Informing future management decisions by comparison of the largest freshwater spring in the southeastern Mojave Desert with groundwater quality from downgradient wells, Mojave Trails National Monument, USA

Abstract Springs are one of the most vital components of desert ecosystems and an essential element in the cultural traditions and heritage of indigenous peoples. Bonanza Spring on the flank of the Clipper Mountains is the largest freshwater spring in the Eastern Mojave Desert, California, USA and lies in the Mojave Trails National Monument. Like many isolated springs in the arid southwestern United States, it can be vulnerable to changes in climate, vegetative changes (particularly those associated with the encroachment of non-native species), and lowering of local piezometric surfaces due to groundwater extraction and pumping wells. There are proposals to export groundwater from this area to urban and suburban areas in southern California, making the potential relationship and hydrogeologic connectivity between Bonanza Spring and agricultural (Cadiz) irrigation wells a resource management concern. In this study, the similarity or dissimilarity of the chemistry and physical properties of groundwater issuing from Bonanza Spring versus Cadiz agricultural wells in the lower Fenner Watershed and Bristol/Cadiz Basin, located over 22 km (13.7 miles) to the southwest and approximately 400 m (1,315 feet) lower in elevation, is considered through a series of concurrent sampling and analysis of groundwater chemistry and isotopic content. Specifically, spring and well water in the Cadiz agricultural area were sampled and analyzed for over a year’s time, also involving evaluation of aqueous physical properties and related biological attributes in the spring ecosystem. Dissimilarities in water quality were found between spring and well waters, suggesting no or poor hydraulic connection between the two.