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Physical and Chemical Lake System INTRODUCTION The physical and chemical properties of Mono Lake de- termine the environment in which its biota live. As changing lake levels change that environment, the biota will be affected accordingly. Solar radiation provides en- ergy for photosynthetic organisms and heats the water. Density, which is a function of temperature and concentra- tions of dissolved and particulate matter, determines in part the stratification or layering of water within a lake. This stratification in turn affects the amount of nutrients and dissolved gases available to organisms in the lake. In alkaline, saline lakes such as Mono Lake, the con- centration and relative proportions of the major ions (so- dium, potassium, calcium, magnesium, sulfate, carbonate plus bicarbonate, and chloride) determine the osmotic envi- ronment for the organisms and the acid-base balance. Pro- cesses such as inputs of chemical constituents from surface waters and groundwater and loss of constituents through sedimentation and precipitation of minerals control the chemistry of the lake. The availability of nutrients (e.g., nitrogen and phosphorus), which enter the surface layer from the atmosphere, inflowing streams, and the more dense bottom layers of the lake, is also critical to the eco- system. 50

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Physical and Chemical Lake System PHYSICAL SYSTEM _ 51 The physical conditions of a lake are determined pri- marily by the shape of its basin, the transparency of the lake water, density variation in and motions of the water, and the local meteorology. Geologic processes that formed the basin set limits for the lake's morphometry. Changes in inputs of water or sediments caused by natural or anthropogenically induced conditions can modify morpho- metric features such as depth or island extent and can effect significant ecological changes. A morphometric des- cription of Mono Lake was derived by Mason (1967) from Scholl et al.'s (1967) bathymetry and USGS topographic maps for a lake level of 6391.2 ft. the mid-July 1964 eleva- tion. Recent bathymetric data (Pelagos Corporation, 1987) permit improved calculation of the lake's hypsographic curve and related morphometric parameters (Figures 3.1 and 3.2~. Transparency of a lake depends upon the quantity and optical properties of the materials dissolved and suspended in the water. The resultant depth of penetration of solar radiation determines the depth to which primary produc- tivity can occur and influences the distribution of heat and hence the density of the water. The transparency of Mono , Lake as estimated by Secchi disk visibility varies from a winter low of 0.5 to 1 m to a summer high of ~ to 12 m (Mason, 1967; Melack, 1983, 1985; Lenz, 1984~. The sea- sonal difference is caused primarily by changes in phyto- plankton abundance. The depth of the euphotic zone (i.e., the depth to which 0.5 percent of incident photosynthet- ically active insolation reaches) ranges friom 4 to 18 m (Jellison and Melack, in press). Measurements of under- water attenuation in the red, blue, and green spectral regions indicate greatest penetration in the green region (Mason, 1967~. The water in Mono Lake differs in physical properties from pure fresh water (Mason, 1967~. First, the thermal capacity per gram is lower; hence fewer calories are re- quired to warm Mono Lake than to warm an equivalent mass of pure water. Second, the viscosity of Mono Lake water is about 20 percent higher than that of pure water. .

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52 z o 6430 6380 6330 6280 6230 - The Mono Basin Ecosystem AREA (1000 acres) 60 55 50 45 40 35 30 25 20 15 10 5 0 1 --a I 1 1 ' 1 ' 1 _ `',_ = - _ 1 1 1 1 1 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 VOLUME (1000 acre~ft) 1960 1950 1935 At o - 1920 1905 FIGURE 3.1 Area capacity for Mono Basin (Pelagos Cor- poration, 1987). 140 130 120 110 _ 100 so Cal at is 80t 70t 60R 50 Mean Depth ---- Maximum Depth " '1 - / ~ / 40 30 0 0 0 0 0 0 0 0 cO ~ US {D ~ 03 ~ O ~ co A) ~ {D (D ~ {D CD to {D {D LAKE ELEVATION (ft above sea level) _ 210 Ann _ 190 180 _ 170 HIS 160 150 140 130 120 110 100 FIGURE 3.2 Morphometric parameters for Mono Basin (from data in Pelagos Corporation, 1987~. Mean depth is on the left, and maximum depth is on the right.

