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.
vPICO presentations: Fri, 30 Apr
Being a proxy for water stress monitoring and as a key element of sustainable water management, evaporation helps to assess the vulnerability of Mediterranean ecosystems to droughts. Estimation of annual basin-scale evaporation rate can be done using cost-effective isotope mass balances approaches that exploit the integrative nature of the river isotopic signal.
In Mediterranean regions, the marked climatic seasonality and uneven precipitation distribution complicates the use of isotope mass balances to obtain basin-scale estimation of average evaporation rates. For example, a mass balance approach carried out on the Tavignanu River watershed in Corsica (France), showed unrealistic evaporation rate estimates of 10% for 2017-2018 and 1% for 2018-2019. These results suggest that not only does evaporation alter the seasonal isotopic composition in the river, but that there is a complex variability of the dominant water reservoirs contributing to the streamflow. Therefore, we propose a modified mass balance approach that includes monthly contribution of the different water sources to the river discharge. This allows the discrimination of isotopic variation occurring by evaporation from that originating by mixing processes. By applying this modified approach, we estimated evaporation rates on the Tavignanu River watershed that were in good agreement with results obtained by hydrological modelling: 40% for 2017-2018 and 46% for 2018-2019, respectively.
The proposed approach can be used to determine evaporation rates in river basins in other semi-arid climates where estimating evaporation is of major concern for water management. More generally, these results should encourage investigations of details in water source contributions to river flow prior to conducing isotope mass balance evaporation estimates. Consequences are expected in several research fields where the portioning of evapotranspiration into components is of interest, including hydrology (e.g. water budget estimations), ecology (e.g. carbon budget estimations) and climatology.
How to cite: Mattei, A., Huneau, F., Garel, E., Santoni, S., and Vystavna, Y.: Basin-scale evaporation rate estimation based on isotopic approach: adaptation to the Mediterranean conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2869, https://doi.org/10.5194/egusphere-egu21-2869, 2021.
Water age and flow pathways should be related; however, it is still generally unclear how integrated catchment runoff generation mechanisms result in streamflow age distributions at the outlet. Here, we combine field observations of runoff generation at the Dry Creek catchment with StorAge Selection (SAS) age models to explore the relationship between streamwater age and runoff pathways. Dry Creek is an intensively monitored catchment in the northern California Coast Ranges with a Mediterranean climate and thin subsurface critical zone. Due to limited storage capacity, runoff response is rapid (~1-2 hours), and total annual streamflow consists predominantly of saturation overland flow, based on field mapping of saturated extents and runoff thresholds. Even though SAS modeling reveals that streamflow is younger at higher wetness states, flow is still typically older than one day and thus older than event water. Because streamflow is mostly overland flow, this means that a significant portion of overland flow must derive from groundwater returning to the surface, consistent with field observations of exfiltrating head gradients, return flow through macropores, and extensive saturation days after storm events. We conclude that even in a landscape with widespread overland flow, runoff pathways may be longer than anticipated, with implications for contaminant delivery and biogeochemical reactions. Our findings have implications for the assumptions built into classic hydrograph separation inferences, namely, that overland flow is not all new water.
How to cite: Lapides, D., Dralle, D., Rempe, D., Dietrich, W., and Hahm, W. J.: Controls on streamwater age in a saturation overland flow-dominated catchment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8102, https://doi.org/10.5194/egusphere-egu21-8102, 2021.
The time a molecule of rain takes to reach the stream is normally substantially longer than the time for discharge to respond to rainfall. This difference arises because hydraulic potentials propagate through landscapes much faster than water itself does; in other words, the celerity of wave propagation is faster than the velocity of water flow. Although these concepts are well established, most catchment studies are restricted to the calculation of the celerity or response time from hydrometric information. However, to understand the storage, release, and transport of water, as well as identify flow paths through the catchment, one needs to estimate both response and travel times, requiring both hydrometric and tracer data.
We analyzed hydrometric and tracer data from two contrasting sites, the pre-Alpine Erlenbach catchment in Switzerland and the Upper Hafren catchment at Plynlimon in Wales. For both sites, hydrometric data and sub-daily isotopic tracer time series are available, enabling the calculation of response times as well as travel time distributions and new water fractions. To gain a deeper understanding of the functioning of the two catchments, we quantified these metrics and distributions for different ranges of antecedent wetness and precipitation intensity. Generally, wetter catchment conditions and higher precipitation intensities yielded faster runoff responses and shorter travel times. Contrasts between travel and response time distributions under varying catchment conditions also facilitated more nuanced insights into catchment functioning and the effects of catchment wetness and precipitation intensity on water storage and release.
How to cite: Knapp, J. L. A., Berghuijs, W. R., von Freyberg, J., and Kirchner, J. W.: Impact of antecedent wetness and precipitation intensity on catchment travel and response times, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10301, https://doi.org/10.5194/egusphere-egu21-10301, 2021.
