HS2.3.3

EDI
Isotope and tracer methods: flow paths characterization, catchment response and transformation processes

Stable and radioactive isotopes as well as other natural and artificial tracers are useful tools to fingerprint the source of water and solutes in catchments, to trace their flow pathways or to quantify exchanges of water, solutes and particulates between hydrological compartments. Papers are invited that demonstrate the application and recent developments of isotope and other tracer techniques in field studies or modelling in the areas of surface / groundwater interactions, unsaturated and saturated zone, rainfall-runoff processes, nutrient or contaminant export, ecohydrology or other catchment processes.

Convener: Michael StockingerECSECS | Co-conveners: Christine Stumpp, Andrea L. PoppECSECS
Presentations
| Fri, 27 May, 13:20–16:38 (CEST)
 
Room L2

Presentations: Fri, 27 May | Room L2

Chairpersons: Michael Stockinger, Christine Stumpp
13:20–13:30
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EGU22-7211
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ECS
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solicited
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On-site presentation
Stefanie Lutz, Andreas Musolff, Boris van Breukelen, Kay Knöller, and Jan Fleckenstein

The riparian zone is a hydrologically and biogeochemically active zone, characterized by mixing of stream water with groundwater and transformation of nutrients such as nitrogen. The riparian zone thus plays a key role in natural attenuation of nitrate pollution. Among the attenuation processes in riparian zones, denitrification is the only one that leads to permanent removal of nitrogen from the riparian system via the release of dinitrogen gas into the atmosphere. In contrast, other biogeochemical processes such as nitrate uptake by plants merely result in a temporary nitrogen retention within riparian zones. While hydrochemical data and endmember modelling can help assess nitrate transformation in riparian aquifers, this does not allow quantifying the extent of nitrate removal via denitrification. In this talk, I will demonstrate how nitrate isotope data can be used in combination with chloride and nitrate concentration data to quantify spatial and temporal variations in the extent of denitrification and mixing between groundwater and surface water. I will illustrate how the application of this approach to a riparian groundwater study site in Central Germany revealed that denitrification is largely exceeded by other processes that merely lead to temporary nitrate removal from the riparian groundwater. In comparable settings, a major fraction of nitrogen inputs is thus likely retained in riparian zones and may eventually be discharged into rivers. Such information is crucial to determine the effectiveness of riparian zones for removing nitrate from aquatic ecosystems, which is highly relevant for many river ecosystems at risk of eutrophication because of high nitrogen inputs from agriculture.

Reference

Lutz, S. R., Trauth, N., Musolff, A., Van Breukelen, B. M., Knöller, K., & Fleckenstein, J. H. (2020). How important is denitrification in riparian zones? Combining end-member mixing and isotope modeling to quantify nitrate removal from riparian groundwater. Water Resources Research, 56, e2019WR025528. https://doi.org/10.1029/2019WR025528

How to cite: Lutz, S., Musolff, A., van Breukelen, B., Knöller, K., and Fleckenstein, J.: Nitrate isotopes reveal the effectiveness of riparian denitrification for nitrate removal from riparian zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7211, https://doi.org/10.5194/egusphere-egu22-7211, 2022.

13:30–13:36
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EGU22-4714
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On-site presentation
Yuliya Vystavna, David Soto, and Jodie Miller

Increased nutrient levels in aquatic systems can trigger issues such as eutrophication, water quality degradation, and algal blooms that have negative environmental and economic impacts. Nitrate contamination makes water unconsumable hence, reducing access to drinking water - a key factor of well-being as recognized in the UN Sustainable Development Goals. Nitrate source identification remains challenging using hydrochemical measurements, but the analysis of stable isotopes in nitrate (δ15N and δ18O) opened the possibility to track sources and processes. The efficiency of this isotopic approach lay in simple and precise field and analytical methods, with low cost and easy sample preparation. Despite the potential and usefulness, nitrate isotopes on their own cannot differentiate closely related sources of nitrate contamination with overlapping isotopic signatures, such as sewage (human sources) and manure (agricultural sources), as well as treated versus raw sewage inputs from the catchment. One solution is to combine isotopic techniques with analysis of compounds of emerging concern (CECs). Some CECs are ideal chemical markers of faecal contamination (sewage or manure) as they are usually linked to a specific source. They are ubiquitous in that source and are persistent and present at detectable concentrations in contaminated environmental samples. Their high solubility in water and low volatility facilitates their use as tracers for components originating in sewage and manure. Our study is focused on the innovative approach of combining stable isotopes with CECs in surface and groundwater to improve nitrogen source tracking and source delineation, and more precise quantification of groundwater/surface water interaction. As a proof of concept, we have combined stable isotopes of nitrate with CECs in surface water (large European river) and groundwater (shallow aquifer) case studies. Preliminary results provide a unique and versatile framework for expanding the use of isotopic techniques to tracing nitrate pollution sources and assessing water quality in the catchments worldwide.

How to cite: Vystavna, Y., Soto, D., and Miller, J.: Improving understanding of nitrate sources in connected river and groundwater systems through linking nitrate isotopes and contaminants of emerging concern, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4714, https://doi.org/10.5194/egusphere-egu22-4714, 2022.

13:36–13:42
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EGU22-662
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ECS
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Virtual presentation
Christina Radtke, Stefanie Lutz, Christin Mueller, Jarno Rouhiainen, Ralf Merz, Xiaoqiang Yang, Rohini Kumar, Paolo Benettin, and Kay Knoeller

For the sake of food production, nutrients like nitrogen (N) are applied on agricultural land to supply crops. However, due to common agricultural practice, the amount of N provided very often significantly exceeds the uptake potential of the plants resulting in a N surplus that accumulates in the soil. Organic soil nitrogen is slowly transformed to nitrate, which is then mobilized by water and moves through the subsurface, with the risk of contaminating receiving water bodies. High nitrate loads cause poor chemical states for 27% of all groundwater bodies in Germany and foster eutrophication in lakes and rivers and by this a loss of biodiversity. The main problem are legacy issues of nitrate pollution, because there is a time lag between N input and nitrate mobilization and transport. Research on nitrate travel times is highly relevant for a reliable prediction of the capability of catchments to store, buffer and release nitrate. However, it is not clear how long nitrate is stored and transported in catchment’s storage. For this study, a 11 km2 headwater catchment with mixed land use within the Northern lowlands of the Harz mountains in Germany was investigated from spring 2017 until the end of 2020. A monitoring program was set up, starting with biweekly samples for the first two years and daily samples for the remainder, with sub-daily samples during precipitation events. Samples were taken from stream water and when available from precipitation water. Nitrate concentrations as well as isotopic signatures of water (δ18O and δ2H) and nitrate (δ18O and δ15N) were analysed. To investigate nitrate travel times, the numerical model tran-SAS (Benettin and Bertuzzo, 2018) was set up und modified for this catchment. Here, a time-variant power law function was used as rank StorAge Selection (SAS) function to select the composition of fluxes considering their age. Nitrate with a distinct δ18O from water, formed during microbial activities in the upper soil zone is transported with leaching water into the subsurface storage where denitrification with the corresponding isotope fractionation occurs. The combination of stable isotopes of water and biogeochemical equations to describe the forming of nitrate isotopes and the fractionation of nitrate isotopes during denitrification, which depends on transit times is a novel tool to investigate nitrate age and nitrate transport. Together with the usage of a SAS-based transit time model to simulate nitrate transport and denitrification in the subsurface, tran-SAS is transformed into a simplified reactive transport model (RTM).

A decoupling between nitrate age and water age as well as between nitrate travel times and water travel times is expected. Especially during precipitation events catchment’s processes and travel times are changing due to altering hydrological conditions. The model allows to investigate the age of water and nitrate during different hydrological conditions. This will become more and more important considering more frequent hydrological extremes (droughts and floods) and associated N mobilization in agricultural catchments.

How to cite: Radtke, C., Lutz, S., Mueller, C., Rouhiainen, J., Merz, R., Yang, X., Kumar, R., Benettin, P., and Knoeller, K.: Nitrate and Water Isotopes as Tools to Resolve Nitrate Travel Times in a Mixed Land Use Catchment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-662, https://doi.org/10.5194/egusphere-egu22-662, 2022.

