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1 Introduction Mono Lake lies at the heart of the Mono Basin in eastern California. The basin supports a variety of wild- life, some of which is dependent on the lake ecosystem. Since 1941, the city of Los Angeles, which owns the water rights to several of the major streams that flow into the lake, has been exporting water from the basin. Between 1941 and 1985, exports averaged 68,100 acre-ft/yr. Between 1969 and 1985, exports generally increased and averaged 90,100 Water and Power (LADWP), 1987~. As a consequence of these water diversions, the lake level has dropped about 40 Questions have been raised about the ef- t~ects of changes in the water level of Mono Lake on the basin ecosystem. With the passage of the California Wilderness Act in 1984, Congress established the Mono Basin National Forest Scenic Area and placed management of the basin under the jurisdiction of the U.S. Forest Service acre-ft/yr (Los Angeles Department of ft since 1941 The Bureau of Land Management previously had had responsibility for managing the area. Since 1982, the state of California has managed the land exposed since 1941 by declining lake lev- els (land below an elevation of 6417 ft above sea level), designated the Mono Lake Tufa State Reserve. The California Wilderness Act of 1984 also contained a request for the National Research Council to review the available scientific information and assess the current un- derstanding of the effects of changes in lake level on the scenic area's ecosystem. This report presents the results 8

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Introduction 9 of that study, which was carried out by the Mono Basin Ecosystem Study Committee of the NRC's Board on Envi- ronmental Studies and Toxicology. The hydrologic drainage basin from which water flows into Mono Lake includes all of the land area of the Mono Basin National Forest Scenic Area (Figures 1.1 and 1.2~. Changes in lake level, which in recent times have resulted primarily from diversions of most of the streams carrying freshwater runoff from the eastern escarpment of the Sier- ra Nevada to Mono Lake, affect the lake system itself, the shoreline and upland portions of the basin, and wildlife in the basin. No streams drain the lake, so the amount of water in it is determined by inputs from rainfall, snowmelt, and springs and loss from evaporation. When inputs are reduced, either by changes in the climate or diversions, the lake level drops. The ions dissolved in the water are con- centrated as water evaporates from the lake surface, lead- ing to increases in salinity with lower lake levels. At higher levels of salinity, the reproduction and survival of the lake's biota, mainly brine shrimp and brine fly, would be affected and the birds that rely on the brine shrimp and brine fly for food would in turn be affected. Other concerns about physical changes in the lake have been raised. In particular, some of the lakers islands would be- come peninsulas if the lake level were to fall. Predators could then prey on birds that customarily nest on the islands. Changes in lake level would also have consequences for other parts of the basin. Along the shoreline, airborne dust would increase if lake level fell and exposed alkaline flats. Rising lake levels could result in damage to the tufa towers, the piliarlike formations that are a distinctive sce- nic resource of the basin. Changes in lake level might also alter the depth of the water table and consequently the shoreline vegetation. In the upland portions of the basin, altered streamflows associated with changes in lake level would affect the riparian vegetation and the fish and other wildlife relying on that habitat. The congressional clirective, House Report No. 98-291 (U.S. Congress, House of Representatives, 1983), specified that the NRC study on the effects of changing lake levels

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10 N N at:: :.: :.:,:.:.:,:2: :. San Francisco\$ .... O 100 200 I I 1 1 SCALE IN MILES MC,NO BASIN The Mono Basin Ecosystem ~0Ho \-~t \::: : .. :. . .' P:~^h:. I eland ~:~ Boundary of Scenic Area o 1 2 3 l SCALE IN MILES FIGURE 1.1 Mono Basin National Forest Scenic Area (courtesy of the U.S. Forest Service). On the ecosystem include, but not be limited to, the fol- lowing: ( 1 ) an inventory of all terrestrial and aquatic species, including current and probable future population levels; (2) the critical lake level needed to support current wildlife populations; (3) the hydrology of Mono Lake;

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Introduction . N 119 W it, ':~d ~< - 1 W\ t'~'\. 'I'll '\ ( ( Saddlebag A, 5~~>Lake _ ;~ ~ _ ~ _ ~0 J ~~ \ - Paoha Islands/ \~ ! ~ 11 /~\'''N errs - .^:J \ / r 38N \ ,~: '.'',ol~ ~""'~ ~ J Reservoir KISS MTS. Aft/ ~ retune:/ ~ Rush A_ '~ ,{ C~Agnew Lake) SCALE IN MILES FIGURE 1.2 Hydrologic drainage of Mono Basin (from Vorster, 1985~. (4) the estimated wildlife populations if Los Angeles continues to exercise its water rights; and (5) the significance of changes in wildlife populations to populations in other areas. In addition, the legislation specified that this study should not address the socioeconomic issue of Los Angeles's water rights. The U.S. Forest Service requested that the committee also consider issues related to the management of the scenic area, including the effects of fire and

