S17

Defining moisture sources and evolution of precipitation is significant for further exploration of complex hydro-climatic interactions, especially under global warming with alternations of evapotranspiration capacity and precipitation moisture source structure. As a sensitive indicator, dexcess has been widely used to quantify the proportion of recycled vapor to precipitation (f_re). However, existing models ignore taking transpiration vapor into account and the calculated f_re tends to be lower than the true value. Herein, it was modified with transpiration vapor considered and applied in Guyuan, China located in a monsoon marginal zone with complex precipitation moisture sources. After modification, the estimated annual average fre was increased from 7.5% to 14.8%. This study highlights the contribution of transpiration vapor to precipitation and provides more information on the formation and evolution of precipitation to better serve future hydro-climatic research. The article has been published in the Geophysical Research Letters (https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL095909).

Figure 1. Conceptual diagram of a modified d-excess-based model emphasizing d-excess for three end-members (advected, evaporation, and transpiration vapor) of precipitation moisture sources.

Figure 2. (a) Map showing the locations of Guyuan precipitation station. (b) Main moisture sources of precipitation in China. (c) Distribution of annual mean monthly precipitation and air temperature in Guyuan.

Figure 3. (a) The LMWL of Guyuan. (b) The meteoric water lines of four seasons in Guyuan. (c) Variations in d-excess and δ¹⁸O over time in Guyuan.

Figure 4. Monthly fluctuations of recycling ratio (f_re) with the original and modified model.

How to cite: Zhang, F., Huang, T., and Pang, Z.: Intensive Quantification of Precipitation Moisture Sources in the Eastern Asian Monsoon Zone: A Modified Deuterium-excess-based Model, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-561, https://doi.org/10.5194/iahs2022-561, 2022.

La Mesa de Los Santos is located in the Eastern Cordillera of Colombia and configures a plateau marked by a shortage of potable surface water. The isotopic study of the rain and its relation to Los Santos Formation phreatic aquifer was carried out. Los Santos Formation is divided into three members: Upper Member (well cemented quartz sandstones), Middle Member (siltstones, claystones and sandstones) and Lower Member (sandstones and conglomerates). Phreatic aquifer groundwater circulates in the Upper Member. On the plateau, 4 stations were installed to collect rainwater samples monthly for stable isotopes (n=46) from October 2020 to September 2021. The seasonal behavior of Oxygen-18 and Deuterium is similar in the four stations, and the Local Meteoric Water Line is δ²H=8.22×δ¹⁸O+13.8. The rain-weighted average values of Oxygen-18 and Deuterium (V-SMOW) in each station are: -8.99‰, -61.4‰ (height=1275masl, P=764mm); -8.78‰, -58.5‰ (height=1678masl, P=1869mm); -8.51‰, -54.5‰ (height=1684masl, P=1469mm); -8.13‰, -52.2‰ (height=1433masl, P=1030mm), respectively. The isotopic composition of the rainwater does not correlate with the elevation or the precipitation height. From the phreatic aquifer, 35 groundwater points (wells, borehole and springs) were monitored for stable isotopes (n=134) in the months of December 2020, February, April, June, and August 2021. Three behaviors were differentiated in the isotopic composition of Oxygen-18. Large temporal variability (differences greater than 1‰ in δ¹⁸O) apply to 10 groundwater points showing δ¹⁸O values between -9.64 and -5.19‰ (with two outliers at -1.1 and -3.8‰), in accordance with the monthly behavior of the rain, considering flows with rapid transit on a monthly scale. 21 groundwater points show a low temporal variability (differences less than 1‰ in δ¹⁸O), presenting a distribution of Oxygen-18 with enriched values towards the north (between -6.71 and -6.00‰) and depleted values towards the south (-8.97 to -8.14‰), which tends to be also consistent with the rain, although with a better mix of groundwater and a slower transit than the previous behavior. Finally, 4 groundwater points present signs of evaporation, showing values of Oxygen-18 between -6.2 and -3.1‰ and d-excess values between -6.4 and +4.3‰, which are related to surface water bodies that undergo evaporation before the infiltration process.

