Session 4 | Using O-H stable isotopes for studying hydrological process understanding and the history of flowing waters

Session 4

Using O-H stable isotopes for studying hydrological process understanding and the history of flowing waters
Conveners: Laurent Pfister, Ilja van Meerveld
Orals
| Wed, 14 Jun, 10:05–12:30|Saints Marcellino and Festo
Poster
| Attendance Wed, 14 Jun, 10:40–11:30|Poster area, Attendance Wed, 14 Jun, 17:00–18:00|Poster area
Orals |
Wed, 10:05
Wed, 10:40
Despite powerful tracer tools for deciphering water sources, flow paths, and transit times, hydrology remains a discipline that is measurement limited. With global change likely triggering increasingly intense hydro-meteorological events in the near future, there is a pressing need for new observational tools operating at unprecedented spatial and temporal scales. The natural abundance of the stable water isotopes (i.e. δ2H and δ18O) offers a suite of possibilities to track water fluxes in the critical zone. These measurements have the potential to serve as a catalyst for process analyses in the critical zone – ultimately delivering entirely new datasets for model calibration and validation. We encourage contributions on isotope-based studies to investigate and model processes within and between the various compartments of the critical zone, challenges related to water extraction techniques and isotope analyses, and novel datasets on past variability in isotope signatures in precipitation and stream water (e.g., from trees, speleothems, freshwater mussels).

Invited speaker: Adrià Barbeta Margarit, Spain
(adria.barbeta.margarit@gmail.com)

Orals: Wed, 14 Jun | Saints Marcellino and Festo

Chairpersons: Laurent Pfister, Ilja van Meerveld
10:05–10:20
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GC8-Hydro-101
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Session 4
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keynote
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Adrià Barbeta, Teresa Gimeno, Lisa Wingate, and Jérôme Ogée

In recent years, the widespread use of laser-based analyzers of the isotopic composition of water (δ18O and δ2H) resulted in an increase in the temporal and spatial resolution of measurements of plant water and their sources. Such datasets revealed previously undetected mismatches between the isotopic composition of subsurface water pools and bulk xylem water usually extracted by cryogenic distillation. To understand the underlying cause of these isotopic mismatches, plant ecophysiologists and ecohydrologists have conducted numerous experiments to address a range of hypotheses. Measurement artifacts produced by water extraction techniques in both bulk xylem water and soil water were claimed to be behind the observed mismatches. However, there is not yet a consensus on a sole mechanism to explain all cases. On the other hand, our research demonstrated the existence of isotopic heterogeneities between the water in different xylem compartments, which also have contrasting degrees of hydraulic connectivity with the transpiration stream. Analogous isotopic patterns were observed in soil water pools and attributed to physicochemical interactions with soil particles. Altogether, it seems that the water pools that are measured matter, and that not all isotopic mismatches can be attributed to methodological artifacts. Given the widespread occurrence of these isotopic mismatches, it is urgent to identify the cause, either natural, artificial, or both. This will allow us to make informed choices of the extraction techniques in each situation and eventually, we could be able to correct potentially biased old datasets. In this regard, we will summarize the most recent findings and suggest research strategies to unravel the underlying mechanisms of isotopic mismatches. In addition, we will outline how such strategies can also provide important insights for closely related disciplines such as plant hydraulics or isotopic analyses of tree-ring archives.

How to cite: Barbeta, A., Gimeno, T., Wingate, L., and Ogée, J.: Towards the mechanistic understanding of plant-source water isotopic offsets, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-101, https://doi.org/10.5194/egusphere-gc8-hydro-101, 2023.

10:20–10:30
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GC8-Hydro-109
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Session 4
Christophe Hissler, Alessandro Montemagno, Richard Keim, and Laurent Pfister

Understanding water dynamics in the Critical Zone is key for designing better water management strategies, particularly in the light of climate change. Of specific interest in this context is the large amount of water exchanged between regolith and trees in forest ecosystems. In the coming years and decades, the frequency of droughts is likely to increase during vegetative periods. The lack of understanding of how and where tree water uptake is taking place across different regolith layers becomes a critical economic and social issue – spanning from water resources to forest management, even in temperate ecosystems.

