As global climate change alters hydroclimatic responses beyond the range of predictability based on historic hydrometeorological records, water resource practitioners are increasingly reliant on new methods of modelling continental and global hydrology. Though local scale heterogeneity and connectivity between hydrologic storages and fluxes tends to be averaged out across large domains, it is precisely these process scale changes that remain crucial as early indicators of climate change. A lack of data at continental scales, and particularly in high latitude regions, can therefore challenge accurate model calibration and evaluation. Efficient and accessible hydrologic prediction tools capable of diagnosing and interpreting continental scale changes in water balance components and overall water supply, ecosystem changes, and uncertainty methods for operational decision-making are needed.

This presentation focuses on the recent advances in large-domain tracer-aided stable isotope modelling and the contributions isotope tracers make on improving hydrologic process representation across large-domains. The influence of process-based model outcomes will be highlighted using examples from cold regions domains, including the propagation of small historical differences into significantly different upper quantile flow predictions. Despite significant advances in tracer-aided modelling, the path forward must include building and supporting global operational monitoring networks, providing standard guidance for integration of tracer-aided approaches, and a focus on building model agnostic workflows and tools that efficiently leverage tracer-aided approaches.

How to cite: Stadnyk, T.: Predicting the unpredictable: Advances in Tracer-aided hydrologic modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2158, https://doi.org/10.5194/egusphere-egu23-2158, 2023.

The snow dominated headwaters of the Colorado River are crucial for the water supply of the south-western US. The current water crisis in the Colorado basin makes understanding runoff processes in mountainous regions more necessary than ever. We present how our observations of stable isotopes of water (²H and ¹⁸O) in the precipitation, stream-, soil-, xylem-, and groundwater at the East River in the upper Colorado River, combined with multiple hydrometric datasets since 2014 (multi-location stream gauging, groundwater levels, soil moisture snow water equivalent, and eddy-covariance fluxes), can be used to rigourously contrain and evaluate an ecohydrological modelling tool to then identify the time and location of snowmelt and groundwater subsidies to runoff and plant water use. To this end, we deployed a new version of the spatially-distributed, process-based model EcH₂O-iso, with a multi-objective model-data fusion procedure. The simulations notably underline the dominant role of snowmelt as a main driver of runoff generation, through its direct contribution to runoff peak during the late spring snowmelt, and to the groundwater recharge that eventually feeds the significant baseflow contribution in this catchment. Our analysis further explores the use of water ages and numerical tracers to better disentangle these cross-seasons carry-over of water between critical zone compartments.

How to cite: Sprenger, M., Kuppel, S., Carroll, R., Ulrich, C., and Williams, K.: An isotope-enabled modeling approach to track snowmelt and groundwater contribution to runoff and root water uptake in a snow dominated mountainous catchment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9031, https://doi.org/10.5194/egusphere-egu23-9031, 2023.

Stable water isotopes are naturally occurring conservative tracers that act as a fingerprint of water sources and ecohydrological fluxes. Previous studies have shown that some of those fluxes, like evapotranspiration and infiltration, are influenced by vegetation. Thus, land use will play an increasingly important role in water partitioning considering projected climate change-induced shifts of patterns in precipitation and increased atmospheric water demand. The sensitivity of different land use types to drought conditions and their influence on water partitioning varies, and still lacks understanding.

We used stable water isotopes to follow the pathway of precipitation into soil at a lowland headwater catchment with multiple land use types (forest, grassland, arable and agroforestry sites) and integrated our data into a one-dimensional, tracer-aided, plot scale model. The model requires precipitation, potential evapotranspiration and leaf area index as input data and the results were calibrated to real time soil moisture and isotope data. The dataset was collected in the long-term experimental Demnitzer Millcreek Catchment (DMC), Germany, over the growing season of 2021 and includes hydroclimatic conditions as well as isotopes in precipitation, soil water and groundwater. The 2021 conditions, though relatively average in terms of wetness, were affected by a dry spring, an exceptionally large summer storm event (~60 mm) as well as “memory effect” of previous intense drought years.

The implementation of the isotope calculations into the model showed that such a simple, low-parameterisation approach with easily accessible input data can be used to estimate the water balance and track isotopic transformations under plot sites with various land use conditions. The most rapid turnover of water was found under arable land use which resulted in short-term crop vulnerability to drought and slow but more rapid recovery and replenishment of moisture deficits. Forest soils showed slower water turnover with lower soil moisture, mainly reflecting higher interception losses and higher transpiration rates. This, together with access to deeper water, means drought stresses build more slowly at forest sites but can last much longer as storage recovery is slow (>1 year) due to high evapotranspiration. Via adapting the model input data, we further simulated drought conditions to assess the “water footprint” of alternative land use under drought stress.

Our study illustrated the potential of stable water isotope data for simplified ecohydrological modelling approaches to quantify water partitioning. The different effects of land use types on ecohydrological fluxes were successfully simulated and their drought resilience was estimated. For the DMC and similar lowland catchments with similar soil types (sand at forest, loam at grassland and crops) and land cover in Central Europe with the modelled drought conditions, forest sites will initially be more resilient but more vulnerable to lasting droughts, while grassland and arable sites tend to recover more quickly, but can be rapidly stressed by short-term severe events. The modelling provides an experimental framework for assessing the differential effects of droughts of varying longevity and severity on alternative land use strategies.

How to cite: Landgraf, J., Tetzlaff, D., Birkel, C., Stevenson, J. L., and Soulsby, C.: Testing drought sensitivity of different land use types via a low parameter isotope-aided ecohydrological model approach in a lowland headwater catchment, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-317, https://doi.org/10.5194/egusphere-egu23-317, 2023.

