Review of Research on Plitvice Lakes, Croatia in the Fields of Meteorology, Climatology, Hydrology, Hydrogeochemistry and Physical Limnology

GEOFIZIKA VOL. 35 2018 DOI: 10.15233/gfz.2018.35.9 Review paper Review of research on Plitvice Lakes, Croatia in the fields of meteorology, climatology, hydrology, hydrogeochemistry and physical limnology Zvjezdana Bencetić Klaić 1, Josip Rubinić 2 and Sanja Kapelj 3 1 Department of Geophysics, Faculty of Science, University of Zagreb 2 Faculty of Civil Engineering, University of Rijeka 3 Faculty of Geotehnical Engineering, University of Zagreb Received 16 April 2018, in final form 22 October 2018 In lakes, several physical, chemical, and biological processes occur simultaneously, and these processes are interconnected. Therefore, the investigation of lakes requires a multidisciplinary approach that includes physics (including the physics of the atmosphere, i.e., meteorology), chemistry, geology, hydrogeology, hydrology and biology. Each of these disciplines addresses a lake from a different point of view. However, lake studies that primarily belong to one field, at least to some extent, report their findings in ways that are associated with other fields; this type of reporting is caused by the inherent interconnections between phe- nomena from different disciplines. Plitvice Lakes, Croatia, are composed of a unique cascading chain of karst lakes, and these lakes have been investigated by numerous authors. Here, we provide an overview of the studies of the Plitvice Lakes Area (PLA) that address meteorology, climatology, hydrology, hydrogeochemistry and physical limnology. Our aim is to synthesize the results from each of these disciplines and make them available to scientists from other related disciplines; thus, this review will facilitate further investigations of the PLA within the natural sciences. In addition, valuable results from early investigations of Plitvice Lakes are generally unavailable to the broader scientific com- munity, and are written in Croatian. Here, we summarize these results and make them available to a wider audience. Keywords: catchment, geosciences, hydrodynamics, karst, tufa barriers Contents List of acronyms and abbreviations ............................190 1. Introduction . 191 2. Lake morphometries . 194 3. Meteorology and climatology ...............................200 4. Hydrology ...............................................214 190 Z. B. KLAIĆ ET AL.: REVIEW OF RESEARCH ON PLITVICE LAKES, CROATIA ... 5. Geochemistry of waters, tufa barriers, lake sediments and soils . 225 6. Physical limnology .......................................243 7. Conclusions .............................................261 References ................................................264 Appendix I . 274 Appendix II................................................275 List of acronyms and abbreviations ASL Above Sea Level BTEX Benzene, Toluene, Ethylbenzene and Xylene CFCs Chlorofluorocarbons DIC Dissolved Inorganic Carbon DM Dispersion Model DO Dissolved Oxigen DOC Dissolved Organic Carbon DOM Dissolved Organic Matter E Eastern EM Exponential Model GIS Geographic Information System GPS Global Position System LAS Linear Alkylbenzene Sulphonates LM Linear Model LPMs Lumped Parameter Models LST Local Standard Time MHS Meteorological and Hydrological Service of Croatia MRT Mean Residence Time N Northern NE Northeastern NW Northwestern OM Organic Matter PAHs Polycyclic Aromatic Hydrocarbons PEC Probable Effect Concentration PFM Piston Flow Model PFMDM Piston Flow Model-Dispersion Model PFMEM Piston Flow Model-Exponential Model PLA Plitvice Lakes Area PLNP Plitvice Lakes National Park PIM Particulate Inorganic Matter POM Particulate Organic Matter SE Southeastern S Southern SW Southwestern TSM Total Suspended Matter VSMOW Vienna Standard Mean Ocean Water W Western GEOFIZIKA, VOL. 35, NO. 2, 2018, 189–278 191 1. Introduction In the past, the Plitvice Lakes (in Croatian, Plitvička jezera) were called the Devil’s Garden (Franić, 1910). Known for their beauty and geomorphologic uniqueness associated with the biodynamic processes of tufa formation, the Plitvice Lakes were the first national park established in Croatia,i.e. , the “Plit- vice Lakes National Park” (in Croatian, Nacionalni park Plitvička jezera, hereafter PLNP) was established in 1949. The PLNP extends over 294.82 km2 (UNESCO, 2017), and the total lake surface area corresponds to approximately 1.949 km2 (Babinka, 2008). The total water volume, according to Gavazzi (1919) and Babinka (2008), has been estimated to be approximately 25.87 and 22.95 million cubic meters, respectively. In 1979, the PLNP was added to the United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage register, and it is the only natural site that belongs solely to Croatia1 (UNESCO, 2017). The PLNP is situated in