Phytoplankton production in the Great Salt Lake, Utah, and a
laboratory study of algal response to enrichment1
D. W. Stephens
Department
of Biology, University of Utah, Salt Lake City
84112
D. M. Gillespie
School of Biology, Georgia Institute of Technology, Atlanta
30332
Abstract
The annual production by phytoplankton in the southern basin of the Great Salt Lake
as estimated at two stations in 1973 averaged 145 g C mm2.The majority of the production
occurred during March and April and was due to an unidentified species of Dunaliellu.
Daily carbon fixation rates averaged 2.13 g C mm2at both locations during this period. A
minor phytoplankton bloom in August, due to a small, unidentified green flagellate contributed 5% of the total annual phytoplankton production. Phytoplankton production was
probably limited during April by self-shading and during the remainder of the year by
the availability of nitrogen, as shown by laboratory bioassays. Crazing by Artemia dina
reduces the phytoplankton population in late summer when nutrient levels have partially
increased due to regeneration. The meromictic character of the lake was indicated by profiles of temperature and density. The monimolimnion is postulated to act as a nutrient
sink, reducing the rate of nutrient release to the mixolimnion.
Despite its size and proximity to, a large
urban area, the Great Salt Lake has been
the subject of few limnological studies. Biological investigation of the lake has been
summarized by Stcphcns ( 1974). In 1970
WC began a program to identify the various
biotic components, inves tigatc their relationships, and determine primaly production of the southern basin of the Great Salt
Lake. Wirick ( 1972) reported on general
planktonic relationships:
through an itcrative model allowing growth of the principal
Dunalklla
uiridis Teodorphytoplankter,
esco, according to available solar radiation
and temperature, and a model which simulatcd grazing of DunaZklZa by the brine
shrimp Artemia salina hc derived an intcgrated model of plankton dynamics. This
model, using reported ingestion rates for
Artemia ( Reeve 1963) coupled with known
population density of Artemia in the lake,
could not predict the rapid annual decline
of Dunaliella populations observed during
April and May. Forcing the model with a
tenfold incrcasc in grazing rate would not
account for the observed dcclinc. Wirick
concluded that another factor, such as nu~’ This work was supported in part by a Univcrsity of Utah Research Committee grant.
LIMNOLOGY
AND
OCEANOGRAPHY
tricnt limitation or algal exocrincs, was involved. However, no algal cxocrines were
reported for Dunaliella isolated from the
Great Salt Lake by Van Ruken and McNulty ( 1973).
Stephcns and Gillcspic ( 1972 ) suggcs ted
that light limitation due to self-shading limited Dunaliella production, and grazing by
brine shrimp was responsible for reductions
in standing crop. Limitation due to nitrogen
or phosphorus deficiency was initially rcjcctcd bccausc these elements wcrc abundant in surface influent to the lake ( Coburn
and Eckhoff 1972). The current study was
undertaken to determine the phytoplankton
productivity
of the lake and to invcstigatc
further possible factors limiting phytoplankton growth.
Methods ancl materials
Great Salt Lake ( Fig. 1) is a shallow,
closed-basin, sodium chloride lake located
in the Great Basin (40”40’N, 112’2O’W).
The lake is 119 km long and 45 km wide
with a mean surface elevation of 1,280 m.
The maximum depth at this elevation is 11
m, with a mean depth of 4.4 m. The mean
surface area is 4.352 X lo5 ha and mean
volume is 1.90 x lOzo m3. A rock-filled rail74
JANUARY
1976,
V.
21(l)
Production
in Great Salt Lake
road causeway complctcd in 1957 divided
the lake into two portions, with the only
intcrchangc of water occurring through two
culverts, The southern basin receives the
majority of surface inflow so that dissolved
solids ( 259 g litcrl ) arc lower than in the
northern basin (275 g liter’ ) ( Cohenour
1966). Two midlako sampling locations in
the southern basin (station A: 40”48’N,
112’18’W; station B: 41”03’N, 112’22’W)
were selected for study, after consideration
of the current patterns infcrrcd by Hahl
and Handy (1969) to be comparable with
the work of Wirick ( 1972).
After early preliminary investigations in
1971 and 1972, each station was sampled at
about 2week intervals beginning in April
1973. Secchi depth and temperatures wcrc
measured, and oblique plankton tows were
taken with
a Clarke-Bumpus
sampler
equipped with a flowmeter and a No. 10
nylon net ( 175+m mesh). Water samples
were collected with an opaque plastic Van
Dorn bottle at the surface and 1, 3, 5, and
7 m. Samples for primary productivity were
incubated at constant depths because the
Secchi-determined compensation depth rcmaincd at or near the monimolimnion
during all months except April. Water samples
were collected in pyrcx bottles which were
immediately iced, transported to the laboratory in a dark cooler, and analyzed within
24 h.
Phytoplankton were counted live on the
day of collection with a hcmacytomcter and
results were calculated as the mean of four
0.9-mm” fields. The number of Artemia includes individuals from nauplius stage to
adult.
