We welcome contributions that use single or multi-tracer strategies to investigate groundwater residence times, groundwater–surface water interactions, sediment transport, fracture and aquifer connectivity, and responses to hydrological extremes and environmental change. eDNA offers a rapidly developing and complementary tracer of transport and connectivity, providing spatially resolved biological signals that reflect hydrological pathways, sediment dynamics, degradation processes, and biogeochemical controls. Together with established tracers, eDNA opens new opportunities to link physical transport processes with ecological patterns and ecosystem functioning.
The session particularly encourages studies that integrate tracers spanning different temporal and spatial scales, combine field observations with laboratory experiments and numerical modelling, or exploit sediment archives to connect present-day dynamics with longer-term records. Contributions presenting innovative sampling strategies, automated or distributed monitoring systems, novel sensors, and citizen science approaches are also welcome.
By uniting hydrogeochemical, isotopic, modelling, and biological tracer communities, this session aims to foster interdisciplinary exchange and advance our ability to characterise water and sediment pathways across complex hydrological systems. It provides a platform to explore how novel tracer or multi-tracer frameworks can improve understanding of transport processes, system vulnerability, recovery times, and sustainable management of water-dependent ecosystems.
High-intensity land use – mainly market gardening on the weathered basalts that form rich horticultural soils – has caused high nitrate concentrations in groundwater and streams discharging from the Pukekohe and Bombay volcanoes, New Zealand, exceeding the national bottom line for nitrate toxicity in rivers and maximum acceptable value in drinking water.
The main nitrate load, from market-gardening activity, infiltrates into large groundwater stores in the basalt formation, discharging mainly through three large springs with a Mean Transit Time (MTT) of 17 and 36 years.
Without denitrification in this groundwater system (no electron donors to facilitate microbial denitrification reactions), the entire nitrate load into the basalt eventually returns to the surface with a lag time of 17 and 36 years at the springs, with high nitrate-N concentrations up to 25 mg/L, causing high nitrate-N concentrations in the receiving streams. Because of the long MTTs of nitrate loads through the basalt, results of potential source-mitigation actions will be delayed.
Tritium data showed that all sampled streams contained younger water in winter compared to summer, indicating activation of shallower flow paths into the streams during the wet season. However, even at winter baseflow, the stream waters were still relatively old, with MTTs 6-12.5 years.
While the passage of the high nitrate load through the basalt formation and the seasonal flushing of nitrate from the pastoral grazing land in the Pleistocene is reasonably well understood, little is known about nitrate sinks within this catchment. Nitrate loads significantly decreased along the course of most of the sampled streams. Some streams, mainly those
in the Pleistocene formation, had near-zero nitrate concentrations despite pastural farming being the predominant land use in their catchments. This implies significant nitrate sinks in these catchments. Better understanding of these nitrate sinks may enable enhancement of natural attenuation of high nitrate loads in these waterways.
Anoxic groundwater discharges, presence of excess nitrogen, and dilution of stream nitrate loads by anoxic groundwater discharges indicate that denitrification in groundwater systems occurs in some formations.
The largest nitrate sinks within the catchment were found within the surface waterways. Nitrate stable isotopes indicate that the main process of nitrate removal from these waterways is through natural denitrification.
In smaller streams and a pond, 80–100% of nitrate from land-use activities was found to have been removed. In two of the largest streams, nitrate-load reductions of c. 30% were observed between sampled sites.
In the Pleistocene formation, with land use mostly pastural farming, nitrate is flushed
out seasonally. This area discharges water and nitrate loads only via shallow flow paths, which are not active in summer. In one stream, nitrate had been completely removed from the water during the low summer flow. But even in winter, when discharges are active,
around 80% of the nitrate is being removed from the water. This nitrate removal may partially occur within the stream bed but could also have significant
How to cite: Morgenstern, U., Buckthought, L., Stenger, R., and Gardner, P.: Groundwater Age and Isotope Tracers to Understand Sources, Flowpaths, and Sinks of Nitrate, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3431, https://doi.org/10.5194/egusphere-egu26-3431, 2026.
Lake Velence is a shallow soda lake, the third largest natural lake in Hungary. It is a valuable protected aquatic ecosystem but at the same time it is exposed to various anthropogenic pressures such as commercial and recreation activities, including water sports and fishing. Its shallow depth makes it susceptible to droughts and evaporation. In recent years, the water level of the lake has decreased dramatically, resulting in changes in water management, declining water quality and conflicts over its multiple uses. Climate change effects in Hungary will likely stress the lake’s water resources and ecosystems even further in the future.
