Identification of the origin of salinization in groundwater using minor ions (Lower Andarax, Southeast Spain)

Abstract

The study of salinization of groundwater in the Detrital Aquifer of the Lower Andarax is highly complex due to the semiarid climate, the presence of evaporites, proximity to the sea and localized geothermal manifestations in the area. The salinization has been characterized by jointly studying the content of various minor ions (B, Br and Li) and a series of ionic relationships (B/Li, SO 4/Cl, Na/Cl, Cl/B). The combined analysis of B and Li enabled the areas with a marked marine influence to be distinguished from those with an evaporite or geothermal influence. Lithium is directly related to water temperature whilst B content increases in more saline areas, since it is associated with the presence of evaporitic and/or marine influences. Bromine analysis enabled the identification of the principal processes that determine the salinity of the water along the coastal zone: the presence of Quaternary marine sediments and present-day marine intrusion. The brackish groundwaters that are related to old raised beaches showed a low Cl/Br ratio. Areas affected by marine intrusion had Cl/Br ratios similar to seawater and higher than in other areas along the coastal zone. At some points on the delta, a mixture of brackish water and recharge water was detected — the recharge water has a sulfate facies, which causes a drop in the Cl/Br ratio and changes the general character of the water in the coastal zone. The coastal zone contains silty-clay intercalations that favor processes of ion exchange, anthropogenic pollution also occurs and together these processes hamper the interpretation of all the processes.