This session invites contributions related to atmo-, cryo-, hydro-, and geosphere isotopic investigations of the water cycle to trace recent and past climate change. Participants are invited to submit papers for a special issue of the SCIE journal Acta Geographica Slovenica (https://ojs.zrc-sazu.si/ags).
Stable isotopes (δ18O and δ2H) and the radioactive isotope tritium (3H) in precipitation are sensitive indicators of spatiotemporal changes in climate and the hydrological cycle, reflecting both large-scale atmospheric oscillations and local hydroclimatic processes. They are widely used to study atmospheric, hydrological, and hydrogeological processes, and the δ18O is a well-established proxy for long-term hydroclimatic variations in paleoclimatic archives like speleothems, ice cores, and tree rings. Thus, stable isotopes in precipitation serve as key tracers of past and present hydroclimatic conditions, providing valuable insights into global climate changes and future trajectories.
Long isotope time series are essential for assessing the climatic dependency of isotopic variability in precipitation, detecting multi-decadal climatic oscillations and identifying trends. In this study, we present the first results from 30 years of isotopic precipitation monitoring in Pisa, Italy (1993-2023), a region characterized by Mediterranean climate. The dataset spans 327 monthly samples and is one of the most extensive and continuous records in the Mediterranean.
Seasonal isotopic variability reflects seasonal climatic fluctuations, with a positive correlation between δ18O and temperature (temperature effect) and a negative correlation with precipitation amount (amount effect). These climatic factors also partly drive sub-seasonal isotopic variability, especially in summer. In winter, higher precipitation is associated with negative phases of the Mediterranean Oscillation Index (MOI) and North Atlantic Oscillation (NAO), and positive phases of the Western Mediterranean Oscillation (WeMO). In spring and autumn, it correlates with MOI and WeMO. These patterns result in significant correlations between δ18O, MOI, and NAO in winter, and δ18O and MOI in autumn, which reveals the influence of large-scale and regional atmospheric patterns in these seasons. Deuterium excess shows negative correlations with temperature and positive correlations with precipitation amount.
Mann-Kendall and Theil-Sen tests reveal no significant trends in δ18O and deuterium excess series over the 30-year period or within individual seasons, except for a positive trend of deuterium excess in winter. Seasonal-Trend Decomposition (STL) also shows no significant trends in deseasonalized data, except for the radioactive isotope tritium, which exhibited a clear decreasing trend both in the raw and deseasonalized data.
These findings highlight the importance of isotopic precipitation studies in understanding hydrological and atmospheric processes and their potential for tracking present and past hydroclimatic changes.
How to cite: Natali, S., Raco, B., Baneschi, I., Catania, M., Giorgi, C., and Zanchetta, G.: Unveiling climate signals and long-term variability from 30 years of precipitation isotopes in Pisa (Italy), EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-381, https://doi.org/10.5194/ems2025-381, 2025.
The stable isotopic composition of hydrogen (δ²H) and oxygen (δ¹⁸O) in precipitation is an established and powerful tool in water cycle investigations. Since Craig (1961) first documented the δ2H-δ18O linear relationship in meteoric water across the globe, the Global Meteoric Water Line (GMWL - δ²H = 8 ∗ δ¹⁸O + 10), researchers have explored the variability in MWLs both globally and locally. The isotopic composition of precipitation reflects fractionation processes during evaporation, condensation, and moisture transport, which are conditioned by the temperature, humidity, and morphological location of each site. Local Meteoric Water Lines (LMWLs) represent the relationship of δ2H-δ18O at one specific site or area and are used for numerous hydrological, hydrogeological, and eco-hydrological applications. A correct computation of LMWLs is, therefore, crucial.
Several statistical regression methods have been employed to compute LMWLs: the Ordinary Least Squares regression (OLS), the Reduced Major Axis regression (RMA); the Major Axis regression (MA, also known as orthogonal regression), the Error-In-Variables regression (EIV) considering measurement uncertainties in δ²H and δ¹⁸O. Some landmark papers correctly argued that, since both δ²H and δ¹⁸O are characterized by measurement uncertainties, the RMA and MA regression must be considered as the most suited for computing LMWLs. RMA and MA thus became the most common regression approaches. However, in those works, variables’ uncertainties are not inserted in RMA and MA equations; and consequently, uncertainties are not used in the following works. A more complete description of the possibility of using EIV regression method to isotopic composition in precipitation analysis is absent in the literature. In this work we present a method, based on a particular case of the EIV, in which the uncertainties on both variables can be different from each other and from one measurement to another. It is a generalization of the MA method (in which the uncertainties on the two variables are equal to each other) and, in its simplest version, it is called the Deming method. We discuss the assumptions to carry out the regression, the statistical methodology, and the evaluation of the goodness of fit. In addition, software tools for computing Deming regression of isotopes in precipitation data will be presented. Finally, three examples will be presented along with LMWLs evaluations. The use of the proposed method provides a better evaluation both of LMWLs parameters and of the associated uncertainties, allowing a better comparison within and between the years of the monitoring periods. This could improve, from that point onward, the analysis of δ2H-δ18O linear relationship in meteoric water. We believe that this is a robust method to compute LMWL and suggest its use in isotope hydrological analyses.