13:42–13:48
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EGU22-13405
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On-site presentation
Isimemen Osemwegie, David Soto, Christine Stumpp, Julien Kalpy Coulibaly, and Barbara Reichert

Coastal environments around the globe provide services and support to the population. However, they are frequently impacted by human-based activities in addition to seawater intrusion problems. These lowland groundwater resources are exposed to a significant amount and types of pollutants, the most significant of which is nitrate. Tracking and quantifying the sources of nitrate that pollute surface and groundwater systems can be challenging without the use of environmental tracers such as nitrate isotopes. This study explored how changes in regional flow paths impact the nitrogen concentrations and origin of pollution in coastal waters during high tides. Water samples were collected from surface (rivers, lagoon and Atlantic shore) and groundwater (wells and boreholes) systems along the east coast of Côte d'Ivoire during the boreal summer (October). Water samples were analysed for major ions, dissolved nitrogen concentrations, coliforms presence/amount, as well as dual nitrate isotopes (δ15N-NO3- and δ18O-NO3-). Bayesian isotope mixing models were conducted to estimate the contributions of potential main sources (wastewater, seawater, atmospheric deposition, and agrochemicals). In some areas, nitrate inputs were found likely coming from wastewater sources. Nitrate concentration in groundwater was high at several sites. Some groundwater samples (n = 7) exceeded the WHO drinking water limit of nitrate concentrations of 50 mg/l, and most groundwater samples had high levels of total coliforms (>500 cfu/100ml). However, great isotope variation found in both surface and subsurface water samples suggested a spatial differential impact and origin of nitrate pollution, which is in agreement with the modelling. These water resources are the primary source of water for 53% of the local population and an alternative domestic water source for 97%, which highlights the importance of determining the main pollution sources for sustainable development. We expected that groundwater may have been better protected from nitrate pollution than lagoon surface water during wet periods, but this might have not been the case.

How to cite: Osemwegie, I., Soto, D., Stumpp, C., Coulibaly, J. K., and Reichert, B.: Tracing nitrate pollution within the Agneby subcatchment, SE Côte d'Ivoire (West Africa), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13405, https://doi.org/10.5194/egusphere-egu22-13405, 2022.

13:48–13:54
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EGU22-353
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ECS
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Virtual presentation
Akhtar Jahan, Tanveer Dar, Usman Khan, Nachiketa Rai, and Sudhir Kumar

The present study explores the signature of stable isotopes (δ18O and δD) and major inorganic solute ion concentrations of Satluj river water and its tributaries to gain insight into the dominant hydrogeochemical process that controls the water chemistry in the Satluj River Basin (SRB), Himalayas, India. In isotopic and geochemical terms, the surface water of SRB is poorly characterized for its whole length; their potential variability has yet to be widely used as an aid in hydrological research. The δ18O values in the SRB range from – 14.50‰ to – 7.35‰ and δD from – 100.30‰ to − 44.70‰, showing general enrichment from Khaab to downstream Harike barrage. The upper reaches of Satluj River and its major upstream tributaries like Spiti and other small streams contributing to the Satluj are relatively depleted in δ18O and δD, possibly indicative of precipitation originating at higher elevations and/ or recharge from snow/glacial meltwater. While lower reaches are relatively enriched in δ18O and δD. The local water line for the SRB was found to be δD = 8.12 × δ18O + 18.89. The higher slope and higher intercept as compared to GMWL indicate a system recharged by snow/glacier meltwater and recycled moisture derived from continental sources in addition to monsoonal climates. In addition, a higher intercept indicates that the moisture source of precipitation (snow/rainfall) in this region originates from the Western Disturbance (WD). The Deuterium excess (d-excess) in the SRB varies between 12.50‰ and 25.81‰ with an average of 17.40‰, which is mostly higher than the long-term average for the Indian summer monsoon (~ 8‰). The higher d-excess value is because of the contribution of moisture from Mid-latitude westerlies. A significant negative correlation of Satluj river water δ18O with elevation was observed with a vertical lapse rate of 0.15‰/100 m. Geochemical analysis showed that the solute concentrations show spatial heterogeneity with decreasing elevation in the SRB. This is related to the complex lithologic compositions and different water sources from different elevations that contribute to the Satluj river. This study also established a relationship between total cation abundance (∑Cat*, corrected for cyclic components) and δ18O in waters of the Satluj mainstream. The variation in δ18O and ∑Cat* along the course of the Satluj is brought about by independent processes, the intensity of chemical weathering in the catchments and associated sub-catchments (tributaries), and altitude effect. ∑Cat* is higher at higher altitudes because of intense weathering, and δ18O is more depleted because the source waters are from depleted snow/glacial melt and cloud that is depleted in 18O because of previous rainouts during its ascent. The relationship between total cation abundance (∑Cat*) and δ18O suggests that ∑Cat* would increase by a factor of 0.93 for every 1‰ increase in δ18O.

 

How to cite: Jahan, A., Dar, T., Khan, U., Rai, N., and Kumar, S.: Investigation of Stable isotope systematics and geochemical signatures of surface water from the Satluj River Basin (SRB), Himalayas, India., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-353, https://doi.org/10.5194/egusphere-egu22-353, 2022.

13:54–14:00
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EGU22-6080
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ECS
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On-site presentation
Lara Speijer, Delphine Vandeputte, Mateusz Zawadzki, Yiqi Su, Mingyue Luo, Yue Gao, Marc Elskens, Pascal Verhoest, Joke Bauwens, Tom Coussement, Frank Elsen, Birte Raes, Steven Eisenreich, and Marijke Huysmans

Re-use of treated wastewater is receiving increasing attention as method to reduce water stress resulting from population growth, socio-economic development and climate change. In 2018, the European Commission issued a policy strategy entailing minimum water quality requirements for water re-use for agriculture and aquifer recharge. However, the environmental impact of such solution is yet to be determined.

The VUB in collaboration with private and public sector partners set up a field experiment in Kinrooi (Belgium) in which the effects of re-using treated domestic wastewater for sub-irrigation of an agricultural field are monitored. This is an interdisciplinary project which includes analyses of the effects on water quality and quantity in the subsurface saturated and unsaturated zone and nearby surface water, the effects on crops as well as research on the public perception.

Within this project, one of the aims is to create an advection-dispersion groundwater transport model to investigate how the chemical composition of the shallow groundwater would change after the treated domestic wastewater is applied through sub-irrigation. Observation data of tracers of the re-used water in the groundwater are needed to calibrate the transport model. Therefore, it is critical to choose a suitable tracer, allowing to unambiguously tell apart the effluent and groundwater end members. Literature suggests the use of chemical properties such as stable isotopes and Cl/Br ratios to use as wastewater tracers. Stable isotopes of hydrogen and oxygen are investigated, but the focus is currently on the use of Cl/Br ratios, which shows promising results. The use of this ratio as tracer is based on the close to ideal conservative behaviour of bromide and chloride ions in water caused by their small size and hydrophilic characteristics. This implies that physical processes such as dilution and evaporation happening in the environment influence the absolute concentrations of the ions but leaves their ratio constant. At the moment, 21 monitoring wells are installed on the field of which 9 monitoring wells have been sampled for data on Cl/Br tracers.

In general, the results indicate that finding a suitable tracer is not straightforward because chemical and isotopic compositions of the groundwater and treated wastewater are often similar. Therefore, the research continues to focus on improving the analytical methods used to analyse the currently used tracers (e.g. Cl/Br ratio and stable isotopes) and on the selection of other tracers such as anthropogenic organic compounds (e.g. pharmaceuticals and artificial sweeteners) to quantify the influence of the effluent end member and to enhance modelling performance.

How to cite: Speijer, L., Vandeputte, D., Zawadzki, M., Su, Y., Luo, M., Gao, Y., Elskens, M., Verhoest, P., Bauwens, J., Coussement, T., Elsen, F., Raes, B., Eisenreich, S., and Huysmans, M.: Re-use of treated wastewater for irrigation and groundwater recharge: environmental impact assessment based on tracer method at the experimental site in Kinrooi, Belgium, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6080, https://doi.org/10.5194/egusphere-egu22-6080, 2022.

