IMPACTS OF REDUCED DISCHARGE ON THE THERMAL HABITAT OF A DESERT SPRING BROOK

Located in southern Nevada’s Moapa Valley National Wildlife Refuge, the springs that form the headwaters of the Muddy River are home to a number of endemic species, including riffle beetles, spring snails, naucorids, and the endangered Moapa Dace. With a growing population nearby in Las Vegas, continued local and regional groundwater development has the potential to reduce discharge to these springs. The impacts of this reduced discharge on the benthic macroinvertebrate (BMI) communities that occupy those spring brooks are poorly understood. Here we describe a spring diversion experiment that was performed in the uppermost reaches of Pederson Springs, the highest springheads on the refuge. Prior to diversions, BMI species present in the springs were collected and enumerated. A fiber-optic distributed temperature sensor cable was then installed in the spring brook, and incremental diversions from the springhead were made to inform a thermal model of the spring brook over a range of discharge rates. The BMI survey was used in conjunction with the full-discharge thermal model to determine the thermal preferences of individual BMI species, and the reduced discharge model was used to examine the impact of lower flows on the availability of various species’ preferred habitats. This work takes a quantitative approach to evaluating the ecological impacts of continued groundwater development.