How to cite: Cetina, M. A., Taupin, J. D., Gomez, S., and Patris, N.: Isotope study of monthly rainfall and its response in the Santos Formation phreatic aquifer, La Mesa de Los Santos, Santander (Colombia)., IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-101, https://doi.org/10.5194/iahs2022-101, 2022.

Complementary to the reduction of fertilizers and pesticides applications, a promising measure against non-point source pollution from agriculture is the implementation of constructed wetlands intercepting polluted surface water. They are widely used to protect sensitive water resources (e.g. aquifers, lakes or rivers), especially when grass strips are bypassed by a subsurface drainage network. Constructed wetlands, intermittently fed during autumn and spring in a temperate climate, are composed of three interacting compartments: sediment layer, vegetation and water column. Pollutant mitigation increases with the time spent by water in contact with the sediment and with vegetation. Its removal potential is mainly driven by the inflow and its distribution over the wetland area. When sparse or in patches, vegetation makes the flow path more complex and can cause shortcuts and dead zones. The challenge is to link the yearly patterns of discharge, hydraulic performance and removal rate, in order to provide guidelines for the design of constructed wetlands.

In this study, the three-dimensional hydrodynamic model Delft3D-Flow was used to simulate flow within a constructed wetland, forced by observed meteorological conditions. Contrary to commonly used bidimensional models, Delft3D-Flow can differentiate flow conditions through immerged and above submerged vegetation. The study site is the constructed wetland (0.5 ha built in 2010) of Rampillon, France, a buffer zone between drained agricultural lands (355 ha subcatchment) and the direct recharge into a karstic aquifer trough sinkholes. The model was validated on continuous outflow concentration measurements and on areal images during two tracing experiments in different flow conditions, using the conservative tracer Rhodamine WT. The hydraulic performance assessment at the yearly scale is based on shortcut and mixing indicators, which are extracted from the distribution of the tracer residence time. The calculation of these indicators at the yearly scale showed that the mixing level does not change significantly and that the shortcuts and dead zones decrease slightly as the flow rate increases.

How to cite: Henine, H., Tournebize, J., Chaumont, C., and Lemaire, B. J.: Tracing and hydraulic modeling of flows in a constructed wetland for the treatment of the pollutants load from drained agricultural lands., IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-527, https://doi.org/10.5194/iahs2022-527, 2022.

Karst hydrosystems are complex systems where the use of water resources is often shared by many actors. The addition of thermal and/or marine components in these systems makes classical methods of investigation difficult to apply. The combined use of geochemical tracers can allow a better understanding of the complex hydrogeological system and application of integrated water resources management. The thermal karst aquifer of Thau (South of France) illustrates the complexity of karst hydrosystems since it is a zone of convergence of young and shallow karst water, hot and mineralized thermal water and marine water (Thau Lagoon and/or seawater). Moreover, recurring phenomena of saltwater intrusion from the Thau Lagoon (i.e. inversac) into the freshwater aquifer can occur, modifying the type of circulation. It is proposed in this study, supported by the Dem'Eaux Thau project (2017-2022), to combine, with classical geochemical tools, tracers of water-rock interaction processes (Sr, Li) and residence time tracers (CFC, SF₆, ³H, ⁴He, ¹⁴C, ³⁶Cl) to better understand the origin of fluxes and to characterize the mixing that takes place in the system. 
Isotopic tools (Sr, Li) allowed to better constrain the thermal reservoir: thermal water flows mainly in a carbonate aquifer (⁸⁷Sr/⁸⁶Sr), fed by deeper flows from bed-rock ([Li]). The residence time of this water estimated by the different tracers (⁴He, ¹⁴C, ³⁶Cl) is consistent and indicates ages of several thousands of years (10 000 to 50 000 years). This water subsequently feed a shallow reservoir (100-300m) through local fractures and mix with variable proportions of recent karst flows. These flows are mixtures of regional flows of about 30 years affected by thermonuclear tests (CFC, SF₆, ³H, ¹⁴C, ³⁶Cl) and more recent local flows contaminated by local anthropic activity (SF₆, NO₃^-). During the inversac phenomenon, fluxes and mixtures are modified bringing a saltwater component to the system. Geochemical tools allow us to quantify the impact of the inversac and to characterize the spatial impact of such contamination by highlighting the connections between the intrusion zone and the different monitoring points. 

