SOME EFFECTS OF LAKE RENEWAL ON PHYTOPLANKTON
PRODUCTIVITY
AND SPECIES COMPOSITION1
Mike Dickman
Institute
of Fisheries,
University
of British
Columbia,
Vancouver
ABSTBACI’
Primary production
in Marion Lake is inversely related to the rate at which water enters
the lake when light intensity
is corrected to a standard level. Increased flushing rates
reduce the phytoplankton
standing crop thereby lowering the total primary
productivity
in the lake. Thus seasonal variations in rainfall in southwestern
British Columbia exert an
appreciable
influence on the annual productivity
pattern of the lake’s phytoplankton.
L‘ake water artificially
enclosed within small areas of the lake produced algal blooms
while phytoplankton
standing crop in the rest of the lake remained low. Nannoplankton
appear to have a selective advantage over larger, more slowly reproducing
forms in Marion
Lake. The production : biomass ratio for Hke phytoplankton
was used as an indication of the
general type of limiting factor affecting the instantaneous rate of productivity
in the lake.
INTRODUCITON
A substantial literature has been gathered concerning nutrients, light, and temperature as limiting factors in phytoplankton production ( Hutchinson 1967). In the
case of a small lake with high runoff, these
factors may be of secondary importance
if considerable plankton standing crop is
being removed by flushing.
Under these
circumstances, primary production, as carbon fixed per individual,
is high because
nutrients would rarely seem to be limiting
since few organisms are competing for
them. Production per unit volume is, however, low due to the paucity of producers
remaining in the water column.
I am grateful for the assistance of K.
Tsumura in preparing the figures and to
B. IIargrave, T. G. Northcotc, G. Gecn,
and I. E. Efford for encouragement and
constructive criticism. I am also grateful
to the Fisheries Research Board of Canada
for financial assistance.
lake is 800 m long and 200 m wide but
has a drainage basin of only 6.5 km2. The
annual rainfall recorded near the lake averaged 240 cm per year over a lO-year
period frolm 1958 to 1968. Runoff is heavy
owing to the shallow soil and the steepness
of the drainage ‘Jasin. During heavy spates,
the lake level may rise as much as 1 m in
24 hr. If heavy rain continues uninterrupted, the entire volume of the lake is
replaced in less than 2.3 days (Efford
1967 ) ,
METHODS
Large plywood enclosures, 3.05 m square,
with sides measuring 1.84 m high were
constructed and placed in Marion Lake at
“X” and “Y” ( Fig. 1). The base of the
enclosures extended 0.40 m into the lake
sediment leaving 1.44 m exposed above
the mud. The m.ean depth of water at
these locations was approximately 1 m, so
that 0.44 m of the enclosures extended
above the surface o,f the lake.
During periods of high inlet discharge,
LAKE
DESCRIPTION
the lake level rose above the tops of the
Marion Lake is situated in the coastal
enclosures. By the time the lake level fell
mountains of southwestern British C’olumbelow the enclosure tops, the water inside
bia (49’91’ N lat and 123’33’ W long) at and outside the enclosures was nearly idenan altitude of 300 m above sea level. The
tical in all respects. Immediately after the
enclosures were flushed following an in1 This study is issued as Canadian International
crease in lake height, the primary producBiological
Program Contribution
No. 15.
tivity and species composition inside and
2 Present address: Department
of Biology, Unioutside the enclosures were recorded. In
versity of Ottawa, Ottawa 2, Ontario.
660
LAKE
PREVAILING
FIG, 1.
RENEWAL
ON
profile
of Marion
Lake,
British
all cases, initial productivity
and species
composition values inside the enclosures
were similar, that is, not significantly
different from those taken at station “A” or
“E” ( Dickman 1968).
Two-liter water samples were removed
from enclosures 4 and 4’ as well as from
stations A and E ( Fig, 1) using a Meyer
sampler. The six other enclosures depicted
in Fig. 1 were also sampled. These results
as well as a full description of the methods
are given in Dickman ( 1968). Samples
were taken at 0.5 m three tirncs a week
from 27 April to 4 June 1967. After the
addition of Lugol’s IKI preservative, the 2liter samples were left undisturbe,d for two
days to allow adequate sedimentation time;
all but the bottom fifth of the water column was then siphoned off. The remaining material was placed in a 500-ml jar
and allowed to resedimcnt. This procedure
was repeated until all the plankton contained in the original 2-liter sample was
concentrated into a lo-ml vial. The height
of the sedimcnted sample in the vial was
used as an index of standing cro,p. Sample
compaction did not vary greatly and co,nsequcntly the index proved fairly reliable.