Stable isotopes of water have been largely used as tracers in ecohydrology, contributing enormously to the development of various hypotheses and interpretations on tree water uptake dynamics and evapo-transpiration fluxes. However, many issues remain when using O-H stable isotopes to trace the origin of the tree water uptake. The lack of standard protocols for tree water sampling and analysis, alongside the little attention given to the effect that tree physiology and biochemistry may have on the isotopic composition of xylem water, is a limitation to the use of these tracers in the regolith-tree continuum.

In this work, we present tree sap O and H isotopic data collected during three years with two different techniques: (i) an in-situ vacuum extraction of the sap flowing in the xylem vessel and (ii) the well-known cryogenic vacuum distillation applied on wood cores. Nine beech trees were sampled at different heights in the root-twigs continuum along a hillslope in the Weierbach Experimental Catchment in Luxembourg. The O-H isotopic signatures of the samples were then compared for observing differences proper to the techniques and/or to potential effects of internal tree processes controlled by either (1) the retention and mixing of water of different ages and/or (2) water exchange in xylem tissues. The isotopic signatures of the xylem water were also compared with the potentially available water sources in the regolith.

We observed a significant difference between the isotopic signatures in water collected with the two different techniques. The water sampling protocol from the root with the in-situ vacuum extraction appears to be more appropriate for the identification of the potentially absorbed water source. We conjecture that roots are the first tree organ that interacts with the regolith water and in which a lesser impact from the internal tree processes can be expected. Our results also show a progressive 18O and 2H enrichment in the xylem water along the root-twig flow path for all studied trees. This enrichment seems to be closely related to the travel-distance inside the xylem: the longer the water is exposed to the internal tree processes, the stronger the modification of its isotopic signature. Finally, the range of the water isotopic signature obtained via cryogenic vacuum distillation is closely related to the tree compartment from which the water was collected from – questioning the contribution to internal tree process understanding from data obtained via this technique.

How to cite: Hissler, C., Montemagno, A., Keim, R., and Pfister, L.: Xylem water isotopic variability in Fagus sylvatica L.: potential impacts for ecohydrology, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-109, https://doi.org/10.5194/egusphere-gc8-hydro-109, 2023.

10:30–10:40
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GC8-Hydro-19
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Session 4
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Claire O'Connor, Caroline Choma, François Delbende, Bernhard Zeller, Aichatou Ndiaye, Hélène Desmyttère, Eric Manouvrier, Ali Siah, Christophe Waterlot, and Kasaina Sitraka Andrianarisoa

Despite numerous studies investigating competition and/or facilitation for soil water resources in alley-cropping systems (AC), share of water at the early stage of trees establishment in AC has been poorly examined. This work aimed to explore the water share between crops and trees after four years of tree establishment in AC at the Ramecourt block design alley-cropping experimental site. In mid-spring, we injected 300 mL of a 10 % deuterated water at 30, 50 and 100 cm soil depth at 1.5 m distance from a referent tree (alder, hornbeam or wild cherry) in AC, in pure-forest control plot with ryegrass (FC) and in a randomly chosen area in monocrop wheat control (CC) plots. The tracer uptake was monitored by collecting tree leaves and wheat and ryegrass (RG) whole-plant samples every two weeks in labeled and unlabeled area. For deuterium natural abundance analyses, the global mean of δ2H was significantly lower for wheat (- 44 ± 4 ‰) than RG (- 27 ± 6 ‰) and trees (- 20 ± 3 ‰), indicating that the most active sites of water absorption were different between these species. The mean wheat δ2H was 2481 ± 523 ‰, 715 ± 218 ‰, and 133 ± 68 ‰ at 30, 50 and 100 cm labeling depth respectively. It was significantly higher in AC (2883 ± 585 ‰) compared to CC (1131 ± 274 ‰) only at 30 cm labeling depth. For trees, the δ2H of labeled samples remained negative unlike wheat. Particularly in AC, alder and wild cherry presented significant higher δ2H 15 and 45 days after labeling, respectively from 50 and 100 cm labeling depth, compared to unlabeled samples. We concluded that trees and wheat took up their water in upper soil layer but in AC, they favored wheat water absorption in topsoil and were able to flexibly shift their water source from deep layer in case of low water availability in the upper soil layer.

How to cite: O'Connor, C., Choma, C., Delbende, F., Zeller, B., Ndiaye, A., Desmyttère, H., Manouvrier, E., Siah, A., Waterlot, C., and Andrianarisoa, K. S.: How do four-year-old intercropped trees share soil water with wheat in temperate alley-cropping experimental site: evidence from 2H2O artificial labeling?, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-19, https://doi.org/10.5194/egusphere-gc8-hydro-19, 2023.

