Quantifying ecohydrological partitioning is important to understand water balance changes in the context of land cover change, and requires better integration of novel field data and improved models. Stable water isotopes are invaluable in understanding how green water fluxes are partitioned in evapotranspiration (ET) as they allow to constrain estimates of the depths of root water uptake that sustain interception I, transpiration T and soil evaporation E. Recent developments allowing for in-situ monitoring now provide prolonged periods of near-continuous isotope time series for multiple landscape compartments of the soil-plant-atmosphere continuum. Such high-resolution isotope data provide an invaluable resource for improving isotope-aided ecohydrological models by allowing to inform model structure, enhance process understanding and constrain flux estimates.
Here, we use concurrent in-situ isotope time series of entire growing periods of soil water, xylem water and atmospheric water vapour in an intensively monitored urban green space in Berlin, Germany. These data were integrated into tracer-aided ecohydrological models with, e.g., isotopes in xylem and atmospheric moisture as simulation targets. Both variables were found to be informative, although xylem isotopes were less stable with ambiguities in terms of the influence of internal ecophysiological processes or methodological problems. Atmospheric vapor sampled at 1, 5 and 10m heights was logistically much simpler and captured well the isotopic signals of I, E and T from the xylem, as well as more regional influences.
We could resolve ET fluxes revealing seasonal changes in dominant sources of root water uptake, as well as time-variant changes in the relative important of E, I and T to ET losses. Inter-species differences between willow (Salix) and maple (Acer) trees were also captured. The study demonstrated the complementarity of different isotope approaches and highlighted the under-utilised potential of atmospheric water vapour in ecohydrological models. We also demonstrated the importance of using non-isotope ecohydrological data (sap-flow and dendrometers) in conjunction as calibration constraints.
How to cite: Tetzlaff, D., Birkel, C., Smith, A., Ring, A.-M., Landgraf, J., and Soulsby, C.: Tracer-aided modelling with in-situ isotope data to advance understanding of ecohydrological partitioning in urban areas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3993, https://doi.org/10.5194/egusphere-egu25-3993, 2025.
Whilst stable water isotopes have enhanced process understanding and tracer-aided ecohydrological modelling in contrasting landscapes around the World, most studies have been undertaken in relatively small catchments with limited anthropogenic management and disturbance. There are clear knowledge gaps in terms of how such approaches can be applied in larger, more complex landscapes with more intrusive management impacts from agriculture, industry and urban areas. Under more dominant influence of human management decisions, the ecohydrological coupling between land use, water storage and water fluxes become even more complicated. Understanding and quantifying these couplings requires improved, integrated modelling of the more natural and more managed components of catchment systems. As water stable isotope (ẟ18O and ẟ2H) are effective in identifying water sources, flow paths and transit times, and have been increasingly applied in tracer-aided hydrological modelling, we use them here to better understand the hydrology of the Spree catchment in Germany. This is a major strategic water resource which provides Berlin’s main drinking water supply, maintains significant agricultural irrigation and sustains local industrial needs. We focus on a 2800km2 sub-catchment; the ET-dominated Spreewald region that has a heterogenous mixed land use (croplands, pastures, forests and urban) but is heavily influenced by water resource management interventions (regulated and unregulated abstractions, inter-basin transfers etc.). We used the spatially distributed tracer-aided model STARR to simulate the effects of natural water storage-flux dynamics and monitored management intervention on stream flow over a 6 year period. We found that conventional spatially-distributed streamflow-based calibration resulted in unrealistic isotope simulations, with large uncertainty in rainfall partitioning, overestimation of soil evaporation and ambiguity of runoff sources. Re-parameterization of the model provided a better constraint on isotope simulations across the model domain with no deterioration of streamflow estimates and a much stronger apportionment of runoff to groundwater and upstream sources. This was further validated against local flux tower data and satellite derived ET products (PML) for the region. However, some sub-catchments within the model domain under-predicted summer stream flows and these were consistent with areas where un-monitored irrigation in riparian croplands likely increases ET and reduces stream flow. The modelling framework used shows promising potential for wider use of isotopes in large scale tracer-aided modelling of complex, heavily managed catchments. Isotopes can help reduce equifinality in traditional water resource modelling and help identify the influence of unregulated human managements effects such as irrigation. However, given the inevitable logistical constraints in isotope sampling over extensive areas, integration with satellite products, such as ET or soil moisture estimates, can help leverage maximum value from available isotope-based insights in large-scale modelling.
How to cite: Zheng, H., Tetzlaff, D., Birkel, C., Wu, S., and Soulsby, C.: Integrating isotopes and remote sensing into large-scale ecohydrological modelling of heavily managed water resource systems in drought sensitive areas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7318, https://doi.org/10.5194/egusphere-egu25-7318, 2025.
