Review: Natural tracers in fractured hard-rock aquifers in the Austrian part of the Eastern Alps—previous approaches and future perspectives for hydrogeology in mountain regions

Abstract

Extensive in-depth research is required for the implementation of natural tracer approaches to hydrogeological investigation to be feasible in mountainous regions. This review considers the application of hydrochemical and biotic parameters in mountain regions over the past few decades with particular reference to the Austrian Alps, as an example for alpine-type mountain belts. A brief introduction to Austria's hydrogeological arrangement is given to show the significance of fractured hard-rock aquifers for hydrogeological science as well as for water supply purposes. A literature search showed that research concerning fractured hard-rock aquifers in Austria is clearly underrepresented to date, especially when taking the abundance of this aquifer type and the significance of this topic into consideration. The application of abiotic natural tracers (hydrochemical and isotope parameters) is discussed generally and by means of examples from the Austrian Alps. The potential of biotic tracers (microbiota and meiofauna) is elucidated. It is shown that the meiofauna approach to investigating fractured aquifers has not yet been applied in the reviewed region, nor worldwide. Two examples of new approaches in mountainous fractured aquifers are introduced:(1) use of CO 2 partial pressure and calcite saturation of spring water to reconstruct catchments and flow dynamics (abiotic approach), and, (2) consideration of hard-rock aquifers as habitats to reconstruct aquifer conditions (biotic approach).

Hydrogeologische Herkunft und geothermisches Potenzial der Thermalquellen von Hintertux, Österreich

“…Zur Untersuchung von Grundwasser im alpinen Bereich gibt es klassische hydrogeologische Methoden, die vor allem natürliche Tracer beinhalten (Hilberg 2016;Kilchmann et al 2004). Diese wurden verwendet, um die Herkunft der Thermalquellen im Kontext ihrer klimatischen und geologischen Rahmenbedingungen zu interpretieren.…”

“…6 Sättigungungsindex Calcit-pCO2-Diagramm nach Hilberg (2016) Fig. 6 Saturation Index Calcite-pCO2 diagram after Hilberg (2016) unterhalb der Interaktionsfläche Grundwasser-vadose Zone in den Zentralgneisen zirkuliert sind. Insofern ist der CO2-Partialdruck Indikator für eine ähnliche, hochalpine Höhenlage des Einzugsgebietes, etwa entsprechend der Grierkarquelle.…”

Integration of photogrammetry from unmanned aerial vehicles, field measurements and discrete fracture network modeling to understand groundwater flow in remote settings: test and comparison with geochemical markers in an Alpine catchment

“…The increase of human population has been inevitably affecting water demand worldwide, and concurrent climate change has been changing natural water abundance also in previously unaffected areas (Hilberg 2016). Quantification and management of water resources is thus becoming a critical issue in geological and environmental sciences, and increasing attention is focused on high mountain areas (e.g., Hilberg and Riepler 2016;Idrizovic et al 2020) where fractured aquifers are particularly hard to be investigated (Berkowitz 2002; Voeckler and Allen 2012; Margat and Van der Gun 2013; Welch and Allen 2014; Hilberg and Riepler 2016).…”

“…Indirect methods are valid alternatives to characterize groundwater flow in these settings. These methods include hydrochemistry surveys using natural and artificial tracers found in spring waters (Cervi et al 2012;Hilberg 2016), fracture analysis at outcrop scale (Chesnaux et al 2009;Voeckler and Allen 2012), and remote sensing techniques by means of unmanned aerial vehicles (UAV), to observe lineaments or to directly derive three-dimensional (3D) fracture measurements from virtual outcrops. The latter is of growing interest in environmental geosciences, as it is less time-consuming and more cost-effective.…”

Application of ERT, Saline Tracer and Numerical Studies to Delineate Preferential Paths in Fractured Granites

“…Tracer tests have been extensively used in mapping flow and transport paths of heterogeneous geologic media (Fetter ; Ptak et al ; Hilberg ). Commonly used conservative tracers for groundwater applications include sodium chloride (NaCl), potassium chloride (KCl), and potassium bromide (KBr) in aqueous solutions.…”