Despite groundwater mapping in the area proving that the lake is at the discharge point of local groundwater flow systems, only the surface water components and precipitation are considered in the lake’s water budget. Numerical models showed that groundwater contributes an annual average of 5% (up to 12%) of Lake Velence's inflows. Considering that the watercourses flowing into the lake are groundwater fed as well, the share of groundwater in the lake’s inflow can be as high as 56%. Revisiting water management practices in the area is thus necessary for the local ecosystem and tourism industry. We assessed surface water-groundwater interactions in the catchment area using natural tracers to collect further evidence on the importance of this connection. Water samples were collected from different water sources: from the lake, inflow streams, an artificial reservoir, and groundwater wells. The samples were analysed for stable isotopes of oxygen and hydrogen, and natural radioactive isotopes of uranium, radium, and radon. Additionally, these geochemical tracers were mapped across the lake, providing a spatially specific signal of groundwater inputs throughout the entire water body. Radon activity concentration was measured by liquid scintillation (LSC) technique and by a radon-in-air monitor with RAD-AQUA attachment (RAD7, Durridge). Uranium and radium were measured using selectively absorbing NucFilm discs and alpha spectroscopy.
The results provided not just physical proof of groundwater inflow into Lake Velence and its inflowing streams but a detailed spatial distribution of these inputs. For example, radon concentrations were significantly higher than expected from just in-situ production alone and was detected even by liquid scintillations technique (1-6 Bq/L) both in the lake and in the streams. Measurements with the RAD7 showed values between 0.017 and 4.72 Bq/L. Uranium values were between 96 and 498 mBq/L. All isotopes combined provide unequivocal evidence that groundwater contribution to lake water budgets is important and that groundwater management has to be reconsidered in order to improve lake water levels and water quality.
The research was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences. This work has been implemented by the National Multidisciplinary Laboratory for Climate Change (RRF-2.3.1-21-2022-00014) project within the framework of Hungary's National Recovery and Resilience Plan supported by the Recovery and Resilience Facility of the European Union.
How to cite: Erőss, A., Baják, P., Bujbáczi, F. L., Hegedűs-Csondor, K., Horváth, Á., Czuppon, G., Bená, E., and Dulai, H.: A multi-tracer approach reveals groundwater inflows to a soda lake and its streams suffering from water shortage in Hungary , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14239, https://doi.org/10.5194/egusphere-egu26-14239, 2026.
The Great Artesian Basin (GAB) in Australia is one of the largest aquifer systems in the world which hosts valuable groundwater resources and supports groundwater dependent ecosystems, townships and a substantial agricultural industry. While groundwater recharge and flow through the GAB and its sub-basins have been studied for decades, the regional-scale discharge mechanisms, e.g. springs, have received a lot less attention. The springs of the Great Artesian Basin hold immense ecological and cultural significance. They have sustained Australian Indigenous communities for millennia and support complex, unique ecosystems that are critical to biodiversity and global heritage protection. Greater confidence on spring source aquifer attribution is a crucially missing part of protecting these unique spring systems as water demands from the contributing aquifers for mineral extraction, agriculture and townships is steadily increasing.
Here, we present an example of spring hydrogeochemistry and aquifer attribution conducted as part of a large collaborative initiative between major Australian federal and state government agencies and universities. The work involves a multi-tracer approach, including major ions, stable isotopes, Sr-isotopes, cosmogenic isotopes as well as dissolved gases concentrations and gas isotope compositions to better constrain the aquifers which contribute to spring discharge in the eastern part of the Great Artesian Basin. We have sampled multiple spring complexes, 29 springs across 6 complexes, across Queensland as well as groundwater bores in the regions around the springs to characterise spring source aquifers and provide baseline data for management decisions. The hydrogeochemistry is combined with conceptual geological models to understand the impact from water abstraction to spring discharge. Isotopes, in particular the Sr-isotopes show significant differences between aquifer units across the Great Artesian Basin.
The information on spring aquifer attribution is crucial to inform decision makers in the process of developing policies to protect these unique springs. The methodology for the spring aquifer attribution can be translated to other large sedimentary basins across the world.
How to cite: Hofmann, H., Raiber, M., McDougall, A., Pearce, J., Wallace, L., Dupuy, M., Wu, J., Marshall, S., Ransley, T., Cendon, D., Bell, E., Hansen, J., Burt, M., and Quealy, A.: An integrated tracer approach to determine spring aquifer attribution in Australia’s Great Artesian Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15256, https://doi.org/10.5194/egusphere-egu26-15256, 2026.
Mountain groundwater systems face imminent changes due an increasing low-snow winter occurrences related to climate change. Understanding how these systems react to the changing water availability is of great importance, especially the dynamics between recent recharge and older groundwater. Environmental age tracers can be useful to inform on the groundwater mixing dynamics in mountain aquifers. However, these mixing dynamics often remain poorly constrained. The radioactive isotope argon-39 (39Ar, T1/2=268 yr) is an important groundwater age dating tracer, filling the dating gap (ca. 50-1000 years) between the widely used tracers tritium and radiocarbon. With the development of the Atom Trap Trace Analysis (ATTA) technique, 39Ar can now be sampled in smaller sample sizes (~5-10 L), making it accessible for sampling in mountainous regions.
