COBISS 1.01 EFFECTS OF THE VADOSE ZONE ON GROUNDWATER FLOW AND SOLUTE TRANSPORT CHARACTERISTICS IN MOUNTAINOUS KARST AQUIFERS – THE CASE OF THE JAVORNIKI–SNEŽNIK MASSIF (SW SLOVENIA) VPLIVI NEZASIČENE CONE NA ZNAČILNOSTI TOKA PODZEMNE VODE IN PRENOSA TOPNIH SNOVI V GORSKIH KRAŠKIH VODONOSNIKIH - PRIMER JAVORNIŠKO - SNEŽNIŠKEGA MASIVA (JZ SLOVENIJA) Metka PETRIČ1, Janja KOGOVŠEK1 & Nataša RAVBAR1 Abstract UDC 556.34(497.471) Izvleček UDK 556.34(497.471) Metka Petrič, Janja Kogovšek & Nataša Ravbar: Effects of the Metka Petrič, Janja Kogovšek & Nataša Ravbar: Vplivi ne- vadose zone on groundwater flow and solute transport char- zasičene cone na značilnosti toka podzemne vode in prenosa acteristics in mountainous karst aquifers – the case of the Ja- topnih snovi v gorskih kraških vodonosnikih - primer Javor- vorniki–Snežnik massif (SW Slovenia) niško - Snežniškega masiva (JZ Slovenija) Tracer tests are rarely applied in mountainous karst aquifers due Sledilni poskusi sodijo med metode, ki neposredno prikazujejo to difficult or limited basic data acquisition, problems of access značilnosti toka podzemne vode. Zaradi oteženih ali omejenih and expected strong tailing effects in tracer breakthrough. They dostopov do osnovnih podatkov, zahtevnosti terenskega dela in are, however, a straightforward method for learning about the pričakovanega dolgotrajnega podaljšanja pojavljanja sledila se characteristics of underground water flow. The main aim of this sledilni poskusi v gorskih kraških vodonosnikih redko izvajajo. study was to better understand the processes of flow and storage Glavni namen te študije je bil boljše razumevanje procesov toka in the karst aquifer and its unsaturated (vadose) zone, which is in skladiščenja v kraškem vodonosniku in njegovi nezasičeni several hundreds of metres thick. A tracer test was conducted (vadozni) coni, ki je lahko debela več sto metrov. Opravljen je with injection from the surface into a shaft in the central part of bil sledilni poskus v osrednjem delu vodonosnika z injiciran- the aquifer. The results were compared to a previous tracer test jem v brezno. Rezultate smo primerjali s preteklim sledilnim with similar injection characteristics (the same tracer, injection poskusom s podobnimi lastnostmi injiciranja (enako sledilo, into shaft vs karren) but with a significantly different vadose injiciranje v brezno oz. škraplje) toda s precejšnjo razliko v de- zone thickness. For this purpose, direct information obtained belini vadozne cone. V ta namen so bile neposredne informaci- through tracer breakthrough curves analysis was modified in je, pridobljene z analizo sledilne krivulje, spremenjene v skladu accordance with the distance factor, normalised as a function of s faktorjem razdalje, normalizirane kot funkcija količine upo- tracer mass injected, and expressed as a residence time distribu- rabljenega sledila in izražene kot porazdelitev zadrževalnega tion. A conceptual model of flow and transport duality through časa. Izdelan je bil konceptualni model dvojnosti toka in the karst system was elaborated: part of the tracer flows rapidly prenosa topnih snovi skozi kraški sistem: del sledila se pretaka through the primary drainage channels, while the other part hitro skozi primarne drenažne kanale, medtem ko je za del tega is predominantly characterised by prolonged retention in less značilno podaljšano zadrževanje v manj prepustnih območjih. permeable zones. The results obtained support the idea that Dobljeni rezultati podpirajo trditev, da debelina vadozne cone the thickness of the vadose zone has a very strong influence on močno vpliva na zadrževalne čase in disperzijo. Poznejši od- residence times and dispersion. The subsequent outflow of the tok sledila in njegovo zaznavanje sta v veliki meri odvisna od tracer and its detection greatly depend on the meteorological meteoroloških razmer. Naša študija kaže, da je z večjo debe- conditions. Our study suggests that the greater the thickness lino vadozne cone njena zaščitna funkcija večja. Poleg tega je 1 Karst Research Institute ZRC SAZU, Titov trg 2, SI-6230 Postojna, Slovenia and UNESCO Chair on Karst Education, University of Nova Gorica, Glavni trg 8, SI-5271 Vipava, Slovenia, e-mails: [email protected], [email protected], janja.kogovsek@ guest.arnes.si Received/Prejeto: 25.05.2017 ACTA CARSOLOGICA 47/1, 35-51, POSTOJNA 2018 METKA PETRIČ, JANJA KOGOVŠEK & NATAŠA RAVBAR of the vadose zone, the better its protective function. In addi- bila študija pomembna tudi z regionalnega vidika, saj nam je tion, the study was also relevant from the regional perspective, omogočila, da natančneje opredelimo jadransko-črnomorsko in that it enabled us to identify more closely the location of the razvodnico. Adriatic–Black Sea watershed. Ključne