Hydrogeological functioning of a karst aquifer deduced from hydrochemical components and natural organic tracers present in spring waters. The case of Yedra Spring (Southern Spain)

Abstract

The major chemical parameters, TOC and natural fluorescence of Yedra spring, Malaga province, southern Spain were moni­tored from April 2008 to March2009. The electrical conductiv­ity and the concentrations of most major ions decreased follow­ing recharge periods. The TOC and NO3–, representing tracers from the soil that infiltrate throughthe unsaturated zone, were found to vary inversely withthe Mg2+ content, whichis a natu­ral indicator of groundwater residence time. Furthermore, a strong, direct relation was found between TOC and the natu­ral fluorescence associated withhumic and fulvic acids. Bothparameters respond similarly to rainfall events, exhibiting sig­nificant increases during recharge followed by reductions dur­ing recession. This relation means that TOC mainly originates from organic acids. The results document rapid infiltration pro­cesses witha lag of less than one day following rainfall, whichis typical of a karst aquifer withconduit flow, rapid drainage and limited natural regulation. The combined use of conventional hydrochemical parameters and natural organic tracers facili­tates aquifer characterization and validates the vulnerability to contamination.