&EPA
                      f nvironmsntal Research
                      Laboratory
                      Duiuth MN 55804
           Hesecpofi snd Development
Effects of Nutrient
Enrichment,  Light
intensity and
Temperature on
Growth  of
Phytoplankton from
Lake Huron
                 LIBRARY
                 U.S. EMVIF.OMEKTAL!
                 EDTSGfl, N.J. 08817
 79-OU9   ^


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                 RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environmental
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                                                 EPA-600/3-79-049
                                                 October 1979
     EFFECTS OF NUTRIENT ENRICHMENT, LIGHT INTENSITY,
AND TEMPERATURE ON GROWTH OF  PHYTOPLANKTON FROM LAKE HURON
                           by

            C. Kwei Lin and Claire L. Schelske
              Great Lakes Research Division
           Great Lakes and Marine Waters Center
                 University of Michigan
                Ann Arbor, Michigan 48109
                    Grant No.  R800965
                     Project Officer

                    J. Kent Crawford
               Large Lakes Research Station
         Environmental Research Laboratory-Duluth
                Grosse lie, Michigan 48138
         ENVIRONMENTAL RESEARCH LABORATORY-DULUTH
            OFFICE OF RESEARCH AND DEVELOPMENT
           U.S.  ENVIRONMENTAL PROTECTION AGENCY
                  DULUTH, MINNESOTA 55804
                        BRARY

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                                DISCLAIMER
     This report has been reviewed by the Environmental Research Laboratory-
Duluth, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency,  nor does mention of
trade names or commercial products constitute endorsement or recommendation
for use.
                                     11

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                                  FOREWORD
     This report contains results of an extensive  set  of  experiments on the
effects of nutrient enrichment on the growth  of  natural  phytoplankton
assemblages from Lake Huron.  It is unique  in that  responses  to added
nutrients were determined for individual  species within  the phytoplankton
assemblages which were naturally occurring  and which were produced by complex
dynamic interactions within the ecosystem.  The  results  clearly show that
phosphorus stimulated phytoplankton growth  more  than any  other nutrient and
is therefore the nutrient which must be controlled  to  prevent accelerated
eutrophication or overproduction of algal bioinass.
                                      iii

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                                  SUMMARY


     This report consists of three major parts:  a seasonal study on effects
of nutrient enrichment on the growth of natural phytoplankton assemblages, ef-
fects of light and temperature on the growth of natural phytoplankton assem-
blages and effects of light and temperature on the growth of three species of
diatoms maintained in laboratory cultures.  Natural phytoplankton assemblages
collected from a station located 43°33'09" and 82°29'11" in southern Lake Huron
were used for bioassays by adding nutrients directly to lake water samples.
Ten experiments were conducted from April to December 1975 to evaluate
nutrients that were limiting phytoplankton production in surface waters of
southern Lake Huron.  In each experiment, responses of the natural phyto-
plankton populations to nutrient treatments were determined by chlorophyll
production and cell counts.  Nutrient treatments including 18 combinations
were divided into two groups:  ALL treatments or lake water (LW) treatments.
The complete set of nutrients used in the experiments, phosphorus, nitrogen,
silica, EDTA, iron, trace metals other than iron and vitamins, were combined
as one treatment designated ALL.  Other ALL treatments consisted of deleting
one or two nutrients from the ALL treatment.  The LW treatments consisted of
single spikes of EDTA, phosphorus, nitrogen and silica added directly to lake
water.  Five levels of phosphorus (1, 3, 5, 10 and 20 pg P/liter) also were
used as ALL treatments.

     Responses to different treatments were varied and complex among treat-
ments during the seasonal study.  Responses were complicated further because
major changes in the species composition of phytoplankton occurred as the
result of treatments; the most obvious effect of this type was the drastic
reduction in proportion of diatoms when silica became limiting in the ALL
treatments.   Other changes were noted at the species level.

     Of the treatments tested, nitrogen had the least effect on chlorophyll
production.   Deleting nitrogen in the ALL treatment usually caused no change
in chlorophyll production in comparison to the complete ALL treatment, and
adding nitrogen in the LW treatment did not increase chlorophyll production.

     Phosphorus, on the other hand, had the greatest effect on chlorophyll
production.   Deleting phosphorus from the ALL treatment in some experiments
resulted in a response similar to that for untreated lake water, but in other
experiments chlorophyll production was greater than in untreated lake water.
However, the maximum response (greatest chlorophyll production) was never
obtained in an ALL treatment with phosphorus deleted, and chlorophyll produc-
tion in the ALL treatments generally increased with increasing phosphorus con-
centrations at levels as small as 1 and 3 yg P/liter in some experiments.  The
response to additions of phosphorus alone to LW varied seasonally but was
always distinct.  Phosphorus as a single factor in treatments was less
                                      IV

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significant in stimulating chlorophyll production during July, August and
September than in other months.

     Deletion of EDTA and Fe-EDTA reduced chlorophyll production greatly in
comparison to the complete ALL treatment, but not as much as deletion of
phosphorus.  Deleting EDTA caused bigger reductions than deleting Fe-EDTA;
however, this was complicated because deleting EDTA apparently caused an
inhibitory effect due to the trace metals in the ALL treatment.  Deleting
trace metals had a small effect, but deleting trace metals and EDTA reduced
chlorophyll production significantly during July, August and September.

     Silica deletion in the ALL treatments usually had a relatively small
effect on chlorophyll production, but occasional depletion in lake water
resulted in drastic reduction in diatom proportion.  Addition of silica as a
single spike had little or no effect on chlorophyll production.

     Phosphorus produced the largest response of any single addition to lake
water and additions of EDTA increased production to a small degree in several
experiments.

     Phosphorus, EDTA, and possible Fe-EDTA were the most important factors
in stimulating chlorophyll production in the ALL treatments.  During the
summer months phosphorus and either EDTA or both EDTA and Fe-EDTA were needed
in the ALL treatment to obtain maximum responses.  During this time neither
phosphorus nor EDTA added singly caused large increases in phytoplankton
growth.
                                                             — 2    — 1
     The effects of light intensities (40, 80, and 160 pEin m   sec  ) and
temperatures (5, 10 and 18°C) on the growth of winter phytoplankton assem-
blages were evaluated under optimum nutrient conditions.  Both chlorophyll
standing crop and cell counts increased with temperature and light intensity.
At 5°C, the effect of light intensity was less than at other temperatures.
Species responses in the assemblage were variable.  Growth of Cyclotella
comensis, the dominant population at the beginning of the experiment,
increased little compared to other species and was greatest at 10°C.
C. stell-igeTa also appeared to grow best at 10°C.  The majority of species
that were present abundantly among various light-temperature treatments, were
eurythermal.  Di-atoma tenue var. elongatum, Fragilcan-a orotonensis, Nitzsahia
acicularis and Synedra filifoxmis were the dominant populations at the end of
the experiment with maximum growth rates ranging from .59 to 1.15 divisions
day"1.  Phosphorus to nitrogen uptake ratios increased with temperature and
with light level at 10 and 18°C as did phosphorus to silica uptake ratios.
Production of chlorophyll per unit of phosphorus and silica consumed increased
with temperature and with light level at 10 and 18°C.

     The effects of light intensity and temperature on the growth of diatoms
was also studied with cultures isolated from the Great Lakes which had been
maintained in liquid culture for at least one year.  A total of twelve species
were maintained in a Chu 10 medium modified by reducing the hardness, trace
metal constituents and organic substances to levels approximating those found
in the upper Great Lakes.  Specific growth rates were determined for three
species, Diatoma tenue var. elongatum, Fragilaria erotonensis and Asterionella
formosa, in separate light and temperature gradient experiments.  The light

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intensity was set at 15, 40, 120 and 300 uEin m~2 sec l and temperature at 5,
10 and 18°C.  The saturation light intensity for optimal growth was approxi-
mately 120 yEin m~2 sec"1 for Diatoma and Asterionella, and 40 pEin m~2 sec"1
for Fragilaria.   Maximum growth rates for all three taxa were similar at 10°
and 18°C, but were significantly reduced at 5°C.  Cellular chlorophyll content,
however, was inversely related to light level, but was affected by temperature
to a lesser degree.  Growth rates from these experiments compared with results
obtained from nutrient enrichment bioassays of natural phytoplankton communi-
ties indicate that the unialgal isolates of the three species have greater
specific growth rates under culture conditions than were obtained from the
same species in natural assemblages growing in enriched natural lake water.

     This report was submitted in fulfillment of grant no.  R800965 by Claire
L. Schelske, Great Lakes Research Division, University of Michigan, under the
sponsorship of the U.S. Environmental Protection Agency.  This report covers
a period from May 1, 1973 to October 31, 1976, and was completed as of October
31, 1976.
                                     vi

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                                  CONTENTS
Foreword	
Summary	    ^v
Figures	viii
Tables 	     *
Acknowledgements	xii

    1.  Introduction 	     1
    2.  Nutrient Enrichment Bioassay 	     3
             Methods 	     3
             Physical-chemical characteristics of sampling site	     6
             Phytoplankton species composition and abundance 	     9
             Nutrient enrichment experiments with natural phyto-
               plankton assemblages	    15
             Discussion	    39
    3.  Effects of Light and Temperature	    42
             Introduction	    42
             Methods	    42
             Results	    46
             Discussion	    57
    4.  Conclusions and Recommendations	    59

References	    61
                                     vii

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                                  FIGURES


Number                                                                   Page

   1     Map of Lake Huron indicating the sample location 	       4

   2     Seasonal variation in total dissolved phosphorus (TOP),
           nitrate and silica concentrations of surface water at
           sampling station 	      10

   3     Seasonal variation in water temperature at sampling station.      11

   4     Seasonal variation of phytoplankton standing crop as
           indicated by chlorophyll a levels and cell numbers ....      12

   5     Effect of nutrient enrichments on phytoplankton growth
           indicated by chlorophyll a level (yg l"1)  and line at  end
           of bar indicates ± one standard deviation.  Experiment
           period 13-23 April 1975	      17

   6     Experiment period 2-12 May 1975.   See Fig. 5 for further
           explanation	      19

   7     Chlorophyll a production in response to varying phosphate
           concentrations.   Experiment period 2-12  May 1975  	      19

   8     Experiment period 2-12 June 1975.   See Fig.  5 for further
           explanation	      21

   9     Chlorophyll a production in response to varying phosphate
           concentrations.   Experiment period 2-12  June 1975  ....      22

  10     Experiment period 1-10 July 1975.   See Fig.  5 for further
           explanation	      23

  11     Chlorophyll a production in response to varying phosphate
           concentrations.   Experiment period 1-10  July 1975  ....      25

  12     Experiment period 23 July-1 August 1975.   See Fig.  5 for
           further explanation  	      26

  13     Chlorophyll a production in response to varying phosphate
           concentrations.   Experiment period 23 July-1 August 1975  .      27
                                    viii

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Number                                                                   Page

  14     Experiment period 19-28 August 1975.  See Fig. 5 for
           further explanation	      29

  15     Chlorophyll a production in response to varying phosphate
           concentrations.  Experiment period 19-28 August 1975. .  .      30

  16     Experiment period 9-18 September 1975.  See Fig. 5 for
           further explanation 	      31

  17     Chlorophyll a production in response to varying phosphate
           concentrations.  Experiment period 9-18 September 1975.  .      31

  18     Experiment period 23 September-2 October 1975.  See Fig. 5
           for further explanation 	      33

  19     Chlorophyll a production in response to varying phosphate
           concentrations  Experiment period 23 September-2 October
           1975	      33

  20     Experiment period 21-30 October 1975.  See Fig. 5 for
           further explanation 	      34

  21     Chlorophyll a production in response to varying phosphate
           concentrations.  Experiment period 21-30 October 1975 .  .      35

  22     Experiment period 10-19 December 1975.  See Fig. 5 for
           further explanation 	      36

  23     Chlorophyll a production in response to varying phosphate
           concentrations.  Experiment period 10-19 December 1975.  .      37

  24     Seasonal variation in effect of nutrient treatments on
           chlorophyll production (ratio of chlorophyll a values
           measured in final and initial days of the experiments).  .      38

  25     Effects of water temperature on growth of Astevionella
           formosa, Dtatoma tenue var. elongation and Frag-Llarta
           orotonens'ls in culture.   Growth is determined by cell
           numbers (except for F. crotonensis) and chlorophyll a
           concentrations  	      54

  26     Effects of light intensity on growth of Asterionella
           fovmosa, Diatoma tenue var. elongation and Fragilaria
           erotonensis in culture.   Growth is determined by cell
           numbers and chlorophyll a concentrations  	      55
                                     ix

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                                   TABLES

Number                                                                   Page

   1    Schedule and Platforms for Routine Sampling 	    5

   2    Nutrient Combinations for Enrichment Bioassay 	    7

   3    Variety and Concentration of Nutrients for Enrichment
          Experiments 	    8
   4    Temperature Levels,  Light/Dark Cycles and Light Intensities
          Programmed for Each Experiment	     8

   5    Seasonal Variation of Species Composition and Population
          Density of Phytoplankton Communities at Sampling Station. .  .    13

   6    Effect of Temperature and Time Delay on Phytoplankton Response
          (yG Chlorophyll a/L)  to Nutrient Enrichment During Summer
          and Winter	    16

   7    The Effect of Various P Concentrations in Complete Enrichments
          (ALL)  on the Growth of the Two Most Abundant Species of the
          23 July 1975 Experiment.   N Indicates Cell  ml"1  and k the
          Number of Doublings day"1  	    29

   8    Chemical Composition of Improved Culture Medium for Great
          Lakes  Diatoms (FM  Medium)	    44

   9    Species  and Origin of Planktonic Diatoms That Have Been
          Isolated and Cultured in Single Species Culture  	    45

  10    Species  Composition  and Abundance of Winter Phytoplankton in
          Southern Lake Huron	    47

  11    Average  Growth Rate  of  Phytoplankton Cultured in 9 Light-
          Temperature Combinations  in 9 Days.   Rates  (r) are Calculated
          as Number of Doubling (Cell Number and Chlorophyll)  per Day  .    48

  12    Effects  of Light and Temperature on Species Growth Rate of
          Enriched Winter Phytoplankton 	    49

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Number                                                                   Page

  13    Chlorophyll Production and Nutrient Consumption in Phyto-
          plankton Culture at 9 Light-Temperature Combinations
          During a 9-Day Period ....................   51

  14    Effects of Light and Temperature on Ratios by Weight, of P,
          N and SI Consumed per Unit ..................   52
  15    Maximum Growth (K^x) rates of Asterionella formosa, Diatoma
          tenue var.  elongation and Fragilaria arotonensis Incubated
          at 3 Temperature Levels ...................   52
  16    Maximum Growth Rates (I^ax) of Astevionella formosa, Diatoma
          tenue var.  elongation and Frag-Llaria orotonensis Incubated
          at 4 Light  Levels ......................   56

  17    Variation of  Cellular Content of Chlorophyll a as Affected by
          Different Light Intensities .................   56

  18    Variation of  Cellular Content of Chlorophyll a as Affected by
          Temperature Levels ......................   57
                                     xi

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                             ACKNOWLEDGMENTS
     We thank Paul Friedrich for his excellent performance in bioassay
experiments and organizing experimental results.  We gratefully acknowledge
the help of Laurie Feldt for phytoplankton identification and counts, and
Jill Goodell and Paul Swiercz for water chemistry analyses.  We are also
grateful to the personnel of the U.S. Coast Guard at Selfridge Air Force Base
who assisted in field sampling.