Precise knowledge of hydrological processes across large scale catchments is crucial to sustainably meet the growing water demand and improve water management strategies in cities. However, it has been always a major challenge to comprehensively understand the hydrology of a large catchment due to the spatial heterogeneity of climate, topography and anthropogenic activities. Combining tracers with hydroclimatic records, this study used seasonal synoptic surveys in 2021 to better understand the water cycling, storage and losses of the intensively managed 10,000 km² catchment of the River Spree in Berlin, Germany. Apart from the upper headwaters, the hydrology of the Spree is heavily regulated by reservoir releases, pumped minewater discharges, engineered flows in wetlands and lakes, water abstractions and urban drainage. Moreover, the catchment is drought-sensitive with potential evapotranspiration often exceeding annual rainfall. This is reflected in the spatial and temporal variability of the isotopic composition of river water. In the steeper, upper headwater areas, the river is dominated by groundwater sources but showing evident influence by rainfall in winter, with a “flashy” rainfall-runoff response. However, flows in the middle part of the catchment have enhanced baseflows and attenuated high flows from extensive reservoir and pumped minewater releases. The reservoir waters are isotopically heavier and reflect the effects of open water evaporation. Fractionation effects strengthen downstream as managed wetland areas and natural lakes further enhance evaporation and attenuate flows. Our estimations on evaporation losses also show that the mine water pumping, water abstractions and wastewater additions largely contribute to the catchment water balance and therefore have pronounced impacts on water evaporations. Seasonally, the effects of evaporation on the isotopic composition of the lower river network are strongest in summer and autumn, though they remain in winter and spring, indicating a large memory effect due to long mean travel times within the river system. Tritium variability along the river reflects inputs of younger and older water in different parts of the river system; though the influence of pumped groundwater means that the mean age of stream water in the lower river is likely to be >50 years. Isotope studies at large scales play a valuable role to in better understanding the hydrology of this complex, heavily modified river system and provide an evidence base for more sustainable management of the potentially fragile water resource situation in the future.

How to cite: Chen, K., Tetzlaff, D., Liu, G., Soulsby, C., and Goldhammer, T.: Synoptic water isotope surveys to understand the hydrology of large intensively managed catchments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-374, https://doi.org/10.5194/egusphere-egu23-374, 2023.

Streamwater temperature is an important water quality parameter, and controls metabolic and other reaction processes. In urban systems, streamwater temperature has been shown to depend substantially on the near-stream land cover: Riparian buffer zones may cool urban streams, while effluent from wastewater treatment plants is known to raise streamwater temperatures. Groundwater contributions can decrease summer and increase winter streamwater temperature, essentially acting as a temperature buffer. In consequence, streamwater temperature is highly dependent on the specific layout of the urban system.

Streamwater temperature fluctuates on annual, seasonal, daily, and diurnal basis, however, storm events may additionally impact streamwater temperature on short time scales. The timing and patterns of streamwater temperature responses to storm events relative to the hydrograph may differ from event to event. Because urban infrastructure is typically designed to rapidly route water to the sewer network to avoid flooding, streamwater temperature response patterns are likely related to event- and site-specific water sources contributing to streamflow. Changes in temperature patterns could thus be linked to changes in water release processes. If we disentangle the various empirical relationships revealing potential physical controls on how water is conveyed to streams in urban areas, temperature could potentially be used as a cheap tracer of water sources and pathways in urban systems, which are typically difficult to assess.

We investigated and quantified different streamwater temperature response patterns to stormflow, to understand predictors of diverse streamwater temperature responses to summer storms. We found that streamwater temperature shows varied response patterns to storms, including temperature increases and decreases. Some of the temperature increases may take the shape of rapid “heat pulses”, a short but relatively high magnitude temperature increase and subsequent drop at the start of the hydrograph. Streamwater temperature responses to storms were event-specific and could be clearly linked to event characteristics. Understanding the streamwater temperature response can thus aid in understanding urban source contributions to streamflow, because the mixing of sources – and the timing of this mixing process – causes a unique streamwater temperature pattern. Likely sources contributing to the streamwater temperature patterns are ponded surface waters and storm drains, or cooler water from the shallow subsurface. These findings indicate that streamwater temperature may be used as a cheap but effective tracer informing the contributions from different source zones in urban catchments.

How to cite: Knapp, J. and Kelleher, C.: Hunting for heat pulses: streamwater temperature responses to summer storms as tracer for urban water sources, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3190, https://doi.org/10.5194/egusphere-egu23-3190, 2023.

Stable isotopes are an important tool to describe the movement of water through the hydrosphere. They are used as tracers to characterize hydrograph properties. In field studies, stable isotope analyses using hourly and bulk end-member calculations can be used to estimate baseflow/precipitation contributions and to relate hydrograph response to land cover across a watershed. To enable proper planning of paved surface expansions and the nature of storm drainage systems, advanced understanding of the influences of spatial land-use patterns on Mediterranean streamflow regimes are needed to support water management in peri-urban catchments. This study focuses on Ribeira dos Covões, a small peri-urban catchment (around 6 km²), located in central continental Portugal. The catchment is composed of sandstone in the west portion (56%) and limestone in the east portion (41%), with some alluvial deposits (3%) in the main valleys. Flow and precipitation data were collected every five minutes during storms for several years. In 2018, sampling campaigns also included the collection of pre-event, event, and post-event water stable isotopes in different seasons of the year for streamflow at four sites, representing distinct land coverage and lithological landscape combinations. Preliminary results using precipitation and baseflow fraction calculations based on oxygen-18 measurements show that the catchment outlet provides a 49% baseflow contribution (old water fraction) at the beginning of the dry season and 36% in the wet season. An 85% baseflow contribution was estimated for Quinta (mainly forest area in sandstone) during the dry season, and 64-74% for Espírito Santo (largely urban in sandstone) during the wet season. The baseflow contribution at Porto Bordalo (urban area in limestone) is not significant because the flow is controlled by precipitation. Further investigation will involve connecting the results of most recent stable isotope data analyses to the approaches that were used in the past (e.g. separation of baseflow based on low-pass digital filters). Such connection will clarify streamflow response from distinct peri-urban pattern and lithological landscape combinations and their contributions to catchment runoff, aiming to explore the similarities and differences among these methods and quantify the effects of hydrological regime and land use changing patterns over time.