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Physical and Chemical Lake System 53 Thus the sinking velocity of plankton may be slowed and the momentum transfer through the water column altered (Mason, 1967~. Density of water is a function of its temperature and the quantity of dissolved and particulate matter. Temporal changes in the variations in density with depth can cause ecologically important consequences. Thermal and chemical stratification occur in Mono Lake, and seasonal and inter- annual differences influence the biota. Mono Lake was monomictic (circulated from top to bot- tom during one season each year) when studied in the early 1960s (Mason, 1967) and from 1978 to 1982 (Melack, 1983~. It began to thermally stratify in late March or early April, remained stratified until November and was holomictic (mixed to the bottom throughout) during the winter. Maximum midsummer temperatures in near-surface, offshore water reach about 20C. Minimum winter temper- atures are near 0C (Figure 3.3~. Nearshore areas and occasionally much of the western bay can be ice covered as freshwater inflows freeze. Exceptionally heavy snowfall and reduced diversions by the City of Los Angeles during 1982-1983 led to a large input of fresh water. The fresh water mixed only partially with the saline lake water. Salinities in the near-surface region declined, and a chemocline (vertical gradient in major solute concentration) developed between 12 and 16 m. Therefore, the lake did not mix to the bottom, and meromixis (incomplete vertical mixing) was initiated in 1983. The mixolimnion (upper mixed layer in a meromictic lake) has deepened each subsequent autumn, and the chemocline was between 16 and 18 m in mid- 1985 (Figure 3.4~. A slight temperature inversion occurs in early spring, with colder mixolimnetic water overlying warmer monimo- limnetic (region below the chemocline in a meromictic lake) water. Within the mixolimnion a thermal stratification and mixing cycle, similar to that previous to 1983, occurs. The thermocline develops above the chemocline and gradually descends to the depth of the chemocline by early autumn. However, large inflows of fresh water in the spring of 1986 have incompletely mixed and caused a secondary diffuse chemocline in the upper 15 m. Calculations of the time required to erode the chemical stratification and permit complete mixing again are possible but difficult and require meteorological data that currently

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54 25 cry I,` 1 5 Tar 5 The Mono Basin Ecosystem i' i__--' I I 1 1 l\ 20 m ,/ _ ~ 1 1 1 1 1 1 1 1 1 J M M J S N 1 979 A 2m 1 20m _\ 1 1 1 1 1 1 1 1 M J S N 1 986 _ ~ 1 1 1 1 J M J M 1980 TIME (months) FIGURE 3.3 Temperature of Mono Lake at 2 and 20 m depth for 1979-1980 and 1986 at a station located approxi- mately halfway between Paoha Island and the south shore. . are unavailable for Mono Lake. Furthermore, the density of Mono Lake is not well-known, and computations that estimate mixing as a function of energy inputs require accurate measurements of the density structure. Densities reported by Mason ( 1967) apply to the lake at a level of 6389.9 ft. and his data as well as those in Herbst ( 1986) and LADWP ( 1986) are expressed only to three decimal places. Only the measurements made with a vibrating den- simeter (Picker et al., 1974) to a precision of +5 x 1 o-6 g/cm3 on water obtained when the lake stood at 6373.3 ft above sea level are of sufficient quality to calculate mixing rates (F. J. Millero, University of Miami, personal commun- ication, 1982~; values for additional levels are needed. Motions of lake water such as horizontal currents, sur- face and internal waves, and turbulent eddies affect distri- butions of physical, chemical, and biological entities.

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Physical and Chemical Lake System o 10 20 _ 30 l l 80 April 13 Augu;t 31 1 55 \ so TOTAL DISSOLVED SOLIDS (~1) 100 FIGURE 3.4 Total dissolved solids as a function of depth in Mono Lake in 1985. Mason (1967) hypothesized that wind-driven currents and internal waves played a role in the erosion and deposition of sediments evident in the shape of the basin. Occur- rences of features such as fronts as indicated by foam lines (Lenz, 1980) and large-scale differences in plankton abundance (Almanza and Melack, 1984; Lenz et al., 1986) indicate the presence of gyres or other circulation patterns. No direct measurements of currents are available. . . . Vertical mixing across the thermocline or chemocline is an important mechanism for injection of nutrients into the euphotic region where phytoplankton grow and for erosion of chemical or thermal stratification. The coefficient of evilly conductivity has been used to calculate vertical mix- ing rates in Mono Lake. Jellison and Melack ( 1986) applied the flux gradient method (Iassby and Powell, 1975) to tem- perature profiles obtained from 10 stations over 3 years. This technique is appropriate only during the period of net