     Appreciation is expressed for the assistance and interest of the Grant
Project Officer, Kent Crawford.
                                     xii

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                                 SECTION 1

                                INTRODUCTION


     It is generally recognized that the Great Lakes have been undergoing
accelerated eutrophication (Beeton 1969) and that phosphorus is an important
nutrient associated with the process (Schelske et al. 1974).  In the upper
Great Lakes it seems clear that additional phosphorus inputs accelerate eutro-
phication (Schelske 1975).  Increased inputs of phosphorus not only enhance
primary production but also may cause depletion of other nutrients.  The shift
in nutrient limitation may cause changes in species composition and succession.
In Lake Michigan, Schelske and Stoermer (1971) predicted that continued silica
depletion resulting from increased inputs of phosphorus would limit the growth
of diatoms and gradually cause a shift from communities dominated by diatoms
to those dominated by blue-green and green algae.  Similar effects due to
limited availability of nutrients such as trace elements and accessory growth
factors such as vitamins and chelates may also occur.

     Schelske et al. (1972) demonstrated that phosphorus, when combined with
small quantities of trace metals, vitamins and a chelate, had a greater effect
on Lake Superior phytoplankton than phosphorus alone.  Deficiencies of minor
nutrients are more likely to occur in oligotrophic lakes than in eutrophic
lakes.  Goldman  (1972) found that a significant deficiency of trace metals
occurred in lakes of high latitudes and high altitudes.  Similarly, vitamins,
biotin and thiamine, have been shown to be important growth factors for many
species of phytoplankton  (Provasoli and Carlucci 1974), and deficiency of these
organics are found in oligotrophic waters (Carlucci and Bowes 1972; Goldman
1972).  Gerloff and Fitzgerald (1975) found that in addition to phosphorus,
vitamin BI, %i2> boron and zinc are limiting nutrients to Great Lakes
Cladophora.  Little is known about the individual effects of these micronutri-
ents on Great Lakes phytoplankton; even less is known about their availability
in open waters of the Great Lakes.

     Sewage effluents probably are still the major source of phosphorus inputs
in the Great Lakes.  As sewage effluents also contain other ingredients that
may stimulate algal growth in some waters, it is important to consider the
combined effects of multiple nutrients and other factors in nutrient enrich-
ment experiments.  Previous results indicate that the predicted effects of
nutrient enrichment based on phosphorus alone are perhaps conservative
(Schelske et al. 1974).

     The temporal changes in species composition and population densities of
phytoplankton assemblage along with background nutrients, light and tempera-
ture regimes of  the water mass would, a priori, affect the  intensity and
variety of limiting nutrients seasonally in the Great Lakes.  To understand
the dynamic features of seasonal nutrient limitation we decided that bio-
assays must be conducted  as frequently as possible during an annual cycle.

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     Nutrient enrichment bioassays have been widely used to study effects of
nutrient supplies and limitation to phytoplankton growth in natural waters.
Although the methods have been designed in various degrees of complexity, two
major approaches are commonly involved in nutrient enrichment experiments:
(1) add nutrients to filtered lake water in which cultured species are inocu-
lated (PAAP 1969; Smayda 1974); and (2) add nutrients to natural water which
contains natural phytoplankton standing crops (Thomas 1969).  The first
approach is useful only in evaluating relative nutrient effects based on total
phytoplankton production for one species and thus has limited value in rela-
tion to evaluating the effects of nutrient conditions on species composition
and succession,  which can be evaluated with the second approach.

     The primary objectives of the present project include:  (1) to determine
the seasonal variations in the effect of phosphorus limitation to phyto-
plankton growth; (2) to determine the effect of nutrient limitations other
than phosphorus; (3) to determine the importance of chemical changes on
growth and succession of phytoplankton assemblages; and (4) to investigate
the effects of light and temperature on phytoplankton growth and nutrient uti-
lization.

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                                 SECTION 2

                        NUTRIENT ENRICHMENT BIOASSAY


     Bioassay experiments were undertaken to determine the effects of nutrients
and accessory growth factors on the growth of naturally occurring phytoplankton
assemblages.  As little information is available on the role these factors play
in regulating phytoplankton production and species composition in the Great
Lakes, these experimental results will fill a critical need for data which can
be used in establishing water quality criteria.

     Data from these experiments will be particularly useful as they were
obtained concurrently with an investigation of limnological conditions, includ-
ing phytoplankton-nutrient relationships, in southern Lake Huron and Saginaw
Bay (Schelske et al., In prep.; Stoermer et al., In prep.).
METHODS

Field Sampling

     Lake water samples containing natural phytoplankton used in the bioassay
experiments were taken from a station at 43°33'9"N and 82°29'11" in southern
Lake Huron (Fig. 1).  This station is approximately 60 km due north of Port
Huron and 15 km offshore from the Michigan thumb.  The location was designated
as station 13 in GLRD's Southern Lake Huron Project (Schelske et al., In prep.)
The water quality of this location was characterized as open southern Lake
Huron segment 7 (IJC 1976), or Zone IV as described by Schelske and Roth
(1973).

     A total of 10 experiments were conducted throughout the year (Table 1).
To take advantage of the ongoing limnological investigations, the first three
samples were scheduled to coincide with ship cruises for the southern Lake
Huron project.  Those samples were taken from the R/V ROGER R. SIMONS around
noon and delivered to the Ann Arbor laboratory about 2200 hr.  After June,
all water samples were taken by U.S. Coast Guard helicopter between 1400-1500
hr.  The helicopter made sampling possible throughout the rest of the schedule
and reduced the time from collection to arrival in the laboratory to less than
4 hrs, about 6 hrs. less than the previous method.  On each date 20 liters of
surface lake water (3-5 m) were collected by casting 5-liter Niskin bottles
from the hovering helicopter.  A 25-kg anchor was attached to the end of the
sampling line to ensure sampling at the desired depth.

     To prevent the phytoplankton samples from being exposed to excessive
light, the water samples were taken with opaque Niskin bottles and immediately

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      MILES
  0  10  20  30  40
   0   20  40  60
   KILOMETRES
FIG.  1.   Map of Lake Huron indicating the sample location.

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             TABLE  1.   SCHEDULE  AND  PLATFORMS  FOR ROUTINE SAMPLING
             Date                              Platform

             April 13,  1975                       Ship
             May 2,  1975
             June 2,  1975
             July 1,  1975                       Helicopter
             July 23,  1975
             August  19, 1975                       "
             September  9, 1975
             September  23, 1975                    "
             October  21, 1975                      "
             December  10, 1975
             March 17,  1976                        "
transferred to a 20-liter rectangular polyethylene container.  During trans-
porting, the water samples were kept in the dark in a well-insulated chest
cooler packed with ice to maintain a stable water temperature.  Normally, the
water temperature varied no more than 1°C between that in the field after
collection and that on arrival in the laboratory.

Laboratory Procedures

     Immediately upon returning to the laboratory in Ann Arbor (between 1730-
1800 hr) , the samples were processed for bioassay experiments, including water
chemistry analyses, chlorophyll determinations and phytoplankton counts.

Water Chemistry —
     After thorough mixing of the lake water sample, a 250-ml sample was
filtered through a 47-mm Millipore filter (0.45 ym pore size), which was used
for chlorophyll a determinations by the method of Strickland and Parsons
(1968).   The filtrate was analyzed for total dissolved phosphorus (TOP),
  3~N and Si02 with a Technicon Auto Analyzer.
Phytoplankton —
     Phytoplankton species composition and abundance were determined at the
beginning and end of the experiments by procedures similar to Stoermer et al.
(1975).  A subsample of 50-ml lake water was fixed with 4% glutaraldehyde and
kept in the refrigerator at 4°C overnight.  The fixed phytoplankton was re-
suspended by shaking and filtered onto a 25-mm AA Millipore filter.  After
partial dehydration through an ethanol series, the filter was embedded in
clove oil, mounted on a 50 x 70-mm glass slide and then covered with a 43 x
50-mm #1 cover glass.  It took approximately two weeks for the preparation
to dry.  After drying, the edges of the cover glasses were sealed with paraf-
fin.  Phytoplankton present in the preparation were identified and counted
using a Leitz Ortholux microscope.  Population estimates given are the average
counts of two radii (10 mm), calculated as number of cells per ml.

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Nutrient Bioassay—
     For bioassay experiments, 250-ml samples of the untreated lake water were
dispensed into 54 numbered 500-ml polycarbonate Erlenmyer flasks.  The flasks
were divided into 18 three-flask sets with each set receiving one of 18 nutri-
ent treatments, shown in Table 2.  The nutrient combination in each treatment
was made up by dispensing 0.5-ml aliquots of separately prepared stock solu-
tions directly into the flasks.  Table 3 gives the nutrient concentrations in
the enriched experiments.  Biotin, cyanocobalamin and thiamine were combined
into one treatment (vitamins) and Cu, Zn, Co, Mn, and Mo into another (trace
metals) to reduce the number of treatments.

     For the April experiment, the enrichment schedule was slightly different
in that NHi+Cl was added as a treatment and P was used at only one level
(20 yg/1).

     After treatment the flasks were positioned by number on a shaker table
and incubated for 9 or 10 days.  Each flask, numbered from 1 to 54, was
repositioned each day according to a randomized table to minimize unevenness
of light received at each position on the shaker table.  All flasks were also
shaken by hand each day, since continuous rotation on the shaker table could
not be used as it caused phytoplankton to clump.

     Day-night cycles and temperatures in the growth chamber for incubating
phytoplankton were programmed according to general seasonal patterns
(Table 4).  The light was provided by 20 40-W cool white fluorescent light
bulbs with intensities of 160 yEin m~2 sec"1 for the summer and 80 yEin m~2
sec"1 for the rest of the year.

     To determine phytoplankton growth during the 9-10 day incubation, 50-ml
samples were taken for chlorophyll analysis from each flask at days 3, 6 and
9 (or days 4, 7, 10).  The filtrate from these samples was used for the same
nutrient analysis.
PHYSICAL-CHEMICAL CHARACTERISTICS OF SAMPLING SITE

     The major sources of water in Lake Huron are the outflows from Lakes
Michigan and Superior.  As indicated by Schelske and Roth (1973), the general
chemical composition of Lake Huron water is a mixture of Lakes Michigan and
Superior, so concentrations of conservation ions over much of the lake are
intermediate between those two head-water lakes.  However, southern Lake Huron
water receives dissolved substances from two other sources.  The major one is
the outflow of water from Saginaw Bay containing inorganic and organic pollu-
tants from the Saginaw River and its tributaries which drain residential,
agricultural and industrial areas.  The second is runoff from the Ontario
shore which increases nutrient concentrations greatly during the spring in a
relatively small nearshore zone.  Chemical analyses of water samples taken
during May-June 1974 indicate that the nutrient concentrations at these inshore
regions along Ontario were markedly higher during this time than in other
nearshore areas of southern Lake Huron (Davis et al., In prep.).   Precipita-
tion and other atmospheric inputs are also important sources of certain

                                      6

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TABLE 2.  NUTRIENT COMBINATIONS FOR ENRICHMENT BIOASSAY

               LW (lake water)
               All1
               All -  P
               All -  N
               All -  Si
               All -  FeEDTA
               All -  FeEDTA - Na2EDTA
               All -  TM
               All -  TM - Na2EDTA
               All -  VT
               LW + Na2EDTA
               LW +  20 yg P
               LW + N
               LW + Si
               All2  (1 yg P)
               All2  (3 yg P)
               All2  (5 yg P)
               All2  (10 yg P)
     indicates the lake water (LW)  enriched with complete
 nutrients listed in Table 3.
2Phosphorus concentration adjusted to the amount shown in
 parenthesis.

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TABLE 3.  VARIETY AND CONCENTRATION OF NUTRIENTS FOR ENRICHMENT
EXPERIMENTS


                                                            Concentration
Nutrients                      Compound                        (pg  I-1)
p
N
Si
KEgPO^
NaN03
Na2Si03 • 9H20
20
200
1,000
Vitamin Mix  (VT)

   Biotin                                                        400

                            Cyanocobalamin                         2
                               Thiamine  • HC1                      2
Trace Metal Mix (TM)
Cu
Zn
Co
Mn
Mo
Fe


CuCl2 • 2H20
ZnCl2
CoCl2 • 6H20
MnCl2 • 4H20
Na2MoOlt • 2H20
FeEDTA
Na2EDTA • 2H20

0.002
5
0.2
50
1.5
10
100

              TABLE 4.   TEMPERATURE LEVELS,  LIGHT/DARK CYCLES
              AND LIGHT INTENSITIES PROGRAMMED FOR EACH EX-
              PERIMENT

Date
Apr 13
May 2
Jun 2
Jul 1
Jul 23
Aug 19
Sep 9
Sep 23
Oct 21
Dec 10
Temp.
(°C)
3-5
3-5
10-12
17-19
19-21
20-23
18-19
16-18
13-15
4-6
L/D Light intensity
(hr) (pEinM~2 sec"1)
11:13
13:11
14:10
14.5:9.5
14.5:9.5
14.5:9.5
12:12
12:12
12:12
9:15
80
80
80
160
160
160
160
160
80
80

-------
nutrients to southern Lake Huron (Delumyea and Petel 1977).

     Detailed background data on water chemistry in southern Lake Huron were
collected by the Canada Centre for Inland Waters in 1971 and the Great Lakes
Research Division, University of Michigan, in 1974.  Figure 2 shows the fluctu-
ation in concentrations of total dissolved phosphorus (TOP), nitrate and silica
of surface water at station 13 from June to December 1975.  The TDP ranged
between 1.46 to 10.13 yg I"1 with average around 4.  The peak concentration
that occurred in August-September gradually dropped to a low level in December.

     The seasonal fluctuation of silica was very different from that of TDP.
While relatively high silica concentrations (>0.8 mg I"1) occurred during
summer and winter, there was a rapid decrease starting in mid-August that
persisted until the end of October.  Lowest values during the fall depletion
were less than 0.2 mg I"1.  This pronounced silica depletion was not recorded
in 1971 during investigations by the Canada Centre for Inland Waters.