Chairpersons: Laurent Pfister, Ilja van Meerveld
11:30–11:40
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GC8-Hydro-92
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Session 4
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ECS
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Giulia Zuecco, Chiara Marchina, Matteo Censini, Diego Todini Zicavo, Giorgio Cassiani, and Marco Borga

In forested catchments, stemflow affects the amount of precipitation reaching the soil, how water infiltrates and transports nutrients into the soil. Recently, the ecohydrological community has shown a renewed interest towards the methods used to quantify the stemflow infiltration area. Stemflow infiltration area is generally estimated based on the ratio between stemflow input rate and the mean soil infiltration capacity, whereas direct observations are rare. Direct estimations of stemflow infiltration areas are usually made by the application of dye tracers, which have proven to be useful for monitoring double-funneling. On the contrary, there are still few observations based on the application of electrical resistivity tomography (ERT) and isotopically-labelled water.

In this study, we present a simple experiment carried out for a beech tree, in a forested hillslope in the Italian pre-Alps. The aims of the experiment were to simulate stemflow by using salt and isotopically-labelled water, and to quantify stemflow infiltration area and volume.

The experiment was performed during a dry period in September 2022, in order to observe marked changes in the isotopic signature of soil water, as well as in electrical resistivity. Stemflow was simulated with a rainfall depth and intensity similar to typical summer storms in the catchment, and by using salt water with an isotopic composition very different compared to the composition of soil water during summer months. Before, during and after the stemflow application, 9 ERT surveys were performed to capture the infiltration dynamics. The collection of soil samples for isotopic analysis was carried out after the experiment, at different distances from the stem and at different depths (e.g., 0-15, 15-30, and 30-45 cm). Soil moisture was also measured at 0-6 and 0-12 cm depths at different distances from the stem.

Preliminary results showed a rapid infiltration of stemflow along the root system of the beech tree, and 24 hours since the start of the experiment the labelled water had infiltrated up to 80 cm into the soil. This simple experiment showed the usefulness of using time lapse ERT surveys, as well as isotopically-labelled water to simulate stemflow and trace double-funneling.

 

 

Keywords: stemflow, electrical resistivity tomography, stable water isotopes, soil water, forested catchment.

How to cite: Zuecco, G., Marchina, C., Censini, M., Todini Zicavo, D., Cassiani, G., and Borga, M.: Tracing stemflow infiltration with a simple experiment using geophysical surveys and stable water isotopes, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-92, https://doi.org/10.5194/egusphere-gc8-hydro-92, 2023.

11:40–11:50
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GC8-Hydro-40
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Session 4
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ECS
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Alessio Gentile, Davide Gisolo, Davide Canone, and Stefano Ferraris

Stable water isotopes are increasingly used for tracking water fluxes in the critical zone offering new possibilities for model calibration and validation. Past studies revealed that the main discrepancies between simulated and measured values in a soil profile can occur when snow-related processes are under investigation. Indeed, the amount and timing of infiltrated meltwater and its isotopic composition remain largely unexplored to date.

In this work we use HYDRUS-1D (H-1D) to simulate water flux and isotope transport in a soil profile and in vegetation over a high-elevation (2600 m a.s.l.) grassland located in Valle d’Aosta (Italy). The H-1D inputs deriving from snow-related processes are computed in two steps: i) the amount of snowmelt is obtained through a classical degree-day model ii) the meltwater isotopic composition is simulated with a recently proposed snow isotope model which further assumes that any rainfall on a pre-existing snowpack mixes with the water stored in the snowpack. Model results have been compared with in-situ observations, including isotope measurements in both soil water and xylem water.

Our results show a satisfactory correspondence between model outputs and observations, but the raised discrepancies indicate other potential processes at play, e.g., soil freezing and thawing, preferential flow, isotopic fractionation, that will demand future attention. In addition, is still an open challenge to collect both meltwater samples for isotopic analysis and snowmelt measurements to validate the results deriving from models that attempt to reproduce the inputs intended for other models.

How to cite: Gentile, A., Gisolo, D., Canone, D., and Ferraris, S.: Reproducing in-situ measurements over a high-elevation grassland using HYDRUS-1D and a snow isotope model, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-40, https://doi.org/10.5194/egusphere-gc8-hydro-40, 2023.

