Characterization of groundwater circulations in a headwater catchment from an analysis of chemical concentrations, Sr-Nd-U isotope ratios, and CFC, SF6 gas tracers (Strengbach CZO, France)
Introduction
The identification of the main water circulation levels in the Critical Zone (CZ) and the determination of the characteristic times of these circulations are among key parameters controlling the CZ functioning and its vertical extension (i.e., Riebe et al., 2017). These parameters also control its future evolution in response to environmental modifications, whether related to global climate change or to human activities of more local impact. This information, in particular, the partitioning between deep and subsurface circulations, is also important to achieve a sustainable management of the world's water resources and to model their future evolution in response to ongoing climate change (e.g., Gleeson et al., 2016; Ameli et al., 2017; Liu et al., 2017; O'Geen et al., 2018; Weill et al., 2019; Ackerer et al., 2020).
Surface and subsurface water circulations, especially in small headwater watersheds, are studied more than deep water circulations occurring in fractured bedrock (e.g., Viville et al., 2012; Brantley et al., 2017). The relatively recent setting up of several tens of meters-deep boreholes on such watersheds, especially those belonging to the so-called Critical Zone Observatories, is now allowing a much better exploration of water circulations and weathering processes in the deeper parts of the CZ (e.g., Brantley et al., 2013; Buss et al., 2013; Chabaux et al., 2017; Hahm et al., 2019; Holbrook et al., 2019; Ranchoux, 2020). These latter studies have systematically evidenced water circulation at great depths in the various explored sites. The hydrogeochemical characteristics of these waters, in particular, their specificity compared to surface waters, should be further clarified to better identify the water-rock interaction processes occurring in the deep CZ and the water circulation residence times in these deep levels.
The purpose of this study, conducted on the Strengbach CZO, France, is to determine the nature and residence time of the various waters circulating in the bedrock of the Strengbach catchment from the surface to ≈100m depth. The Strengbach basin has been the subject of relatively extensive hydrogeochemical studies in the past for surface waters (springs, soil solutions, streams), which today allows us to have a fairly good knowledge of their geochemical composition in major elements as well as Sr, Nd, and U isotopic ratios. These elements and ratios are relevant tracers when we seek to decipher the main water-rock interactions involved in biogeochemical and hydrogeochemical cycles (e.g., Aubert et al., 2001; Riotte and Chabaux, 1999; Tricca et al., 1999; Chabaux et al., 2011, 2013, 2019; Durand et al., 2005; Schaffhauser et al., 2014; Pierret et al., 2014, and references therein). All these data have led us to propose a first order relatively solid interpretative framework on the nature of water-rock interactions controlling the geochemical composition of surface waters in the Strengbach catchment.
In the current study, we propose to establish the hydrogeochemical typology of the deeper waters of the Strengbach CZO by a multi-method geochemical approach that combines the analysis of the above tracers (i.e., major and trace elements, Sr, Nd, and U isotope ratios) with the analysis of anthropogenic gases, namely, chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6). These latter elements are indeed suitable for determining the water ages and/or residence times in aquifers for relatively recent periods, 0–70 years or a little more, depending on the interpretative models used (e.g., Busenberg and Plummer, 1992; Corcho Alvarado et al., 2005; Plummer et al., 1998; Jankovec et al., 2017; De Montety et al., 2018; Cao et al., 2020). In particular, anthropogenic gases were successfully applied to estimate mean water transit time in fractured aquifers (Cook et al., 1996, 2005; Plummer et al., 2000; Bockgard et al., 2004; Ayraud et al., 2008; Jaunat et al., 2012; Roques et al., 2014a, b; Marçais et al., 2018). The results presented here on the Strengbach CZO highlight the interest of combining these different geochemical tracers to explore the hydrological functioning of the deep CZ.
Section snippets
Site presentation
The Strengbach catchment is a small 0.8 km2 granitic catchment in the Vosges mountains (northeastern France) at an altitude ranging between 880 and 1150 m a.s.l. with fairly steep slopes (mean slope of 15°) (Fig. 1). It is an equipped environmental observatory where meteorological, hydrological, and geochemical data have been recorded since 1986 (Observatoire Hydrologique et Géochimique de l’Environnement/Hydrological and Geochemical Environmental Observatory, OHGE; http://ohge.unistra.fr) and
Water sampling procedure
For the present study, 10 sampling campaigns, covering the diversity of hydrological contexts encountered on the catchment, were conducted over the period 05/2015–10/2018 (Fig. 2) for collecting water from springs CS1, CS2, CS3, CS4, RH3, and ARG, piezometers pz3, pz5, and pz7, and deep boreholes F5, F6, F7, and F8. Piezometer and borehole water were sampled with a pump descended to the chosen depth after generally 10 min of pumping, which is the time required to renew the water in the well.