Exploring the isotopic composition of precipitation and streamflow in small catchments and the event and pre-event components of precipitation events using two-component isotopic hydrograph separation may better explain the overall catchment behaviour, more specifically the sources of water origin. This study’s main objective is to investigate the origin of water for different streamflow gauges in a small agricultural catchment, which represent different runoff generation mechanisms. The analysis will be performed in the Hydrological Open Air Laboratory (HOAL) in Austria, a 66 ha experimental catchment dominated by agricultural land use (Blöschl et al., 2016). One of the main specialities of this research catchment is that several tributaries of the catchment representing different runoff generation mechanisms are gauged, such as tile drainage flow or saturation excess runoff from erosion gullies. Two-component isotopic hydrograph separation (for both 18O and 2H) will be conducted for five streamflow gauges (catchment inlet and outlet, two erosion gullies and a tile drainage system) for multiple events in the period 2013-2018. The results will be linked and interpreted using additional observations such as time-lapse images of overland flow, electric conductivity measurements, groundwater level changes, evapotranspiration measurements, etc. The aim is to explain and discuss the processes of rainfall-runoff generation in small agricultural catchments.
Blöschl, G., et al. (2016). The Hydrological Open Air Laboratory (HOAL) in Petzenkirchen: A hypothesis‐driven observatory. Hydrol. Earth Syst. Sci., 20(1), 227–255. doi: 10.5194/hess‐20‐227‐2016.
How to cite: Széles, B., Parajka, J., Holko, L., Wyhlidal, S., Schott, K., Stumpp, C., Hogan, P., Pavlin, L., Strauss, P., and Blöschl, G.: Isotopic hydrograph separation in a small agricultural catchment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6209, https://doi.org/10.5194/egusphere-egu21-6209, 2021.
Hydrologists continue to be challenged in accurately predicting spatial variation in storage, runoff, and other hydrological processes in both natural and disturbed landscapes. Lakes and wetlands are important hydrologic stores in Precambrian shield watersheds. Identifying how they affect streamflow, independently and/or collectively is a challenge. Tracer-aided hydrologic modeling coupled with field-based stable isotope surveys offer a potentially powerful approach to investigation of mesoscale streamflow generation processes because the influence of evaporative enrichment generates a distinct signature of the surface water endmember, and continuous and distributed simulated streamflow can be tested against field observations under a range of flow conditions. The main objectives of this research are to investigate the influence of lakes and wetlands on streamflow generation by developing application of the tracer-aided hydrologic model isoWATFLOOD for the ~ 15275 km2 Sturgeon - Lake Nipissing - French River (SNF) basin located on the Precambrian Shield in Northeastern Ontario, Canada. Monthly surveys of δ18O and δ2H in river flow were collected between 2013 to 2019 (weekly to monthly) across eight sub-catchments, with supporting observations of volumes and stable isotopes in snowcores, snowmelt, precipitation and groundwater. Application of the hydrologic model isoWATFLOOD to the SNF Basin is developed for the first time, allowing for simulation of discharge and stable isotopes in streamflow and soil moisture across multiple sub-catchments. In model building, consideration of differences in quaternary geology, landcover, and sub catchment locations are considered. Landcover ranges from the boreal forests to impervious urban areas, while dominated by temperate forest, with some coverage of agriculture/disturbed impacted systems; several major sub-catchments having hydropower regulations. Previous statistical analysis has highlighted the importance of wetlands, lakes, and quaternary geology as influential on differences in hydrologic and isotope response in SNF watershed, as a result, model building is considering different landcover types as lakes and wetlands. Six different Landover are considered for generating Group Response Units (GRUs). The model is calibrated using discharge and stable water isotope. IsoWATFLOOD can represent variation in streamflow generation across the study area. Identifying the different impacts of lakes and wetlands on streamflow generation processes in study area by applying isoWATFLOOD for the SNF watershed will be the main achievement of this study.
How to cite: Tafvizi, A., James, A., Stadnyk, T., Yao, H., and Ramcharan, C.: Investigation of Lake and Wetlands Influence on Streamflow in Mesoscale Precambrian Shield Watersheds Using IsoWATFLOOD, A Tracer-Aided Hydrologic Model , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5907, https://doi.org/10.5194/egusphere-egu21-5907, 2021.
High nutrient concentrations despite mitigation measures and reduced inputs are a common problem in anthropogenically impacted catchments. To investigate how water and solutes of different ages are mixed and released from catchment storage to the stream, catchment-scale models based on water transit time from StorAge Selection functions (SAS) are a promising tool. Tracking fluxes of environmental tracers, such as stable water isotopes, allows to calibrate and validate these models. However, this requires collection of water samples with an adequate temporal and spatial resolution, while sampling in catchments at the management scale is often limited by the high costs of the instruments, maintenance and chemical analysis. Therefore, temporal and spatial interpolation techniques are needed. This study demonstrates how to deal with sparse tracer data in space and time, and evaluates if these data are valuable to constrain the subsurface mixing dynamics and transit time with SAS modelling. We simulated water isotope data in diverse sub-basins of the Bode catchment (Germany) and calibrated the SAS function parameters against the measured streamflow isotope data. We tested four different combinations of spatial and temporal interpolation of the measured precipitation isotope data. In terms of temporal interpolation, monthly oxygen isotopes in precipitation (δ18OP) collected between 2012 and 2015 were converted to a daily time step with a step function and sinusoidal interpolation. In terms of spatial interpolation, the model was tested with raw values of δ18OP collected at a specific sampling point and with δ18OP interpolated using kriging to gain the spatial pattern of precipitation. The effect of the spatial and temporal interpolation techniques on the modeled SAS functions was analyzed using different parameterizations of the SAS function (i.e., power law time-invariant, power law time-variant and beta law). The results show how tracer input data with different distribution in time and space affect the SAS parameterization and water transit time. Moreover, they reveal preference of the sub-basins to mobilize either younger or older water, which has implications on how water flows through a catchment and on the fate of solutes.