Routine brine analyses consisted of dcnsity determination
(ASTM hydromctcrs),
pH using a Leeds and Northrup
mctcr
equipped with calomcl electrodes, total dissolved plus suspended orthophosphate by
the ascorbic acid technique and .total filtcrable phosphate following pcrsulfatc digcstion (Am. Public Health Assoc. 1971))
reactive nitrate (using cadmium reduction)
and reactive nitrite (Strickland and Parsons
1968 ) , and ammonia nitrogen by distillation
and ncsslcrization (Am. Public Health As-
41°
4oo40’
. 112’30’
I >O
II 3”
l?ig. 1. Great Salt L‘ake, Utah. Contour intervals in meters above sea level, adapted from a
Utah Geological and Mineralogical Society map.
Points A and B mark sampling stations used in
1972-1973.
determinations
sot. 1971) . Calorimetric
were made using a Bausch and Lomb Spectronic 20. Due to the salt error introduced
in most brine analysts, all standards were
prepared with a synthetic medium consisting of rcagcnt grade chemicals representing
the average composition of the salts in the
southern basin of the lake as reported by
Cohcnour ( 1966). In addition, periodic
analyses for recovery were made by additions of varying amounts of phosphate, nitrate, borate, and ammonium salts to’ the
lake water. This combination of proccdurcs
verified the calibration curves used in the
sample analyses.
Analysis of the brines for total CO2 prcsentcd several problems. Distillation
(Vollenwcider 1969) was discarded because of
equipment limitations and the riced to process a number of samples rapidly; WC used
classical titration
methods (Am. Public
Health Assoc. 1971). Determination of pH
with
phcnolphthalcin
and bromcresol
green-methyl red indicators gave more consistcnt results than potcntiomctry.
Since
76
Stephens and Gillespie
the pH 4.6 end point of bromcresol grccnmethyl red was depressed to pH 4.0 by the
salt cffcct, all titrations are reported to $1
4.0.
The boron content of the Great Salt Lake
in the areas of our investigation averaged
35 mg liter1 in 1972 and 1973 (Utah Gcol.
Miner. Surv. unpublished),
This concentration of boron, when added to synthetically
prepared water simulating the Great Salt
Lake but unbuffered by phosphates, silicates, and carbonates, resulted in an average increase in titratable alkalinity of 35
mg litcrl.
We did not encounter phosphate
levels in the lake in excess of 2 mg P liter-l;
silica levels reported by Hahl and Handy
( 1969) were generally belo,w 5 mg liter-l.
This indicates that borate is the only noncarbonate buffer system contributing
appreciably to titratablc alkalinity.
As boron
levels could not be measured concomitantly
with alkalinity, a boron correction was dcrived from the experimentally measured 85
mg litcrl alkalinity contributed by an average boron concentration of 35 mg liter-*
and the average titratable alkalinity of 404
mg liter-l which we encountered in the
lake. Total carbonate alkalinity was rcprescntcd as titratable
alkalinity X 0.79 to
compensate for the borate effect. Titration
curves were cons tructcd periodically
according to procedures of Mason (1967) to
verify the buffering effect of noncarbonatc
systems. Titration of lake water to pH 3.5
from the usual pH of 8.2 typically required
8-9 meq liter-l of acid. Return titration to
pH 8.2 required about 2 mcq liter-l of base,
indicating a 20-25% contribution to buffering by noncarbonate systems.
Due to the lack of reliable dissociation
constants for carbonate species in dcnsc
brines, corrections of carbonate alkalinity
to total CO, as given in IIarvcy ( 1955)
were not attempted. At lower chlorinity
levels there is a slight linear relationship betwecn chlorinity
and apparent carbonate
dissociation values; at levels in the Great
Salt Lake ( 87s0), the specific activity of
ions in solution would have increased to
the point that any correction would be minimal. Extrapolation
from tables in Strick-
land and Parsons ( 1968) was thercforc rejected in favor of uncorrected carbonate
data to calculate total available inorganic
carbon.
Carbon-14 methodology-Water
filtered
through a No. 10 nylon net to rcmovc the
zooplanktcrs was used to fill paired 150-ml
light and dark bottles under shaded conditions. Each bottle was syringe-inoculated
with 1 ml of 14C sodium carbonate (3.926
&i ) from a sterile 20-ml strum vial and
rcsuspcnded from a polyurethane
buoy.
Separate 20-ml vials of isotope prcparcd
from a single large batch were used for
each scrics of six to ten bottles. The absolute activity of working solutions was dctermined by liquid scintillation counting. Incubations ranged from 4-7 11,between 1000
and 1800 hours MST; samples were immcdiately iced and filtered within 4 h.
