Displays

The separation of runoff into different components, typically some “event” (or “new”) water as opposed to some “baseflow” (or “old”) water, is a task that has been attracting hydrologists for decades. The ability to separate runoff sources has implications for our understanding of hydrological processes and to predict changes due to e.g. deforestation or urbanization. Although the methodology has notably evolved during the years, the most conventional and widespread application involves a two-component separation achieved through stable isotopes or electrical conductivity measurements. Use of this approach is based on a strong assumption that is difficult to test in the field: the signatures of the two end-members either do not change during the event or their variations can be taken into account. By using extensive numerical tests, this contribution explores the limits of this assumption. Results highlight the importance of considering the time-varying contribution of soil water, which is not event-water nor baseflow, and show that the method can easily lead to incorrect estimates when the above assumption is not met.

How to cite: Benettin, P.: Exploring the limits of conventional hydrograph separation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5695, https://doi.org/10.5194/egusphere-egu2020-5695, 2020.

Hydrologic tracer timeseries data (e.g. of stable water isotopes in rainfall and streamflow) have often been analyzed by extracting summary metrics (like the mean transit time) that provide some information about the storage and turnover of water in a watershed, but are laden with ad hoc, implicit, and questionable assumptions. Consequently, inferences about water age and runoff generation processes may be artifacts of the methods, rather than true implications of the tracer data. Potentially more reliable metrics have been suggested recently (e.g. the ‘young water fraction’) but these do not make full use of the information content of the data. The StorAge Selection (SAS) approach relaxes the common (highly questionable) assumption of steady-state flow, and thus allows the full time-variability of the transit time distribution to be captured. However until now its application has required ad hoc functional forms and relationships to be chosen for the underlying SAS function and its time-variability. This introduces artifacts that can skew estimates of the volume and sensitivity of water turnover rates within the catchment, inhibit inference of complex or multi-modal distributions, and is a subjective complication that presents a barrier to use of the approach.

Is it possible to make extract information about catchment water storage, turnover, and transit times without imposing ad-hoc assumptions, and instead allow the data to guide us? Can we obtain a clearer view of how these systems retain and release water of different ages at different rates, and vary how they do so over time? Can doing so allow us to better test hypotheses, tell richer stories about transport in dynamic hydrologic systems? 

Three recent advances toward doing so have recently been developed. The first is to unify the analysis of flux quantity and age (or water celerity and velocity) in the form of an ‘age-ranked storage-discharge relationship’. This relationship captures how the discharge of water of different ages changes when there is a change in the overall discharge. It thus provides a clearer view of the catchment mechanics driving streamflow generation and thus discharge age dynamics.

The second is Multiresolution Estimation of StorAge Selection (MESAS), a non-parametric statistical learning method for determining this relationship. This method avoids the need to specify a functional form – instead the shape of the function is iteratively determined from a coarse to a fine resolution, up to a limit at which the capacity of the data to meaningfully constrain the form is maximized.

The third is the development of computational techniques to accelerate the statistical learning implementation using an explicit Jacobian formulation and GPU acceleration.

How to cite: Harman, C.: A statistical learning approach to extract information from hydrologic tracer timeseries, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11765, https://doi.org/10.5194/egusphere-egu2020-11765, 2020.

Although their contribution was neglected in the past, inland waters play a significant role in the carbon cycle and affect CO₂ global balance. Streams and rivers are now considered not only as pipelines but as active reactors able to collect and transform carbon from terrestrial ecosystems trough drainage, erosion, deposition and respiration. Quantifying the transfer of carbon from the terrestrial to the riverine ecosystems is thus of crucial importance to fully appreciate carbon cycle at the watershed, regional and global scales. Such transfer is largely controlled by the processes occurring in the critical zone where the carbon and water cycles are tightly coupled. Previous studies investigated how hydrological drivers can affect Dissolved Organic Carbon (DOC) concentration in streams highlighting an hysteretic and unsteady behavior for the DOC-discharge relationship. In this study, we focus on the drainage flux from hillslopes to stream and river networks during rainfall events combining a transport model for water and a model of carbon degradation in soil. Using high-frequency records of chloride and DOC in Plynlimon catchments (UK), we employ the recently developed StorAge Selection (SAS) theory to evaluate water travel time and its partition as evapotranspiration, discharge and storage. We combine this approach with the reactivity continuum  theory to model  carbon degradation along the flow paths using a gamma-distribution as probability density function of the quality. The developed model can thus predict not only the flux of DOC released from hillslopes but also its quality (i.e. lability). We also show how the variability of the DOC-discharge relationship can partially be explained by hydrological fluctuations.

How to cite: Grandi, G. and Bertuzzo, E.: Watershed dissolved organic carbon transport: a modeling approach combining water travel times and reactivity continuum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9033, https://doi.org/10.5194/egusphere-egu2020-9033, 2020.

Well-established relations between concentrations of total suspended solids (TSS) and the hydrophobic polycyclic aromatic hydrocarbons (PAHs) in bulk water samples make PAH ideal tracers to understand water and solid transport in catchments during high discharge events. In the study presented here, we trace particle-bound PAH concentrations in the Ammer River, Germany (annual mean discharge of 0.87 m³ s^-1), during a rain event to deepen knowledge on particle origin and hydrological processes in the catchment. High-resolution temporal monitoring of discharge, TSS, particle characteristics, and PAHs was conducted over the course of an event at two sampling sites at the Ammer River. The sampling sites are located in the upper catchment and ~ 8km downstream of the upper sampling site at the outlet of the gauged catchment (134 km²), while the downstream sampling sites integrates inflowing water from tributaries and a wastewater treatment plant. High PAH particle loading demonstrates that particles in the river originate mainly from urban areas, introduced into the stream via combined sewer systems located in the upper catchment. These particles dominate the suspended particle flux over the temporal course of the event. Despite the integral suspended particle flux being nearly constant in between both sampling sites, particle quality changes which is represented by a decreased integral PAH flux and an increasing proportion of particulate organic carbon in the suspended particles. Decrease of PAH particle loading in the downstream direction suggest dilution by ‘cleaner’ particles from either un- or less contaminated or possibly leached sediments entering into the river. This shows that particle exchange between suspended and river bed sediments is more pronounced in downstream direction, demonstrating that sediment mobilisation plays a role for the overall particle flux. These results suggest that the catchment response of the Ammer River regarding the particle flux during rainfall is mainly dominated by the combined sewer system though particle exchange processes are also relevant. Urban tracers are hence helpful for understanding solid transport in catchments.

How to cite: Glaser, C., Zarfl, C., Rügner, H., Lewis, A., and Schwientek, M.: Urban tracers for the characterization of particle transport processes in an agricultural catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10468, https://doi.org/10.5194/egusphere-egu2020-10468, 2020.

The time water resides within a catchment has important implications for the water availability and quality for both ecosystem and human use. Here, we look at the short-term water transport using the concept of young water fraction (F_yw), defined as the proportion of water that is younger than 2-3 months. The study was conducted for the 0.56 Km² sub-humid Can Vila catchment (Vallcebre Research Catchments). During a period of over 58 months, the isotope ratios (²H and ¹⁸O) of rainwater was sampled at 5-mm rainfall intervals and stream water was sampled at variable time intervals (30 minutes to 1 week) depending on flow.

The early results of this research revealed intense dynamics of F_yw in relationship with discharge: F_yw had values between 0 for low flows and around 1 for the highest flows. Yet, the high variability of discharge and flashy response behaviour in this catchment along with the relatively large discharge sensitivity (S_d) of F_yw implied that even if the maximum sampled discharges were exceeded by only 0.01% of time, about 25% of the F_yw associated to the highest flows were estimated to be missed by the stream water sampling. This behaviour may be associated with a response dominated by saturation runoff generation mechanisms during wet episodes, which are known to drive the main hydrological response of this catchment.

