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Estimating groundwater recharge in arid or semiarid regions can be a difficult and complex task, since it is dependent on a highly variable set of spatial and temporal hydrologic parameters and processes that are dependent on the local climate, the land surface properties, and subsurface characteristics. As a result, traditional methods for estimating the recharge can result in a wide range of derived values. This is evident in the southeastern Mojave Desert, where calculated recharge estimates by previous investigators that range over an order of magnitude (from ~2500 to ~37,000 acre feet per year) are reported. To narrow down this large span of recharge estimates to narrower and more plausible values, this study evaluates the previous recharge estimates in this region, to examine the sources of variability in the reported results and to constrain the recharge estimates based on the hydrologic conditions and the radiocarbon age-dating of spring flows—even without knowledge of the precise subsurface hydrology. The groundwater age and perennial flow characteristics of springs in this study could not be derived from waters sourced solely from local recharge. Therefore, the springs in this study require a significant groundwater contribution to their overall discharge. A previously described conceptual site model in the region established that Bonanza Spring is similarly hydrologically connected to the regional basin-fill aquifer, based on geologic and geochemical/isotopic analyses, and this conceptual site model for where perennial spring water is sourced should readily be extended to these other perennial springs in this region.

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In arid landscapes where fresh water is a limiting resource, the expression of groundwater in springs sustains important landscape functions, globally-recognized biodiversity hotspots, and both aquatic endemic and wide-ranging terrestrial species. Desert springs and associated groundwater dependent ecosystems are threatened by unsustainable groundwater pumping, and the Mojave Desert has seen extinctions of species due to the human use and modification of springs. To support changes in policy and management that would address the vulnerabilities of springs to unsustainable groundwater extraction and other threats, a better understanding of current spring condition is needed. Here we present the results of a comprehensive survey of Mojave Desert springs including hydrological and ecological observations, and an eDNA pilot study. Together, these investigations provide information about the present status of Mojave Desert springs, conservation challenges that they face, and needs that must be met to protect them. We also provide an overview of the current state of federal and state policy that could be used to better manage these critical freshwater resources.

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