14:00–14:06
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EGU22-8917
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ECS
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On-site presentation
Jon Golla, Julien Bouchez, Jean-François Didon-Lescot, Jean-Marc Domergue, Nadine Grard, Pierre-Alain Ayral, Didier Josselin, and Jennifer Druhan

Concentration-discharge relationships have been extensively utilized to infer the routing of water and pathways of (bio)geochemical reactions in the Critical Zone. To date, relatively little complementary development of stable isotope ratio - discharge relationships has been made, despite the fact that these tracers are commonly used to disentangle weathering reactions in the fluids draining from headwater systems. A process-based understanding of the extent to which fluid flow rates, antecedent hydrological conditions, and water age distributions impact these isotopic signatures in stream or river exports would present a pivotal advancement in the quantitative analysis of Critical Zone structure and function. Here, we explore how these factors regulate variations in stable lithium isotope ratios (expressed as δ7Li) of streamflow and the underlying water-rock interactions recorded by this signal during periods of hydrological transience. We present novel data sets collected during two distinct flooding events in Sapine Creek, a small, granitic catchment located on the southern flank of the Mont-Lozère, France and part of a Critical Zone Observatory within the French OZCAR Research Infrastructure. The data from this site are used to parametrize and validate an isotope-enabled, multicomponent reactive transport model capable of running transient simulations designed to mimic two sampling conditions at Sapine: (1) a storm preceded by a low-flow period and (2) a storm event during the wet season. The models are initiated from an unweathered granite subject to steady state uplift and infiltration. From this point, two synthetic storm events are simulated. Simulation of a storm event ending a period of dry conditions results in a net increase in streamflow lithium isotope ratios due to enhanced secondary mineral formation promoted by relatively long water residence times. In contrast, when the model is used to simulate a succession of relatively larger (~2 times greater in magnitude) storms during a wet season, a net decrease in δ7Li is observed. These lower isotope ratios are a consequence of attenuated secondary mineral formation. These preliminary results and trends demonstrate the influence of antecedent hydrological conditions and storm intensity on the magnitude and duration over which stream δ7Li is perturbed and, hence, the seasonal dependence of this signal as a record of transient behavior.

How to cite: Golla, J., Bouchez, J., Didon-Lescot, J.-F., Domergue, J.-M., Grard, N., Ayral, P.-A., Josselin, D., and Druhan, J.: Stream lithium isotope ratios record antecedent and transient hydrological conditions in catchment weathering exports, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8917, https://doi.org/10.5194/egusphere-egu22-8917, 2022.

14:06–14:12
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EGU22-9628
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Virtual presentation
Luisa Hopp, Jana Kehr, and Katharina Blaurock

Export of carbon from terrestrial catchments remains a poorly understood flux within the global carbon budget. In order to better understand the release and in-stream transport of dissolved organic carbon (DOC) in a small forested headwater catchment within the Bavarian Forest National Park (Germany), we characterized the stream-groundwater exchange along the headwater stream. We divided a 3000 m long stretch of the headwater stream into three topographically delineated sections that consisted of a steep upstream section (length 620m, elevations 888-967 m a.s.l.), a transition section (length 770 m, elevations 805-855 m a.s.l.) and a flat and wide downstream section (length 1330 m, elevations 770-805 m a.s.l., outlet of headwater catchment). Using sequential tracer injections of known masses of sodium chloride, we determined stream discharge and lateral exchange fluxes between stream and the surrounding riparian zone in the three stream sections and evaluated the effects of the resulting hydrologic turnover on stream water composition. We also compared the calculated lateral exchange fluxes with previously measured longitudinal profiles of Radon activities that can be used to locate groundwater inflow points. Discharge increased over the investigated 3000 m stretch in downstream direction, as expected, although the transition section did not show any change in discharge. The analysis of recovered tracer masses revealed that in the steep upstream section, the exchange fluxes consisted mainly of inflow of water into the stream. The transition section was characterized by an absence of exchange fluxes. In the downstream section, however, large inflows were offset by slightly lower outflows, resulting in a very pronounced exchange between stream water and riparian zone groundwater in this flat valley bottom. The spatial pattern of exchange fluxes was supported by the longitudinal Radon profiles, which pointed to a marked groundwater inflow in the downstream section. Our results suggest that the dominant source area of in-stream DOC at the outlet of our headwater catchment is the flat and wide valley bottom in the downstream section as most of the DOC released into the stream along the steep upstream section will be removed from the stream during the passage through the downstream section.

How to cite: Hopp, L., Kehr, J., and Blaurock, K.: Elucidating source areas of in-stream DOC by characterizing stream-groundwater exchange in a low mountain forested headwater catchment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9628, https://doi.org/10.5194/egusphere-egu22-9628, 2022.

14:12–14:18
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EGU22-9097
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ECS
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Virtual presentation
Sonia Valdivielso, Enric Vázquez-Suñe, Christian Herrera, and Emilio Custodio

In the peripheral aquifer of the Salar de Atacama, recharge is a key term of the water balance. This recharge is produced under arid conditions in the sub-basins surrounding the Salar and is dominated by medium salinity water due the intense evapo-concentration conditions. To solve the uncertainty in closing the water balance in the Salar de Atacama basin, this study aims to characterize the isotopic composition of precipitation, groundwater and surface water and to identify the recharge area. The results show that winter precipitation is more depleted in heavy isotopes, δ2H and δ18O, than summer precipitation. Surface water is evaporated and it has the same isotopic footprint as groundwater in each sub-basin, indicating that surface water runoff is a main recharge component. The meteoric source of surface and underground water in the basins of the Altiplano-Puna Plateau is isotopically lighter than the other waters found in the Salar de Atacama basin, although there is no significant transfer of isotopically lighter water to the peripheral aquifer of the Salar de Atacama from areas significantly outside the hydrographic basin.

How to cite: Valdivielso, S., Vázquez-Suñe, E., Herrera, C., and Custodio, E.: Identification of the recharge zone using stable isotopes in the Salar de Atacama, Chile, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9097, https://doi.org/10.5194/egusphere-egu22-9097, 2022.

14:18–14:24
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EGU22-1280
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ECS
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On-site presentation
Justine L. Myovela, Godson Godfray, and Mohamedi Salimu

This study focuses on water quality assessment and hydrological aspects around northern Mara Sub-Goldfield (Tanzania). A total of 26 water samples were collected from different sampling sites for physicochemical characterization and H-O isotopes analysis. Parameters such as pH, electrical conductivity (EC), Total Dissolved Solids (TDS), Total Suspended Solids (TSS), and total hardness were analyzed for each water sample. The 18O/16O and 2H/1H ratios were measured in water samples and expressed as δ18O and δ2H relative to Vienna Standard Mean Ocean Water (V-SMOW). The study revealed that the majority of drinking water sources meet the recommended World Health Organization (WHO) and Tanzania Bureau of Standards (TBS) levels. Drinking water from Kegonga community borehole (pH=6.62, EC=1690 µs/cm, TDS=1080 mg/l), shallow well east of Ingwe Dam (pH=7.32, EC=1720 µs/cm, TDS= 1000mg/l), shallow well south of tailings dams (pH=7.6, EC=2670 µs/cm, TDS=1780 mg/l) and traditional well (pH=5.76) are not suitable for drinking purposes. Isotopic values of studied water samples have shown a wide variation from -28.5 to 21.4 ‰ for δ2H, -5.37 to 2.37 for δ18O ‰, and -3.7 to 16.08 ‰ for D-excess values. The slope of Local Meteoric Water Line (δ2H = 5. 9 δ18O + 5.51; R2=0.94) is slightly lower than the slope of Global Meteoric Water Line (δ2H = 8.2 δ18O + 11.27; R2=1), which indicates that the majority of studied water samples have been isotopically modified. The study demonstrated that the majority of groundwater has been recharged by more evaporated sources likely wastewater from tailings dams. This finding is supported by the consistency of isotopic signature and physicochemical parameters of several groundwater sources with those of surface water discharged from the mines.

Keywords: groundwater-surface water interaction; water quality; stable isotopes; d-excess; Tanzania

How to cite: Myovela, J. L., Godfray, G., and Salimu, M.: Physicochemical parameters and stable isotope composition of water in Northern Mara Sub-Goldfield, Tanzania: Implications for groundwater-surface water interaction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1280, https://doi.org/10.5194/egusphere-egu22-1280, 2022.