How to cite: Ranchoux, C., Ladouche, B., De Montety, V., Seidel, J.-L., and Batiot-Guilhe, C.: Combining residence time and isotopic tracers for a better understanding of the fresh and marine water recharge and groundwater flux of a karstic thermal aquifer, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-389, https://doi.org/10.5194/iahs2022-389, 2022.

Chemistry of groundwater is heavily affected by water-rocks interactions. Major elements in groundwater provide valuable indications on main aquifer rock types but requires strong lithological contrasts. Carbonate rocks differ because of deposit conditions and diagenesis and it bears significant implications for groundwater flow. It is established that trace elements in carbonates depend on deposit environment and diagenesis (Gholami Zadeh et al., 2019; Hood et al., 2018; Li et al., 2020). In waters from carbonate aquifers, variation of trace elements contents is observed at different spatial and temporal scales (Dematteis, 1995; Morgantini et al., 2010; Schürch et al., 2004). While some of this variability is due to recharge characteristics, in the absence of anthropic contamination the main process affecting trace elements contents is water-rock interactions. This leads to the potential for trace elements to be a natural tracer of limestone rock types.

This work aims to develop a natural tracer of limestone rock types that could distinguish the fingerprints of the different sub-reservoirs of carbonate aquifers.

To this purpose, we studied the Fontaine de Vaucluse karst system (southern France). It has a large recharge area (~ 1160km²; Ollivier, 2020) composed of Upper Barremian limestones of inner/outer platform, slope and basinal environnements (Masse and Fenerci-Masse, 2011; Léonide et al., 2012). We analysed major and trace elements of a set of 107 rock samples representative of the complete lithologie, facies and rock type properties of these carbonates. We also performed a one-year sampling campaign on 17 flow points: 12 in unsaturated zone from the LSBB gallery (lsbb.cnrs.fr), 3 springs, 1 stream losses, and at the main outlet of the karst system. In addition to trace elements we also monitored major elements, stables isotopes, TOC and fluorescence of natural organic matter.

A hierarchical clustering was performed with trace element contents of rock samples. It splits data into four groups according to facies description (inner/outer platforms, slope, basin). In water, first results show temporal and spatial variation of trace elements of Fontaine de Vaucluse system.

These promising results hint that trace element seem to be relevant natural tracers of the path taken by water in different limestones.

How to cite: Serène, L., Batiot-Guilhe, C., Mazzilli, N., Léonide, P., Emblanch, C., Resongles, E., Freydier, R., Causse, L., Babic, M., Dupont, J., Simler, R., Blanc, M., and Massonnat, G.: Use of trace elements to distinguish flows from different types of carbonated rocks, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-329, https://doi.org/10.5194/iahs2022-329, 2022.