After the standing crop had been calculated, a l-ml subsample was removed from
the vial to make a permanent quantitative
slide mount ( Dickman 1968). A colTcction
for the percentage detritus in the sample
661
PRODUCTIVITY
SPRING
I
WIND
Contour
EFFECTS
‘N
Columbia,
with
insets of the wooden
enclosures.
was also, made using these quantitative
slide mounts. All the phytoplankton
in 90
randomly selected microscope fields was
counted for each slide: 30 under oil immcrsion, 30 under high dry, and 30 under
medium power.
Additional
water samples were withdrawn from the same locations on these
days and inoculated with 4 @i of carbon14 (Goldman 1963). The samples were
incubated from 1000 to 1400 hours in the
lake near station E at a depth of 0.51 m.
After incubation,
the samples were collected in a light-tight box, transported, and
filtered through HA 0.45~p-pore-diameter
Millipore
membrane filters.
The filters
were then dried in a desiccator and sent
to the International Agency for the Determination of 14C in Denmark.
Inlet discharge was recorded on a continuous recorder operated by the Canadian
Department of Northern Affairs and National Resources. During December and
January, the recorder at the inlet of Marion
Lake broke down; therefolre, values for
this period are from estimates based on
discharge data from the nearby North
Alouette River. Light duration and precipitation were measured at the University of
British Columbia Department of Forestry
Field Station which is located less than
1.5 km from Marion Lake. Light intensity
measurements were made using a record-
MIKE
DICKMAN
.
FIG. 2. Primary
productivity
values from outside ( open circles ) and inside ( closed circles ) the
enclosures over a six-week period. Arrows indicate
dates on which high inlet discharge resulted in the
kake level rising above the tops of the enclosures.
ing pyrheliometer
placed on a platform
1.5 m above the lake’s surface.
FIG. 3.
side ( open
enclosures
as in Fig.
Standing crop measurements from outcircles > and inside ( closed circles ) the
over a six-week period.
Arrows, same
2.
differed more than 1C from the water temperatures outside the enclosures.
Since
temperature was not consistently different, it is unlikely that it played a significant role in increasing primary production
within the enclosures.
RESULTS
Primary productivity
within the enclosures increased toi nearly four times the
value found outside the enclosures (Fig,
2). Standing crop increased in a similar
manner ( Fig. 3 ) . In four weeks, algal
blooms were evident within both enclosures. These blooms (>100 cells/ml) were
generally composed of small Chlorophyta
such as Oolqstis sp. or Elukutothrix sp. In
contrast, no blooms occurred in the lake
itself and primary productivity
in the lake
outside the enclosures remained low. On
7 April, a persistent heavy rain resulted
in the level of the lake rising above the
tops of the enclosures. Fo,llowing this
flushing of the enclosures (arrows, Figs. 2
and 3)) productivity
and standing crop inside the enclosures declined sharply and
then slowly began to increase again.
Temperatures within the enclosures rarely
18
33
,30
E”
H 24
i >,
4
1 ‘*
i lb
,*
9
6
J
FIG. 4.
Daily
inlet discharge
during 196&1967.
into Marion
Lake
LAKE
RElNEWAL
S
0
I
l-
J
J
A
EFFECTS
I
N
ON
I
0
I
J
I
I
F
M
I
A
M
1967
1966
FIG. 5. Mean daily primary productivity
bars are from the 1963-1964 data of Efford
663
PRODUCTIVITY
measured at E at 0.5 m during 1967-1968.
( 1967), recorded From station A at 1 m.
A comparison of the annual pattern of
light intensity ( g cal cm-2 day-’ ) with the
annual primary productivity
curves, was
made by Efford ( 1967); the amount of
light recorded during spring and fall was
similar although primary productivity
was
low in spring and high in fall. The annual
primary
productivity
pattern fro’m my
1966-1967 data is similar to the one described by Efford (see Fig. 5). Annual
changes in light intensity, therefore, do not
appear to be well correlated with primary
productivity.
The annual inlet discharge pattern (Fig.
4) was compared with the annual primary
productivity
pattern ( Fig. 5) and the two
were inversely related. When inlet discharge was plotted against primary productivity on days having similar mean light
intensities (only days having 0.50 4 0.05 g
cal cm-2 hr-1 were used in these calculations) a significant correlation was found
( Fig. 6). As the inlet discharg,e and consequently the lake’s flushing rate increased,
primary productivity
( mg C m-3 hr-1 )
Variegated
decreased. Thus high inlet discharge was
associated with low primary productivity
(r = 0.57 with 66 df and “p = <O.Ol ).