A technique was developed for determining fixed llrC in the samples by liquid scintillation counting. A lo-50-ml subsample
from the bottles was filtered through a 25mm Cclotate filter ( Millipore Corp.) with
a porosity of 0.5 pm. Filtration was kept
at 0.5 atm to prevent cell damage. Filtered
lake water (2 ml) was added as a standard
rinse and the algal-filter complex put in a
standard scintillation vial. NCS solubilizer
( 2 ml) was added, the vial capped, and the
algae were allowed to digest overnight at
ambient tcmpcraturc, the filter being inert
to the basic digestion. After digestion, 10
ml of a standard scintillation cocktail (5 g
PPO + 0.2 g POPOP liter-l toluenc) was
added. The samples were allowed to dark
acclimate 4 h in a spectrometer; they wcrc
then counted for three 5-min periods, and
the average was calculated. Counting efficiency was determined by the channels ration technique ( Bush 1968) with original
calibration curves dctermincd with an internal standard ( 14C thiamine) added to varying weights of filtered algae (Pugh 1970,
1973 ) .
Surface incubations were not successful
until a modified buoy was introduced late
in the study. We therefore had to assume
constant production rates from the surface
to 1 m in order to estimate production.
Production
in Great Salt Lake
Production rates at each depth were calculated according to Goldman et al. ( 1969)
and then integrated through the water column using Simpson’s formula and trapezoidal approximation to yield values in mg
C rnB2h-l. In calculation of daily rates from
hourly rates, we assumed that photosynthesis per unit radiation was constant throughout the day and that nutrient dcplction did
not occur within the experimental bottles.
The fraction of daily incident light during
the incubation period was described by the
following equation, which adjusts for incubations nonsymctrically
spaced about midday (modified from Platt 1971).
F=
(F)
+&[sin(Ft2)
-sin(Ft’)l
In this equation h is daylength in hours
for each sampling day as given in nautical
almanacs for the appropriate latitude, tl
and t2 rcprescnt hours, plus or minus, refcrenced to local noon for the start and end
of the incubation.
Daily production was estimated by dividing the total production during the incubation period by the corresponding F value
to give production
in mg C m-2 day-l.
Monthly production was calculated by avcraging all daily values for that month and
multiplying the result by the average number of days in a month (30.4).
Algal bioassay methodology-We
used
the bioassay techniques outlined by the
Joint Industry/Government
Task Force on
Eutrophication
( 1969 ) . The test alga was a
Dunaliella
(possibly D. viridis)
isolated
from the Great Salt Lake in April 1973 and
maintained in PAAP medium. Bioassays
were conducted at 27°C with constant shaking of the 500-ml flasks by a reciprocating
shaker. Preliminary
experiments at the
PAAP-recommended
illumination
of 4,304
lux were unsuccessful because of light limitation, an inherent limiting factor in many
bioassays (O’Brien 1972). The data reported wcrc obtained under 8,070 (2270)
lux illumination
( 1.59 X 10” ergs cme2) sup-
77
plied by banks of “cool-white” fluorescent
tubes. Centrifugation
to separate cells
from nutrient media and constant shaking
did not adversely affect growth of the flagellate algae. The following additions of
carbon (as NaHC03), nitrogen (as NaNO&
phosphorus ( as I&HPOd), tither singly or
in combinations, were made to lake waters :
1 mg N liter-l, 0.05 mg P liter-l, 10 mg C
liter*, 1 mg N + 0.05 mg P liter-l, 1 mg N
+ 0.05 mg P + 10 mg C liter-l. Monimolimnetic water collected at 8.5 m and used in
one enrichment series was stripped of H2S
by displacement with pure oxygen. Difco
pcptone extract was added to on& series of
The trace elements mixture
cnrichmcnts.
used in the bioassay additions consisted of
1 ml liter-l of PAAP combined trace clcments. Inherent toxicity of the lake water
was investigated by the addition of PAAP
nutrients to separate controls. All assays
were run in triplicate; the average is rcported. Algal cells were counted with a
hemacytometcr.
Chlorophyll
determination was according to Strickland and Parsons ( 1968) using SP equations for chlorophyll
a and a Beckman model DB
Chemical analysts of
spectrophotomctcr.
lake water used in the bioassays were according to the Environmental
Pro tee tion
Agency ( 1971) .
Results
Field investigation-Average
daily productivity and solar radiation for stations A
and B arc given in Fig. 2. Extrapolation
from 1971 phytoplankton data (Fig. 3) indicatcs that there could have been considcrablc production during late March 1973,
but production was not actually measured.
Production could only have been negligible
during December, January, and February
due to low light intensities, low temperaturcs ( generally
l-9°C ) , and rcduccd
standing crop (1 x 10F cells litcrl).
We
assumed that maximum production
rates
during Dcccmber, January, and February
would bc no greater than production in November and would be directly proportional
to algal standing crop, which remained at
or below 1 X loo cells liter-l.
Production
Stephens and Gillespie
78
250
0
JFMAMJJASOND
TIME
IN
MONTHS,1973
Fig. 2. Monthly arithmetical averages of daily
production rate and radiation. O-Station
A; Ostation B; n-estimated
production; dashed line
-radiation.
was, therefore, cstimatcd to bc 5.57 mg C
m-2 day-l for December and January, using
the November daily production rate of 5.57
mg C m-2 at a population density of 1 X lo6
cells liter-l.