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56 The Mono Basin Ecosystem accumulation of heat by the lake. Results for the spring and early summer of 1983, 1984, 1985, and 1986 indicate a marked decrease in vertical mixing in the region near the chemocline once meromixis is established. When combined with vertical profiles of ammonium, this result produces a reduced supply of this limiting nutrient as a consequence of meromixis. Further discussion of the interactions among the thermocline, chemocline, ammonium, and algae in terms of nutrient silnolv to the t~hvt~nl~nl~t~n it Nag ;^ chapter 4. ~~ _~ ~ ,7 _ - an_ ~^~) ~4 4~ PA~11 L~ 111 -line motions and thermal structure of Mono Lake are closely related to the motions and thermal structure of the overlying atmosphere. Surface winds may hasten the over- turning or mixing of the lake. For example, strong north- erly winds of 1 or 2 days' duration following a deepening cyclone in fall have been identified with the irregular overturning of Lake Tahoe (Paerl et al., 1975~. CHEMICAL SYSTEM Chemical Composition of the Water The major components determining the chemistry of the water in Mono Lake are the major ions, major nutrients (nitrogen and phosphorus), trace elements, and dissolved oxygen. These components are discussed in the following sections. Major Ions Because the present-day alkaline, saline lakes have geochemical evolution of lake (103 to 104 years), Mono ^^ . . . . chemistries of concentrated been determined by the waters over geological time Lake water is not strongly at ~ ecteo by relatively recent changes (on the order of 10 to 1 o2 years) in the chemistries of influent streams and hot springs. This has been demonstrated by Scholl et al. (1967), who calculated that the chloride age of the lake was about 31,000 years (C1- in the lake/the annual input of C1- to the lake), and Mason (1967), who made similar cal-

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Physical and Chemical Lake System 57 culations. For practical purposes the major ion composi- tion of Mono Lake is determined by dilution, evaporation, and the concomitant dissolution or precipitation of minerals. In 1980 (LADWP, 1984) and presumably at present, the major ion composition of Mono Lake is approximately as follows: 96.8 percent Na+, 3.0 percent K+, and 0.2 percent Mg2+; 46.3 percent CO32- plus HCO3-, 37.8 percent C1-, and 15.9 percent SO42- (as the equivalent percentages of the cations and anions, respectively). In simple terms, Mono Lake water is a triple water because it contains relatively large concentrations of carbonate plus bicarbon- ate, chloride, and sulfate. Triple waters possibly form in alkaline, saline lakes in which sulfate reduction has been low over much of geologic time. Salinity as total dissolved solids (TDS) can be reported as grams per liter (mass/volume) or grams per kilogram (mass/mass). In this report, salinity data are given in grams per liter because experimental investigations involv- ing the biota of Mono Lake have consistently used this unit. In general, presenting salinity data for saline waters in grams per kilogram is preferred. One can convert grams per liter to grams per kilogram by divicling by the density (liters per kilogram). Nitrogen and Phosphorus Nitrogen and phosphorus are often found to limit the abundance or productivity of algae. For Mono Lake, reli- able values for inorganic nitrogen have only recently become available (Jellison and Melack, in press); previously published data (e.g., Winkler, 1977) were obtained with un- satisfactory methods. Concentrations of inorganic nitrogen are usually low in the upper mixed layer. Nitrate is less than 1 ~M, and ammonium is less than 3 ~M, except in the late summer, when values can reach ~ to 12 ,uM. In the anoxic water below the thermocline or chemocline, ammonium concentrations can be very high and have exceeded 200 ,uM in recent years. Phosphate concentra- tions are substantial (about 800 to 1000 EM) throughout the lake.