     Nitrate concentrations in open Lake Huron water are normally high (>200
yg N I"1) due to the nitrate-rich water flowing in from Lake Superior.  The
seasonal pattern in 1975 was similar to that of silica, with a marked decrease
in late summer and early fall.

     The seasonal temperature distribution in the surface water at station 13
is shown in Fig. 3.  The low temperature recorded in early spring was about
5°C.  On the open lake temperatures from January to the end of April, a period
which was not sampled, would be less than 5°C with the minimum being about 0°C
(IJC 1976).  Gradual warming begins in early May and reaches its maximum at
22°C during late August.
PHYTOPLANKTON SPECIES COMPOSITION AND ABUNDANCE

     The seasonal variation in phytoplankton standing crop, as determined by
cell counts, is given in Fig. 4.  Unlike the bimodal pattern of phytoplankton
abundance for many temperate waters that exhibit spring and fall maxima, the
seasonal cycle in Lake Huron only showed small variations in cell counts with
a fall maximum.  Starting with a low spring standing crop (aa. 500 cells
ml""1), phytoplankton numbers increased over the summer and reached the annual
maximum at 3,000 cells ml"1 in early September.  This large standing crop
lasted until December.

     Although chlorophyll values are often used to indicate phytoplankton bio-
mass, we find that they deviated considerably from cell counts during the
spring and winter periods (Fig. 4) when the maximum chlorophyll values were
found.  Chlorophyll maxima tended to follow a bimodal pattern with highest
values in the spring and fall and lowest values during the summer.

     The pronounced changes in the quantity of chlorophyll per cell (cellular
contents of chlorophyll) during the study are most likely due to two factors.
One is the seasonal variation of dominant species with different cell volumes
that may make the cell numbers less meaningful for biomass measurements.
Examining the abundance and species composition of the phytoplankton

-------
            I.I
            1.0
           0.9
           OB

        r; 0.7
         I 0.6

        0*0.5
        en
           0.4

           0.3

           0.2
           0.1
  300
-r- 280

 »260

Z 240

0°220

  200

   180
   160

    10

                                        133
                   J     J     A     S    0     N     D
                                   MONTHS

       FIG. 2.  Seasonal variation in total dissolved  phosphorus
       (TOP), nitrate and silica concentrations  of  surface  water
       at sampling station.
assemblages in Table 5, we find that the fall community  is predominated
absolutely by Cyalotella eomensis.  The relatively  small cell  size  of  this
species, with approximate cell volume 400 pm3 (Vollenweider  1969),  may in
comparison to larger cells also contain a relatively  small amount of pigment
per cell.  On the other hand, the winter-spring communities  are  comprised of
smaller numbers of C. oomensis but a greater abundance of larger species, such
as Asterionella formosa, Fragilaria erotonensis and Tabellar-ia fenestrata.-
The cell volume of those species ranges between 700 and  4,000  ym3.
                                      10

-------
          22


          20


          18
        O

        UJ '6
        tr
        UJ
        Q.
           14
        cc.
        UJ
           12
           10
                                I
                    M
J     A    S
   MONTHS
            FIG.  3.   Seasonal variation in water temperature at
            sampling station.
     The second factor is that different light and temperature levels between
summer and winter may cause great variation in the cellular content of chloro-
phyll within species.  It has been shown that the chlorophyll content of
numerous algae is inversely proportional to light intensity during growth
(Kirk and Tilney Bassett 1967; Brown and Richardson 1968; see Section 3
of this report).  Prolonged exposure to high light intensity also causes photo-
destruction of chlorophyll (Kok 1956).

     The species composition and population density of phytoplankton assem-
blages in the surface water of southern Lake Huron between April 1975 and March
1976 are summarized in Table 5.  Approximately 100 species were recorded in the
11 samples.  The species composition in a single sample varied between 9 and-
38 entities with fewest species in the period from July to October.  Like the
other Great Lakes, phytoplankton communities in Lake Huron are overwhelmingly
dominated by a large number of diatom taxa.  Among them, Cyclotella and
Fpagilana were most abundant.
                                      11

-------
2.7



2.0


1.8


1.6






1.2
    .0
X
CL
O
tr 0.8
o
0.6



QA


02


0.
                                                                ^	^
                                 CHLOROPHYLL a

                           0—0  CELL  NUMBER
      4-13
                                 J_
           5-2
6-2
7-1
                                     J_
7-23   8H9

    1975
                                              9-9   9-23   10-2!
                                                                             \  _
                                                                         J_
                                                                36



                                                                32


                                                                28 <\T
                                                                    O

                                                                24 f



                                                                20 *

                                                                    _l
                                                                16 _J
                                                                                        O
                                                                                     12
                                                                                     8
                                                                      12-10    3-17

                                                                            1976
                                         DATES
     FIG. 4.  Seasonal variation of phytoplankton standing crop as indicated by
     chlorophyll a levels and cell numbers.

-------
TABLE 5.  SEASONAL VARIATION OF SPECIES COMPOSITION AND POPULATION DENSITY OF PHYTO-
PLANKTON COMMUNITIES AT SAMPLING STATION

BACILLARIOPHYTA
Aohnanthes alevei var. rostrata
A. exigua var. eonstriata
Amphora ovalis var. pediaulis
A. subcostulata
Asterionella f omasa
Coseinodisaus subsalsa
Cyalotella atomus
C. aomensis
C. aomta
C. crypt-Lea
C. miahiganiana
C. oaellata
C. operaulata
C. pseudostelligera
C. stelligera
Cyelotella aomta auxospore
Cyelotella comensis auxospore
Cymbella subventricosa
Diatoma tenue var. elongatwn
Fragilaria brevistriaia var. inflata
F. aapuaina
F. aonstruens
F.. aonstruens var. minuta
F. arotonensis
F. intermedia
F. intermedia var. fallax
F. pinnata
Hannaea araus
Melosira granulate.
M. islandioa
U. italioa subsp. subartiaa
Navioula oostulata
N. lanaeolata
N, pupula
Nitzsahia aeieu-laris
N. dissipata
N. kutzingiana
N. palea
N. reeta
N. sigma
K. spieuloides
Nitzschia sp. #1
Nitzsahia questionable sp.
Rhizosolenia eriensis
R. graailis
Stephanodisaus alpinus
S. astraea
S. minutus
S. subtilis
S. tennis
S. transilvaniaus
Stephanodisaus sp. #14
Stephanodisaus sp. #15
Surirella angusta
Synedra filiformis
S. minuscula
S. ostenfeldii
S. parasitiaa
S. ulna
Tabellaria fenestrata

4-13


78

25
4

2
42
2
2
29



6

4
6
2
67

2


2
27




6
2

2





2
11
2

21
34
2

2


2

2


63

5-2


134

6
34
4

6
48
4
42



15

25


11





2




10
17

4


2


19
38

2
21
46





40



2
36
1975
6-2 7-1 7-23 8-19 9-9 9-23 10-21


17 11 6

59 218 911 1535 2959 2884 2964
4 2 2
2
2 2 2 15
24 2

4 22
21 258 762 13 42 8
2
6

11 2

126 6


166 23 17 23
2
2
11
22 2
2


2
2
2
2
2

4



2
2
46 63
163 109 4 2

2
2
8
2




52 21 6
2
29 2 2

4
71

12-10
11
4

15
4
2869
4




19


2
11
2
13

2
11

11



2




4

2






4






4



4



6

1976
3-17
2
2
2
54
2
626
2

19
9

26



37

135

2
233

5
5


70
2
2
2

5
2

7
2
2


2
7



2




2
2
30


2
5
61
                                          13

-------
TABLE 5 (continued)
                        1975

CHLOROPHYTA
Crucigenia quadi>ata
Golerikinia radiata
Scenedesmus bicellularis
S. quadrioauda
Tetraedron minimum
Ankistrodesmus sp. #2
Chlorella sp. #1
Cosmariim sp. #1
Gloeocystis sp. #1
Mougeotia sp. #1
Oedogoniim sp. #1
Oocystis sp. #1
Oocystis spp.
Undetermined green colony sp. #4
CHRYSOPHYTA
Dinobryon divergens
D. sertularia
Mallomonas alpina
M. pseudoeoronata
Species ineertae sedis
Dinobryon cysts
CRYPTOPHYTA
Rhodomonas minuta var. nannoplanctiaa
CYANOPHYTA
Anabaena subcylindrica
A. incerta
A. thermalis
Gomphosphaeria laeustris
Oscillatoria bornetii
0. limnetiaa
0. retzii
Anabaena sp. #3
Microeystis sp. #1
Osoillatoria sp. #1
Osoillatoria sp. #2
Undetermined flagellate spp.
1 species
Total cells/ml
4-13 5-2 6-2 7-1 7-23 8-19 9-9 9-23 10-21
27 13 4
4
6
2 2 2
2
8 48
2
2 2
2 2
6 8
6
2
21
2 2
4
2 2 13
2
2 4
84 4 11
4222
2
2
8 2
8 2
2
59 111 44 61 4 109 111 136
31 29 32 18 11 9 19 14 17
519 691 932 785 1761 1611 3140 3083 3209
12-10 3-17
2
2 2
2 2
2
23
2
13
130
38 49
32 38
3242 1427
           14

-------
     The most prominent feature of the phytoplankton assemblage in Lake Huron
 is  the occurrence of Cijclotella oomensis, due not only  to its large relative
 abundance but also to its limited distribution in the Great Lakes.  This
 species was previously reported in Lake  Superior  (Holland 1965; Schelske et al.
 1972).

     As indicated by the available information on distribution, C. comensis
 appears to be an open-lake oligotrophic  species.  However, the abundant occur-
 rence of this particular diatom reached nearly 3,000 cells ml"1 in open Lake
 Huron from September through December 1975.  If this diatom is sensitive to
 nutrient enrichment and responds with increased standing crops, then it has the
 potential to develop excessive growths which may  create a serious water manage-
 ment problem.
NUTRIENT ENRICHMENT EXPERIMENTS WITH NATURAL PHYTOPLANKTON ASSEMBLAGES

     Phytoplankton responses to nutrient enrichments in each of the 10 experi-
ments were evaluated by changes in chlorophyll concentrations and phytoplankton
populations.  The complete set of chlorophyll data for all the experiments is
shown in Appendix 1.  Due to the large number of species present and the
diverse response of different species to various nutrients in each experiment,
results of phytoplankton counts are discussed only for the predominant species,
and examples for the detail species responses are given in Appendix 2.

     Logistical problems are often encountered when natural phytoplankton
communities are used for nutrient bioassay experiments, particularly when the
sampling location is distant from the laboratory.  Under such circumstances,
transporting samples may require such a long period of time that water temper-
ature, oxygen tension and other conditions may be altered, causing serious
effects on the natural populations of phytoplankton.

     Two specific experiments, one in the summer and the other in the winter,
were conducted to determine the effect of changes in temperature and length
of storage on phytoplankton responses to nutrient enrichment.  Water samples
collected with routine procedures on 1 July and 10 December 1975 were used
for the experiments.  Upon returning to the laboratory, two 2-liter water
samples were kept separately in the dark at two temperature levels—4° and
20°C.  At intervals of 4, 24 and 48 hrs, three 250-ml samples at each tempera-
ture were transferred to 500-ml polycarbonate Erlenmyer flasks and spiked with
complete nutrients (ALL treatment, Table 2).  These flasks were then placed in
a growth chamber with temperature set at the field level—18° and 5°C for 1
July and 10 December, respectively.  The phytoplankton growth response was
determined by chlorophyll a biomass at days 3, 6 and 9.  As a control, one
set of lake water with as little temperature change as possible was also spiked
with complete nutrients and incubated without delay at the field temperature.
Light levels for all experiments were 160 yEin m~2 sec"1 with continuous
illumination.

     The effect of temperature and time delay on phytoplankton growth is shown
in Table 6.  Chilling the summer sample to 4°C for 4 hrs prior to nutrient
enrichment drastically reduced the chlorophyll production, from 30.5 yg I"1 in

                                       15

-------
   TABLE 6.   EFFECT OF TEMPERATURE AND TIME DELAY ON PHYTOPLANKTON RESPONSE
   (yg CHLOROPHYLL a/1) TO NUTRIENT ENRICHMENT DURING SUMMER AND WINTER
                                       Incubation period (days)

                                    July 1                 December 10
treatment period (h)
Control
Cold (4 + 1°C)


Warm (18-20°C)


0
4
24
48
4
24
48
0
0
0
0
0
0
0
0
.64
.64
.64
.64
.64
.64
.64
3
0.35
0.36
0.20
0.20
0.38
0.41
0.26
6
1.63
0.35
0.29
0.30
1.28
1.24
1.57
9
30.
1.
1.
0.
11.
9.
4.
5
65
03
81
24
50
69
0
1.95
1.95
1.95
1.95
1.95
1.95
1.95
3
1.56
1.62
1.52
1.56
1.48
1.55
1.92
6
1.73
1.80
1.98
2.16
1.86
2.38
2.48
9
2.73
3.27
3.32
3.96
3.60
4.65
5.61
the control to 1.65 yg 1 *.  The effect on the sample stored at the warm
temperature was less than at the cold temperature.  In general, the longer the
delay in the July experiment prior to nutrient enrichment bioassay, the smaller
the response, presumably due to increased damage to phytoplankton with time.
On the other hand in the December experiment, the response increased generally
with the delay period.

     In the control experiment on the July sample, flagellates were the
important entity of the phytoplankton community.  They increased from 44 to
36,186 cells/ml in 9 days after nutrient enrichment.  These flagellates were
rare in other seasons and appeared to be sensitive to environmental changes.

     From this experiment,  we conclude that chlorophyll production resulting
from nutrient enrichment can be drastically affected by temperature fluctua-
tion and storage time before the experiment is initiated.  The effects appar-
ently are complex and may have been secondary efforts resulting from changes
in species compositions; experimental conditions may have created an environ-
ment well-suiter1 for particular species.

Experiment 1 (13-23 April 1975)

Chlorophyll—
     The maximum increase of chlorophyll, 1.67 to approximately 4.8 yg/1, was
obtained for several treatments.  Eliminating N, Si, Fe, TM, EDTA and VT from
the ALL treatment had little effect on the final standing crop of chlorophyll
(Fig. 5).  With the exception of phosphorus, adding single nutrients did not
increase the yield significantly over that in the LW treatment.  Adding
phosphorus alone, however,  increased the yield nearly as much as was obtained
from the ALL treatment.  This result obviously indicated that phytoplankton
growth at this time of the year was not limited greatly by nutrients other
than phosphorus.