250.
PRIMARY
PRODUCTIVITY
(mg C/m’
per hr)
AT CONSTANT
LIGHT
FIG. 6. Primary productivity
with light intensity corrected
to a standard level against inlet
discharge.
A correlation
coefficient
of 0.57 with
66 df was found significant
( p = <O.Ol ).
664
MIKE
DICKMAN
DISCUSSION
Marion Lake is similar to many other
small lakes that act as temporary impediments to the flow of water from inlet to
outlet ( Brook and Woodward 1956). Such
lakes are unusual because of the major role
that flushing plays in regulating their primary pro,ductivity.
The high flushing rate
of these lakes exerts its effect on both the
type and the quantity of phytoplankton
inhabiting their waters. Species which reproduce fast enough to offset their removal
by flushing dominated the plankton of
Marion Lake (95% of the phytoplankton
are nannoplanktcrs, i.e., l-10 p long; Dickman 1968). These small, predominantly
flagellated organisms have high reproductive rates (Findencgg 1965). The fact that
desmids and large diatoms, both abundant
in the periphyton of the lake where they
are unaffected by flushing, are nearly absent from the lake’s plankton reinforces
the hypothesis that the flushing rate may
be a dominant selective pressure in determining the species composition of the phytoplankton of this lake,
The relationship between phytoplankton
productivity
and the flushing
rate in
Marion Lake has provided the basis for a
general model about types of limiting factors. Whether such a model is valid cannot
be determined
from the Marion Lake
study alone but it is worth stating here,
as it attempts to bring together a large
number of related observations regarding
limiting factors.
Raymont (1963) stated that at one extreme a population’s size is determined almost exclusively by grazing intensity while
at the other extreme it may be limited by
nutrients. These extremes can be classified
with respect to phytoplankton
as : 1) factors which limit productivity
by SU~~~VSSing the rate of reproduction of individual
organisms (resource limitation such as nutrients, light, temperature), and 2) factors
which limit productivity by removing individuals from the lake’s plankton (grazing,
flushing, disease). The former will be referred to as “resource” factors and the
latter as “cropping”
factors. Populations
limited by one factor behave quite differently from those limited by the other.
Populations limited by cropping factors
respond by increasing their productivity
per individual (Slobodkin 1960) while those
limited by resource factors have low productivity per individual
but may have a
relatively high productivity
per unit volume because of the high standing crop
often associated with resource-limited populations. Consequently, knowledge about
a lake’s primary productivity
alone or the
standing crosp alone is insufficient to allow
dctcrmination
of which factor is limiting
the primary productivity.
Furthermore, it
is important to determine which of these
two general factors is limiting the productivity of the phytoplankton
because this
information is likely to explain a great deal
about the kind of interaction occurring between the different trophic levels within
the lake. The production to biomass ratio
(mg C fixed m-3 hr-l)/(mg C m-3 of standing crop) can be used as an index in determining which limiting factor is most likely
to be do,minating the productivity
of the
phytoplankton
in a lake at any particular
time. If the quotient (production per unit
biomass) is low, it is probable that a
resource factor is more important in limiting the primary productivity
than a cropping factor and vice versa. It should be
emphasized that this constitutes an instantaneous measure and care should bc taken
not to, generalize about the type of limiting
factor operating in a particular lake unless
the production to biomass ratio is calculated with data taken throughout the year
from representative
stations and depths.
The production to biomass ratio has also
been used by Margalef (1963, p. 360) as
an index of species and pigment diversity:
“We get a bloom of plankton and the state
of lower maturity is reflected both in a
decreased diversity at all the [trophic]
levels, and in an increased ratio-primary
production/biomass.”
High diversity is indicated by a low P : B quotient. It follows,
therefore, that high diversity is more likely
to bc cncountercd in resource-limited communities than in those limited by cro,pping
LAKE
RENEWAL
EFFECTS
ON
PRODUCTIVITY
665
factors. This relationship was borne out in tributed most to the low rate of primary
productivity
recorded there.
my study.
2. Wooden enclosures constructed in the
As previously
mentioned,
the species
composition of the phytoplankton can also lake prcvcnted water from leaving them.
standbe used as an indication of the type of As a result, both the phytoplankton
ing crop and primary productivity
were
factor limiting its productivity.
In Marion
significantly
higher within the enclosures
Lake, small plankton capable of passing
than in the lake two weeks after the enclothrough a No. 25 net (0.064-mm-diameter
mesh) contribute about 95% of the lake’s surcs had been flushed.