Knowing not only quantities but also pathways of water through a catchment is crucial for an in-depth understanding of hydrological processes. This is particularly true when aiming to understand the pathways of pollutants in the environment. We use a geochemical end-member mixing approach to validate the water transfer predicted by a process-based distributed hydrological model (J2000) developed over the Claduègne rural mesoscale catchment (42 km²) under Mediterranean climate. This hydrological model represents explicitly the heterogeneity of the catchment through hydrologic response units, including 6 land cover and 4 lithology classes. It also includes a detailed representation of human activity (drinking water extraction, wastewater effluent discharge, urban overland flow, irrigation, livestock breeding). It was calibrated on streamflow discharge at three hydrometric stations throughout the catchment. It tracks water volumes through the catchment by spatial origin and four different flow processes (overland flow, subsurface storm flow; and slow and rapid groundwater flow). The mixing model distinguishes water originating from six end-members, including subsurface water from two types of lithology (sedimentary [sed] vs. basaltic [bas]) and two classes of land cover (crop and pasture [open] vs. shrubland and forest [closed]) as well as overland flow [OF] and urban sources. Each end-member was characterized by dissolved concentration of 47 elements in water samples collected at different locations and under various hydrological conditions (97 samples in total), quantified via Inductively Coupled Plasma - Mass Spectrometry (ICP-MS).
End-member signatures were repeatedly drawn from Weibull distributions fitted to samples for each end-member. Non-negative mixing contributions were optimized in order to represent measured concentrations at the outlet. Only draws resulting in a sum of contributions of 100 % (±5 %) were kept; the average of the 100 best drawn combinations (least residuals) was used as final contribution. The end-member mixing model was applied to 256 samples taken at high frequency (up to 2 h-1) during flood events (14 and 4 events at the Claduègne and Gazel outlets, respectively), in addition to low-flow samples collected at different seasons.
The contribution of overland flow was zero most of the time and peaked during flood events, with proportions up to 80-90 %. The urban contribution was mostly below 10 %, with some higher values during low flow periods.
Results were compared to tracking results from the hydrological model, run at an hourly time step. Direct per-sample correlations between the two models had the following pearson R values: urban: 0.60, OF: 0.52, sed closed: 0.54, sed open: 0.41, bas closed: 0.23, bas open: 0.31. All were significant with p<0.05, except bas closed (p<0.1). In a more qualitative way, the two models agreed on patterns over the course of flood events and over the seasons, as well as contribution-discharge relationships. We demonstrated that these two independent approaches produce coherent results, validating the hydrological model’s representation of water transit through the catchment.
How to cite: Hachgenei, N., Branger, F., Nord, G., Masson, M., Legout, C., Perron, C., Duwig, C., Spadini, L., and Coquery, M.: Validation of water transit traced by a distributed hydrological model using a geochemical end-member mixing approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15918, https://doi.org/10.5194/egusphere-egu25-15918, 2025.
Water transit times are key indicators of how catchments store and release water, as well as tracers and contaminants. Water exiting a catchment is characterized by a transit time distribution (TTD), which reflects the variability of flow paths and the mixing of individual water parcels before reaching the stream. Since TTDs cannot be measured directly, they are typically inferred from time series of tracers in precipitation and streamflow. However, not all water carries the same information, as streamflow TTDs usually consist of a narrow range of young waters that contribute significantly to streamflow, while a much broader range of older waters accounts for only a small stream water fraction. The concern is that the tracer signal from these older waters may be masked by measurement uncertainties, making it difficult to accurately capture the right tail of the transit time distribution and thus to determine the age of the oldest waters in streamflow. Previous studies suggest that seasonally variable tracers such as oxygen-18 (18O) cannot help inferring water ages beyond 4–5 years, whereas tritium (3H) may extend this limit up to 100 years. However, these results rely on limited theoretical evidence, which calls for more in-depth investigation.
In this study, we investigate the maximum age up to which the shape of the transit time distribution can be reliably constrained before the signal of the oldest waters becomes completely hidden among measurement uncertainties. Our analysis covers a wide range of typical transit time distribution shapes and two key tracers: 18O and 3H. Our results indicate that water with transit times longer than 1–3 years does not typically produce detectable variations in the 18O signal, while for 3H, this limit extends further, but unlikely beyond 10 years. This suggests that the maximum age that can be accurately estimated using these tracers is significantly lower than previously assumed. Furthermore, we show that this age limit has important implications for estimating mean transit times, as the tail of the transit time distribution strongly influences this metric. Our findings highlight the need for a more cautious interpretation of TTD tails and encourages the use of alternative statistics beyond mean transit times to characterize TTDs across catchments.
How to cite: Miazza, R. and Benettin, P.: The Unconstrainable Tails of Catchment Transit Time Distributions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16589, https://doi.org/10.5194/egusphere-egu25-16589, 2025.
In hydrological modeling, multiple combinations of parameter sets can alter catchment processes and local velocities, while still achieving the same overall streamflow (i.e., celerity), underscoring the equifinality theorem. Improving model calibration by incorporating new dimensions of information helps narrow down the range of viable models, leading to a more accurate representation of system behavior. This study investigates how different combinations of hydrometric and isotopic cross-output targets—including groundwater levels (GWL), streamflow rates (Q), and stream stable water isotopic compositions (δ18O)—influence parameter sensitivity patterns, calibration processes, and subsequently inform the dominant flowpath of the system. The research was conducted on the Pallas sub-arctic catchment in northern Finland using HydroGeoSphere (HGS), the fully integrated, physically based hydrological model. The study employed a workflow consisting of global sensitivity analysis (SA), automated parameter estimation (PE), and parameter uncertainty analysis (UA), assisted by PEST++, across multiple scenarios targeting different combinations of observables (GWL, Q, and δ18O).