                                      16

-------
                      z
                      UJ
                      IU
                      cc
                         ALL (P2g)

                         ALL-P •>

                         ALL-N

                         ALL-Si
                         ALL-Fe
                         ALL-TM
ALLrEDTA
                         ALL-TM-EDTA
                         ALL-VT
                          LW+P
                         LW+   ,
                         EDTA  '
                         LW+NH3
                         LWtNOi
                         LW+Si  H
                         LW   II
                            I      35
                         CHLOROPHYLL «   (jig
                     FIG. 5.  Effect of nutrient
                     enrichments on phytoplankton
                     growth indicated by  chloro-
                     phyll a level  (yg I"1)  on  the
                     last day "of the experiment.
                     Line at end of bar indicates
                     ± one standard deviation.
                     Experiment period 13-23
                     April 1975.

     Low lake water temperature (oa. 4°C), on the other  hand,  was undoubtedly
a factor that limited the yield of chlorophyll  under  the experimental condi-
tions.

Phytoplankton —
     The population density of phytoplankton in April at the beginning of the
experiment was approximately 500 cells ml"1  among approximately 30 species.
The majority of species were diatoms with the assemblage being dominated by
Asterionella formosa (15%), Fragilaria crotonensis  (13%),  Tdbellar-ia fenestrata
(12%), and Cyolotella ooeliata (8%).  Other  than diatoms,  flagellates, account-
ing for 11% of the total assemblage, were an important group.
                                       17

-------
      With  nutrient  enrichment,  the total number  of  cells  increased  substan-
 tially  over  the  9-day  incubation.  Sufficient nutrients were present  in  the
 ambient lake water  (LW)  to double the population size.  The dominant  diatom
 species in the original  samples remained generally  as major constituents dur-
 ing  the experiment  in  all the nutrient treatments.  Fr>agilca"ia arotonensis
 increased  from the  original 13% of the assemblage to 42%  and 62% in treatments
 ALL-TM  and LW +  NH4, respectively.  Drastic reduction of flagellates,  however,
 occurred in  most treatments.

 Experiment 2 (2-12  May 1975)

 Chlorophyll—
      Pronounced  differences in chlorophyll production resulted from different
 nutrient treatments in this experiment (Fig. 6).  Phosphorus added  alone, again,
 produced the greatest  effect on chlorophyll production among the individual
 nutrient spikes, increasing chlorophyll to a level  about  four times greater
 than  the LW  treatment.  Little effect resulted from the other single  additions
 of nutrients.

      The ALL treatment with P at 20 yg 1-1 level increased chlorophyll produc-
 tion  to 8.2  yg 1 1, about five times greater than the LW  control.   Elimination
 of either  Fe or  EDTA from ALL treatment reduced  the chlorophyll yield to 6.38
 and 6.35 yg  I"1.

      Responses for ALL-P and LW were similar, indicating  that P was the  only
 or most important nutrient limiting phytoplankton growth  in early May.  Under
 these phosphorus-limited conditions the addition of P in  increments (1,  3, 5,
 10 and  20  yg I"1) resulted in a progressive increase of chlorophyll production
with  an obvious  increase at the level of 1 yg P I"1 (Fig.  7).

      Comparing ALL  (P20) and LW + P20 indicates that the  ambient level of
nutrients  excluding phosphorus supported a phytoplankton  standing crop about
 60% as large as obtained with the ALL treatment.  The level in LW + P was
comparable to ALL + P5 indicating that other nutrients were limiting.  Addi-
tional growth above these levels would depend on simultaneous additions of P
and other nutrients, most likely Fe and EDTA.

Phyt oplankton—
      The species composition and abundance of phytoplankton in May was similar
 to April, with two obvious exceptions.   In May considerably more flagellates
 (> 100 cells/ml, 16% of the assemblage) were present;  the dominant pennate
diatom,  Fragilaria crotonensis,  was replaced by the centric diatoms
Stephanodiseus subtilis and Cyolotella stelligera.

      In the ALL  (P20)  nutrient enrichment,  total cell numbers increased from
 691 to 5,643 cells ml"1.   Fragilaria erotonensis, accounting for 25% of the
population, was the most abundant species.   In fact, this species and
Fpagilapia capucina were the taxa that  dominated the phytoplankton communities
of other nutrient treatments (ALL-P,  ALL-N, ALL-Si,  ALL-Fe, ALL-Fe-EDTA,
ALL-VT,  LW + P,  LW + N, LW + Si).   It is interesting to note that those two
species almost disappeared in ALL-TM treatment and an initially subordinate
                                      18

-------
8r
               z
               Ul
               UJ
               IT
                      (P20)
                  ALL (PIO)
                  ALL (f>3)
                  ALL (P,)
                  ALL-P
                  ALL-N
                  ALL- Si
                  ALL-F«
                  ALL-EDTA
                  ALL-TM
                  ALL-TM-EDTA
                  ALL-VT
                  LW +
                  EDTA
                  LW+P
                  LW+Nll
                  LW
                     135
                     CHLOROPHYLL a
                FIG. 6.   EXDeriment period  2-12
                May  1975.   See Fig. 5 for
                further  explanation.
       7.   Chlorophyll a production in response  to  varying
 phosphate concentrations.   Experiment period 2-12 May 1975,
                            19

-------
Synedz>a  spp. became most  abundant  (>  23%).  Under  low P  conditions,  Cyolotella
stelligera  and  C. comensis  tended  to  dominate  the  assemblage.

Experiment  3  (2-12 June 1975)

Chlorophyll—
     Phytoplankton growth in this  experiment was affected by a greater number
of  treatments than in the previous experiments.  Although the chlorophyll  bio-
mass decreased  from 2.0 to  1.1 yg  chlorophyll  a I"1  in LW,  chlorophyll concen-
trations  in some  treatments increased 40-fold  (Fig.  8).

     Single additions of  P  and EDTA to LW increased  the  chlorophyll  concentra-
tions compared  to the LW  control.  Addition of P increased  concentrations  about
five-fold and EDTA doubled  concentrations.

     Chlorophyll concentrations increased 40-fold  in  treatments ALL  (P20),
ALL-N, ALL-TM and ALL-TM-EDTA.  Greater chlorophyll  production in the two  latter
treatments  in which TM was  eliminated indicated inhibition  due to TM in  the ALL
treatments.  The inhibition effect was particularly  obvious in the ALL-EDTA
treatment which had only  one-fifth the chlorophyll of  the ALL-TM or  ALL-TM-EDTA
treatments, indicating the  inhibitory effect of TM was compensated by the
addition of EDTA.

     The fact that removal of P (ALL-P) severely limited the chlorophyll pro-
duction to  2.2 yg I"1, combined with  the effect of LW + P,  clearly shows P as
the primary limiting nutrient.  Chlorophyll production increased linearly  as
P was added at 1, 3, 5, 10 and 20 yg I"1 (Fig. 9); unlike the April  experiment
it did not  follow a hyperbolic relationship.

     At increasing concentration of P the limiting effects  of EDTA,  Fe,  VT and
Si were evident (Fig. 8).  Eliminating each one of these nutrients from  ALL
reduced the chlorophyll production to 8.4, 13.9, 20.8  and 27.7 yg I"1, re-
spectively.  In the absence of chelating capacity supplied  through EDTA,
chlorophyll yield equalled that of ALL (P5).

Phytoplankton—
     Rh-izosolenia graciUs was the dominant species at the beginning of  this
experiment comprising 17% of the population.   In the ALL treatment,  the  phyto-
plankton standing crop increased from 930 to 30,800 cells ml"1.

     Fragilaria capuoina  predominated in most  of the combined nutrient treat-
ments reaching 18,000 cells ml"1 or 60% of the assemblage in ALL (P20) in
which it grew at an average rate of 0.88 doubling day-1.  With reduced concen-
trations of P in the ALL  treatments the relative abundance of Fragilaria
aapuo-ina decreased.   The  standing crop, however, increased almost exponen-
tially with the addition  of P at 1, 3, 5, 10 and 20 yg I"1,  which gave 1,652,
3,025,  3,583,  16,126 and  30,880 cells ml"1, respectively.

     As with the effect on chlorophyll production, the removal of EDTA,  Fe,
Si and VT reduced phytoplankton cell counts from 30,800 cells ml"1 in the
complete treatment to 8,590, 9,100, 8,350,  and 16,400  cells ml-1, respectively.
                                      20

-------
ft1 Tl
X H
I—1 •
03
O 00 ^
rt
H-
O M
• T3 o
n>
rt w
T)
i-t
o' <"
O
NJ ^
Jj O M
M 3) 0
O
C X
3 -< r\j
(D C~ *
M .
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                              P04-PUgL")
          FIG.  9.  Chlorophyll a production  in  response  to
          varying phosphate  concentrations.   Experiment
          period 2-12 June 1975.
Experiment 4 (1-10 July 1975)

Chlorophyll—
     The chlorophyll biomass (0.64 yg I"1) in lake water at the start of the
experiment in July was at a seasonal low, but responses to different nutrient
enrichments were remarkably large (Fig. 10).  In the previous experiments an
initial chlorophyll decrease often occurred during the first few days of
incubation which was then followed by positive responses in all treatments,
including that in the unenriched lake water.  In the present experiment, the
initial chlorophyll decline did not recover in LW + N, LW + Si or LW + EDTA
                                      22

-------
           UJ
              ALL (P20>

              ALL (P|0)
              ALL
                MALL (P3)

               HALL(P|)

               II ALL-P
              ALL-N
              ALL-Si
              ALL-Fe
              ALL-EDTA
              ALL-TM
              ALL-TM-EDTA
              ALL-VT
               LW+EDTA

               * LW-I-P

               LW + N

              It LW4Si

               LW
                                 12     16     20     24
                                CHLOROPHYLL a  (ugL~')
28
      32
36
             FIG.  10.   Experiment period 1-10 July 1975.  See Fig. 5
             for  further  explanation.
treatments.  The addition of P (LW + P) resulted  in  a distinct  chlorophyll
increase from 0.64 to 0.91 yg I"1; it also produced  a larger  standing crop
than the LW control.

     Responses to combined nutrient enrichments were substantial—increasing
chlorophyll concentration from 0.64 to 30 yg  I-1.  The  maximum  chlorophyll
yield was reduced by half by eliminating Si,  Fe,  or  EDTA.   The  removal of TM
plus EDTA and EDTA alone caused reduction of  chlorophyll yield.  As in the
previous experiment the treatment ALL-TM yielded  the largest  response, indicat-
ing TM were inhibitory; however, the results  of ALL-TM-EDTA and ALL-EDTA
indicate the chelating capacity of EDTA was important in producing maximum
yields.  ALL-VT, like ALL-EDTA and ALL-TM-EDTA, also caused a large reduction
in yield.
                                       23

-------
      The fact that the chlorophyll production was similar between LW + P and
 ALL-P treatments obviously indicated that phosphorus alone had little effect
 on the growth of phytoplankton,  but that  other nutrients in the ALL treatment
 were needed to greatly increase  chlorophyll production.

      In the ALL treatments with  increasing P concentrations,  chlorophyll pro-
 duction was not greatly affected at P concentrations of  3 yg  I"1  or less
 (Fig.  11).   A large increase in  yield occurred when  the  concentration of P was
 increased  from 3 to 5  yg I"1.

 Phytoplankton—
      The number of species (18)  in July was considerably less  than  in the
 previous months.   Pennate diatoms were reduced in species and  cell  counts as
 centric diatoms became dominant.   Two species of  centrics,  Cyolotella
 stelligera  and C.  aomens-is,  accounted for 60% of  total population.
 Rhizosolen-ia spp.  and  flagellates made up an important subordinate  group.

      Phytoplankton populations responded  to nutrient enrichments  in a manner
 strikingly  different from previous experiments, in that  immense flagellate
 blooms  were common.  In the  complete nutrient enrichment,  ALL  (P20),  flagel-
 lates  increased from < 50 cells  to 36,186 ml"1, comprising  64%  of the assem-
 blage.   Abundant numbers  apparently only  occurred  in the ALL treatments  where
 the  P  concentration was greater  than 10 yg I"1.   On  the  other hand,  removal of
 TM + EDTA and  VT which reduced the chlorophyll production compared  to ALL (P20)
 also drastically reduced  the flagellates  to 2,536  and 1,093 cells ml'1,
 respectively.

 Experiment  5  (23 July-1 August 1975)

 Chlorophyll—
     The chlorophyll biomass in open  lake water remained  at its seasonal  low,
 0.63 yg  1~  .   Like  the previous July  experiment,  several  combined nutrient
 enrichments  resulted in large increases in chlorophyll up  to standing  crops  as
 large as 40  yg  1 1.  The  initial  chlorophyll  decline during the incubation
 period did not  return  to  the initial  level in  all  single  nutrient enrichments
 (LW + Si, LW +  N, LW + EDTA); however, concentrations of  chlorophyll  in LW + P
 and  LW + EDTA  treatments were about  two times  greater than those of control,
 LW + Si and LW  + N  (Fig.  12).  These  results  indicate that nutrients  in addi-
 tion to phosphorus were needed for  increased  growth  of phytoplankton.

     The maximum response obtained  (43.2  yg chl I"1), resulting from ALL  (P20),
was little affected by  deleting Si or N.    In  other treatments, deletion of Fe,
 EDTA and VT reduced chlorophyll production  to approximately half the maximum
value.  Deleting TM along with EDTA drastically reduced chlorophyll production
 to 3.4 yg 1~ ,  an order of magnitude  smaller  than that of complete medium; but
again the effect of removing only TM was  slight.  The fact that production in
ALL-P treatment was greater than that in LW + P indicates that limitation due
 to other nutrients was more acute than the availability of P.   In the ALL treat-
ments concentrations of chlorophyll increased greatly from 5 to 20 yg P liter,
but were not affected greatly at 3 yg P liter"1 or less  (Fig.  13).
                                       24

-------
32r
                           P04-PO»«L~')
  FIG.  11.   Chlorophyll a production in  response  to varying
  phosphate concentrations.   Experiment  period  1-10 July  1975,
                               25

-------
TREATMENT
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            B I
           FIG. 13.  Chlorophyll a production in response to varying
           phosphate concentrations.  Experiment period 23 July-
           1 August 1975.
Phytoplankton—
     Although the phytoplankton standing crop in lake water at the beginning
of the experiment was low based on chlorophyll concentration, the total cell
numbers, 1,760 cells ml"1, were larger due to the increased abundance of two
small centric diatoms, Cyclotella oomensis and C. stell-igeTa comprising 52
and 43% of the assemblage, respectively.  Flagellates accounted for 3% of the
assemblage and were apparently the next most important component.  Only 11,
species were identified in samples for this experiment.

     In the ALL (P20) enrichment, total phytoplankton counts reached 94,666
cells ml"1 of which Cyclotel'La stell-igeTa and flagellates accounted for 86

                                      27

-------
 and 12%, respectively.  Those two entitites also retained their absolute domi-
 nancy in most of the other nutrient enrichments; however, the removal of
 individual nutrients in the ALL treatments, except for Si or N, resulted in
 substantial reductions of standing crop.  The most severe reduction was caused
 by deleting P, TM + EDTA and Fe which resulted in much smaller standing crops
 of 2,792, 10,146 and 17,872 cells ml"1, respectively.