Given an initial population
size of 1 X 10” cells liter1 for 31 January
and a reported doubling rate of 100 h at
10°C for a Dunaliella
isolated from the
Great Salt Lake ( Van Auken and McNulty
1973)) the maximum population that could
accrue by 15 February would be about 15
X 10G cells literl.
If we use the average
November daily rate of 5.57 mg C rne2, avcragc February production was 84 mg C
ms2 day-l. The estimated March production of 1,423 mg C m-2 day-l was b,ascd on
an algal crop of 60 x lo6 cells liter1 (Wirick
1972) and a 6 April production rate of 23.71
mg C mm2day-l for a population of 1 X 10”
cells liter-l. Summation of average monthly
productioa provides an estimated annual
production of 222.72 g C rnB2 for station A
and 68.26 for station B. A considerable portion of the total production (73% for station
A, 15% for station B ) occurred in April and
coincided with the peak standing crop. The
relatively low productivity
estimated for
sta.tion B during April is the result of a 2-h
incubation
begun late in the day (1430
hours ) which undoubtedly
underestimated
Standing crop declined
actual production.
Fig. 3. Plankton
composition.
. -Phytoplankton 1971, station B; O-phytoplankton
1973,
station A; A-Artemia
1973, station A.
during May and remained below 1 X IO6
cells liter-l with carbo,n uptake remaining
below 40 mg C mm2day-l through July. A
300% increase in standing crop during August was accompanied by increased carbon
uptake at both station A, 7.66 g C mm2day-l,
and station B, 5.14 g C m-2 day-l. The phytoplankton population was then grazed by
the expanding numbers of Artemia, resulting in a decrease in standing crop and carbon uptake during Scptembcr. A slight increase in standing crop, 1.88-3 X lo6 cells
lit&r-l, during October was also accompanied by an increase in carbon uptake rates.
Declining temperature and solar radiation
during November begins the annual winter
decrease in standing crop and production
which lasts until March.
After the decline in the Dunuliella population in May 1973, a smaller (7 pm X 4
pm) flagellate appeared, which comprised
the majority of the phytoplankton
population for the rest of the year. This organism
and the larger Dunuliella sp. [identified for
the work of Van Auken and McNulty (1973)
by I-1. C. Bold] were mcntioncd by Kirkpatrick ( 1934) and designated ChZamydomonas types a and b. The small form was
responsible for a minor peak in production
at both stations during August and October
1973 (Fig. 2). No other phytoplankters
were found.
Carbon uptake profiles at both stations
for various days during 1973 are presented
Production
0
350
T3
I5
‘9
79
in Great Salt Lake
CARBON
UPTAKE
400
(
(
0\ 1
0‘.
0\
Is
\
z
I
I/
d
,’
I”
(mg Cm’”
d\/b
i1’
:v
h -I)
LaW
n
6 APR
t
0
4501
I
5
15 APR
I JUL
28 MAY 9JUN
6147
II
PHYTOPLANKTON
CARBON
UPTAKE
0
0
25
0
IO
20
.
0 3
24
I
1 5
37
.5 d
I8JUL
3
(x IO6 liter”)
(mg C m -3h ‘1)
IO
1 201
0I
5I
\
\
I
‘0
B
No
\
No
1’
i
: 0’ 0’
d
28JUL
0
67
8
3
IIAUG
25AUG
381
123
I
1
0
IO 0
5
PHYTOPLANKTON
15SEP
I
0
I P 0 0 0 061
d
l4OCT
I I2
30
I
3
> 3
(x lOGliter”)
IINOV
6
I
6
i
Fig. 4. Station A, 19’13. Daily carbon uptake, Secchi depth, and phytoplankton distribution.
l Carbon uptake; O-phytoplankton.
Ve,rtical line indicates Secchi depth; total daily uptake in mg C
in-” given under date.
in Figs. 4 and 5. If WC USCthe relationship
of 5 X Secchi depth as a rough measure of
the euphotic zone (Verduin 1956)) WC find
that the entire mixolimnion was within the
euphotic zone except during April. Production rates at station A were highest during
April and were apparently light-limited
bclow 3-4 m. Rates at both stations tended
to be low from May to August, when inci-
dent radiation was greatest. Production
during April was maximal within the upper
3 m, but later in the year tended to be maximal at 5-7 m, suggestive of possible photoinhibition during periods of high illumination and light penetration. This is in accord
with Ryther’s (1956) report that photosynthesis within the Chlorophyta
in general
declined to 5-10s of that at light saturation
80
Stephens and Gillespie
CARBON
080103
UPTAKE
(mgC mb3h ‘I>
0 3 0 25
25APR 28 MAY 9JUN
342
8
26
t
I
01500
Fig. 5.
t
I
18JUL II AUG I5 SEP
26
169
6
1
.I
0 6 0
5 (
3060
PHYTOPLANKTON
(x IO6 liter”)
Station B, 1973. Explanation
I4 OCT
144
5
same as Fig. 4.