14:24–14:30
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EGU22-6477
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ECS
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On-site presentation
Amanda Carneiro Marques, Emily Kumpel, John Tobiason, and Christian Guzman

The assessment of surface-groundwater fluxes is crucial for understanding pollutant pathways through the natural environment. Several techniques to characterize these surface-subsurface interactions have been applied as an attempt to quantify these fluxes in the humid temperate Northeastern USA. Most recently, stable isotopes are considered to be an important tool to describe the movement of waters through the hydrosphere. This study was conducted in the Quabbin-Wachusett Reservoir System, which supplies water for the Boston Metropolitan Area in Massachusetts and depends on water quality management based on environmental trends. Recent trends indicate that despite efforts to reduce road salt application during the winter, salt indicator trends are still increasing in the watershed. Salt transport characterized by monitoring trends of specific conductivity and chloride across the watershed demonstrate that subsurface water concentrations are significantly higher than the streams and reservoir (for chloride, median value is 204 mg/L for wells and 102 mg/L for streams). The present investigation hypothesizes that salt infiltrates through the subsurface during the cold months (October-March) and then releases back to surface water throughout the year. Since groundwater can act as salt storage, an important question for water management relates to the timeframe needed to observe a reduction of salt presence in the watershed after road salt reduction policies and other mitigation strategies take place. To investigate this, oxygen isotopes are being used to identify the dominant hydrological pathways influencing groundwater recharge patterns.  Stable water isotope compositions for warm precipitation (δ18O -2.14 to -8.98 per mille), cold precipitation (δ18O -4.57 to -13.57 per mille), and groundwater (δ18O -8.27 to -9.66 per mille) were used to assess proportional recharge dominance via local winter and summer precipitation isotope end-members. Preliminary analyses indicate that the groundwater recharge is winter dominant (92% obtained from the winter bias seasonal recharge ratio Rwinter/Rannual; values >= 80% represent winter dominance), thus the applied road salt during cold months can be contributing to sustained increases in conductivity in the groundwater. The results show potential dynamics that explain higher levels of specific conductivity and chloride in the subsurface water and the continued increases in stream and reservoir concentrations. Further investigation is being conducted with larger datasets in order to have a better understanding of sample frequency needed to be representative of the system’s predominant seasonal recharge and runoff generation patterns, as well as, how the water isotopic composition is variable spatially and temporally in the region.

How to cite: Carneiro Marques, A., Kumpel, E., Tobiason, J., and Guzman, C.: Using Stable Isotopes to Assess Surface-Groundwater Interactions and Contaminant Pathways in a Drinking Water Supply Watershed System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6477, https://doi.org/10.5194/egusphere-egu22-6477, 2022.

14:30–14:36
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EGU22-9590
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ECS
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Presentation form not yet defined
Natalie Ceperley, Anthony Michelon, Harsh Beria, Torsten Vennemann, and Bettina Schaefli

 

The characterization of surface-subsurface water exchange in snow-dominated catchments is key to predicting streamflow generation under a warming climate. Stable isotopes of water (SIW) as flow path tracers have become very popular in such environments despite sampling challenges related to access in harsh winter conditions and the fact that such analyses remain costly compared to other natural tracers such as electric conductivity and water temperature. However, SIW alone capitalize on the well-known difference of the SIW ratios from water originating as summer rainfall versus winter snowfall, which propagate into the water stored in the subsurface and into streamflow.

In this presentation, we report our conclusions on the potential of year-round SIW samples to characterize the hydrological processes in the high elevation Vallon de Nant catchment (13.4 km²), located in the Western Swiss Alps. SIW ratios are shown to be particularly useful to characterize the interplay of direct (surface) and subsurface snowmelt input to the stream network during winter and early snow melt periods. We furthermore show that subsurface flow plays a critical role during all melt periods and our tracer data points towards the presence of snowmelt even during winter base flow.

We furthermore demonstrate the added value of soil and water temperature measurements to interpret SIW ratios in snow-dominated environments, by giving additional information on snow-free periods, on flow path depths and on temporary fast connections between surface and subsurface flow.

How to cite: Ceperley, N., Michelon, A., Beria, H., Vennemann, T., and Schaefli, B.: Studying the dynamic of a high Alpine catchment through the scope of multiple natural tracers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9590, https://doi.org/10.5194/egusphere-egu22-9590, 2022.

14:36–14:42
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EGU22-11790
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ECS
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On-site presentation
Amine Boukra, Matthieu Masson, Corinne Brosse, Loïc Richard, Mahaut Sourzac, Edith Parlanti, and Cécile Miège

Dissolved organic matter DOM corresponds to a complex mixture of molecules and macromolecules playing a major role in terrestrial and aquatic biogeochemical process. DOM heterogeneous composition allows it to have innumerable interactions with organic and inorganic compounds, affecting both their bioavailability and mobility in the environment. At the watershed scale, there are many sources of DOM towards the river such as diffuse inputs by leaching of different types of soils (e.g. forest, meadows, crops, urban impermeable areas...) or urban point inputs (storm overflows, WWTP discharges, stormwater discharges....). However, the influence of of all these sources on the composition of the aquatic DOM remains poorly understood to this day.

In this context, the main objective of this study was to build a methodology to detect the different sources of DOM in the rivers. Using a detailed characterization of DOM, the aim was to identify physicochemical markers and construct source-specific fingerprints. For this purpose, approximately 150 samples were collected from natural and anthropogenic sources of DOM (forest, agricultural, wastewater and urban runoff). All samples were analyzed using an innovative approach based on the use of a wide range of analytical techniques: dissolved organic carbon measurement, optical properties (UV-Visible, 3D fluorescence, size exclusion chromatography coupled with UV-fluorescence detection) and molecular composition (high-resolution mass spectrometry coupled with liquid chromatography). A large amount of data has been generated, and processed by classical (Anova, TukeyHSD) and multivariate (PCA, MFA, DFA) statistical approaches.

The results obtained allowed highlighting optical and molecular markers relevant for the identification of the selected sources. These markers inform on specific characteristics of DOM, such as the size of the molecules, the aromaticity content, the degree of humification, polarity and reactivity. In addition, complementarities and redundancies between optical and molecular characterization techniques is investigated. This research also contributes to select relevant markers for geochemical tracing models.

How to cite: Boukra, A., Masson, M., Brosse, C., Richard, L., Sourzac, M., Parlanti, E., and Miège, C.: Multi-analytical approach to investigate sources of dissolved organic matter in a peri-urban watershed, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11790, https://doi.org/10.5194/egusphere-egu22-11790, 2022.

14:42–14:48
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EGU22-11867
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ECS
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Virtual presentation
Nimo Kwarkye, Elisabeth Lehmann, Ivo Nischang, Jürgen Vitz, Ulrich Schubert, Thomas Ritschel, and Kai Totsche

The transport of colloidal organic matter (OM) in soil is governed by colloidal hydrodynamics and frequently features strong interactions at the biogeochemical interfaces provided in the soil pore space. Conventional reactive tracers used to study solute transport usually fail to cover the hydrodynamics of small-sized colloidal OM. This impedes a clear observation of transport phenomena that are characteristic for these OM fractions. Tailor-made poly(ethylene glycol) (PEG) is available in a molar mass range featuring similar hydrodynamic sizes as colloidal OM. Thus, characterizing the transport of PEG could help to decipher the transport behavior of colloidal OM in soil.
We studied the transport of PEG in soil columns filled with homogenized Cambisol material. PEG was labelled with fluorophores to enable a highly resolved and sensitive detection via fluorescence spectroscopy. Parallel factor analysis (PARAFAC) was applied to the measured excitation-emission matrices to estimate the concentration of PEG in the column effluent. Additionally, batch experiments were conducted to determine the adsorption isotherms of PEG with the column substrate and typical soil minerals.
The resulting breakthrough of PEG was retarded by about an order of magnitude and with a pronounced tailing when compared to the breakthrough of non-reactive NaCl. The retardation points towards organo-mineral associations. This was corroborated by the adsorption observed in batch experiments with high maximum adsorption capacity with homogenized soil and clay minerals. The observed tailing may be due to the varying molecular dimensions of PEG contributing to kinetic interactions with soil minerals.
With representative hydrodynamics, varying molecular dimensions as colloidal OM and the possibility of forming organo-mineral associations with soil minerals, tailor-made PEGs are promising candidates to also follow the transport of other colloidal OM.