Nevertheless, these results are obtained when all the samples are lumped for the whole 58 month period, but when different 12-month windows are investigated, the behaviour of F_yw becomes more intricate. Indeed, the wetter year was associated with the largest F_yw and S_d values, but drier years had irregularly varying values poorly correlated to precipitation or runoff statistics. Thus, other runoff generation mechanisms previously identified, including Hortonian-type overland flow in small degraded areas, that lead to runoff of new (and hence young) waters for low to moderate flows, will play a special role.

Current research is comparing F_yw analyses for groups of events of the same class, supported by hydrograph separation analyses and hydrometric indicators, for better understanding the dynamic and complex response of F_yw in this catchment. Our work further advances the understanding of limitations and opportunities of the F_yw approach.

How to cite: Gallart, F., Llorens, P., Cayuela, C., Sprenger, M., Latron, J., and Saurat, P.: Young water fractions at diverse time scales are driven by varying runoff generation processes in a Mediterranean small research catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18122, https://doi.org/10.5194/egusphere-egu2020-18122, 2020.

Effective water resource management can benefit from estimations of when water entered the catchment and how long it takes to flow to the outlet. In this context, the so-called young water fraction (F_yw) based on seasonal input and output tracer cycles is becoming increasingly used as robust tool to compare the hydrological function of catchments. In seasonally cold environments, this F_yw estimation is complicated by the fact that a large part of the precipitation will be in the form of snow, will be stored before melting and becoming available as water, resulting in a distinct winter low flow and summer high flow season. Nevertheless, F_yw might enclose extremely interesting information in such environments since they incorporate the relationship between late summer and autumn flow and the previous winter’s snow input.  However, most currently available methods for F_yw estimation do not explicitly account for the seasonal shift of water input from snow. Therefore, we propose a novel framework to explicitly account for this “snowmelt” delay in F_yw and explore related uncertainties using experimental data from three high-elevation Alpine catchments, the Vallon de Nant in Switzerland, and the Noce Bianco at Pian Venezia and the Bridge Creek Catchments in Italy. Experimental data from these environments expose some limitations of existing methods in accounting for unavoidable sampling inconsistencies. Using our method that explicitly accounts for snowmelt, we found extremely low F_yw in these three Alpine catchments: 6%, 13%, and 31%. In this contribution, we will present our method in detail and highlight emerging challenges and implications of the F_yw estimation.

How to cite: Ceperley, N., Zuecco, G., Beria, H., Carturan, L., Michelon, A., Penna, D., Larsen, J., and Schaefli, B.: Reduced fraction of young water in Alpine catchments with increased seasonal snow cover , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9413, https://doi.org/10.5194/egusphere-egu2020-9413, 2020.

Hydrological responses to precipitation events in headwater catchments often vary in space and time. Understanding of such patterns leads to constrain runoff generation mechanisms and flow pathways. The use of stable isotopes of water combined with classical hydrometrics have increased in recent years to elucidate the response behavior of runoff components and their drivers in runoff generation. However, most of the previous studies dealing with investigation of catchment responses were limited to daily to monthly data, at which potential fine-scale variations could not be captured. Recently, few studies applied high-temporal resolution sampling of stable isotopes of water to investigate isotopic response variation within precipitation events. Sampling sources were mostly limited to streamflow and precipitation. An important, yet poorly known mechanism is the response of shallow groundwater to precipitation.

In this study, we used an automated in-situ mobile laboratory to continuously sample stable istopes of multiple sources, including stream water, groundwater and precipitation every 20 mintutes. The study was realized in the Schwingbach Environmetal Observatory (SEO) in Hesse, Germany. Hydrograph seperation technique was applied to quantify the share of event and pre-event water contribution to the stream and to estimate response times of maximum event water fractions in the stream water and the groundwater for 20 events in the dry year 2018. We investigated the control of precipitation and antecedent wetness hydrometrics on response characteristics using Spearman rank correlation analysis.

High-temporal resolution sampling of multiple sources captured the fine-scale variation of isotope concentrations in stream water and groundwater sources during the precipitation events indicating that the Schwingbach is a highly responsive, pre-event water dominated creek. More than 79% of the runoff consisted of pre-event water. Short response times combined with soil moisture variations of different depths revealed the linkage between shallow groundwater in near-stream zones and the stream itself. As a response of the dry conditions in 2018, an extended crack network developed that acted like adrainage system causing rapid delivering of water to the stream network. Event water contribution increased with increasing precipitation amount. Pre-event water contribution was moderately affected by precipitation amount, while antecedent wetness did not influence the runoff generation. The response time of stream water and groundwater was controlled by mean precipitation intensity. A two-phase system was identified, at which the response times of stream water and groundwater started to decrease after reaching a threshold of mean precipitation intensity (0.5 mm h¹).

How to cite: Sahraei, A., Kraft, P., Windhorst, D., and Breuer, L.: The use of high-temporal resolution, in-situ sampling of stable isotopes of water to capture fine-scale hydrological responses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10524, https://doi.org/10.5194/egusphere-egu2020-10524, 2020.

Forest water use has been difficult to quantify. One promising approach is to measure the isotopic composition of plant water, e.g.
the transpired water vapor or xylem water, which often differs from that of other water vapor sources. Traditionally such
measurements have relied on the extraction of wood samples, which provide limited time resolution at great expense, and risk
possible artefacts. Utilizing a borehole drilled through a trees’ stem, we propose a new method based on the notion that water
vapor in a slow-moving airstream approaches equilibration with the much greater mass of liquid water in the xylem. We present
two empirical data sets showing that the method can work in practice. We then present theoretical models estimating the
equilibration times and exploring the limits at which the approach will fail. Given long enough boreholes and slow enough flows,
the method provides a simple, cheap, and accurate means of continuously estimating the isotopic composition of the source water
for transpiration.

How to cite: Marshall, J., Cuntz, M., Beyer, M., Dubbert, M., and Kuehnhammer, K.: Borehole equilibration: testing a new method to monitor the isotopic composition of tree xylem water in situ, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18750, https://doi.org/10.5194/egusphere-egu2020-18750, 2020.

Due to continuous changes in the meteorological conditions of Mediterranean regions, it is becoming increasingly important to improve knowledge of hydrological and hydrogeological recharge processes and their dependency on climate conditions to adapt the use of limited water resources. Within the IsoMed project (isotope hydrology in Mediterranean areas), soil profiles were sampled in November 2018 and February 2019, from various hydrogeological settings in Cyprus to estimate groundwater recharge using stable isotope equilibration methods combined with soil water balance modeling. A total of 11 soil profiles were taken from the Troodos massif (Galata and Platania) and the Mesaoria plain in Deftera, Nicosia. A vertical profile of stable isotopes has been determined with a 2 cm resolution and measured with Tunable Diode Laser spectrometry. Percolation through the soil profile has been estimated based on the convolution of a seasonal input function using advection-dispersion transport models. In Galata, groundwater percolation estimates range from 20-30 mm/y on clayey soil with natural vegetation to 100-120 mm/y at an irrigated terraced orchard. The results in Platania vary from 20-60 mm/y at steep hillslopes under natural vegetation and amount to 220-340 mm/y in the root zone at the irrigated site with olive trees in Deftera. The comparison of groundwater percolation rates based on stable isotope profiles with those derived from soil water balance modeling indicates a significant bias. While percolation rates correspond well to results obtained from a daily soil water balance model for irrigated fine-grained soils in the plain, recharge rates obtained from stable isotope profile methods on coarse-grained hillslopes tend to be much lower than expected. The observed bias suggests that stable isotope methods, regardless of water extraction or equilibration technique, mainly record the isotope signal of matrix flow. Thus, macro-pore and preferential flow components in coarse-grained soils may not be accounted for. Data collected from the same profiles in late autumn and spring suggest that macro-pore and preferential flow constitute a major component of percolation in coarse-grained shallow hillslope soils of Troodos indeed, without leaving measurable isotope traces in the soil water profile. Additional approaches need to be applied in conjunction with methods based on the evaluation of soil water isotope profiles to overcome this limitation.