(538-8,070 lux) when intensity reached the
equivalent of full noon sunlight (8.6-10.76
X 10” lux ) . The vertical distribution
of
phytoplankton showed no obvious correlation with production rates or with nitrogen
and phosphorus concentrations.
The random distribution
of the flagcllatc
aIgae
leads us to bclicve that currents rather than
active mobility determine population distribution.
The increase in phytoplankton
standing
crop in August was accompanied by incrcascd carbon fixation rates. A considcrable increase in the Artemia population
several weeks earlier (Fig. 3) may have resulted in enrichment from excretion of ammonia and other nuricnts (see Johannes
1968). Although
ammonia nitrogen was
not obscrvcd to increase in August, it
could have been immediately absorbed by
the phytoplankton
with only a short residence time in the water.
No phytoplankton
productivity
rates
showed increases attributable to enhanccment due to herbivore grazing as was observed in laboratory systems by Cooper
(1973).
Population fluctuations o,f A. salina (Fig.
3) were largely determined by the avail-
ability of its primary food source-the
two
phytoplankters.
Nauplii from over-wintering eggs appeared in April 1973 when water
tempcraturcs reached lo”-14°C
and algal
crop was maximum. Artemia populations
consist entirely of nauplii in April and averagcd 48% nauplii in May 1973. Population peaks in July and August 1973 consisted of 66% and 75% nauplii and overlap
a minor phytoplankton
bloom. Population
composition in 1973 was similar to that in
1970-1971 ( Wirick 1972), with maximum
population densities of 12-18 Artemia liter-l
each year in April and May. No increase
in Artemia was reported for August 1970.
The animals die off late in November when
water temperatures drop below 6°C (Rclyea 1937).
In gcncral, values for nitrate-N, nitrite-N,
ammonia-N, and phosphate-P varied with
time but not depth. Data from station A
( Fig. 6) were typical also of station B.
Gibor (1956) reported the optimum phosphorus concentration for Dunaliella &i&s
under laboratory conditions to be 4.5-22.7
mg P liter-l, with considerable growth also
at O-4.5 mg P liter-l. Thomas (1964) found
Dunaliella primolecta to bc limited by a
phosphorus concentration
of 620 ,ug P
Production
81
in Great Salt Lake
900
27
-i
:600
lT
300
(r
2.150
i
Z
100
F
2
ii
l3
z
50
0
AMJJASON
TIME
IN
MONTHS,1973
levels and phytoplankton
Fig. 6. Nutrient
populations for station A, April-November
1973.
0 -Phytoplankton;
A--ammonia nitrogen as N;
n-nitrate
nitrogen as N; O-dissolved + suspended orthophosphate as I?; a-total
filterable
phosphorus as P.
liter-1 under laboratory conditions.
Concentrations of readily assimilable dissolved
and suspended orthophosphate within the
Great Salt Lake were generally greater
than 500 lug P lit&
during our 1973 study,
indicating that phosphorus was never critically depleted. Total filterable phosphate,
that part of the total phosphorus pool which
passes through a 0.45~pm filter and including “soluble” organic phosphorus, declined
during June, gradually increased through
August, declined in October, and increased
in November. The increases in total filterable phosphorus during August and Novembcr correspond to increases in Artemia
and may bc the result of organic phosphorus excretion or of the initial stage of remineralization of dead organisms, The declinc in orthophosphate during May may
reflect demands on the phosphorus pool by
the expanding DunaZieZZu population during
April. In addition, bacterially induced nutrient immobilization
of phosphorus and nitrogen during this time may also account
for the reduced nutrient levels.
Nitrogen at 3.5 mg liter-l was found to be
limiting under laboratory conditions (mean
growth constant 0.1058 h-l as opposed to
0.1354 h-l in N-rich cultures ) for D. primo-
Fig. 7. Temperature
tion A, April-November
isoplcths
1973.
(“C)
for sta-
Zecta (Thomas 1964). The nitrogen requircments of DunaZieZZu in the Great Salt
lower than
Lake must be considerably
nitrate and amthose of D. primolecta:
monia nitrogin were never encountered in
excess of 600 pg N liter-l during 1973, yet
considerable -phytoplankton
-production was
evident. DunaZieZZa viridis can use ammonia
as a nitrogen source but the growth rate is
higher with nitrate (Gibor 1956). The red&ion in nitrogen during May was accompanicd by a decline in the phytoplankton
standing crop and in carbon uptako rates,
Following the April bloom, nitrate remained
below 40 lug N literl through November.
Ammonia was the most abundant form of
nitrogen throughout the year, with nitrite
typically absent. Ammonia and nitrate nitrogcn did not increase until September,
suggesting low rates of nitrogen rcmineralization similar to those reported by Antia
et al. (1963). The 1973 nitrogen pattern
was similar to that in 1971-1972 in the
Great Salt Lake (Porcella and Holman
1972 ) ,
IIandy ( 1967) rcportcd a heavy brine
from about 8 m to the bottom throughout
the central portion of the Great Salt Lake.