How to cite: Kwarkye, N., Lehmann, E., Nischang, I., Vitz, J., Schubert, U., Ritschel, T., and Totsche, K.: The Mobility and Interaction of Poly(ethylene glycol) in Column Experiments with Cambisol, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11867, https://doi.org/10.5194/egusphere-egu22-11867, 2022.

Coffee break
Chairpersons: Michael Stockinger, Christine Stumpp
15:10–15:20
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EGU22-8287
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solicited
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Virtual presentation
Daniel B. Nelson, David Basler, and Ansgar Kahmen

Hydrogen and oxygen isotope values of precipitation are critically important quantities for applications in Earth, environmental, and biological sciences. However, direct measurements are not available at every location and time, and existing precipitation isotope models are often not sufficiently accurate for examining features such as long-term trends or interannual variability. This can limit applications that seek to use these values to identify the source history of water or to understand the hydrological or meteorological processes that determine these values. We developed a framework using gradient boosted regression tree-based machine learning, which we used to implement a procedure for calculating isotope time series at monthly resolution using available climate and location data. Here we present two new updates to our model, Piso.AI, one of which applies the original approach to new climate predictor data to extend the time series to the 1950-2020 time interval, and the second of which uses a restricted set of predictors to allow time series to be generated that span the range from 1901-2020 with slightly reduced accuracy compared to the original model. Both new products can be applied over most of Europe, and were trained on the historic archive of precipitation isotope data available from the Global Network of Isotopes in Precipitation. These model products facilitate simple, user-friendly predictions of precipitation isotope time series that can be generated on demand and are accurate enough to be used for exploration of interannual and long-term variability in both hydrogen and oxygen isotopic systems. These predictions provide important isotope input variables for ecological and hydrological applications, as well as powerful targets for paleoclimate proxy calibration, and they can serve as resources for probing historic patterns in the isotopic composition of precipitation with a high level of meteorological accuracy. Predictions from our modelling framework are available at https://isotope.bot.unibas.ch/PisoAI/.

How to cite: Nelson, D. B., Basler, D., and Kahmen, A.: An updated model for generating historic precipitation isotope time series from machine learning applied in Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8287, https://doi.org/10.5194/egusphere-egu22-8287, 2022.

15:20–15:26
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EGU22-6106
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Virtual presentation
George Melikadze, Ladislav Holko, Mariam Todadze, Aleksandre Tchankvetadze, Aleksandre Gventsadze, Merab Gaphrindashvili, Ramaz Chitanava, and Tornike Chikadze

We present preliminary results of the monitoring of oxygen and hydrogen isotopes in the water cycle of Georgia. The objective of the monitoring is to create maps of isotopic composition of precipitation over Georgia, estimate seasonal amplitudes in the isotopic composition of precipitation, and relationships with the surface and ground waters. Monthly cumulative precipitation samples have been collected since 2013 at 17 sites over entire Georgia at elevations 14 m a. s. l to 2220 m a. s. l. Local meteoric water lines (LMWLs) indicated differences between western, central, and eastern Georgia. Although the LMWLs slopes were mostly not substantially different, only the highest stations (Bakuriani and Gudauri) exhibited slopes that were slightly greater than 8.  The lowest LMWL slope (7.4) was found for stations Chaladidi and Sabueti located in western and central Georgia. LMWL derived for Gudauri (the Greater Caucasus) had a significantly greater intercept (19.9) than at all other sites. Isotopic gradients in delta 18O and delta 2H calculated between stations Tbilisi (430 m a.s.l.) and Gudauri (2220 m a.s.l.) were -0.26 per mil and -1.8 per mil per 100 m, respectively. Monthly samples were collected in several major rivers (Rioni, Mtkvari, Alazani, Iori). Isotopic composition of the greatest Georgian river Mtkvari was best correlated with precipitation in the central Lesser Caucasus (Bakuriani and Sabueti) and southern slopes of the eastern Greater Caucasus (Lagodekhi). One-fourth of groundwater samples were collected in boreholes between mid-July and mid-August and almost all samples from the second half of September (i.e. in the periods without groundwater replenishment) contained evaporated water. Slopes of the evaporation lines were 5.4 and 4.8, respectively.

How to cite: Melikadze, G., Holko, L., Todadze, M., Tchankvetadze, A., Gventsadze, A., Gaphrindashvili, M., Chitanava, R., and Chikadze, T.: Mapping stable isotopes of oxygen and hydrogen in precipitation, surface waters and groundwaters of Georgia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6106, https://doi.org/10.5194/egusphere-egu22-6106, 2022.

15:26–15:32
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EGU22-9346
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Virtual presentation
Enric Vázque-Suñe, Sonia Valdivielso, Ashkan Hassanzadeh, Emilio Custodio, and Rotman Criollo

The determination of aquifer recharge zones is necessary for optimal and sustainable management of water resources. Stable isotopes (δ18O and δ2H) are an effective tool to better understand the relationship between precipitation and groundwater. However, there are areas in the world such as northern Chile, where there is a lot of available isotopic information on groundwater but very heterogeneous isotopic information on precipitation. This study contributes to a better understanding of the spatial and meteorological variables that control the isotopic composition in precipitation in Northern Chile and to estimate these meteorological and stable isotopes in precipitation. Results show that in summer, the significant features for temperature, relative humidity and precipitation are altitude-latitude, latitude and altitude-latitude respectively. The stable isotopes of precipitation are controlled by temperature, altitude, latitude, longitude, and precipitation. The monthly estimation models of temperature, relative humidity and precipitation and three isotopic models (summer, winter and annual) are created based on the controlling features.

How to cite: Vázque-Suñe, E., Valdivielso, S., Hassanzadeh, A., Custodio, E., and Criollo, R.: Factors that control the isotopic composition of precipitation in northern Chile, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9346, https://doi.org/10.5194/egusphere-egu22-9346, 2022.

15:32–15:38
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EGU22-3350
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ECS
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Virtual presentation
Zibo Zhou, Ian Cartwright, and Uwe Morgenstern

Streams may be connected to a large store of water, such as regional groundwater, and/or sustained by smaller near-river stores (such as riparian groundwater). Documenting the sources of water in streams is important for understanding catchment water balances, protecting riverine environments from pollution, and predicting the efforts of near-river pumping. Additionally, streams connected to large water stores will be buffered against the impacts of short-term climate variability (such as droughts that last a few years). Many techniques that document groundwater-stream water interaction allow the location and fluxes of baseflow to be determined but do not constrain from where in the catchment the baseflow is derived. The mean transit time (MTT) represents the time taken for water to migrate from where it is recharged in the catchment to where it discharges into the stream. Estimating the MTTs of stream water allows the volume (V) of the water store that sustains streamflow (Q) to be estimated (V=Q×MTT). This study compares the water stores sustaining streamflow in contrasting rivers in southeast Australia based on tritium MTTs calculated using lumped parameter models. Perennial streams (Oven, Yarra, Latrobe, and Gellibrand Catchments) have long MTTs (4 to 179 years) that are higher at low streamflows. By contrast, the MTTs of similar size intermittent streams (Deep Creek, Wimmera, and Gatum Catchments) range from <1 to 35 years (and are mostly less than 20 years). The estimated volumes of the catchment contributing to streamflow are 3 to 5 orders of magnitude smaller than those in comparable perennial streams. These differences reflect the limited connection between the intermittent streams and the deeper regional groundwater system compared with the perennial streams, especially at low flows. Rather, intermittent streams may be sustained mainly by smaller younger reservoirs in the riparian zone. These intermittent streams will be more susceptible to short-term climate variabilities and changes to flow regimes may have significant impacts on water supplies and the health of the riverine system. Intermittent streams are globally distributed in a range of environments, especially in semi-arid areas. Climate change and water stress have resulted in many perennial streams gradually becoming intermittent and this trend is expected to increase. In southeast Australia, around 30% of catchments have not recovered following multiple drought years between 1996 and 2010 (the Millennium Drought), and streamflow has kept declining. The increased intermittence fundamentally changes the catchment water balance, specifically making regional groundwater less important, and increases the reliance of these streams on more vulnerable small young water stores.