The SA results showed that a combined target of isotopic (δ¹⁸O) and hydrometric data (GWL + Q) produced similar sensitivity patterns to targeting stream isotopes alone (δ18O), underscoring the crucial role of isotopes in constraining system behavior. UA results revealed that models calibrated with both hydrometric and isotopic data (Q, GWL, and δ18O) yielded the narrowest parameter uncertainty bounds, followed by the isotope-only calibration. The hydrometric-only calibration (Q and GWL) exhibited the widest uncertainty range, highlighting the role of isotope data in constraining parameter distributions, and correspondingly reducing model forecast uncertainty.
While models with different calibration targets showed similar performance in streamflow rates, stages, and isotope composition across various hydrograph stages, water balance analysis revealed variations in internal processes and flowpaths. Ground surface water partitioning (e.g., infiltration rates) was consistent across setups, but subsurface processes differed notably. Models calibrated with isotope data exhibited greater groundwater recharge via rapid deep percolation, facilitated by enhanced soil water–groundwater connectivity. While Other setups showed minimal groundwater recharge and increased soil water storage. Incorporating isotopic data emphasized vertical flowpaths essential for matching isotope observations, altering subsurface water partitioning and storage dynamics.
Isotope-enabled calibration in fully integrated physically based models enhances flowpath representation, narrows plausible parameter combinations, and provides more constrained prediction envelopes, offering a robust approach for reliably informing sustainable water management strategies.
How to cite: Nimr, O. A., Marttila, H., and Ala-Aho, P.: The Role of Stream Water Isotopes in Integrated Hydrological Model Calibration and Flowpath Identification, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9924, https://doi.org/10.5194/egusphere-egu25-9924, 2025.
Livestock animals are commonly treated with veterinary pharmaceuticals (VPs), and their residues often enter the environment through manure applied to soil. A fraction of these residues may be further transported to surface waters through intricate transport mechanisms. Here, we examine the temporal dynamics of VPs in lowland surface waters of an agricultural catchment in the Netherlands, utilizing information on VPs concentrations in manure and surface water measurements. We develop a parsimonious catchment-scale transport model for VPs that is based on time-variable water transit time distributions. The transport model considers multiple processes experienced by the VPs during their transfer to the stream network, including evapoconcentration, sorption and degradation. Our results suggest that, despite the mean water transit times of several years typical of lowland catchments, as well as relatively strong VP sorption or rapid degradation, detectable amounts of VPs in the order of 1–10 ng/L may reach the stream ecosystem through fast flowpaths characterized by short transit times. Therefore, VPs may be used as tracers of short water flowpaths in agricultural catchments.
How to cite: Benettin, P., Rakonjac, N., Miazza, R., Rinaldo, A., and Ritsema, C.: Veterinary Pharmaceuticals in surface waters as tracers of short water transit times, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4462, https://doi.org/10.5194/egusphere-egu25-4462, 2025.
A better understanding of the hydrological dynamics of aquatic ecosystems is of vital importance for assessing their ecological functions and predicting their responses to climate change. Hydrology has been shown in several studies to be a major driver of ecosystem processes in the catchment of Lake Lunz, which is part of the Global Lake Ecological Observatory Network. Stable isotopes of the water molecule (δ18O-H2O and δ2H-H2O) are a valuable tool for understanding water flow and temporal dynamics in complex, karstic catchments. Using stable isotopes, we complemented an ongoing monitoring program that samples the lake catchment and initiated a daily precipitation sampling scheme. Our objective is to examine the insights achievable from daily sampling of precipitation regarding stream hydrology. The study site is a subalpine, karstic catchment of 18 km2, overlaid with shallow soils. The data that will be discussed in this presentation covers the period from October 2021 to October 2024 spanning three hydrological years. We collected daily and monthly precipitation samples in the proximity to the outlet of the catchment (elevation 604 m.a.s.l.) and stream grab samples within the regular monitoring programme.
The outcomes of the daily stable precipitation isotope analysis revealed that the widest range in precipitation occurs during winter, with values ranging from -17 to -2.8‰ for δ18O-H2O. Conversely, the most depleted precipitation daily sample was measured during a major rain event in September 2024 with -21‰ for δ18O-H2O. River grab samples reflected the average catchment precipitation ± 1‰ that was calculated based on isoscapes for δ18O-H2O. Several heavy rain events were recorded with depleted isotope ratios. A three-component hydrograph separation suggested that recent water contributes between 10 and 50% to the stream flow and high precipitation events shifted the isotopic composition of the river. However, d-excess indicated that these events contributed little to base flow and groundwater recharge. Daily precipitation isotopes improved hydrograph separation based on stable isotopes, providing the opportunity to understand the contribution of different precipitation events to base flow.
Incorporating stable water isotopes into routine monitoring of the Lake Lunz catchment presents a significant potential to understand the water sources and their temporal dynamics. This offers an opportunity to place the ecological studies conducted in Lake Lunz within a hydrological framework and better comprehend how the system might respond to climate change impacts, including river intermittency, extreme rainfall events, decreased winter precipitation, and the thawing of the snow cover during winter.
How to cite: Harjung, A., Machado, D., Hager, H., Laura, C., Katrin, A., Stefan, T.-W., Yuliya, V., Kainz, M., and Wassenaar, L.: Daily atmospheric precipitation stable water isotopes help disentangling water flow paths and sources at a long-term limnological research station , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16623, https://doi.org/10.5194/egusphere-egu25-16623, 2025.