How to cite: Borriero, A., Lutz, S., Kumar, R., Nguyen, T., Attinger, S., and Fleckenstein, J.: Investigating the value of regional water isotope data on transit time and SAS modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11174, https://doi.org/10.5194/egusphere-egu21-11174, 2021.
Stable isotope analysis of hydrogen and oxygen is one of the important methods used to model the hydrological cycle. Oxygen and hydrogen isotopic investigation of river water, its tributaries, and groundwater of its catchment from the Satluj basin was undertaken to estimate the contributions of the main sources comprising discharge during major periods throughout a hydrologic year.
Estimation of the snow/glaciers melt contribution is also very important for tracing the sources and processes regulating the flow from the provenance and reservoirs in the context of global warming, for estimating flood flow, and for other water resource development activities in large parts of the Indian subcontinent. Water samples were collected during the non-monsoon season at increasing altitudes. In this work, in addition to stable isotopes, we also assessed the water quality using various physicochemical parameters and geochemistry of the water.
From isotopic analyses of river water samples, the mean value of the δ18O was found to be ~ -13‰, and the mean value of δD was found to be~ -85‰. For the samples from Satluj tributaries, the mean value of the δ18O was ~ -11‰, and the mean value of δD was ~ -69‰. A mean value of -8.4‰, was found based on the δ18O measurements of the groundwater samples, while the average δD value was found to be ~ -55‰.
For the mainstream and tributary, LWL, y = 8.2604x +20.208, and range of d-excess (>10‰) and y = 8.2079x + 22.182 and d-excess > 10‰ indicates a system recharged by sources of recycled moisture derived from continental sources in addition to monsoonal climates. For the groundwater data, the slope is 6.7, and d-excess ranges from 7‰ to 17‰. These observations are suggestive of the monsoonal source of Indian Ocean precipitation that has experienced significant evaporation during the non-monsoon season.
Our new data clearly shows that the surface water whether mainstream, tributary, and groundwater isotopes are homogenized from regional trends in precipitation, modified by evaporation, and are thus greatly influenced by latitude, elevation, and patterns of climate.
How to cite: Jahan, A., Khan, M. U., Rai, N., Maurya, A. S., and Kumar, S.: Stable isotope geochemistry of Oxygen and Hydrogen: A case study of the Satluj River Basin, India , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2375, https://doi.org/10.5194/egusphere-egu21-2375, 2021.
We have used stable isotopes of oxygen and hydrogen (δ18O and δD) which are important tracers for understanding various hydrological processes, to assess the spatial and temporal variability due to dual moisture sources in the Upper Jhelum River Basin (UJRB) of the north-western Himalayan region. The HYSPLIT back trajectory analysis shows large variability in spatial moisture transport pathways over the region during Southwest monsoon (SWM) and is mainly restricted to the Mediterranean Sea during Western disturbances (WDs). The isotopic composition of precipitation is significantly controlled by temperature and Relative Humidity during precipitation events from WDs; however, this control is found to be weak during the SWM.
Stable isotope signatures of precipitation are found to show a well-defined altitudinal effect (δ18O=0.19‰/100m) and a negative correlation with ambient temperature (R² = 0.65, p<0.01 for WDs & R²=0.48, p>0.1 for SWM). Mixing various tributary waters with different isotopic compositions leads to variability in the Jhelum River’s (JR) isotopic composition along its course. The observed spatial variability of δ18O and d-excess results from the exchange processes between groundwater and surface water. The higher depletion of precipitation during WDs leads to depletion of surface and groundwater and produces enrichment due to the evaporative loss of heavier isotopes due to drier weather conditions during SWM. Evaporation signals are more prominent in shallow groundwater (SGW) and lake water, indicating SGW being discharged in the proximity of lake water bodies. The isotopic values in the upper reaches are observed to be depleted, potentially due to inputs from melting glaciers and snow. In the middle, it reaches slightly enriched, likely due to shifts in groundwater and rainfall inputs. In the downstream, due to increased residence time and flat topography, the isotopic composition is relatively enriched, potentially related to the evaporative losses of heavier isotopes. The d-excess values in UJRB are found to vary between 11‰ to 20‰ with an average value of ~17‰, which is relatively higher than the long-term average observed for the Indian summer monsoon (~8‰), and Upper Indus in the Ladakh region (11.7‰) but almost similar to observed for Lower Indus (18‰).
