Flow dynamics in a karst aquifer studied by means of natural and artifiial tracers: a case study of the Malenščica and Unica karst springs

Abstract

The Malenščica and Unica karst springs on the southern edge of Planinsko Polje are recharged from a complex karst system that is characterised by interchange between surface and subsurface flow. For periods of two hydrological years from 2007 to 2009 and one hydrological year from 2013 to 2014, selected physical properties of water (precipitation, water level and discharge, temperature, electrical conductivity -EC) were measured at various sites of the system. Time series data were elaborated using various methods. First, the characteristic values of measured parameters were compared, then an alternative method was employed to evaluate the measurement results using the frequency distribution diagram of long-term EC data sets. The temporal variations of EC in various hydrological conditions were analysed and apparent groundwater flow velocities were assessed on the basis of the time lags between the peaks (maximums) or troughs (minimums) of the EC curves of the sinking streams and springs. The aim of the study was to understand the relationships between different parts of the recharge area and their changing contributions to the springs in various hydrological conditions. The results, which were validated by the findings of previous tracer tests using artificial tracers, indicate that the use of selected natural tracers provides a comprehensive understanding of the functioning of karst aquifers. IzvlečekKraška izvira Malenščica in Unica, na južnem robu Planinskega polja v jugozahodni Sloveniji, se napajata iz obsežnega kraškega vodonosnika, za katerega je značilno prepletanje površinskih in podzemnih tokov. V obdobju dveh hidroloških let od 2007 do 2009 in v obdobju enega hidrološkega leta od 2013 do 2014 smo na različnih mestih znotraj kraškega sistema merjeni izbrani fizikalni parametri (padavine, nivo vode in pretok, temperatura, specifična električna prevodnost -SEP). Časovne serije podatkov smo analizirali z uporabo različnih metod. Najprej smo primerjali karakteristične vrednosti merjenih parametrov, potem smo privzeli alternativni način obdelave rezultatov merjenja z uporabo diagramov frekvenčne porazdelitve dolgotrajnih časovnih serij vrednosti SEP. Analizirali smo časovno spremenljivost vrednosti SEP v različnih hidroloških razmerah in na osnovi določitve časovnih zamikov med vrhovi in doli krivulj SEP za ponikalnice in izvire ocenili navidezne hitrosti toka podzemne vode. Cilj raziskave je bil razumevanje odnosov med različnimi deli zaledja in spreminjanja njihovih deležev pri napajanju izvirov ob različnih hidroloških razmerah. Rezultati, ki so bili primerjani z izsledki predhodno izvedenih sledenj z umetnimi sledili, potrjujejo primernost uporabe izbranih naravnih sledil za izboljšanje razumevanja delovanja kraških vodonosnikov.

Analyzing climate change and surface-subsurface interactions using the Postojna Planina Cave System (Slovenia) as a model system

“…Overall, discharge of the Pivka River is more variable, indicating the buffering effects of the karst system between the insurgence (Pivka River) and resurgence (Unica spring). Other physico-chemical parameters (water temperature and conductivity) provided more insights into the complex nature of this karst aquifer (Petrič 2011;Petrič 2017).…”