Soil and xylem water samples are increasingly collected for isotope analysis to study the movement of water within the soil-plant-atmosphere continuum in alpine ecosystems. However, the low sampling frequency, mainly due to severe winter weather conditions and impervious topography, remains a significant obstacle for building a comprehensive, data-driven understanding of hydrological processes in high-elevation environments.
This study focuses on integrating a newly proposed snow isotope model with HYDRUS-1D to simulate the movement of water and isotopes through the soil-plant-atmosphere continuum in a mountain grassland at 2550 m a.s.l. in the Aosta Valley, northwest Italy. While uncertainties remain regarding the timing and distribution of infiltration during snowmelt and variations in snow isotopic composition, the combined modeling approach successfully reproduces patterns of soil moisture, evapotranspiration, and isotope behavior at the site.
A key finding is the seasonal origin of water: winter-derived water (i.e., snowmelt) primarily contributes to groundwater recharge through soil percolation, while summer-derived water (i.e., rainfall) dominates plants transpiration. Evidence supporting this seasonal pattern comes also from observed isotope dynamics in both the monitored spring water and xylem water. Notably, during the 2022 drought, the ecosystem relied more heavily on winter-origin water to support evapotranspiration, providing a glimpse into how such systems might adapt to future conditions with higher temperatures and reduced snowfall.
This work was supported by the NODES project, funded under MUR – M4C2 1.5 of the PNRR with resources from the European Union - NextGenerationEU (Grant agreement no. ECS00000036), as well as the MUR PRIN project SUNSET (202295PFKP_003).
How to cite: Gentile, A., Brighenti, S., Zuecco, G., Gisolo, D., Canone, D., Hamza, T., and Ferraris, S.: Seasonal origin of water in a high-elevation grassland: insights from a modelling approach using a snow isotope model and HYDRUS-1D , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9827, https://doi.org/10.5194/egusphere-egu25-9827, 2025.
Stable isotopes of hydrogen (deuterium-δD) and oxygen (oxygen-18-δ¹⁸O) are considered ideal tracers in addressing issues related to the research, development, and management of water resources. These isotopes circulate with groundwater within the hydrogeological system and are generally unaffected by physico-chemical processes. Consequently, they are widely used to determine the origin, recharge elevation, and mixing mechanisms of groundwater. In this study, in-situ physico-chemical parameters (electrical conductivity [EC], temperature, pH, dissolved oxygen [DO], and stable isotopic composition (δ¹⁸O and δD) of the shallow groundwater system in the Kahramankazan Basin (Ankara) were examined during dry (November 2021) and wet (April 2022) periods. Previous studies indicate that the shallow groundwater system in this area has been under stress for the past 40 years due to sand-gravel mining activities and groundwater over-abstraction. As a result, the thickness of the aquifer reportedly decreased from 15–45 m to 10–25 m over the years. In-situ analyses of the samples collected during the dry period showed that EC, pH and DO values varied from 600 to 6740 μS/cm, 7.18 to 7.92 and 2.51 to 7.15 mg/l, respectively. The isotopic compositions of groundwater during the dry period ranged from -8.1‰ to -9.5‰ for δ¹⁸O (mean: -8.82‰, n=9) and from -54.7‰ to -63.4‰ for δD (mean: -60‰). During the wet period, EC values slightly decreased, ranging from 563 μS/cm to 5070 μS/cm. Some samples deviated from the Local (Ankara) Meteoric Water Line (δD = 8δ¹⁸O + 11.54). For these samples, as expected, the effect of evaporation was greater during the dry period compared to the wet period. Recharge elevations, determined from the relationship between δ¹⁸O and elevation obtained in previous studies, were found to range from 820 m to 1274 m, consistent with the topography. This study revealed that along the flow path of the alluvial aquifer, there is a notable increase in EC values and isotopic enrichment of stable isotope values due to an increase in evaporation and the adverse impacts of urbanization.
How to cite: Arslan, Ş., Alpaslan, B., Özler, M., and Canbaz, S.: Hydrogen and oxygen stable isotopes in the shallow groundwater system in Kahramankazan Basin (Ankara, Turkiye), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-824, https://doi.org/10.5194/egusphere-egu25-824, 2025.
Atmospheric chloride deposition (ACD) is an essential parameter in estimating potential groundwater recharge. However, ACD observations are still limited to a few sparsely distributed sites and/or short time intervals, which are insufficient to characterize regional distribution over a longer time scale, putting into limitation the usefulness of the easily accessible environmental chloride method for tracking groundwater dynamics in future studies. Considering the mass balance between chloride input from precipitation and soil Cl storage in the unsaturated zone, we combined 3H- and Cl-based tracing techniques to inversely reconstruct the long-term average or historical time series of ACD from the Cl stored in soil profiles. Our results highlight the proposed methods can effectively exclude fertilization impacts and perform satisfactorily in estimating ACD. However climatic and geographic factors had should be taken seriously when reconstructing ACD. A better understanding of groundwater recharge in unsaturated zones is ultimately critical for water resource management, especially in semi-arid environments with deep soils.
How to cite: Huang, Y., Ji, W., and Li, Z.: Reconstructing Atmospheric Chloride Deposition Using Chloride-Tritium Tracers Stored in Deep Loess, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10100, https://doi.org/10.5194/egusphere-egu25-10100, 2025.