This layer was present from about 7.5 m to
the bottom at both stations in 1973 and was
remarkably resistant to mixing cvcn during
periods of storm activity. The meromictic
character of the lake is evident from isopleths of water temperatures at stati.on A
82
Stephens and GiZZespie
Table 1. Chemical analyses of Great Salt Lake waters used in laboratory bioassays. Concentrations
given in mg liter-‘. Analyses performed by Water Quality Laboratory, State of Utah Department of
Health, according to procedures recommended by Environmental Protection Agency ( 1971) .
Collection
date
18 Jul
14 Ott
Surface
Surface
Arsenic,
Barium,
dissolved
dissolved
0.15
0.00
Boron, dissolved
Calcium, dissolved
15.35
840
Chromium,
hex.
as Cr
Mercury,
Nickel,
sus. & diss.
dissolved
4,000
sus.
& diss.
* Our analyses.
+ Analyses performed
0.06
3,250
0.00
44,000
40,000
0.27
Silica,
dissolved
as SiO2
Tot. alkalinity
as CaC03
Tot. hardness as CaC03
iron,
14.30
0.00
0.012
Potassium,
dissolved
Silver,
dissolved
Sodium, dissolved
Zinc, dissolved
Tot.
Turbidity
0.006
0.190
0.00
0.00
1,703
0.28
Copper, dissolved
Iron, dissolved
Lead, dissolved
Magnesium, dissolved
Manganese, dissolved
Collection
date
'18 Jul
14 Ott
14 Ott
Surface
Surface
8.5m
7.00
410
1.00
493
5.70
113,000
68,500
246
0.64
Hydroxide
as OH0.02
SulEate as S0428,400
Surfactant
as MBAS
0.02
Total diss. solids
(18OOC) 135,220
8.15
PH
Phosphate,
ortho as PO4
0.60
Nitrate
as N
0.15
Nitrite
as N
0.00
Total Kjeldahl
N
2.s5+
Ammonia as NH3-N
1.69+
Hydrogen sulfide
Laboratory
9,100
as JTU
Bicarbonate
as HCO:
Carbon dioxide
as CO2
Conductivity
umhos cm'1
at 25OC
Chloride,
dissolved
Carbonate alk. as CaC03
Fluoride,
diss. as F
density
(16OC)
1.090*
8.20*
0.7L*
0.25
0.00
23.00+
0.165*
1.097*
7.80*
0.36*
0.04*
o.oo*
15.00+
5.50*
2.00*
1.180*
3.8
by Ford Chemica'l Laboratories,
for the period April-November
1973 (Fig.
7). At no time were monimolimnetic
temperatures equivalent to those of the mixolimnion. The mixolimnion did not stratify
thermally and appears to bc well mixed
from the end of May through October.
Monimolimnetic
water maintained an average specific gravity of 1.18 g ml-l (range
1.175 to 1.182) throughout the study, never
approaching the lower density ( 1.092) of
the mixolimnetic
water. The dark bro;wn
color and odor of samples collected frolm
the monimolimnion indicated anaerobic hydrogen sulfide production which was verified on several occasions by measurement
of 3-6 mg l&S liter’.
Lin et al. ( 1972)
charac terizcd the monimolimnetic
water as
anaerobic, with pH near 7.5 and conductivity 20% greater than overlying
waters.
Analysis of monimolimnctic
water collected
in October 1973 at 8.5 m, (Table 1) indicatcs considerable ammonia and organic
Salt
Lake City,
Utah.
nitrogen resulting from the degradation of
dead plankton, Ephydra larvae, and Atiemia eggs and fecal pellets.
Laboratory bioassays-Chemical
analyses
of Great Salt Lake water used in the algal
bioassays arc given in Table 1. A complete
analysis was made for only the initial assay
series. The effects of various additions to
water collected in July and October are
prescntcd in Figs. 8-11. Experimental
flasks required 9 days to reach the maximum phytoplankton
population
when a
mixture of 5% or 10% (by volume) monimolimnctic water and lake water was used
( Fig. 8) as compared to 12 days for most
nutrients.
The stimulatory
effect of the
monimolimnctic
water was exhausted by
the twelfth day, and phytoplankton
numbers declined more rapidly than with other
nutrient additions.
In all single nutrient assays, the addition
of 0.05 mg P liter-l failed to stimulate
Production
83
in Great Salt Lake
180
10% monimolimnion l
5% monimolimnion 0
*o
-
[lmg N+.05mg
P+liter’l
Img N liter-’ l
.05 mg P liter”
*
800
r
ImgN+.O~mgP+l0mg
C
+ 40 mg peptone
liter”
A
ImgN+.05mgP+IOmg
C liter’lo
IO mg C liter”
0
control
-t
-I
w
0
80
0
-
40-
0
3
DAYS60F
15
18
INSCUBA~ON
Fig. 8. The effect of nutrient additions to water collected 18 July 1973 from station A. Laboratory bioassay flasks inoculated with Dunahella.
growth, populations generally following the
declining growth pattern of the controls.
