Volcanic Arsenic Sources and Seasonal Hydrogeochemistry in the El Salado Basin, Jalisco, Mexico

This study investigates the hydrogeochemical processes that shape groundwater and surface water quality in the El Salado basin, a volcanically influenced region in western Mexico. A total of 36 samples, 19 in spring and 17 in summer, were collected from thermal springs, shallow wells, and surface water bodies to evaluate seasonal variation in water composition. Major ions and physicochemical parameters were analyzed, and principal component analysis was applied to identify dominant geochemical controls. Results indicate that water–rock interaction is the main process influencing solute concentrations, especially in thermal zones linked to the La Primavera volcanic system. Spring waters reflect dilution and carbonate buffering, while summer samples exhibit higher salinity, longer residence times, and increased influence from evaporative concentration and redox-sensitive species. Arsenic levels exceeded 0.05 mg/L in several thermal springs, with geochemical associations suggesting a geological origin related to the dissolution of arsenic-bearing minerals and geothermal fluid input. The findings reveal a clear seasonal reorganization of hydrogeochemical patterns, emphasizing the role of climatic conditions in modulating water chemistry. This study provides a scientific basis for seasonally adaptive monitoring and management strategies in volcanic aquifer systems facing increasing demand for high-quality groundwater.