To estimate water transit time distributions and aquifer storage thickness in catchments, measurements of water isotopes are used routinely. Water isotopes (e.g., D2O/H218O) are generally considered to behave identically to water molecules (H2O); they are thus considered fully representative of water movement and preferred over inert chemical tracers for catchment assessment purposes. However, laboratory-scale measurements presented here show that water isotopes exhibit anomalous transport behavior that is essentially identical to that of inert chemical tracers. For both water isotopes and inert chemical tracers, subject to anomalous transport, the measured mean tracer velocity – of both water isotopes and inert chemical tracers – is not equal to the mean water velocity (Darcy velocity). The often-manifested inequality between apparent mean water velocity and estimated mean tracer velocity must therefore be recognized when estimating catchment properties. For example, accounting for anomalous transport of water isotopes can significantly reduce estimates of aquifer storage thickness over an entire watershed.
How to cite: Berkowitz, B., Elhanati, D., Zehe, E., and Dror, I.: Water isotopes exhibit anomalous transport: implications for assessment of catchment properties, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1631, https://doi.org/10.5194/egusphere-egu25-1631, 2025.
Nitrogen loading due to urbanization, industrialization, and agricultural expansion is increasing in tropical regions, and releases nitrogen into water as nitrate ion (NO3―), causing negative effects on the environment. However, there are limited studies on the nitrogen loadings and NO3― sources in the watershed with mixed tropical land use. To address this gap, this study aims to determine the NO3― sources and tropical land use effect on the nitrogen loadings in the Langat River basin, Malaysia, which includes tropical rainforest upstream, urban areas midstream, and oil palm plantation areas downstream. The stream and irrigation water in oil palm plantations and the river water were collected during the wet and dry seasons. The samples were analyzed for major dissolved ion concentrations, water isotope ratios (δ2H and δ18O of H2O), and nitrate nitrogen and oxygen isotope ratios (δ15N and δ18O of NO3―). The NO3―concentration ranged from 1.41 mg/L to 19.09 mg/L in river water and from 0.13 mg/L to 2.44 mg/L in the stream and irrigation water in the oil palm plantation, much lower than in river water. The NO3― concentration was higher in the dry season than in the wet season, likely due to flushing during the wet season and water retention during the dry season. The δ15N-NO3― and δ18O-NO3― ratios ranged from -2.52‰ to 19.12‰ and from -3.62‰ to 23.90‰, respectively. The stream water in oil palm plantations showed a low value of δ15N-NO3―, while the irrigation water isotope values were high. This could be due to denitrification and absorption by oil palm trees during the discharge from the oil palm plantation to the outside as irrigation drainage. The NO3― concentration decreased with an increase in the proportion of forest area in the catchment, assuming each water sampling point to be the outlet. In contrast, NO3― concentration increased with the proportion of built-up areas. The δ15N-NO3― decreased as the proportion of oil palm plantations increased. These findings indicated that NO3― discharge from tropical rainforests could not contribute substantially to river water. The main sources of nitrate in river water could be ammonia fertilizer from plantation areas and sewage water from urban areas. Overall, as in previous studies, fertilizers and sewage were identified as the main sources of nitrate ions in tropical urban and agricultural areas. In addition, this study in the case of oil palm plantations revealed that although denitrification and oil palm trees absorb the NO3―, the δ15N-NO3― in the river water showed fertilizer-derived runoff, indicating that the impact of the plantations on water quality cannot be overlooked.
How to cite: Ogiya, M., Sakakibara, K., Nurhidayu, S., Shabir, Y., Nakamura, T., and Tsujimura, M.: Relationship Between Nitrate Sources and Tropical Land Use in the Langat River Basin, Malaysia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7748, https://doi.org/10.5194/egusphere-egu25-7748, 2025.
The alpine zone has been considered to have poor water storage. However, recent studies have shown that alpine vegetated areas possess water storage function. But differences in the water storage between soil and bedrock and the processes of the runoff of stored water are still not clear. Therefore, we aimed to make clear the water storage functions of alpine vegetation areas by focusing on runoff processes of groundwater. We conducted field surveys from July to October 2023 on Mt. Norikura (3,026 m), a stratovolcano in central area of Japan. These were conducted in two adjacent catchments with differing land cover types: a bare area covered with debris and a vegetated area covered with soil and dominated by Japanese stone pine (Pinus pumila). During the study period, we monitored water levels in streams and precipitation within both areas. Additionally, biweekly field surveys were conducted to measure water temperature, pH, and electrical conductivity (EC) for precipitation, snowmelt water, stream water, and spring water, as well as to collect water samples. We analyzed them for the oxygen and hydrogen stable isotope ratios, the concentrations of major dissolved inorganic ions, SiO2, and radon (Rn-222). The radon concentration was measured by liquid scintillation counter. The stream in the bare area dried up after the snowmelt season whereas that in the vegetated area gradually decreased and did not dry up throughout the study period. In the δ-diagram of oxygen and hydrogen stable isotope ratios, spring water from the bare area plotted along the local meteoric water line (LMWL), while spring water from the vegetated area plotted with a gentler slope than the LMWL. This result indicates that the spring water in the vegetated area is influenced by evaporation from canopy interception. In the vegetated area, the concentrations of major dissolved inorganic ions (particularly SO₄), SiO₂, and radon in the spring water were all higher than those in the bare area. This indicates that spring water undergoes ion exchange with clay minerals and SO4 leaching from volcanic sulfide minerals, indicating a longer and deeper flow path compared to bare spring water. Additionally, the spring water in the vegetated area has no large fluctuation in water temperature, concentration of major dissolved inorganic ions, SiO2, and radon. This indicates the contribution of groundwater from the bedrock layer. The spring water in the vegetated area, a largely negative correlation was observed between discharge and radon concentration, while only a weak correlation was found between SiO2 and discharge. This indicates that groundwater from the bedrock layer passed through the soil layer, allowing radon to undergo gas exchange with the gas phase. These results indicate that in the bare area, the coarse-grained sediment structure allows rainfall to quickly reach the bedrock surface and flow out rapidly over the bedrock. However, in the vegetated area, the developed soil restricts rainfall runoff. This likely promotes groundwater recharge into the bedrock layer, forming an aquifer and indicates a water storage function.