How to cite: Zhou, Z., Cartwright, I., and Morgenstern, U.: Mean transit times help understand the volume of catchment water required to sustain streamflow in contrasting southeast Australian rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3350, https://doi.org/10.5194/egusphere-egu22-3350, 2022.

15:38–15:44
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EGU22-7314
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ECS
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On-site presentation
Klara Nagode, Aljaž Pavšek, Urška Pavlič, and Polona Vreča

River water represents the spatial and temporal integrator of the isotopic composition of precipitation in a catchment area. Stable isotope measurements of oxygen and hydrogen (δ18O and δ2H) in stream waters and precipitation are widely applied to investigate hydrological pathways and transit times. In this study, we apply the stable isotope approach to improve knowledge on the hydrological characteristics of the River Sava, Slovenia, by performing monthly sampling of river water at two locations: Brod and Šentjakob and precipitation at one location (Ljubljana–Reactor), between 2020 and 2021. Gathered data was used for preliminary estimations of water transit times in streamflow. Moreover, different methods were used to determine the Local Meteoric Water Line and comparison with precipitation data for the period 1981–2021 to estimate temporal changes and transit times of the River Sava at selected locations.

The climatic characteristics of the investigated area are also reflected in δ18O and δ2H of precipitation that has been monitored since 1981. The δ18O and δ2H values of precipitation reveal strong seasonal variations, while the tracer output signal in the River Sava is dampened. Site-specific long-term (1981–2021) covariation of δ18O and δ2H is also in good agreement with Global Meteoric Water Line (GMWL), while short-period lines (2020–2021) differ in slope and intercept but lie close to the line GMWL. A longer time series is more suitable for the determination of the LMWL, as the error is much higher for shorter two-year periods. 

The exponential flow model produced mean stream water transit times of 4.2 and 3.1 years at Sava Brod and Sava Šentjakob, respectively, whereas estimated transit times were longer compared to the results of previous investigations. Although the identified results are hydrologically plausible, the limitation of this and previous studies are presented as uncertainties resulting from a short sampling period and low sampling frequencies.

How to cite: Nagode, K., Pavšek, A., Pavlič, U., and Vreča, P.: Stable isotopes of The River Sava as a tool for transit time investigations: a case study Ljubljansko polje, Slovenia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7314, https://doi.org/10.5194/egusphere-egu22-7314, 2022.

15:44–15:50
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EGU22-3898
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ECS
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On-site presentation
Anna Leuteritz, Victor Gauthier, and Ilja van Meerveld

In catchments with poorly drained soils, a significant part of the lateral flow on hillslopes takes place at or near the soil surface. However, there is still little knowledge about these shallow flow pathways and the factors that affect their temporal and spatial variability. Therefore, a better understanding of overland flow and shallow subsurface flow is required to enhance our understanding of runoff generation and solute transport at the catchment scale.

We installed 14 plots on vegetated hillslopes in the Studibach catchment in the Swiss pre-Alpine area that is underlain by poorly drained gleysols. We measured the overland flow and shallow subsurface flow rates at small (3 m wide) trenches, as well as the groundwater level near each plot. We, furthermore, sampled precipitation, overland flow and subsurface flow, soil water, groundwater, and stream water over a two-month period to obtain information about the stable water isotope and geochemical composition. Isotope hydrograph separation and end-member mixing analysis were used to determine the event water fractions and to quantify the fractions of precipitation, soil water, and groundwater in overland flow and lateral subsurface flow. In this presentation, we will present the first results on the temporal and spatial variability in the occurrence, amount and chemical composition of overland flow and shallow subsurface flow and describe how these are related to rainfall event characteristics and topographic position.

How to cite: Leuteritz, A., Gauthier, V., and van Meerveld, I.: Spatial and temporal variability of near-surface flow pathways in a Swiss pre-alpine headwater catchment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3898, https://doi.org/10.5194/egusphere-egu22-3898, 2022.

15:50–15:56
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EGU22-4127
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Virtual presentation
Sopio Vepkhvadze, Peter Malik, George Melikadze, Mariam Todadze, Ludmila Ghlonti, and Tornike Tchikadze

The impact of climate change had caused that precipitation has significantly decreased in Georgia which caused significant decrease of surface water flows and depletion of groundwater amounts in natural springs. In the same time, the waters recharged in karstic aquifers, occurring on the southern slopes of the Greater Caucasus Mountains, can be considered as alternative groundwater resources for the communities in lowlands and the adjacent foothills. Here, about half of the renewable groundwater resources in artesian basins and confined groundwater systems in Georgia can be considered as belonging to the above mentioned water-bearing horizon. In order to assess water resources, the pathways between the recharge zones along the Caucasus and aquifers need to be addressed and risks of groundwater contamination along these pathways need to be evaluated.

On the territory of West Georgia, hydrogeological and hydrogeochemical surveys were performed in order to define the main hydrogeological features of the region. In the frame of this research, more than one hundred water sources (springs, wells, boreholes, rivers) were sampled during 2019. Physical parameters (pH, O2, EC, temperature) were measured on site during sampling. Water samples were collected for chemical (major ions) and isotope analysis (18O and 2H). Karstic areas of West Georgia were covered by mapping. Isotopic composition of water in the study area evolves according to a line parallel with the global meteoric water line. Available isotopic data indicate several groups of groundwater types. Some of them very probably represent older waters, with substantially long mean residence time. Samples with pronounced isotope composition variability indicate the evolution of groundwater isotopic composition from the recharge area in the mountains through river valleys to the exfiltration areas. Deuterium excess shows higher values, typical for mountain precipitation and snow in mountain ranges. The conjunctive use of isotopic approaches demonstrates a high potential for future water resources studies in Georgia.

How to cite: Vepkhvadze, S., Malik, P., Melikadze, G., Todadze, M., Ghlonti, L., and Tchikadze, T.: Assessment karstic water origin along South slope of Grate Caucasus Mountain range , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4127, https://doi.org/10.5194/egusphere-egu22-4127, 2022.

15:56–16:02
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EGU22-3772
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ECS
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On-site presentation
Lisa Kuhnert and Thomas Wöhling

Rising trends in the concentrations of dissolved organic carbon (DOC) exported from catchments can be observed in many places around the world, including in the catchment of the river Große Ohe (19 km²) in the Bavarian Forest National Park (Germany). During flood events, DOC is mainly exported via hydrological pathways due to the activation of loaded pre-event water, affecting for example aquatic ecosystems and the use of surface water for drinking water supply.

In previous work, the uppermost soil horizon, enriched with DOC through microbial decomposition of organic matter, was identified as the main source of DOC. However, more recent data show that soil properties play an important role in flood genesis, but are minor for DOC export. More important are the contributions of existing wet areas in the catchment, which provide good conditions for the solution of organic carbon. During rain events, these wet areas become connected to stream runoff and are the main source of DOC exports from the catchment.

We sampled and analysed three flood events with different hydrological conditions and used the results for multi-tracer flow separation and end ember mixing analyses. To do this, we collected water samples from the stream runoff, precipitation water, groundwater and soil water from various locations in the catchment and analysed them for DOC, SiO2, K+, Fe2+ and other cations and anions. Observations of the fingerprints of DOC and K+ show significant differences between water from the uppermost soil horizons (high DOC- and K+-concentrations) and the wet areas (high DOC-, low K+-concentrations). K+ results from the decomposition of organic matter and is mainly present in stemflow and water from the uppermost soil horizons.

During the flood event, we observe a significant correlation between instream DOC-concentration and runoff, but no correlation between instream K+-concentration and runoff. Nevertheless, instream DOC- and K+-concentrations increase at the beginning of the event, leading to the assumption that rapid surface runoff contributes to stream runoff in the first phase of the flood event. As the event progresses and the discharge continues to rise, K+ decreases rapidly, while DOC mainly follows the pattern of the hydrograph. In addition, we consistently observed a delay between the peaks of discharge and DOC concentration of approx. 1.5 - 2 hours. Both facts indicate that these are the fingerprints of the wet areas, which, depending on the hydrological conditions, take some time to “fill up and overflow”. The water of these wet areas then gets connected to the stream and leads to a delayed DOC release.

