Isotopes, Geochemistry, Citizen Science and Local Partnerships as Tools to Build upon a Fractured Understanding of the Hydrology of the Northern Patagonia Mountains

Abstract

The rural Town of Patagonia in Southeastern Arizona is facing uncertainty around the future availability of groundwater resources in the area. This uncertainty is due to extended drought and increased groundwater extraction by the mining industry in the Northern Patagonia Mountains, which are located south of the Town. To address this uncertainty, and advance the hydrologic understanding of the area, this two-phase project was formulated with partner groups working in the Patagonia area. The first phase was analysis of isotope ratios and geochemistry of springs and wells in the Northern Patagonia Mountains to better conceptualize groundwater movement within the mountain's fracture system and determine the hydrologic connectivity between the mountains and the Sonoita Creek alluvial aquifer. The results indicate that major mapped faults within the mountain block, including the Harshaw Creek Fault, appear to be conduits of groundwater movement. The Mountain Front Fault, which separates the mountains from the basin, appears to obstruct groundwater flow, resulting in distinct water chemistry and Pleistocene-aged groundwater in select areas northwest of the fault. Southeast of the fault, most mountain springs and wells produce water recharged from modern precipitation. Fossil water was found within the mountains, however, the quantity of fossil water in the mountains is unknown. Mountain front recharge and focused mountain block recharge via Harshaw Creek partially recharge the Sonoita Creek alluvial aquifer from which the Town of Patagonia pumps for its municipal water source. The results of this research indicate that drought is the primary concern for springs in the study area and the secondary concern is the resultant impact on groundwater flow in stream channel sediments around Harshaw Creek and its tributaries. This improved conceptual understanding of groundwater flow informed the second phase of this research: education on groundwater movement by means of a well owner training and recommendations for monitoring steps. Regular collection of data by the citizen science group or other stakeholder groups working in the area will allow for monitoring of groundwater resources by residents living in the watershed. Monitoring also will contribute to future hydrologic studies within the basin and will aid in making management decisions around water use by the Town Council.