A multi-tracer approach to delineate groundwater dynamics in the Rio Actopan Basin, Veracruz State, Mexico

Pérez Quezadas, Juan; Heilweil, V. M.; Cortés Silva, Alejandra; Araguas, Luis; Salas Ortega, María del Rocío

A multi-tracer approach to delineate groundwater dynamics in the Rio Actopan Basin, Veracruz State, Mexico | Une approche multi-traceurs pour la détermination de la dynamique des eaux souterraines du bassin de la rivière Actopan, Etat de Veracruz, Mexique Un enfoque de trazadores múltiples para delinear la dinámica del agua subterránea en la cuenca del Río Actopan, Estado de Veracruz, México 多重示踪剂方法描述墨西哥韦拉克鲁斯州Rio Actopan流域地下水动力学 Uma abordagem multi-traçadores para delinear a dinâmica das águas subterrâneas na Bacia do Rio Actopan, Estado de Veracruz, México

2016

Pérez Quezadas, Juan | Heilweil, V. M. | Cortés Silva, Alejandra | Araguas, Luis | Salas Ortega, María del Rocío

Geochemistry and environmental tracers were used to understand groundwater resources, recharge processes, and potential sources of contamination in the Rio Actopan Basin, Veracruz State, Mexico. Total dissolved solids are lower in wells and springs located in the basin uplands compared with those closer to the coast, likely associated with rock/water interaction. Geochemical results also indicate some saltwater intrusion near the coast and increased nitrate near urban centers. Stable isotopes show that precipitation is the source of recharge to the groundwater system. Interestingly, some high-elevation springs are more isotopically enriched than average annual precipitation at higher elevations, indicating preferential recharge during the drier but cooler winter months when evapotranspiration is reduced. In contrast, groundwater below 1,200 m elevation is more isotopically depleted than average precipitation, indicating recharge occurring at much higher elevation than the sampling site. Relatively cool recharge temperatures, derived from noble gas measurements at four sites (11–20 °C), also suggest higher elevation recharge. Environmental tracers indicate that groundwater residence time in the basin ranges from 12,000 years to modern. While this large range shows varying groundwater flowpaths and travel times, ages using different tracer methods (¹⁴C, ³H/³He, CFCs) were generally consistent. Comparing multiple tracers such as CFC-12 with CFC-113 indicates piston-flow to some discharge points, yet binary mixing of young and older groundwater at other points. In summary, groundwater within the Rio Actopan Basin watershed is relatively young (Holocene) and the majority of recharge occurs in the basin uplands and moves towards the coast.

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