Mono Lake is a hypersaline lacustrine water body located in the Great Basin of the western USA.
The lake is situated at the western base of the southern Sierra Mountains, and is unusually rich in a host of diverse minerals.
This lake has experienced significant drawdown in lake levels and secondary salinization due to the rapidly expanding population in Southern California; however, conservation steps have been taken to limit future water extraction, in order to protect the lake ecology.
With elevated pH level and a rich assortment of dissolved minerals, Mono Lake comprises a highly productive aquatic ecosystem, albeit of limited biodiversity. As a well defined stable basin, Mono Lake is arguably one ot the oldest lakes in North America.
Terrestrial margins of the lake are comprised chiefly of a sagebrush scrub plant community. In 2009, a novel life form was discovered in Mono Lake, consisting of a bacterium that is able to metabolize and incorporate arsenic as an essential building component of its cellular structure.
Limnology and Chemistry
Mono Lake is thought to be one of the oldest lacustrine bodies in North America, and is judged to have existed for at least 760,000 years. The rich variety of dissolved mineral salts derive from leaching of chemicals from the surrounding and lakebed rocks. The ions plentiful in Lake Mono include not only sodium, chloride, potassium and carbonate, but also calcium, strontium, sulfate, iodide, arsenate, tungstenate, fluorate and boride. The pH level of Mono Lake is quite high, with these basic waters realizing pH values of approximately ten.
|Historic Mono Lake elevation. Source: Hopkins and Kavounas (2002)|
Tributary rivers to Mono Lake include Rush Creek, Lee Vining Creek, and Mill Creek. It was diversion of these freshwater inflows by the Los Angeles Department of Water and Power in 1941 for consumption over 330 miles (540 km) south, that caused the 1941-1982 decline in Mono Lake levels. Subsequent to massive lake drawdowns, water levels dropped precipitously, reaching a minimum in 1982.
Since that time a program of lake restoration has brought the lake volume to 60 percent of its 1941 volume, with an ultimate target of realizing 70 percent of the 1941 baseline. In the period of lake shrinkage, salinity rose from 50,000 to 90,000 milligrams per kilogram. One of the consequences of lake volume decline was the observed formation of gaylussite (a rare sodium-calcium carbonate) crystals in the deeper water areas; this formation was due to elevated pH and sodium concentrations arising in the smaller volume lake.
An unintentional, consequence of ending the water diversions was the creation of meromixis. During the period of intense water diversions the lake was monomictic, implying that at least once annually the deeper waters mixed with the upper layers, conveying nutrients and oxygen to the bottommost layers. In meromixis, deep layers do not become thoroughly mixed, so that deeper layers are more saline than the water near the surface, and are typically almost devoid of oxygen. As a result, changing from monomixis to meromixis significantly alters the lake ecology.
Mono Lake is a nitrogen limited lake, such that the production of ammonium and its vertical mixing are instrumental in controlling algal growth. Turbidity measured by the Secchi Disk method ranges from a value of 0.5 to 1.0 meters in the winter up to eight to twelve meters at the summer high, with the variation due to phytoplankton density.
Within the most recent five million years, the endorheic Mono Basin was formed via basin and range crustal stretching, admixed with volcanic activity, combined with faulting along the western Sierra Mountains base. About five million years before present (b.p.), the Sierra Nevada was merely an eroded low lying range of hill topography, with no trace yet of the Mono Basin or Owens Valley. From 4.5 to 2.5 million years b.p., massive amounts of basalt were extruded from present day Cowtrack Mountain. Subsequent volcanic eruptions carried on from 3.8 million to 250,000 b.p. These events transpired chiefly northwest of Mono Basin and produced Cedar Hill, Aurora Crater and Mount Hicks.
The actual realization of the Mono Basin is thought to have come about approximately 760,000 years b.p., at the approximate time of the Long Valley eruption. Sediments beneath the ash layer suggest that Mono Lake may be a relict of a very sizable prior lake that once covered a large part of present day southeastern California, Nevada and western Utah. Conspicuous ancient shorelines of that prehistoric mega-lake are visible today above Lee Vining, California and along higher ground to the northeast of Mono Lake.
