Quantification of groundwater fluxes and hyporheic exchange in streams and rivers using radon

Benjamin Gilfedder1, Sven Frei1
1 Hydrology, Limnologische Forschungsstation

P 8.5 in Isotope and tracer methods in hydrogeology



A quantitative understanding of groundwater-surface water interactions is vital for sustainable management of water quantity and quality. The noble gas radon-222 (Rn) is becoming increasingly used as a sensitive tracer to quantify groundwater discharge to wetlands, lakes, and rivers: a development driven by technical and methodological advances in Rn measurement. However, quantitative interpretation of these data is not trivial, and the methods used to date are based on the simplest solutions to the mass balance equation. Here we use a new finite element method coupled with the parameter optimisation model PEST to solve the Rn mass-balance to quantify groundwater fluxes to the Rote Main River and the Salzach River. We show how that by using standard methods major errors can be made, but the new method is able to deliver stable groundwater fluxes and hyporheic exchange parameters. This talk will illustrate how Rn can be used as a powerful natural tracer for quantifying groundwater fluxes to streams and rivers.