In all cases, addition of 1 mg N liter-l rcsultcd in increased phytoplankton
growth
for 9-12 days; after this nitrogen became
exhausted or another factor became limiting and growth declined. Addition
of
mixtures of 1 mg N liter-l + 0.05 mg P
liter-l resulted in- growth greater than in
the controls but not greater than with nitrogen alone. Mixtures-of nitrogen and phosphorus produced a greater percentage of
healthy cells at the end of the 15-H-day
assays, as shown by the results of chlorophyll extraction ( Fig. 11) . The low chlorophyll values for 18 July were from cxtractions made after the populations
had
rapidly declined. Extractions for 14 October were made shortly after growth was
maximum.
The addition of 10 mg C liter-l to water
collected in October resuitcd in a very small
increase in phytoplankton
numb&
(Fig.
9) and a decrease, compared to the control,
in chlorophyll a at the end of 15 days ( Fig.
11). The reason for the high
- chlorophyll
- _
content of the control for this scrics is not
-
Fig. 9. The effect of nutrient additions to water collected 14 October 1973 from station A. Laboratory bioassay flasks inoculated with Dunakda.
known. The combination of nitrogen, phosphorus, and carbon stimulated growth over
the control but not to the levels of nitrogen
alone or of nitrogen and phosphorus. Chlorophyll a values ( Fig. 11) indicate that nitrogcn and phosphorus may be more stimulatory than cithcr nutrient alone.
Although Gibor (1956) and Van Auken
400r
T
; 300
C
-
UJ
g
v)
;
w
0
I
/
ImgN+.05mg
P+lOmg
C liter-/A
200
100
I
0
2
4
DAYS
OF
6
8
INCUBATION
IO
I2
Fig. 10. The effect of nutrient additions to
water collected 14 October 1973 from station A.
Laboratory bioassay flasks inoculated with Dunaliellu. PAAP trace elements used (Jt. Ind. Gov.
Task Force Eutrophication 1969).
84
Stephens and Gillespie
I8JUL
73
CONTROL
N
P
N+P
5 O/oM
IO O/oM
140CT
73
CONTROL
N
P
N+P
C
C+N+P
C+N+P+
PEP I
l4OCT
73
(l2-day assay)
CONTROL
I
1
C+N+P
C+N+P TRACE
I
0
IO
CHLOROPHYLL
(198)
I
20
g (yg liter-‘)
(45)
30
Fig. 11. Chlorophyll a concentrations at the conclusion of bioassays. Nutrients added per liter:
carbon, 10 mg; nitrogen, 1 mg; phosphorus, 0.05 mg; monimolimnetic water (M) 5$%, 10%; PAAP
( trace) elements 1 ml; peptone (PEP) 40 mg.
and McNulty
( 1973) reported DunaZieZZa The peptone-cnrichcd
cultures exhibited
to be completely autotrophic Van Auken
considerable turbidity due to increased bactcrial growth; this was also noted by Fred( pcrsomal communication)
reported difficrick ( 1924) and Kirkpatrick ( 1934).
culty in maintaining some axenic populaThe effects of the addition of 1 ml of
tions of a Dunaliella from the Great Salt
Lake without the addition of pcptone to PAAP trace elements per liter to water colthe medium. He did not experience this lected in October arc shown in Fig. 10.
problem with nonaxenic cultures. The ad- Trace clcmcnts stimulated growth although
dition of 40 mg of pcptonc extract per liter
not as much as mixtures of nitrogen, phosto a mixture of 1 mg N + 0.05 mg P + 10 phorus, carbon, and peptone. Chlorophyll
a values ( Fig. 11) substantiate the growth
mg C liter-l rcsultcd in massive stimulation
results, indicating greater production in the
of growth (Fig. 9). Although phytoplankmore complc te nutrient mixtures.
ton numbers in peptonc-enriched
cultures
were higher, the size of the individual cells
was smaller than the avcragc 5 pm x 8 Conclusions
pm DunaZiella, a characteristic
of rapid
Phytoplankton
production in the southern basin of the Great Salt Lake in 1973
growth ( Carlucci and Silbernagel 1969).
Production
in
Great Salt Lake
85
was significant primarily during March and Mann (1973) found that on a global scale,
geographical variations in primary producApril with daily carbon fixation arithmctitivity correlates better with geographical
tally averaging 2.13 g C m-2. An unidentivariations in available light than with gcofied spccics of DunaZieZZu was responsible
for most of the annual production, but in- graphical variations in available nutrients.
Autoinhibition
of DunuZieZZa by cxtracclcreases in standing crop and carbon uptake
in August and October were due to’ a lular products is not shown by the work of
smaller, unidentified
green flagellate. The Van Auken and McNulty ( 1973) nor by our
bioassays for toxicity.
average annual phytoplankton
production
The availability of inorganic nitrogen in
rate of 145 g C rns2 would make the lake
naturally eutrophic ( 75-250 g C rnw2 yrl ) Great Salt Lake water appears toI bc the
factor limiting
DunaZieZZa standing crop
according to the scheme of Rodhc ( 1969).
