Mono Basin lies in east central California, directly east of Yosemite National Park. It is a shallow depression surrounded by the Sierra Nevada on its west, volcanic uplands on its north and east, and a chain of young explosive volcanoes, the Mono Craters, on its south. It lies at an elevation of around 6,381 feet and is roughly 25 miles wide. The bottom of Mono Basin is occupied by Mono Lake.
From the sedimentary record Mono Lake is estimated to be at least 730,000 years old, and therefore one of the oldest bodies of water in North America. It stretches 13 miles east to west by eight miles north to south. In the geologically recent past, volcanoes erupted in Mono Lake's waters to form several islands. The largest island, Paoha, came into existence less than 325 years ago. Most of Paoha is covered by light-colored lakebottom sediments thrust above the surface as lava rose and spread beneath Mono Lake. The second largest island, Negit, has a more complex history, dating back approximately 1,700 years.
The lake level is maintained by five major streams draining the eastern Sierra Nevada mountain range. In 1941, the Los Angeles Department of Water and Power began diverting Lee Vining Creek, Walker Creek, Parker Creek and Rush Creek to meet the growing water demand in LA. In this work, the effects of the diversions of these four tributaries to Mono Lake on the Mono Basin ecosystem will be discussed. In 1990 the LADWP was ordered to limit these diversions. How this was achieved and how well the ecosystem recovers is also a part of this work.
2. Extent of the diversions
The Los Angeles Department of Water and Power (LADWP) began exporting water from the Mono Basin in 1941. By 1970, diversions from Mono Lake's tributaries were close to total. From the mid 1970s until the 1990 preliminary lake level injunction, exports averaged 83,000 acre-feet per year.
In 1941, before the diversions, the lake s volume was 4.3 million acre-feet at 6,417 feet above sea level, and its surface area was 55,180 acres. The current (May 8, 1997) lake level is 6,382 feet above sea level, its volume is 2.5 million acre feet, and its surface area is 44,000 acres. About 10,000 acres of lakebed are exposed.
3. Effects of the diversions
3.1 Changes in Mono Lake s salinity Mono Lake is a perennial, closed lake. Because it has no water outlet, the salts and minerals brought in by the Sierra streams collect in the lake water. Mono Lake contains mainly dissolved carbonates, sulfates and chlorides. They are concentrated as fresh water evaporates, rendering the lake hypersaline. In 1913 the salinity was 42 g/l. After the diversions the lake s volume almost halved, and the salinity almost doubled. In 1991 a salinity of 97 g/l was measured. The current value is approximately 82 g/l.
A result of the hypersalinity in the lake is the formation of tufa, a mineral formations that grace Mono Lake's shores. They were formed by calcium-bearing springs bubbling up through the lake s carbonated waters. Calcium and carbonate combined to form a solid and precipitate out of solution as tufa. As the lake waters receded, these tufa emerged and became exposed.
3.2 Brine shrimp threatened Few species live in Mono Lake. The unusual water chemistry precludes fish and most other aquatic organisms from surviving there. One species that is abundantly present in Mono Lake is the brine shrimp (Artemia monica). At peak densities, over 55,000 brine shrimp crowd a cubic yard of lake water; the overall population exceeds four trillion individuals and weighs over six million pounds dry weight.
Mono Lake's brine shrimp do not exist anywhere else on Earth. They have adapted over time to the peculiar chemistry of Mono Lake. They are unique among brine shrimp in that they produce encysted diapause embryos that sink to the lake bottom where they overwinter. These cysts were estimated to reach critical hydratation at a salinity between 140 and 160 g/l. Researchers concluded that Artemia monica would cease to exist within this salinity range and doubted that it could hatch beyond this limit, which is imposed by the requirement of metabolic processes for minimal amounts of cellular water.
As water diversions to Los Angeles caused the lake's salinity to increase, the brine shrimp population was adversely impacted. Decreasing shrimp population affected the algae growth in the lake. Usually, by June the brine shrimp have grazed away the algae, improving the visibility from two to three feet in winter, to a tenfold in summer. With less shrimp grazing them, the algae bloom and can complete cover the lake surface.
The beginning disappearance of the brine shrimp also impacted the birds, that feed on them. The abundance of shrimp used to attract millions of birds. In most lakes, fish predation keeps the numbers of invertebrates to relatively low levels. In Mono Lake however, shrimp productivity was high and the absence of fish assured the birds easy and plentiful meals. As the shrimp population decreased, so the bird population decreased.
The Fish and Wildlife Service was petitioned in 1987 to list the Mono Lake brine shrimp as endangered. In 1994 however, the Service determined that the established lake conditions should provide adequate protection for the long-term existence of the Mono Lake brine shrimp, leading to the finding that listing as a threatened or endangered species is not warranted.
