Isotopic studies on groundwater in the porous formations of the eastern part of the Pannonian depression

The study in question covered the terraced system of aquifers in the north-eastern end of the Pannonian Depression situated in the western part of Romania. A topical arrangement has been used to discuss the results (based on analyses of 3H, 14C, 2H, 18O and 13C), since this kind of arrangement makes it possible to describe the regional situation and to show the specific procedures by which the isotope techniques were applied. As far as meteoric water is concerned, determinations were made of the input signal values and of the variability in the isotopic composition of the water as a function of temperature and altitude. An anomaly in the continental effect was detected in the region. In the case of groundwater, certain aspects were considered: isotopic stratification, regional inter- and intra-system circulation, origin and genesis. In connection with the first aspect, a clear stratification for the first four types of water was established throughout the region. Interesting results were obtained on intra-system circulation with the help of radiocarbon. The analyses made it possible to consider the applicability of the various models under geochemical conditions characterized by penetration of large amounts of CO2. Isochrone maps showed that radiocarbon could satisfactorily reflect the hydrodynamic situation. It was established that groundwater originated from local infiltration, whereas the water of the aquifers of medium depths I and II was recharged at average altitudes of 200 and 500 m. The origin and genesis of deep water are more complex. In origin it is a mixture of two components - meteoric palaeo-infiltration water and syngenetic water -in proportions varying according to the size of the surface. The delta18O-Cl- parabolic correlation revealed genetic changes in certain types of water due to isotopic exchange with the matrix. (author)