How to cite: Krüger, N., Külls, C., Bruggeman, A., Eliades, M., Christophi, C., Rigas, M., and Eracleous, T.: Groundwater recharge estimates with soil isotope profiles – is there a bias on coarse-grained hillslopes? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9840, https://doi.org/10.5194/egusphere-egu2020-9840, 2020.

Hillslope soils developed on volcanic ash (Andosols) provide key hydrological services such as water storage and streamflow regulation in montane environments. Yet, little is known about how they influence subsurface water flow paths and flow transport and mixing dynamics. To fill this knowledge gap, we analyzed a unique 3-year dataset of hourly precipitation, soil moisture, and groundwater level and weekly precipitation and soil water stable isotope data collected along a steep hillslope transect underlain by Andosols. In combination with a detailed characterization of soil properties, we investigated how these soils influence water transport and tracer mixing in the subsurface. Our results indicate that the high organic matter (33-42%) and clay (29-31%) content of the soils’ organic horizon and an abrupt change in hydraulic conductivity between the highly conductive rooted soil layer and a low conductive underlying layer results in a perched water layer that remains near saturated year-round. Despite the formation of the latter, our isotope-based water age estimations depict that water resides within the organic horizon of the soils for short periods (2-4 weeks). The dynamics of soil moisture suggest a fast transfer of hydraulic potentials (few hours) along the entire soil profile in response to rainfall events. This hydraulic response is explained by the exponential shape of the soils’ water retention curves that facilitate a rapid vertical mobilization of water through the porous soil matrix. These findings indicate that the hydrological behavior of volcanic ash soils resemble that of a “layered sponge” in which vertical flow paths are dominant despite the formation of a perched water layer. 

How to cite: Mosquera, G., Windhorst, D., Breuer, L., and Crespo, P.: A Wet Layered Sloping Sponge? The Role of Volcanic Ash Soils in Water Transport and Tracer Mixing at a Tropical Hillslope, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-932, https://doi.org/10.5194/egusphere-egu2020-932, 2020.

The volume and scale of mountain-block groundwater circulation plays an important role in watershed hydrologic function; carbon, geochemical and nutrient budgets; and response to climate change.  However, mountain block groundwater remains one of the least understood components of the hydrologic cycle.  In this project, we investigate the role of bedrock groundwater circulation on groundwater age and isotopic tracer concentration on soil-mantled mountainous hillslopes.  We perform numerical modeling of variably saturated soil, saprolite and bedrock groundwater flow, groundwater age, and transport of a suite of environmental tracers including stable isotopes of water, tritium, dissolved CFC’s and SF₆.  We use these models to investigate patterns of bed-rock groundwater circulation, and the distribution as well as integrated discharge of groundwater age and tracer concentration.  We identify first order processes controlling the spatial distribution and volume of groundwater circulation on hillslopes, the partitioning between slope parallel through-flow versus bedrock recharge, and the resulting hillslope age and tracer dynamics. Monte-Carlo simulations are used to evaluate the relative role of topography, soil characteristics, underlying lithology and antecedent moisture conditions in governing the age and tracer distribution. The basic relationships derived provide new insight into the role of bedrock groundwater recharge and discharge on hillslope age and tracer distribution.  Model results are compared with observed patterns of water level and stable isotopes measured in soil and bedrock groundwater on hillslopes in west-central Montana, United States. These results can be used to help hydrogeologists develop better conceptual models and estimates of bedrock groundwater circulation in upland catchments and its role in watershed hydrologic and biogeochemical function.

How to cite: Gardner, W. P.: Spatial and Temporal Patterns of Soil and Bedrock Groundwater Age and Age Tracer Concentration on Soil-Mantled Mountainous Hillslopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12668, https://doi.org/10.5194/egusphere-egu2020-12668, 2020.

A growing number of studies indicate that bedrock groundwater is an important component of streamflow in mountain watersheds, yet mountain fractured-rock aquifers remain poorly characterized largely due to a lack of wells. Environmental tracer data from springs and tunnels can provide useful information, but are limited by the fact that spring occurrence is sporadic, and tunnels often disturb the natural groundwater system by acting as deep drains. We present dissolved noble gas, age tracer (³H, ³He/⁴He, and SF₆), chemistry, and temperature data from two relatively deep (46 and 81 m) boreholes and multiple shallow hand-drilled stream-side piezometers in Redwell Basin, Colorado, USA. The snowmelt-dominated watershed is underlain by sub-horizontally bedded, hydrothermally altered (sulfide-rich) sandstones and shales, and is being studied to better understand hydrogeochemical processes controlling sulfide weathering and metal exports from mineralized mountain headwater catchments. The boreholes were completed with multi-level monitoring wells allowing discrete-depth sampling, and the stream-side piezometers provided integrated samples of groundwater discharge at various points along the stream course. The chemistry of deeper groundwater at depths >10-20 m is markedly different from that of shallow groundwater: pH is 7-8 versus 4-6; specific conductance is 400-600 versus 100-300 μS/cm; and concentrations of multiple metals (e.g., Fe, Zn) are lower by a factor >5. Apparent ³H/³He and SF₆ ages for the shallow groundwater are mainly 5-15 yr, whereas the deeper groundwater is dominantly premodern (>60 yr old) with high terrigenic He concentrations of 4-8 times solubility. Preliminary results from a 2D coupled heat and fluid flow model calibrated with the tracer-based ages and temperature data from the two deep boreholes suggest that active groundwater circulation (Darcy velocities >1 cm/yr) below a depth of 10-20 m is unlikely. This circulation depth is considerably shallower than previously reported depths of generally 100-200 m for mountain watersheds (these being underlain dominantly by crystalline rock), and is probably due to low vertical hydraulic conductivity (K) of the altered sedimentary rocks. Noble gas, age, and chemistry data from the piezometers suggest little to no deep, stream-parallel flow from upper to lower parts of the basin, further supporting relatively shallow active groundwater circulation. The age and chemistry of the piezometer samples also display spatial variations likely attributable to K anisotropy in the bedrock aquifer. The tracer, chemistry, and temperature data thus provide information critical for the development of reliable conceptual and numerical hydrogeochemical models of the watershed.

How to cite: Manning, A. H., Ball, L. B., Wanty, R. B., Verplanck, P. L., and Williams, K. H.: Using environmental tracers to characterize groundwater flow in an alpine watershed underlain by sedimentary rock, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11384, https://doi.org/10.5194/egusphere-egu2020-11384, 2020.

Diverse tools do exist to study the pathway from the source of a contamination to groundwater and related springs. The backward approach, i.e. sampling spring water to determine the origin of contamination, is more complex and requires multiple information. Microbial source tracking using host-specific markers is one of the tools, which however has shown to be insufficient as a stand-alone method, particularly in karst groundwater catchments.    

A karst spring in the Swiss Jura Mountains was studied with respect to the occurrence and correlation of a set of fecal indicators, including classical parameters as well as a number of bacteroidale markers. Sporadic monitoring proved the impact on spring water quality, mainly during high water stages. Additional event-focused sampling over varying recharge intensities evidenced a more detailed and divergent pattern of individual indicators. In particular, the results arose the question how to interpret peaks of human fecal markers in the rural-dominated catchment.