11:50–12:00
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GC8-Hydro-45
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Session 4
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ECS
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Anna Leuteritz, Victor Gauthier, and Ilja van Meerveld

In steep humid catchments with a low permeability soil layer close to the surface, lateral flow at or near the soil surface is an important runoff mechanism. In these catchments overland flow and shallow (i.e., near-surface) subsurface flow also play a crucial role in nutrient and sediment mobilization and transport, and thus affect stream water chemistry. However, due to the lack of data on the spatial and temporal variability in the occurrence of overland flow and shallow subsurface flow and their isotopic signature, it is still poorly understood how rainfall event- and site characteristics affect the onset and mixing of these near-surface flow pathways.

We installed 14 small (1 m wide) runoff plots in a 20-ha headwater catchment in the Swiss pre-Alpine area that is underlain by Gleysols and Flysch bedrock. We coupled hydrometric measurements and stable water isotope data to infer the source (groundwater, soil water, and rainfall) of overland flow and shallow subsurface flow during rainfall events during the snow-free seasons of 2021 and 2022. Rainfall was sampled sequentially at two locations. The isotopic composition of pre-event water was determined based on the soil and groundwater samples taken at each plot prior to the event. Preliminary isotope hydrograph separation results for five rainfall events indicate a median event water fraction over all plots and events of 87% for overland flow and 58% for shallow subsurface flow and a very large variation in the event water contributions (30100% for overland flow and 9100% for shallow subsurface).

In this presentation, we will provide an overview of these new data on the temporal and spatial variability of isotopic composition in overland flow and shallow subsurface flow and describe how the event water fractions depend on rainfall event- and site characteristics (topographic position, vegetation cover, and antecedent moisture conditions). 

How to cite: Leuteritz, A., Gauthier, V., and van Meerveld, I.: Event water fractions in overland flow and shallow subsurface flow in a pre-Alpine headwater catchment in Switzerland, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-45, https://doi.org/10.5194/egusphere-gc8-hydro-45, 2023.

12:00–12:10
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GC8-Hydro-2
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Session 4
Fuqiang Tian and Sihan Zhao

An experimental headwater catchment has been setup in a typical monsoon-influenced semi-humid mountainous forest of North China and long-term field measurements of hydrological processes have been conducted. Samples were collected for isotope (δ18O and δ2H) and hydro-chemical analysis since 2014. Based on long-term hydro-chemical and isotopic data, the principal components of streamflow were defined and fractional components of stream flow separations were estimated, the result shows that groundwater and streamflow isotopic compositions are very similar and streamflow is controlled by a deep groundwater system that is recharged only in one or two large events (or clusters of events) each year. The two-component isotope hydrograph separation has been applied in 6 intensively sampled events, the results suggest that groundwater makes up 63-94% of the storm runoff,event water plays a relatively tiny role. Based on numerical modeling and statistics methods, impact of rainfall and hydraulic conductivity heterogeneity on Hortonian overland flow patterns have been analyzed, possibilities of Hortonian overland flow occurrence have been estimated in different climatic and underlying occasions, the result shows due to high permeability and low rainfall intensity, in more than 95% of total events, Hortonian overland flow couldn’t occur in the study area. Runoff generation mechanism in semi-humid mountainous catchment have been revealed based on multi-scale measurements and numerical modeling, when rainfall intensity and duration are lower than certain threshold, surface runoff generation is consisted of groundwater runoff, direct rainfall on channel and saturation overland flow. Onsite observation shows that surface runoff contributing area in the watershed mainly distributed in riparian zone, and our result shows saturation overland flow is the dominant type of surface runoff generation in most summer rainfall events.

How to cite: Tian, F. and Zhao, S.: Runoff generation mechanism in a headwater experimental catchment with semi-humid monsoon climate in North China, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-2, https://doi.org/10.5194/egusphere-gc8-hydro-2, 2023.

