Strontium, SO42-/Cl- and Mg2+/Ca2+ ratios as tracers for the evolution of seawater into coastal aquifers:: the example of Castell de Ferro aquifer (SE Spain)

The strontium content and the SO42-/Cl- and Mg2+/Ca2+ ratios were used as natural tracers of the residence time of seawater intrusion into the Castell de Ferro aquifer. Analysis of these parameters indicated the existence of two principal flowpaths in the aquifer. The first flows through the eastern part of the aquifer, through the karstified Castell de Ferro massif; it accommodates a larger and more rapid flow, so that the residence time is shorter, leading to lower SO42+/Cl- ratios, lower Sr2+ content and higher Mg2+/Ca2+ ratios. The second flowpath is in the western sector, and flows exclusively through alluvial deposits; the flow here is slower, particularly that flowing towards the sea. Thus the residence time of the water here will be longer and there is scant flushing of the intruded seawater; this is manifested in the high Sr2+ content, high SO42+/Cl- and low Mg2+/Ca2+ ratios. (C) 2003 Academie des sciences. Published by Elsevier SAS. All rights reserved.