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58 The Mono Basin Ecosystem Studies of phytoplankton samples from Mono Lake experimentally enriched with ammonium show an increase in growth, evidence that phytoplankton production is limited by the amount of ammonium in the lake (Jellison and Melack, 1986~. To evaluate the relative importance to the algae of nitrogen supply from external and internal sources, Allison and Melack (1986) compared nitrogen data on rain and stream inflows to nitrogen data on brine shrimp excre- tion and vertical mixing. Inputs from the watershed and airshed were negligible. In the spring, adult brine shrimp are absent, and the supply of ammonium from the deeper water via mixing was less than algal demand. During mid- summer, brine shrimp excretion was adequate to meet the algal needs, and upward vertical mixing was low. In the autumn, as the mixed layer deepens and brine shrimp num- bers decline, the supply of ammonium from vertical mixing and entrainment became larger than the brine shrimp excretion. Trace Elements Alkaline, saline lakes generally contain comparatively large concentrations of a variety of minor elements. In Mono Lake the most abundant minor element is boron at approximately 460 mg/1 (LADWP, 1984~. Boron concentra- tions in Mono Lake are among the highest recorded for any lake (Whitehead and Feth, 1961~. The alkaline earth metals are all found in lower abundance than boron (Sr2+ = 120 mg/1, Mg2+ = 33.4 mg/1, and Ca2+ = 4.1 mg/1), based on average values in Dana et al. (1977~. The halogens are observed in moderate to high concentrations (F- = 48 mg/1 and Br~ = 40 my/. Fluoride concentrations of this mag- nitude should prevent some organisms from inhabiting the lake (Kilham and Hecky, 1973~. Other nonnutrient minor elements listed in Dana et al. (1977) are arsenic (15.5 mg/l), lithium (10 mg/1), iodine (7 mg/1), and tungsten (4 mg/~. Compilations of trace metal concentrations are presented in Mason (1967) and Dana et al. (1977~. Average values for Mono Lake water (in micrograms per liter) are as follows: Fe = 420, Al = 40, Ti = 30, Mn = 20, and Cu = 10. How-

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Physical and Chemical Lake System 59 ever, these values should be redetermined using modern analytical techniques. Dissolved Oxygen In hypersaline waters, such as those in Mono Lake, oxy- at concentrations well below those Hence, dissolved oxygen concentrations, while near saturation, are moderate to low in the upper mixed layer (Melack, 1983; Lenz, 1984~. Spring values are between 4 and 7 ma/ 1, summer and autumn values are be- tween 2 and 6 ma/ 1. Below the thermocline or chemocline the water is without oxygen. gen reaches saturation in fresh water. . Inputs of Chemical Constituents from Surface Water and Groundwater The geochemical origin of the mineral content of moun- tain spring and stream waters flowing from the Sierra Nevada is well known (Feth et al., 1964; Garrets and MacKenzie, 1967; Stoddard, in press). Snowmelt derived from precipitation and groundwater become charged with carbon dioxide and interact with the soil and primarily granitic bedrock. . . . Chemical weathering ensues, and plagio- clase, biotite, and K-feldspars, for example, may be weath- ered to kaolinite. The mean chemical composition of the perennial springs in the Sierra Nevada as determined bY Feth et al. (1964) is very similar to the chemical composi- tion of the major streams that flow from the mountains into Mono Lake. The order of concentration of cations and anions in moles is: Ca2+ > Na+ > Mg2+ ~ K+ and HCO3- > SO42- > C1-. Analyses of surface ~ ~ ~ ~ ~ A ~ ~ ~ water and groundwater are pre- sented In LADWP (15~. The observed chemical differen- ces between surface and well waters indicate that calcium- dominated surface waters evolve into sodium-dominated well waters owing to evaporative concentration and subsequent precipitation of calcium carbonate. Calcium-dominated sur- face waters have conductivities (an index of concentration) of less than 300 ~mhos/cm (13 out of 13 cases), while