The contribution of moisture from each source (WDs and SWM) are estimated using a two-component mixing model. The moisture source contribution over UJRB via WDs is 75%(±20) from the Mediterranean Sea and 20%(±10) from SWM. WDs contribution over UJRB is higher than in the Trans-Himalayan region in the Ladakh (Indian sector in the east) but smaller in Lower Indus Basin (Pakistan sector in the west). Hence, the influence of moisture of WDs decreases from west to east along the Himalayan region. This work based on stable isotope geochemistry of oxygen and hydrogen highlights the effects of meteorological and physiographic controls on the moisture dynamics and contributes to explain the spatial and temporal variability of hydrologic processes in the region.
How to cite: Dar, T., Rai, N., and Kumar, S.: Implications for water cycle dynamics in the Upper Jhelum River Basin of North-Western Himalayas based on hydrogen and oxygen isotope signatures of precipitation, surface water, and groundwater, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1077, https://doi.org/10.5194/egusphere-egu21-1077, 2021.
The forest stand can significantly affect the snow deposition and consequently the runoff during the melt period. This study focuses on water and element fluxes from snowpack in two Czech boreal headwater lake catchments with different forest stands (mature vs. regenerating after bark beetle tree dieback) using isotopic and hydrochemical tools. Sampling and analysis of the surface water, precipitation and snowpack throughout one hydrological year enabled us to estimate the isotopic balance and chemical snowpack evolution, but also the snowmelt contribution in lakes inlets and outlets.
Isotopic signatures of the snowpack were seasonal, with δ2H amplitudes of -25‰ in the mature and -17‰ in the regenerating forest catchments. The mature forest had a ~1 month longer duration of snow cover and higher concentration of solutes in the precipitation and snowpack. In both catchments, heavier isotopes (18O and 2H) preferentially left the snowpack, which was saturated with rainwater. This resulted in the final spring snowmelt being enriched with lighter isotopes (16O and 1H). Ions were also eluted from the snowpack during rain-on-snow events and partial snow melting throughout the winter, causing fluxes of diluted water at the end of the snowmelt. Our results demonstrate the hydrological and hydrochemical variability of the snowpack, which in the future may even increase with rising temperatures and changes of precipitation patterns.
How to cite: Juras, R., Vystavna, Y., Paule-Mercado, M. C., Schmidt, S. I., Kopacek, J., Hejzlar, J., and Huneau, F.: Effects of snowmelt on the runoff dynamics in two catchments with different forest stands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15057, https://doi.org/10.5194/egusphere-egu21-15057, 2021.
Rising concentrations of dissolved organic carbon (DOC) in inland waters are observed and investigated intensely in the last decades. The development of adaptive measures requires the forecasting of DOC-exports from catchments. Since DOC is exported from river catchments along hydrological pathways it is evident that the investigation of runoff generation, retention and travel times along flow paths are important to quantify DOC-loads and to develop a forecast model.
To gain comprehensive insights in runoff formation and DOC export in a small forested catchment in the Bavarian Forest National Park we apply a nested multi-tracer approach, combining experimental and analytical methods with the aim to develop a hydrological forecast model which is able to reproduce the dominant mobilization- and export processes of DOC in forested mountain catchments. The use of multiple tracers combines different approaches to determine source areas, flow paths and retention times of runoff water in catchments. Stable isotopes (d2H, d18O) are suitable as natural tracers to estimate contributions from precipitation to stream discharge. With the additional use of geochemical tracers (e.g. DOC, SiO2) contributions from groundwater and the organic and mineral soil horizons can be estimated. Combined with a nested approach these analyses can be conducted on different spatial scales, enabling the development of scalable prognostic models of runoff formation in catchments.
To complement the limited information from historic data sets we instrumented two hill transects to observe lateral contributions from hill slopes and to investigate potential preferential flow paths. Water samples from stream-, soil-, ground- and precipitation water were collected during two flood events and analysed for stable isotopes and chemical compositions. To support the nested approach, the sampling sites were chosen at strategical sites within the catchment, including the instrumented hill transects and the stream network from the creek to the catchment outlet.
Preliminary results of stable isotope analysis show, that after dry periods nearly no event water seems to contribute to runoff formation, whereas after wet periods the proportions can be up to 40 %. A strongly delayed reaction of the groundwater was observed which suggests that deep groundwater is not contributing to stream flow, but a possible mobilization of pre-event water in the riparian zone was observed as a response to precipitation events.
A likely major source of DOC is in the organic soil horizons due to storage and degradation of organic material. This is supported by higher DOC-concentrations in the soil water from these horizons. In how far residence times, precipitation intensities and flow paths activation from different source areas influence concentration peaks of DOC in the stream will be analysed in the next steps.
The results of the recent field campaign help to identify the dominant processes of runoff generation and DOC mobilization on different temporal and spatial scales and for different antecedent system states. The data and insights gained from the field campaign will be used to develop and calibrate process models for hypothesis testing and further analyses to eventually develop a forecast model for DOC mobilization.
How to cite: Rommel, L. and Wöhling, T.: Hydrological analysis of runoff generation in a forested mountain catchment using a nested multi-tracer approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11112, https://doi.org/10.5194/egusphere-egu21-11112, 2021.