      As P was the controlling limting factor, its addition at 1, 3, 5, and
 10 yg 1   with an abundant supply of other nutrients in the ALL treatments
 increased phytoplankton counts to 5,468, 10,053, 31,183 and 70,697 cells ml"1,
 respectively.  In those communities Cyclotella stelligera comprised 64, 76,
 84 and 94% of the cell counts,  respectively.   Although the abundance of
 Cyclotella comensis (911 cells ml'1) was initially more abundant than that of
 C.  stelligera (762 cells ml"1), the latter obviously became dominant during
 the experiments (Table 7).  The growth of C.  comensis was slow except at ALL
 (P20), but its doubling rate of 0.41 was much less than the 0.75 measured for
 C.  stelligera at that concentration.

      Flagellates were another important component of the phytoplankton com-
 munity in this experiment.  They responded dramatically to the complete
 nutrient  enrichment,  increasing in 9 days from 60 cells ml-1  in the initial
 sample to 11,900 in the ALL (P20)  treatment.   Unlike diatoms,  flagellates were
 not substantially affected by the treatments  ALL-EDTA or ALL-Fe.   On the other
 hand,  their  growth was  severely limited in the absence of EDTA and trace metals
 (ALL-TM-EDTA)  or vitamins  (ALL-VT).   Eliminating either reduced the flagellate
 populations  to 510 and  3,260 cells ml"1.

 Experiment 6 (19-28 August 1975)

 Chlorophyll—
     As in the July experiments,  the initial  chlorophyll  concentrations  re-
 mained at  the  seasonal  low,  being  0.7  pg  I"1.   Chlorophyll  yield,  however,  in
 the ALL (P20)  treatment was  only  13.0  yg  I"1,  approximately one-third  the  con-
 centration in  the  23  July  experiment (Fig.  14).  Among all  the  treatments,
 removal of trace metals  (ALL-TM) produced  the  maximum growth.   This  indicated
 the background level  of trace metals might  be  high  so that  addition  of  these
 elements was  inhibitory to phytoplankton  growth at  this particular occasion.
 Although  the  lake water concentrations  of N and  Si  declined considerably from
 the previous month, deletion of those nutrients  from  ALL did not cause a
 significant  decrease  of  chlorophyll  production compared to  ALL  (P20).   Effects
 of  deleting  Fe,  EDTA  and VT  were  also  small.

     ^In this experiment there was no apparent  threshold effect at low P concen-
 trations  (Fig. 15).  Production of chlorophyll appeared to  increase with in-
 creasing concentrations of P but the large  error associated with ALL  (P3)
would probably mask any threshold effect if one was present.

Phytoplankton—
     Very few species of diatoms were observed in the lake water at the begin-
ning of the experiment other than a large population of Cyclotella comensis
 (1,535 cells ml"1) and small populations of C. comta and C. michiganiana.
                                       28

-------
TABLE 7.  THE EFFECT OF VARIOUS P CONCENTRA-
TIONS IN COMPLETE ENRICHMENTS (ALL) ON THE
GROWTH OF THE TWO MOST ABUNDANT SPECIES OF
THE 23 JULY 1975 EXPERIMENT.  N INDICATES
CELL ml"1 AND k THE NUMBER OF DOUBLINGS
day"1
PO^-P addec
(ug I'1)
1
3
5
10
20










l-
z
LU
3
<
Ul
o:
K



CyolotetZa Cyalotella
I oomensis stelli-gera
N k N k
1,140 0.04 3,514 0.25
1,187 0.04 7,703 0.37
1,350 0.06 26,389 0.57
1,605 0.09 81,378 0.75
11,891 0.41 67,090 0.72



ALL ( P gQ) •" 	 1
ALL(P,0) *--*
ALL (P5) l--i
1 -4 fl 1 1 ( P . \

H ALL(P,)
ALL-P
ALL-N 1-1


ALL-Fe •--•


All T M t— - - J

ALL-TM-EDTAI 	 1
ALL-VT M
I LW+E DTA
T, LW^P
i LW+N
t LW + Si
LW
111 I ||
               4      8     12     16

                  CHLOROPHYLL a
20
     24
         FIG. 14.  Experiment period  19-28
         August 1975.   See Fig. 5  for further
         explanation.
                      29

-------
             FIG. 15.  Chlorophyll a production  in response  to varying
             phosphate concentrations.  Experiment period 19-28 August
             1975.
Nutrient enrichment caused distinct changes in species .composition.  First,
when lake water was enriched with N, Si and at low levels of P in ALL treat-
ments (1-5 yg I"1), C. oomensis remained predominant  (> 95%) with small fluctu-
ation in total numbers.  Second, ALT, treatments, including deletion of N, Si,
Fe, and EDTA, increased flagellate populations to densities as large as 13,473
cells ml  .  Flagellates were, however, replaced by Fpagilayia Gvotonens'is
when trace metals or vitamins were deleted.  These results suggest that while
abundance and species composition of diatom populations are effectively
controlled by phosphorus availability, the abundance of flagellates may be
increased by trace metals and vitamins.

Experiment 7 (9-18 September 1975)

Chlorophyll—
     The chlorophyll production resulting from various nutrient enrichments
was similar in magnitude to that of 19 August, except the inhibitory effect of
trace metals was not as pronounced as in the-previous month (Fig. 16).  Removal
of N, Si, Fe, EDTA, TM + EDTA and VT from ALL resulted.in similar responses,
producing two-thirds of the maximum chlorophyll yield obtained in ALL (P20).
In comparison,  these deletions actually limited yield to a level similar to
responses obtained at 10 yg P I"1 (ALL P10).   What these results indicate is
that the nutrients other than phosphorus would not be limiting in the original
lake water as long as the enrichment of P is less than 10 yg I"1.  The addi-
tion of P, when combined with other nutrients in ALL, stimulated growth at
low levels of phosphorus but only caused a pronounced effect when P was
greater than 5 pg I-1 (Fig. 17).

Phytoplankton—
     Both the number of species and total cell counts increased two-fold in
the initial samples compared with the previous experiment.  The increase in
                                     30

-------
 ALL
 ALL (P|0)
 ALL (P5) I
    ti ALL (P3)
     ALL (P,)
  " ALL-P
 ALL-N
 ALL-Si
 ALL-Fe
 ALL-EDTA
 ALL-TM
 ALL-TM-EDTA
 ALL-VT
   LW+EDTA

   LW+P
  LW +
  LW-t-Si

  LW
  — 1
   I
5     7     9     II     13
   CHLOROPHYLL « (jigLH)
                                             15
FIG. 16.  Experiment period  9-18  September 1975.
Fig. 5 for,further explanation.
                                                   17    19
                                    See
FIG.  17.   Chlorophyll  a production  in response  to
varying  phosphate concentrations.   Experiment
period 9-18 September  1975.
                    31

-------
 the cell  numbers  was  primarily  due  to  Cyclotella  oomensis? with  2,960  cells
 ml~ .   The number of  flagellates  accounted  for  only  3.5% of  the  population,
 increasing from the previous  5  to 108  cells ml"1  in  this experiment.

     Response  patterns  of  phytoplankton  to  nutrient  enrichments  were similar
 to  those  observed in  the 19 August  experiment.

     Flagellate populations increased  over  two  orders of magnitude  in  treat-
 ments ALL (P20) and ALL-Si, ALL-FeEDTA and  ALL-TM, with the  maximum increase
 to  33,789 cells ml"1  occurring  in ALL-Si,   The  relatively small  diatom popula-
 tions  (<  6,000 cells  ml"1) on the other  hand, were most likely due  to  silica
 limitation in  the initial  assemblage because the  silica level in lake  water
 was at  the seasonal low (0.15 mg  I"1)  during this period.  Diatoms, however,
 were dominant  in  treatments ALL-TM, ALL-EDTA, ALL-VT, and in treatments which
 were enriched  with only one factor.  As  an  initial dominant  species,
 Cyclotella oomensis remained dominant  when  lake water was treated with indivi-
 dual nutrients or  EDTA, but Fragilar>ia capucina and  Cyolotella stelligeva
 outnumbered other  species  of diatoms in  treatments ALL-TM-EDTA and ALL-VT,
 respectively.

 Experiment  8 (23  September-2 October 1975)

     During initial preparations  in the  laboratory,  ALL-Fe,  ALL-TM-EDTA and
 LW  + EDTA were not set  up  correctly so results of these treatments are not
 available  for  this experiment.

     In the lake,  water temperature was beginning to decrease and the  chloro-
 phyll level increased from the seasonal low to 1.34  yg I"1,  but  the maximum
 response to nutrient  enrichment was less than in the summer  experiments
 (Fig. 18).

     Addition  of P alone (LW + P) produced  greater chlorophyll concentrations
 than spikes of other  elements to  lake water, indicating that phosphorus limited
 phytoplankton  growth.

     In this experiment, the maximum responses to nutrient enrichment occurred
 in the ALL  (P20),  ALL-N, ALL-TM and ALL-VT  treatments (Fig.  18).   These results
 indicate that  TM was  inhibitory because yield was greatly reduced when EDTA was
deleted and that vitamins were not essential in producing maximum responses.
 In previous summer experiments deletion of vitamins had produced yields
considerably smaller  than the maximum.

     Chlorophyll production increased with  increasing phosphorus concentration
 in the ALL treatments  with no indication of a threshold effect (Fig. 19).

 Experiment 9 (21-30 October 1975)

Chlorophyll—
     The chlorophyll biomass in the initial lake water samples was 1,42 yg I"1,
a substantial increase from the minimum of 0.64 yg I"1 in July and August.  In
comparison with summer experiments,  the maximum chlorophyll yield resulting
from nutrient additions was considerably smaller in this experiment (Fig. 20).


                                      32

-------





h-
Z
UJ
«
TREAT!
AL

L (P2O> '
ALL(P|0) M
ALL(P5) »'

i
1
At
AL
11 ALUP^
ALL(P,)
"ALL-P

_L-N ' '
,
.L-Si ' "" '
ALL-EDTA ^ H
AL

.L-TM
ALL-VT i 	 1
              LW+P
            LW+Si

            LW
              I
3579

 CHLOROPHYLL a (jjgLH)
                                                  13
          FIG. 18.  Experiment period 23 September-
          2 October 1975.  See Fig. 5 for further
          explanation.
i
O
    B  I
         10
    P04-P(pfl L'1)
    FIG. 19.  Chlorophyll a production in response to
    varying phosphate concentrations.  Experiment
    period 23 September-2 October 1975.
                          33

-------
                       z
                       IU
                       UJ
                          ALL (P20)

                          ALL (P|0)
                          ALL
                          ALL (P3)
                          ALL(P,)M
                          ALL-PH
                          ALL-N
                          ALL-Si
                          ALL-Fe
                          ALL-EDTA   u
                          ALL-TM
                          ALL-TM-EDTA
                          ALL-VT
                              "LW+-EDTA
                            M LW-t-P
                             LWf N

                             LW+Si

                             LW
                                        JL.
                                  357
                               CHLOROPHYLL a
                         FIG.  20.   Experiment period 21-30
                         October 1975.   See Fig. 5 for
                         further explanation.
Among the individual nutrient  enrichments  (LW treatments),  EDTA exerted the
greatest effect and P the  second largest.

     In the ALL (P20) treatment, the  chlorophyll  standing  crop (10.2 yg I"1)
was tenfold greater than that  in lake water.   Removal of TM,  TM + EDTA or VT
from the ALL treatments produced responses  only slightly smaller than the ALL
(P20). treatment.  ALL-Si and ALL-EDTA treatments  reduced the  growth to one-
half and one-third respectively of the ALL  (P20)  treatments.

     As in previous experiments, the  chlorophyll  level was  progressively
greater with increasing P  levels (Fig. 21).   Chlorophyll yield increased
slowly at P levels ranging from 1 to  10 yg  I"1 and  rose sharply at the 10 to
20 yg 1~  levels.   The drastic growth reduction,  due  to removal of EDTA (ALL-
EDTA),  produced an effect  that was similar  to  adding  3 yg P I"1.   This means
                                      34

-------
                  B I
             O
                        10
                    P04-PUL"1)
                  FIG.  21.   Chlorophyll a production in response to
                  varying phosphate concentrations.   Experiment
                  period 21-30  October  1975.
that the chelating capacity of EDTA was needed to enhance chlorophyll produc-
tion above 3.40 yg l~^ under the conditions of the ALL treatment.  Part of
this effect may have been due to trace metal toxicity as removal of trace metals
in the ALL treatment did not affect the maximum response.

     Removal of Si and Fe in the ALL treatments also produced smaller responses,
reducing chlorophyll concentrations to about half of the maximum.

Phytoplankton—
     The natural phytoplankton community was characterized by unispecific
dominance and low species diversity..  Among the recorded- 17 species, Cyolotella
oomensis accounted for 92% of the total count of 3,208 cells ml"1.  Flagellates,
comprising 4% of the assemblages, were the second most abundant entity.  Most
of the remaining counts were attributable to colonial green algae.

     In the various nutrient enrichments Cyolotella comensis retained its
absolute dominance.  In the ALL (P20) treatment, this taxon increased from the
original 2,963 to 35,814 cells ml"1, with an average growth rate at 0.4
doubling day
            -1
However, population size was severely limited to 2,606, 5,398
and 5,864 cells ml"1 by deleting P, EDTA and Si, respectively.  In the ALL
treatments at different P levels, the growth rate of Cyclotella oomensis
apparently increased with increasing P concentrations.

Experiment 10  (10-19 December 1975)

Chlorophyll—
     The chlorophyll level in the natural lake water (LW) was 1.9 yg I"1,
which was one of the largest chlorophyll concentrations for initial water
samples.  Relative responses by phytoplankton, however, in this experiment
were very small compared to previous experiments (Fig. 22).  Even with the
ALL (P20) treatment, chlorophyll increased only to 2.7 yg I""1.  Addition of P,
EDTA or Si in LW resulted in slight 'increases in chlorophyll relative to LW.

     Production of chlorophyll in the ALL treatments of different P levels was
                                      35

-------
ALL (P20
ALL(P|0)
ALL(P5
ALL (P3)
ALL(P )
ALL-P i
ALL-N
ALL- Si
ALL-Fe >
I
ALL-TM
^
ALL-VT
•'
LWfP 'i
LW+N i
LW+Si
LW
ii
> i

> I

n

ALt
M
••At
1 1
LW
                                            n ALL-TM-EDTA
                                         I     3
                                 CHLOROPHYLL a
                            FIG. 22.  Experiment period 10-19
                            December 1975.  See Fig. 5 for
                            further explanation.
enhanced little at concentrations greater than 3 yg 1 1 (Fig. 23).  The small
amount of chlorophyll production in this experiment probably resulted from low
temperature and light regimes under which the effect of nutrients are of
secondary importance.