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60 The Mono Basin Ecosystem sodium-dominated well waters have higher conductivities (17 out of 18 cases). Four out of forty cases cannot be explained easily. Sodium was the dominant cation in one surface water and one well water with low conductivities (<300 ,umhos/cm), and calcium was the dominant cation in two well waters with high conductivities. The chemical composition of the springs varies some- what, but the springs are primarily dominated by sodium and carbonate plus bicarbonate (32 out of 35~. Paoha 1, Solo TT, and Dry Creek are the only spring waters in which chloride predominates over carbonate plus bicarbon- ate (Lee, 1969; LADWP, 1984~. The temperatures of the springs range from 7.~C at Bridgeport (LADWP, 1984) to 86C at the hot springs on Paoha Island (Lee, 1969~. The seasonal variability of hot spring temperatures and chem- istries has not been determinecI. Although the major ion chemistries of many springs are known, the contribution of the springs to the overall chemical budget of the lake cannot be calculated. This calculation would require data on the contribution of the springs to the basin's moisture budget, information that is not available (see chapter 2~. Data for the chemistry of atmospheric precipitation in the vicinity of Mono Lake are given in Melack et al. (1982~. Tufa Pinnacles Associated with Springs Tufa towers are formed by precipitation of calcite, high-magnesium calcite, and aragonite. This precipitation results from two related processes. First, there is the strictly inorganic precipitation of carbonate minerals that occurs when calcium-containing spring or stream waters mix with the carbonate-rich waters of Mono Lake. Calcium carbonate should precipitate directly when the ion activity product of the mixture of waters exceeds the solubility product of any of the carbonate minerals in question. However, in natural waters, supersaturation is commonly observed. High concentrations of phosphorus, for example, may inhibit the formation of calcium carbonate. The con- centrations of phosphorus in Mono Lake are high (see

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Physical and Chemical Lake System 61 above section on nitrogen and phosphorus). Second, the precipitation of calcium carbonate is enhanced by the activities of photosynthetic organisms. The formation of tufa pinnacles about the orifices of sublacustrine springs is a result of inorganic precipitation and the activities of mat-forming benthic algae, which can guide the precipita- tion of calcium carbonate minerals and thus determine the morphology of the resulting tufa pinnacles. Because photo- synthesizing algae take up CO2, they lower CO2 tensions in the microenvironment of calcium carbonate precipitation. The lowered CO2 tensions result in elevated CO32- activi- ties and enhanced precipitation of carbonate minerals. The mat-forming algae in Mono Lake are primarily filamentous green algae, diatoms, and blue-green algae (Scholl and Taft, 1964; Herbst, 1986~. Losses of Salts and Other Substances Substances are lost from the lake through sedimentation, deflation, and aerosol production. The amount of organic and inorganic materials lost from the lake water to the sediments of Mono Lake remains unknown. Comprehensive sedimentological and paleolimnological investigations have not been undertaken within the main basin of the lake, although uplifted Pleistocene sediments on Paoha Island (Lajoie, 1968; Reed, 1977) have been studied. Reed (1977, citing various authors) gives an average sedimentation rate for Mono Lake of approximately 0.40 m per thousand years. On the basis of his own research on the organic biogeo- chemistry of Mono Lake sediments, Reed estimates that 4 percent of the organic matter produced as a result of pri- mary production becomes sediment. Losses of salts by deflation and aerosol production occur in all closed basin lakes, but few quantitative data are available. Langbein (1961) discusses the primary mech- anisms responsible for the loss of salts to the atmosphere from concentrated lakes. He also points out that salts precipitated at the margins of lake basins may become unavailable to a lake in two ways. First, they may be blown away by the wind (deflation). Second, they may become covered over in such a way that they do not

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62 The Mono Basin Ecosystem redissolve when the lake level rises. The consequences of deflation at Mono Lake are clearly illustrated by the air quality problems that occur in the vicinity of the lake (Kusko and Cahill, 1984~. Geochemical Evolution The geochemical evolution of waters in the Mono Basin to a brine of Mono Lake's present-day chemical composi- tion can be explained in terms of the rock weathering / evaporative concentration / mineral precipitation model of lake water evolution (Garrels and MacKenzie, 1967; Eugster and Hardie, 1978~. However, the geochemical evolution of the water in Mono Lake is complicated by the presence of several volcanic hot springs that flow directly into the lake. In the first part of the following discussion the geo- chemical evolution of waters in the Mono Basin will be examined without taking the possible effects of the hot springs into account. At the end of this section the pos- sible effects of the hot springs chemistry on the lake will be explored. Atmospheric precipitation falling on the drainage basin interacts primarily with igneous and metamorphic silicate rocks according to the following generalized equation: cation A1 silicate (silicate rocks) + H2CO3 + H2O ~ HCO3- + H4SiO4 + cation ~ A1 silicate (clay minerals) where H2CO3 represents CO2 (aq) + H2CO3 concentrations above equilibrium levels (Stumm and Morgan, 1981). Garrets and MacKenzie's (1967) classic paper on the origin of the chemical compositions of spring and lake waters models the geochemical evolution of waters flowing from the Sierra Nevada. Judging from their chemical composi- tions (see LADWP, 1984), waters in the Mono Basin (including those flowing from the Mono Craters) evolved in . a slm1 ar manner. Available chemical analyses (Lee, 1969; LADWP, 1984) of the surface waters, wells, and springs are important because they indicate that the dilute waters of the Mono Basin in general contain higher molar concentrations of

