engleski

Northern Velebit (Croatia) karst hydrological system: results of a preliminary 2H and 18O stable isotope study

Researching the hydrogeological properties of karst systems is very challenging due to their ex- treme heterogeneity. A grey-box approach in karst research combines the results from classical hydrogeological methods with direct observations within the karstic underground, i.e. in the caves. Isotope research has become a widely used method in the investigation of karst systems. The results presented are of a preliminary 2H and 18O stable isotope study of the Northern Vele- bit karst system (Croatia) employing the grey-box approach. Groundwater samples were col- lected during two summer expeditions in deep caves within the karst massif. Monthly precipita- tion samples were also collected (at three locations between approx. 900 m and 1600 m altitude), as well as water samples at some of the most significant springs, i.e. discharge outlets of the system. For a single expedition, the stable isotope composition is almost constant, i.e. the stable isotope measurements are within the measurement error across the complete cave profile. Simi­ lar characteristics across different caves during the same year were also noted. Samples of wa- ter from the springs were taken during base-flow conditions and they have similar isotopic con- tents to the cave water. The results obtained indicate that homogenization of the water already occurs within the subsurface epikarst zone above the sampling locations in the caves, but a fu- ture extended sampling campaign during variable hydrologic conditions is needed to confirm this. The final research goal is to establish a conceptual grey-box model for the functioning of this complex hydrogeological system.

caves, hydrogeology, karst, Northern Velebit, stable isotopes

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