Phytoplankton—
     A large number of phytoplankton species (32) were present in the cold
water at the initiation of the experiment.  The previously dominant species,
Cyelotella comensis, still maintained its large population (2,869 cells ml 1),
which comprised 89% of the community.  The second most abundant taxon was
Anabaena spp., which accounted for approximately 5% of the total cell numbers.
The occurrence of this blue-green alga was highly untimely since it normally
blooms in eutrophic warm waters.  We speculate that it originated from
Saginaw Bay where blue-green algae bloomed until late fall.
                                      36

-------
                                     P04-P(«L~')
                  FIG. 23.  Chlorophyll a production in response  to
                  varying phosphate concentrations.  Experiment
                  period 10-19 December 1975.
     The phytoplankton response to nutrient enrichment was sluggish.  Other
than CycloteVia aomensi-Sj which fluctuated between 3,000-6,000 cells ml"1
among various nutrient treatments, little change was noticed in other taxa.
Unlike earlier experiments, C.  eomensis did not respond positively with
increasing P concentration.  In fact, the population size in the complete
nutrient with 20 yg PI"1 was smaller than at lower P levels.

     Seasonal trends of chlorophyll yield as results of various nutrient en-
richments fluctuate over a wide range, as indicated by the' ratio of final and
initial chlorophyll level of the experiment period (Fig. 24).  The variation
of phosphorus concentration in ALL treatments resulted in growth more or less
parallel to the nutrient concentrations, with maximum differential response
in July and minima during the beginning and the end 6f the annual cycle.  A
similar seasonal trend also occurred in those ALL treatments with individual
nutrient deletion, except that in ALL-TM-EDTA where a marked reduction in
growth took place in July.  In this group of treatments, deleting of P, EDTA,
VT and FeEDTA effectively reduced chlorophyll yield as compared to ALL during
June through July.  Deletion of TM, however, resulted in yield larger than
ALL in the 2 June, 1 July and 19 August experiments.  Another set of treat-
ments was single spikes of P, EDTA, NOa and Si in. the lake water.  The over-
all growth response was relatively small in comparison with that of ALL treat-
ments (notice the different scale in Fig. 25).  Phosphorus addition produced
the largest chlorophyll in most of the experimental periods except that of
23 September and' 21 October during which the largest production was due to
EDTA addition.  In fact, the effect of EDTA .addition was also apparent during
early summer.
                                      37

-------
                              CHLOROPHYLL RATIO (FINAL/INITIAL )
                                                                                      CHLOROPHYLL RATIO (FINAL/INITIAL)
      Cb O
U>
00
                                                                                                                                         CHLOROPHYLL  RATIO (FINAL/INITIAL).

-------
DISCUSSION


     The results of the nutrient enrichment experiments can be compared in
several different ways.  First is evaluating the responses of various treat-
ments relative to the maximum effect obtained as the response in the ALL treat-
ment.  This comparison shows the effects relative to what can be termed the
maximum standing crop.  The second comparison is the effect of deleting various
components of the ALL treatment.  If the deletion does not decrease the maximum
standing crop the substance being tested is considered to have no effect or not
to be limiting; however, a decrease in the maximum standing crop can be due
either to the substance being limiting or to an interaction between other
factors in the treatments.  For example, deleting EDTA in some experiments
apparently resulted in a decreased response due to inhibitory reactions of
trace metals.  The final comparison is the effect of adding single substances
to lake water, a comparison which can be made to the control, i.e. lake water
which received no nutrient treatment, and to ALL treatments in which the factor
was either deleted or used at different concentrations.

     This study provides data for comparison of nutrient effects from both
the ALL treatments and single additions, thereby strengthening conclusions
drawn from the results.  The ALL-P treatment frequently resulted in larger
standing crops of chlorophyll than the LW + P treatment.  In these experiments,
we must assume that the increased concentrations of other nutrients in the ALL
treatment increased the availability of phosphorus naturally occurring in the
water which then stimulated phytoplankton growth, or that another factor was
also limiting.  The large effect of phosphorus additions can be seen by compar-
ing the ALL-P treatment with the other ALL treatments containing different
levels of phosphorus.  It is also obvious that if the LW + P treatment produces
a larger standing crop of chlorophyll than the LW (control), then phosphorus
must be limiting in the system.  Results of both ALL + P treatments and LW + P
treatments clearly indicate that phosphorus additions increased phytoplankton
growth.

     The levels of phosphorus added in the ALL treatments were related to the
size of the standing crop produced.  In most experiments the standing crop
increased with the level of phosphorus, although there were some exceptions.
Most of these exceptions were in experiments that were conducted at low temper-
ature and light.  In some of the experiments the addition of 1.0 yg P/liter
produced a larger standing crop than the ALL-P treatment, and in all experi-
ments the effect of adding phosphorus was apparent with additions as small as
5 yg P/liter.  These results indicate that phosphorus affected the growth rate
at very low concentrations; more than 5 yg P/liter were never needed to obtain
a response in the ALL treatments.  No experiments were conducted on levels of
phosphorus in LW treatments.
                                      39

-------
     Additions  of phosphorus greater  than  5 yg P/liter produced massive  stand-
 ing  crops  of  chlorophyll.  With these extreme nutrient enrichments,  the  result-
 ing  chlorophyll concentrations were large  enough to be classified  in the
 category of nuisance blooms and certainly  would be considered characteristic
 of highly  eutrophic waters.  In all experiments, with the exception  of 19
 August, the ALL + 20 P  treatment produced  the largest standing crop  of
 chlorophyll.

     ALL minus  trace metals consistently produced large effects compared to
 ALL  treatments  other than ALL + 20 P.  On  19 August it produced the  largest
 effect.  With the exception of the 21 October and possibly the 23  July experi-
 ments, the effect of ALL-TM was as large as the effect for ALL + 20  P or was
 comparable to the maximum effects obtained.  These results clearly indicate
 that trace metals, with the exception of iron which was added separately, were
 not needed to stimulate algal growth.  It  is possible, however, that iron or
 the Fe-EDTA added in the ALL treatments could have influenced trace metal
 availability.   These effects could not be  tested with the experimental design
 employed.

     Results indicate that EDTA was an important factor in stimulating algal
 growth.  LW + EDTA in three experiments produced greater growth than lake
 water alone, indicating that EDTA increased nutrient availability.  Deletion
 of EDTA in the ALL treatment had a pronounced effect on algal growth, generally
 producing  chlorophyll levels smaller  than  those for the ALL-TM-EDTA  treatment,
 and indicating  that trace metals added without EDTA produced a toxic or
 inhibitory effect on algal growth.   The deletion of Fe (which included EDTA)
 did not affect algal growth as much as deleting EDTA in the ALL treatments.

     Deletion of TM and EDTA in the ALL treatments appeared to produce
 responses which varied seasonally,  with the most pronounced effects occurring
 in July and August.   Results from these two months indicate that growth was
 reduced when both TM and EDTA were deleted.  During the same times, however,
 the addition of EDTA alone did not increase chlorophyll concentrations over
 those in the LW control.  These results indicate that trace metals may have
 been limiting during the summer.

     In most of the experiments,  the deletion of vitamins in the ALL treat-
ment resulted in smaller than the maximum  standing crops of chlorophyll.   The
 responses of ALL-VT, however, were as large in all but one experiment as the
 effect observed for ALL + 10 P.

     In general, one can conclude that the effects of Fe-EDTA, EDTA,  TM and
VT were small in comparison to the effects of phosphorus in the ALL treatments,
and deletion of these factors reduced the  standing crops of chlorophyll to
 those observed for additions of  either 5 or 10 yg P/liter in ALL treatments.
Generally,  chlorophyll standing  crops produced without these substances were
 large enough to be classified as  excessive or nuisance algal blooms.

     Deletion of N in the ALL treatments had little or no effect on production
of chlorophyll.   Even in the experiments in which this treatment had  a smaller
 effect than the maximum (19 August  and 9 September),  the standing crop of
 chlorophyll was as large as that  produced  in ALL + 10 yg P.   The effect of

                                      40

-------
adding N to LW was even smaller and in no experiment produced standing crops
of chlorophyll which exceeded those found in the LW control.

     Deletion of Si(>2 also had little effect on the production of chlorophyll.
Even though the maximum response was obtained in only two experiments (2 May
and 23 July), the concentrations produced on the remaining dates were always
at least as large or larger than those in the ALL + 10 P treatment.  Deleting
silica had a major effect on species composition, clearly reducing the propor-
tion of diatoms in the phytoplankton assemblage, particularly when compared
to the ALL treatments with different levels of phosphorus.  This effect was
most pronounced during the period when silica levels in the lake were minimal.

     One of the principal conclusions of this study is that phosphorus added
as a single enrichment or deleted from a complete nutrient enrichment had the
greatest effect of any treatment on chlorophyll production by phytoplankton.
The results of the experiments which support this conclusion agree well with
results from other experiments conducted on the upper Great Lakes, Lake Michi-
gan, Lake Superior and Lake Huron which also lead to the conclusion  that
phosphorus is the main growth-limiting nutrient  (Schelske et al.,  1978).
                                      41

-------
                                 SECTION  3

                    EFFECTS OF LIGHT AND TEMPERATURE
INTRODUCTION

     Despite abundant information on species composition and abundance of
Great Lakes phytoplankton except Lake Huron, few data have been collected in
the winter period due to logistical problems associated with winter sampling.
Phytoplankton samples collected in southern Lake Michigan during the ice-free
season showed that there were a large number of species which occurred abun-
dantly when the water temperature was at 5°C or less (Stoermer and Ladewski
1976).  It is difficult, however, to sort out the effects of temperature and
light from nutrient factors under natural conditions.  The seasonal change in
chlorophyll level and standing crop in Lake Huron clearly indicates increasing
trends during the fall and the largest chlorophyll standing crop in December.
In early winter the phytoplankton community also was composed of a greater
number of species despite decreasing water temperature and intensity of
incident light.
     Two experiments were conducted to evaluate the effect of light and tem-
perature on phytoplankton growth.  The first experiment determined how winter
phytoplankton (natural assemblage enriched with nutrients) are affected by
various light and temperature regimes.  The second experiment involved
(1) culturing phytoplankton isolated from the Great Lakes in a defined medium
under laboratory conditions, and (2) determining growth rates of three of
these species at different light intensities and temperatures.

METHODS

Natural Assemblages


     The experiment was designed to determine the effect of light and tempera-
ture on the growth of nutrient-enriched phytoplankton.  Nine combinations of
three light intensities  (40, 80 and 160 yEin m   sec   ) and three water temper-
atures  (5, 10 and 18°C) were used with each combination run in triplicate.   In
a walk-in growth chamber  (Forma Scientific Econoline), three rectangular plexi-
glass containers (40 x 25 x 25 cm) were placed side by side.  Each container,
holding ten 250-ml polycarbonate flasks, was a constant temperature water bath
with temperature being maintained at the desired level by circulating water
through a heating coil or refrigerated bath  (Forma Scientific Masterline 2095).

     The light source was 24 fluorescent tubes (40-W cool white) that provided
a light intensity of 160 yEin nr2 sec'1 at flask level.  To decrease the light
level to 80 and 40 yEin m   sec" , the flasks were shaded with cone shaped
plastic screens.  In addition to the nine light and temperature combinations
which received nutrient enrichment, an extra flask containing unenriched lake
water was placed in each water bath without screens as a control.  All
treatments were incubated with a light-dark cycle of 13-11 hrs for a period of
10 days during 17-27 March 1976.

                                      42

-------
     The natural phytoplankton samples were obtained from the same location
with the same procedures used for the routine bioassay experiments.  Precau-
tion was taken to keep the water temperature less than 5°C during transport.
Following the routine procedure, aliquots were taken from the lake water
sample for analysis of P, N, Si, and chlorophyll, as well as for determina-
tions of the species composition and abundance of phytoplankton.  The phyto-
plankton sample was then used in the light-temperature experiment.  Each of
the 27 250-ml culture flasks was filled with 150-ml aliquot of lake water and
0.5 ml of each of the nutrient stock solutions (see Table 3) was added, giving
the initial nutrient concentrations for P, N and Si02 of 39, 602 and 2,108
yg I"1, respectively.  Samples were taken from each flask to determine growth
response by chlorophyll production at days 4 and 9.  The concentrations of P,
N and Si in the filtrate samples were also analyzed at days 4 and 9.  The
species composition and abundance of phytoplankton communities in each treat-
ment were determined at the end of the experiment.

Isolated Species

     Techniques used for isolation are described in Handbook of Phycological
Methods  (Stein 1973).  Most commonly, we used one of two procedures:   (1) One
cell of a selected species was isolated from the natural phytoplankton popula-
tions with a micropipette and transferred to 2 mi of liquid medium in a 5-ml
culture tube;   (2) A sample of mixed phytoplankton species was poured onto agar
plates and incubated for about one week.  Species that multiplied in colonies
were transferred through a series of subcultures on agar to eliminate bacterial
contamination and then transferred to liquid culture.  While most pennate dia-
toms could be obtained using either technique, few centric species would grow
on agar plates.

     All of the initial cultures were incubated  in a growth chamber with light
intensity at ca. 160 yEin m~2 sec"1 in a 12/12 day-night cycle and temperature
at 18°C.

     Sources for phytoplankton samples were Lake Huron, Saginaw Bay and Lake
Michigan.  At the beginning, we used modified Chu 14 medium  (Patrick 1964) for
isolating pennate diatoms, including Astevionella formosa, Fragilaria orotonen-
sis, Diatoma tenue var. elongatwn and Tdbellaria sp.  Isolates of centric
species, however, would not grow in this medium longer than 2-3 weeks.  An
improved medium FM  (Table 8) was therefore developed and proved more suitable
for maintaining Great Lakes diatoms in culture.  In the new medium, we increased
Ca, Mg and HC03 concentrations and lowered trace metals.  In the original Chu
medium (Chu 1942), trace metals were added in concentrations above 1 mg/1,
which is likely to inhibit sensitive organisms.

     Using the new formulated medium, we isolated and maintained clone cultures
of 12 species of Great Lakes planktonic diatoms.  The origin of these isolates
is listed in Table 9.