Long-term isotope values of river water provide information on hydrological flow pathways and atmospheric exchange and can be used to determine the origins of hydrogen and oxygen stored in animal and plant tissues. However, development of isotope maps for rivers is currently limited by methods to spatially interpolate point measurements to values for entire river networks. Catchment environmental characteristics and structures that affect river water isotope values also affect downstream reaches via flow, but many (such as man-made dams) are no more likely to affect nearby unconnected catchments than distant ones. Hence, distance-based geospatial and statistical interpolation methods used to develop isoscapes for precipitation and terrestrial systems may be less appropriate for river networks. We developed a modified ‘water balance’ river isotope mapping method to consider the effects of reach-scale catchment environmental characteristics and applied it across the entire stream network of New Zealand. This network comprises over 600,000 reaches and over 400,000 kilometres of rivers. The method uses national rainfall precipitation isoscapes, a digital elevation layer, a national river water isotope monitoring dataset (currently over 3 years of monthly sampling at 58 sites) and reach scale environmental attribute databases that cover New Zealand’s river network. δ2H and δ18O isoscapes produced showed an improved fit to validation data, compared to a model for which residuals between observed and simulated isotope values were applied as a correction factor across the river network using the ordinary kriging method. Hence, we show how a water balance modelling approach can provide an improved representation of long-term river water δ2H and δ18O values when combined with a correction for catchment environmental attributes.
How to cite: Dudley, B., Yang, J., Shankar, U., and Graham, S.: A method for predicting hydrogen and oxygen isotope distributions across a region’s river network using reach-scale environmental attributes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3646, https://doi.org/10.5194/egusphere-egu21-3646, 2021.
Alluvial aquifers are generally highly productive in terms of groundwater and are therefore particularly exploited. The study site is a drinking water production facility located on the alluvial plain of the Rhône river, France. This site consists of several pumping wells and observation piezometers organized along the riverbank. The site is continuously supplying water to neighboring agglomerations with intermittent pumping. In this situation, the pumping produces a piezometric depression allowing leading to a water exchange from the river to the aquifer which is a common feature in the case of alluvial aquifer exploitation along a riverside.
The four pumping wells and five piezometers were equipped with continuous automatic temperature and water level measurement probes, the river stage is monitored as well. These data are used to determine the exchange (direction and magnitude) between the aquifer and the river. Although pumping is intermittent, it does not allow a sufficient recovering of the natural piezometric level, i.e. the aquifer is permanently below the river stage.
In addition to the automatic probes, additional data acquisition campaigns were carried out. During these campaigns different tracers were used such as conductivity, stable isotopes of water and radon activity. Together with the continuously measured temperature, these various tracers were used to identify hydrodynamic variables and parameters, such as Darcy’s velocity, dispersivity, transit times. A MODFLOW model was developed, integrating the site geometry and hydrodynamic context, with the Rhone River at the western boundary and the Ouveze river at the eastern boundary. Model calibration was performed using the study site piezometric records and the optimization package PEST. The flow was reproduced at the site for two situations, a natural situation without groundwater pumping, and the exploitation situation with the groundwater withdrawals. Finally, the tracer’s data were integrated into the model to reproduce the transport of different tracers, in order to quantify the exchanges and the water fractions coming from the different hydraulic boundaries.
How to cite: Texier, J., Gonçalves, J., Stieglitz, T., and Vallet-Coulomb, C.: Assessing Surface water- alluvial aquifer water exchange using a multitracer approach and modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14509, https://doi.org/10.5194/egusphere-egu21-14509, 2021.
We conducted a systematically integrated surface water and groundwater interaction study in the Kosimegafan in north India using the stable isotopes (δ18O and δ2H) of water and depth to water level data. In a field campaign in December 2019, we have collected a water sample from 65 different locations for isotopic analysis. This includes 21 samples from the groundwater and 44 from different surface water bodies (Kosi River-02, streams-09, waterlogged patches-29, and canal-04).
The δ18O and D-excess values of groundwater and waterlogged samples show marked spatial variation across the study area. Using a two-component mixing model, we estimate the fraction contribution of streams and rainwater in the groundwater and waterlogged patches. This shows a marked spatial and depth-related variability in stream water contribution to the groundwater recharge and varies from about 83% (maximum) at 6 m below ground level (bgl) to 45% (minimum) at 9 m bgl. We also analysed the spatial and temporal variation in groundwater levels from 1996 to 2017. During this period, the water level shows a significant variation from 1.1 to 7.8 m bgl. Further, using the water table fluctuation approach, we estimate the recharge rate. We found a higher recharge rate (22 mm/year) in the central part of the western lobe and northern part of the central lobe, and minimum (1 mm/year)in both the northern part of the western and southern part of the central lobe of the Kosi fan. This study provides new insight into the recharge processes in the study area.
How to cite: Beg, Z., Joshi, S. K., Gaurav, K., and Kumar, S.: Spatial distribution of groundwater-surface water connectivity in the Kosimegafan, north India, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14145, https://doi.org/10.5194/egusphere-egu21-14145, 2021.