How to cite: Nigro, M., Barsanti, M., Natali, S., Vreča, P., and Penna, D.: Meteoric Water Lines in isotope hydrology: a guide to Error-In-Variables regression, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-386, https://doi.org/10.5194/ems2025-386, 2025.
The ratio between the heavy and light stable isotopes in precipitation is an effective tool in answering questions in e.g., hydrology, climatology, biogeochemistry etc., but only if spatiotemporally sufficient data is available provided by precipitation monitoring networks. However, when data from multiple sources are gathered into large databases these can contain errors that can severely impact research outcomes. The most common practices of stable isotope database filtering applied static thresholds not accounting for the spatially dynamically changing nature of the variable. We propose a distance-based outlier detection approach to identify erroneous or inconsistent data points by deriving adjustable elevation corrected averaged isotope values for nearby stations within an adjustable search radius (0 < R ≤ 500 km, default: 100 km), thus dynamic error threshold.
The IsoQC tool is showcased on the records from the precipitation stable isotope network of Slovenia and its vicinity. It enables an objective and reproducible analysis of spatial and temporal patterns of nearby precipitation stable isotopic records by employing thresholds for dissimilarity between regional averages and individual station records. The interactive nature of the application allows users to explore spatial and temporal variations in precipitation isotope compositions, identify anomalous data points, and assess regional isotope patterns in real time.
The IsoQC app allows users to upload their own datasets to analyze stable isotope records from monthly precipitation samples. The data upload module supports MS Excel and CSV formats. To ensure proper functionality, the uploaded data must contain specific columns like station identifier, date, coordinates and isotope data. The proposed tool supports the standardized quality control of isotope records across different databases and facilitates harmonious interoperability based on FAIR data principles.
Keywords: precipitation stable isotopes, δ2H, δ18O, d-excess, outlier detection, Slovenia
Acknowledgement: The research leading to these results received funding from Slovenian Research and Innovation Agency under Grant Agreements P1-0143, J6-3141, J6-50214, N1-0054, N1-0309, from IAEA under Grant Agreements F31006, F33024, F33031, RER7013, RER7017 and SLO7001; and from the National Research, Development and Innovation Office (NRDI) Fund project No. SNN-143868.
How to cite: Hatvani, I. G., Erdélyi, D., Vreča, P., Lojen, S., Žagar, K., Gačnik, J., and Kern, Z.: Online screening tool for precipitation stable isotopes records: Hybrid distance / density based outlier filtering approach via Interactive web application , EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-638, https://doi.org/10.5194/ems2025-638, 2025.
Long-term meteorological datasets are fundamental for understanding the dynamics of Earth's climate and hydrological systems. Isotopic compositions of precipitation, primarily δ¹⁸O and δ²H, reflect integrated atmospheric processes including moisture source regions, transport pathways, and local climatic conditions such as temperature and precipitation amount. Systematic, long-term observations allow researchers to detect seasonal cycles, inter-annual variability, and long-term trends in atmospheric circulation and hydrometeorological patterns. These datasets are essential for calibrating and validating isotope-enabled climate models and paleoclimate proxies, thereby improving reconstructions of past climate conditions and predictions of future change. Furthermore, they provide a critical reference for assessing the impacts of climate change on regional water resources and identifying shifts in precipitation regimes. As such, long-term precipitation isotope records are indispensable tools in both climate science and water resource management.
This research aims to present evaluation of long-term monthly composite isotope in precipitation records from two Slovenian Isotope in Precipitation (SLONIP, https://slonip.ijs.si/) stations, namely Ljubljana and Portorož, that were compared with neighbouring records from Vienna, Graz and Zagreb.