     To demonstrate the effect of light and temperature on phytoplankton
growth, a preliminary experiment was conducted, using clonal cultures of
three phytoplankton species that commonly occur  in the Great Lakes.  These
species are Astevionella formosa, Diatoma tenue var. elongatwn and Fragilavia
erotonens-is, isolated from either Lake Michigan or Saginaw Bay.
                                      43

-------
TABLE 8.  CHEMICAL COMPOSITION OF IMPROVED CULTURE MEDIUM
FOR GREAT LAKES DIATOMS  (FM MEDIUM)
Chemical compounds
Ca(N03)2 ' 4H20
Na2Si03 ' 9H20
KC1
MgS04 ' 7H20
CaC03
NaHC03
CaCl2 ' 2H20
K2HP04
FeCl2 • 6H20
Na2EDTA ' 2H20
ZnCl2
CoCl2 ' 6H20
Na2Mo04 ' 2H20
MnCl2 ' 4H20
H3B03
CuSO, ' 5H90
Concentration
mg/1 yg/1
76.0
50.0
20.0
102.0
10.0
160.0
58.7
4.0
0.968
2.5
0.05
0.01
0.01
0.50
1.00
0.01
Thiamin '  HC1
Cyanocobalamin
Biotin
pH (adjusted with 1  M Tris to 8.5)
100.0
  0.5
  0.5
                                44

-------
          TABLE 9.   SPECIES  AND  ORIGIN  OF PLANKTONIC  DIATOMS  THAT
          HAVE BEEN ISOLATED AND CULTURED IN SINGLE SPECIES CULTURE


          Saginaw Bay

                  Astem-onella formosa
                  Swri,Tella  ovata
                  Synedra ulna
                  Fragilapia oapuoina

          Southern Lake Huron (bioassay)

                  Stephanodisaus alpinus
                  S.  niagarae
                  Melosira italioa
                  Tdbellai>i,a fenestrata
                  T.  floeculosa

          Lake Michigan

                  Diatoma tenue  var. elongation
                  Fragilapia orotonensis
                  Stephanodiscus tenu-is


     Separate experiments were carried  out to determine the effects of light
intensity and the effects of temperature.  To obtain light gradients, a frame
with four shelves was placed directly underneath a light bank of 24 40-W fluo-
rescent light tubes.  The light  intensity at each level of the four shelves
was adjusted with layers of  screens to  15, 40, 120 and 300 yEin m~2 sec"1.
The experiment was run with continuous  illumination at 18°C.

     The apparatus for maintaining temperatures was described in the Methods
of Section 3 of this report.  Growth rates of the three cultured species were
determined at 5, 10 and 18°C, with continuous illumination of 160 yEin m~2
sec"1.  All the cultures were preconditioned to respective light and tempera-
ture regime for 2 days before growth measurements were made.

     As mentioned earlier, stock cultures of unispecific phytoplankton were
maintained at 18°C and 160 yEin m~2 sec"1.  For light- or temperature-
gradient experiments, the exponentially growing stock culture of each species
was inoculated into 250-ml Erlenmyer flasks containing 100 ml freshly prepared
growth medium.  The population density after inoculation normally was about
103 cells ml"1.  All the experiments were done in triplicate.

     To determine growth rates of each species under various light and temper-
ature conditions, small aliquots (5 ml) taken at day intervals 3-4 throughout
the experimental period (10-12 days) were used to determine chlorophyll a and
population density.  Cell counts were made as described by Palmer and Maloney
(1954) and chlorophyll was determined by the method of Strickland and Parsons
(1968).  Numbers of doublings for chlorophyll concentration and cell number
were calculated as specific growth rates.  The maximum growth rate was
determined by plotting the growth curve and calculating the steepest slope
between two sampling dates.

                                        45

-------
 RESULTS

 Natural  Assemblage

      Table  10  shows  the  species  composition  and  abundance  of  phytoplankton in
 southern Lake  Huron  lake water samples at  the beginning  (10 December  1975)  and
 the  ending  (17 March 1976) of the winter season.  The  total phytoplankton  pop-
 ulation  in  the December sample was 3,242 cells ml"1, declining to  1,426  in
 March.   But the number of species identified increased from 32 to  38  during
 this  period.  Diatoms that made up over 90% of the total population were
 dominated by Cyolotella comensis in December.  This taxon  appeared in great
 abundance (2,869 cells ml"1) in the early  winter and declined drastically
 through  March  (626 cells ml"1).  However,  the substantial  decrease in total
 cell  counts did not  reduce the chlorophyll level, which, on the contrary,
 increased from 1.95  to 2.9 yg chl I"1 in December and March samples,  respec-
 tively.

      Several diatom  species which occurred abundantly in samples collected
before December became more or less rare during the early winter period when
 the phytoplankton was dominated by Cyolotella oomensis.  Those entities which
declined were Astevionella formosa,  Cyolotella stell-igera,  Diatoma tenue var.
elovgatim.,   Fragilavia oapuoina,  F.  arotonensis,  Melosi-ra islandioa, Synedva
filifoim-is  and Tabellaria fenestrata.   However,  as Cyolotella oomensis
dominance decreased  in March, these species again developed significant popula-
tions.   It  is noteworthy that blue-green algae,  Anabaena and Osai-llatoria
species,  also occurred in significant numbers in the December sample.  The
occurrence  of those  eutrophic,  normally warm-water algae was highly untimely.
Most likely, they flushed out of Saginaw Bay where blue-green algae bloomed
heavily  throughout the fall (Stoermer, personal communication).

 Phytoplankton  Response to Nutrient Enrichment Under Various Light-Temperature
 Regimes—
      The different light and temperature regimes resulted  in  significant
 effects  on  species composition, population size  and chlorophyll production.
 As shown in Table  11, the increasing  light and temperature levels  not only
 increased the species complexity, but also promoted total  growth as measured
by cell  counts and chlorophyll.   At the lowest temperature (5°C),  however,
 the effect  of varying light intensity was  small.  It is interesting to note
 that  the effects of  light and temperature  on phytoplankton growth  compensated
each other.   For example, the population size at 10°C—160 yEin m~2 sec"1 was
similar  to  that at 18°C—80 yEin m~2 sec"1.

     In general,  both phytoplankton populations and chlorophyll production  are
influenced  positively with increasing light and temperature;  but the  growth
rates for the two parameters show considerable variation for each  light-
temperature combination.   At 5°C, the rate of cellular multiplication was
relatively  small but was affected greatly by different light intensities.   In
comparison,  chlorophyll was produced at a much higher rate (0.45)  and
influenced  little by light levels at 5°C.   The maximum growth rate for both
cell number (0.78)  and chlorophyll (0.83)  occurred at the combination of 10°C
and 160 yEin m~2 sec"1.
                                      46

-------
TABLE 10.  SPECIES COMPOSITION AND ABUNDANCE OF WINTER PHYTOPLANKTON
IN SOUTHERN LAKE HURON

BACILLARIOPHYTA
Ashnanthes clevei. var. rostrata Hust.
A. exigua var. oonstr-iGta (Grun.^ Hust.
Amphora ovalis var. pedioul-Ls (Kutz.) V.H.
A. subcostulata Stoerm. and Yang
Asterionella formosa Hass.
Coscinodiscus subsalsa Juhl.-Dannf.
C. Gomensis Grun.
C. eomta (Ehr.) Kutz.
C. michiganiana Skv.
C. ocellata Pant.
C, stelligera (Cleve and Grun.) V.H.
Cymbella subventricosa Cholnoky
Diatoma tenue var. elongation Lyngb.
Fragilaria brewistriata var. inflata (Pant.)
F. oapucina Desm.
F. construens var. nrinuta Temp, and Per.
F. orotonensis Kitton
F. intermedia var. fallax Grun.
F. pinnata Ehr. n
M. islandioa 0. Mull. n
M. italiaa subsp. subartioa 0. Mull.
Navioula eostulata Grun.
N. laneeolata (Agardh) Kiitz.
Nitssehia acicularis (Kutz.) Win. Smith
N. dissipata (Kutz.) Grun.
N. kutzingiana Hilse
N. palea (Kutz.) Wm. Smith
N. recta Hantz.
N. sigma (Kutz.) Wm. Smith
Nitsschia questionable sp.
Rhizosolenia eriensis H. L. Smith
S. minutus Grun. ex Cleve and Moll
S. transilvanieus Pant.
Stephanodisaus sp. #15
Surirella angusta Kutz.
Synedra filiformis Grun.
S. parasitioa (Wm. Smith) Hust.
S. ulna (Nitz.) Ehr.
Tabellar-ia fenestrata (Lyngb.) Kutz.
CHLOROPHYTA
Soenedesrms bioellularis Chod.
S. quadrioauda (Turp.) Brlb.
Arikistrodesrms sp.
Cosmariwn sp.
Dates
12-10-75

0
11
4
0
15
4
2869
4
0
0
19
2
11
Hust. 2
13
2
11
11
0
2
0
0
0
4
0
2
0
0
0
0
4

4
0
0
4
0
6
0

0
2
2
2

3-17-76

2
0
2
2
54
2
626
2
19
9
26
0
37
0
135
2
233
5
5
70
2
2
2
5
2

7
2
2
2
7
2
0
2
2
30
2
5
61

2
2
2
0
                                   47

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                                                        	Dates	
                                                        12-10-75     3-17-76
CYANOPHYTA
Andbaena sp.
Andbaena subcylindrica Borge
Oscillatovia vetzii
Unidentified flagellate spp.
Number of species
Total cells/ml

129
23
13
38
32
3242

0
0
0
49
38
1427
     The total number of species that occurred in the 9 light-temperature
combinations in the 9-day culture period was approximately 130, which were
apparently latent winter flora.  The occurrence of those latent species ranged
between 29 and 52 entities among the different combinations of light and tem-
perature.

     In spite of the large number of phytoplankton species appearing among the
various light and temperature levels, communities were invariably dominated by
a few Diatom species that were abundant in the field.  These species included
Asterionella formosa,  Cyolotella oomensis, C. stelligeva, Diatoma elongatum,,
Fragilaria. crotonensis,  F.  intermedia var. fallax, Nitzschia acicularis,,
Stephanodisous alpinus and S. minutus.  The growth rates for most of these
species were apparently enhanced by the combination of increasing light and
temperature  (Table 12).  Cyolotella oomensis, .the most abundant taxon in the
    TABLE 11.  AVERAGE GROWTH RATE OF PHYTOPLANKTON CULTURED IN  9 LIGHT-
    TEMPERAUTRE COMBINATIONS IN 9 DAYS.  RATES  (r) ARE CALCULATED AS NUM-
    BER OF DOUBLING  (CELL NUMBER AND CHLOROPHYLL) PER DAY
Growth rate
Temperature Light
(°C) (yEin m^sec"1)
5 40
80
160
10 40
80
160
18 40
80
160
No.
species
29
38
31
41
42
46
42
47
52
cell
ml
2453
4300
4917
7395
11335
18562
6613
19526
34331
r
0.09
0.18
0.20
0.26
0.33
0.78
0.25
0.42
0.51
chlorophyll
yg l"1
9.78
9.77
9.03
15.63
42.49
51.59
24.48
72.04
138.36
r
0.45
0.47
0.45
0.47
0.75
0.83
0.40
0.76
0.79
                                       48

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TABLE 12.  EFFECTS OF LIGHT AND TEMPERATURE ON SPECIES GROWTH RATE OF  ENRICHED
WINTER PHYTOPLANKTON

Species
Asterionella formoaa


Cyclotella oomeneie


Cyclotella. etelligera


Diatoma elongatum


Fragilaria arotoneneis


fragilaria intermedia var.
-.fallax

liitZBahia aeicularis


Synedra filifofmie


Tabellaria feneetrata


Stephanodieaus alpinus


S. minutue


Light
(yEin/m2/sec)
40
80
160
40
80
160
40
80
160
40
80
160
40
80
160
40
80
160
40
80
160
40
80
160
40
80
160
40
80
160
40
80
160
Initial
cells/ml
54
54
54
626
626
626
26
26
26
37
37
37
233
233
233
5
5
5
5
5
5
30
30
30
61
61
61
2
2
2
2
2
2
5°C
cells/ml
253
426
471
790
1215
1427
67
129
98
122
383
341
434
743
1363
—
123
84
72
173
177
116
196
191
258
122
129
24
19
17
22
44
17

k
0.25
0.33
0.34
0.04
0.11
0.13
0.15
0.26
0.21
0.19
0.37
0.35
0.10
0.18
0.28
—
0.51
0.45
0.42
0.56
0.57
0.21
0.30
0.29
0.22
0.10
0.10
0.40
0.36
0.34
0.38
0.49
0.34
10"C
cells/ml
646
642
1112
1247
1298
2054
304
544
854
272
772
1535
1808
2406
4058
484
662
176
623
1617
2585
400
620
895
353
500
274
55
211
239
35
153
139

k
0.40
0.40
0.49
0.11
0.12
0.19
0.39
0.49
0.56
0.32
0.49
0.60
0.33
0.37
0.46
0.73
0.78
0.57
0.77
0.93
1.00
0.41
0.48
0.54
0.28
0.34
0.24
0.53
0.75
0.77
0.46
0.69
0.68
18°C
cells/ml
712
1356
1496
648
751
681
162
248
453
309
1331
2371
1598
4870
9152
264
434
623
758
2622
6820
295
1782
3564
358
637
798
104
393
813
55
638
1428

k
0.41
0.52
0.53
0.01
0.03
0.01
0.29
0.36
0.46
0.34
0.57
0.66
0.31
0.49
0.59
0.63
0.72
0.77
0.80
1.00
1.15
0.37
0.65
0.76
0.28
0.38
0.41
0.63
0.84
0.96
0.53
0.92
1.05

-------
 initial  sample,  (626 cells ml^1) grew  at  the lowest rate  in all  light-
 temperature  combinations.  It appears  to  be a cold water  species, whose
 growth rate  at 10°C was  one order of magnitude greater than that at 18°C.

      In  general,  there are compensatory effects between light intensity and
 temperature  on the growth rates of most species, especially at light levels
 above 80 yEin m~2 sec"1  and 10°C.  In  the field, the compensatory factors are
 further  complicated by seasonal variation and depth distributions.  It is
 evident  that the  optimal light-temperature regime for many phytoplankton
 species  exists during the year at some depth in the lake, except during winter,
 when  the water temperature is less than 10°C throughout the water column.  How-
 ever, optimal growth rates of most natural phytoplankton  populations are rarely
 realized in  oligotrophic waters where nutrient limitation often  overrules the
 effects  of physical factors.  Furthermore, phytoplankton  populations must
 acquire  specific  optimal growth rates  in  the physical environment through
 temporal adaptation.  In the lake, phytoplankton populations to  survive must
 adapt continuously as cells are sedimented and transported vertically by water
 movements.

 Light-Temperature Effects on Phytoplankton Nutrient Consumption
      Consumption rates of P, N and Si varied markedly among the light-
 temperature treatments.  While P was consumed at similar rates at all light-
 temperature levels,  the  consumption of N and Si was affected by light and
 temperature  (Table 13).  For example, the total amount of P consumed in 5°C-40
 and 18°C-160 yEin nT2 sec'1 was 21.33 + 1.25 and 33.74 + 0.52 yg 1-1 respect-
 ively.   The N consumption under these corresponding conditions were 29.09 +
 2.70  and  433.54 + 16.09  yg I"1.   The range in Si consumption under these
 conditions differed by a factor of seven.

