engleski

CHARACTERISATION OF THE GACKA RIVER BASIN KARST AQUIFER (CROATIA): HYDROCHEMISTRY, STABLE ISOTOPES AND TRITIUM-BASED MEAN RESIDENCE TIMES

The Gacka River basin aquifer is a highly-developed karst system, located in the Croatian Dinarides. It is mostly composed of permeable Jurassic and Cretaceous carbonate rocks, and clastic sedimentary rocks of Paleogene age. Gacka River provides high quality water for the entire region. About 10 perennial and over 20 seasonal springs are located at 450 to 460 m a.s.l. (above sea level). Three major springs (Pećina, Majerovo and Tonkovića) provide 57 % of the mean annual river flow. Similarities between the average groundwater temperatures as well as between the average specific electrical conductivity values of the springs imply that they are fed from aquifers with similar mean residence times (MRT). The mean δ18O contents of Majerovo, Tonkovića, and Pećina are around -10.1‰, -9.2‰ and - 8.9‰, respectively, revealing differences in the mean recharge area elevations. Compared to the temporal amplitude of the 18O signal of precipitation, the 18O signal variations of the springs are substantially attenuated because the recharges occurring at different times are well mixed within the aquifers. This indicates MRTs of more than just a few years. Serially connected exponential-plug type unsteady lumped-parameter models run on an annual time scale resulted in rather satisfactory matches between the observed and calculated tritium contents for the springs studied. The models revealed similar MRTs (and corresponding reservoir volumes) for Pećina, Tonkovića and Majerovo of 12 years (470 Mm3), 12 years (1190 Mm3), and 12.2 yr (1210 Mm3), respectively. Plug flow conditions dominate in about 90 % of the total aquifer volumes.

Gacka; karst; δ18O; tritium contents; lumped-parameter model; MRTs

nije evidentirano