Groundwater salinization is a major threat to coastal aquifers worldwide, particularly in arid and semi-arid regions subjected to intensive groundwater use. Understanding the behavior of individual coastal aquifer systems is therefore essential to support effective groundwater management. This study evaluates the spatiotemporal salinization patterns of the Costa de Hermosillo aquifer system, located at the coastal margin of the Sonoran Desert, using 357 groundwater samples collected in 2009 and 2016, primarily from the most productive and shallow hydrogeological unit. Multivariate and hydrogeochemical analyses suggest that seawater intrusion is the dominant driver of total dissolved solids and chloride enrichment, strongly linked to long-term overexploitation. Inland, heterogeneous nitrate and sulfate distributions suggest the influence of anthropogenic inputs, including urban wastewater infiltration and irrigation return flow. Temporal comparisons indicate a decrease in nitrate concentrations, likely reflecting improved wastewater treatment, alongside a significant increase in sulfate, which may be associated with enhanced water-rock interaction processes previously linked to irrigation practices. 15% of samples exceed drinking water guideline limits, and 47% exhibit poor irrigation water quality, highlighting potential risks for human consumption, soil salinization, and agricultural productivity. This study provides one of the most comprehensive recent assessments of salinization processes in the Costa de Hermosillo aquifer system and emphasizes the need to reduce groundwater abstraction and strengthen wastewater and irrigation management to prevent further degradation of the aquifer. Because the interpretations are based on major ions and previous studies, future investigations incorporating more sensitive tracers are needed to better constrain the mechanisms responsible for groundwater salinization.