The island of Tenerife (Canary Islands, Spain) relies on basalt-hosted aquifers to provide 90% of water for agriculture and human consumption. The island is characterised by a low-permeability core, overlain by permeable materials which are cut by impermeable dykes. The effect is a compartmentalised aquifer, which is exploited sequentially as each “pocket” of water is exhausted. The island is home to ~1 million people (with an additional 5 million visiting tourists per year), and although rain/snowfall can be heavy in winter storms, it is unpredictable from year to year, and rapid surface water run off occurs due to the steep geography. While net recharge into the upper zones of the Tenerife aquifer have been quantified (around 2 months between intense rainfall and water table fluctuations), water must then follow a tortuous path to recharge lower zones and aquifer “pockets”. Water recharge to the coastal aquifers is also interrupted and extracted during its journey. Human and agricultural pressure is highest near the coast, and has led to intensive exploitation of existing wells and horizontal galleries. In response to the intensification of water extraction and slow recharge rates, marine intrusions into the coastal aquifers of Tenerife have occurred, traditionally recorded by rising chloride levels and resulting in well/gallery closures as well as increased pressure on other extraction sites. However, in a volcanic ocean island setting, natural processes can mimic the appearance of salinisation in a coastal aquifer. Management of aquifer resources require careful consideration of seawater incursions vs. volcanic degassing contributions vs. ocean island rainfall. Full hydrochemical breakdown of 43 coastal aquifer extraction sites reveal seawater intrusion is affecting the western coastal aquifer, with the agreement of multiple parameters. The strontium isotopic signature of well samples was also measured, because it is not subject to the biological or physical fractionation processes of other isotopic systems, thereby forming distinct reservoirs for groundwater (87Sr/86Sr of host rock), and seawater. 87Sr/86Sr signatures suggest the northern coastal aquifers are also subject to seawater incursions. This parameter may be a more sensitive indicator than chlorides and conductivity markers for salinisation, especially in an ocean island environment where coastal aquifers are subject to intensive land use practices, seawater spray, and affected by diffuse volcanic degassing.
How to cite: Coldwell, B., Cordero, M., Pérez, N. M., Amonte, C., Asensio-Ramos, M., Melián, G., and Padrón, E.: An over-used ocean island coastal aquifer, Tenerife (Spain) – tracing inputs for improved resource management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15003, https://doi.org/10.5194/egusphere-egu21-15003, 2021.
Precipitation of calcite from water fractionates strontium (Sr) isotopes because of preferential incorporation of light (86Sr) isotopes into the solid phase, making continental carbonates one of the most 88Sr depleted reservoirs. It was suggested that carbonate precipitation is the most likely process controlling δ88/86Sr composition of karst water. Therefore, the 88Sr enrichment of river water could be used for the estimation of Sr and carbonate precipitation at catchment scale.
In the present study, we report on trace element partitioning and Sr isotope fractionation between tufa and water in the groundwater fed karst river Krka (Croatia). Water and tufa along with samples of bedrock and soil as the main contributors of dissolved and particulate Sr at seven main waterfalls and cascades along a 33 km section of the river were analysed for trace element and Sr isotope composition (δ88/86Sr).
The highest δ88/86Sr values were measured in soils and in siliciclastic rocks, while in limestone, the δ88/86Sr values were similar to those of old tufa precipitated in the period between 96 and 141 ky BP. Recent tufa, however, was considerably depleted in 88Sr. The isotope fractionation between water and recent tufa varied a lot and was inversely correlated with Mg and Sr partitioning coefficients, while correlations with precipitation rates and temperature were rather weak. The δ88/86Sr of recent tufa was strongly correlated with the stable isotope composition of organic carbon, which indicates that apart from hydrochemical, hydraulic parameters and temperature, plants and microbial communities that knowingly stimulate the tufa formation also affect the isotope fractionation of Sr.
How to cite: Lojen, S., Jamil, Q., Zuliani, T., Rovan, L., Kanduč, T., Vreča, P., Štrok, M., Bura Nakić, E., and Cukrov, N.: Sr isotope fractionation in a karst river: case study of Krka, Croatia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6059, https://doi.org/10.5194/egusphere-egu21-6059, 2021.
The Cameroon Volcanic Line (CVL) in Central Africa hosts numerous volcanic lakes. While Nyos and Monoun lakes in western Cameroon were well studied following the catastrophic release of CO2 that occurred in 1980s, other volcanic lakes such as those of the Adamaoua Plateau remain less documented. Although some of these (Mbalang and Tizon) have been investigated through their sedimentary archives in order to reconstruct past-environments, the functioning of these hydro-systems located in the northern part of the CVL is not well constrained. Here, we characterize the hydrological functioning of five volcanic lakes by coupling classical hydrology methods and isotope tracers. Specifically, we assess water residence time in these lakes using radioactive (36Cl) and stable isotopes of water.
36Cl is a cosmogenic isotope of chlorine produced naturally in the stratosphere by spallation of 40Ar induced by cosmic-rays and has been massively injected into the atmosphere by nuclear tests during the 1950s. This pulse of bomb-36Cl can thus be used as a tracer to estimate recharge rates in the unsaturated zone and to constrain water transit times at a regional scale. While water stable isotopes have been widely used to establish lakes hydrological balance in Sahelian regions, only a few studies have been reported to date using 36Cl for the same purpose in tropical areas.
