, M.: Distinguishing between different sources of recharge in a complex binary karst aquifer: a case study of the Unica springs (SW Slovenia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14951, https://doi.org/10.5194/egusphere-egu24-14951, 2024.

During flood events, due to extreme hydraulic loading in recharge areas of aquifers, groundwater flow dynamics can change, causing a risk of pathogens being flushed into aquifers used for drinking water supplies. Extreme flood events, as they are increasingly experienced with climate change, have potential to cause impacts not seen before, and drinking water sources that were free of pathogen contamination in the past may become contaminated in the future.

As an example, in the Heretaunga Plains, Hawkes Bay, contaminated water from heavy rain inundated paddocks entered an unconfined part of the aquifer and drinking water wells in it, resulting in >6260 cases of illness including 42 hospitalizations, and Campylobacter infection contributed to at least four deaths.

Most of the c. 30 drinking water wells in the Heretaunga Plains, including those supplying the cities of Hastings and Napier, are, however, in the confined part of the aquifer and these were not affected by pathogen contamination. But will more extreme flood events, predicted with climate change, eventually also compromise drinking water sources in the confined aquifer which were deemed safe in the past? Wells in the confined aquifer have shown indications of changing groundwater flow dynamics, for example variable water age, and changing hydrochemistry after flood events, which might be associated with younger water, bearing the risk of pathogen intrusion.

On 13 and 14 February, 2023, Cyclone Gabrielle lashed Hawke’s Bay, with record rainfalls causing rivers to burst their banks causing a death toll of 11. To improve understanding of the impact of the extreme hydraulic loading on the aquifers through such events, specifically changes to the water flow dynamics with potential for new, previously unrecognised contaminant pathways and associated risks for drinking-water supply wells, we measured age-tracers in selected wells again, two months after Cyclone Gabrielle. Comparing the results of this survey with age-tracer data from just three months prior to the cyclone provided an opportunity to test how extreme events like
Cyclone Gabrielle change groundwater flow dynamics in confined aquifers.

On 12 and 13 April 2023 we re-sampled for age tracers a selection of drinking-water supply wells in partnership with Hastings District Council and Napier City Council, and of private and monitoring
wells in the central and marginal confined parts of the aquifer system in partnership with
Hawkes Bay Regional Council.

The data indicate that groundwater ages in these wells have not changed significantly because of Cyclone Gabrielle. The wells that showed slight changes in age-tracer concentrations consistently showed older water after Cyclone Gabrielle. Other wells, despite showing no detectable changes in age-tracer concentrations, contained water that was more evolved after the cyclone, indicated by decreased dissolved oxygen and elevated methane, ammonia, and phosphorous concentrations.

These observations all point toward older (probably deeper) groundwater having been
pushed into the active groundwater flow paths by the increased hydraulic loading. With no younger water detected in the investigated wells following Cyclone Gabrielle, there is no indication of increased risk of pathogen contamination in the confined aquifer system following extreme flood events.

How to cite: Morgenstern, U.: Did Cyclone Gabrielle increase the risk of pathogen contamination for drinking water supply wells in the confined aquifer of the Heretaunga Plains, New Zealand?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20783, https://doi.org/10.5194/egusphere-egu24-20783, 2024.