Major element concentrations
Major element data for spring, piezometer, and borehole water analyzed for this study are presented in Supplementary Materials (SM Tables 2a and 2b; 3a, 3b; 4a, 4b).
Discussion
Geochemical data, whether elementary concentrations, 87Sr/86Sr and (234U/238U) ratios, or tracer gases (CFC and SF6), show a systematic distinction between the values measured in spring and piezometer water, on the one hand, and in deep borehole water, on the other hand. These data also show second-order variability between the different piezometers and between the different deep water sampled in the boreholes.
Conclusion
This study presents the water geochemical characteristic of the Strengbach catchment at different depths to bring better constraints of the deep alteration process, which occurs in a small granitic catchment. For this purpose, spring water (i.e., water circulating in the first meter of a saprolite aquifer), water from piezometers (i.e., from 10 to 15 m deep), and deep water (from 50 to 120 m-deep boreholes) were sampled and analyzed under different hydrological conditions (high, intermediate,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This work benefited from fruitful discussions with V. Vergnaud, E. Chatton, G. Schaefer, A. D. Schmitt, S. Rihs, and colleagues from the CANTARE ANR Program, i.e., F. Gal, C. Dezayes, C. Lerouge, and P. Négrel. The study was financially supported by a Ph. D. scholarship awarded to C. Ranchoux by the University of Strasbourg, France. It was also supported by the French ANR Program under grant agreement ANR-15-CE06-0014 (Project CANTARE- Alsace). The drilling and equipment of the Strengbach
References (93)
- et al.
Relationship of present saline fluid with paleomigration of basinal brines at the basement/sediment interface (Southeast basin–France)
Appl. Geochem.
(2011) - et al.
REE fractionation during granite weathering and removal by waters and suspended loads: Sr and Nd isotopic evidence
Geochem. Cosmochim. Acta
(2001) - et al.
Evidence of hydrological control of Sr behavior in stream water (Strengbach catchment, Vosges Mountains, France)
Appl. Geochem.
(2002) - et al.
Compartmentalization of physical and chemical properties in hard-rock aquifers deduced from chemical and groundwater age analyses
Appl. Geochem.
(2008) - et al.
Toward a conceptual model relating chemical reaction fronts to water flow paths in hills
Geomorphology
(2017) - et al.
Solubility of chlorofluorocarbon 113 in water and seawater
Deep-Sea Res.
(1995) - et al.
The solubility of sulfur hexafluoride in water and seawater
Deep-Sea Res. Part I
(2002) - et al.
Heterogeneous behaviour of unconfined Chalk aquifers infer from combination of groundwater residence time, hydrochemistry and hydrodynamic tools
J. Hydrol.
(2020) - et al.
238U-234U-230Th chronometry of Fe- Mn crusts: growth processes and recovery of thorium isotopic ratios of seawater
Geochem. Cosmochim. Acta
(1995) - et al.
Geochemical and isotopic (Sr, U) variations of lake waters in the Ol’khon Region, Siberia, Russia: origin and paleoenvironmental implications
Compt. Rendus Geosci.
(2011)
Regolith formation rate from U-series nuclides: implications from the study of a spheroidal weathering profile in the Rio Icacos watershed (Puerto Rico)
Geochem. Cosmochim. Acta
Groundwater ages in fractured rock aquifers
J. Hydrol.
The practicalities of using CFC and SF6 for groundwater dating and tracing
Appl. Geochem.
U isotope ratios as tracers of groundwater inputs into surface waters: example of the Upper Rhine hydrosystem
Chem. Geol.
Recharge processes and vertical transfer investigated through long-term monitoring of dissolved gases in shallow groundwater
J. Hydrol.
Localization of base cations in particle size fractions of acid forest soils
Geoderma
Mineral evolution in acid forest soils of the Strengbach catchment
Geoderma
Characterization and evolution of dissolved organic matter in acidic forest soil and its impact on the mobility of major and trace elements (case of the Strengbach watershed)
Geochem. Cosmochim. Acta
REE characteristics and Pb, Sr and Nd isotopic compositions of steel plant emissions
Sci. Total Environ.