Stable isotope data from precipitation samples were analysed using the R programming language, involving data cleaning, seasonal and annual aggregation, rolling mean calculation (precipitation-weighted and unweighted), breakpoint detection, and type II regression modelling (reduced major axis and major axis regressions), along with visualization of trends and distributions. Non-parametric statistical tests (Mann-Kendall, Sen’s slope, Kruskal-Wallis) were used to assess temporal and seasonal significance. The applicability of air back-trajectory analysis using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model was also explored to help explain the observed trends.
Activities for this presentation were funded in last decade by the ARIS (Grants P1-0143, N1-0054) and IAEA (CRP F33024, F31006, TC RER7013, TC RER7017).
How to cite: Gačnik, J., Vreča, P., Žagar, K., Kern, Z., and Hatvani, I. G.: Long-term isotope records of precipitation in Slovenia, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-208, https://doi.org/10.5194/ems2025-208, 2025.
The δ18O (isotopic composition of oxygen) paleothermometry relies on the temperature-dependent 18O/16O isotope fractionation between H2O and CaCO3 during calcite precipitation from carbonate-rich water. An understanding of the relationship between the δ18O values of drip water and local precipitation is thus essential for the uncertainty management of paleoclimate reconstructions from cave flowstone formations. Therefore, a two-year monitoring of the stable isotope composition of drip water at 15 drip sites in the cave (Jama v Dovčku, SE Slovenia), and a three-year monitoring of monthly precipitation at the nearest national precipitation station (Planina v Podbočju) were conducted as a part of a paleoclimate study using stalagmites as climate archives. The δ18O-δ2H correlations and d-excess were analysed in precipitation and 15 drips, where the mean groundwater travel times (MTT) were also calculated from the degree of damping of amplitudes of sine wave functions fitted to the monthly δ18O and δ2H data of precipitation and drip water.
The MTT was 1.43-4.24 years and 1.58-3.71 years calculated from δ18O and δ2H values, respectively. The estimates were not correlated with the roof thickness above the drips, nor with the mean δ18O values of drip water at individual sites, however, a moderate negative correlation (R = -0.53) was observed between the roof thickness and the average δ18O values of drip water. The average δ18O values of individual drips varied and the variability exceeded the interannual differences in annual average δ18O values of precipitation. The d-excess of precipitation and individual drips was the same within the measurement uncertainty of δ18O and δ2H values; however, the slopes of δ18O vs. δ2H correlation lines were at most drips lower than in precipitation. At four out of 15 drip sites with MTT larger than 2.5 years, the δ18O and δ2H values were not correlated at a level of p = 0.05. Several possible explanations were explored, e.g., evaporation in the epikarst, mixing of slow- and fast-moving water, and different fractions of young water at individual drips caused by complex geometry and intricate underground connections in karst aquifers.
Acknowledgment: This study was supported by the Slovenian Research and Innovation Agency, research project J1-2478, programme P1-0143, and the Slovenian National Commission for UNESCO (UNESCO Intergovernmental Hydrological Programme).
How to cite: Lojen, S., Vreča, P., Rusjan, S., Žagar, K., Kanduč, T., Tičar, J., and Lipar, M.: Water isotopes from precipitation to groundwater: insights from drip water monitoring at a transect of a karst aquifer (Jama v Dovčku, SE Slovenia), EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-634, https://doi.org/10.5194/ems2025-634, 2025.
Isotope studies of various components of the water cycle are a cornerstone of contemporary climate and environmental research. These studies utilize stable isotope compositions of oxygen and hydrogen in ice, snow and meltwater, along with other parameters, and provide important insights into past and present climate conditions, hydrological processes, ice dynamics, and broader environmental changes. Enhanced understanding of the Earth's climate history derived from isotope analyses contributes significantly to refining predictive climate models and informs sustainable management strategies addressing future climatic, environmental, and water resource challenges.
However, physio-chemical and isotopic data on water cycle components frequently remain scattered, inconsistent, and incomplete, particularly isotope datasets generated from numerous short-term research projects worldwide. Therefore, consolidating and publicly sharing these data is essential, forming a critical foundation for climate-smart sustainable development and informed decision-making.
Climate change, characterized by increasing air temperatures, altered precipitation patterns and diminishing snow cover, has driven unprecedented glacier retreat globally. Such retreat impacts hydrological regimes profoundly, causing water scarcity and heightened drought risk due to reduced meltwater contributions, while concurrently increasing flood risk.