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Physical and Chemical Lake System 63 bicarbonate than calcium. As a result of calcite (calcium carbonate) precipitation (see Eugster and Hardie, 1978), essentially all of the calcium initially present will be removed from solution as these waters are concentrated by evaporation. The shift from calcium dominance in the stream waters to sodium dominance in the more concen- trated wells and springs is presumably a consequence of the precipitation of calcite and related minerals. The chemical composition and geochemical evolution of Mono Lake is controlled primarily by mineral precipitation. Sodium, potassium, sulfate, carbonate plus bicarbonate, and chloride are concentrated by evaporation, while calcium, magnesium, and silicon are not. If Mono Lake becomes 1.4 times more concentrated than it is at present (about 125 g/l), minerals containing sodium will begin to precipitate. R. J. Spencer (University of Calgary, personal communica- tion, 1986) has constructed a geochemical model that indi- cates that bona (NaHCO3.Na2CO3.2H2O), mirabilite (Na2SO4.10H2O), and natron (Na2CO3.10H2O) start to pre- cipitate at low temperatures (near 0C) at these salinities. The solubilities of these minerals depend mainly on ion activities, temperature, and CO2 tension. Even though potassium is concentrated by evaporation, it is continuously lost from inflowing waters and lake brine as a result of exchange and fixation on clays (Spencer et al., 1985~. Sul- fate can be removed as a result of sulfate reduction and subsequent precipitation of metal sulfides or the loss of hydrogen sulfide to the atmosphere, but the high sulfate concentrations in the lake indicate that sulfate reduction is not a particularly important process in Mono Lake. Mira- bilite precipitation, on the other hand, can potentially remove considerable quantities of sulfate. Carbonate is currently lost from solution by the precipitation of car- bonate minerals (see below). Once the concentration of the lake reaches approximately 125 g/1, carbonate plus bicarbonate will begin to precipitate in winter as bona and patron. Chloride is very soluble in Mono Lake water, and it does not precipitate until saturation with respect to ha- lite (NaCl) is reached. This will not occur until the lake is about 10 times more concentrated than it is at present. Calcium, magnesium, and silicon are not concentrated by evaporation, and their concentration in Mono Lake is

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64 The Mono Basin Ecosystem determined by a variety of processes. Calcium precipitates as calcite, high-magnesium calcite, and aragonite. Some magnesium is removed as aragonite, but much of it may be lost from solution owing to the formation of clay minerals rich in magnesium and silicon (see Jones and Wier, 1983~. Silicon is taken up by diatoms and then lost to the sedi- ments, or it is utilized in the formation of clay minerals. In addition to mineral precipitation and dissolution, ions can be lost or gained by lakes owing to interactions with pore fluids. In lakes with fluctuating level, ions will dif- fuse into or out of the sediments as the concentration of the lake changes (Spencer et al., 1985~. Volcanic hot springs are very complex, but they can be viewed as being composed primarily of meteoric waters (derived from the atmosphere) that circulate to consider- able depths in the earth, where they interact with mag- matic gases and are heated (White, 1 957a,b). The mineral salts in hot-spring waters come largely from the original meteoric waters (e.g., Mono Lake water), condensed mag- matic gases, and rock-water interactions at depth (White, 1 957a; Ellis and Mahon, 1964~. Neither the moisture budget of the Mono Basin nor the geochemistry of the hot springs is known sufficiently to determine if the mineral salts from the hot springs (in excess of those contained in the orig- inal meteoric waters) have markedly affected the chemistry of Mono Lake water. The major effects that volcanic hot springs of the sodium chloride type should have on the waters of Mono Lake are to increase the relative proportions of sodium and chloride among the major cations and anions, respectively, and to increase the loading of silicon, boron, fluoride, bro- mide, iodide, lithium, and arsenic to the lake (White, 1 957a,b). Hot-spring waters such as those flowing from Paoha No. 1 on June 21, 1968 (Lee, 1969) are enriched in chloride ions (equivalent percentage among the anions equal to 47 percent) in comparison to Mono Lake water (equiva- lent percentage among the anions equal to 38 percent). Paoha No. 1 also contains high concentrations of fluoride (26.5 mg/1) and boron (227 mg/1), but these high concentra- tions are expected if Mono Lake was the original source of much of the meteoric water flowing from the hot spring. The minor elements (listed above) in Mono Lake water can

