The use of isotopes for karst water research in the Northern Calcareous Alps

Since 1995, the northern Calcareous Alps at the border between Upper and Lower Austria have been studied intensively by the authors, integrating data on hydrogeology, isotope hydrology and tectonics. The area is dominated by dolomites and limestones which serve as large-scale karst water reservoirs. Monthly analyses of groundwater isotopic compositions (3H, δ2H and δ18O) reveal detailed information on groundwater flow, age, and areas of recharge. In moderately karstified dolomites, springs typically provide low and steady discharge draining a dense pattern of small-scale fissures. The aquifers possess large storage volumes, good retention capacity, long groundwater residence times and reduced effects of rainwater mixing. Springs in karstified limestone or dolomite, on the other hand, typically show highly dynamic hydrographs, short residence times and quick responses to daily rain events. Combining isotope data with information on precipitation and baseflow within a GIS allows to put constraints on size and location of recharge areas. (author)