A multiple-tool approach, complementing fecal indicator monitoring with artificial tracer experiments and natural tracers measurements, assessed the input, storage and transfer of potential contaminants in order to specify the origin of both ruminant and human fecal contaminations. Natural tracers allowed for distinguishing between water components from the saturated zone, from the soil/epikarst storage, or from freshly infiltrated rainwater. Furthermore, the breakthrough of injected dye tracers, and their remobilization during subsequent recharge events, respectively, were correlated to the occurrence of fecal markers. System’s residence time distribution over discharge, deduced from numerous former dye tracing tests, also allowed for attributing maximum travel distances to their arrival.

The findings of the approach hypothesize the origin of human fecal contamination at the spring being in relationship with septic tanks undergoing concentrated overflow already at moderate rainfall intensities. Those intensities are, however, not sufficient to transport diffuse ruminant contamination through the vadose zone. Linkage with vulnerability assessment and land-use information can finally better locate the potential source points. Such toolbox provides not only useful basics for groundwater protection and catchment management, but also insight into general processes governing fate and transport of fecal contaminants in a karst groundwater environment.

How to cite: Sinreich, M.: Multiple-tool approach of combining microbial markers with artificial and natural tracers to specify the origin of fecal contamination in a karst groundwater catchment , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19440, https://doi.org/10.5194/egusphere-egu2020-19440, 2020.

In this study, analytical solution method which can evaluate and quantify the impacts of partial mass reduction by remedial action performed in study site is applied to estimate the unknown DNAPL source mass and dissolved concentration using long-term monitoring data collected from 2009 to 2019. Also, noble gas tracer method was applied to identify the partitioning processes which can be happened in TCE contaminated site. By using the source zone monitoring data during about 10 years and analytical solution, initial dissolved concentration and residual mass of TCE in spilled period at the main source zone were roughly estimated 150 mg/L and 1000 kg, respectively. These values decreased to 0.45 mg/L and 33.07 kg direct after an intensive remedial action performed in 2013 and then it expected to be continuously decreased to 0.29 mg/L and 25.41 kg from the end of remedial actions to 2020. From results of quantitative evaluation using analytical solution, it can be evaluated that the intensive remedial action had effectively performed with removal efficiency of 70% for the residual source mass during the remediation period. From the results of noble gas analysis, the distance from TCE source zone was divided into three groups from Zone 1 to 3. Zone 1 includes samples that are the closest from the TCE main source, and are highly partitioned to TCE compared to other zones. Zone 3 samples show least accordance with either of the fractionation lines, showing that sampling points are influenced highly by other mechanism rather than partitioning to TCE. Also, it is identified that seasonal variation of groundwater level can be affected to the distribution of noble gas at around TCE source zone. Samples from only “High TCE” zone are plotted along with ideal batch equilibrium and Rayleigh fractionation line again and divided into two groups according to their sampling date. From August 2018 to October, 2018, samples shift from right to left in the figure, getting closer to Rayleigh fractionation line. In August, noble gas was relatively in equilibrium between groundwater and TCE. However, as water table rises, noble gas became touch with residual TCE locating above the previous water-level, which is a receiving fluid in water-TCE system. Results of this study was support that it was able to estimate the unknown quantitative information for TCE contamination and noble gas as the indicator of DNAPL contamination could be applied in allocating the DNAPL source which is relatively hard to estimate.

How to cite: Lee, S.-S., Cho, I.-R., Ju, Y., and Lee, K.-K.: Finding the Information of the Unknown DNAPL Residual Source using various tracer data, Wonju, Korea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6766, https://doi.org/10.5194/egusphere-egu2020-6766, 2020.

Investigations of tap water and its source groundwater reflect combined features of regional hydrological processes and human activities including the changes in water supply system (WSS). In this context, multi-parameter characterization can present a reliable tool to propagate the geochemical “fingerprints” of water source from natural or artificial mixing. If the geochemical composition of different water source end members is significantly different, we can estimate the proportions of source water and their changes from particular source to tap.

To test this hypothesis, we performed a 24 hours sampling experiment of tap water in April 2019 at selected location in Ljubljana (i.e. at Jožef Stefan Institute), where groundwater from two different water fields and aquifers (i.e. from Kleče at Ljubljansko polje and Brest from Ljubljansko barje) is mixed. In-situ measurements of temperature, electrical conductivity and pH were performed and 25 water samples were collected hourly for determination of isotopic composition of oxygen (δ¹⁸O), hydrogen (δ²H) and dissolved inorganic carbon (δ¹³C_DIC), ⁸⁷Sr/⁸⁶Sr isotope ratio and major (Ca, K, Mg and Na) and trace elements (Ag, Al, As, B, Ba, Cd, Co, Cr, Cu, Fe, Li, Mn, Mo, Ni, Pb, Rb, Sb, Se, Sr, Tl, U, V and Zn).

The diurnal variations of parameters are not very large; however, temporal differences of some parameters (e.g. Ba, Mg) indicate that proportion of groundwater from Kleče and Brest water fields changed during the experiment. Based on observed temporal differences during the 24 hours experiment we could identify three different patterns: a.) higher values in the beginning and at the end and lower in between (i.e. δ¹⁸O, δ¹³C_DIC, Ca, Na, B, Ba, Cr, Li, Sr); b.) lower values in the beginning and at the end and higher in between (i.e. K, Mg, As, Mn, V) and c.) higher values at the beginning of experiment (i.e. Cd, Co, Cu, Fe, Mo, Ni, Pb, Sb, Zn). The first and the second pattern (a and b) indicate the mixing of different groundwater from different water fields with different geochemical characteristics. The third pattern (c) however indicates the influence of release of elements due to corrosion of water supply system. Based on results of 24 hours experiment and additional information on functioning of water supply system changes in proportion of water from Kleče and Brest water fields will be estimated.

How to cite: Nagode, K., Kanduč, T., Zuliani, T., Bračič Železnik, B., Jamnik, B., and Vreča, P.: What can short temporal changes of stable isotope ratios and geochemical parameters of tap water at a single sampling site tell us?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7323, https://doi.org/10.5194/egusphere-egu2020-7323, 2020.

The key to understand the deterioration of the quality of urban water resources is to know the impact of urbanization on the entire waterway, which can change dramatically during the extreme climatic events. Various geochemical parameters, including stable isotope ratios of light elements (H, O, C), represent an important tool to investigate water sources, transport routes, and the mixing of individual components of the water cycle. They are indispensable in urban hydrology, both for characterizing drinking water resources and for evaluating changes within a complex water system.

In Slovenia, the majority of the population is supplied with drinking water from groundwater. In Ljubljana, the capital city of Slovenia, groundwater represents the main drinking water resource.  Therefore, the knowledge and understanding of the groundwater vulnerability is important for the protection and management of water resources. In Ljubljana, the water is supplied through the central water system (WSS), more than 1.000 km long, according to the legislation and the latest standards from five different wellfields (Kleče, Hrastje, Brest, Jarški prod and Šentvid). Despite the established water protection areas, the water supply areas are exposed to the pressures of urbanization, industry, transport, agriculture and old environmental burdens, which are often unknown.

In the past, various short-term isotopic studies have been conducted and the Ljubljansko polje and Ljubljansko barje aquifers were characterized. In addition, the sources, paths and interactions of water were determined and the obtained data were used to improve the conceptual model.

