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The Untersberg is a heavily karstified massif at the Austrian-German border south of the City of Salzburg. Tracer tests conducted in the 1960s and 1970s showed that large parts of this massif are drained to the Fürstenbrunn spring, the main karst spring in the area. A deep karst flow system was previously postulated below this spring assuming that karst water infiltrates directly into the porous aquifer of the Salzburg Basin (Brandecker, 1974).Here we present results from a hydrological study shedding new light onto the karst water flow system of the Untersberg and the adjacent porous aquifer. We analysed a series of springs at Untersberg as well as a number of wells in the basin. The mean alti- 18tude of the spring's catchments was assessed using a δ O altitude gradient of -0.14 ‰/ 100 m, calculated from precipitation data. A mean residence time of ca. 0.4 yr was obtained for water emerging at the Fürstenbrunn spring. In addition to the highly constant water temperature and electrical conductivity of this spring water, this rather long residence time underscores the unusual behaviour of the Fürstenbrunn spring compared to large karst springs in other karst regions of the Northern Calcareous Alps. Monito- 18ring wells near the Berchtesgadener Ache show the same mean δ O values as the latter and also a very similar pattern throughout the year confirming the infiltration of this river into the porous aquifer. Further towards the basin, rainfall is the dominant source of recharge. Neither physical nor hydrochemical nor stable isotope data point towards karst water infiltration into the porous aquifer. In addition, the data of this study show that large fluctuations of the groundwater body in the basin also occur in winter when the discharge from the Untersberg karst system is very low.Der Untersberg ist ein stark verkarsteter Gebirgsstock an der deutsch-österreichischen Grenze südlich der Stadt Salzburg. Markierungsversuche in den 1960er und 1970er Jahren zeigten, dass die Fürstenbrunner Quelle, die die bedeutendste Karstquelle des Untersberges ist, große Teile dieses Karstmassivs entwässert. Darüber hinaus wurde unterhalb dieser Quelle ein "tiefer Karst" und somit eine Infiltration von Karstwasser in den Porenaquifer des Salzburger Beckens angenommen (Brandecker, 1974

Nowadays, the contamination of groundwater and soils by highly hazardous and toxic chlorinated solvents is a global issue. Over the past years, different remediation strategies have been developed, involving injection of reactive solutions and/or particles. However, a major difficulty is the monitoring of injected particles during the injection and after secondary mobilisation by groundwater flow. This study is focussed on the development of directly traceable particles by combining fluorescein with Layered Double Hydroxides (LDHs). We present here the facile and easily tuneable synthesis of fluorescing LDHs (Fluo-LDH) via co-precipitation under supersaturation conditions. Their ability to mimic particle sizes of previously studied reactive LDHs, which proved to be able to adsorb or degrade chlorinated organic solvents from aqueous solutions, was investigated as well. Tests using a novel Optical Image Profiler (OIP) confirmed that the fluorescent LDHs can be easily detected with this tool. Even LDHs with the lowest amount of fluorescent dye were detectable. Together with the use of an OIP, which is capable of exciting the fluorescent material and collecting real-time pictures, this can provide a new, efficient, and cost-effective method for in situ tracing of injected particles in the subsurface.

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