In the critical zone, infiltrated surface water within porous media drives many biogeochemical processes that lead to a natural attenuation of contaminants. In the case of induced bank filtration (IBF), quantifying residence time is required to anticipate water quality issues. Due to combined hydroclimatic regimes and variable pumping sequences, groundwater flow is unsteady and classical residence time quantification approaches often fail to account for such dynamics. Radium is a geogenic element with four isotopes offering ideal half-life ranges for estimating groundwater residence time. Its potential to characterize water mixing processes or date seawater has been widely proven. These advances were supported by the development of affordable analysis devices such as delayed coincidence counters (RaDeCC). In freshwater, the radium adsorption ability on the porous matrix affects its mobility and reduces its availability in dissolved form. These direct consequences of adsorption i) restrict the representativity of water samples, ii) impact the ability to measure dissolved radium by RaDeCC and iii) drastically reduce the temporal range for using radium as a chronometer of surface water residence time in an aquifer. Without a paradigm change, radium as a temporal tracer in freshwater won’t reveal its full potential. However, the third point may be appropriate for tracing dynamics of unsteady flow such as those prevailing for infiltrated surface water in IBF site. A two-years study led in an IBF site equipped with eight wells and 10 piezometers allowed 200 samples to be analysed with a RaDeCC for 223, 224, 228 and 226 radium isotopes. Preliminary results suggest that dissolved radium is more controlled by flow than by a differential adsorption, as no clear correlation was found between dissolved radium and geochemistry (ORP, pH, EC). The spatial distribution pattern of short-lived isotopes at the site was related to the pumping regimes. Annual amplitudes of dissolved radium isotopes presented a periodicity for all the wells. These first results show a satisfactory tracer response to spatial and temporal hydrodynamic flow changes, either from natural or anthropogenic origin in critical zone.

How to cite: Veuille, S., Baudron, P., Barbecot, F., and Claveau-Mallet, D.: Evaluating radium as a time tracer for infiltrated surface water in unsteady surface -groundwater interaction areas, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-507, https://doi.org/10.5194/iahs2022-507, 2022.

Chemical and isotopic tracers are powerful tools to study the water cycle and may constitute complementary methods in areas where instrumental records are insufficient. Tritium has been used routinely up to the 2000’s, but because of its short half-life, the bomb-³H spike of the 1960’s is today hardly distinguishable from the natural background level. Bomb-produced ³⁶Cl offers an alternative tool, due to the conservative behavior of chloride and the large amounts of ³⁶Cl released during the marine nuclear tests of the 1950’s.

In this study, we use the bomb-³⁶Cl pulse to assess the residence time of water in five volcanic lakes (Mbalang, Tabere, Tizon, Gegouba and Baledjam) of the Adamawa plateau in the northern region of the Cameroon Volcanic Line. Sediment cores from Mbalang and Tizon have been studied previously for paleo-environments, but otherwise, the Adamawa lakes received little attention so far.

The lakes chloride content is low (0.009-0.035 meq/L) but higher than that of the rainwater samples (0.0019-0.0095 meq/L). In all the lakes, the ³⁶Cl/Cl ratio (1*10^-12 to 3*10^-12 at/at) is higher by at least one order of magnitude than the natural atmospheric ratio (0.2*10^-12 at/at) as determined previously from groundwater measurements in the lake Chad basin and in the Northern Saharan CT aquifer (Bouchez et al.2019, Hadj Ammar (2016)). These high ratios are a definite signature of the nuclear imprint, and thus of the lakes memory of atmospheric deposition, as already observed by our group in lake Chad, Iro and Fitri (Bouchez et al. 2019, Poulin (2019)). These data can then be used to determine the hydrological budget of the lake, independently of any water flux measurement, based on a simple one-box model assuming steady state for water and chloride. Indeed, simulating the transient response of the lake’s ³⁶Cl to the bomb pulse allows us to estimate simultaneously the water residence time and the evaporation/precipitation ratio. Results from this model, as well as discussion of their comparison with classical hydrologic data will be shown at the meeting.

References:

Bouchez C. et al. 2019, (Paper in Scientific Report)

Hadj Ammar F. 2016 (Thesis)

Poulin C. 2019 (Thesis)

How to cite: Abba, S., Hamelin, B., Deschamps, P., Ngounou Ngatcha, B., Garcin, Y., and Team, A. s. t. e. R.: Thermonuclear 36Cl, a new tritium-like tracer of the hydrologic cycle. Application to the water residence time in Cameroon volcanic lakes, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-373, https://doi.org/10.5194/iahs2022-373, 2022.