How to cite: Carneiro Marques, A., Ferreira, C. S. S., Martínez-Carreras, N., Kalantari, Z., and Guzman, C. D.: Characterizing landscape influences on hydrological flow pathways in a peri-urban Mediterranean catchment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10782, https://doi.org/10.5194/egusphere-egu23-10782, 2023.

    River damming alters biogeochemical cycles in river continuum. Yet, its effect on the biogeochemical behavior of riverine strontium (Sr) is still unclear. Here, we measured riverine ⁸⁷Sr/⁸⁶Sr in both dissolved and particulate phases and relevant parameters in karst cascade reservoirs of Southwest China, and simulated ⁸⁷Sr/⁸⁶Sr fractionation during biological processes through experimental incubation of model phytoplankton. The results showed that the dissolved ⁸⁷Sr/⁸⁶Sr was rather homogeneous across the water body and nearly identical to inorganic particulate-bound ⁸⁷Sr/⁸⁶Sr, and reservoir Sr mainly sourced from carbonate weathering. However, the dissolved Sr concentrations were stratified and increased with depths of the reservoir water columns. This stratification was likely caused by phytoplankton and the precipitation and dissolution of calcite, with the stratified strength controlled by reservoir hydraulic loads. A long-term loads along cascade reservoirs thus could result in a significant increase in dissolved Sr concentrations rather than ⁸⁷Sr/⁸⁶Sr. The culture experiment indicated that the dissolved Sr was massively captured by the phytoplankton during which insignificant ⁸⁷Sr/⁸⁶Sr fractionation occurred. Thus, the ⁸⁷Sr/⁸⁶Sr of reservoir phytoplankton would conserve the dissolved ⁸⁷Sr/⁸⁶Sr. The distinctly lower ⁸⁷Sr/⁸⁶Sr of phytoplankton than terrestrial organic particulates highlights its potential to distinguish autochthonous and allochthonous sources of reservoir particulate matter. This study demonstrated that damming largely alters the elemental and isotopic distribution of riverine Sr and would deepen the understanding of Sr biogeochemistry in dammed rivers.

How to cite: Qiu, X. and Wang, B.: Effect of damming on riverine strontium geochemical behavior: Evidence from 87Sr/86Sr analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2273, https://doi.org/10.5194/egusphere-egu23-2273, 2023.

The northeastern states of India have extensive deposits of coal among other minerals. Coal mining activities contribute significantly to the economy of these states, providing livelihood to a substantial segment of the populace. Unscientific mining practices have contributed adversely to environmental health of the region, particularly to aquatic systems. Acid mine drainage (AMD) discharge from the mines pollute the streams and rivers, causing serious deterioration of the aquatic environment. Stable isotopes combined with physico-chemical parameters are a promising tool for understanding pollution sources, hydrological processes, factors influencing such processes, and fate of pollutants in hydrological systems. The present study was conducted in AMD affected streams & rivers flowing through the states of Arunachal Pradesh, Nagaland, Assam and Meghalaya in northeast India in two different seasons (pre-monsoon (PRM) & post monsoon (POM)). Water samples were analyzed for 24 physicochemical parameters including the major ions. Stable isotopes of oxygen & hydrogen in water samples were estimated. The results of both sampling seasons are significantly different and reveal that water samples of all sampling sites are dominated by presence of high SO₄^2- in both the sampling seasons; abundance of major ions during PRM are in order SO₄^2->Mg²⁺>Ca²⁺>HCO₃^->Na⁺>Cl^->NO₃^->K⁺>NH₄⁺>F^- and during POM are in order SO₄^2-> Ca²⁺>Mg²⁺>HCO₃^->Na⁺>Cl^->NO₃^->K⁺>NH₄⁺>F^-. The stable isotopes of water (δ¹⁸O & δD) analysis results indicated enrichment during the POM sampling season. δ¹⁸O (‰ V-SMOW)  ranged between -8.60 to -4.95 during PRM and -6.60 to -3.94 during POM, δD (‰ V-SMOW) ranged between -58.29 to -29.63 during PRM and -41.40 to -28.69 during POM. The deuterium excess (d-excess ‰) ranged between 5.70 ~ 17.94 during PRM and 1.57 ~ 14.49 during POM. The hydrochemical characteristics of water during both sampling seasons were deciphered through comprehensive analysis of hydrochemistry (piper diagram, durov plot, gibbs diagram, ion ratios, chadha’s plot) and stable isotopes. The results are discussed.

How to cite: Kumar, V., Paul, D., and Kumar, S.: Seasonal Variation in Stable Isotopes and Physico-chemical Characteristics of AMD Affected Water Bodies in Northeast India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-859, https://doi.org/10.5194/egusphere-egu23-859, 2023.

Hydrological interactions between surface water and groundwater are key processes to describe the watershed water cycle including lake water hydrology. Understanding these processes is important for quality and quantity controls of water resources and their future management. Water originating from mining/hot spring regions gives significant impacts on local water resources. However, hydrological processes of how the discharged water with unique water quality affects different water bodies have not been fully understood. Therefore, the study aims to investigate features of surface water and groundwater interaction forming lake hydrology in a highly acidic Tamagawa hot spring region, in Japan. For this, the river water, spring water, and lake water at 51 locations in total were sampled. Lake water collection with depths of 0, 50, 100, 200, 300, and 400 m was undertaken at the center of Lake Tazawa. A variety of environmental tracers such as pH, EC, DO, inorganic ion concentrations, oxygen/hydrogen stable isotopes, CFCs, and SF₆ in collected water samples were measured.