We report on a study sampling groundwater for 39Ar from three bedrock monitoring wells of ~10-70 m depth along a mountain hillslope underlain by fractured shale in the East River Watershed near Crested Butte (Colorado, USA). Measured 39Ar concentrations show a downslope increasing gradient from 1.5 times enrichment, compared to modern concentration, on the upslope to 17 times atmospheric abundance at the bottom of the slope. Modeling results show that the observed elevated 39Ar activities in the groundwater can be reproduced by subsurface production of 39Ar in the rock, predominantly due to muon capture reactions, which has been recently demonstrated in a Danish sand aquifer (Musy et al., 2023). The results and their implications will be discussed in the hydrogeological context of the study area.
Musy, S., Hinsby, K., Troldborg, L., Delottier, H., Guillon, S., Brunner, P., and Purtschert, R., 2023. Evaluating the impact of muon-induced cosmogenic 39Ar and 37Ar underground production on groundwater dating with field observations and numerical modeling. Sci. Total Environ., Volume 903, 166588, ISSN 0048-9697
How to cite: West, C., Thiros, N., Neumann, F., Urbach, K., Wachs, D., Hieronimus, E., Meienburg, F., Mandaric, N., Junkermann, A., Oberthaler, M., Aeschbach, W., and Gardner, W. P.: Elevated Argon-39 Concentrations in Groundwater of a Sub-Alpine Fractured Mountain Aquifer in the East River Watershed, CO, USA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18174, https://doi.org/10.5194/egusphere-egu26-18174, 2026.
Predicting elemental cycles and maintaining water quality under increasing anthropogenic influence requires knowledge of the spatial drivers of river microbiomes. However, understanding of the core microbial processes governing river biogeochemistry is hindered by a lack of genome-resolved functional insights and sampling across multiple rivers. Here we used a community science effort to accelerate the sampling, sequencing and genome-resolved analyses of river microbiomes to create the Genome Resolved Open Watersheds database (GROWdb). GROWdb profiles the identity, distribution, function and expression of microbial genomes across river surface waters covering 90% of United States watersheds. Specifically, GROWdb encompasses microbial lineages from 27 phyla, including novel members from 10 families and 128 genera, and defines the core river microbiome at the genome level. GROWdb analyses coupled to extensive geospatial information reveals local and regional drivers of microbial community structuring, while also presenting foundational hypotheses about ecosystem function. Building on the previously conceived River Continuum Concept, we layer on microbial functional trait expression, which suggests that the structure and function of river microbiomes is predictable. We make GROWdb available through various collaborative cyberinfrastructures, so that it can be widely accessed across disciplines for watershed predictive modelling and microbiome-based management practices.
How to cite: Borton, M. and the GROWdb USA: Drops to Data: Harnessing Participatory Science to Decode Aquatic Microbiomes Across the United States, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14131, https://doi.org/10.5194/egusphere-egu26-14131, 2026.
Characterizing the influence of glacial meltwater on groundwater recharge remains a significant challenge due to the complex geology, rugged topography of high-mountain environments and overlapping isotopic fingerprints of potential recharge sources in some settings. In the Peruvian Central Andes, the Mantaro aquifer serves as the primary water source for human consumption in Huancayo city. While surface water resources are increasingly threatened by the accelerated retreat of the Huaytapallana Cordillera glaciers, the specific impact of glacial retreat on groundwater storage remains unknown. This study investigates the hydrological connectivity between Huaytapallana glacier meltwater and the Mantaro aquifer by integrating microbial DNA metabarcoding and stable isotope analysis 2H and 18O in water. We collected 32 samples including water (from glacier meltwater, lakes, springs, streams, and groundwater) and sediments in the Shullcas basin. Microbial biomass was collected by filtration and DNA was extracted. The V3-V4 region of the 16S rRNA gene was sequenced using Illumina Next-Generation Sequencing (NGS). Bioinformatics processing was conducted via the DADA2 pipeline in R platform. We analyzed microbial community composition, alpha/beta diversity, and shared taxa (ASVs/genera) to identify biological tracers. At the same time, monthly stable isotope data 2H and 18O from 2025 were analyzed using dual isotope plots to determine seasonal recharge sources.
Isotopic signatures indicate that groundwater consists of a stable mixture across both dry and rainy seasons, with precipitation, glacier meltwater and surface rivers identified as primary recharge sources. Microbial analysis identified 12,989 ASVs and 695 genera. Taxonomic analysis revealed that the top 10 genera in terms of relative abundance were Hgcl clade, Flavobacterium, Brevundimonas, Sphingorhabdus, Romboutsia, Fusibacter, Pseudarthrobacter, Cypionkella, Sphingomonas, and Ferruginibacter. Alpha and beta diversity analysis and the detection of the genus CL500-29 marine group y Pseudarthrobacter in both meltwater and groundwater supports the existence of a cold, oxygenated hydrological glacial origin for recharge. Although 317 genera were shared across all sites, 12 genera were found exclusively in both glacier meltwater and groundwater. This exclusive community comprises psychrotolerant, oligotrophic, and acidotolerant taxa, including degraders of ancient organic matter (Granulicella, Cellulomonas) and taxa associated with ice environments (Subtercola, Arcticibacter).
