Silenced Springs?

In his right hand, Don Sada clutches a simple kitchen sieve; in his left, he holds a Tupperware container. As I look on, the 58-year-old ecologist from Reno's Desert Research Institute plunges into a thick stand of watercress that obscures the headwaters of Big Springs Creek, an exuberant stream that issues from multiple springs at the southern end of Snake Valley, along the flanks of the Snake Range in east-central Nevada. "Let's see what's here," he says, stooping to part the watercress and drag his sieve through the stream's pebble-strewn bottom. "I've got springsnails," he shouts.

Peering into the container, I see about a dozen dots that appear as animate as baby peppercorns. The dots are snails, so small that the whorls that mark their shells are all but invisible. These diminutive gill-breathers belong to a species -- Pyrgulopsis anguina -- found near the source of just three springs, all of them in Snake Valley.

The snails are part of an ancient assemblage of aquatic organisms found here and in other Great Basin valleys. Fifteen thousand years ago, agile minnows now confined to spring-fed pools and streams swam through the shallows of great lakes and rivers. Springsnails, and the type of habitat they occupy, may have existed here for some 5 to 6 million years, ever since the end of the Miocene, the geological epoch during which Nevada's corrugated basin-and-range began to form. But now many of these little spring dwellers are in trouble, due largely to us, the brash newcomers who, barely two centuries ago, began pushing into the territory west of the 100th meridian.  

Between the late 1800s and the start of the 21st century, Sada says, habitat destruction and the introduction of non-native species caused the extinction of a dozen genetically unique Great Basin fishes along with at least three mollusks. Still other extinctions have been but narrowly averted. Of some 4,000 springs Sada and his colleagues have examined, barely 60 can be considered remotely pristine. The rest have been subjected to unremitting abuse, notably by cattle and wild horses, which have trampled riparian margins, and by ranchers and farmers, who've canalized spring brooks and diverted their water.

"This spring looks pretty healthy," Sada says of Big Springs, "but if you look, you can see it's been disturbed. All those grasses over there are non-native, as is this clover. And over there, it looks like it's been dug out." Not far from Big Springs is Needle Point Spring, which used to spill into a trough and pond used by cattle and wild horses. Its flow faltered in 2001, shortly after nearby wells started withdrawing groundwater for irrigation.

Now, Snake Valley's springs face a new threat: the Southern Nevada Water Authority's controversial plan to pump groundwater from Snake and other remote valleys and ship it south, to the Las Vegas metropolitan area. A decade or so from now, a 285-mile-long pipeline could carry more than 100,000 acre-feet of water south each year -- more than enough to flood a city the size of Las Vegas to the depth of one foot. (See sidebar: Vegas forges ahead with pipeline plan).

In another era, a project this stunning in scale might have been hailed as smart, imaginative, even visionary. But that was before the environmental consequences of extracting large amounts of water from arid Western lands became so apparent. Across the region nowadays, rivers are in trouble, as are many aquifers. In extreme cases, water tables have dropped by several hundred feet, causing streams to dwindle, spring flow to wane, trees and shrubs to wither. Many rural and urban areas now suffer from land subsidence. As groundwater is removed, surrounding sediments can compact and slump, undermining buildings and highways. Parts of the Las Vegas Valley have sunk as much as six feet, and areas in Arizona and California have dropped anywhere from 15 to 30 feet.

This dismal track record casts a long shadow over the planned water diversion and lends credibility to those who question its eventual costs. The concern is further magnified by the size of the planned withdrawal. According to hydrological models submitted to the Nevada state engineer by project opponents, the utility's pumps will likely cause a severe water table drop across a very large area, extending well beyond the targeted valleys. And yet the full picture of the impacts may not emerge for decades, even centuries.

Where springs are concerned, what worries Sada most is the potential for harmful synergy -- the cumulative impact of all the strain being placed on the small, vulnerable ecosystems he has spent the past quarter-century studying.

• Water