Since 1960, the Aral Sea in Kazakhstan has lost 90 percent of its volume. Iran’s Lake Urmia has declined even more quickly, shrinking by that amount since 2000. In the United States, the story of Walker Lake in Nevada is similar, though the rate of decline has been slower.
Walker Lake lost 90 percent of its volume beginning roughly a century ago, around the time farmers and cattlemen established communities in Walker Basin. The lake, about 120 kilometers (75 miles) southeast of Reno, is fed from the north by the Walker River and has no natural outlet. Its water comes mostly from spring snowmelt running down from the Sierra Nevada, but much of that water is diverted before it reaches the lake; it is used to irrigate alfalfa fields and pasture grass in the Antelope, Bridgeport, Smith, and Mason valleys.
As the inflow of fresh water has declined, the concentration of dissolved solids (mainly salt) in the lake has increased—from 3 grams per liter in the 1880s to 17 grams per liter now, making the lake about half as salty as seawater. As has been the case with other shrinking salt lakes, a sharp increase in salinity had a major effect on fish and other wildlife. Of the 17 fish species that historically lived in Walker Lake, only 3 were still present in 1979. The Lahontan cutthroat trout is listed as a threatened species and only survives in the lake because of stocking.
Over several decades, Landsat satellites have observed the water level change at Walker Lake. This pair of false-color Landsat images shows it on October 22, 1988, (top) and October 22, 2017 (bottom). The lake sits in a valley between the Wassuk Range to the west and the Gillis Range to the east. Cottonwood, willow, Russian olive, tamarisk, and grasses grow along the banks of the Walker River. Pinyon-juniper forests grow on the eastern slopes of the Wassuk Range.
In a study published in Nature Geoscience, a team of scientists led by Wayne Wurtsbaugh of Utah State University discussed how water managers might respond to save Walker Lake and other declining salt lakes. They calculated that increasing the inflow of fresh water to Walker Lake by 24 percent would decrease salinity levels enough to preserve lake ecosystems and wildlife. Doing the same for Lake Urmia would require an 83 percent increase. In the case of the Aral Sea, water managers proposed saving a small section of the lake—about 5 percent of its former size—to maintain fish populations even as the rest of the basin dries out.
“There is a tendency to invoke ‘climate change’ as the culprit for the decline of saline lakes without fully understanding all of the hydrological balances,” the scientists said. “Climate change—with warmer temperatures, increased evaporation, and altered precipitation—does indeed represent a pervasive long-term problem for saline lakes sustainability, [but] water development (agriculture, mining, and cities) in arid basins generally represents a larger and more immediate challenge.”
NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland.
