Salinities ranged from 77 to 98 gm/l across the interface and sodium, chloride, sulphate, and carbonate were the major ions in both the upper and lower water mass. At the same time the midsummer density difference between 2 and 28 m brine depths that was due to temperature was approximately 0.5 x 10-2 gm/cc. In 1984 this chemical stratification accounted for a density difference of 1.2-1.5 x 10-2 gm/cc between the 2 and 28 m water depths. Earlier, in 19, the lake had also become meromictic when exceptionally large volumes of freshwater runoff led to a rapid 2.6 m rise in surface elevation of the lake (Jellison and Melack, 1993). In 1994, an unintentional consequence of lessening drainage water diversions from the Mono basin into the LA aqueduct was the onset of a period of anthropogenically induced “meromixis” (Jellison et al., 1998). The more usual state of the lake is monomictic (annual mixing). In years with large fresh water inputs the lake may become meromictic. It implies that lake waters were fresh in the Pleistocene at times the various high lake level terraces were formed. It clearly shows that as lake levels fall the lake salinity increases. (2011) document this relationship (Figure b). Historic salinity and lake levels measurements can be related, exponentially, Zimmerman et al. Interestingly, the anthropogenic lowering of lake water level in the last half-century and the associated increase in lake salinity is still well within the range of natural fluctuations experienced by Mono Lake in the last 2,000 years (Figure). The projected stabilized lake elevation is 1948.3 m, but reference to the water level changes over time argues this may not be attained in the next few years. The current lake level is 1945.2m asl (as of January, 2020). To prevent further desiccation of the lake, some water from the former distributaries has been rediverted back into Mono Lake, which is now slowly refilling after reaching an all time low of 1942.2 m asl in 1982 (Figure a). Subsequent lower lake levels exposed numerous calcitic tufa mounds and pinnacles on the lake floor and enlarged the portion of the lake floor made up of subaerial saline mudflats. Water levels were as high as 1958 metres above sealevel, before the diversion of Mono’s tributary streams. In the 50 years following the diversion, Mono Lake water level dropped more than 10 metres, the lake water volume was cut in half, while the alkalinity and salinity of the lake waters doubled (Figure). In 1941 the State Resources Board diverted the distributaries that fed Mono Lake into the Los Angeles aqueduct. The Mono Lake Committee formed in response and won a legal battle that has forced the City of Los Angeles to partially replenish the lake level.įrom 1850 until the middle of last century the lake water level rose some 5 metres, then the water needs of the City of Los Angeles caused a drastic water fall. When the City of Los Angeles diverted water from the freshwater streams flowing into the lake, it lowered the lake level, which imperiled the migratory birds. This saline lake has an unusually productive ecosystem based on brine shrimp that thrive in its waters, and provides critical habitat for two million annual migratory birds that feed on the shrimp and alkali flies ( Ephydra hians).\] Historically, the Native American Kutzadika'a people derived nutrition from the alkali flies' pupae, which live in the shallow waters around the edge of the lake. Calcite accumulates, sometimes with an ikaite precursor, where resurging groundwaters degas on the lake floor and can form spectacular biogenically-bound towers of tufa. Some of the lake bottom laminites are slumped, possibly initiated by ongoing volcanic disturbance (Figure b Benson et al., 2003). lanthanides and actinides, including naturally high levels of arsenic in bottom brines Tomascak et al., 2002).Ĭalcium carbonate (calcite and aragonite) precipitates spontaneously from the lake waters and makes up 3-10 % of the laminite sediment on deeper tufa-free bottoms, the remainder is detrital. The high pH (≈9.8) and alkalinity of lake waters leads to high concentrations of volcanic elements that ordinarily have short residence times in lakes (i.e. Major anion content of lake brines is divided almost evenly between chloride, sulphate, and bicarbonate. Current free surface brine volume is ≈3.2 km 3, surface area is 184 km 2, annual total inflow is around 283.7 x 10 6 km3 and current salinity is around 90,000 ppm. Mono Lake, an endorheic meromictic alkaline saline lake with an average depth of 17m, in a volcanically active area at the edge of the Sierra Nevadas, California (Figure a), which has been accumulating laminated lacustral sediments since 760 ka.
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