ABSTRACT
In the past two decades, the relative abundance of oxygen isotopes had frequently and successfully been used to separate groundwater discharge components in surface water, to determine mean transit times and the topographic height of precipitation and to characterise different types of karst water. The above analyses had been mainly conducted on a longterm basis. In the study presented δ18O had been used to analyse single storm events in the Gallusquelle catchment of the Swabian Alb, SW. Germany, which allowed to distinguish between a fast and a slow spring discharge component. The signal of the relative abundance in spring water after storm events is characterised by a bimodal breakthrough, a short sharp peak, showing the arrival of the fast conduit flow component and a broad peak indicative of the discharge of the slow karst water. Assuming simple mixing, the fast groundwater component can be quantified to range between 5% and 10%, depending on the characteristics of the recharge event. This information is a prerequisite to quantify groundwater recharge for a karst-groundwater flow model. The model takes into account the duality of the flow system, fast conduit flow and slow flow in small fissures by employing a double-continuum approach. The calibrated flow model had been successfully used to model the breakthrough of the isotope signal.