Despite the complex geology and the 20 km distance between the Huaytapallana Cordillera and the Mantaro aquifer, our findings confirm a direct hydrological and biological connectivity between the glacier and aquifer. This link is evidenced by shared microbial taxa (specifically psychrotolerant taxa) and stable isotope signatures. Currently, we are further quantifying the proportion of glacial meltwater that contributes to aquifer recharge and estimating the travel time from the glacier to the extraction wells. These ongoing analyses are crutial for predicting the long-term impact of glacier retreat on water availability. Our results emphasize the need to integrate glacial dynamics into groundwater management plans and high-mountain recharge programs to ensure sustainable water supply for the Shullcas River basin.
How to cite: Mamani Larico, A. J., de la Cruz Solano, H., Gonzales-Llontop, M. J., Frisbee, M., Custodio Villanueva, M., and Boza Espinoza, E. T.: Glacial-Groundwater connectivity through DNA Metabarcoding and stable isotope tracers in Peruvian Central Andes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15995, https://doi.org/10.5194/egusphere-egu26-15995, 2026.
Two-dimensional (2-D) hydrodynamic models based on high resolution bathymetric data from Airborne Lidar Bathymetry (ALB) surveys and cross-profile surveys are widely used to describe spatial flow variability in river systems and are particularly important in restored and widened river reaches, where flow patterns are highly heterogeneous. In parallel, environmental DNA (eDNA) has emerged as a cost-effective and non-invasive tool for biodiversity monitoring. However, linking eDNA signals to hydraulic processes in complex river geometries remains a key challenge, limiting its application for assessing restoration success.
This study investigates the relationship between hydrodynamic conditions and fish eDNA dispersion and occurrence in a restored alpine river reach. The study site is located on the Inn River between Stams and Rietz in Tyrol, Austria, where as part of river restoration measures, bank protections were removed to widen the river and side arms were created to provide hydraulically diverse conditions for habitats. A controlled eDNA source, consisting of a cage containing dead eels (Anguilla anguilla), was placed in a side arm of the restored reach. Water samples were collected at multiple locations downstream and across the river and filtered on site. The eDNA was extracted from the filters and analysed for fish DNA using metbarcoding and general fish primers. Additionally, all samples were screed for eDNA of eel using qPCR and the total amount of overall fish eDNA from was determined for each sample.
The spatial distribution and occurrence of eDNA from fish is analysed in relation to simulated hydraulic parameters, including flow velocity and water depth, derived from a 2-D hydrodynamic model. The results provide insights into how local flow conditions influence eDNA transport and dilution in restored river sections. This improved process understanding supports the use of eDNA as a monitoring tool for river restoration projects and contributes to the ecological assessment of restored reaches in line with the European Water Framework Directive.
How to cite: Anwer, M. A., Schletterer, M., Traugott, M., and Aufleger, M.: 2-D Hydrodynamic Modelling of eDNA Dispersion and Occurrence in a Restored Alpine River Reach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17721, https://doi.org/10.5194/egusphere-egu26-17721, 2026.
Both the quantity and quality of water in streams is influenced by the flowpaths of water as it moves through the subsurface. Hydrologic flowpaths are interconnected with streamflow recession dynamics as highly nonlinear recessions are indicative of the drainage front rapidly receding towards the hydrologic divide. However, quantifying these flow paths remains a challenge with geochemical or isotope-based tracer methods when underlying geologic or temporal structures have limited variation. As DNA sequencing has advanced rapidly, it has been observed that microbial communities are also affected by changes in hydrologic dynamics and thus might indicate flow paths. Currently, the predictive capacity of genomic information about hydrologic flowpaths is unknown. Here we show that Amplicon Sequence Variants (ASVs) and the microbial metagenome is predictive of various summertime baseflow recession dynamics in the Pacific Northwest of the United States. Evaluation of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with genes measured during recessions demonstrates that multiple plant specific genes such as zeatin biosynthesis show elevated presence during highly nonlinear recession periods (p =0.051). Overall, we find the phylogenetic annotated metagenome is able to accuracy predict bi-weekly mean log discharge (R2 = 0.79), sample date discharge (R2 = 0.22) and recession non-linearity (R2 = 0.66). By linking microbial metabolic pathway profiles to hydrologic behavior, we identify potential biological indicators of watershed recession dynamics and the pathways that water flows through in the subsurface. These findings offer a promising approach for integrating microbial ecology with hydrologic modeling, advancing our understanding of how water drains from catchments.
How to cite: Good, S., Avila, C., and Crump, B.: Microbial eDNA Predicts Hydrologic Recession Dynamics , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14480, https://doi.org/10.5194/egusphere-egu26-14480, 2026.
