Comparison of waters and sediments of Kupa River and Rječina River rising under the same mountain range, but belonging to two distant watersheds (North-western Croatia)

This work presents first complementary geochemical and stable isotope investigations of Risnjak Mountain karstic aquifer system in north-western Croatia. This aquifer is an important source of drinking water for both countries Croatia and Slovenia. The two main rivers, namely the Kupa River and the Rjecina River discharge the same mountain range, but belong to two different watersheds. Their springs are only 22 km apart, and located in scarcely populated areas. Kupa flows through limestones and dolomites in National Park Risnjak until it meets its largest tributary Cabranka. Rjecina flows first through flysch and carbonates before it enters the Adriatic Sea. At its lower course it flows through the densely populated town of Rijeka. For effective management of water resources the baseline data were collected. Sediment fraction