However, isotopic studies of water circulation in the drinking water supply system (WSS), which would cover the simultaneous characterization of water sources and changes within the WSS, have not been performed so far. In order to assess the usefulness of isotopes more systematically, we performed the first more detail sampling of water from WSS of Ljubljana in autumn 2018. Sampling was carried out at 103 locations that were selected according to the type of facility in the WSS (i.e. 41 wells, 7 joint exits from water pumping station, 22 water reservoirs, 2  water treatment locations, 13 fountains, and 19 taps) and according to 9 different WSS areas. Additional samples were collected on River Sava, important infiltration source of groundwater, and at outflow from Ljubljana central wastewater treatment plant. This contribution focuses on presentation of changes of different parameters (i.e. temperature, electrical conductivity, pH, total alkalinity, δ¹⁸O, δ²H and δ¹³C) in WSS of Ljubljana.

How to cite: Vreča, P., Nagode, K., Kanduč, T., Bračič Železnik, B., and Jamnik, B.: Application of stable isotope ratios in drinking water supply system of Ljubljana, Slovenia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7180, https://doi.org/10.5194/egusphere-egu2020-7180, 2020.

New scientific advances based on integrating water management approaches have been developed in order to reduce the environmental footprint. Cranberry production is one of the most influential cultures in Canada, where water is substantial for irrigation, harvesting, and frost control. The cranberry farms are considered closed-circuits. Water is mainly recycled in large pools, increasing the risk of accumulation of chemical substances affecting the quality of irrigation water. The use of isotopic geochemistry provides an additional layer of information for studying hydrological phenomena in agriculture.

The main objective of this project is to identify the sources and sinks of the water in a typical cranberry farm with the help of isotopic hydrology technics and groundwater surveys.

Water samples for stable isotope of the water molecule analysis (16O, 17O, 18O, 1H, 2H)  were collected during the growing season from May to September (from 2017 to 2020). Preliminary results have shown that isotope hydrology technics can be used to trace the water pathway is a cranberry farm by using the mixing model. 

These results can help to implement integrated water management procedures helping to increase fruit yields and to reduce environmental impact. Isotope mixing model also makes it possible to assess water losses by infiltration into the aquifers and by evaporation.

How to cite: Gadomski, J., Gumiere, S., Gumiere, T., Bordeleau, G., and Rousseau, A.: Tracking water pathways and origins in cranberry production: Isotope hydrology application , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11099, https://doi.org/10.5194/egusphere-egu2020-11099, 2020.

The direct liquid-vapour equilibration (DLVE) method is a new method to measure the stable isotopes of oxygen and hydrogen in soil pore water. Advantages of DLVE are (a) minimum sample handling, (b) direct isotope measurement from the samples without the need of extracting the water, (c) comparatively low costs, (d) and high reliability. However, the impact of different water content and equilibration times on the isotope measurement of different soil types is not well understood yet. Therefore, this study focuses on advancing our knowledge of the effect of different soil types and soil water contents on the isotope measurement of the DLVE method. Three different types of soil (sand, silt and clay) representing sediment samples with different pore sizes were saturated using tap water with a known isotopic value in a water bath. Different degrees of saturation (100%, 80%, 60% and 40%) were established, placed in Ziploc bags and equilibrated for different time spans ranging from 1 hour up to 8 days at constant surrounding temperature (about 20^oC). The isotope measurements were obtained using cavity ring down laser spectroscopy (CDRS) for each test samples. The time taken for the H₂O_(liquid)-H₂O_(vapour) equilibration for different soil textures and different water contents in Ziploc bags were determined. Results showed that sandy soil samples took shorter time to reach isotopic equilibrium with the headspace in the Ziploc bags compared to clayey soil which took comparatively longer for the same soil saturation level. Regardless of the soil type, 100% saturated soil samples took shorter time to reach liquid-water equilibration compared to low saturated soil samples. These findings could lead to protocols of soil sample measurements using DLVE regarding the influence of different soil textures and soil moisture contents.

How to cite: Vadibeler, D., Stockinger, M., Wassenaar, L. I., and Stumpp, C.: Influence of soil texture and degree of saturation on the equilibration time of water isotope in closed systems using direct H2O(liquid) - H2O(vapour) equilibration method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17547, https://doi.org/10.5194/egusphere-egu2020-17547, 2020.

Treatments on plantation forests, such as thinning, have a significant effect on the quality and quantity of water resources in the watersheds in Japan. However, few studies have performed intensive observations regarding the effects of thinning on the groundwater flow process with combined use of tracers, specially over a long period of time.

In this study, stable isotope analysis and hydrological observations were applied to investigate the temporal variation of spring water and groundwater mean residence time in a small watershed at Mount Karasawa, Tochigi Prefecture, Japan. We have monitored the research area since 2010, with periodical sampling once a month for 9 years, with a lack of data in some years after the thinning.  We analyzed the date for three different time periods, those are: Before Thinning, from July 2010 to September 2011, Soon After Thinning, from November 2011 to October 2013 and Long After Thinning, from September 2017 to August 2019.

The mean residence time of spring water and groundwater were evaluated by using the stable isotopes of hydrogen and oxygen as tracers, then estimating their d-excess variations using two Lumped-Parameter Models, Exponential-Piston Flow Model and Dispersion Model. The SF₆ concentrations were used as an Apparent Age analysis for determination of the model’s parameters. Both models show a tendency of the mean residence time getting older Soon After Thinning and then getting younger again Long After Thinning.

According to a selection of the best model for this area, the Exponential-Piston Flow Model shows that the spring water mean residence time was 25 months Before Thinning, 30 months Soon After Thinning and 26 months Long After Thinning; the groundwater at 15m deep mean residence time was 39 months Before Thinning, 46 months Soon After Thinning and 38 months Long After Thinning and the groundwater at 30m deep mean residence time was 38 months Before Thinning, 47 months Soon After Thinning and 45 months Long After Thinning. These results suggest that Soon After Thinning there is a reduction of forest interception and tree evapotranspiration, leading to an increase in infiltration and groundwater storage. Then, Long After Thinning, the forest interception and tree evapotranspiration rise back again with the recovery of the understory vegetation, which leads to a decrease in infiltration and groundwater storage.

How to cite: Silveira Baptista, I., Tsujimura, M., and Onda, Y.: Long-term Temporal Variation of Mean Residence Time in Spring and Groundwater After Thinning at a Forested Headwater Catchment , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6522, https://doi.org/10.5194/egusphere-egu2020-6522, 2020.

In 2016–2018, during Russian Arctic Expedition on Svalbard (RAE-S) we have collected the samples of atmospheric precipitation, terrestrial waters, snow and ice on West Spitsbergen island in the vicinity of Grønfjorden. The measurements of stable water isotope content (δ¹⁸O and δD) in the atmospheric precipitation collected in Barentsburg has allowed to draw the Local Meteoric Water Line and to analyze the relationship between the isotopic content and air temperature. Aside from this, the d-excess values in precipitation (d_exc = δD – 8δ¹⁸O) was interpreted as a marker of the moisture source. This fact was confirmed by HYSPLIT modelling of atmospheric moisture. It has been demonstrated that the isotopic content of the surface waters (lakes and rivers on mountain glacier valleys) clearly points to the dominating type of feeding (atmospheric, ground) of these hydrological objects. We have discovered the small annual variability of the isotopic composition of Lake Kongress water during 2 years and defined the sources of water in its tributes: 13 of them have atmospheric source and 9 with ground source. In general, isotopic content of water in the vicinity of Grønfjorden (mean values are: δ¹⁸O = –10,3 ‰, δD = –72,5 ‰) is higher than in other regions of Svalbard.

How to cite: Skakun, A., Ekaykin, A., Kozachek, A., Tchikhachev, K., Vladimirova, D., and Verkulich, S.: Stable isotopic content of atmospheric precipitation and natural waters in the vicinity of Barentsburg (Svalbard) in 2016-2018., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13048, https://doi.org/10.5194/egusphere-egu2020-13048, 2020.