Assessing the ecological quality of inland waters is key to managing resources and guiding sustainable agriculture practices. In EU member states, the monitoring of surface waters is based on the Water Framework Directive (WFD; 2000/60/EC), which links the ecological status with anthropogenic pressures. For this, the framework introduced the biological quality elements (BQEs) that are used to establish ecological status. Among BQEs, a key element for assessing nutrient enrichment reflecting eutrophication is phytoplankton, for which several multi-metric indicators have been proposed and used for different types of lake and river water bodies. Among the metrics included in phytoplankton indicators, biomass, cyanobacterial contribution to total phytoplankton and composition are routinely integrated. However, classical phytoplankton measurements are based on the microscopic identification of several morphologically dubious taxa, cryptic and rare species, especially in the pico- and nanoplankton. Thus, eDNA high-throughput sequencing is emerging as a cost-effective, massively parallel approach to resolve morphology-based bottlenecks on phytoplankton water quality indicators. Aiming to propose and develop a multi-metric eDNA-based water quality indicator, we applied a staggered strategy using SSU rRNA gene metabarcoding of planktonic communities across lakes of different typologies in Greece and Cyprus. First, the mirroring of metabarcoding normalized abundance data, presented as relative number of reads per taxon, with conventional estimates of phytoplankton abundance and biomass was attempted. We found that correcting for unicellular eukaryotic rRNA gene copy number based on taxon-specific biovolume data provided reliable coupling of biomass-based metrics and read numbers. Then, assessment metrics were selected to reflect eutrophication conditions in the eDNA-based indicator through ecological modelling tools, including multiple linear regression models and random forest predictors. Among the tested metrics, the most fitted were the relative number of cyanobacterial reads, the dominance of bloom forming taxa, and the ratio of harmful:non-harmful groups or taxa. Using eDNA tools will further lead to the development of emerging indicators of additional quality elements, such as bacterioplankton, zooplankton, and functional diversity. Bacterial groups, albeit not included in the WFD legislation, can play key roles in nitrogen, phosphorus, and organic carbon cycling, with metabolic pathways that process many of the pollutants associated with eutrophication. Zooplankton species are the link between primary producers and higher trophic levels, containing taxa that are directly linked to eutrophication. In addition, by integrating shotgun metagenomics to resolve the underlying gene content, the functional genetic capacities of planktonic communities can be associated with environmental stressors reflecting the overall water quality. By associating phytoplankton metacommunity dynamics (composition, functional traits, and indicator taxa metrics), to hydro-ecological connectivity gradients, eDNA can provide a scalable tool for assessing ecosystem health, resilience, and the impacts of fragmentation or homogenization.
How to cite: Genitsaris, S., Moustaka-Gouni, M., Alonaris, E., Kolisis, F., Polykarpou, P., Dörflinger, G., Dimitriou, E., Kormas, K., Omirou, M., and Soulis, K.: Development of multi-metric eDNA-based indicators of water quality based on planktonic microorganisms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5858, https://doi.org/10.5194/egusphere-egu26-5858, 2026.
Living organisms are constantly shedding DNA in to their environment. Some portion of that DNA may
eventually become bound to sediments, buried, and later recovered in an ancient DNA laboratory. Many
studies have used such ancient DNA from sediments to study past ecosystems, or to zoom in on the
population genetics of specific organisms. The source, the specific route that this DNA took on its way to
adhering to a mineral particle, and the subsequent fate of that mineral particle are critically important to
the interpretation of the genetic results, yet in many studies are unknown. Here we examine data from
several studies to investigate the source of ancient DNA in lake, terrestrial, and archaeological
sediments.
How to cite: Vernot, B. and Nota, K.: On the origins of DNA in sediments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21321, https://doi.org/10.5194/egusphere-egu26-21321, 2026.
The subarctic North Pacific serves as a critical repository for terrestrial organic matter, yet the limited taxonomic resolution of traditional isotope and biomarker proxies constrains our ability to identify both its source taxa and source regions. Therefore, the source and transport dynamics of terrestrial organic matter in this basin remain poorly understood. Here we use land-plant sedimentary ancient DNA (sedaDNA) metabarcoding as a high-resolution proxy to trace the taxonomic composition and continental source regions of terrestrial organic matter, performing a same-proxy comparison between marine sediment cores from off-Kamchatka and the Bering Sea and lake records from Siberia and Alaska. We obtained unprecedented taxonomic resolution of terrestrial plant signals in both marine sediment cores, revealing a persistent, taxonomically coherent assemblage dominated by riparian taxa (e.g. Salicaceae). The comparison between marine and lake records reveals that marine archives largely represent a nested subset of the regional terrestrial taxon pool, with riparian vegetation overrepresented and steppe-tundra herbs and conifers underrepresented relative to lakes. This reflects integration across catchments, with hydrological filtering further amplifying these abundance contrasts in marine archives. A few region-specific indicator taxa (e.g. Spiraea salicifolia and Shepherdia canadensis) could be identified, providing direct taxonomic evidence for continental source attribution. Across the glacial–deglacial–Holocene transition, land-plant DNA assemblages in marine records shifted significantly, capturing changes in source taxa. These shifts are accompanied by changes in the coupling between marine and lacustrine records, highlighting dynamic source–sink connectivity over time. Our results demonstrate the potential of sedaDNA as a high-resolution tool to trace terrestrial organic matter in high-latitude oceans, highlighting the need for expanded DNA reference databases and further research into taphonomic processes affecting DNA in marine sediments.
