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OCR for page 50
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
OCR for page 51
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.
.
OCR for page 52
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.
OCR for page 53
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 20°C. Minimum winter temper-
atures are near 0°C (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
OCR for page 54
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.
OCR for page 55
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
OCR for page 56
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-
OCR for page 57
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.
OCR for page 58
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-
OCR for page 59
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
OCR for page 60
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
86°C 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
OCR for page 61
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
OCR for page 62
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
OCR for page 63
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 0°C) 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
OCR for page 64
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
OCR for page 65
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.
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Representative terms from entire chapter:
mono basin