In Slovenia, the Pleistocene glaciation reshaped up to 9% of the landscape. Today, however, only two small glaciers remain – Triglav Glacier and Skuta Glacier. Additionally, more than 200 caves containing permanent ice are documented in the Slovenian Cave Registry. Both glaciers and ice caves are located at relatively low altitudes, rendering them particularly sensitive indicators of recent climate change.
This presentation summarizes past and ongoing isotope investigations focusing on ice from Slovenian glaciers (e.g., Triglav Glacier and Skuta Glacier) and ice caves (e.g., Viševnik Ice Cave, Ivačičeva Cave, Triglav Shaft, Snežna Cave and Paradana Cave). By integrating these results with existing physio-chemical and isotope data from regional precipitation, snow, snowmelt, surface water, and groundwater, this consolidated data offers water resource managers critical insights into hydrological variability and anticipates future changes in Slovenian water sources.
Activities for this presentation were funded by the ARIS (Grants P1-0143, P6-0101, I0-0031, J6-3141, J6-50214) and IAEA (CRP F33031, TC RER7013, TC RER7017).
How to cite: Vreča, P., Žagar, K. Ž., Tičar, J., and Zorn, M.: Isotopic characteristics of Slovenian glacier and cave ice as indicators of climatic and hydrological change , EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-150, https://doi.org/10.5194/ems2025-150, 2025.
In times of climate change, when drinking water resources and the water needed for the survival of groundwater-dependent ecosystems, such as lowland forests depend on the availability of water, the sustainable use of groundwater requires strategic planning based on an assessment of the amount of groundwater available. To properly assess and plan the amount of available and accessible water resources, it is first necessary to understand the processes of the water cycle.
About 25 years ago (in 2000), a high mortality rate was observed in the groundwater-dependent ecosystem (GDE) of several lowland oak forests in Slovenia and Europe. Understanding the processes of the hydrological cycle is becoming increasingly important, mainly because of the high mortality of these forests, whose main problem is probably the lowering of the groundwater table and the reduced accessibility of water to these trees as a result of changes in weather patterns or the regime and amount of precipitation recharging the aquifers in the area of these forests.
By short-term monitoring of the composition of stable water isotopes (δ18O and δ2H) in precipitation in the area of lowland oak forests Murska šuma (northeast Slovenia) and Krakovski gozd (southeast Slovenia), we have obtained important results on the variability of the precipitation signal, which will be compared with the results of the neighbouring long-term stations (e.g. Murska Sobota, Ljubljana, Vienna, Graz and Zagreb). In the future, we will expand our research and also monitor the isotope signal of stable water isotopes in soil, groundwater and xylem water of adult trees. This will allow us to assess the origin of water sources used by trees and to identify physiological responses to changing climatic conditions such as drought stress or altered precipitation regimes. By integrating water isotope data into ecological and hydrological models, we can better predict how trees will respond to current and future climate change, providing information for conservation strategies and sustainable management practices.
Activities for this presentation were funded in last decade by the Slovenian Research Agency (Grants P1-0143, N1-0054, N1-0309 and P1-0020), IAEA (CRP F31006, TC RER7013, TC RER7017, SLO7001) and projects Mladi forum and FREYA which are co-funded by the Slovenian Research and Innovation Agency within the framework of Developmental funding pillar.
How to cite: Koren Pepelnik, K., Rman, N., Žagar, K., and Vreča, P.: The role of isotopes in precipitation in assessing the impact of climate change on forest mortality, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-469, https://doi.org/10.5194/ems2025-469, 2025.
Keywords: precipitation, river water, subsurface water, climate conditions, δ18O, δ2H, 14C groundwater ages
This study presents a comparative isotopic hydrological assessment of two continental catchments: the Koppány Stream in Hungary and the Ledava Stream in Slovenia. Stable oxygen (δ¹⁸O) and hydrogen (δ²H) isotopic signatures were monitored to investigate water source contributions, flow paths, and residence times under varying hydrological conditions.
The Koppány catchment, located in southwestern Hungary, spans approximately 660 km², with dominant agricultural land use and patches of natural forest. The Ledava catchment, extending across the Hungary-Slovenia border, covers 1,940 km² and shares similar climatic characteristics but features more lowland areas. Annual precipitation averages are 630 mm for Koppány and 798 mm for Ledava.
From 2022 to 2024, δ¹⁸O and δ²H measurements were conducted on precipitation, surface- and subsurface water (shallow and deep groundwater) in both catchments. Results show comparable isotopic values in precipitation across the two sites. In both catchments, river and groundwater exhibit smaller isotopic variability than precipitation. Subsurface water is more depleted than river water and precipitation, especially in deeper aquifers.