3.3 Bird s nesting and resting sites threatened Nearly one hundred species of waterbirds visit Mono Lake's shores and islands. Nesting birds consist of California Gulls (50,000, just over 80% of California's breeding population and second largest colony in the world after the Great Salt Lake in Utah) and Snowy Plovers (400, 11% of the state's breeding population). Migratory birds include Eared Grebes (750,000+, 30% of the North American population), Wilson's Phalaropes (80,000, 10% of the world population), Red-necked Phalaropes (60,000, 2-3% of the world population), and 79 other species of waterbirds.
Mono Lake has been designated an international shorebird reserve. With its surrounding wetlands and its tributary streams, it serves as a critical migratory stop in the arid interior of western North America. Birds pause here for days or weeks, fattening on the abundance of brine shrimp and flies in preparation for the long flight to come. Few alternative sites remain for hungry waterbirds. Most of the major wetlands on their long migrations along the Pacific's interior flyway have already disappeared.
The diversions and dropping lake level not only impacted the bird s major food source, it also impacted the freshwater streams and wetlands, as will be discussed next. Furthermore, the islands, previously important nesting sites, became peninsulas. Coyotes, raccoons, and other mainland predators found their way over the landbridge to chase the birds and feed on their eggs. It is estimated that today ducks and geese arrive in numbers less than 1% that of pre-diversion times.
3.4 Desiccation of Mono Lake's tributary streams The pre-diversion streams maintained aquatic and riparian habitats of unique and rich complexity that supported self-sustaining, productive fisheries.
The Rush Creek bottomlands were the premier fishery in the Mono Basin, producing brown trout weighing 3/4 to 2 pounds fairly consistently . The bottomlands were characterized by a wide dense riparian corridor, wooded marshlands, wet meadows, ponded water, abundant springs and a system of narrow steep-sided, low gradient channels. The spring systems and the natural high water table supported dense stands of riparian vegetation and provided lush watercress beds that produced important trout foods. The Rush and Lee Vining Creek deltas also had important meadow, marsh and wetland habitats for waterfowl.
The water diversions by the LADWP caused the desiccation of the streamside forests leaving the stream banks highly vulnerable to erosion. In years when snowmelt runoff was greater than the diversion and storage capacity of aqueduct system, large sudden flood flows were released down the creeks. These flood flows, in conjunction with the lowering of Mono Lake, resulted in major incision tributary deltas and groundwater tables and left former side channels stranded above the newly incised main stream channels. Thousands of tons of floodplain sediments were washed into Mono Lake. The erosion resulted in a shifting, widening and straightening of the primary channels, reduced flows and the widening of the channels eliminated overbank flooding which, in turn, reduced the vigor of riparian vegetation and wetlands.
The loss of the riparian community had serious impacts on the fishery of Rush and Lee Vining Creeks. A total of 204.4 acres of mature riparian vegetation had been lost on the four streams by 1989. Losses of over 100 acres of meadow and wetland acreage had also occurred.
The adverse impacts of these floods events were in direct contrast to the effects of flood flows prior to diversions. Formerly, the well-vegetated floodplain surface would trap sediments when flood waters flowed over channel banks, spreading seeds, moisture and bank-building soils. The riparian systems had been built and maintained by flooding.
3.5 Air quality grown poor The exposed part of the lakebed is composed of a mixture of sulfate-rich evaporite salts, clastic sediments and volcaniclastic materials, and is enriched in arsenic deposited by sublacrustine hydrothermal activity.
Several researchers have documented and quantified the nature, extent, and environmental impact of dust storms derived from the exposed playa of Mono Lake. When no dust was observed (about 9 days in 10), the air at Mono Lake was among the cleanest air in California. On days during which dust was observed, the 24-h mean values of suspended dust averaged 580 g/m3, almost six times greater than the then-California state standard for total suspended particulates. Essentially all of the dust consisted of playa materials. The dust events violate the California air quality standards for sulfates, and contain enough arsenic to cause an increased cancer risk in humans. Almost all Mono Lake dust particles are of a size of about 11 m or smaller, and are therefore capable of causing irritation to the human respiratory tract.
It is thought that deposition of alkaline dust from the Mono Basin has the potential to eventually change the soil chemistry and structure of vegetation communities in areas downwind of the playa.
4. Litigation and Legislation Chronology
Citizens living around Mono Lake got concerned about the degradation of the Mono Basin ecosystems and their effects on human health. They united themselves in 1978 in the Mono Lake Committee, a non-profit group dedicated to protecting and restoring the Mono Basin Ecosystem; educating the public about Mono Lake and the impacts on the environment of excessive water use; and promoting cooperative solutions that protect Mono Lake and meet real water needs without transferring environmental problems to other areas.