How to cite: Tani, K., Sakakibara, K., Hirota, M., Tsujimura, M., Fujino, M., and Suzuki, K.: Role of Soil and Bedrock Layers on Water Storage in a Vegetated Alpine Headwater under the Asian Monsoon Climate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8819, https://doi.org/10.5194/egusphere-egu25-8819, 2025.
This study presents new data on the chemical composition, content, and distribution patterns of stable oxygen and hydrogen isotopes in natural waters from the Issyk-Kul intermountain artesian basin. This area has significant balneological potential due to the abundance of mineral waters with diverse temperatures, chemical and gas compositions, and total dissolved solids (TDS). The uniqueness of this region lies in the coexistence of two distinct types of mineral waters: fissure-pore waters confined to intermountain artesian basins and fissure-vein waters associated with tectonic fault zones in rock massifs.
The study is based on field research conducted in the Issyk-Kul basin, located in the Tien Shan region. The temperature of mineral waters at the sampling sites varies widely (16.2-52.3°C), as does TDS, which depends on the hydrogeological structure. CO₂-rich waters with low TDS (0.3-0.5 g/L) form within rocks and open fractures, while carbon dioxide-nitrogen or nitrogen-methane waters with TDS ranging from 2.0 to 35.0 g/L are associated with significant sedimentary cover thickness. A common pattern in anion composition is observed, as all mineral waters contain sulfate (SO₄²⁻) and chloride (Cl⁻) ions. Sodium (Na⁺) consistently predominates in the cationic composition.
The content of stable isotopes of oxygen (δ18O) and hydrogen (δD) in the studied waters also varies significantly, from -13.9‰ to -8.5‰ for δ18O and from -95.8‰ to -66.0‰ for δD. Most data points on the δ18O-δD binary diagram align with the global meteoric water line, indicating an infiltration origin with a pronounced altitude effect.
It was also established that the trace element composition of thermal waters serves as a marker for the hydrogeological conditions of their formation and circulation: waters from the sedimentary cover of intermountain artesian basins are enriched with Sr, Ba, Mn, B, Mo, and U, whereas waters from rocky massifs contain elevated concentrations of F, Rb, W, and Sc. The calculation of the water migration coefficient revealed a dependence of the accumulation rate of trace components on the type of host formation and the hydrogeological conditions of water formation.
Ion-salt geothermometers were applied to estimate the deep formation temperatures of the mineral waters, revealing a broad range of values (21.4-144.8°C). These results reflect diverse formation conditions for the studied waters.
How to cite: Baranovskaya, E., Kharitonova, N., and Chelnokov, G.: Hydrogeochemistry of thermal waters in the intermountain basin of the Tien Shan Region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10533, https://doi.org/10.5194/egusphere-egu25-10533, 2025.
Global changes are increasingly pushing for more sustainable resources, such as geothermal energy. The thermal waters of the karst system in Budapest (Hungary) have so far been used mainly for balneological purposes. It is thus expected that in the near future they will more intensely be used for geothermal purposes as well. To this end, a comprehensive research project has been launched by the Geological Survey of the Supervisory Authority for Regulatory Affairs to gain a better understanding of the system and to assess the impact of future projects via numerical simulations. One task of this research was to perform a geochemical water sampling campaign to gain simultaneous geochemical results and characterize a baseline. In this project, also the most abundant natural radioactive isotopes in groundwater, uranium, radium and radon were measured, which were previously successfully used in the natural discharge areas to characterize fluids of different flow paths. Now, these natural tracers were applied in the entire regional study area.
Liquid scintillation technique was used to measure the activity concentration of radon. For radium and uranium, an innovative method, selectively adsorbing Nucfilm discs measured by alpha spectrometry was applied.
Based on the first results, the radon content in water samples was either below the detection limit or less than 40 Bq/L. However, 284 Bq/L activity concentration was measured in one location, which is high compared to the 100 Bq/L value for drinking water. Fluid mixing was hypothesized here.
Uranium activity concentrations were also low (8-17 mBq/l), which is associated with the mostly reductive conditions of the sampled groundwater. The reducing environment of higher order flow paths is confirmed by our sampling results by the measured higher radium contents. The radium content of the samples ranged from 10 to 1823 mBq/L. The highest radium content was found in sample BPGT-08, which with its high dissolved solid content suggests the presence of waters with a long groundwater residence time and a possible connection with organic matter (hydrocarbons). The other radium activities show similar values to those measured by previous studies in the region. For two water wells, we contributed to the interpretation of the total alpha measurements by measuring the activity concentrations of radium and uranium as alpha decay radionuclides. Our measurements allowed for the characterisation of groundwater flow systems, the identification of different geochemical environments and possible fluid mixing.