The river water upstream of the Tamagawa River showed a pH of <3.0 and characteristic Ca-Cl type water quality due to the influence of a highly acidic hot spring. The other river and spring waters were almost neutral and of the Na-HCO₃ type water quality. Lake Tazawa water was weakly acidic (pH 5.5, Ca-Cl type water quality), suggesting that the water in the lake originated mainly from the Tamagawa River. Vertical profiles of environmental tracers of lake water at the center of Lake Tazawa indicated that dissolved oxygen concentrations were above 87% saturation even at depths greater than 100 m, suggesting that a rapid lake circulation was occurring. The multiple uses of gas tracers (SF₆ and CFC-12) suggested that water age is 4 and 12-20 years in the water close to the lake surface and water deeper than 50 m, respectively. The binary plot of SF₆ and CFC-12 concentration indicated that the exponential mixing primarily governs lake water circulation processes. Moreover, calculations of the water balance of Lake Tazawa for the five-year period from 2011 to 2015 inferred that groundwater inflow into Lake Tazawa from the surrounding area may have occurred at a rate of at least 5-12 mm/day. These findings suggest that the inflow of groundwater and river water into Lake Tazawa is responsible for the lake's water quality and a part of rapid lake water circulation.

How to cite: Sakakibara, K., Mizushima, S., Hodoki, Y., Tsujimura, M., Suzuki, K., and Park, H.: Water quality and water circulation formation of a deep lake on the basis of interaction between surface water and groundwater in a highly acidic hot spring region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1503, https://doi.org/10.5194/egusphere-egu23-1503, 2023.

Stable isotopes (δ¹⁸O) and tritium (³H) are frequently used as tracers in environmental sciences to estimate age distributions of water. However, it has previously been argued that seasonally variable tracers, such as δ¹⁸O, generally and systematically fail to detect the tails of water age distributions and therefore substantially underestimate water ages as compared to radioactive tracers, such as ³H. In this study for the Neckar river basin in central Europe and based on a >20-year record of hydrological, δ¹⁸O and ³H data, we systematically scrutinized the above postulate together with the potential role of spatial aggregation effects to exacerbate the underestimation of water ages. This was done by comparing water age distributions inferred from δ¹⁸O and ³H with a total of 12 different model implementations, including lumped parameter sine-wave (SW) and convolution integral models (CO) as well as integrated hydrological models in combination with SAS-functions (IM-SAS).

We found that, indeed, water ages inferred from δ¹⁸O with commonly used SW and CO models are with mean transit times (MTT) ~ 1 – 2 years substantially lower than those obtained from ³H with the same models, reaching MTTs ~ 10 years. In contrast, several implementations of IM-SAS models did not only allow simultaneous representations of stream flow as well as δ¹⁸O and ³H stream signals, but water ages inferred from δ¹⁸O with these models were with MTTs ~ 16 years much higher than those from SW and CO models and similar to those inferred from ³H, which suggested MTTs ~ 15 years. Characterized by similar parameter posterior distributions, in particular for parameters that control water age, IM-SAS model implementations individually constrained with δ¹⁸O or ³H observations, exhibited only limited differences in the magnitudes of water ages in different parts of the models as well as in the temporal variability of TTDs in response to changing wetness conditions. This suggests that both tracers lead to comparable descriptions of how water is routed through the system.  our results provide evidence for a broad equivalence of δ¹⁸O and ³H as age tracers for systems characterized by MTTs of at least 15 – 20 years. The question to which degree aggregation of spatial heterogeneity can further adversely affect estimates of water ages remains unresolved as the lumped and distributed implementations of the IM-SAS model provided inconclusive results.

Overall, this study demonstrates that previously reported underestimations of water ages are most likely not a result of the use of δ¹⁸O or other seasonally variable tracers per se. Rather, these underestimations can be largely attributed to choices of model approaches and complexity not considering hydrological next to tracer aspects. Given the additional vulnerability of SW and CO model approaches in combination with δ¹⁸O to substantially underestimate water ages due to spatial aggregation and potentially other, still unknown effects, we, therefore, advocate avoiding the use of this model type in combination with seasonally variable tracers if possible, and to instead adopt SAS-based or comparable model formulations.

How to cite: Wang, S., Hrachowitz, M., and Schoups, G.: Stable water isotopes and tritium tracers tell the same tale: No evidence for underestimation of catchment transit times inferred by stable isotopes in SAS function models., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6333, https://doi.org/10.5194/egusphere-egu23-6333, 2023.

How to cite: Schwemmle, R. and Weiler, M.: Consistent modelling of transport processes and travel times – coupling hydrologic processes with StorAge Selection functions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-457, https://doi.org/10.5194/egusphere-egu23-457, 2023.

Nowadays, a wide range of water extraction/vapor equilibration techniques for obtaining soil and plant water isotopic composition (δ¹⁸O and δ²H) is applied by various ecohydrological disciplines. Here, researchers need to rely on accurate and precise measurements of water isotope ratios for tracing water movement through the critical zone. Previous research has shown that utilizing isotope ratio infrared spectroscopy (IRIS) to analyze water or vapor samples containing co-extracted/-equilibrated organic contaminants (e.g., methanol, ethanol) has the potential to result in significant inaccuracies through spectral interferences. However, the scientific community and the manufacturers have not effectively addressed the inaccuracies caused by organic contaminants. While some hardware solutions for combusting organics as well as some software solutions exist for spectral interference detection during liquid water IRIS analysis, limited tools exist for the post-correction of direct vapor-mode IRIS data e.g., from in-situ water vapor measurements or from the direct water vapor equilibration laser spectrometry method (DVE-LS).

