Relative importance of the saturated and the unsaturated zones in the hydrogeological functioning of karst aquifers: The case of Alta Cadena (Southern Spain)

Abstract

Summary From analysis of the hydrodynamic and hydrochemical responses of karst springs, it is possible to know the behaviour of the aquifers they drain. This manuscript aims to contribute to the characterization of infiltration process, and to determine the relative importance of the saturated zone and of the unsaturated zone in the hydrogeological functioning of carbonate aquifers, using natural hydrochemical tracers. Thus, chemical components together with temperature and electrical conductivity (both punctual and continuous records) have been monitored in three springs which drain Alta Cadena carbonate aquifer, Southern Spain. An evaluation of the percentage of the electrical conductivity frequency peaks determined for each of the three springs is linked to the chemical parameters that comprise the conductivity signal. One of these springs responds rapidly to precipitation (conduit flow system), due to the existence of a high degree of karstification in the unsaturated zone and in the saturated zone, both of which play a similar role in the functioning of the spring. Another spring responds to precipitation with small increases in water flow, somewhat lagged, because the aquifer has a low degree of karstification, even in the unsaturated zone, which seems to influence its functioning more strongly than does the saturated zone. The third spring drains a sector of the aquifer with a moderately developed degree of karstification, one that is intermediate between the other two, in which both the unsaturated zone and the saturated zone participate in the functioning of the spring, but with the latter zone having a stronger influence. These three springs show different hydrogeological functioning although they are in similar geological and climatic contexts, which show the heterogeneity of karst media and the importance of an adequate investigation for groundwater management and protection in karst areas.