Atmospheric pollution in an urban environment by tree bark biomonitoring–Part I: trace element analysis
Chemosphere
“Excess air” in groundwater
J. Hydrol.
Degradation rates of CFC-11, CFC-12 and CFC-113 in anoxic shallow aquifers of Araihazar, Bangladesh
J. Contam. Hydrol.
Hydrochemical data and groundwater dating to infer differential flowpaths through weathered profiles of a fractured aquifer
Appl. Geochem.
Evidence for terrigenic SF6 in groundwater from basaltic aquifers, Jeju Island, Korea: implications for groundwater dating
J. Hydrol.
Spectrophotometric Winkler determination of dissolved oxygen: re-examination of critical factors and reliability
Mar. Chem.
Inter-laboratory comparison of the analyses of sulphur hexafluoride (SF6) and three chlorofluorocarbons (CFC-11,-12 and-113) in groundwater and an air standard
Appl. Geochem.
Hydrograph separation using isotopic, chemical and hydrological approaches (Strengbach catchment, France)
J. Hydrol.
Geochemical tracing and hydrogeochemical modelling of water–rock interactions during salinization of alluvial groundwater (Upper Rhine Valley, France)
Appl. Geochem.
Hydrogeochemical modeling (KIRMAT) of spring and deep borehole water compositions in the small granitic Ringelbach catchment (Vosges Mountains, France)
Appl. Geochem.
Determining the turnover time of groundwater systems with the aid of environmental tracers: 1. Models and their applicability
J. Hydrol.
Dating groundwater with dissolved silica and CFC concentrations in crystalline aquifers
Sci. Total Environ.
Coupled hydrogeochemical modelling using KIRMAT to assess water-rock interaction in a saline aquifer in central-eastern Tunisia
Appl. Geochem.
Modeling the impact of temperature on the saturation state and behavior of minerals in the Soultz-sous-Forêts geothermal system
Geothermics
Atmospheric dust contribution to the budget of U-series nuclides in soils from the Mount Cameroon volcano
Chem. Geol.
Flow of river water into a karstic limestone aquifer—2. Dating the young fraction in groundwater mixtures in the Upper Floridan aquifer near Valdosta, Georgia
Appl. Geochem.
Monitoring of geochemical and isotopic (Sr,U) signatures in soil solutions for the evaluation of soil weathering evolution (the Strengbach case)
Chem. Geol.
(234U/238U) activity ratios in freshwaters as tracers of hydrological processes: the Strengbach watershed (Vosges, France)
Geochem. Cosmochim. Acta
Hydrological behavior of a deep sub-vertical fault in crystalline basement and relationships with surrounding reservoirs
J. Hydrol.
Groundwater sources and geochemical processes in a crystalline fault aquifer
J. Hydrol.
Geochemical and isotopic (U, Sr) tracing of water pathways in the granitic Ringelbach catchment (Vosges Mountains, France)
Chem. Geol.
Calcium biogeochemical cycle at the beech tree-soil solution interface from the Strengbach CZO (NE France): insights from stable Ca and radiogenic Sr isotopes
Geochem. Cosmochim. Acta
Evidence of CFC degradation in groundwater under pyrite-oxidizing conditions
J. Hydrol.
Impact of atmospheric deposition, biogeochemical cycling and water–mineral interaction on REE fractionation in acidic surface soils and soil water (the Strengbach case)
Chem. Geol.
Rare earth elements and Sr and Nd isotopic compositions of dissolved and suspended loads from small river systems in the Vosges mountains (France), the river Rhine and groundwater
Chem. Geol.
Erosion and weathering fluxes in granitic basins: the example of the Strengbach catchment (Vosges massif, eastern France)
Catena
Solubilities of chlorofluorocarbons 11 and 12 in water and seawater
Deep-Sea Res.
Cited by (0)
- 1
Present address: HydroSciences Montpellier, Montpellier University, CNRS, IRD, 34000 Montpellier, France.
- 2
Present address: Institut des Géosciences de l'environnement, CNRS, Université Grenoble Alpes, Grenoble INP, IRD, 38000 Grenoble, France.