For our study, we applied three different water extraction and vapor equilibration techniques (i.e., DVE-LS, in-situ water vapor measurements and cryogenic vacuum extraction) to four types of vegetables (cauliflower, celery root, kohlrabi and potatoes). We investigated how co-extracted organic contaminants (i.e., methanol and ethanol) via the different methods affect the isotopic ratios between liquid and vapor CRDS measurements of our vegetable samples. Through applying different CRDS instrument-specific post-correction options, we could reduce isotopic discrepancies and maximize the accuracy and precision of CRDS measurements from vegetables.

We could show that all vegetables produced species-specific different amounts of organic contaminants, which affected the isotope ratios obtained via the different extraction or vapor equilibration techniques in different ways. Clear relationships between DVE-LS samples and spectral parameters indicated co-equilibrated contaminants which we used for a technique-specific ‘organics-correction’. Whereas, results obtained from in-situ water vapor measurements were the least affected by organic contaminants and showed the smallest data spread. Those were also comparable to results from cryogenic vacuum extraction for some type of vegetables.

Our study underlines the importance and necessity of plant water vapor isotope data post-correction and highlights the need for a definitive and general protocol in order to prevent ill-founded ecohydrological data interpretations.

How to cite: Orlowski, N., Wengeler, L., and Herbstritt, B.: How to deal with spectral interferences when measuring water stable isotopes of plants?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2231, https://doi.org/10.5194/egusphere-egu23-2231, 2023.

Current methods for tracing the surface infiltration of meteoric groundwaters rely on isotope geochemistry and dye tracers, which can be used to determine groundwater age and altitude at the point of infiltration. Temporal and spatial variability in atmospheric conditions, and water-rock interactions, can make the interpretation of isotopes uncertain. Low tracer recovery and long residence times often make dye tracers impractical. Here, we propose a new method of groundwater tracing based on fingerprinting of natural dissolved organics (derived from local flora and fauna). We validate our method at the Grimsel Test and Mont Terri underground rock laboratories in Switzerland, located within fractured crystalline rock (granite) and sedimentary systems, respectively. Based on a non-targeted approach using two-dimensional gas chromatography, we derive detailed organic fingerprints for groundwater, surface soils, and lakewater and river water samples from each location. These organic fingerprints are then compared to determine the near-surface infiltration environments feeding individual groundwater samples. Using principal component analysis, we show that individual groundwater samples can be identified as having derived from identifiable surface sources. Our research demonstrates that dissolved natural organic molecules, and their relative abundance, are sufficiently well-preserved in groundwater over timescales of several decades, that they can be used to discriminate the near-surface environment(s) through which meteoric groundwater has infiltrated. Organic fingerprinting could prove a powerful tool for an improved understanding of groundwater flow systems, particularly when used in combination with other complimentary tracing techniques.

How to cite: Stillings, M., Lunn, R., and Shipton, Z.: Fingerprinting dissolved organic compounds: A potential tool for identifying the surface infiltration environments of meteoric groundwaters, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16229, https://doi.org/10.5194/egusphere-egu23-16229, 2023.

Streamflow in the glacierized catchments over the Tibetan Plateau receives multi-recharge sources, such as rainfall, melt water from snowpack and glacier, and groundwater. Identifying their contributions to streamflow is challenge but it is vital for understanding streamflow and its composition in response to climate change. In this study, based on high-resolution isotopic (¹⁸O) and hydrochemical (Cl^-) data in the Yangbajing (YBJ) catchment of the Tibetan Plateau in China, we found that the hydrograph in a year can be separated into five segments, each of which is constituted of two or three dominant recharge sources. Thus, we developed a stepwise EMMA (end-member mixing analysis) method to partition the hydrograph and calculate contributions of water sources to streamflow in each segment of the hydrograph. Results show that the overall contributions of deep and shallow groundwater, melt water from glacier and snowpack, and precipitation are 21.8%, 9.8%, 37.5%, 8.5% and 22.4%, respectively, in a year. Specifically, in the low flow period (January 8 - April 26), streamflow is fed by deep and shallow groundwater (75.2% and 24.8%, respectively). In the early rising period of hydrograph (April 27-June 9) when temperature begins to rise, streamflow fed by deep groundwater decreases and its contribution by snow melt water increases (52.5% and 47.5%, respectively). In the fast-rising period (June 10-June 30), streamflow fed by deep groundwater is minor (4.8%) while snow and glacier melt water becomes the dominant recharge sources to the stream water (52.8% and 42.4%, respectively). In the summer period of July 1- September 23, the streamflow is highest, and the greatest glacier melt water and rainfall contributes to 52.4% and 36% of the stream flow, respectively. In the recession period (September 24 - January 7) when temperature drops and rainfall ceases, streamflow is fed again by deep groundwater and shallow groundwater (45.7% and 54.3%, respectively).

How to cite: Li, G., Chen, X., Gao, M., and Wang, Y.: Identifying contributions of multi- recharge sources to streamflow by using a stepwise approach based on isotopic and hydrochemical signals in a glacierized catchment over Tibetan Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2292, https://doi.org/10.5194/egusphere-egu23-2292, 2023.

The concept of young water fraction, introduced by Kirchner (2016) and defined as the fraction of streamflow that was stored less than about 2-3 months in the catchment, is increasingly used in catchment intercomparisons studies to understand and conceptualize the hydrological processes governing the catchment's functioning. However, the development of perceptual models is not always as straightforward as it may seem. Past works have shown that high mountainous catchments worldwide reveal small young water fractions. These low young water fractions at high elevations have been explained by different hydrological processes, including deeper vertical infiltration promoted by the presence of both fractured bedrock and freely draining soils (e.g., luvisols and cambisols) and long groundwater flow paths driven by the topographic roughness. But, a harmonious explanation of how the relevant mechanisms in mountainous catchments lead to low young water fractions at high elevations is missing.