3. The ratio of standing crop (numbers
total phytoplankton
primary productivity
( carbon
( Effo’rd 1967). Thus the high rate of per liter ) to primary productivity
water renewal observed in the lake ap- fixed per unit volume per hour ) expressed
pears to have given smaller organisms
as primary productivity per individual may
be a reliable indication
of the type of
( nannoplankton,
capable of rapid rcproproductivity.
duction) a selective advantage over spe- factor limiting phytoplankton
A lake in which predation, flushing or
cies reproducing
at a slower rate. The
latter are more likely to be discharged from
other so-called cropping factors are importhe lake before they have attained a sig- tant may have low primary productivity
nificant standing crop. When flushing was per unit volume while its primary proprevented in the wooden enclosures, larger
ductivity
per individual
would generally
species such as Oolcystis sp. and H&obe much higher than a lake in which the
thrix sp. attained bloom concentrations al- phytoplankton
was limited by a critical
though their density in the lake itself
resource such as a lack of phosphate or
remained insignificant.
Such observations
light. Thus, information about both physupport the hypothesis of Margalef (19612) toplankton standing crop and productivity
that cropping factors tend to retard the may be prerequisite
to determining
the
rate at which a succession progresses most probable limiting
factor operating
toward maturity. The species composition
within any given lake.
of the phytoplankton
in Marion Lake is
4. Although nannoplankton
comprised
indicative
of what Margalef (1967) de- the dolminant algal type in the lake, the
scribed as the first or least mature stage relative abundance of nannoplankton
in
in his successional series.
the enclosures was much lower than it was
Although
a lake’s phytoplankton
pro- in the lake itself. Algal blooms occurring
ductivity may be extremely low, it would
in the enclosures were dominated by relabe of little value to conduct tests of pos- tively large species such as Oocystis sp.
sible limiting nutrients o,r other resources
and Eluktothrix
sp. This supported the
when both the species composition and the hypothesis that flushing per se alters both
P : B ratio for that lake give clear indicadensity and species composition of the
tion that cropping factors rather than re- phytoplankton.
source factors arc responsible for limiting
5. A continuum may exist bctwecn what
its primary productivity,
is defined as a stream or a lake (Brook
and Woodward 1956). Marion Lake apSUMMARY
pears in such a continuum more as a
stream than as a lake.
1. The flushing rate in Marion Lake,
British Columbia, is very high, At times
REFERENCES
the water within the lake flushes in less
than 2% days. Such a high flushing rate BROOK, A. J., AND W. B. WOODWAIU>. 1956.
Some observations
on the effects of water
greatly reduces the phytoplankton
standinflow and outflow on the plankton of small
ing crop by removing these organisms via
lakes.
J. Animal Ecol., 25: 22-35.
the outlet, that is, “cro8pping” them. the
DICKMAN, M.
1968. The relation of freshwater
paucity of phytoplankton
in the lake conplankton productivity
to species composition
666
MIKE
during induced
successions.
Ph.D. Thesis,
University
of British
Columbia,
Vancouver.
11.5 p.
EFFORD, I. E. 1967. Temporal
and spatial differences
in phytoplankton
productivity
in
Marion Lake, British Columbia.
J. Fishcries
Res. Board Can., 24: 2283-2307.
GOLDMAN, C. 1963. The measurement
of primary productivity
and limiting
factors
in
freshwater
with carbon-14,
p. 103-113.
In
M. S. Doty red.], Proc. Conf. Primary Production
Measurement
Marine
Freshwater.
U.S. At. Energy Comm. TID 10-7633.
IIUTCHINSON, G. E. 1967. A treatise on limndogy, v. 2. Wiley.
1115 p.
FINDENEGG, I.
1965.
Relationships
between
standing
crop
and prim,ary
productivity.
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Mem. 1st. Ital. Idrobiol.,
18( Suppl.):
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ductivity
in aquatic
Univ.
Calif. Press, Berkeley.
1966. 464 p.
MARGALEF, R. 1962. Succession in marinc populations.
Advan.
Frontiers
Plant Sci., 2:
137-188.
-.
1963. On certain unifying principles in
ecology.
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-.
1967.
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Helgolaender
Wiss. Meeresuntersuch.,
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RAWONT, J. E. G. 1963. Plankton and productivity in the oceans.
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660 p.
SLOBODKIN, L.
1960.
Ecological
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level.
Am. Naturalist, 94: 213-236.