The findings are used to develop a predictive model for runoff generation and DOC mobilization. Since the identified processes are closely linked to the characteristics of the catchment (topography, hydrotopes, ...), the results have to be compared with other catchments in order to generalize them and ensure the transferability of the model to similar catchments. In the event of success, such forecast models are important tools, e.g. for drinking water suppliers who have to react quickly to changing DOC concentrations to ensure water quality standards.

How to cite: Kuhnert, L. and Wöhling, T.: Discriminating runoff source areas in a small forested catchment using a multi-tracer approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3772, https://doi.org/10.5194/egusphere-egu22-3772, 2022.

16:02–16:08
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EGU22-9190
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ECS
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On-site presentation
Alessio Gentile, Ivan Bevilacqua, Davide Canone, Natalie Ceperley, Davide Gisolo, Mesmer N'Sassila, Maurizio Previati, Giulia Zuecco, Bettina Schaefli, and Stefano Ferraris

High Alpine catchments are precious water-resources since they act as natural storage reservoirs, storing water in the snow cover and in the subsurface and thereby providing water during the dry seasons. Thus, a deeper knowledge of the hydrological functioning of these systems is necessary, in particular to make climate change projections. The role of seasonality is crucial in these catchments that generally exhibit a snow-dominated hydro-climatic regime.

Here we use high-frequency observations of stable isotopes of water to identify the seasonal origin of streamwater in a high-elevation Alpine catchment located in the Valle d’Aosta Region, Italy. We quantify the relative contribution of winter and summer precipitation reaching the stream through the Seasonal Origin Index (SOIQ), calculated using the δ18O values and the volumes of precipitation and streamflow. Highly negative SOIQ values are obtained suggesting that streamwater is mainly composed of winter precipitation. Conversely, the Seasonal Origin Index for evapotranspiration (SOIET), which can be directly inferred from SOIQ, returns a positive value reflecting that plants preferentially take up water deriving from summer precipitation.

These findings allow us to develop a conceptual model of this Alpine system. This conceptual model suggests:

  • a deep infiltration component, mainly composed by snowmelt water, reaching the stream through a preferential flow.
  • a shallow infiltration component, predominantly represented by summer rainfall, that dominates the shallow soils and that is used by plants.

Therefore, we presume a seasonal compartmentalisation of water in this high-elevation catchment.

Nevertheless, a previous study in Switzerland revealed SOIQ ≈ 0 for the Allenbach and Dischmabach snow-dominated catchments, indicating that similar fractions of summer and winter precipitation become streamflow. This different result achieved in systems with an apparently similar functioning highlights the need for a deep insight into the flow paths governing high-elevation catchments and it opens the way for new challenges to understand the hydrological processes hidden behind this difference.

How to cite: Gentile, A., Bevilacqua, I., Canone, D., Ceperley, N., Gisolo, D., N'Sassila, M., Previati, M., Zuecco, G., Schaefli, B., and Ferraris, S.: Seasonal compartmentalisation of water in a grassland at 2600 m a.s.l., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9190, https://doi.org/10.5194/egusphere-egu22-9190, 2022.

16:08–16:14
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EGU22-10348
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ECS
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Virtual presentation
Andrea L. Popp, Nicolas Valiente, Kristoffer Aalstad, Sigrid Trier Kjær, Peter Dörsch, Alexander Eiler, and Dag O. Hessen

High latitude regions are experiencing global warming more rapidly and significantly than any other region of the Earth. A warmer climate has already severely altered the cryosphere. Cryospheric changes such as snowpack reduction are known to be strongly coupled with the entire hydrologic cycle. However, relatively little is known about the nexus between snow cover changes, source water contributions to groundwater and surface water bodies and associated biogeochemical cycling in aquatic systems. 

To better understand the rapid changes occurring in cold region environments, we obtained field- and satellite-derived data from two sub-arctic catchments (one glaciated, one unglaciated) in the north-western corner of the Hardangervidda mountain plateau (South Central  Norway). During 2020 and 2021, we analyzed various water sources including streams, lakes, groundwater, snow and ice for environmental tracers (major ions, stable water isotopes, radon-222) and greenhouse gases (GHG; CO2, CH4 and N2O). Combining the environmental tracer data with a Bayesian end-member mixing modelling approach (Popp et al., 2019) allowed us to partition water source contributions to streams and lakes. Moreover, we used the noble gas radon to assess hyporheic exchange flow and short water residence times (Popp et al., 2021). To estimate snow cover anomalies in 2020 and 2021 compared to a five-year mean, we retrieved fractional snow cover durations (fSCDs) from 2016 to 2021 by merging Sentinel-2 and Landsat 8 imagery over Finse and applying a spectral unmixing algorithm (Aalstad et al., 2020). 

According to the satellite-derived data, 2020 was exceptionally snow-rich, while 2021 was a snow-poor year. Initial results suggest that the snow-poor year (2021) resulted in comparatively longer groundwater and stream water residence times. As expected, in 2021, surface waters and groundwaters showed lower fractions of snow and ice meltwater. This signal is, however, less pronounced in the unglaciated catchment. With this approach, we aim to hone our understanding of the response of water source partitioning and associated biogeochemical cycling, particularly greenhouse gas concentrations, to climate change-induced alterations in the snowpack. 

References:

Aalstad, K., Westermann, S., & Bertino, L. (2020). Evaluating satellite retrieved fractional snow-covered area at a high-Arctic site using terrestrial photography. Remote Sensing of Environment, 239, 111618,  http://dx.doi.org/10.1016/j.rse.2019.111618

Popp, A. L., Scheidegger, A., Moeck, C., Brennwald, M. S., & Kipfer, R. (2019). Integrating Bayesian groundwater mixing modeling with on-site helium analysis to identify unknown water sources. Water Resources Research, 55(12), 10602– 10615. https://doi.org/10.1029/2019WR025677

Popp, A. L., Pardo-Alvarez, A., Schilling, O., Musy, S., Peel, M., Purtschert, R., et al. (2021). A framework for untangling transient groundwater mixing and travel times. Water Resources Research, 57. https://doi.org/10.1029/2020WR028362

How to cite: Popp, A. L., Valiente, N., Aalstad, K., Trier Kjær, S., Dörsch, P., Eiler, A., and Hessen, D. O.: The impact of snow cover changes on source water contributions and associated biogeochemical cycling in high latitude catchments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10348, https://doi.org/10.5194/egusphere-egu22-10348, 2022.

16:14–16:20
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EGU22-11177
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ECS
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On-site presentation
Jared van Rooyen, Celine Meyer, Lucia Ortega, and Jodie Miller

During 2017-2018, the City of Cape Town, South Africa faced an unprecedented drought crisis with the six main water storages supplying Cape Town falling to a combined capacity of just under 20%. Throughout the crisis, groundwater was considered the most important alternative urban water supply source but also the most vulnerable to contamination through accidental return flows from the municipal network, private residences and agricultural industries. This project aimed to constrain the stable isotope chemistry of the water supply network in the Stellenbosch municipality and monitor the augmentation of groundwater into the network using stable isotopes. Long-term monitoring points have been established at 35 tap water sites, 20 private wells as well as at the 3 supply reservoirs that feed the municipal network. Rainwater (4 locations) and local surface water (6 locations) were also monitored over the one-year sampling period in 2021. Preliminary data show distinct isotopic signals associated with each supply reservoir as well as in the local groundwater. Rainfall is predominantly received in the winter season (May-Aug) and typically has more negative isotope delta values. Typical residence times in storage dams and reservoirs appear to be between 2-3 weeks in the winter and 3-4 weeks in the summer, according to stable isotope hydrograph separations. Domestic water supply is consolidated at 2 water treatment facilities in Stellenbosch, where isotope values of all 3 supply reservoirs mix. The amounts of water received from each reservoir changes throughout the year according to dam levels, this change is evident in the stable isotope values at the tap water sample locations. The data also shows significant return flow into the alluvial aquifer system during warmer months when private stakeholders’ water consumption is at its highest. Groundwater is expected to supplement this urban supply network in Q1-2 of 2022 and will likely disrupt the current distribution of stable isotopes in the network, providing further insight into the potential return flow into the local groundwater system. For longer term monitoring, tap water locations that receive the same supply have been identified and single locations (8 in total) have been selected to monitor through 2022 to optimise the monitoring network. Similarly, only 4 rainfall collection sites will continue monitoring. Interested stakeholders and policy makers include municipal supply managers as well as local farmers and industry that can use this data to develop water management strategies and identify areas where leaks or overuse is likely. Hydrograph separations would be more accurate with longer term monitoring rainfall, reservoir and tap water by identifying trends in storage residence time, mixing and release schedules throughout the supply systems. Although the data indicates that there are return flows into local groundwater, these results could not distinguish the mechanisms by which water is entering the system. Further monitoring in targeted areas is needed to constrain if return flows originate from leaks, irrigation or other urban recharge processes.