Using a data set composed of 27 study catchments, located both in Switzerland and in Italy (of which 22 are from the previous work of von Freyberg et al., 2018), we explore both the drivers and the conceptualization of the processes that potentially clarify this surprising result. We assume that this lowering can be explained by groundwater storage potential and the interplay of the seasonal dominance of hydrological processes. For groundwater storage potential we use the proportion of catchment area covered by Quaternary deposits (a parameter that is readily available for the studied catchments). For the interplay of seasonal processes, we use the length of the low-flow period as a measure for the duration of the groundwater (in terms of age, old water) dominated recession period.

Our results suggest that the length of the low-flow period is clearly the main driver of low young water fractions at high elevation. Here, the long winter period, characterised by absence of liquid water input and hence by a low-flow regime, promotes a progressive emptying of the groundwater storage. Even during summer, recent snowmelt and rainfall that transit through the subsurface push out old groundwater into the stream, as reflected by high proportions of baseflow also during high-flow periods. However, during summer, the relative share of old water remains lower than during winter and accordingly, the longer the winter period (with very low young water fractions), the lower the annual young water fraction. Quaternary deposits could play a role in reducing young water fractions via their capacity to store groundwater, but further detailed geological information would be necessary for a complete picture about the role of geology.

How to cite: Gentile, A., Canone, D., Ceperley, N., Gisolo, D., Previati, M., Zuecco, G., Schaefli, B., and Ferraris, S.: What explains low young water fractions at high elevations?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1230, https://doi.org/10.5194/egusphere-egu23-1230, 2023.

Conceptual models of catchment hydrological functioning are crucial to understand and predict runoff and the tracer responses during rainfall events, and thus for sound water resources management and pollution mitigation measures. In this study, we use hydrometric and tracer data (stable isotopes, major ions and electrical conductivity (EC)) collected in the Ressi catchment, a 2-ha watershed in the Italian pre-Alps, to test our existing conceptual model of runoff generation mechanisms. This model was based on previous hydrometric measurements and isotope data for selected events and highlights the importance of precipitation and antecedent conditions for hillslope-riparian zone-stream connectivity. More specifically, we determined if the temporal variability in the concentration-discharge relations can be explained by event characteristics, i.e., rainfall event size, intensity, and antecedent moisture conditions.

The Ressi catchment is characterized by high seasonality in runoff response, due to the seasonality in rainfall (high in fall) and evapotranspiration (high in summer). Discharge and rainfall have been measured continuously since August 2012. Stream water, precipitation, shallow groundwater and soil water samples were collected for tracer analyses during 20 rainfall-runoff events between September 2015 and August 2018. All samples were analyzed for EC, isotopic composition (²H and ¹⁸O) and major ion concentrations. To investigate the possible controls on the concentration-discharge relations, we determined the main event characteristics (e.g., total event rainfall, rainfall intensity, antecedent soil moisture and depth to water table, runoff coefficient) for each event.

Based on previous applications of isotope- and EC-based hydrograph separation in the Ressi catchment, we expected different dynamics of the major ions in stream water, depending on the magnitude of the rainfall-runoff events. For all major ions, we hypothesized a dilution effect, and a more marked response for large, long duration events with wet antecedent conditions. The temporal dynamics of calcium, magnesium, sodium and sulfate concentrations confirmed our hypotheses. On the contrary, nitrate, potassium and chloride concentrations sometimes increased at the onset of the event, before a later dilution. These temporal dynamics led to complex hysteretic relations with discharge that could not be explained by the event characteristics. We attribute the rapid increase in the concentrations of these solutes to a quick flushing from the dry parts of the stream channel and the near surface-soil layers of the riparian zone at the onset of the event. The revised conceptual model for the geochemical response of this catchment should, therefore, include a rapid flow pathway that leads to the mobilization of nitrate, chloride and potassium ions, and describe the rapid establishment of hydrological connectivity along the streambed and the near-channel zones.

Keywords: concentration-discharge relation; major ions; electrical conductivity; stable isotopes; hysteresis; forested catchment.

How to cite: Zuecco, G., Marchina, C., Gelmini, Y., Penna, D., Borga, M., and van Meerveld, I.: Testing a conceptual model of runoff generation processes for a small pre-alpine catchment with tracer data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12668, https://doi.org/10.5194/egusphere-egu23-12668, 2023.

Communities downstream from mountainous regions rely on snowmelt for water supply. As climate change reduces the reliability of the snowpack in these regions it is important to understand how and when rain and melt water are stored and released as runoff. In mountainous regions the prediction of water movement is especially complex because water storage capacity and overall water input magnitude and form vary over short distances given variable geology, geomorphology, and topography. We used water stable isotopes (WSI) and water chemistry (ions and cations) to investigate seasonal water sources and contributions in a 64 km² headwater mountain catchment in Oregon (USA). In one study, we collected > 1,000 synoptic samples between 2021 and 2022 across different seasons in 12 headwater streams (600–1,200 m in elevation and drainage areas 0.1–5 km²) and analyzed them for WSI. Results demonstrate that despite season there are localized variations in WSI within less than 1-km² between catchments underlain by similar geology but characterized by different geomorphic history of mass wasting events (landslides and earthflows). We also observed weak relationships between elevation and WSI in some streams suggesting that their sources of baseflow are not directly controlled by seasonal precipitation but by differences in storage over spatially variability geomorphic history.  In a second study, we investigated relative streamflow contributions from five tributaries (0.7–17 km2) over the whole year based on weekly WSI and water chemistry in grab and precipitation samples. We found strong differences across streams; the most interesting was a spring-fed stream, whose water contribution varies widely throughout the year, resembling a snowmelt system (with high relative water input in the summer). The depleted WSI signal and relatively high cations concentrations of this stream reveals higher elevation snowfall is moving to the stream through relatively long flow paths. This stream is underlain by porous lava flows demonstrating a strong geologic control on runoff generation. The contribution of this stream to the whole watershed is over 27 times larger in the summer compared to any other season. This finding challenges the idea of streamflow scaling with drainage area because the effective drainage area of this stream varies between 0.8 and 47 km² while the topographic derived drainage area is 0.7 km².

