Spring hopes eternal. Dr. Don Sada has studied the aquatic ecosystems of more than three hundred Great Basin and Mojave Desert springs in an effort to preserve them for the future. Photo by Laurie Sada

Across the western United States and northern Mexico, thousands of small springs, seeps, and wetlands provide the sole source of moisture in miles of inhospitable desert. Many of these small water sources are virtually unknown, while others have been fully developed for urban use, agriculture, recreation, native wildlife preservation, and even geothermal energy generation. Some of these springs gained notoriety as important waypoints in the American western migration of the nineteenth century. Others, for many millennia, have filled a critical role as the only point of relief in a parched landscape, with the most meager only barely darkening the surface of the ground.

In the past few years, a remarkable story of ecological transformation, adaptation, and survival spanning millions of years has been emerging from these small water holes, crusty seeps, and muddy playas. But it is a tale that is losing chapters as fast as they are being discovered. Within the most arid landscape of North America, scientists have discovered one of the largest collections of aquatic diversity existing anywhere in the world, let alone in a desert. At the same time, scientists are watching this newly revealed diversity disappear at what may be the fastest rate of any ecology on the North American continent.

Imagine, in this arid landscape, a past vast network of connected waterways—giant lakes, freely flowing streams and rivers, and thriving marshes—from the northern Great Basin to the Chihuahuan Desert of northern Mexico. In the Intermountain West, surface waters would be linked from the Owens Valley, along the eastern slope of the Sierra Nevada, south to Death Valley and the Amargosa and Mojave rivers, then on to the southwest and the San Bernardino River, and to the Colorado River in the southeast. Within these interconnected waterways, a few species of snails, known collectively as springsnails, gradually spread their range west from the Colorado River region and south from the Owens Valley to encompass the entire area.

An early success in preserving unique habitats. Jackrabbit Spring is one of about 50 in the Ash Meadows system. The right biodiversity of this area, unexpected for such a harsh setting, was protected by the area's designation as a National Wildlife Refuge in 1984. It is located approximately 90 miles northwest of Las Vegas in the Amargosa Valley of southern Nye County, Nevada. Photo by Don Sada

This watery network, covering different expanses of this region at different times, was the result of periodic wet, or “pluvial” periods in North America’s climate. During the past two million years, these high water stands occurred at roughly 100,000-year intervals, with the lakes and rivers rising for the last time about 13,000 years ago.

Each time the region dried up, the springsnails and other aquatic species were stranded in isolated colonies, surviving only within the sharply defined boundaries of the small springs, seeps, and wetlands. When large lakes and rivers disappeared, the salts and minerals of the local soils, and the geochemistry and geothermal aspects of the surviving aquifers, concentrated their influence on the small, residual ecosystems. As the several springsnail species adapted to the conditions of each inhabitable water source, an inevitable process of divergent evolution began to create the multiple species being discovered continually today.

Limited habitat, critical resource. Only a few feet across, the McNett Ranch Spring in Fish Lake Valley supports a tui chub habitat, one example of an endemic fish population that has managed to coexist with cattle. The srpingsnail population disappeared form this sprong when its outflow was blocked to create a pond. Photo by Don Sada

Dr. Don Sada, an aquatic ecologist in DRI’s Division of Hydrologic Sciences, says, by the broadest definition, there are likely more than 100,000 springs, spring-fed wetlands, and seeps in the Western U.S., many of which have—or once had—unique ecosystems boasting their own unduplicated collections of aquatic species and riparian lifeforms that survived along the fringes.

“Many of these springs and wetlands have disappeared. Others are capped and piped to tanks, small settlements, farms, and ranches, or they have been obliterated by cattle or wild horses, or simply altered by tourists visiting popular rest stops or natural history sites,” Sada says. In other cases, adjacent groundwater development inadvertently diverted or reduced the supporting aquifer until groundwater no longer reached the surface.

As many as there are, according to Sada, “smaller springs have not had much scientific attention, until very recently. It’s only been in the last few years that attention has broadened from work on large springs, and the ecological importance of small springs has been recognized. Until a few years ago, nobody really had a clue that small springs are ecologically important; unfortunately this was after many had been severely altered.”

A prehistoric network of lakes and rivers. Scientists believe cliamte conditions produced large lakes connecte by rivers that allowed early species of springsnails and various fish to spread from Owens lake to the Colorado River.

For the past decade, Sada has been one of the leading scientists involved in an emerging effort to discover and describe the significance of these unique ecosystems. He says there is a growing cooperative effort among federal, state, and local resource managers, land owners, water utilities, and public interest groups, all working together to figure out a method to preserve this disappearing diversity amid conflicting claims and objectives.

While species of fish and amphibians have had the early glamour roles in this story, in fact, the central and most numerous actors are a multitude of virtually microscopic snails, that class of the phylum Mollusca known as gastropods. Not surprisingly, they have been historically overlooked in favor of horses, cows, and other large animals in the Intermountain West whose economic or environmental significance was easy to understand.

The study of snails—malacology—has existed for several hundred years, but, in the past, it almost always focused on species in larger systems. “A few nineteenth century naturalists noted the presence of snails in western desert springs,” says Sada, “but the first serious modern attempt to scientifically define the wealth of snail biodiversity in the Great Basin really did not occur until Dr. Dwight Taylor started his studies in the 1940s.”

Then it was not until the 1980s that Sada, then with the U.S. Fish and Wildlife Service in Nevada, and Dr. Robert Hershler, who is now a zoological curator with the Smithsonian Institution in Washington, D.C., began discovering the amazing “snails’ tale” of widespread adaptation and survival. Their examination of the proliferation of snail species throughout the West—specifically species of springsnails within the family Hydrobiidae—began at Ash Meadows in southern Nevada and now has spread to hundreds, if not thousands, of sites.

They picked a good starting point. Ash Meadows, with about 50 fresh water springs, was already the focus of a major environmental controversy surrounding the endangered Devils Hole pupfish. The area, now a National Wildlife Refuge, has a higher number of endemic (locally originating) species for its given area than any other place in the United States, and is second only to Quatro Cienegas in Cohuilla, Mexico, in all of North America.
“Refuge status is protecting that site,” notes Sada, “but across the West, pressure to develop scarce water resources, plain carelessness or neglect, and simple lack of awareness are rapidly claiming other springsnail habitats.”

But there is a glimmer of hope.

In 1998, six federal land management and resource agencies, along with the Smithsonian Institution and The Nature Conservancy, signed a Memorandum of Understanding to work to conserve the nearly 100 species of springsnails in habitats on federal and Nature Conservancy lands in the Great Basin. The agencies and involved scientists are working to identify threatened habitats and raise the awareness of a broad range of springs stakeholders throughout the West (See Conference sidebar at right).

“The likelihood of losing a great many more of these springsnail species is extremely high,” says Sada. “But finally there’s a genuine awareness beginning to take hold that this biodiversity resource is priceless, both for its endemic species and for the knowledge they hold about the natural history of the West.”

–John Doherty