AQUIFER DELINEATION FOR GROUNDWATER MANAGEMENT IN A DEVELOPING ARID KARSTIC BASIN: CUATROCIÉNEGAS, COAHUILA, MEXICO

This research uses an integrative approach to delineate recharge pathways to springs in the arid karstic Cuatrociénegas Basin, Coahuila, Mexico, using sparse hydrogeologic data (spring water geochemistry, isotopes, temperature, and discharge), catchments delineated in GIS, surface geophysics, and geologic maps. Springs occur in lines parallel to the Sierra San Marcos, a 2,300-m high Cretaceous carbonate anticline that divides the 1,200 km² valley into west and east sub-basins. Groundwater-dependent ecosystems in this UNESCO Reserve host over 70 endemic species threatened by groundwater pumping in adjacent valleys. Few hydrogeologic data exist and the location and timing of recharge are poorly constrained; this complicates recharge area delineation and groundwater management. Analysis of tritium and stable isotope (²H and ¹⁸O) of the springs suggest older regional groundwater flow predominate with younger local recharge also occurring between 1,500 and 2,300 m – the elevation of mountains surrounding the Cuatrociénegas Basin and throughout the Sierra Madre Oriental of northeast Mexico. The hydrogeologic model is distinct for east and west sub-basin springs. The west sub-basin contains fracture-controlled springs with relatively high and constant discharge, elevated temperatures, and high conductivity. The east sub-basin is comprised of dozens of stratigraphically-controlled small springs adjacent to alluvial fans with lower temperature, lower conductivity, and relatively low discharge affected by precipitation. Noble gas analysis and tritium/helium (³H/³He_trit) age dating of basin-wide springs suggest mountain recharge older than 50 years predominates. The springs discharge from both regional flow systems and local mountain recharge so that management should also be regional extending beyond the Cuatrociénegas Basin. The approach can be applied to similar developing aquifer systems globally with sparse hydrogeologic data.