How to cite: van Rooyen, J., Meyer, C., Ortega, L., and Miller, J.: Stable Isotope Techniques for the Evaluation of Water Sources for Domestic Supply in Stellenbosch, South Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11177, https://doi.org/10.5194/egusphere-egu22-11177, 2022.

16:20–16:26
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EGU22-223
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ECS
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Presentation form not yet defined
Christian Marx, Dörthe Tetzlaff, Reinhard Hinkelmann, and Chris Soulsby

The hydrology of major cities is controlled by complex networks of both natural and engineered flow paths and characterised by spatio-temporal variations in connection and disconnection of water sources. Here, we traced the transformation of stable water isotopes through the urban critical zone, in Berlin, Germany. The Panke catchment is heavily influenced by a wastewater treatment plant (~700,000 inhabitants), and legacy effects of water management during the past century. Two and a half years of daily stream isotopes revealed the complicated interactions between the groundwater fed-stream and urban impacts, such as wastewater effluents and “imported” transboundary water sources, and urban stormwater overflows. To mitigate the effects of the latter, urban greenspaces are important to store and release water more naturally to imitate the “sponge-city” concept and retain water in the urban landscape. We therefore also investigated stable water isotopes at the plot scale in three parks in Berlin. We sampled grassland and urban forest sites during the dry year of 2020. Soil and xylem isotopes of different tree species and under grassland revealed shallower root water uptake from grasslands and greater recharge by younger waters. As evapotranspiration accounts for about 90% of rainfall, ecohydrological dynamics in urban green spaces were shown to be largely disconnected from urban runoff generation. Isotopes were shown to be invaluable tools in multi-scale understanding of urban hydrology and have great potential in contributing to the evidence base needed to develop policies for more sustainable urban water management in the face of increased urban growth and climate change.  

How to cite: Marx, C., Tetzlaff, D., Hinkelmann, R., and Soulsby, C.: Stable water isotopes to understand sources, pathways and ages of water in complex urban settings, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-223, https://doi.org/10.5194/egusphere-egu22-223, 2022.

16:26–16:32
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EGU22-8681
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ECS
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Virtual presentation
Leisan Khasanova, Antonia Longobardi, Ilmir Khasanov, and Alexey Elizaryev

Key words: Mass balance filtering, baseflow, BFI, time-resolution, electrical conductivity, permeability

Baseflow plays an important role in sustaining freshwaters quality and quantity at the global scale. Quantitative estimates of baseflow are necessary but no direct observations are available to the purpose, thus hydrograph filtering appears as a valid solution to quantify the baseflow process. The mass balance filter (MBF), based on electrical conductivity (EC) observations, is one of the most objective filtering techniques.

The aim of the present study is to analyze the impact of data time resolution in the assessment of the long-term scale baseflow index (BFI, the ratio between baseflow and total flow) by hydrograph filtering. The MBF method was used to estimate the long-term BFI of 64 catchments across Continental United States ranging from about 5 to 50000 Kmq, from arid to continental climate conditions and accounting for 5 to 10 years of continuous observations. Streamflow and EC data were collected from the United States Geological Survey (USGS) National Water Information System website at the 15 minutes time resolution and aggregated at the daily scale. BFI15, the BFI computed at the 15 min time resolution, was compared with BFI24, that is with the BFI computed at the daily scale. The difference among the two indices was investigated in relation to catchment climate and physiographic characteristics.

The large dataset was divided into two groups, a poorly-drained group and a well-drained group on the base of the catchment permeability assessed by the GLobal HYdrogeology MaPS (GLHYMPS) project. The first group corresponds to BFI values < 0.5, the second to BFI values > 0.5. Overall the BFI15 was found to be larger than BFI24, with an average difference of about 7%, probably caused by the fact that at finer time scale a wider spectra of streamflow processes and components can be detected, more evidently during the peak flow conditions. The average difference drops to 1% in the case of the well-drained hydrological systems, which appear likely the less impacted by the monitoring time resolution and increase on average to 11% (with maximum values approaching 50%) in the case of the poorly drained systems.

 

How to cite: Khasanova, L., Longobardi, A., Khasanov, I., and Elizaryev, A.: Impact of data time resolution in long term baseflow index assessment from mass balance filtering, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8681, https://doi.org/10.5194/egusphere-egu22-8681, 2022.

16:32–16:38
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EGU22-11417
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Presentation form not yet defined
Ramon Holzschuster, Daniel Elster, Martin Kralik, and Christine Stumpp

Alpine regions are becoming more sensitive to climate change and to understand the hydrogeological processes that follow extreme climatic events (flooding, drought, heavy precipitation and fast snow melt), the hydrologic conditions and geologic realities need to be understood. Our research project “Understanding of Extreme Climatological Impacts from Hydrogeological 4D Modelling” (EXTRIG; funded by the Austrian Academy of Sciences) contributes to this challenge by applying an innovative interdisciplinary approach in an Austrian alpine research area (Sibratsgfäll, Vorarlberg) with a catchment of 5 km² situated at an altitude between 800 and 1.400 m based on a cooperation between hydrogeologists, meteorologists, social scientists and the local population.

This poster study emphasizes on preliminary results of applied hydrogeological methods conducted between 2019 and 2021 to understand the local water cycle.

  • To determine surface discharge, radar monitoring stations was installed at each of the four main streams, flowing into the main river beneath the village. Calibration of the results was conducted with several salt dilution measurements. Additional salt dilution measurements helped to estimate diffuse surface and groundwater discharge into the main river.
  • Precipitation was measured in Sibratsgfäll (906m) and compared with precipitation measurements of two nearby weather stations and with past precipitation measurements of the area since 1990.
  • Evapotranspiration was calculated as ET0 with the Hargreaves method in two different approaches, one using the air temperature reconstructed from surrounding weather stations, the other using temperature measurements from the monitoring station in Sibratsgfäll.

The resulting data was used to calculate the amount of water infiltrating into the ground via water balance calculation. The yearly precipitation from December 2019 including November 2020 sums up to 2.600 mm/a and approx. 50% discharges via the main streams. Evapotranspiration can be estimated to be 22 to 32% with a large uncertainty leaving 18 to 28% of precipitating water to diffuse discharge and infiltration into the groundwater. Estimating that surface-near discharge is at least 10%, between 8 and 18% of precipitating water may infiltrate into the ground. Diffuse surface near discharge has shown to be higher after snow melt and in summer, but almost absent during colder periods. Furthermore, a complex network of shallow agricultural drainages may only partially dewater to streams but also contribute to surface-near discharge.

The monitoring of the stable 2H/18O-isotopes in a meteorological station (906m) and of Flysch-springs close to the mountain ridge of the recharge area allow to differentiate the recharge altitude. The vertical unsaturated infiltration in silt/sand dominated glaciolacustrine sediments were estimated by seasonal variation of 2H/18O-isotopes in soil-water to be 1m/year approximately. Precipitation in the Flysch dominated area at higher altitudes is transported slope-parallel in the upper part of the glacial sediments. The Mean Residence Time (MRT) of the shallow groundwater (<40m) estimated by a combination of isotopes 2H/18O, 3H/3He, 13C/14C and tracer gases (CFC, SF6) indicate ages between some months and 4 years. Deeper (>40m) artesian wells in the western part are dominated by MRT older than 30 years.

How to cite: Holzschuster, R., Elster, D., Kralik, M., and Stumpp, C.: Alpine water cycle unraveled by hydrogeological measurements, isotopes (18O/2H, 3H, 3He, 14C) and tracer gas analyses (CFC-11,-12,-113, SF6), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11417, https://doi.org/10.5194/egusphere-egu22-11417, 2022.