Conservation of Mojave Desert springs and associated biota: status, threats, and policy opportunities

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.

Influence of Desert Springs on Habitat of Endangered Zuni Bluehead Sucker (Catostomus discobolus yarrowi)

ABSTRACT Located on the southeastern part of the Colorado Plateau, the Zuni Mountains are home to the endangered Zuni Bluehead Sucker (ZBS) (Catostomus discobolus yarrowi). A 4-year study was conducted on a low-flow (<80 cm3/s) hillslope spring and intermittent stream, that are home to one of the three remaining ZBS populations. Seasonal measurements of physical and hydrochemical parameters were used to estimate the contribution of groundwater to the stream and to identify geologic and hydrologic controls for the spring discharge. Seasonal concentrations and standard deviations (s) of Mg2+ were used to determine that the spring water (5.6 mg/L; s = 0.4) and surface water up-gradient from the spring input (10.7 mg/L; s = 11.2) is from different sources. Surface water down-gradient from the spring input maintain ZBS populations and is a mixture of spring water and up-gradient surface water. Mass solution mixing was used to determine spring water contributes up to 99 percent of the down-gradient water during drier seasons. Isotopes (δD, δ18O, 3H) indicate that the spring water has been recharged primarily from snowmelt within the last 70 years, while up-gradient surface water is seasonal runoff from rain and snowmelt. Continuous monitoring of dissolved oxygen (DO) mean concentrations (up-gradient = 1.6 mg/L and down-gradient = 5.7 mg/L) indicated that surface water up-gradient from the spring input are anoxic and unable to support ZBS. Surface water down-gradient from the spring input maintain appropriate DO concentrations due to perennially discharging spring waters re-aerating downstream habitats.