Over the years the Mono Lake Committee, working with several other organizations, has pursued litigation which can be divided into two broad categories:
1. The protection of Mono Lake through the enforcement of the Public Trust Doctrine. This ancient legal doctrine protects navigable bodies of water for the use and benefit of all the people. In a 1983 precedent-setting decision, the California Supreme Court ruled that the state has an obligation to protect places such as Mono Lake as far as feasible , even if this means a reconsideration of past water allocation decisions.
2. The protection of fisheries in the streams tributary to Mono Lake through the enforcement of California Fish and Game codes. These codes, which can be described as a legislative expression of the Public Trust, were previously unenforced. Section 5937 states: the owner of any dam shall allow sufficient water at all times to pass over, around, or through the dam, to keep in good condition any fish that may be planted or exist below the dam . Section 5946 states: no...license to appropriate water (in portions of Mono and Inyo counties) shall be issued...unless conditioned upon full compliance with section 5937 .
These legal principles are the basis of the landmark September 28, 1994 decision made by the State Water Resources Control Board (SWRCB), in which the LADWP's water licenses were amended. In the decision, the state had to comply with Fish and Game code requirements for Mono Lake's tributary streams, and, on top of the water needed to protect the fisheries, ensure that the lake's public trust values (such as air quality, scenic and wildlife values) were protected.
The following is a brief history of the Mono Lake litigation. 1984: the court issued a temporary restraining order requiring the LADWP to release 19 cfs into lower Rush Creek. 1989: the court granted a preliminary injunction for a period of one year to halt the lake's decline and stabilize the level of Mono Lake at 6,377 feet above sea level. At the request of the SWRCB, the court stayed the Mono Lake litigation for four years to allow the SWRCB to conduct an Environmental Impact Report and subsequent hearing to recondition the LADWP's water rights licenses to comply with the Public Trust Doctrine and the Fish and Game codes. 1990: the court set interim flows for Rush, Lee Vining, Parker, and Walker creeks and ordered the LADWP to help re-establish the conditions that benefited the fisheries prior to 1941 . 1991: the court renewed the preliminary injunction which required that Mono Lake be maintained at an elevation of 6,377 feet until the completion of the SWRCB process to amend the LADWP licenses and until all legal appeals of that decision are exhausted.
September 28, 1994: the SWRCB issued its landmark decision D-1631 amending the LADWP's water diversion licenses in the Mono Basin. D-1631 calls for a lake level of 6392 feet, which is estimated to take about 20 years to achieve. During this period, some diversions will be allowed to Los Angeles. Once the lake reaches 6392 feet, the LADWP will be able to divert, on average, 31,000 acre-feet of water, or about one third of LA s historical diversion from the Mono Basin. D-1631 also orders the LADWP to develop plans to restore waterfowl and stream habitat damaged as a result of diversions, and to pay implementation costs associated with the restoration.
Minimum flows and maintenance flows are spelled out for all of the diverted streams. The minimums are based on a wet/normal/dry year classification and are lower from October through March. These minimum flows range from 25 cfs to 54 cfs for Lee Vining Creek, from 4.5 to 6 cfs for Walker Creek, from 6 to 9 cfs for Parker Creek, and from 31 to 68 cfs for Rush Creek.
The yearly average export from the Mono Basin depends on the level of Mono Lake on April 1. Below 6,377, no diversions are allowed. Between 6,377 and 6,380, diversion of 4,500 acre-feet is allowed. Between 6,380 and 6,391, diversion of 16,000 acre-feet is allowed.
Once the lake reaches 6,391, a new set of restrictions applies. No diversions are allowed if the lake drops below 6,388. Diversion of 10,000 acre-feet is allowed when the lake is between 6,388 and 6,391. All water (estimated to be on average 37,000 acre-feet) in excess of required stream flows (89,000 acre-feet) is allowed to be diverted when Mono Lake is above 6,391. If the lake has not reached 6,392 by the year 2014, the State Water Resources Control Board will re-examine the situation.
The target lake level of 6392 feet, (which is still 25 feet below its pre-diversion elevation) is thought to incorporate an adequate buffer to protect the brine shrimp and other components of the ecosystem from extreme salinity during prolonged drought. The islands will be surrounded by plenty of protective water, and the dust storms should be reduced to acceptable levels.
5. Completed restoration
The restoration of Mono Basin streams began in 1984 with the establishment of court-ordered temporary flows in Rush Creek. Lee Vining Creek got rewatered in 1986 and Walker and Parker Creeks in 1990. Since September 1994, Rush, Lee Vining, Walker and Parker creeks have permanent water flows and restoration of the streams' fisheries and riparian ecosystems has started.
On Walker and Parker creeks, portions of channels obliterated by years of diversions and grazing were restored through rewatering, elimination of grazing and a combination of hand labor and the use of heavy equipment. Grass sod that filled the channels was lifted out to reveal the native spawning gravels. The recovery of meadow-lined deep channels has been extensive but a few issues remain, such as fish passage and the by-pass of sediments at the diversion dams, the rewatering of distributary channels and the stabilization of stream banks disturbed by a gravel quarry at the mouth of Parker Creek.