How to cite: Bujbáczi, F., Balczó, L., Horváth, Á., Hegedűs-Csondor, K., Bena, E., Szabó, Z., Szűcs, A., Tihanyi-Szép, E., Gál, N., Szőcs, T., Falus, G., and Erőss, A.: Radionuclides as natural tracers of the groundwater flow systems in the thermal karst system of Budapest, Hungary , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15536, https://doi.org/10.5194/egusphere-egu25-15536, 2025.
Land-Atmosphere (L-A) interactions play a crucial role in current as well as future weather and climate. Since the resulting feedback mechanisms depend on L-A water pathways a sound understanding of the hereto related processes is required to depict them realistically in models and to further improve model performance. Stable water isotopes fungate as natural indicators of the hydrological cycle and can hence be used to assess the performance of climate models by comparing observational data with modeled isotope data.
Therefore, the fully coupled atmospheric hydrological modeling system WRF-Hydro-Iso with its innovative “-Iso” implementation is appropriate. Tracing water pathways with WRF-Hydro-Iso, we aim to improve our understanding of the relationship and interactions between groundwater, soil moisture, plant transpiration, soil evaporation, isotope signature and L-A feedback.
For a project domain in central Europe with a 5 km resolution the forcing data of ERA5 reanalysis and iCESM isotope climatology is used. In this session, first results of the WRF-Hydro-Iso modeled isotopes and L-A interactions are presented. The modeled isotopes are assessed with the TROPOMI atmospheric water Deuterium dataset, while L-A interactions are assessed with terrestrial water budgets and isotopic signatures of the water budget components.
How to cite: Sill, H., Arnault, J., Fersch, B., and Kunstmann, H.: Impact of Terrestrial Hydrology on L-A feedback and Isotope Signatures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16058, https://doi.org/10.5194/egusphere-egu25-16058, 2025.
High-latitude regions are challenging to model due to their inherent data scarcity. This limitation hampers our ability to gain robust process understanding and forecast how these regions will respond to global warming and land-use changes. Additionally, these regions are undergoing rapid changes driven by melting snow and ice with far-reaching implications for downstream areas.
In this study, we demonstrate the value of isotope-aided hydrological modeling in improving process understanding and model reliability. Using data from two well-instrumented high-latitude catchments—the Krycklan Catchment Study and Abisko in Sweden—we developed detailed hydrological models in HYPE (Hydrological Predictions for the Environment). We applied a multi-objective calibration approach that includes stable isotopes of water alongside traditional flow data for model calibration and validation. This approach enhances the robustness of model-internal water source partitioning and provides additional insights beyond flow-only calibration.
This work is part of the Water4All project ISOSCAN, which investigates how stable isotopes of water, collected through Citizen Science initiatives, can advance hydrological modeling. By comparing flow-only calibrated models with isotope-aided multi-objective calibrated models, we evaluate the contribution of stable isotopes in improving model performance. We explore the potential of high-information-content data (such as stable isotopes of water) collected by Citizen Scientists to overcome data scarcity challenges and enhance the reliability of hydrological models in high-latitude regions.
How to cite: Popp, A., Gustafsson, D., Gudasz, C., Pers, C., Ahmed, M. I., Musuuza, J., Karlsson, J., Laudon, H., and Stadnyk, T.: Isotope-aided hydrological modeling to enhance process understanding in high-latitude catchments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17865, https://doi.org/10.5194/egusphere-egu25-17865, 2025.
Tracer-based approaches play a crucial role in advancing our understanding of hydrological processes, particularly in determining catchment transit time distributions (TTDs). TTDs describe the distribution of water ages in fluxes leaving a catchment, providing critical insights into flow paths, storage, and transformation processes. Despite the value of these analyses, applying tracer-based methods often remains challenging due to the high costs and practical difficulties associated with comprehensive sampling strategies. Multi-tracer approaches are particularly valuable because different tracers (e.g., stable isotopes and tritium) provide additional information of catchment transit times, enabling more comprehensive system characterization. In this presentation, we present a methodological approach to assess the optimization of sampling strategies for tracer-based TTD modeling using isotopic data and the SAS (StorAge Selection) framework trough an information-theoretic approach. In this context, sampling design refers to the systematic evaluation of the informational contribution of individual samples and their combinations in estimating transit time distributions (TTDs). Specifically, we quantify the information content of individual tracer samples, assess how different combinations of samples collectively enhance the accuracy of TTD estimations, and evaluate and present the effectiveness of different sampling strategies. Additionally, we compare the information content of different tracers (e.g., deuterium and tritium) with SAS-based transit time models and evaluate how each tracer improves the precision of TTD predictions. The tested sampling strategies included baseline and event-based strategies. Our approach builds on recent advancements in hydrological theory, including the use of multi-tracer methods and the SAS framework. The results will provide a detailed comparison of the information content of different samples, tracers, and sampling designs, highlighting the relative contribution of deuterium and tritium to inform TTD analysis. The results from this study will contribute to informing hydrological field campaigns by providing guidelines on optimal sampling strategies for TTDs estimation. By that, guidelines for optimal sampling protocols for information gain balanced with cost for field work can be developed in the future. The findings will promote the broader application of tracer-based methods in hydrology, offering practical solutions for data-scarce environments and enhancing sustainable water management practices.