How to cite: Lu, H., Stoof-Leichsenring, K. R., Weiß, J. F., Zimmermann, H. H., Lembke-Jene, L., and Herzschuh, U.: Tracing terrestrial organic matter dynamics in the subarctic North Pacific using sedimentary ancient DNA metabarcoding, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19846, https://doi.org/10.5194/egusphere-egu26-19846, 2026.
Over the past two decades, hydraulic tomography (HT) has been proven as a robust method for subsurface heterogeneity characterization with high resolution, which is critical for predicting solute transport.
In this study, HT was used to characterize the hydraulic conductivity (K) distribution within a laboratory sandbox aquifer, following established workflows from previous studies. The influence of estimated K fields on model calibration and validation performance was evaluated. Additionally, tracer injection data were considered as a key factor in the analytical framework. The simulated concentrations were compared to the observed data using inverse results derived from multiple modeling approaches, coupled with the classical advection–dispersion equation.
The analysis yielded the following results: 1) geostatistical inversion provided better heterogeneity characterization compared to geology based zonation model, particularly in terms of hydraulic head data; 2) geostatistical inversion exhibited enhanced performance over the geology-based zonation model in predicting solute transport as evidenced by tracer concentration data, when injection data was incorporated into the inverse modeling framework; 3) breakthrough curve analysis revealed that solute transport predictions derived from HT still exhibited notable limitations, highlighting the need for further improvements; 4) overestimation issue identified in the HT results is linked to factors beyond observational error.
Overall, this study highlights that the advantages of geostatistical inversion are obvious in heterogeneity characterization, and the involving of the tracer injection data is critical for improving solute transport prediction.
How to cite: qiu, H., Hu, R., and Huang, Y.: Comparative predictions of solute transport with hydraulic tomography in a laboratory sandbox aquifer: the importance of the injection data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-150, https://doi.org/10.5194/egusphere-egu26-150, 2026.
The hyporheic zone is the shallow subsurface beneath and adjacent to streams characterized by bidirectional groundwater-surface water exchange. This exchange can intensify during high-flow events, driving stream water into streambanks where it may persist as bank storage for weeks to months. However, groundwater ages in shallow near-stream wells (often used as proxies for hyporheic exchange) are frequently interpreted with exponential mixing assumptions that may not be valid under prolonged bank storage. As a result, bank-infiltrated water can be misidentified as young groundwater discharge, leading to biased estimates of stream-aquifer exchange and erroneous source attribution. In this study, we quantify how flood-driven bank infiltration perturbs near-stream groundwater age distributions in Pyeongjeong Stream (Chungcheongnam-do, South Korea) by integrating hydraulic head, electric conductivity (EC), and tritium data. Event-scale hydraulic gradients show that flood onset rapidly enhances stream-to-aquifer flow as stream stage rises faster than groundwater head. Consistent with this mechanism, EC-stage hysteresis indicates contrasting recovery behavior: stream EC decreases during precipitation events and quickly returns to pre-event levels, whereas groundwater EC remains suppressed much longer, implying persistent bank-stored water and delayed flushing. Tritium concentrations further support sustained contributions of modern recharge and/or infiltrated stream water. We then evaluate transit time distributions (TTDs) using conceptual mixing models that explicitly represent episodic bank infiltration and extended storage. The resulting TTDs deviate from a single exponential form, exhibiting a composite structure that combines a short-transit event component with a broader, older background associated with bank storage. These results highlight the need to account for flood-driven bank infiltration to interpret near-stream groundwater ages and to constrain the water sources and timescales governing hyporheic zone exchange and associated solute transport.
Keywords: Hyporheic exchange, Bank infiltration, Flood event, Transit time distribution
Acknowledgement: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (RS-2025-00552981).
How to cite: Kim, Y. J., Kaown, D., Lee, S.-H., Seok, H.-Y., Lee, S.-S., and Lee, K.-K.: Evaluation of flood-driven bank infiltration effects on hyporheic zone groundwater age distributions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2299, https://doi.org/10.5194/egusphere-egu26-2299, 2026.