The regional Quaternary aquifer of the Lake Chad Basin represents a major resource crossing several countries in the Sahel region. It is intensively used for many purposes, including drinking water supply, domestic uses, breeding and irrigation. However, this resource already undergone the climate change effects and the strong pressure of human activities. For instance, some authors shown that in Cameroon, the NO₃^- contents have increased by a factor of six between 1993 and 2013. It is therefore urgent to propose pragmatic water management strategies in this region, which will be based on a total understanding of the aquifer functioning. To achieve this objective, major ions chemistry and isotopic tools were combined. It is the first time that a such multi-proxy study is conducted in the region. Chemical analyses revealed that the geogenic influence is marked by dissolution, hydrolysis of silicate minerals, and possible cation exchanges. The nitrates content up to 1500 mg/l confirm the high impact of anthropogenic activities on this resource. Water stable isotopes show the contribution of surface water in addition to actual rainwater, in the recharge of the aquifer while ³H and ¹⁴C highlight that the Quaternary aquifer gathers both recent and old groundwater (~1500 years). Above all, these radioactive tracers helped to identify the different flow paths: a shallower one (under an active recharge from river and rainwater), a deep one (with the lowest concentrations in ³H and ¹⁴C, more protected from surface pollutants and dominated by geogenic processes) and an intermediate level attesting a mixing between the deep and shallower levels. Finally, thanks to δ¹⁵N-NO₃ and δ¹⁸O-NO₃ three main sources of nitrates were identified: (i) deposits of nitrogenous organic matter (animal excrement, manure, household waste); (ii) naturally synthesized nitrate in the soil; and (iii) nitrate from nutrients of the paleo-sea. A conceptual model of the regional Quaternary aquifer can then now be proposed in 02 points: (i) the existence of distinct flow paths with the deep one which is strategic especially for drinking purpose and (ii) the dependence of the aquifer to perennial rivers.

How to cite: Nlend, B., Song, F., Ngo Boum-Nkot, S., Huneau, F., Garel, E., Nkoue, R., Mahamat Nour, A., and Etame, J.: Multi-isotopic approach to identify groundwater flow paths, relationships with rivers and sources of contaminants in the Regional Quaternary Aquifer of the Lake Chad Basin., IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-12, https://doi.org/10.5194/iahs2022-12, 2022.

How to cite: Santoni, S., Garel, E., Huneau, F., Gillon, M., Babic, M., and Mattei, A.: How can geochemistry and isotope hydrology tools tell us about alluvial groundwater-wetlands interactions and subsequent carbon balance? Case of the Moltifau Mediterranean peatland (Corsica Island, France), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-261, https://doi.org/10.5194/iahs2022-261, 2022.

The hydrology of non-perennial (temporary) rivers under climate change (UPH 3) affects not only dry regions but could affect all climates, because most of the catchment headwaters already have (or will have) temporary regimes. Most temporary rivers undergo a pools phase when surface flow ceases but surface water remains in disconnected pools. These pools offer many ecosystem services, such as the provision of refuges for aquatic species. Nevertheless, the hydrology of this pools phase is poorly known because gauging stations or hydrological models do not inform about what happens after the cessation of flow.

We implemented a methodology to estimate the time since disconnection of pools from the river flow when they are sampled, based on the study of water stable isotopes. In pools disconnected from groundwater, the isotopic modification of the water allows us to estimate the relative volume of water evaporated (Gonfiantini, 1986). To test this methodology, within the Vallcebre Research Catchments (42º12’N and 1º49’E ) an artificial pool, covered with a transparent lid to prevent the input of rainfall, was installed. From July to November 2020, water volume of this pool was weekly measured and sampled for isotopic analysis. In parallel, meteorological variables were monitored and rainfall was also sampled for water stable isotopes.

The results obtained in the artificial pool were satisfactory but showed two aspects not reported in previous publications: i) the customary application of isotopic fractionation equations using weekly averaged atmospheric conditions strongly underestimated the observed changes, and ii) when about 60% of pool water had evaporated, its isotopy became so enriched with heavy isotopes that periods of heavy isotopes depletion instead of enrichment happened.

