The study of hydrodynamic behaviour of a complex karst system under low-flow conditions using natural and artificial tracers (the catchment of the Unica River,SW Slovenia) |
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Authors: | Nata?a Ravbar Juan Antonio Barberá Metka Petri? Janja Kogov?ek Bartolomé Andreo |
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Institution: | (1) Karst Research Institute at ZRC SAZU, Titov Trg 2, 6230 Postojna, Slovenia;(2) Department of Geology, Faculty of Science, Centre of Hydrogeology of University of Malaga (CEHIUMA), University of Malaga, 29071 Malaga, Spain |
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Abstract: | In this study a multi-tracer test with fluorescent tracers was combined with time series analyses of natural tracers to characterize
the dynamics of the solute transport through different recharge pathways and to study hydraulic behaviour of a binary karst
system under low-flow conditions. Fluorescent tracer testing included the introduction of uranine, amidorhodamine G, or naphthionate
at three injection points. Sampling and monitoring took place at two karst springs (Malenščica, Unica) and at two underground
rivers (Pivka, Rak) recharging the Unica River at the Polje of Planina, SW Slovenia. Other monitored parameters included precipitation,
spring or underground river discharge, water temperature, and electrical conductivity. Water samples were collected and analyzed
for total organic carbon, Mg2+, SO4
2−, and NO3
− in the laboratory. In the study area, results of the tracer test suggest that contaminant transport in karst may be retarded
for several weeks during low-flow conditions followed by increases in contaminant concentrations after subsequent rainfall
events. Based on interpretation of tracer concentration breakthrough curves, low apparent dominant flow velocities (i.e.,
between 5.8 and 22.8 m/h through the well developed karst conduits, and 3.6 m/h through the prevailing vadose zone with a
dominant influence of a diffuse recharge) were obtained. Together with analyses of hydro-chemographs the artificial tracing
identified different origins of water recharging the studied aquifer. During prolonged low-water conditions the Malenščica
spring is mainly recharged from the karst aquifer and the Unica spring by the sinking Pivka River. After more intensive rainfall
events allogenic recharge from Cerknica prevails in the Malenščica spring, while the Unica spring drains mainly the allogenic
water from the Pivka Valley. These findings of alternating hydraulic connections and drainage areas due to respective hydrological
conditions are important and should be considered when monitoring water quality, implementing groundwater protection measures,
and optimizing future water exploitation. |
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