The Kishi and Ulken Almaty rivers drain glacierized catchments in the northern Tien Shan, Kazakhstan. Both rivers supply water for the Almaty agglomeration with population around 2.5 million. Changes in discharge of these [and many other regional] rivers are affected by changes in all components of the cryosphere (seasonal snow, glacier ice, ground ice) as well as precipitation and ground water. Uncertainties of projections of water availability in the context of the observed climatic warming are an important economic and politic issue in this region. Knowledge of the extent, to which discharge of these rivers depends on different sources of nourishment, is important for the formulation of regional adaptation strategies and policies.

A comprehensive data set on concentrations of daily values of stable isotopes of oxygen and hydrogen, temperature, precipitation, and discharge was collected in both catchments in 2017 and 2018 in order to characterize contribution of different sources of water to total discharge. There is a clear correlation between isotopic concentrations in stream water with temperature, precipitation and discharge enabling separation between contributions of ground water (δ²H=–78.25 ‰; δ¹⁸O=–11.80 ‰), snow melt (δ²H=–84.56 ‰; δ¹⁸O=–13.20 ‰), and glacial melt (δ²H=–78.97 ‰; δ¹⁸O=–12.41 ‰). Analysis of isotopic signatures of sources of water shows separation between seasonal snow, glacier ice, rock glaciers and permafrost.

Following these preliminary results, the sampling programme has been extended in 2019 to the Ulken Almaty and Kishi Almaty (Kazakhstan), Ala-Archa and Chon Kyzyl-Cuu (Kyrgyzstan), Chirchik (Uzbekistan), Varzob-Kofarnihon (Tajikistan) catchments in 2019-2020 enabling the development of the most comprehensive data set on water isotopes in Central Asia.

How to cite: Saidaliyeva, Z., Shahgedanova, M., Wade, A., Yapiyev, V., Kapitsa, V., Kasatkin, N., and Severskiy, I.: Characterising water sources in glacierized catchments in the northern Tien Shan using stable isotopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-807, https://doi.org/10.5194/egusphere-egu2020-807, 2020.

Baseflow is fed by groundwater to a large fraction. Estimating water quantity and quality from groundwater stores is essential for water management. However, there are few datasets available that contain detailed water chemistry analysis on high spatial resolution across multiple headwater catchments in (high) Alpine environments. This information is essential to analyze mixing processes on catchment scale from distinct landscape features.

We use two data sets: i) water chemistry analysis snapshot sampling campaigns in 7 headwater streams during low‑flow periods across Switzerland, and ii) a detailed chemical screening (every 25 m) in one selected catchment during baseflow, including electric conductivity and temperature. Major ions, stable isotopes, TOC, DOC, trace elements were analyzed for some of the samples (> 80). These data reveal the chemical fingerprint of the contributing groundwater sources. The chemical composition of these contributing sources to baseflow is largely influenced by weathering products depended on lithology and geomorphology. Using maximum likelihood calculations, we define the ion composition and the isotopic signature of the potential major endmembers (up to three), based on the mixed samples along the main stem.

The proposed methodology allows to i) reduce uncertainty of the endmembers, and ii) quantify the relative contribution of different lithology and geomorphological features to streamflow and shows iii) which spatial scale of input information is needed to analyze mixing processes from various groundwater sources. Our results show how the contribution of different lithologies, along with topography and geomorphological features, varies spatially throughout Alpine headwater catchments.

How to cite: Floriancic, M. G., Roques, C., and Jimenez-Martinez, J.: Estimating mixing processes of sources contributing to baseflow in Alpine headwater catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1721, https://doi.org/10.5194/egusphere-egu2020-1721, 2020.

The identification of origin, flow paths and transit times of water in catchments is an important component for process-based model development for runoff prediction. Hydrological studies offer, combined with isotope data, the possibility to quantify interactions between different compartments in catchments. In the context of this work it is examined to what extent event sampling of precipitation, streamflow, soil water and groundwater and the evaluation of their isotopic ratios δ²H and δ¹⁸O enable complex hydrological process investigations in the small forested mountain catchment of the river Große Ohe in the Bavarian Forest National Park. Within this study process analyses are carried out on small scales, e.g. runoff formation on hill slopes and on catchment scale as integrative process analysis. The water samples were collected during a small flood event and analysed for the isotope ratios δ²H and δ¹⁸O using a Picarro. A hydrograph separation was carried out through a comprehensive evaluation of the concentration profiles during the event. In combination with further hydrological and soil hydrological observations possible areas of origin and retention times of the water were determined. A strongly delayed reaction of the groundwater was observed which suggests that groundwater is not contributing to stream flow during a flood event, but a possible mobilization of pre-event water in the riparian zone can be observed as a response to precipitation events. The knowledge gained hereby is the basis for further process analysis and model development.

How to cite: Rommel, L. and Wöhling, T.: Hydrological analysis of runoff formation in a small forested mountain catchment using δ2H and δ18O ratios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10309, https://doi.org/10.5194/egusphere-egu2020-10309, 2020.

Catchment travel time distributions (TTDs) are an integrative measure of time-varying flow paths and hydrological processes, commonly derived from tracer data (e.g. 2-H, 3-H). Recently, it has been argued that the use of stable isotopes of O and H compared to tritium neglects the long tails of TTDs and thus truncates our vision on streamflow age. However, the reasons for the truncation of the TTD remain obscured by methodological and data limitations, including different mathematical models and sampling strategies. In this study, we apply composite SAS functions to a forested headwater catchment in Luxembourg, where the complexity of streamflow generation leads to flow paths with highly different TTDs. We calibrate the model with high-frequency (sub-daily) deuterium measurements, as well as nearly 30 tritium stream samples collected over a two-year period. We simulated TTDs based on each tracer individually and jointly. We found that, when using the two tracers in a coherent methodological framework, both tracers result in similar TTD and storage for the studied catchment. We found small differences in the TTDs that might be explained by calculation uncertainties, as well as by the limited sampling frequency for tritium. Using both stable and radioactive isotopes of H as tracers reduced uncertainties in the water age and storage calculations. While tritium and stable isotopes delivered redundant information about younger water, the use of both tracers leveraged the more specific information content of tritium on longer ages in the system. The two tracers had overall different information contents. We found that 30 tritium samples contained more bits of information than approximately 1000 deuterium samples, underlying the importance of complementing stable isotopes studies with tritium data.

How to cite: Klaus, J., Rodriguez, N., Pfister, L., and Zehe, E.: Reconciliation of catchment travel times derived from tritium and deuterium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7713, https://doi.org/10.5194/egusphere-egu2020-7713, 2020.

The processes of spring flood formation associated with intensive snow melting are becoming less and less predictable, and forecasts of such important characteristics as maximum discharge and water level do not fit into the allowable ranges of error. In some areas, a sharp decrease in river runoff was observed, followed by catastrophic floods, associated with the anomalous hydrometeorological conditions and an unfavorable combination of flow-forming factors. All this testifies to the change in runoff formation processes in regions with a significant share of snow-fed rivers. A new method of storing processing and visualizing of the information is developed to bridge the gap between point data on river runoff and globally distributed data on characteristics affecting the genetic components of runoff. The use of new model for separating runoff into genetic components was verified by isotope hydrograph separation.

Under unsteady climate conditions, the isotope signature of river water within a year and on a multi-year scale is an important indicator of the response of hydrological system to change (associated with different amounts of snow in the winter and different contributions of snow melting to the river and groundwater reservoir). Observations at the local site of the Protva River catchment on the European Plain showed that over 9 years (in 2009-2010 and in 2019), the groundwater component did not change its isotopic characteristics: δ18О = -12.3 ‰. The intra- and interannual fluctuations associated with different amounts of atmospheric precipitation entering the upper groundwater horizon practically did not shift oxygen isotope composition of water. In 2014, the weighted average annual value δ18О of the precipitation for Moscow was -12.1‰ (Chizhova et al., 2017). The δ18О value of precipitation in the summer months varies from -3 to -10 ‰. In Protva river runoff in mid-summer the contribution of precipitation is from 16 to 34% according to the isotope hydrograph separation. This work was supported by RSF project 19-77-10032.

