In the arid West, few disputes generate as much acrimony as a city's thirst for water and environmentalists' desire to protect a pristine watershed. Perhaps nowhere has disagreement on this point been more intense than in the battle over Mono Lake, the unique natural wonder sculpted out of the Sierra Nevada region of California more than 500,000 years ago. For decades, burgeoning Los Angeles has taken fresh water from the streams that feed the saline lake. These diversions have caused the level of the lake to drop to the point where environmentalists believe its unique ecology is threatened.
A report released Tuesday by the National Research Council could have a bearing on the dispute. It warns that a 10- to 20-foot drop in Mono lake's current level would begin to cause noticeable changes in its ecosystem. It also says that a decline of 30 feet or more would make the lake too salty to support populations of brine shrimp and brine flies, adversely affecting millions of birds that feed there.
``There is no question that drops beyond 10 feet are going to have a noticeable negative impact,'' says Duncan Patten, head of the Center for Environmental Studies at Arizona State University. He chaired the National Research Council panel that conducted the study.
Advocates on both sides of the dispute take some solace in the study. Environmentalists contend it confirms their long-held belief that continued diversions from the lake will eventually lead to its ``death,'' while water officials in Los Angeles note that it says the lake is fine at current levels.
The report is the outgrowth of congressional action in 1984 that designated the lake a national scenic area and mandated the National Academy of Sciences to undertake the study. Although the report assesses the environmental impact of different water levels, it sidesteps the political question of whether diversions from the Mono Basin should continue.
Mono Lake has no outlets. This means water can only escape through evaporation, leaving the lake with its peculiar chemistry: more than twice as salty and six times as alkaline as the Pacific Ocean. These waters support a chain of life that begins with microscopic plants, includes brine shrimp and brine flies, and ultimately takes wing with a host of birds. Up to one-quarter of the world's California gulls feed here, as do prodigious populations of ducks and sandpipers. The area is also known for its austere beauty: two volcanic islands, the Mono craters, and numerous ``tufa towers'' - chalky rock formations.
Since 1944 the City of Los Angeles has been drawing water from several streams that feed the lake - drawing down an average of 100,000 acre-feet a year over the past two decades. The water accounts for 17 percent of the city's needs.
The level of the lake has dropped some 40 feet since the diversions began, though in recent years heavy snowmelts in the Sierras have resulted in large influxes of freshwater into the basin.
The report concludes that a lower lake level will have an adverse impact - beyond a certain point. A 10-foot decline, the scientists say, would increase the salinity of the lake to the point where it would affect some algae, which in turn would impact brine fly feeding and the nesting habits of birds. A 20-foot drop would begin to affect shrimp populations, which would threaten the food supplies of some species, primarily gulls and grebes. Lower levels could increase air pollution by exposing more of the lake bed and increasing the ``frequency and severity of dust storms,'' the study says.
But not all the changes would be negative. The scientists found that modest drops of the lake's level would increase the size of the nesting area for some birds.
Environmentalists have at least four lawsuits seeking to prevent the city from drawing down too much water.
``The report really affirms ... that the diversions, if continued, will slowly poison the ecosystem,'' says Martha Davis of the Mono Lake Committee.
City water officials, for their part, are hesitant to commit to maintaining a minimum lake level ``without knowing what alternate sources [of water] are available,'' says Duane Georgeson of the Los Angeles Department of Water and Power.