Abstract
For the adequate protection of karst springs it is important to understand the functioning of karst systems in their recharge areas. Besides tracer tests with artificial tracers, tracings with natural tracers, such as temperature, are a very useful research tool, especially in complex karst systems with various types and sources of recharge. Detailed monitoring of water levels and temperatures of the Malenščica karst spring, as well as of the intermittent Cerknica Lake and Kotliči spring in its recharge area, indicated that temperature is a good tracer in winter and summer periods, especially when the Cerknica karst polje is flooded. High or low air temperatures influence the temperature of water, which sinks at the Cerknica polje and flows rapidly through karst channels toward the springs. Detailed analysis of selected events enabled calculation of the velocity of groundwater flow toward the Malenščica spring under different hydrological conditions. The estimated values are in accordance with the velocities previously defined in this area, based on several tracer tests with artifi cial tracers. From the results, it is possible to assess the transport velocities of contaminants under different hydrological conditions. This is important information for the protection of the Malenščica spring, which is captured for the public water supply.
Highlights
Karst aquifers are very vulnerable to various sources of pollution
High oscillations of water temperature of the Malenščica spring were detected by measurements in the period from June 1999 to December 2001
Propagation of temperature signals through the underground system in the catchment of the Malenščica spring was analysed under different hydrological conditions
Summary
Karst aquifers are very vulnerable to various sources of pollution. To protect them properly, it is important to understand the characteristics of groundwater flow in their recharge areas. It is a parameter that carries information on the hydraulic and thermal conditions in the karst interior (GENTHON et al, 2005). It can be considered as a nonconservative tracer due to the exchanges of temperature between water and rock along the underground flow. When recharge water enters the aquifer system and flows downgradient through the conduits, the initial temperature difference will decrease due to the heat-exchange at the water-rock interface. In complex karst aquifers, significant changes of temperature under a variety of hydrological conditions are a consequence of the inflows of water with different characteristics from various parts of the recharge area
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