In this study, together with major elements and stable isotopes, we analyzed 36Cl contents in water from lakes Mbalang, Tabere, Tizon, Gegouba and Baledjam around Ngaoundere, to assess residence time in these lacustrine systems. 36Cl/Cl ratios range from 1400.10-15 to 2800.10-15 at/at and are significantly higher than the natural baseline as assessed by data obtained in local groundwater or at a larger scale in the Lake Chad Basin (36Cl/Cl ~200.10-15 at/at, see Bouchez et al., Scientific Reports, 2019). These 36Cl/Cl ratios above the natural baseline are clearly tagged with the bomb-36Cl footprint. We will illustrate at the meeting how a simple transient-state one-box model can be used to explain why these lakes have different 36Cl/Cl ratios, and how these results can help to constrain the E/I ratios of the lakes, and be compared with their hydrological characteristics and stable isotopes signatures.
How to cite: Abba, S., Hamelin, B., Deschamps, P., Garcin, Y., Badoga, D., Tamonkem Adzeh, R., Djangue Moustapha, B., and Ngounou Ngatcha, B.: Assessing the residence time of water in volcanic lakes of north Cameroon using bomb-36Cl and stable isotopes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9821, https://doi.org/10.5194/egusphere-egu21-9821, 2021.
The origin and distribution of unwanted thermogenic gas in aquifers and domestic water wells in petroliferous basins are of continuing concern. Most published studies to date consider only a few water wells with little or no information on fugitive gases from nearby energy wells. We mapped δ13C of hydrocarbons in 1,124 domestic water wells and fugitive gases (many thousands) from energy wells of Alberta, Canada. About 90% of the water wells that exsolve hydrocarbons produce methane derived locally by microbes. The δ13C of these biogenic methanes vary regionally and follows topography, suggesting in situ generation of methane within a flowing aquifer perhaps following a Rayleigh constrained generation process. Some domestic water wells have free thermogenic butanes, propane and ethanes indicating the impact of thermogenic gas on the aquifer. The δ13C of these thermogenic sourced gases impacting domestic water wells matches those of nearby energy wells indicating their failure as the ultimate source of thermogenic gas in domestic water wells. The impacted water wells are geographically grouped. Our regional mapping of hydrocarbon gases in domestic water wells has identified specific, kilometre scale regions needing detailed hydrogeological and geochemical investigation.
How to cite: Gonzalez Arismendi, G. and Muehlenbachs, K.: Identifying the regional impact of deep thermogenic gas on aquifers in Alberta, Canada by comparing multilayered isoscape maps of domestic water wells and fugitive gases from energy wells, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8954, https://doi.org/10.5194/egusphere-egu21-8954, 2021.
Bacteriophages are numerous, tremendously diverse and ubiquitous in the environment. Since the 1960s, bacteriophages have been proposed as new tracers to investigate the hydrological processes in addition to conventional tracers (i.e. isotopes, salts, dyes). Their dynamic into water (i.e. surface water, groundwater) have been well studied. However, the soil compartment known for its important microbial activity, have been few characterized in terms of bacteriophage diversity. Hence, in the present study, the objective is to investigate the transport of soil viral population from the soil matrix to the soil water compartment. This mobilization from the soil matrix is mainly driven by the adsorption/desorption mechanisms to which bacteriophages are subjected. Therefore, in order to understand the dynamics of the bacteriophage population, both soil and soil water were sampled from the Weierbach forest, located in the Attert River basin (Grand-Duchy of Luxembourg) at the topsoil level (i.e. 0-20 cm) over a period of one month. Due to a lower abundance of the microbial population in soil water, an enrichment method was carried out to increase the concentration. Subsequently, a shotgun metagenomics analysis was performed on the soil and soil water samples to obtain the DNA sequences, which were then sorted using bioinformatics and statistical analyses, allowing ultimately the identification of the viral populations. The moving of the bacteriophage populations from the soil to the soil water provides information on their transport capacity, in particular by taking into account environmental conditions such as air and soil temperatures, precipitation, soil humidity, soil pH, etc.
Key words: bacteriophages, soil, water, transport, environmental conditions
How to cite: Florent, P., Cauchie, H.-M., and Ogorzaly, L.: Mobilization of bacteriophages from soil matrix to soil water in the Attert River basin: A case study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12113, https://doi.org/10.5194/egusphere-egu21-12113, 2021.