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12 The Mono Basin Ecosystem grazing on the ecosystem, effects of public access to tufa formations, effects of lake level on air quality, and an inventory of vegetation types in the basin. Because different lake levels have different conse- quences for the various resources of the Mono Basin (e.g., lake biota, bird populations, tufa towers, shoreline vegeta- tion, and riparian habitat), the committee approached its task by analyzing a series of lake levels both above and below the current level. Chapter 6 of this report discusses in detail the consequences of each of these lake levels. Chapters 2 through 5 discuss the available literature and provide background information for the analysis in chapter 6. Chapter 2 describes the hydrology of the Mono Basin; chapter 3, the physical and chemical lake system; chapter 4, the biological system of the lake; and chapter 5, the shoreline and upland systems. In the remainder of this introduction, the climatology, physiography, and geology of the Mono Basin and the prehistoric and historic fluctua- tions in lake level are briefly described, and Mono Lake is compared with other saline lakes. CLIMATOLOGY, PHYSIOGRAPHY, AND GEOLOGY OF THE MONO BASIN Mono Basin., which lies in eastern California approxi- mately 190 mi east of San Francisco and 300 mi north of Los Angeles, is a closed hydrologic basin walled in by the steep-faced eastern escarpment of the Sierra Nevada on its western side and by Great Basin ranges on the north, south, and eastern sides (Figure 1.2~. Within the basin is * The reader will note that no attempt has been made to impose consistency of style on units of measure throughout the report. The use of English units of meas- ure is still conventional in many of the disciplines central to the subject of this report, but when the original meas- urements were made in metric units they were retained in that form.

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Introduction 13 Mono Lake, known as a terminal lake because under natu- ral conditions all the runoff and groundwater seepage from the basin terminate in the lake. Estimates of the areal extent of the basin range from 634 to 801 mi2. The differences are attributable to the difficulties of interpreting the drainage divide in the east- ern and southern parts of the basin and the inclusion of 69 mi2 of alkali flats in Nevada that might have subsurface connections to the basin (Vorster, 1985~. The Mono Basin lies on the border of two major physi- ographic provinces--the Sierra Nevada and the Great Basin. The topography of the basin varies greatly. Elevations range from approximately 6,380 ft above sea level at the lake surface (in August 1986) to approximately 13,000 ft at the crest of the Sierra Nevada. The basin is characterized by large seasonal and annual variability in precipitation. A majority of the precipitation occurs in winter in the form of snow. Both amount of precipitation and temperature vary considerably in the basin as a function of elevation and distance from the Sierra Nevada. The variability in precipitation is attributed in part to the complex effect of the mountains on Pacific storms. Episodes of strong winds occur throughout the year but are most frequent in the late fall through spring. The historical record of climate is relatively short; measurements of air temperature and precipitation in the Mono Basin have been made since 1951, whereas descrip- tions of many regional weather events date back to the mid- 1 800s. Other important information, such as rain and snowfall records in the nearby Sierra, is available for the period since 1924 and is maintained by LADWP. Analyses of these data can be used to define mean values of month- ly air temperature and precipitation and the relative fre- quency of occurrence of extreme events. Of particular importance to the Mono Basin ecosystem are the occurrence of periods of prolonged drought and of episodes of heavy precipitation and climatic trends resulting from natural events or anthropogenic effects. Prehistoric cli- mate can be inferred from geologic evidence including gla- cial moraines, old shorelines, alluvial deposits, and volcanic ash layers, and also from paleobotanic evidence in pack-rat middens and tree rings.

