Isotope Composition of Precipitation, Groundwater, and Surface and Lake Waters from the Plitvice Lakes, Croatia

Ines Krajcar Bronić,Andreja Sironić,Damir Borković,Ivanka Lovrenčić Mikelić,Zoran Kovač,Nada Horvatinčić,Jadranka Barešić

doi:10.3390/w12092414

Abstract

The application of tritium, 2H, and 18O in the characterization of the precipitation, groundwater, and surface and lake water of the Plitvice Lakes (PL), Croatia, over the 1979–2019 period is presented. An increase in the mean annual air temperature of 0.06 °C/year and in the annual precipitation amount of 10 mm/year is observed. The good correlation of the tritium activity concentration in the PL and Zagreb precipitation implies that the tritium data for Zagreb are applicable for the study of the PL area. The best local meteoric water line at PL was obtained by the reduced major axis regression (RMA) and precipitation-weighted ordinary least squares regression (PWLSR) approaches: δ2HPWLSR = (7.97 ± 0.12) δ18O + (13.8 ± 1.3). The higher deuterium excess at PL (14.0 ± 2.2 ‰) than that at Zagreb reflects the higher altitude and influence of the Mediterranean precipitation. The δ2H in precipitation ranges from −132.4‰ to −22.3‰ and δ18O from −18.3 ‰ to −4.1‰. The much narrower ranges in the groundwater (<1‰ in δ18O, <10‰ in δ2H) indicate the good mixing of waters in aquifers and short mean residence times. The higher average δ2H in all three karst springs observed after 2003 can be attributed to the increase in the mean air temperature. The mean δ2H and δ18O values in the surface and lake water increase downstream due to the evaporation of surface waters. There is no significant difference between the surface water line and the lake water line (2011–2014). The stable isotope composition of the surface and lake waters reacts to extreme hydrological conditions.

Highlights

Karst is a special type of landscape that is formed by the process of karstification—i.e., the dissolution of soluble carbonate rocks, mostly limestone and dolomite
The aim of this paper is to present various isotope studies of different types of water bodies from the early period of isotope applications to the most recent one (2018) at the Plitvice Lakes
The aim of the paper is to evaluate the most important hydrological inputs to the Plitvice Lakes, detect the possible influence of climate change on karst groundwater, and eventually show what conclusions could be drawn after a long-term and rather comprehensive study of a certain area by isotopic techniques

Summary

Introduction

Karst is a special type of landscape that is formed by the process of karstification—i.e., the dissolution of soluble carbonate rocks, mostly limestone and dolomite. Conduits, and fissures store relatively large quantities of groundwater, and such karst aquifers are capable of providing large supplies of water for human consumption. The precipitation water quickly infiltrates underground, creating a system of interconnected flow paths, and eventually re-appears at the surface as springs. Especially in areas with a high permeability, can be very vulnerable to contamination and can enable the fast transport of contaminants through the aquifers, which can result in the degradation of water quality [1,2,3,4]. The assessment of the impact of human activities and recent climate changes on karst waters has to be properly considered [5].

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