The analysis of the information available showed that the first problem could be attributed to the fact that time averages of weather conditions strongly overestimated air humidity during the periods of active evaporation. Therefore we decided to weight air humidity measures with proxies of evaporation flow like vapour pressure deficit or global radiation. When the fractionation equations were applied using flow-weighted air humidity, they adequately reproduced the observed pool water isotopy, including the late periods of heavy isotopes depletion.   

How to cite: Gallart, F., González-Fuentes, S., Llorens, P., and Latron, J.: Isotopic fractionation of water in river pools. The effect of diel atmospheric variations and eventual depletion of heavy isotopes., IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-378, https://doi.org/10.5194/iahs2022-378, 2022.

It is important to understand how precipitation is stored in catchments, released via evapotranspiration (ET), or recharges aquifers and streams. We investigated this partitioning of precipitation using stable isotopes of water (²H and ¹⁸O) at the Can Vila catchment in the Spanish Pyrenees mountains. The isotope data covered four years, comprising >550 rainfall and >980 stream water samples. They were complemented by fortnightly plant-water-isotope data sampled over eight months. The isotope data were used to quantify how long it takes for water to become evapotranspiration or discharged as streamflow, using StorAge Selection (SAS) functions. We calibrated the SAS functions using a conventional approach, fitting the model solely to stream water isotope data, as well as a multi-objective calibration approach, in which the model was simultaneously fitted to tree-xylem-water isotope data.

Our results showed that the conventional calibration approach was not able to adequately simulate the observed xylem isotope ratios. However, the SAS model was capable of adequately simulating both observed streamwater and xylem water isotope ratios, if those xylem water isotope observations were used in calibration. This multi-objective-calibration approach led to a more constrained parameter space, facilitating parameter value identification. The model was tested on a segment of data reserved for validation, showing a Kling-Gupta Efficiency of 0.72, compared to the 0.83 observed during in the calibration period.

The water age dynamics inferred from the model calibrated using the conventional approach differed substantially from those inferred from the multi-objective-calibration model. The latter suggested that the water supplying evapotranspiration is much older (median age 150-300 days) than what was suggested by the former (median age 50-200 days). Regardless, the modeling results support recent findings in ecohydrological field studies that highlighted both subsurface heterogeneity of water storage and fluxes and the use of relatively old water by trees. We contextualized the SAS-derived water ages by also using young-water-fraction and endmember-splitting approaches, which respectively also showed the contribution of young water to streamflow was variable but sensitive to runoff rates, and that ET was largely sourced by winter precipitation, that must have resided in the subsurface across seasons.  

How to cite: Sprenger, M., Llorens, P., Gallart, F., Benettin, P., Allen, S., and Latron, J.: A multi-objective parameterization of StorAge Selection functions based on stable isotopes sampled at the catchment outlet and in trees to constrain water age estimations for runoff and evapotranspiration fluxes, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-356, https://doi.org/10.5194/iahs2022-356, 2022.

Streamflow is the major factor influencing the evolution of solute concentration in river water and different modelling approaches exist to characterize the dependency of concentration to discharge: the simplest are based on measurable quantities (stream discharge and stream water concentration) but do not allow for an explicit, physical, flow-path interpretation; the more complex are based on mixing assumptions with different end-members sources, but require the knowledge of (unmeasurable) flow components. We present here an approach allowing to combine the simple concentration-discharge (C-Q) models with the Mass Balance (MB) mixing approach. This combined model tested on high-frequency ionic concentration series from the ORACLE-Orgeval observatory (France), where it clearly outperforms the commonly-used models applied separately. Thanks to the temporal density of the dataset, model performances are tested at different hydrological scales.

How to cite: Tallec, G., Tunqui Neira, J. M., Andréassian, V., and Mouchel, J.-M.: A combined mixing model for high-frequency concentration-discharge relationships, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-658, https://doi.org/10.5194/iahs2022-658, 2022.