Volcanic arsenic sources and seasonal hydrogeochemistry in the El Salado Basin, Jalisco, Mexico

This study examines the hydrogeochemical processes that regulate groundwater and surface water quality in the El Salado Basin, a volcanic-geothermal region in western Mexico. Seasonal sampling during spring and summer included thermal springs, wells, and surface waters to evaluate major ions, physicochemical parameters, arsenic, and boron. Piper diagrams, principal component analysis, clustering, and spatial interpolation were applied to identify dominant processes and seasonal patterns. Results show that sodium-bicarbonate facies and elevated As-B concentrations are controlled by geothermal water-rock interaction in zones influenced by the La Primavera Volcanic Field. Seasonal dilution during summer reduces solute concentrations, while redox and evapoconcentration effects modulate trace-element mobility. Interpolation maps demonstrate that arsenic hotspots coincide with geothermal discharge areas. The findings clarify the geogenic origin of arsenic in the basin, reveal how seasonal hydrology reorganizes hydrogeochemical signatures, and provide a methodological framework for interpreting trace-element mobilization in volcanic aquifers.