Stable isotopes as indicators of saline intrusion in the aquifer Valle de Boca Abierta, Sonora, México

Abstract

The seawater intrusion problem began to occur in coastal areas where there is a high demand for groundwater. In Mexico this problem is present in 18 aquifers, mainly in northwest area. In the State of Sonora, the aquifers of “Costa de Hermosillo”, “Valle de Guaymas”, “Caborca”, and “Mesa Arenosa de San Luis” present irreversible damage due to excessive extraction. Today the water isotopes are useful to understand characteristics of aquifers. The use of isotopes allows it to perform timely analysis for future estimated behaviors. The present study was conducted in the Boca Abierta Valley aquifer which is adjacent to the “Valle de Guaymas” aquifer. It was taken 25 water samples, which were collected in 18 agricultural wells, 6 drinking water wells and 1 directly from the sea. Physical-chemistry analysis, (electrical conductivity, pH, solids, sulphates, chlorides, calcium, magnesium and potassium) were performed. Laser spectroscopy was used for the analysis of stable isotopes, (oxygen-18 and deuterium). Ionic relations derived from physicchemical analysis support the isotopic information, reflecting the behavior of the aquifer. Therefore, the isotopic enrichment is caused by high levels of evaporation, due to location and the climate of semi-desert conditions providing an isotopic fractionating, as it is the case of well 147, rich in isotopes, but does not appear with saline intrusion problems in the physical-chemistry relationships. However, the 133 presents clear issues of salinity, closely related to the degree of seawater intrusion.