How to cite: Segura, C., Perry, Z., and Ortega Melendez, J.: Geologic and geomorphic setting control of water sources and flow paths in mountainous headwater catchments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9603, https://doi.org/10.5194/egusphere-egu23-9603, 2023.

Iceland is young (the oldest rocks ca 16M years) and characterized by active and widespread volcanism, defined along a Neovolcanic rift zone.  More than 90% of the Icelandic bedrock is of basaltic origin. The permeability of the Tertiary lava pile is 1-4*10^-14 m² but for younger geological formations especially within geothermal areas the permeability is several orders of magnitude higher due to active fissures and faults. The deeper crust has however a very low permeability as pores and fissures are filled with secondary minerals.

Due to the high permeability in the upper crust groundwater is often mixed with water components originating from different conditions, of different age and in some cases also affected by water-rock interaction.   Thus groundwater dating is complex and to succeed in estimating groundwater residence time it is of vital importance that interdisciplinary methods are applied to understand the geochemistry, geology and hydrology of a specific groundwater system.

In this presentation an overview of using stable water- and carbon isotopes to estimate groundwater residence time is given. It is demonstrated how stable water isotopes including the second order parameter; deuterium excess, can be used to estimate relative ages. Also how radiocarbon age estimations have successfully been used when comprehensive corrections for “dead carbon” from the bedrock and CO₂ gas from the deep crust or mantle are applied together with δ¹³C to correct for modern carbon of organic origin.

How to cite: Sveinbjornsdottir, A., Stefánsson, A., and Arnórsson, S.: Groundwater Residence Time in Iceland Depicted by Stable Water- and Carbon Isotopes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5977, https://doi.org/10.5194/egusphere-egu23-5977, 2023.

Groundwater ages are key indicators for flow and transport processes as well anthropogenic and geogenic solutes that impact groundwater quality. Commonly, lumped parameter models (LPMs) are applied to interpret environmental tracers, like chlorofluorocarbons (CFCs) or tritium. LPMs require a steady state assumption and they are less complex, computational demanding and data intensive compared to transient numerical models. But when steady-state assumptions are valid for groundwater age simulations is questionable.

An initial sampling campaign of CFCs measured in 9 wells at different depths on a 0.47 km² subcatchment of the Krycklan catchment in 2017 revealed a groundwater age stratification with depth that was representative for the area¹. Mean groundwater ages at the water table (2-6 meters depth) in the unconsolidated till overburden were already 30 years and increased with depth to the deepest sampling at 30 meters. These results indicate a lag of rejuvenation caused by a subsurface discharge zone that evolves between two soils types with different hydrogeological properties. The comparison of the steady-state numerical simulation and LPM has proven that the LPM yields an overall recharge rate and estimation of the extent of the subsurface discharge zone.  Seasonal changes of recharge were not expected to impact the age stratification. But repeated sampling in 2021 and 2022 has shown a clear shift of the groundwater age stratification. Numerical modeling is used to understand that transient effect.

References:

¹Kolbe, T, Marçais, J, de Dreuzy, J-R, Labasque, T, Bishop, K. Lagged rejuvenation of groundwater indicates internal flow structures and hydrological connectivity. Hydrological Processes. 2020; 34: 2176– 2189. https://doi.org/10.1002/hyp.13753

How to cite: Kolbe, T., Marçais, J., Vergnaud, V., Yvard, B., Chamorro, A., and Bishop, K.: Transient effect on groundwater age distribution – age measurements disprove steady state assumption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13138, https://doi.org/10.5194/egusphere-egu23-13138, 2023.

During prolonged drought periods surface water contributions via bank filtration to drinking water production sites located on alluvial aquifers can become increasingly relevant due to associated changes in the hydraulic boundary conditions. Considering the predicted increase of occurance probabilities for hot and dry summers in the humid climate zone, these sites might be prone to an increased risk related to anthropogenic emissions into the connected surface water bodies in the near future.

We studied these processes at two well fields (8 active wells in total) located on the alluvial aquifer of the river Kyll, Germany, about 1 km downstream of the community of Kordel and the city´s waste water treatment plant. For six months we sampled bi-weekly water quality parameters in the wells (horizontal distances to the river varied between 30 and 420 m) and at three locations at the river Kyll. Samples were analyzed for stable water isotopes, EC, pH, DO, DOC, major ions, metals and selected pharmaceutical products. Based on a mixing analysis using major ion data we quantified the mean surface water contribution for each well, varying between 40 and 95 %. Using a darcian modelling approach based on continuous pumping rates, hydraulic gradients, existing information on hydraulic conductivities and the possible geometric connectivity of each of the wells to the river we were able to infer potential residence time distributions for the estimated surface water contributions for each of the wells. Comparing these distributions with nutrient gradients and oxic conditions we find significant correlations with the 0.05 quantile shortest residence time estimations, only. Resulting residence times of surface water contributions within the alluvial aquifer range from several days to weeks instead of previously estimated months to years. Dynamics in stable water isotope patterns in rainfall, surface water and groundwater show as well changes in surface water and groundwater composition within two weeks following the changes in the rainfall isotopic composition. Contrary to nutrient dynamics, the trace organic compounds, i. e. pharmaceutical products did not show spatial or temporal patterns, but a constant, substance specific degradation which leads to the conclusion that trace organic compound retention occurs in the nutrient rich near proximity of the river bed, i.e. the hyporheic zone.