This rate is somewhat lower than those for under laboratory conditions, according to
other hypcrsaline environments:
Lake Wc- our algal bioassays and Porcclla and Holman ( 1972). Averages of nitrate-N in lake
rowrap, Australia, 435 g C rn-” (Walker
1973); Alviso saltern, California, 700 g C water collected after April have ranged
from our values of 0.03 mg liter-l to 0.18
me2 (Carpelan 1957); Borax Lake, Califormg liter-l, considerably below the levels renia, 386 g C mm2(Wctzcl 1964); Mono Lake,
ported to be limiting for D. primolecta
California, 1,000 g C rns2 ( Mason 1967).
(Thomas 1964). We found ammonia nitroHowever, little is kno,wn of the production
rates of the benthic blue-green algae Coc- gcn to remain below 0.7 mg liter-l during
summer 1973; it was below 0.5 mg liter-l
cochloris elabens Drouct and Daily, which
forms calcareous reefs covering about 10% for summer 1972 (Porcclla and Holman
of the bottom of Great Salt Lake, and the 1972). Phosphorus (total filterable + dissolved and suspended orthophospha tc ) consecondary production rates of its associated
ccntratioa never fell below 1 mg P literl
Ephydra larvae. Inclusion of the benthic
production
with that of DunaZieZZu and during 1973. Laboratory bioassays using
Great Salt Lake water indicated that mixcoupled with a potential phytoplankton
conversion efficiency of 53% for Artemia
tures of nitrogen and phosphorus clid not
(Gibor 1957) would indicate a system of stimulate growth more than nitrogen alone,
high primary and secondary productivity.
but resulted in greater chlorophyll producPrevious modcling studies (Wirick 1972) tion as measured shortly after maximum
have indicated that grazing by Artemia
population
growth. Carbonate alone did
cannot account for the annually observed
not stimulate growth appreciably, and when
rapid decline in DunaZieZZu. However, the
added together with nitro,gen and phosfeeding of large populations of Artemia
phorus,
stimulated growth less than just nimay limit standing crops during the latter
trogen
and
phosphorus. The addition of 1
part of the summer when nutrient levels in
ml
liter-l
of
PAAP combined trace elcmcnts
the lake are increasing and can support a
to
nitrogen-,
phosphorus-, and carbon-engrcatcr phytoplankton population than that
observed. Light limitation imposed by the richcd waters resulted in a rapid increase
mass of algal cells may be the initial factor
in ccl1 numbers. The relatively high populimiting production and restricting natural
lation density of DunuZieZZu in these cultures
Dunaliella population size below 250 x lo6 was maintained over a longer period than
cells liter-’ during the April bloom when the in single elcmcnt enrichment series, an d
compensation depth is 3-4 n-r. This agrees chlorophyll a values in the more complete
with the conclusion of Van Aukcn and Mcadmixtures were four to six times grcatcr
Nulty ( 1973) that the doubling time for a than single element or double element enDunaZieZZa isolated from the Great Salt Lake
richments.
approaches infinity when light intensities
The ability of pcptonc extract in combifall below 1 klux. Also, Brylinsky
and nation with nitrogen, phosphorus, and car-
86
Stephens and Gillespie
bon to stimulate phytoplankton
growth
could be attributed
to several factors.
Tract elements or amino acids in the peptone may have been directly available to
the expanding Dunaliella po,pulation. Alternatively, the bacterial growth evidenced
by the turbidity in the flasks may have provided nutrients secondarily to the algae by
increasing the rate of nutrient cycling. In
addition, organic complcxing may have increased the availability
of inorganic nutricnts to the DunaZieZZa. Due to the relatively
large amount of pcptone added (40 mg
liter-l ) , considcrablc quantities of nitrogen,
phosphorus, or other nutrients present may
have provided an auxiliary nutrient source
in which no factor was limiting over the
15-day assay.
The meromictic character of the lake is
evident from thermal profiles and variations
in specific gravity. Despite the large fetch
area and shallowness, the monimolimnion
retained its integrity throughout the period
of observation in 1973. The monimolimnctic layer may act as a nutrient sink in
which denitrification
could result in considerable loss of nitrogen from the system
(see Kuznetsov 1968) and rates of nitrification and ammonification
arc reduced, resulting in a diminished turnover rate for nitrogen and possibly other elements. The
stability of this layer, imparted by its dcnsity and hydrogen sulfide content, prevents
the physical and biological nutrient distribution and cycling that operate in the sediment zones of most lakes (Porcella ct al.
1972 ) .
Our conclusions of nitrogen limitation
following the April bloom arc in agrecmcnt
with Hornc’s ( 1972) belief that the rate of
nitrogen turnover becomes important once
the supply of winter nutrients has been exhausted by a spring bloom. Additionally,
in concentrated brines where ionic interactions are abundant and nonidcal behavior
of aqueous solutions common, the statement
of Stumm and Morgan (1970) that the activity 0E nutrients is of greater importance
than their concentration should bc cmphasized.
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Submitted:
17 October 1974
Accepted: 1 August 1975