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.
Highlights
Karst aquifers are very complex systems with heterogeneous structure and various types of porosity
At the Unica karst spring, in the Rak and Pivka cave streams and in the Rak and Pivka rivers, water levels, T and electrical conductivity (EC) were measured using Onset HOBO water level and conductivity data loggers. For both measuring periods all data were collected at 30-minute intervals and the discharges for the Malenščica and Unica springs were calculated on the basis of stage-discharge curves prepared by the Slovenian Environmental Agency
The largest range of values is characteristic for the river Pivka. It is recharged by karst springs with higher EC values, which after precipitation events are significantly lowered by surface streams from flysch areas
Summary
Karst aquifers are very complex systems with heterogeneous structure and various types of porosity. They are characterised by concentrated recharge with sinking streams or diffuse infiltration through karstified terrain. Underground, water flows through karst conduits, fissures and pores of different sizes towards karst springs, where it again flows out onto the surface. Pollutants – the consequence of various human activities in the sensitive karst environment – can spread quickly and represent an increasing threat to the quality of karst springs. Karst aquifers as important sources of water supply are highly vulnerable to pollution. For the efficient planning of protection measures it is essential to understand their functioning and to consider the characteristics of groundwater flow and solute transport within karst systems
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