How to cite: Chizhova, J., Kireeva, M., Tebenkova, N., and Kositsky, A.: Quantitative estimation of genetic components in the seasonal runoff of a small river by the graphoanalytic and isotopic method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7080, https://doi.org/10.5194/egusphere-egu2020-7080, 2020.

Hydrological response covered by disturbed forest catchments are in a focus of hydrologist last decades, mainly because the connection with widespread droughts. In this study, we compare two mountain catchments in Šumava Mts. (Czech Republic), both with small glacial lakes. Plešné lake catchment is characterised by disturbed forest by a bark beetle calamity. Contrary, Čertovo lake catchment features with undisturbed forest. Both catchments have comparable geological, climate setting and origin forest types. Stable isotopes of water were used for determining the hydrological pathways and water residence time. The results show that the state of the forest significantly affects the water balance of the catchments, but the mean residence time seems to be independent on this. On the other hand, even small changes in water residence time are important for the solutes and nutrients transport in the catchments. The lakes are fed by surface and subsurface water originating from liquid precipitation in and mostly snow in winter. The isotopic analysis helps to understand how much the snow cover affects the water balance during the hydrological year in two catchments with different forest stands.

How to cite: Juras, R., Vystavna, Y., and Hnilicová, S.: Disturbed forest affects the hydrological processes in a small mountain catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22346, https://doi.org/10.5194/egusphere-egu2020-22346, 2020.

The headwater catchments in the humid tropical forests are of major hydrological importance for regional and global climate systems and provide essential ecosystem services such as water supply for other ecosystems and industrial use in the lowlands. Anthropogenic pressure together with global environmental changes critically alter the hydrological functioning of these catchments. However, limited knowledge jeopardizes a proper water resources management of such water towers.

To contribute to filling this gap, we conducted a field monitoring of hydro-climatic and isotopic data (01.2013 – 07.2018) in a pristine tropical rainforest catchment (3.2 km²) in Costa Rica and used this data to test hypotheses about water age dynamics. The Spatially-Distributed Tracer-Aided Rainfall-Runoff model for the tropics (STARRtropics) was applied in high temporal (hourly) and spatial (10m) resolution. The best-obtained model simulations reflected a highly variable range and distribution of water ages. Nevertheless, superficial flow paths with young water contributions (40 months at most) dominate the streamflow generation entirely. The maximum water age was independently evaluated calculating the tritium-derived baseflow mean transit time. The highest simulated ages of transpiration flux varied between 12 days and 5.5 months depending on the soil depths where the water was uptake. Soil water age peaked at 5.4 months and groundwater at 40 months. The oldest stream water age, integrating all catchment processes, reached 24 months. Overall, the water age increased during dry conditions. The frequency of water ages reflected high occurrences of young water for transpiration flux and streamflow in their respective ranges. Maximum occurrences were reported for transpiration with 10 hours and streamflow with 2.8 months. The soil water age presented a bimodal distribution with peaks of 2.8 and 4.4 months and groundwater age occurrences peaked at 32 and 37 months. Spatially, high age dynamics of transpiration flux were associated with a higher leaf area index on the northern hillside in relation to the southern hillside. The oldest soil water was related to more developed soils and the groundwater age increased towards the bottom of the catchment. In the context of the tropics, our study is one of the first that quantitatively evaluated water age dynamics and distributions, and globally using such a high spatial and temporal resolution with a non-stationary perspective. These findings will support decision-makers to manage the water resources and ecosystem in the humid tropics and reduce the research gap regarding hydrological processes of tropical headwater towers under environmental changes.

How to cite: Correa, A., Birkel, C., Gutierrez, J., Dehaspe, J., Duran-Quesada, A. M., Soulsby, C., and Sánchez-Murillo, R.: Young water dominance in the humid tropics in Costa Rica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11960, https://doi.org/10.5194/egusphere-egu2020-11960, 2020.

The need to understand how urbanization impacts the hydrological cycle and creates a complex, hybrid system of artificial and natural flow paths is an increasing focus of research.  A key question is how routing processes are affected by preferential flow of urban runoff into storm drains and infiltration trenches, and how this affects catchment travel time distributions of water and groundwater recharge. Isotopic tracers are commonly used in hydrology in order to identify dominant runoff sources, track flows paths and estimate water ages. However, isotope studies in urban areas are surprisingly scarce.  Here, we address this research gap by using stable isotopes for a preliminary investigation of the effects of urbanization on the stream flow generation and groundwater  discharge in the Panke catchment (230 km²) in the northern part of Berlin. The Panke is highly urbanised, with the built areas occupying 30% of the catchment, and a waste water treatment plant (WWTP) for around 700,000 people. Daily isotope samples of precipitation and streamflow were collected through the transition period from summer (dry) to winter (wet) conditions. In addition, spatially synoptic surveys in summer and winter gathered samples from throughout the catchment surface water drainage network and numerous groundwater wells. The natural hydrology of the catchment is groundwater-dominated, with isotopes indicating that an aquifer of glacial sands and gravel still providing the main source of runoff in the catchment headwaters, upstream of Berlin. Increasingly downstream, urban impacts become more dominant, especially during high flows when urban storm drains are active. In addition, the isotopic imprint of discharge from a WWTP dominates baseflow composition in the lower catchment. This preliminary work will be extended throughout 2020 and ultimately seek to inform models to quantify how the travel time distributions of the catchment have changed due to urban drainage, and how both impermeable surfaces and urban green space affect the spatial distribution of groundwater recharge.

How to cite: Marx, C., Soulsby, C., Hinkelmann, R., and Tetzlaff, D.: Using stable isotopes to understand water flow paths and ages in complex urban catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-414, https://doi.org/10.5194/egusphere-egu2020-414, 2020.

Coastal lagoons are unique and complex ecosystems. Resulting from both terrestrial (fresh groundwater and surface water) and marine water influences, these ecosystems are often maintained by direct or indirect groundwater supplies and collectively known as groundwater dependent ecosystems (GDEs). Because they provide a wide range of ecosystem goods and services on which a large part of the human population depends, coastal GDEs are considered as complex socio-economic and ecological component worldwide. The increasing human development in coastal areas induces yet a strong pressure on water resources and the expected effects of climate change could exacerbate the pressures on these environments. To limit the risks of degradation and to ensure the sustainability of ecosystem services, the implementation of proper water resources management strategies is essential. This requires a strong knowledge of the environmental and socio-economic trajectories of hydrosystems, and particularly of the behavior and role of groundwater.

To this end, only the combined use of several tools allows a global understanding of the spatial and temporal dynamics of the system. The correlation between isotopic tracers (¹⁸O, ²H, ³H, ¹⁵N, ¹¹B), anthropogenic contaminants (organic micro pollutants) and mapping approaches (land-use and vulnerability) allows a historical analyze of the hydrosystem. In addition, to better constraint the hydrosystem hydrological behavior, it is also possible to highlight the current status of water resources, the historical legacy of pollutants and the consequences of past developments and practices, which continue to jeopardize the current quality of the water resource. This methodology was applied to a Mediterranean hydrosystem, in connection with a coastal lagoon (Corsica Island, France). The identification of degradation processes and their chronology could then be traced back in time.

