Using Water Isotopes and Solute Chemistry to Investigate the Hydrology of Surface Water in the Cienega Creek Watershed

Erin Gray, Rachel Tucci, and Jennifer McIntosh 

Department of Hydrology and Atmospheric Sciences

The University of Arizona

Analysis of water stable isotopes and solute chemistry can reveal the source of water in surface water systems, and the nature of the hydrologic connection between surface water and local and regional groundwater. This research uses water stable isotopes (18O, 2H, 34S, 13C), solute chemistry, and tritium to investigate the seasonal sources of water in wetlands (cienegas), Cienega Creek, and the riparian aquifer within the Las Cienegas National Conservation Area (LCNCA) in the upper Cienega Creek Watershed, an area of unique biodiversity in Southern Arizona. Seasonal samples of streams, springs, and shallow groundwater from piezometers along the length of Cienega Creek were analyzed. Wells tapping into basin groundwater were also sampled. Preliminary results suggest that surface water and water in the shallow alluvial aquifer is a mixture of primarily basin groundwater recharged prior to the 1950’s with a smaller component of more recent recharge. The apparent reliance on basin groundwater implies that surface water in LCNCA could be impacted by changes in the regional water table. This insight, as well as baseline hydrologic data that this research provides, will aid research efforts and help inform groups interested in the preservation of surface water within LCNCA regarding future management decisions.