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14 The Mono Basin Ecosystem In October 1986, the surface area of the lake was ap- proximately 69 mi2 (Pelagos Corporation, 1987), with a maximum depth of approximately 150 ft. There are two large islands and numerous small islets in the lake. Paoha Island has an area of approximately 3 mi2, and Negit Island is approximately 0.5 mi2. Because no streams drain from the lake and ions dis- solved in the streamflow and groundwater seepage concen- trate as the lake evaporates, Mono Lake is highly saline and alkaline. It is currently about 2.5 times as saline as the Pacific Ocean (LADWP, 1987~. As is characteristic of saline lakes, Mono Lake supports a small number of pro- ductive species' mainly brine fly (Ephyd~ra hians), brine shrimp (Artemia monica), and a few species of algae. Large numbers of migrant waterbirds use the lake and rely on the brine shrimp and brine flies for food. No fish live in the lake. (See chapter 4 for a detailed discussion of the biology of Mono Lake.) A distinctive feature of the Mono Basin is the tufa towers, formed underwater as calcium in freshwater springs combines with carbonates in the lake water. The deposits accumulate and form picturesque towers. As the lake level has receded, the tufa towers have been exposed (see front cover). Considerable work has been done on the geologic his- tory of the Mono Basin (see Appendix C). In geologic terms, the basin is a tectonic depression filled with sedi- ment. To the west of the basin are Mesozoic granites and Paleozoic metamorphics of the Sierra Nevada escarpment. To the north, east, and southeast are the Miocene volcan- ics of the Bodie Hills, Anchorite Hills, and Cowtrack Moun- tain. To the south are ()uaternarv volcanics mnstlv rhvn- litic glass, of the Mono Craters and Glass Mountain. The basin is filled with 500 to 1350 m of glacial, fluvial, lacus- trine, and volcanic deposits. The ground surface comprises glacial tills and gravelly fluvial deposits. These are pre- dominant in the west near the hash of the sierra N~v~rln ~ . , , , . . ~ . . . ~ . . . .. . ~ , . . . ~ . . . . ~ ~ canny, wlnonlown pumice covers areas to the north, east, and southeast of the lake. The area became a closed basin about 3 million years ago, when a combination of faulting of the eastern scarp of the Sierra Nevada and downwarping of the north and

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Introd action 15 south sides of the basin occurred. The area is still tec- tonically active. Mono Craters have been intermittently erupting for the last 33,000 years. PREHISTORIC AND HISTORIC FLUCTUATIONS IN LAKE LEVEL Mono Lake, which is approximately one-half million years old, is one of the oldest lakes in North America (Lajole, 1968~. During the last glaciation (the Wisconsin), the level of the lake was much higher than the current level of 6380 ft above sea level. This Pleistocene lake is known as Lake Russell. Fluctuations of the lake level from 23,000 through 12,500 years ago (the Tioga advance of Wis- consin glaciation) are summarized by Lajole ( 1968~. The lake may have reached its maximum extent 22,000 years ago, when it overflowed into the Owens Valley. At that time, the lake was 7 times deeper and 5 times larger in surface area than it is today. At its minimum during glaciation, the lake probably stood near 6600 ft. only a few hundred feet higher than the current level. Stine ( 1984) has reconstructed the fluctuations in lake level over the past 3500 years using geomorphic, biotic, historic, and radiocarbon evidence along with information from sedimentary sequences and tephra exposed in the stratigraphy (Figure 1.3~. The figure indicates that the lake was at its lowest about 1850 radiocarbon years before the present. Though the lake level has been lower in prehistoric time than it has been more recently, the volume of water was probably greater than it would be for the same lake level today. Changes in the lake's morphometry resulting from volcanic activity on the lake floor during the past 600 years have altered the relationships between lake elevation and volume (S. Stine, University of California, Berkeley, personal communication, 1986~. The most significant dis- placement of water has occurred with the formation of Paoha Island from volcanic activity and uplift of lake sedi- ments sometime between 1723 and 1850 AD. Because the area is volcanically active, uncontrollable geologic processes could again alter the relationship between lake elevation and volume in the future.

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b 16 6500 ~ 90 _ I,- 80 _ z 70 _ 0- 60 _ 50 _ ~ 40 _ c, 30 _ A: 20 _ ~ 10 _ oh 6400 _ 90 _ 80 _ 6370 _ The Mono Basin Ecosystem 1980 \ | Radiocarbon date | 610 BP Mono Craters Tephra \~ 1990 BP Mono Craters T6phr~ 1190 BP blono Craters A ~ ; J Ice Bl7EmPuon ~ ~ \ ~ ~ ~ .~ \~) \,,r \,, 1 1 ~ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 , 1 35 34 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 RADIOCARBON YEARS BP (x100) 1975 ~ - 1970 o 1965 1960 1955 ~ D: 1950 @, 1945 1940 FIGURE 1.3 Surface fluctuations of Mono Lake 3500 BP to present (Stine, 1984~. (BP is relative to 1950.) LADWP has kept records of lake levels since 1912. Lake levels have been estimated back to 1857 using carto- graphic, historical, and climatic evidence. Figure 1.4 shows these estimated and measured historic lake levels. Water has been diverted from the basin since 1941. The level of the lake fell approximately 45 ft. from 6417 ft in 1941 to 6372 ft. the historic low stand, in 1982. The years since 1982 have been wet, and the lake level has risen approximately ~ ft. to 6380 ft. as of August 1986. COMPARISON OF MONO LAKE WITH OTHER SALINE LAKES Saline lakes occur on every continent and often are the only surface water in dry regions (Hammer, 1986~. Most inland saline lakes are shallow and fluctuate widely in sa- linity, area, and depth. In contrast, large, deep lakes such as Mono Lake usually experience muted salinity variation (Langbein, 1961~. However, gradual changes in depth and salinity, mainly as a consequence of climatic variations and human modification of inflows, do occur for even the larg- est lakes. Among saline lakes there is a wide variety of chemical compositions and total salt contents because of the broad