It appears that the current deterioration is mainly due to a legacy pollution resulting from the development of policies implemented 60 years earlier. In the case of coastal GDEs that are highly anthropized and subject to ever-increasing development, this methodology proposes new key elements for the establishment of relevant management strategies to ensure the future sustainability of water resources.

How to cite: Erostate, M., Huneau, F., Garel, E., and Pasqualini, V.: Multi-method approach combining isotopic tracers, anthropogenic contaminants and mapping to retrace socio-environmental trajectories of groundwater-dependent coastal hydrosystems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18387, https://doi.org/10.5194/egusphere-egu2020-18387, 2020.

Widespread permafrost thaw in Canada's western Arctic has led to formation of shoreline retrogressive thaw slumps (SRTS), a process influential in modifying water and biogeochemical balances of tundra lakes. To investigate hydrological effects of SRTS, water sampling campaigns were conducted in 2004, 2005 and 2008 for paired lakes (pristine vs catchments disturbed by SRTS) in the upland region adjacent to the Mackenzie Delta, Northwest Territories, Canada. An isotope balance model to estimate evaporation/inflow, precipitation/inflow, water yield and runoff ratio was developed incorporating seasonal evaporative drawdown effects and a vapour mixing model to simulate gradients in Beaufort Sea marine air versus continental moisture sources. Site- specific water balance results reveal systematically higher evaporation/inflow and precipitation/inflow for lakes with active SRTS compared to undisturbed lakes, and typically higher ratios for lakes with stabilized versus active SRTS. For lake catchments, water yield is found to be higher for active SRTS sites compared to undisturbed and stabilized SRTS sites, suggesting that slumping is an initial but not a sustained source of water delivery to lakes. Catchments with history of wildfire are found to have lower water yields, attributed to reduced permafrost influence. Conceptually, we define a thaw trajectory whereby undisturbed sites, active SRTS, stabilized SRTS, and ancient- SRTS define progressive stages of permafrost thaw. We postulate that release of additional runoff is mainly due to permafrost thaw in active SRTS which also promotes lake expansion, talik formation, and subsurface connectivity. Eventual stabilization of slumps and reduced runoff is expected once permafrost thaw sources are exhausted, at which time lakes may become more reliant on replenishment by direct precipitation. The effect of snow catch in slumps appears to be subordinate to thawing based on eventual decline in runoff once thaw slumps stabilize. Improved, site-specific hydrologic understanding will assist ongoing research into carbon cycling and biogeochemical feedbacks.

How to cite: Wan, C. and Zhou, Z.: Isotopic constraints on water balance of tundra lakes and watersheds affected by permafrost degradation, Mackenzie Delta region, Northwest Territories, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18415, https://doi.org/10.5194/egusphere-egu2020-18415, 2020.

Abstract

Wetlands play an important role in the hydrologic cycle and are also regarded as major water reservoirs. Hydrochemistry application is an important tool which enables the evaluation of water type, water-rock interactions, discharge and recharge mechanism of wetlands. The aim of this study is to clarify the hydrogeochemical processes involving recharge and discharge mechanism of the wetland system and determine the hydrochemical characteristics of the wetland water, based on groundwater and surface water chemistry data. Within this scope; a detailed geological, hydrological, hydrogeological, hydrochemical and isotopic studies were performed in the Seyfe Lake catchment. Seyfe Lake and its surroundings, which is located in Mucur district, approximately 16 km northeast of Kirsehir, Turkey, is a first degree natural reserve and Ramsar Site. First field campaign was carried out in September 2019 and twenty three sampling points were selected in the study area. Sampling points were chosen from the wetland area and wells and springs that are located in the recharge area. Physicochemical parameters such as pH, specific electrical conductivity, temperature and discharge rates of the water samples were measured in-situ. Temperature, specific electrical conductivity and pH of the water samples ranges from 14.5°C to  21.2°C, from 370 µS/cm to 30500 µS/cm and from 7.15 to 8.65, respectively. Discharge rate of the springs are between 0.02 and 1 l/s. These waters have neutral to slightly alkaline character. Stable isotopes and hydrochemistry are used to identify possible recharge areas, origin of waters, groundwater-surface water relation and water-rock interactions. The δ²H and δ¹⁸O values of the water samples ranges between -27.61‰ to -80.88‰, and -11.97‰ to 0.86‰, respectively in the Seyfe wetland area. The results of this study will contribute to a better understanding of groundwater dynamics and hydrochemical processes in the wetland area.

Key words: Hydrochemistry, Stable isotopes, Wetland, Ramsar site, Seyfe Lake, Kirsehir

How to cite: Yurteri, C.: Hydrochemical evaluation of a groundwater system connected to a wetland: A case study in the Seyfe Lake wetland, Kirsehir, Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-27, https://doi.org/10.5194/egusphere-egu2020-27, 2020.

Stable isotopes of hydrogen and oxygen (²H and ¹⁸O) are often used for quantification of water budgets of lakes and other surface water bodies, in particular for the assessment of underground components of those budgets [1]. Recent advances in laser spectroscopy enabled simultaneous analyses of ²H, ¹⁸O and ¹⁷O content in water, with measurement uncertainties comparable (¹⁸O) or surpassing (²H) those routinely achieved by off-line sample preparation methods combined with conventional IRMS technique [2]. This open up the doors for improving reliability of isotope-aided budgets of surface water bodies by adding third isotope tracer (¹⁷O).

Here we present the results of a field study aimed at assessing water balance of a small groundwater-controlled lake (surface area ca. 40 ha, mean depth 5.2 m) located in southern Poland. The lake has no surface inflows and outflows and is heavily exploited for recreational purposes during the summer season. Thus, the renewal rate of water in the lake is of primary importance for proper management of this system.

The lake has been extensively monitored during one–year period (from October 2018 till September 2019). Four sampling campaigns were conducted on the lake to collect water samples for isotope analyses. In addition, regular observations of lake water temperature and meteorological parameters (air temperature, precipitation amount, relative humidity, wind speed) were conducted on the shore. Also, monthly precipitation samples were collected for isotope analyses.

The lake budget was constructed separately for each isotopic system (²H, ¹⁸O, ¹⁷O), with groundwater inflow and outflow fluxes treated as unknowns. The isotopic composition of net evaporation flux was calculated using Craig-Gordon model [3]. Isotope mass balance calculations revealed that groundwater fluxes derived from ²H-based budget deviate substantially from those obtained for ¹⁸O and ¹⁷O isotope. It turned out, that most likely reason of this discrepancy is the assumption generally made in constructing isotope balances of small lakes that atmospheric water vapor “seen” by the evaporating lake, is in isotopic equilibrium with local precipitation. Instead, when the local water vapor “seen” by the lake was assumed to be a mixture of local free atmospheric moisture (in equilibrium with local precipitation) and the vapor produced by the lake itself, consistent water budget for all three isotope systems could be obtained.

Acknowledgements: The presented work was supported by National Science Centre (research grant No. 2016/23/B/ST10/00909) and by the Ministry of Science and Higher Education (project no. 16.16.220.842 B02)

References:

[1]  Rozanski K. Froehlich K. Mook WG. Technical Documents in Hydrology, No. 39, Vol. III, UNESCO, Paris, 2001 117 pp.     

[2]   Pierchala A, Rozanski K, Dulinski M, Gorczyca Z, Marzec M, Czub R, Isotopes in Environmental and Health Studies, 2019 (55) 290-307.

[3]   Horita, J. Rozanski K. Cohen S. 2007. Isotopes in Environmental and Health Studies, 2007 (44), 23-49.

How to cite: Rozanski, K., Pierchala, A., Dulinski, M., Gorczyca, Z., and Czub, R.: Triple isotope balance of groundwater controlled lake , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8105, https://doi.org/10.5194/egusphere-egu2020-8105, 2020.