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Isotope and chemical analyses of water and tufa in the Zrmanja River, Croatia

In this study we present preliminary results of isotope analyses of tufa deposits and chemical analyses of water in the Zrmanja River. The Zrmanja River is 69 km long, located in the Dinaric karst, the NW Dalmatian plateau, and flows into the Adriatic Sea (Novigradsko more Bay). The area is influenced by Mediterranean and continental climate. The Zrmanja River and its tributary the Krupa River are characterized by tufa precipitation in water stream forming tufa bariers. The aim of this study is reconstruction of palaeoenvironment / paleoclimate settings from fresh-water carbonates/tufa and comparison with the similar areas in the Dinaric Karst (Plitvice Lakes, the Krka River). The activities include sampling of water in the Zrmanja River at several locations in all seasons, in situ measurements of water (T, pH, conductivity), separation of dissolved inorganic carbon (DIC) from water, sampling of recent tufa at several locations along the river course and sampling of fossil tufa deposits. The analyses of 13C and 14C age / a14C will be performed for tufa deposits and DIC, and water analyses will include determination of Ca, Mg, bicarbonate and dissolved organic carbon (DOC) concentrations. For the investigation we have chosen 6 points for water sampling along the water course from spring to town Obrovac, 50 km downstream. Calculated saturation index of CaCO3 based on measured parameters showed good conditions for tufa precipitation in the most part of Zrmanja River. Radiocarbon activity of DIC (a14CDIC) measured from the Zrmanja River spring downstream showed slight increase from 80 to 90 pMC. 14C age of old tufa barrier Gazin Kuk showed the age from 2600 to 5600 yr BP (age not corrected for hard water effect). The results of tufa and water analyses will be used for determination of the conditions for tufa precipitation in the Zrmanja River ; determination of time period of tufa precipitation ; comparison of 14C and U-Th ages of tufa ; determination of initial 14C activity of tufa in the Zrmanja River area. The work was performed within the project 1623 "Reconstruction of the Quaternary environment in Croatia using isotope methods" financed by the Croatian Science Foundation for period 2014 – 2018.

14C; 13C Isotope; water; tufa; Zrmanja River

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