besede: kraška hidrogeologija, sledilni poskus, nezasi- Key words: karst hydrogeology, tracer test, unsaturated zone, čena cona, konceptualni model, tok in skladiščenje podzemne conceptual model, groundwater flow and storage, source pro- vode, zaščita vodnih virov. tection. INTRODUCTION Aquifers of mountainous karst and high karst plateaus et al. 2014; Biondić et al. 2016; Fehér et al. 2016; Kaufmann supply manifold ecosystem services such as regional wa- et al. 2017). These studies are very important, since they all ter budgets and freshwater supply, as well as supporting contribute to better understanding of the aquifer’s intrinsic the rich and unique biodiversity of the underground wa- properties, which is a prerequisite for proper interpreta- ter ecosystem. These aquifers, which are also headwater tion and prediction of their behaviour, and for test hypoth- catchments, are increasingly threatened by numerous eses or assumptions. Despite a considerable amount of ba- environmental problems such as global climate change, sic research and theoretical studies, as well as practical case contamination, overuse and environmental degradation. study analyses and test site applications, numerous ques- To better protect and manage mountain karst resources, tions related to the hydrogeological functioning of karst a deepening of knowledge about flow and storage mecha- aquifers, such as infiltration mechanisms, flow and storage nisms is necessary. processes, etc., remain unanswered. The behaviour of high karst plateaus and moun- Tracer tests represent an appropriate technique for tainous karst aquifers is poorly known, especially as re- studying the recharge and transport properties of water gards characteristics of flow in the unsaturated (vadose) and/or contaminants (flow velocities, longitudinal dis- zone (Maloszewski et al. 2002; Mudarra & Andreo 2011; persion, retardation, etc.), and catchment delineation Turk et al. 2015). Such aquifers usually cover an area of (Hauns et al. 2001; Benischke et al. 2007). However, they several tens or hundreds of km2 and have a complex hy- are usually less frequently applied in karst high plateaus drogeological structure. Recharge and subsurface flow and mountains, since they can be costly and long-lasting. mechanisms are conditioned by orography, meteoro- Furthermore, information acquisition is often very dif- logical conditions (i.e., strong snowmelt or precipitation ficult or limited, injection and sampling sites may pres- events), vegetation cover and hydraulic gradients, as well ent difficulties of access, and strong tailing effects in the as by the geological and structural context (Kogovšek & tracer breakthrough may be expected (Massei et al. 2006; Petrič 2004; Becker 2005; Müller et al. 2013). Ground- Kogovšek & Petrič 2014; Lauber & Goldscheider 2014). water flow is often dominated by an unsaturated zone In order to investigate the above scientific and prac- that is several hundreds of metres thick, where extremely tical aspects, and to contribute to better understanding heterogeneous flow and storage processes prevail, often of the behaviour of mountainous karst aquifers, the pres- controlled by geological structure and tectonics (Last- ent study focuses on the hydrogeology of the Javorniki– ennet & Mudry 1997; Simsek et al. 2008; Goldscheider Snežnik karst massif of the Classical Karst in SW Slove- & Neukum 2010; Turk et al. 2013). Flow processes are nia. The main aim of the study was to obtain more infor- highly dependent on respective hydrological conditions mation on groundwater flow within a large karst aquifer causing groundwater fluctuations of several tens of me- and to develop a conceptual model of solute transport tres and variations of flow velocity by several orders of characteristics through the mountainous karst aquifer. magnitude. Consequently, the watershed boundaries and The initial assessment concerns the effects of the prevail- flow directions are variable and often very difficult to- de ing factors on solute transport within the karst system termine (Ravbar et al. 2011; Stevanovic et al. 2016). and flow towards the springs at the aquifer’s margins In recent years, infiltration, flow and transport which represent the erosional base. A further aim was to through karst aquifers has been thoroughly studied using evaluate the protective function of the vadose zone. The various methods and techniques including natural and final aim was to identify the main underground drainage artificial tracers observed at cave drips or at aquifer out- routes and to delineate the main watershed between the lets, and modelling (e.g., Emblanch et al. 2003; Perrin et al. Adriatic and Black Sea basins. An element of more local 2003; Birk et al. 2004; Pronk et al. 2009; Doummar