Volcanism proceeds currently in the local area, with the most recent eruption having been witnessed about 1660 AD; that event produced Paoha Island now present in the lake. A correlative outcome of this most recent volcanic event was the Panum Crater along the shoreline of Mono Lake, a formation consisting of a rhyolite lava dome and cinder cone.
fish life; however, there is a highly productive ecological system, with algae, brine shrimp (Artemia monica) and brine flies (Ephydra hians) being anchors of the food chain, all supporting avian species, higher trophic level feeders.With the high pH and mineral concentrations, Mono Lake supports no
Artemia monica is the only macrozooplankter in Mono Lake, with first generation individuals hatching from overwintering cysts. This species exerts a strong grazing pressure on phytoplankton, and is an important regenerator of ammonium. Furthermore, A. monica is a key food source for over one million Black-eared grebes in the autumn, as well as many other avian species. Pioneering microbiology research in the 1930s by Benjamin Elazari-Volcani identified the presence of the phytoflagellate Dunleilla viridis.
The lake is a major breeding site for the California gull (Larus californica) and a critical stopover feeding place for Black-eared grebes (Podiceps nigricollis). Furthermore, significant populations of Snowy plover (Charadrius nivosus) feed here along their migration routes. Other migratory shorebirds resting and feeding at Mono Lake are American avocet (Recurvirostra americana), Wilson's phalarope (Phalaropus tricolor) and Red-necked phalarope (Phalaropus lobatus).
Like all hypersaline and high pH water bodies, Mono Lake is a habitat for a number of extremophile organisms, e.g. taxa which are able to out-compete other biota due to their ability to permform metabolic functions in an environment which has high concentrations of salts and;or highly basic (low hydrion concentrations) waters. As is the case in most such extreme environments, the majority of its extremophiles have not yet been identified, due to the fact that most are microscopic organisms, such as bacteria or archaea.
Mono Lake contains a rod-shaped extremophile bacterium GFAJ-1 that can metabolize the chemical element arsenic. This discovery by NASA has significant implications for the likelihood of finding other lifeforms on planetary bodies with substantially different chemical compostion from the Earth. All life on Earth has been historically viewed as containing essential atomic elements: carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur in cellular construction. The occurrence of bacterium GFAJ-1 is a departure from this classical thought, since arsenic has replaced the usual valence role of phosphorus in the new bacterium.
The most iconic visual feature of Lake Mono are tufa towers formed by underwater springs rich in ionized calcium; these calcium rich waters mix with high carbonate lake waters, producing deposition of calcium carbonate. Since the formation only occurs underwater, the emergent towers testify to the decline in surface level since 1941, the date when massive water diversions to the rapidly expanding human population of Southern Calfornia commenced.
Terrestrial Ecology and Soils
The Mono Basin lies in an ecoregion termed the Central Basin and Range (designated by the U.S. EPA as ecoregion 13 of North America); the entirety is composed of northerly trending fault-block ranges and intervening drier basins. The principal plant community is sagebrush scrub. Valleys, lower slopes, and alluvial fans are either shrub- and grass-covered, or shrub-covered. In general this ecoregion is drier than the Sierra Nevada, cooler than the Mojave Basin and Range, and warmer and drier than the Northern Basin and Range. Soils grade upslope from Aridisols or Entisols to Mollisols. The chief land use is primarily used for grazing, but major extents are essentially open space or wilderness.
Prominent plants include Single-leaf pinyon (Pinus monophylla), Antelope bitterbrush (Purshia tridentata), Littleleaf horsebrush (Tetradymia glabrata), Arrowleaf balsamroot (Balsamorhiza sagittata) and Desert peach (Prunus andersonii). Fauna present include sage grouse, kangaroo rats, mule deer, black-tailed jackrabbits, coyotes and mountain lion.
The Native American Kutzadika'a people consumed not only migrating birds visiting the lake, but also larvae of the brine flies that live in the lake. This tribe, a band of the Northern Paiute, chose the Mono Lake area in spite of its harsh climate, because of the high biomass productivity of the lake ecosystem. The word Mono derives from Monachi, a Yokut term for the tribes that lived on both the east and western side of the Sierra Mountain range. The Kutzadika'a people lived on the western Sierra, although tribes in these desolate areas of the Great Basin are known to have engaged in trade with tribes such as the Chumash as far away as the California coast.
In the prehistoric era the adjacent Owens Valley was inhabited by the Panamint tribe at the southern end of the Owens Basin; however, at this time the Mono tribe occupied the north and central parts of the Owens Basin.
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