In the Ledava catchment, river water displays less negative isotopic values than mean precipitation, with an upstream (Polana) station showing slightly enriched signatures compared to a downstream (Čentiba) station. Shallow groundwater aligns well with river water isotopic composition, while deeper groundwater is more depleted but not as strongly as in the Koppány catchment. In the Koppány catchment, the seasonality of the stable isotopes in the streamwater was compared to the amplitude of precipitation. The study revealed the effect of the reservoirs on the evaporation and the presence of waters of different origins in the stream.
The pattern observed in the δ¹⁸O and δ²H values indicates that the deep groundwater infiltrated under colder climatic conditions than today, likely during glacial conditions. δ¹⁸O and δ²H values of deep groundwaters were detected as more negative than those of shallow (young) groundwaters. Accepting the correlation between stable isotope composition of Hungarian groundwaters and temperature, deep groundwaters have infiltrated in 6 to 8 oC colder climate than the current temperature. Their Ice-age infiltration is supported by the oldest 14C groundwater ages of 16 to 21 ka, close to the Last Glacial Maximum (LGM). Their 3H content being lower than the detection limit (<0.5 TU), also confirms the old groundwater ages. The oldest groundwaters and the lowest δ¹⁸O and δ²H values were found near the Koppány Stream, but they contribute only a small portion to the stream's baseflow.
Acknowledgements
The research presented herein was supported by the National Research, Development and Innovation Office (OTKA project grant number SNN 143868). The authors also acknowledge the financial support received by the Slovenian Research Innovation Agency (ARIS) for project N1-0309 and research program P1-0143.
How to cite: Clement, A., Hatvani, I. G., Jolánkai, Z., Kardos, M. K., Kern, Z., Deák, J., Palcsu, L., Lojen, S., Milačič Ščančar, R., and Vreča, P.: Seasonality in precipitation stable isotopes and isotope hydroclimatological signals in surface- and subsurface waters: comparative study from a Hungarian and Slovenian catchments, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-597, https://doi.org/10.5194/ems2025-597, 2025.
Targeted sampling campaigns were carried out at the high elevation permafrost zone of the Dry Andes for a systematic multiannual isotopy hydrological investigation to reveal the potential role of thawing permafrost in the regional water cycle. Ephemeral lakes and streams were sampled between 2018 and 2024. Elevation of the sampling spots ranged from 5,240 to 5,900 m asl. Ground ice samples representing the topmost 20–30 cm of the frozen section were excavated in the 2024 field season. The stable hydrogen and oxygen isotope composition (δ2H and δ18O) of the samples was determined by laser spectroscopy (LGR LWIA-24i) and tritium (3H) activities were analyzed using the 3He-ingrowth method at the Institute for Nuclear Research, Debrecen, Hungary.
Stable hydrogen and oxygen isotope composition of fresh snow samples collected in late February, 2018 were -69.5‰ for δ²H and -10.33‰ for δ18O, the 3H activity was 5.36±0.10 TU. Stable isotope composition of surface waters collected around the Ojos del Salado between 2018 and 2024 ranged from -114.3 to -31.4‰ for δ²H, and from -15.32 to -2.0‰ for δ18O. Tritium activities of the samples ranged from 4.7 to 10.8 TU. Ground ice samples showed a narrow range around -40.8‰ for δ²H and -4.2‰ for δ18O, with tritium activity concentrations 6 and 6.6 TU.
Neither the snow sample, nor the surface water samples yielded as negative isotopic values as expected. Snow and stream water samples exhibit a relatively more depleted composition in heavy isotopes and fit well to the Northern Chile meteoric water line (MWL), while lake water samples usually show relatively more enriched composition and are scattered below the regional MWL. Water stable isotopic characteristics suggest that freezing of liquid water, presumably with high freezing rate and relatively thick boundary layer characterized the formation of ground ice samples. The 3H data of the ground ice samples argue for the recent (< 8yrs) origin of these subsurface ice accumulation.
Acknowledgement: The research was supported by the National Research, Development and Innovation Office (NRDI) Fund project K-147424.
How to cite: Nagy, B., Ruiz-Pereira, S., Túri, M., and Kern, Z.: Water isotope signatures of lakes, streams and ground ice from the Ojos del Salado, Dry Andes – interannual fluctuations and moisture sources, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-635, https://doi.org/10.5194/ems2025-635, 2025.
Supporters & sponsors