12:10–12:20
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GC8-Hydro-75
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Session 4
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ECS
The study of stable O-H isotopes to assess the features of the genesis of artesian waters in the sedimentary basins of South Kazakhstan based on
(withdrawn)
Dr. Malis Absametov, Dr. Erkebulan Zhexembayev, Dr. Yermek Murtazin, Dr. Jay Sagin, and Dr. Dinara Adenova
12:20–12:30
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GC8-Hydro-14
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Session 4
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Christian Moeck, Andrea Popp, Matthias S. Brennwald, Rolf Kipfer, and Mario Schirmer

Assessing hydrological processes, water ages and mixing ratios is crucial for sustainable water management. The surface and subsurface heterogeneity necessitate the application of multiple tracers to quantify uncertainty when identifying the above mentioned processes and observational tools operating at high temporal resolutions are required. Although a variety of tracers exists, their interpretation can differ considerably due to the mentioned heterogeneity, underlying tracer assumptions, as well as sampling and analysis limitations. 

For our urban hydrological observatory, we used stable water isotopes (e.g., 2H and 18O), chlorinated solvents (e.g., perchloroethylene (PCE)), dissolved gas concentrations (e.g. He, Ar, Kr, N2, and O2), dye and heat tracers, chemically (persistent) anthropogenic markers (e.g., artificial sweeteners) and  3H and tritiogenic 3He concentrations to assess water flow paths and mixing between artificially infiltrated surface water and groundwater. Moreover, we explain the origin and spatial distribution of PCE contamination found at our study site with our multi-tracer approach.

Especially, the recent developments of portable field-operated gas equilibrium membrane inlet mass spectrometer (GE-MIMS) systems provide a unique opportunity to measure dissolved gas concentrations, such as 4He with a high temporal resolution at relatively low costs. Although the GE-MIMS are not capable of providing apparent water ages, 4He accumulation rates are often obtained from 3H/3He ages and it has been shown that non-atmospheric 4He concentrations determined in the laboratory (e.g., by static (noble gas) mass spectrometry) and by field-based (GE-MIMS) methods closely agree. This agreement allowed us to establishing an inter-relationship between 3H/3He apparent water ages and the non-atmospheric 4He excess (e.g., calibrating the 4He excess in terms of residence time).

We demonstrate that the 4He excess concentrations derived from the GE-MIMS system serve as an adequate proxy for the experimentally demanding laboratory-based analyses. We combined the obtained water ages with hydrochemical data, water isotopes (δ18O and δ2H), and PCE concentrations to understand water flow dynamics and applied a developed Bayesian model to a tracer set, which includes the 4He analyzed on-site to determine water-mixing ratios. We demonstrate that important information about flow and transport during changing boundary conditions (e.g., infiltration rates) can only be identified with a high temporal resolution data set and that the gained information from multiple tracers and methods offered more insight and accuracy than from a single tracer.

How to cite: Moeck, C., Popp, A., Brennwald, M. S., Kipfer, R., and Schirmer, M.: Combined use of multiple tracers to identify water flow dynamics and pollutant transport, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-14, https://doi.org/10.5194/egusphere-gc8-hydro-14, 2023.

Poster: Wed, 14 Jun, 10:40–11:30, 17:00–18:00 | Poster area

Chairpersons: Laurent Pfister, Ilja van Meerveld
P12
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GC8-Hydro-4
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Session 4
Andreas Wieser, Uta Ködel, Andreas Güntner, Christian Rolf, Theresa Blume, Peter Dietrich, Jan Handwerker, Dina Khordakova, Martin Kohler, Erik Nixdorf, Marvin Reich, and Heiko Thoss

MOSES (Modular Observation Solutions for Earth Systems) is a research initiative comprising nine Helmholtz research centres which are part of the research field “Earth and Environment”. MOSES focuses on 4 research areas covering Ocean Eddies, Permafrost Thaw, Heat Waves, and Hydrological Extremes. Highly flexible and mobile observing systems, combining the expertise of the involved Helmholtz Institutes, were developed to study effects along full event chains in highly dynamic situations (such as floods or droughts) as well as the long-term trends in environmental systems.

To study Hydrological Extremes, the Elbe river basin in Germany was selected as investigation area during the implementation phase of MOSES. The measurements in headwater catchments of the Elbe river includes several campaigns, coordinated by the Karlsruhe Institute of Technology (KIT). These campaigns took place in the Mueglitz Valley in the Eastern Ore Mountains, Germany, aiming at the investigation of the effects of extreme rainfall events along an entire process chain from the origination in the atmosphere, over the land-surface and the subsurface including their storage dynamics, up to flood generation in the contributing sub-catchments. The Institute for Meteorology and Climate Research - Department Tropospheric Research (IMK-TRO) of KIT provides essential data on the formation and evolution of heavy precipitation events, as well as high resolution measurements of precipitation distributions and evaporation. The Research Centre Jülich (FZJ) study the handover of water vapour and trace substances into the upper troposphere and even into the lower stratosphere.