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Physical and Chemical Lake System 65 come either from the volcanic hot springs or from rock weathering in the Mono Basin. Sufficient hydrological and geochemical information is not available to distinguish one source from the other. REFERENCES Almanza, E., and J. M. Melack. 1985. Chlorophyll differ- ences in Mono Lake (California) observable on Landsat imagery. Hydrobiologia 122:13-17. Dana, G. L., D. B. Herbst, C. Lovejoy, B. Loeffler, and K. Otsuki. 1977. Physical and chemical limnology. Pp. 40-42 in An Ecological Study of Mono Lake, California, D. W. Winkler, ed. Institute of Ecology Publication No. 12. Davis, Calif.: University of California, Institute of Ecology. Ellis, A. J., and W. A. J. Mahon. 1964. Natural hydrother- mal systems and experimental hot-water/rock interactions. Geochim. Cosmochim. Acta 28:1323-1357. 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. Feth, J. H., C. E. Roberson, and W. L. Polzer. 1964. Sources of mineral constituents in water from granitic rocks, Sierra Nevada, California and Nevada. Geochem- istry of water. U.S. Geological Survey Water-Supply Paper 1 535-I. Washington, D.C.: U.S. Geological Survey. 70 pP. Garrets, R. M., and F. T. MacKenzie. 1967. Origin of the chemical compositions of some springs and lakes. Pp. 222-242 in Equilibrium Concepts in Natural Water Sys- tems. Advances in Chemistry Series No. 67. Washington, D.C.: American Chemical Society. Herbst, D. B. 1986. Comparative Studies of the Population Ecology and Life History Patterns of an Alkaline Salt Lake Insect: Ephyd~ra (Hyd~ropyr~cs) Hians Say (Diptera: Ephydridae). Ph.D. dissertation, Oregon State Univer- sity, Corvallis. 222 pp. Jassby, A., and T. Powell. 1975. Vertical patterns of eddy diffusion during stratification in Castle Lake, California. Limnol. Oceanogr. 20:530-543.

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66 The Mono Basin Ecosystem Jellison, R., and J. M. Melack. 1986. Nitrogen supply and primary production in hypersaline Mono Lake. Eos Trans. Am. Geophys. Union 67:974. Jellison, R., and J. M. Melack. In press. Photosynthetic activity of phytoplankton and its relation to environ- mental factors in hypersaline Mono Lake, California. In Saline Lakes, J. M. Melack, ed. Developments in Hydro- biology. Dordrecht, Netherlands: Dr W. Junk Publishers. Jones, B. F., and A. H. Weir. 1983. Clay minerals of Lake Abert, an alkaline, saline lake. Clays Clay Miner. 31:161 -172. Kilham, P., and R. E. Hecky. 1973. Fluoride: geochemical and ecological significance in East African waters and sediments. Limnol. Oceanogr. 18:932-945. Kusko, B. H., and T. A. Cahill. 1984. Study of Particle Episodes at Mono Lake. Final Report to California Air Resources Board on Contract A1-144-32. Davis, Calif.: University of California, Air Quality Group, Crocker Nuclear Laboratory. 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 PP. Lee, K. 1969. Infrared Exploration for Shoreline Springs: A Contribution to the Hydrogeology of Mono Basin, California. Ph.D. dissertation, Stanford University. 216 PP. Lenz, P. H. 1980. Ecology of an alkali-adapted variety of Artemia from Mono Lake, California, USA. Pp. 79-96 in The Brine Shrimp Artemia. Vol. 3. Ecology, Culturing, Use in Aquaculture, G. Persoone, P. Sorgeloos, O. Roels, and E. Jaspers, eds. Wetteren, Belgium: Universa Press. Lenz, P. H. 1984. Life-history analysis of an Artemia population in a changing environment. J. Plankton Res. 6:967-983. Lenz, P. H., S. D. Cooper, J. M. Melack, and D. W. Winkler. 1986. Spatial and temporal distribution patterns of

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