engleski

Enviromental tracer application study at a Dinaric Mountains karst water system, the Gacka River Basin (Croatia)

Karst water systems are notoriously difficult to describe due to their complex subterranean networks ; springs may be fed not only by large reservoirs, but also through fast channels. This requires an analysis of many experimentally accessible quantities together with rather elaborate model calculations. The Gacka River area is an important Croatian karst water system with multiple springs, exposed to a complex mountain-continental climate with Maritime influence. In a combination of isotopic, meteorological and hydrological data we were able to extract quite detailed information. Gacka River has over 20 (partly intermittent) springs, of which the eight most important ones were sampled in this study. Beside the usual quantities as temperature, pH value and electrical conductivity, the sampled waters were analyzed for their 2H, 18O, noble gas, 3H and CFC content The stable isotopes δ2H and δ18O were analyzed at the Stable Isotope Laboratory SILab ; the CFC, 3He and 3H analyses have been performed by the IAEA Vienna. Five out of eight springs have nearly identical delta values indicating that they are connected to the same reservoir. The δ18O values were used to determine the mean catchment altitudes. The stable isotope delta values of all springs are varying in a narrow range although the recharge isotope signal has a time variable oscillation. This dampened stable isotope signal of the karst groundwater demonstrates the good mixing in the aquifer. In addition, it gives a first indication that the mean ground water residence time MRT of most springs is longer than a few years, with only one of the studied springs having a short MRT of about 1 year. Quantitative MRT values for karst springs can be obtained from unsteady state lumped tracer modeling applications.

isotope tracers; noble gas; CFC; karst; Croatia

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