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Introduction 6425 :E 6420 ~ 6415 0 6410 ~ 6405 Al 6430 6425 0 6420 ~ 6415 OCR for page 8
18 The Mono Basin Ecosystem they represent a significant fraction of inland saline water. Melack (1983) selected a subset of such lakes with mor- phometric and chemical similarities to Mono Lake (Table 1.1 ) and attempted to decipher ecological characteristics that could increase understanding of Mono Lake. Only seven lakes met Melack's criteria, although additional lakes may be found in Tibet, south central USSR, and Mongolia. A comparative limnological analysis of even these seven lakes is confounded by the scant data available on some. General characteristics of these lakes include locations at moderate to high altitude in mountainous terrain and alka- line, sodium-rich waters, usually with high phosphate. Supersaturated dissolved oxygen, abundant animals and sea- sonally high algal populations, and low transparencies indi- cate that some of the lakes are productive. live in these lakes; all except Mono contain fish. new species The large and wide-ranging literature on saline lakes, recently reviewed by Hammer (1986), has particular rele- vance to Mono Lake in a few areas. Most pertinent are biogeographic studies of the tolerance of aquatic organisms to salinity, geochemical analyses of saline waters as a function of dilution and concentration, paleoecological ex- amination of the extent and rates of changes of salinity, and investigations of vertical mixing, especially the occur- rence of incomplete mixing, or meromixis. In the context of our overall understanding of lakes, both saline and fresh, Mono Lake is of particular scientific value. Mono Lake is one of the oldest lakes in North America; it is far older than the many lakes formed within the past 15,000 years as the last continental glaciers re- treated. The large quantity of carbonate dissolved in Mono Bake has prolonged the attainment of equilibrium with car- bon- 14 produced by the atmospheric testing of nuclear weapons and has provided an excellent opportunity to ex- amine gas exchange between the atmosphere and lakes (Pen" and Broecker, 1980~. Such studies have a bearing on the extent of global warming to be expected from carbon dioxide increases associated with the burning of fossil fuels. Recent measurements showing that radionuclides can be many times more soluble in Mono Lake than in marine or fresh waters (Simpson et al., 1980, 1982; Anderson et al., 1982) may have important implications for radioactive ~ . . .

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Introduction 19 TABLE 1.1 Geographic, Morphometric, and Chemical Char- acteristics of Large, Deep Salt Lakes Altitude Area Mean depth Salinity Lakea Location (m) (km2) (m) (g/1) Mono (1, 2) 3800'N, 11900~W 1942 150 19 90 Walker (3) 3845'N, 11840'W 1207 154 20 10.7 Qinghai Hu (4) 3650'N, 10010'W 3196 4635 19 12.5 Shala (5, 6) 730'N, 3830,W 1567 409 89 16.8 Van (7, 8) 38N, 43E 1720 3600 53 22.2 Panggong Tso (9) 3342'N, 7845'N 4241 279 26 12.9 Karakul (10) 3900`N, 7330'E 3952 370 210b 10 aNumbers in parentheses indicate original sources cited in Melack (1983), as follows: (1) Mason (1967), (2) Los Angeles Department of Water and Power (personal communication, 1982), (3) Koch et al. (1979), (4) Academia Sinica (1979), (5) Morandini 1941, (6) Loffredo and Maldura (1941), (7) Gessner (1957), (8) Langbein (1961), (9) Hutchinson (1937), and (10) Ergashev (1979). bMaximum depth. NOTE: The criteria for selection of these lakes were a mean depth greater than 15 m, an area greater than 100 km2, and an athalassic salinity greater than 1Q g/1 and less than 100 g/1. SOURCE: Melack (1983). waste disposal in these environments. Another consequence of the high carbonate concentrations is the formation of calcite-impregnated defluidization structures in the littoral sands around the lake. These structures, which can be mistaken for animals' burrows, show that not all tubelike formations are evidence of biological activity (Cloud and Lajoie, 1980~. Of further relevance to Precambrian paleo- ecology is the recent speculation that the ancient sea had high alkalinity, high pH, and low calcium and magnesium concentrations, much as Mono Lake does today (Kempe and Degens, 1985~. REFERENCES Anderson, R. F., M. P. Bacon, and P. G. Brewer. Elevated concentrations of actinides in Mono Science 216:514-516. 1982. Lake.