Forest disturbance resulting from bark beetle infestation is becoming a widespread phenomenon due to climate warming and changing precipitation patterns. Such disturbance could result in alterations of streamflow and stream geochemistry. Our previous study found that these changes developed relatively rapidly after infestation and have long-lasting (decadal-scale) effects. Furthermore, infestation-induced changes in event-scale dynamics of in-stream electric conductivity (EC) – discharge (Q) relations were found to be considerable, impacting even the annual average EC-values. In this study, therefore, all rainfall-induced runoff events occurring during an 11-year period were identified and their distinct EC-Q relations were evaluated. The evaluation was done based on 10-min high-frequency monitoring of Q and EC and in four experimental catchments (~4 km2 each; located in the Sumava Mountains, Central Europe), having different forest cover (disturbance) stages. Furthermore, snapshot sampling was carried out to map EC and chemical parameters (N, DOC, etc.) in different hydrological landscape units (riparian area, hillslope, and terrace) and in multiple vertical layers of soil (surface, soil, and groundwater). Results showed that after infestation the EC-Q hysteresis loops at the event-scale shifted from positive to negative relationships, implying changes in the subsurface chemical composition and runoff patterns. Specifically, healthy forest systems required event flows to mobilize substances in the soil and groundwater systems as the groundwater level rose into the relatively conductive, shallow part of the soil profile during an event. Such flush-driven systems were known for their release of large fractions of total annual in-stream substance loads showing a positive EC-Q relationship. By contrast, after infestation-induced tree mortality, the mobilization and downward percolation of nutrients and carbon from litter and decomposing needles may be considerable even during moderate rain and infiltration events. When the system is flooded under event conditions, substance-enriched soil water and groundwater may be mixed with and diluted by low-salinity event water, leading to a negative EC-Q relationship. This study exemplifies how EC monitoring techniques can be used as an alternative to high-cost geochemical monitoring in quantifying complex rainfall-runoff processes as well as runoff generation processes, allowing for long monitoring periods at high temporal resolution and reasonable costs.
How to cite: Su, Y. and Langhammer, J.: Geochemical transformation of forested catchments following bark beetle infestation: Evidence from EC hysteresis during rainfall-runoff events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15614, https://doi.org/10.5194/egusphere-egu21-15614, 2021.
Meghalaya, also known as ‘abode of clouds’, is a state located in north-eastern part of India, blessed with abundance of water resources. In the last few decades, extensive coal mining in different parts of Meghalaya has caused detrimental changes in the environment, particularly the aquatic systems. Acid and metal loaded effluents (also known as acid mine drainage or AMD), resulting from the exposure of sulphide mineralization to oxidizing conditions from abandoned or active mining areas, are the principal environmental problems today. Sulphate (SO42-) is a major contaminant and attracts widespread attention as the dominant form of sulphur in coal mining affected aquatic systems. The increased presence of SO42- in ecosystems affected by mining activities has immense negative environmental and human health effects. Low pH and high heavy metal concentrations have been reported from streams flowing in and around the coal mining area in Meghalaya rendering the water quality to be very poor and unfit for use as potable water.
Stable isotopes have emerged as a promising environmental tracer to understand different environmental functions and processes. Valuable information on the sources and processes can be obtained from the stable isotope ratios of chemical elements in environmental samples as the sources and processes influence history of the samples. Stable isotopes analysis combined with hydrochemical analysis enhances our understanding of transformation and environmental fate of different compounds in water bodies and can provide precise information about factors responsible for controlling water chemistry of different water bodies.
Stable isotopes of sulphur and oxygen combined with hydrochemical parameters were used as a tool for determining origin, transformation and fate of sulphur in AMD affected water bodies in Meghalaya.The study was conducted on two rivers affected by AMD, viz. Myntdu River and Lunar-Lukha River, flowing in the Jaintia Hills region of Meghalaya. The water samples collected are analysed for hydrochemical parameters and stable sulphur and oxygen isotopes (δ34S and δ18O in aqueous SO42-). The stable isotopes of sulphur and oxygen were also analysed in the coal samples from the nearby mining areas. The result provided an insight into the transformational processes of sulphur in these two AMD affected rivers and the environmental fate of sulphur.
How to cite: Kumar, V., Paul, D., and Kumar, S.: Stable isotopes as a tool for determining transformation and fate of sulphur in AMD affected water bodies in Meghalaya, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14226, https://doi.org/10.5194/egusphere-egu21-14226, 2021.
The assessment of the biogeochemical cycles in coastal environments often relies on riverine inputs as the main source of nutrients and other dissolved compounds from land to the ocean. However, the discharge of groundwater through continental margins, commonly known as Submarine Groundwater Discharge (SGD), is also recognized as relevant sources of nutrients to the coastal ocean, particularly in oligotrophic and semi-arid environments, such as the Mediterranean Sea. In this study, we use radioactive tracers (radium isotopes and radon) to i) quantify the magnitude of SGD-driven nutrient fluxes to a Mediterranean cove (Cala Pudent, Menorca, Balearic Islands) and ii) characterize the nutrient transformations occurring in the beach before groundwater discharges to the sea. Cala Pudent is a limestone coastal cove with a restricted connection to the open sea. In this system, groundwater from a permanent spring infiltrates through an organic substrate dominated by thick deposits of seagrass (Posidonia oceanica) leaf litter and flows into the sea. This substrate, together with the dynamic groundwater-seawater mixing, are chiefly influencing the nutrient enrichment and transformation occurring in the beach and thus modulating the SGD-derived nutrient input to the sea. The ecological implications of these inputs are also assessed, particularly for the Posidonia oceanica and Cymodocea nodosa meadows located near the study site.
How to cite: Rodriguez-Puig, J., Alorda-Montiel, I., Diego-Feliu, M., Alorda-Kleinglass, A., Rodellas, V., and García-Orellana, J.: The role of seagrass leaf litter in the SGD-derived nutrient fluxes in Cala Pudent (Menorca, western Mediterranean), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15881, https://doi.org/10.5194/egusphere-egu21-15881, 2021.
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