Accurate prediction of groundwater flow dynamics is often limited by the assumption of spatially uniform aquifer properties, which can result in biased hydraulic head estimates. Although the depth dependence of aquifer parameters is well recognized, most available analytical solutions remain confined to homogeneous aquifer systems. This study presents a two-dimensional transient analytical model for a regional single-layer aquifer subjected to a fluctuating water table, explicitly incorporating depth-dependent hydraulic conductivity and specific storage, along with pumping effects. The analytical solution is obtained using the Generalized Integral Transform Technique (GITT), which implicitly enforces continuity of hydraulic head and flux across depth variations without the need for iterative eigenvalue estimation, thereby providing a robust framework for representing stratified aquifer behavior. Model verification is conducted using a benchmark single-layer solution, and independent validation is performed through COMSOL Multiphysics simulations, demonstrating excellent agreement. The influence and reliability of model parameters are further evaluated using global sensitivity analysis. A key novel contribution of this work is the identification of chaotic flow behavior within a single-layer Tóthian basin, examined using the Finite-Time Lyapunov Exponent (FTLE). The results reveal that chaotic dynamics are most pronounced near the upper boundary, where FTLE values are significantly higher than in deeper regions, with further intensification observed under periodic injection in a single-well system. Overall, the proposed analytical framework addresses a critical gap in transient single-layer groundwater flow modeling, enhances the theoretical understanding of stratified aquifer systems, and provides a reliable benchmark for numerical simulations and field-scale groundwater studies.
How to cite: Maurya, S., Sarmah, R., and Sonkar, I.: An Analytical Model of Chaotic Advection in Regional Groundwater Flow Driven by Periodic Water Table Fluctuations and Depth-Dependent Aquifer Properties, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7228, https://doi.org/10.5194/egusphere-egu26-7228, 2026.
StorAge Selection (SAS) functions describe how catchments selectively remove water of different ages in storage via discharge, providing insights into subsurface flow paths and solute export behavior. SAS-based models have been used to study conservative and reactive solute exports and are typically calibrated against in-stream solute concentrations. However, as the simulated transit times in these models are not explicitly linked to physical processes, questions remain regarding the consistency of SAS-derived transit times with transit times derived from physically based model. To evaluate the validity of transit times obtained from SAS-based models such as the conceptual mHM-SAS model (Nguyen et al. 2021), we employ the 3D physically-based model HydroGeoSphere coupled with particle tracking. The physically based model coupled with particle tracking can explicitly simulate catchment water storage dynamics, spatial heterogeneity in subsurface flow and solute transport pathways, water ages, and transit time distributions (TTDs). We hypothesize that both modeling approaches are expected to reproduce comparable nitrate concentration dynamics and concentration–discharge relationships at the catchment outlet, but may differ in water age compositions due to conceptual differences between the models. Through this comparison, we can evaluate the capabilities and limitations of mHM-SAS model to simulate catchment-scale nitrate export and clarify the conditions under which the mHM-SAS model may be sufficient for rapid prediction of concentrations in heterogeneous agricultural catchments. Overall, this study demonstrates that particle-tracking-based SAS functions derived from a physically based model can provide a robust benchmark for evaluating the physical consistency of calibrated SAS-based models.
Nguyen, T. V., R. Kumar, S. R. Lutz, A. Musolff, J. Yang, and J. H. Fleckenstein (2021). Modeling Nitrate Export From a Mesoscale Catchment Using StorAge Selection Functions. Water Resources Research, 57(2), https://doi.org/10.1029/2020WR028490
How to cite: Wang, Q., Yang, J., Nguyen, T., Musolff, A., and Fleckenstein, J.: Physically Constrained Storage Age Selection (SAS) Functions: Benchmarking SAS-based Simulations of Catchment Nitrate Export, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13224, https://doi.org/10.5194/egusphere-egu26-13224, 2026.
In the context of climate change and the increasing frequency of droughts, sustainable water resource management has become a major challenge worldwide, particularly in Mediterranean and arid regions such as central Chile. In systems strongly constrained by both climatic and anthropogenic pressures, understanding (i) recharge processes and (ii) groundwater-surface water partitioning in catchments and their associated sensitive coastal wetlands is essential for effective catchment-scale management.
This study aims to characterize the origin of freshwater within the semi-arid coastal Huaquén catchment and the associated perennial wetland located at its outlet to the Pacific Ocean. Fully distributed numerical models, calibrated at the regional scale, indicate significant inter-catchment groundwater flow, suggesting the contribution from deep and potentially old groundwater to the shallow aquifer and, consequently, to the coastal wetland. This hypothesis is tested using a multi-tracer approach applied to groundwater and surface water samples collected at multiple locations across the catchment.
The investigation integrates water geochemistry, strontium isotopes to identify source variations, stable water isotopes (δ¹⁸O) to constrain recharge and hydrological processes, chlorofluorocarbons (CFCs) as groundwater age tracers, and noble gases to identify recharge areas. By combining these tools, this study assesses the respective contributions of surface water, shallow groundwater, and deeper groundwater to the hydrological functioning of the catchment and the coastal wetland.
How to cite: Euzen, C., Leray, S., Vicuña, S., Williams, M., Quinteros, M., and Bouchez, C.: Tracing groundwater recharge and contributions to perennial coastal wetlands in a semi-arid Chilean catchment using an integrated geochemical, isotopic, and groundwater dating approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14373, https://doi.org/10.5194/egusphere-egu26-14373, 2026.
