Spatial Distribution of Isotopes in Groundwater of Slovakia * P. P. Povinec 1 , A. ivo 1 , M. RichtÆrikovÆ 1 , R. Breier 1 , …. LœLan 2 , P. K. Aggarwal 3 , L. AraguÆs-AraguÆs 3 1 Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, SK-84248 Bratislava, Slovakia 2 Department of Applied Informatics, Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia 3 Isotope Hydrology Section, International Atomic Energy Agency, A-1400 Vienna, Austria, Povinec@fmph.uniba.sk Abstract: Spatial distribution of 14 C, d 13 C and d 18 O in groundwater found on the territoty of Slovakia is presented for the first time. Preliminary investigations suggest large isotopic heterogeneity, although the data density is still not good enough to draw more precise conclusions. A vertical distribution of 14 C in groundwater of the itný ostrov confirms that the majority of groundwater has 14 C content below 20 pmc, except a small area on the north-west, where we see, at the surface and subsurface (around 500 m), younger waters with 14 C values around 30 pmc. An interesting feature is the existence of old waters with 14 C values below 10 pmc, which are surprisingly seen from the surface down to 200 m water depths. 1. Introduction Isotopes as environmental tracers have been extensively used during the last decades to study the water cycle, to better understand the origin, dynamics and interconnections of the different elements of the hydrologic cycle. It has been possible to study the present day distribution of water isotopes in the atmosphere, in the rain water, river water, groundwater, and then trace the past isotopic compositions affecting many processes, such as atmospheric circulation, rain and snow formation, groundwater formation, ecology and paleoclimatology [1]. Radioactive and stable isotopes have been used to address the key aspects of the water cycle, e.g. the origin, dynamics and interconnections of the different elements of the water cycle [25]. Fortunately, with the development of the IAEAs Global Network of Isotopes in Precip- itation (GNIP) database, it has been possible to use isotopes in hydrological, ecological and climate studies, as input functions have been available for many areas of the world [6]. A lot of isotope data have been collected and several isotope databases have been developed. The GNIP database (www.GNIP.IAEA.org) has provided the key data for the application of iso- topes in hydrology, but also in climatic and ecological studies. Recently this monitoring ac- tivity has been enlarged to isotopes in the total water cycle, and the new isotope database (Isotope Hydrology Information System (ISOHIS; www.ISOHIS.IAEA.org), covering also Acta Physica Universitatis Comenianae Vol. LLI, Number 1&2 (20092010) 143153 * ) Dedicated to Prof. tefan Æro and Assoc. Prof. Martin Chudý, Ing. Rudolf Janík to 75th and 70th anniversaries, respectively.