How to cite: Babaei, F., Arora, M., Bogena, H., Western, A., and Klaus, J.: Using Information Theory to Optimize Sampling of Isotope Tracers for Transit Time Estimation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18903, https://doi.org/10.5194/egusphere-egu25-18903, 2025.
Headwater streams in valleys comprise land surfaces with deep flow paths as well as impervious surfaces where urban centers have developed strategically near water. The impaired Mill River Watershed discharges into the Connecticut River of the Northeastern US after flowing through heterogenous land-uses in a valley system. In this study, we young water fractions across from watershed sources contributing to the CR as well as to Lake Warner. We compare theses dynamics and the inuence of urban, agricultural, and rural land use from May 2021 to November 2024, on the young water fraction (Fyw ) and mean transit times (MTT) using stable water isotopes (δ 2H, δ 17O, and δ 18O) across 13 sites (collected monthly) within the Lake Warner-Mill River watershed (LWMRW) of the Connecticut River Valley. In addition, we monitored 3 storms in Spring, Summer, and Fall to determine proportions of stream pre-event flow that coincides with pollutants such as dissolved organic carbon (DOC). Finally, we performed synoptic sampling at 33 sites between and just after storm to further compare the spatial expression on flow across the network. The local meteoric water line for the 3.25 years of collected data was δ H = 7.5 δ O+ 9.5 (n=254), with high variability of the precipitation isotopes mean stable water isotope composition of -7.3 per mille (oxygen-18, δ O) and standard deviation (SD) of 3.7 per mille. For the monthly surface water collected data, mean results were similar. Forested sites had mean of -7.92 per mille (SD = 0.53), urban sites -7.69 per mille (SD = 0.88), and agricultural sites -7.57 per mille (SD = 0.74). Correspondingly, Fyw was 0.17 (rural), 0.29 (urban), and 0.24 (agricultural), with rural sites having the longest MTT (327 days) and urban sites having the shortest MTT (189 days). Mean transit times for forested sites declined in value as mean O18 of the streams increased, however there was no trend for urban sites. During the three storm events, a high proportion of pre-event flow was determined to contribute to the hydrograph. In September 2024, this transported over 3 mg/L DOC at its peak. Interestingly, the synoptic showed the most enriched samples across the 33 sites in late fall rather than mid-summer sampling. This work contributes to efforts at better understanding the hydrological dynamics of the watershed network and its heterogeneous contributions to Lake Warner and the Connecticut River.
How to cite: Guzman, C., Vera, R., and Nsubuga, T.: Small head water contributions in a heterogenous watershed of the Connecticut River Valley, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21804, https://doi.org/10.5194/egusphere-egu25-21804, 2025.
Posters virtual: Fri, 2 May, 14:00–15:45 | vPoster spot A
EGU25-20562 | ECS | Posters virtual | VPS11
Identification of surface water and groundwater interaction in a non perennial river using hydrogeochemistry and stable isotopesFri, 02 May, 14:00–15:45 (CEST) | vPA.3
Studying of surface water and groundwater interaction is crucial in understanding the changes in the ecosystems, thus affecting the quality as well as the quantity of hydrology of the catchment. Non -perennial rivers account around 50% of the world’s rivers and such interaction plays a prominent role in determination of seasonal availability and quality of such catchments. The present study aims to identify the river water and groundwater interaction using hydrogeochemistry and stable isotopes in Cauvery, a major non-perennial river of southern India. The river water as well as groundwater was collected once in four months from 2013 to 2021. The samples were analysed for major ions from 2013-2021 whereas stable isotopes δ18O and δ2H were analysed during 2018 and 2021. Inverse modelling was carried out to understand the hydrogeochemical reactions during surface water and groundwater interaction. Both river water and groundwater was dominanted by Ca-Mg-HCO3 and Na-Cl type. Seasonal variation of major ions in river water and groundwater shows similar variation. The inverse modelling indicates the weathering of hornblende, plagioclase, biotite, K-Feldspar into stable clay minerals along with the leaching of major ions into the water. The stable isotopes indicates that both river water falls between precipitation and the evaporation during wet seasons, whereas few samples have been isotopically enriched during the dry season as a result of evaporation, suggesting that groundwater contributes to the river water. Also, the interaction between river water and surface water is more evident during wet seasons, whereas during dry periods the interaction persists in headwater regions. falls between precipitation and the evaporation during wet seasons, whereas few samples have been isotopically enriched during the dry season as a result of evaporation, suggesting that groundwater contributes to the river water. The present study on river water and groundwater interactions acts a baseline framework in developing sustainable water management in non-perennial rivers. The temporal variation of major ions between groundwater and river water shows similar pattern, indicating their interrelationships. The isotope results shows that groundwater and river water falls between precipitation and the evaporation during wet seasons, whereas few samples have been isotopically enriched during the dry season as a result of evaporation, suggesting that groundwater contributes to the river water. The weathering of hornblende, plagioclase, biotite, K-feldspar occurs during groundwater -river water interaction which then transforms to stable clay minerals. It was evident that at the lower part of the basin, the river water discharges into groundwater during the wet periods and vice versa during dry seasons. Thus, this current study on river water- groundwater interactions act as a baseline knowledge in developing sustainable water management plan in the river basins.
How to cite: Ramesh, R., Lingaiah, K., and Lakshmanan, E.: Identification of surface water and groundwater interaction in a non perennial river using hydrogeochemistry and stable isotopes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20562, https://doi.org/10.5194/egusphere-egu25-20562, 2025.