Understanding the spatio-temporal dynamics of groundwater resources is essential to anticipate future water availability under climate change and support sustainable management under competing uses. In this study, we develop a hydrological model of the Volvic volcanic aquifer system (France) using GARDENIA®, based on more than 30 years of hydroclimatic and abstraction data. This dataset allows the reconstruction of the catchment water budget and its temporal evolution. Builded on previously established groundwater residence times (Nevers et al., 2025), we integrate here age-based constraints into hydrological modelling. We first demonstrate that this coupling links groundwater ages to aquifer responses and provides a more physically consistent representation of system behaviour under future climate scenarios. Incorporating residence time information led to the distinction of two hydrodynamic units, capturing contrasted flow dynamics within the aquifer. Results of the modelling show that both climate variability and water withdrawals impact aquifer water budgets and discharges at the system outlet. Increasing frequency and duration of heatwaves and droughts enhance water demand for drinking water supply, bottling, and agriculture, thereby reducing water availability for environmental needs. Using DRIAS climate projections (Météo-France), we simulate future changes in water availability and resource allocation. Although focused on the Volvic basin, this approach is transferable to other groundwater-dependent regions and supports integrated water resource management under climate uncertainty.
How to cite: Nevers, P., Celle, H., Labbe, J., Aumar, C., Nicolau, N., and Faucon, M.: Age-based constraints as a foundation for hydrological modelling of volcanic aquifers under global change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18310, https://doi.org/10.5194/egusphere-egu26-18310, 2026.
This research outlines work conducted by the Geological Survey of Spain (IGME-CSIC) within the SIGLO-PRO project (PID2021-128021OB-I00/AEI/ https://doi.org/10.13039/501100011033/FEDER, UE) to characterise groundwater residence times in the Campo de Montiel aquifer. The study combines numerical particle-tracking simulations using MODPATH with existing empirical groundwater dating based on tritium measurements undertaken by CEDEX (Centro de Estudios y Experimentación de Obras Públicas, Spanish Ministry of Transport and Sustainable Mobility) across multiple sampling campaigns between 1971 and 2007.
A total of 61 observation points were incorporated, including wells and springs, each with one to four measurements collected over four multi-decadal sampling periods. Backward particle-tracking simulations were initiated from these sampling locations, using columns of particles in wells and radial distributions around springs to approximate natural recharge capture zones and flow pathways across the carbonated aquifer system.
Model outputs indicate that the mean groundwater residence time across the network ranges between approximately 13 and 36 years, in broad agreement with the tritium-derived ages. Although both approaches contain inherent uncertainties, their convergence supports the robustness of the residence-time estimates and suggests the aquifer behaves as a moderately slow-turnover groundwater reservoir under current recharge conditions.
Travel time across the unsaturated zone has been also considered. Although limited field evidence is available for this parameter in the Campo de Montiel system, estimates informed by previous carbonated aquifer studies suggest lag times of several months, and alternative methods—such as those proposed by Fenton et al.—are being evaluated to refine these values further. These preliminary results will be incorporated into future modelling iterations to improve understanding of recharge-to-discharge transit times, particularly for springs where shallow pathways may dominate.
Overall, the integration of particle tracking and isotopic dating provides a coherent first-order estimate of groundwater age structure for the Campo de Montiel aquifer. These findings form a basis for assessing vulnerability, understanding contaminant transport potential, and evaluating future scenarios of groundwater abstraction and recharge variability under climate and land-use change.
How to cite: Gómez-Gómez, J.-D., Baena-Ruiz, L., Pulido-Velázquez, D., Aguilera-Alonso, H., Mejías-Moreno, M., and Grima-Olmedo, J.: Integrating MODPATH modelling and tritium data to assess groundwater residence time in the Campo de Montiel Aquifer (Spain)., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12987, https://doi.org/10.5194/egusphere-egu26-12987, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot A
EGU26-21596 | ECS | Posters virtual | VPS8
Comprehensive Evaluation of Baseflow Separation Methods for Peninsular IndiaTue, 05 May, 14:15–14:18 (CEST) vPoster spot A
Reliable baseflow estimation plays a crucial role in water resource management across India's monsoon-dominated landscapes, where groundwater contributions sustain river flows through extended dry periods. This study addresses persistent data limitations in Central and Southern India by first compiling daily streamflow records from 4,862 basins sourced from the India Water Resources Information System (IWRIS), followed by rigorous pre-processing and quality control steps that yielded suitable data for analysis across hundreds of representative basins. A comprehensive evaluation of 12 baseflow separation methods was then conducted using Kling-Gupta Efficiency (KGE) against hydrologically verified baseflow benchmarks, revealing digital filter techniques, particularly the Eckhardt filter (median KGE of 0.88) as superior to conventional graphical methods across diverse hydrological regimes. These findings affirm digital filters' reliability for capturing baseflow variability in monsoon recharge areas and arid inland zones, laying a strong foundation for advanced hydrological modeling in data-constrained environments.
Keywords: Baseflow Separation, Digital Methods
How to cite: Samyuktha, P., Dubey, S., and Gautam, S.: Comprehensive Evaluation of Baseflow Separation Methods for Peninsular India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21596, https://doi.org/10.5194/egusphere-egu26-21596, 2026.