The Helmholtz Centre for Environmental Research (UFZ) and the German Research Centre for Geosciences (GFZ) studies the catchment storage dynamics and runoff generation during flood and drought events by absolute and relative gravimeters, soil moisture monitoring with wireless sensor networks as well as with stationary and roving Cosmic Ray measurements, and river water level and discharge monitoring.

The presentation will explain the research questions and introduce the field and monitoring set up and the methods applied.

How to cite: Wieser, A., Ködel, U., Güntner, A., Rolf, C., Blume, T., Dietrich, P., Handwerker, J., Khordakova, D., Kohler, M., Nixdorf, E., Reich, M., and Thoss, H.: MOSES Campaigns to Study the Evolution of Hydrological Extremes in the Mueglitz Valley, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-4, https://doi.org/10.5194/egusphere-gc8-hydro-4, 2023.

P13
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GC8-Hydro-13
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Session 4
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ECS
Turk Guilhem, Laurent Pfister, Bernd Schöne, Christoph Gey, Frankie Thielen, Christophe Hissler, François Barnich, and Loïc Léonard

The ongoing intensification of the hydrological cycle calls for the identification and assessment of factors controlling catchment resilience to climate change. Stable isotopes of O and H in streams and precipitation are cardinal tools in this respect – notably for investigating questions related to water source, flowpaths and transit times. However, the spatial and temporal variability of these tracers remain largely unknown – essentially due to the limited availability of long historical time series of O-H isotope signatures in stream water, as opposed to the multi-decadal records in precipitation of the IAEA’s GNIP database (https://www.iaea.org/services/networks/gnip).

Based on their quality as natural archives of in-stream environmental conditions, freshwater mussels have been recently used for complementing stream water δ18O isotope records. With an average life span of ca. 10 years (up to 200 years for the freshwater pearl mussel), their potential is significant, considering the fact that nearly 1200 freshwater bivalve species inhabit a large variety of river systems and lakes around the globe (Pfister et al., 2018). Our proof-of-concept work has shown that δ18O values extracted from their shells closely mirror the variance of the measured stream water δ18O – both showing a strong damping of the precipitation signal. In our follow-up study, we leverage prior work by Schöne et al. (2020) on potential links between the NAO index, precipitation isotope signatures and subsequent interdecadal variabilities in reconstructed stream water δ18O signals for three catchments located in Sweden. Using freshwater bivalve shell δ18O as a proxy of stream water δ18O signatures, we hypothesize that interdecadal shifts in atmospheric circulation patterns translate into modifications of δ18O isotope signatures in precipitation and subsequent stream water δ18O signals – the latter potentially revealing changes in young stream water fractions related to fast flow paths. In parallel, we stipulate that the long-term δ18O signal in precipitation can be retrieved from historic records and reanalysis data of climate variables, as well as from synoptic atmospheric circulation classifications.

Here we focus on findings gained from a unique dataset of 5 years-worth of sub-daily precipitation O-H isotope data from the Belvaux (L) meteorological station, comprising 1443 rainfall samples. We investigated the links between local climate variables, the rainfall amount, atmospheric circulation patterns, and the precipitation δ18O signal. Our results show (i) an anticipated strong temperature-induced seasonality of the δ18O signal, characteristic for semi-continental sites, (ii) a weak but significant amount effect, (iii) a circulation type-dependant influence of local climate variables on the δ18O signal, and (iv) a high variability at the event-scale – indicating the influence of complex frontal systems and moisture recycling. We leveraged these findings for building a multiple linear regression model, explaining up to 50 percent of the variability of the δ18O signal at sub-daily resolution and closely matching the isotopic signal when applying moving averages over periods within a monthly range.

How to cite: Guilhem, T., Pfister, L., Schöne, B., Gey, C., Thielen, F., Hissler, C., Barnich, F., and Léonard, L.: Reconstructing the history of flowing waters from freshwater mussels in the context of interdecadal climate variability, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-13, https://doi.org/10.5194/egusphere-gc8-hydro-13, 2023.