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20 The Mono Basin Ecosystem Cloud, P., and K. R. Lajole. 1980. Calcite-impregnated clefluidization structures in littoral sands of Mono Lake, California. Science 210:1009- 1012. Eugster, H. P., and L. A. Hardie. 1978. Saline lakes. Pp. 237-293 in Lakes: Chemistry, Geology, Physics, A. Lerman, ed. New York: Springer-Verlag. Hammer, U. T. 1986. Saline Lake Ecosystems of the World. Monographiae Biologicae 59. Dordrecht, Nether- lands: Dr W. Junk Publishers. 616 pp. Harding, S. T. 1962. Water Supply of Mono Lake Based on Past Fluctuations. Water Resources Archives. University of California, Berkeley. Unpublished report. Kempe, S., and E. T. Degens. 1985. An early soda ocean. Chem. Geol. 53:95-108. LajoIe, K. R. 1968. Late Quaternary Stratigraphy and Geologic History of Mono Basin, Eastern California. Ph.D. dissertation, University of California, Berkeley. 379 pp. Langbein, W. B. 1961. Salinity and Hydrology of Closed Lakes. U.S. Geological Survey Professional Paper 412. Washington, D.C.: U.S. Government Printing Office. 20 PPe Los Angeles Department of Water and Power. 1987. Mono Basin Geology and Hydrology. Los Angeles, Calif. Melack, J. M. 1983. Large, deep salt lakes: a comparative limnological analysis. Hydrobiologia 105:223-230. Meyer, G. H., M. B. Morrow, O. Wyss, T. E. Berg, and I. L. Littlepage. 1962. Antarctica: the microbiology of an unfrozen saline pond. Science 138:1 103- 1 104. Nissenbaum, A., ed. 1980. Hypersaline Brines and Evapo- ritic Environments. Proceedings of the Bat Sheva Sem- inar on Saline Lakes and Natural Brines. Developments in Sedimentology 28. Amsterdam: Elsevier. Pelagos Corporation. 1987. A Bathymetric and Geologic Survey at Mono Lake, California. Report prepared for Los Angeles Department of Water and Power. San Diego, Calif. Peng, T.-H., and W. S. Broecker. 1980. Gas exchange rates for three closed-basin lakes. Limnol. Oceanogr. 25:789-796. Simpson, H. J., R. M. Trier, C. R. Olsen, D. E. Hammond, A. Ege, L. Miller, and J. M. Melack. 1980. Fallout

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Introduction 21 plutonium in an alkaline, saline lake. Science 207:1071- 1073. Simpson, H. I., R. M. Trier, I. R. Toggweiler, G. Mathieu, B. L. Deck, C. R. Olsen, D. E. Hammond, C. Fuller, and T. L. Ku. 1982. Radionuclides in Mono Lake, Califor- nia. Science 216:512-514. Stine, S. 1981. A Reinterpretation of the 1857 Surface Elevation of Mono Lake. California Water Resources Center Report 52. Davis, Calif.: University of Califor- nia, California Water Resources Center. 41 pp. Stine, S. 1984. Late Holocene lake level fluctuations and island volcanism at Mono Lake, California. Pp. 21-49 in and Tephrochronology Rierran Crest. S. Stine. Holocene Paleoclimatology and Tephrochronology East and West of the Central Sierran Crest, S. Stine, S. Wood, K. Sieh, and C. D. Miller, eds. Field Trip Guide- book for the Friends of the Pleistocene, Pacific Cell, October 12-14, 1984. Palo Alto, Calif.: Genny Smith Books. U.S. Congress, House of Representatives. 1983. Establish- ing the Mono Basin National Forest Scenic Area in the State of California. House Report 98-291. Washington, D.C.: Committee on Interior and Insular Affairs. 16 pp. Vorster, P. 1985. A Water Balance Forecast Model for Mono Lake, California. Master's thesis, California State University, Hayward. Earth Resources Monograph No. 10. San Francisco, Calif.: U.S. Forest Service, Region 5.