the inland mountainous area of Cro- atia at altitudes between 450 and 1280 m. It is located between the mountains Mala Kapela (1280 m), Lička Plješivica (1640 m) and Medveđak (884 m), i.e., between the latitudes 44°44’34’’ N and 44°57’48’’ N and longitudes 15°27’32’’ E and 15°42’23’’ E (Babinka, 2007; NPPL, 2007). In total, the chain of 16 lakes is approximately 9 km long and is located in a forested karst environment (Fig. 1). At higher altitudes, beech-fir forest is found, while beech forest is dominant in the areas adjacent to the lakes. The lakes de- scend from 637 m above sea level (hereafter ASL) in the south to 475 m ASL in the north (Meaški, 2011), and they are interconnected with cascades and water- falls. They are grouped into 12 Upper Lakes (in Croatian Gornja jezera, lakes 1–12 in Tab. 1) and 4 Lower Lakes (in Croatian Donja jezera, lakes 13–16 in Tab. 1). The highest, southernmost Prošće Lake is fed from the south and west by the Matica River (which is mainly produced by the confluence of the Bijela rijeka and Crna rijeka springs, while additional, smaller inflow originates from Kavga, Pećina, and Ljeskovac sources, and a few weak, intermittent sources) and Sušanj spring, respectively. Downstream of the lakes, below the Sastavci waterfall, the Korana River starts. The Upper Lakes are mostly built on a Triassic low permeable dolomite base that forms a hydrogeological barrier, while the Lower Lakes and the Korana River canyon are on highly permeable upper Cretaceous lime- stone bedrock (Polšak et al., 1967; Polšak, 1969; Velić et al., 1970). At the most upstream portion of the Korana River, the initiation of tufa formation processes 1 In total, 10 sites are associated with Croatia, and the three of them are transboundary (one natural – Primeval Beech Forests of the Carpathians, and two cultural – Stećci Medieval Tombstones Graveyards and Venetian Works of Defence). Among the seven sites belonging solely to Croatia, six are cultural (the Episcopal Complex of Euphrasian Basilica in Poreč, the Cathedral of St. James in Šibenik, the Historic City of Trogir, the Historical Complex of Split with the Palace of Diocletian, Stari Grad Plain in Hvar Island, and the Old City of Dubrovnik), while Plitvice Lakes National Park is the only natural site (UNESCO, 2017). 192 Z. B. KLAIĆ ET AL.: REVIEW OF RESEARCH ON PLITVICE LAKES, CROATIA ... and the establishment of new tufa barriers, i.e., the initiation of the genesis of new lake systems, is found. Moreover, the same portion of the Korana River is characterized by significant underground water loss from the riverbed downstream of the Korana Bridge (Rubinić et al., 2008). One of the most unique and valuable characteristics of Plitvice Lakes is the tufa formation and the consequent creation of barriers that divide the lake chain into individual lakes. The processes involved in the formation, maintenance and growth of tufa barriers (Pevalek2, 1924, 1935, 1938) strongly depend on the frag- ile composition of the physical, chemical and biological conditions in the lakes. This formation process occurs within a very narrow range of water temperatures, under specific chemical conditions of the water flowing over barriers, and under the presence of specific aquatic primary producers (i.e., algae, bacteria and moss). Moreover, it generally depends on the quantity of flowing water and the water velocity (e.g., Pavletić, 1957; Matoničkin and Pavletić, 1960; Kempe and Emeis, 1985; Srdoč et al., 1985; Chafetz et al., 1994; Špoljar et al., 2011). Therefore, this sensitive biodynamic process and the preservation of Plitvice Lakes can easily be endangered by human activity. This threat was recognized long ago by Roglić (1951) and Petrik (1961), who identified possible lake eutrophication due to the development of tourism and the consequent increase in waste production. A few decades later, Böhm (1997) listed a number of already observed negative effects from the intense development of tourism in the area, such as the construction of roads passing through the PLNP. Since this was a main road from the inland area to the coast, it was laden with heavy traffic; consequently, this roadway contributed to the pollution of the PLA, which included lead, nitrogen oxides, and photochemical pollutants. Another problem was the increased construction of new hotels and other buildings, which was accompanied by shortages in drinking water and the lack of a proper sewage system. Simultaneously, the number of tourists was increasing. For example, during the period of 1970-1990, up to 900,000 tourists visited the PLNP each year; furthermore, on Sundays and national holidays during the summer season, the daily number of visitors was as high as 10,000. Moreover, in the last decade, the number of visitors has been even higher.

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