P14
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GC8-Hydro-81
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Session 4
Daniele Penna, Stefano Brighenti, Marco Borga, Francesco Comiti, Andrea Dani, Ginevra Fabiani, Julian Klaus, Francesca Sofia Manca di Villahermosa, Chiara Marchina, Laurent Pfister, Federico Preti, Paolo Trucchi, Matteo Verdone, Giulia Zuecco, and Konstantinos Kaffas

A holistic understanding of ecohydrological processes that regulate the variability of tree water use, water flow pathways through the soil and to groundwater and the stream, and the transit time of water at the catchment scale is still challenging. In this work, we rely on an integrated dataset of isotope tracers and hydrometric data to show new evidence on the main ecohydrological processes and their controls that link runoff origin, sources of tree water uptake, and water transit time in a small mountain, forested catchment in central Italy.

The Re della Pietra experimental catchment is located in the Tuscan Apennines. The catchment is 2 km2 in size and ranges in elevations between 650 and 1280 m a.s.l.. Forests cover more than 95% of the area, and the main tree species are beech and oak trees, with a much smaller proportion of conifers. Mean annual precipitation is around 950 mm. We collected water samples from April 2019 to January 2023 from precipitation, throughfall, soil, groundwater, springs, stream at different sections, and xylem of beech trees, and determined their isotopic composition. Weather data, streamflow, soil moisture, groundwater level, and throughfall were monitored in a 0.3 km2 headwater sub-catchment. Stream stage and electrical conductivity as additional tracer were measured in three stream sections from the headwater sub-catchment down to the Re della Pietra outlet. Streamflow, groundwater, spring flow, and soil moisture are characterized by a marked seasonality, reflecting the strong seasonal variability in the meteorological forcing, typical of the Mediterranean climate.

Based on field observations and preliminary data analysis, we aim to test the following hypotheses:

  • i) Trees growing along a steep hillslope in the headwater sub-catchment use different water sources (soil water vs. shallow groundwater) as a function of their topographic position.
  • ii) Hillslope soil water is an important contributor to streamflow only during wet conditions (i.e., in winter, late fall, and early spring).
  • iii) Spring water flows through shallow pathways and is a negligible contributor to streamflow, especially during dry conditions.
  • iv) Water transit time increases as a function of increasing catchment size (i.e., increasing drainage area).

The results will contribute to the conceptualization of the interrelated ecohydrological processes driving water fluxes in Mediterranean forested catchments.

How to cite: Penna, D., Brighenti, S., Borga, M., Comiti, F., Dani, A., Fabiani, G., Klaus, J., Manca di Villahermosa, F. S., Marchina, C., Pfister, L., Preti, F., Trucchi, P., Verdone, M., Zuecco, G., and Kaffas, K.: Flow pathways, transit time, and tree water sources: linking ecohydrological processes with stable isotopes in a small forested catchment, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-81, https://doi.org/10.5194/egusphere-gc8-hydro-81, 2023.

P15
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GC8-Hydro-94
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Session 4
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ECS
Nariman Mahmoodi, Christoph Merz, and Michael Schneider

Comprehension of the hydrological process and accurate estimation of major water balance components are substantial for a prosperous hydrologic model application. Analyses of changes in the stable hydrogen and oxygen isotope composition of surface water and groundwater can be employed to estimate evaporation losses and to define the origin of water and the way it moves in a specific region. This study aims at a better understanding of the water cycle of lowland lakes (Groß Glienicker See, Sacrower See) in Berlin-Brandenburg state, Germany, using stable water isotopes (oxygen-18, deuterium). To get that done, an isotopic mass balance model (HydroCalculator) was applied to compute the evaporative losses over inflow from the lakes’ water bodies under a steady-state hydrologic regime condition. The isotopic signatures of precipitation, water samples from eight observation wells, and from different depths of the lakes’ water within the time period of September 2022 to Jan 2023 classify the lakes into flow-through types which are fed by shallow groundwater. The estimated fractional water loss by evaporation is slightly higher in Groß Glienicker See (35%) in comparison to Sacrower See (33%). This is due to the different depths and areas of their water bodies.

How to cite: Mahmoodi, N., Merz, C., and Schneider, M.: Application of the stable isotope compositions of water for quantifying evaporative losses, A European vision for hydrological observations and experimentation, Naples, Italy, 12–15 Jun 2023, GC8-Hydro-94, https://doi.org/10.5194/egusphere-gc8-hydro-94, 2023.