On Lee Vining Creek, several historic channels have been reopened and rewatered, providing fish habitat and recharging the groundwater table so that riparian vegetation can become reestablished across portions of the former floodplain. Willow, cottonwood, and Jeffrey pine seedlings have been planted generally in areas too removed from the stream channels to be regenerated naturally. Livestock grazing was excluded from the riparian corridor to promote vegetative recovery. A stream bed topography of pools and cobble bars have been defined in sections of channels that have lost former complexity.
The SWRCB ordered a continuation of the above kinds of measures plus the construction of a sediment by-pass system at the diversion dam. Most likely there will be an emphasis on the promotion of the recovery of the riparian forest across the floodplain.
6. Remote sensing of Mono Lake
Mono Lake and its islands can easily be recognized on MSS satellite pictures. The USGS has a whole series of Landsat images on the web, from 1972 to 1992. The coordinates for Mono Lake on the search page are path 42 and row 34 (Landsat 4 &5) or path 45 and row 34 (Landsat 1, 2, 3).
Quantitative analysis of these images is difficult, since no information on scales or distortion corrections are given, so they might differ for the different images. Also, when reading the color satellite pictures with NIH image, they are converted to a black and white image, destroying much of the contrast, so the lake borders are not easily distinguishable anymore. However, qualitative analysis is still possible. On the images, the growing of the islands and the appearance of a landbridge in the late 80 s is clearly visible. The picture shown on the next page is taken in September 1992, and corresponds to bands 1, 2 and 4.
7. Conclusions
Because of its high salinity and alkalinity, Mono Lake, is thought to be a relatively simple ecosystem. It has become the focus of an environmental controversy over the effects of 50 years of diversions of water from tributary streams to supply water to Los Angeles.
The ecological consequences of changes in lake level and salinity associated with continuing diversions are noticeable. Diversions lowered the lake level, increased the salinity, decreased the air quality, changed the availability of aquatic habitats, and altered the configuration of the shoreline and of islands that support breeding colonies of gulls.
These obvious impacts on the Mono Basin ecosystem and human health did not influence the Los Angeles Department of Water and Energy though. They had acquired the water rights and were not willing to give them up without a fight, even if this meant destroying the animal life in and around the lake. The fight came when concerned Mono Basin citizens created the Mono Lake Committee, which took the LADWP to court. After years of court battles, the Mono Lake Committee achieved an amendment of the LADWP water rights for all the tributaries. Meanwhile, the LADWP has received large funds to look for alternative means of water supply.
Hopefully, the lessons learned from Mono Lake will lead them to choose a more environmental friendly way to meet the water demands, like water re-use. Also, efforts could be made to reduce the amount of water spend in Los Angeles, since studies show that a relatively large percentage is simply wasted in residential areas.
Meanwhile, the Mono Basin area has to cope with a degraded environment. Although the diversions are limited now, the ecosystem cannot recover its original state without help. The wetlands, streams and fish and bird habitat have to be actively restored. This is a difficult and expensive task, and there is no way in telling if it will ever get to way it used to be.
8. Resources
EROS home page @
http://edcwww.cr.usgs.gov/eros-home.html
Global Land Information System @
http://edcwww.cr.usgs.gov/webglis
(choose digital satellite and areal data -
Multispectral Scanner Landsat Data - search) or go to
http://edcwww.cr.usgs.gov/Webglis/glisbin/search.pl?LANDSAT&865523084
Mono Lake Homepage @
http://www.monolake.org/ and links therein
WHSRN-California/Mono Lake @
http://www.wetlands.ca/wi-a/whsrn/monolake.html
Endangered Status Not Warranted For Mono Lake Brine Shrimp @
http://www.r1.fws.gov/news/9565nr.html
Great Basin Ecosystem @
http://www.blm.gov/education/great_basin/water_resource.html
Gill-TE (1996) Eolian Sediments Generated By Anthropogenic Disturbance Of Playas: Human Impacts On Geomorphic System And Geomorphic Impacts On The Human System Geomorphology, V 17, P218-224
Shivik-JA, Crabtree-RL (1995) Coyote Activity Levels In Relation To Presence Of California Gulls At Mono-Lake, California California Fish And Game, V 81, 1, P 22-28
Kondolf-GM, Vorster-P (1993) Changing Water-Balance Over Time In Rush Creek, Eastern California, 1860-1992 Water Resources Bulletin, V 29, 5, P 823-832
Drinkwater-LE, Crowe-JH (1991) Hydration State, Metabolism, And Hatching Of Mono Lake Artemia Cysts Biological Bulletin, V 180, 3, P 432-439