To those unfamiliar with the desert reaches away from the shores of popular Lake Mead, the fact that there are well over 80 springs and seeps in the Lake Mead National Recreation Area may be the most surprising fact to come out of a recent Desert Research Institute study of the area.
In the parched, rocky landscape of the 1.5-million-acre National Recreation Area along the Nevada-Arizona border, a search for water anywhere away from the banks of the lake or the Colorado River seems to qualify easily as a fool's errand.
Karl Pohlmann, an assistant research hydrologist in DRI's Water Resources Center in Las Vegas, led a project for the National Park Service to determine where, in such a dry setting, the water that supports many of these desert springs originates.
"We expected to find that the regional aquifers--the ground water flow systems originating far outside the recreational area--would be a prominent source," Pohlmann explains. "The most significant and unexpected finding of the study was the existence of so many springs that discharge groundwater from small flow systems. These are systems that receive most or all of their recharge in local drainage basins from local precipitation."
The locally derived springs comprise more than a third of the total counted in the area. Some of the springs are seasonal, and the total amount of water discharged by all of them is much less than the discharge of the major area waterways. These include the Muddy and Virgin rivers which also depend on regional ground water flow, and the Colorado River.
"The amount of water from these small springs may not be great," Pohlmann says,"but it is often the only source of water for a number of small, diverse plant and animal habitats that add a lot to the recreation area. They are critical to the area's natural character."
And it's not just one desert to contend with here. Three of America's four desert ecosystems--the Mojave, the Great Basin, and the Sonoran--come together, each adding distinct character to the area's uniqueness.
According to Pohlmann, the National Park Service has been inventorying the springs in the area for several decades. With the recent population boom in the adjacent Las Vegas Valley--and the accompanying demand for ground water--the service wanted to determine the source of the springs' waters to protect them and the fragile ecosystems they sustain.
Assisted by DRI Water Resources Center colleagues Jenny Chapman and Sam Earman, and David Campagna of the College of William and Mary, Pohlmann applied advanced chemical and geological analytical methods to determine the nature of the origins and pathways of the ground water serving the desert springs.
Pohlmann's methods included scrutiny of stable isotopes of hydrogen and oxygen in the water and analyses of tritium remaining from atmospheric nuclear detonations from the early days of the Nevada Test Site's activities. The region's complex geology, which forces ground water through rock systems that have varying structures, chemistries, and composition, also added clues--such as naturally occurring radioactive residues of uranium-- as well as challenges, to the project.
As the popularity of the Lake Mead National Recreation Area continues to grow along with the local population, the National Park Service's efforts to preserve the desert's natural diversity will be aided by Pohlmann's study.