These results demonstrate how quantitative and qualitative surface water contributions to groundwater / drinking water wells can have an increased relevance under drought conditions than previously anticipated.

How to cite: Schuetz, T. and Förster, A.: Infering the relevance of bank filtration processes for drinking water production sites on alluvial aquifers under drought conditions using residence time distributions and water quality parameters, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16851, https://doi.org/10.5194/egusphere-egu23-16851, 2023.

The Upper Jurassic aquifer (UJA) within the South German Molasse Basin (SGMB) is the most important exploration horizon for geothermal energy supply in Bavaria. The UJA shows a heterogeneous geology with karstic features and deep fault-zones. The result is a complex hydrogeology consisting of different groundwater types which differ significantly in their hydrochemical and isotopic composition.

Despite the great interest in the Upper Jurassic aquifer for geothermal energy supply, leading to numerous scientific studies, the exact apparent groundwater age, the infiltration area and the regional flow system remain yet unknown.

In this study we are using a multi parameter approach for the determination of apparent groundwater age distributions with the innovative ¹⁴C_DOC and ⁸¹Kr methods and combine them with hydrochemistry data and stable water isotopes (δ¹⁸O/δ²H).

Our results indicate that the UJA system consists of at least two groundwater components: an up to now unknown young meteoric water component from the Pleistocene/Holocene transition and an older Pleistocene component. The apparent ¹⁴C_DOC ages increase from south to north and show some evidence that the infiltration area of the UJA is located in the southern part of the SGMB and a groundwater flow directed to the north.

How to cite: Winter, T. and Einsiedl, F.: Characterisation of the regional groundwater flow system in the South German Molasse Basin using apparent groundwater age distributions with 14CDOC and 81Kr, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15240, https://doi.org/10.5194/egusphere-egu23-15240, 2023.

Anomalous transport processes are frequently observed in radial flow to wells in highly heterogeneous aquifers. This is generally related to the presence of preferential flow pathways that bypass the sediment matrix, thus leading to the formation of fast flow channels, whose magnitude depends on the geological entropy of the system. Tracer tests can be effectively combined with laboratory or field-scale experimental campaigns to understand better the interlinkage between heterogeneity and preferential flow, and to distinguish hydraulically active and inactive regions. Despite considerable past research efforts, these mechanisms are only partially understood. To advance the current understanding, we study transport processes in a laboratory-built highly heterogeneous aquifer under radial flow conditions. The experimental device (200 x 200 x 100 cm) consists of 2527 randomly distributed cells (10 x 10 x 5 cm) of 12 different porous mixtures assembled in 7 layers to form a 35 cm-deep aquifer. This particularly design is intended to maximize the geological entropy of the aquifer, which is equipped with 37 piezometers placed in a radial configuration at different distances from the central (pumping) well. Multiple conservative tracer tests were conducted by injecting a mixture of deuterated water (D₂O) and Potassium Bromide (KBr) into different piezometers, and then by analysing the resulting Breakthrough Curves (BTCs) at the central pumping well. BTCs reveals features peculiar of anomalous transport, such as non-symmetry, early peaks and tailing, which depend on the injecting location. This, jointly with the incomplete mass recovery after 48 hours, suggests the simultaneous presence of fast flow in highly conductive regions, which exchange mass with quasi-immobile portions of the aquifer. By dealing with tests individually, it is seen that curves for the two tracers have a similar trend, with almost perfect overlap in the part before the peaks. Differences in the tailing of the BTCs between the two tracers, that exhibit different molecular diffusion coefficients, indicate the importance of diffusion mechanism taking place in the porous matrix.

How to cite: Brunetti, G. F. A., Stumpp, C., Fallico, C., Severino, G., and De Bartolo, S.: Multi-tracer tests to disentangle mobile-immobile regions in a highly entropic aquifer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6934, https://doi.org/10.5194/egusphere-egu23-6934, 2023.

We performed an intensive monitoring and sampling of groundwater in Tokyo Metropolitan area to investigate the groundwater flow system from upland to lowland areas. We took 83 groundwater samples at 39 locations, 25 stream water samples, 7 spring water samples from August 2018 through June 2021. We also observed the spatial distribution of hydraulic head in the groundwater. The stable isotopic composition of oxygen 18 and deuterium, SF₆ concentration, and solute ions concentrations were determined on all water samples.

The SF₆ age of groundwater in the upland area ranges from a few years to 40 years, whereas that in the lowland area ranges from 40 years to more than 80 years. The solute concentrations are characterized by Ca-HCO3 type in the upland, whereas that is categorized in Na-HCO3 or Na-Cl type. In addition, d¹⁸O of the groundwater in the upland ranges from -10.4 per mil to -8.8 per mil, whereas that in the lowland ranges from -9 per mil to -8 per mil.

The hydraulic head distribution shows that the unconfined groundwater flows from west to east directions in parallel with the topographical surface, and the confined groundwater flows from south-west toward north-east directions in parallel with the bedrock surface topography.

The results show that the groundwater flows from west toward east directions across the border of the upland and the lowland, and it flows across the boundary of the aquifers, meaning the unconfined groundwater recharges the confined groundwater in an area where a certain amount of unconfined groundwater is pumped up.

How to cite: Tsujimura, M., Nagano, K., Sato, K., Suzuki, T., and Asakura, H.: Groundwater flow system as determined by multi-tracer approach in Tokyo Metropolitan area, Japan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13728, https://doi.org/10.5194/egusphere-egu23-13728, 2023.