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Suitability of precipitation waters as semi-artificial groundwater tracers
- Binder, Martin, Burghardt, Diana, Engelmann, Christian, Tritschler, Felix, Simon, Elisabeth, Prommer, Henning, Dietrich, Peter, Liedl, Rudolf, Händel, Falk
- Journal of hydrology 2019 pp. 123982
- electrical conductivity, groundwater, hydrogeochemistry, ion exchange, laboratory experimentation, migratory behavior, models, porous media, rain, sediments, snowmelt, stable isotopes, tracer techniques, uncertainty
- In this study the suitability of precipitation waters as semi-artificial and multi-component groundwater tracers is investigated and potential applications as well as limitations are discussed. Specifically, we analyzed their migration behavior during laboratory-scale experiments with groundwater-saturated porous media. Artificially 2H- and 18O-labelled water as well as natural precipitation waters were injected into sediment-packed columns and traced via stable isotope analysis. Their migration behavior was compared to that of widely used tracers. These flow-through experiments were underpinned by a batch reactor study and by hydrogeochemical modeling. While most artificial isotope applications showed a high stability and conservative transport behavior for all tested sediments, the breakthrough curves observed in some experiments with rain and snowmelt were unsteady. This was most likely caused by the small ratio between the tracer’s isotopic difference compared to the background signal and the available analytical precision. The minimum ratio required for effectively reducing uncertainties during data evaluation showed to depend significantly on experimental conditions but should not decrease below ∼10 during peak breakthrough and preferably be higher. Furthermore, our study illustrates that measurements based on using the precipitation waters’ inherent low electrical conductivity can be significantly biased by water-sediment reactions. The batch study and reactive transport simulations confirmed this observation while revealing mineral reactions and, to a minor extent, also ion exchange as the underlying processes.