The Lake Mead National Recreation Area encompasses 1.5 million acres along the Colorado River.

Number, Sources of Springs Surprising in Study of Lake Mead Recreation Area

In the parched, rocky landscape of the 1.5-million-acre Lake Mead 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.

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.

So, to those unfamiliar with the desert reaches away from the shores of the popular lake, the fact that there are well over 80 springs and seeps may be the most surprising fact to come out of a recent DRI study of the area. 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 some of these desert springs originates.

"We expected to find that the regional aquifers--the ground water flow systems originating outside the recreational area--would be a prominent source," Pohlmann explains, "but it was the existence of so many springs entirely or primarily of local origin that is the most significant and unexpected finding of the study."

The locally derived springs comprise more than a third of the total counted in the area. Some of the springs are seasonal, others flow underground part of the year, and the total amount of water produced by all of them is much less than the major area waterways--the Muddy, Virgin, and White rivers--all of which are heavily dependent on regional ground water flow.

Karl Pohlmann at Bridge Springs on the southwest border of the recreation area, showing the marks left by water seeping through a fault in the rock wall. Though the flow is low and intermittent, the spring is essential to the survival of surrounding plant life.

"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."

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 pin down the source of the springs' waters to protect them and the fragile ecosystems they sustain.

Springs in Black Canyon, just below Hoover Dam, are influenced by minerals in the rock through which it passes and by the immense pressure of the water behind the dam.

Assisted by DRI Water Resources Center colleagues Jenny Chapman and Sam Earman, and David J. 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 ranged from scrutiny of water's hydrogen and oxygen components' stable isotopes, to analysis of tritium remaining from atmospheric nuclear detonations from the early days of the Nevada Test Site's activities and naturally occurring radioactive residues of uranium. The region's complex geology, which forces ground water through rock systems that have varying structures, chemistries, and compositions, also added clues, as well as challenges, to the project.

As the popularity of the Lake Mead Recreational Area continues to grow along with the local population, the National Park Service's commitment to preserving the desert's natural diversity will be aided by Pohlmann's study.