     As  increasing light intensity and water temperature stimulated greater
 chlorophyll production proportionally larger amounts of N and P were required,
 except different light intensities at 5°C had little effect on chlorophyll
production and nutrient  consumption.

     Further analysis of nutrient consumption and corresponding chlorophyll
production revealed  that the nutrient ratios for chlorophyll productivity
varied drastically in different  light-temperature regimes (Table 14).   The P
and Si ratios of nutrient to chlorophyll were consistently higher at the low
 temperature (5°C) and decreased  progressively at 10° and 18°C.   At the two
upper temperature levels, these  ratios decreased as light intensity increased.
The N ratio,  however,  remained relatively constant  under all environmental
 conditions.
                                      50

-------
TABLE 13.  CHLOROPHYLL PRODUCTION AND NUTRIENT CONSUMPTION IN PHYTOPLANKTON CULTURE AT 9 LIGHT-
TEMPERATURE COMBINATIONS DURING A 9-DAY PERIOD.

Temperature
5


10


18


Light
40
80
160
40
80
160
40
80
160
Chi a production
(yg I-1)
6
6
6
12
.92 +
.93 +
.17 +
.77 +
39.63 +
48
21
69
135
.73 +
.62 +
.18 +
.50 +
0.76
0.10
0.19
0.12
3.03
1.09
0.59
3.56
11.82
Nutrient consumption
P (yg I'1)
21.33
22.85
24.23
26.94
32.10
32.93
25.71
33.98
33.74
+ 1.25
+ 0.53
+ 1.51
+ 0.45
+ 0.52
+ 0.59
+ 2.71
+ 0.09
+ 0.52
N
29
22
21
71
139
196
65
219
433
(yg I-1)
.09 +
.94 +
.92 +
.69 +
.46 +
.46 +
.37 +
.39 +
.54 +
2.70
8.27
13.49
9.79
23.93
18.81
3.79
27.98
16.09
Si (mg I'1)
0.30
0.31
0.32
0.43
0.82
1.16
0.54
1.35
2.12
+ 0.04
+ 0.04
+ 0.05
+ 0.04
+ 0.07
+ 0.07
+ 0.13
+ 0.07
+ 0.01

-------
         TABLE 14.   EFFECTS OF LIGHT AND TEMPERATURE ON RATIOS BY WEIGHT,  OF P,
         N AND Si AS CONSUMED PER UNIT
Temperature
(°C)
5


10


18


Light
(pEinM-2sec-1)
40
80
160
40
80
160
40
80
160
Nutrient consumption
(yg/pg ch)
P
3.08
3.30
3.93
2.11
0.81
0.68
1.20
0.49
0.25
N
4.20
3.31
3.55
5.61
3.52
4.04
3.02
3.17
3.20
Si
43.74
43.71
52.79
33.38
20.72
23.80
25.04
19.58
15.66
Ratio
P:N:S
1:1.36:14.04
1:1.00:13.25
1:0.90:13.43
1:2.65:15.82
1:2.84:25.58
1:5.94:35.00
1:2.68:20.87
1:6.47:39.96
1:12.80:62.64
Isolated Species

      Figure 25 shows the growth curves of Asteri.onel'La formosa, Di-atoma tenue
var. elongatum and Fvagilar-ia avotonensis at the three temperature  levels.
During a 10-day culture period, both population density and chlorophyll
production increased exponentially.  The growth rate of Diatoma sp., however,
decreased after the seventh day at higher temperature levels.  In most cases
growth rates of chlorophyll and population increased with temperature and
those two growth parameters were similar for each temperature after three days
of culture.  Slower growth rates in the initial culture period at the lower
temperatures may have resulted from the organisms' acclimation to different
temperature levels since the inocula were grown at 18°C.  As shown  in Table 15,
the maximum growth rates of both chlorophyll and the population for the  three
diatoms were considerably smaller at 5°C than at 10° and 18°C.  While the
maximum rates for cell division among the three taxa were similar between
10° and 18°C, the rates for chlorophyll increases were slightly higher at 18°C
than at 10°C.
       TABLE 15.  MAXIMUM GROWTH (Y^ay) RATES OF Asterionella fovmosa,
       Di-atoma tenue var. elongatum AND Frag-Llar-ia cpotonensis INCUBATED
       AT 3 TEMPERATURE LEVELS

Temperature

Species
Asterionella
Diatoma tenue



cell
fofmoec.
var . e longatum
Fragilaria orotonensis
0.
0.
0.
6
3
6
5
chl
0.
0.
0.
(°C)
10
a
4
6
5
cell
1.0
1.1
0.8
chl
0.
0.
0.
a
8
9
9
18
cell
1.
1.
0.
0
0
9
chl a
1.1
1.2
1.1
                                      52

-------
     The effect of light intensity on the growth patterns of the three
cultured phytoplankters is shown in Fig. 26.  The results show that the satura-
tion light intensity required for optimal growth is approximately 120
m
 i *- e» d^> """* *
sec  ,  and that the higher light intensity of 300 yEin m 2 sec"1 inhibits
chlorophyll production during exponential growth.  However, the population
growth rates of Asterionella formosa and Diatoma tenue var. elongatwn are
nearly identical rates at the two upper light levels.

     While the specific growth rate of these algae changed throughout the
exponential period, the maximum specific growth rate at different light levels
also varied (Table 16).  Asterionella formosa, though reached its maximum
growth rate at the highest light intensity, maintained a relatively high cell
division rate over a wider light range (40-300 yEin m"2 sec"1) than Diatoma
elongatwn, which required higher light levels (> 120 pEin m"2 sec"1) for
maximum growth rate.   Fragilaria crotonensis, as shown by chlorophyll
doublings per day, grew at the maximum rate at 40 yEin m"2 sec"1 and at a slow-
er rate at 300 uEin m~2 sec"1.

     As the light intensity affects chlorophyll and population growth different-
ly, considerable variation in the cellular content of chlorophyll occurred.
As shown in Table 17, the cellular chlorophyll content in Asterionella formosa
and Diatoma tenue var. elongatwn varied from 0.4 to 2.0 and from 1.0 to 3.6 pg
cell"  for these respective species.  Generally, the content is inversely
proportional to the light levels.  The largest variation in chlorophyll content
occurred between 15 and 300 pEin m""2 sec"1 on day 9 and is approximately four-
fold for Asterionella and three-fold for Diatoma,  It should also be noted
that the chlorophyll content of Asterionella cell tends to be much less vari-
able at lower light intensity than that at higher light levels throughout the
culture period; and it appears to be opposite in Diatoma.

     Variations in temperature also cause fluctuations in cellular chlorophyll
content (Table 18), but to a smaller degree than the light effect.  Chlorophyll
content ranges from 1.3 to 2.9 pg chl cell'"1 for Fragilaria, from 1.7 to 2.5
for Diatoma and from 0.9 to 1.7 for Asterionella.  These ranges for each
species are therefore generally less than two-fold as opposed to three- and
four-fold variations observed for the effects of light.
                                      53

-------
  10*
  ,05
T
 -I
 S

 10
 -I
 -I
 UJ
 o
  10'
  10
        A3TERIONELLA FORMOSA
        CELL NUMBER
        O—O S'C
        D—n 10* c
        X	X 18'C
        CHLOROPHYLL a
        O—O 9'C
        D-a io«c
        >—X 18* C
DIATOMA TENUE VAR. ELONOATUM
CELL NUMBER
 O-O S'C
 D-a 10'C
 X—X  IB'C            _^---
CHLOROPHYLL a        / *
 O-O 5' C         '
 D-D 10* c
 X—X 18* C    x/
            /
           /
           /
FRAGILARIA CROTONEN3I3

CELL NUMBER
 O-O S'C
 a-a io'c
 *—X I8*C
CHLOROPHYLL Q.
 0--O S-C
 D-D 10-C
 X—K I8«C


                                                                                                                         10*
                                       x-
                                       X
                                       a.
                                       O
                                       a:
                    S      7
                      DAYS
                                    10
      3      S      7

              DAYS
                                                                          10
            5      7

              DAYS
                                                                                                                 10
     FIG.  25.   Effects  of water temperature  on growth of  Asterionella  formosa,  Diatoma tenue var.  elongation
     and Fragilaria ovotonensis in  culture.   Growth is determined by cell numbers  (except  for F.  oTotonensis)
     and chlorophyll a  concentrations.

-------
                                                            CELLS  ML '
o  (u  <^i
o  3  M
3  Q.  (TJ
O
ft  **|

2  3  £
IT  (fcj  O'
H   CO
 ft   H-
 C   rt
 i-i  ^
 (D
 •    O


 O  OQ
 i-l   H
 O   O
 S   «
 rt   rt
H- O
0)  hh
(D  Oj
rt  cf
(C  <»
H  ^
3  ^.
H-  O
3  S
(B  TO
cr  ft
                  5
                  <0
                                                                                                      I    1   i
M  O
    03
3  ft
fD  s^.
H  ft
CD  
-------
TABLE 16.  MAXIMUM GROWTH RATES (Kmax) OF Astevionella formosa,, Diatoma
tenue var. elongation AND Fragilaria erotonensis INCUBATED AT 4 LIGHT
LEVELS
                        15
                      Light (yEinM~2 sec

                   40           120
300
Species
cell  chl a   cell  chl a   cell  chl a   cell   chl a
Asterionella
   formosa          0.5   0.5     0.9   0.7     1.0    1.0      1.2     1.2

Diatoma tenue
   var. elongatum   0.3   0.6     0.6   0.6     0.9    1.0      1.0     1.0

Fragilaria
   orotonensis       -    0.7      -    1.3      -     1.2       -      0.8
 TABLE 17.  VARIATION OF CELLULAR CONTENT OF CHLOROPHYLL a AS AFFECTED BY
 DIFFERENT LIGHT INTENSITIES

Chlorophyll a (pg cell 1)
Species
Diatoma elongation


Asterionella formosa


Light
(yEin m~2sec~1)
15
40
120
300
15
40
120
300
0
1.3
1.3
1.4
1.0
1.5
1.1
1.4
1.7
2
1.8
1.9
1.7
1.0
1.2
1.3
1.1
0.7
Days
4
2.1
2.6
2.1
1.2
1.3
1.2
1.3
0.5
7
2.5
2.3
1.7
1.1
1.5
1.5
0.8
0.4
9
3.6
2.8
1.9
1.3
1.8
1.9
1.1
0.5
11
3.4
2.9
1.9
1.3
2.0
1.8
1.5
1.0
                                     56

-------
 TABLE 18.   VARIATION  OF  CELLULAR CONTENT OF  CHLOROPHYLL a AS AFFECTED BY
 TEMPERATURE LEVELS
                              Temperature
                                               Chlorophyll a  (pg cell"
                                                         Days
Species
Fragilaria crotonensis


Diatoma elongatwn


Asterionella formosa


(°c)
5
10
18
5
10
18
5
10
18
0
1.3
1.3
1.3
1.7
1.7
1.7
1.2
1.2
1.2
3
1.6
2.3
1.9
1.7
1.8
2.3
1.3
1.4
1.4
5
1.5
2.2
2.6
2.5
2.4
2.4
1.2
1.1
1.6
7
1.8
2.5
2.5
2.2
1.8
2.2
1.1
1.2
1.5
10
1.1
2.9
2.2
1.6
2.0
1.6
0.9
1.4
1.7

DISCUSSION

     In temperate lakes, water temperature in the euphotic zone fluctuates
over a wide range from season to season, and light also fluctuates seasonally
and is attenuated with depth in the water column.  It is obvious that the
effect of light and temperature in addition to nutrients affect phytoplankton
development in the water column.  To understand the phytoplankton succession
and distribution in the Great Lakes it therefore will be necessary to obtain
data not only on nutrient requirements but also on the effects of light and
temperature.

     The effects of light intensities and temperatures on the growth of
phytoplankton assemblages must be evaluated under optimum nutrient conditions.
In the present experiment both chlorophyll standing crop and cell counts in-
creased with temperature and light intensity.  At 5°C, the effect of light
intensity was less than at other temperatures.  Species responses in the
assemblage were variable.  Growth of Cyclotella eomensis, the dominant popu-
lation at the beginning of the experiment, increased little compared to other
species and was greatest at 10 C.  C.  stell-igera also appeared to grow best
at 10 C.  The majority of species that were present abundantly among various
light-temperature treatments, were eurythermal.  Diatoma tenue var. elongatum,
Fragelaria crotonensis, Nitzschia acieularis and Synedra filiformis were the
dominant populations at the end of the experiment with maximum growth rates
ranging from .59 to 1.15 divisions day  .  Phosphorus to nitrogen uptake
ratios increased with temperature and with light level at 10 and 18 C as did
phosphorus to silica uptake ratios.  Production of chlorophyll per unit of
phosphorus and silica consumed increased with temperature and with light
level at 10 and 18°C.


                                      57

-------
     The effects of light intensity and temperature on the growth of diatoms
studied with cultures isolated from the Great Lakes were similar to those of
using natural phytoplankton assemblages.  Specific growth rates were deter-
mined for three species, Diatoma tenue var.  elongatwn, Fragilar-ia orotonensis3
and Asterionella formosa3 in separate light  and temperature gradient experi-
ments.  The saturation light intensity for optimal growth was approximately
1200 yEin m~^ sec"-*- for Diatoma and Asteri-onella,  and 40 yEin m"^ sec"1 for
Fragilaria.   Maximum growth rates for all three taxa were similar at 10°
and 18°C, but were significantly reduced at  5°C.  Cellular chlorophyll
content, however, was inversely related to light level, but was affected by
temperature to a lesser degree.  Growth rates from these experiments compared
with results obtained from nutrient enrichment bioassays of natural phyto-
plankton communities indicate that the unialgal isolates of the three species
have greater specific growth rates under culture conditions than were obtained
from the same species in natural assemblages growing in enriched natural lake
water.

     Differences in growth rates between the natural phytoplankton assemblages
grown in enriched natural lake water and unialgal cultures of phytoplankton
isolated and grown in a defined nutrient medium may have resulted for a number
of reasons.   1) Natural or "wild" phytoplankton populations may be expected
to undergo physiological adaptations as environmental conditions are changed
from those existing in natural lake water to those existing in an artificial
medium in the laboratory.  2) Isolation into culture inherently selects for
the fastest growing individuals of a population, essentially without regard
to other fitness factors which would affect the population in the natural
environment.  3) Naturally occurring assemblages may be composed of taxa whose
optimal growth condition is not present at the time of collection (temperature
for instance may not be optimal for growth!).  Cultures, on the other hand,
are usually specifically adapted to the experimental regimen.  4) Inter-
specific competition in natural phytoplankton assemblages may produce
conditions in which the growth rate of individual populations will be lower
than maximal or at a rate less than that which would be obtained if the
species were being grown in unialgal culture.  Differences due to inter-
specific competition could result even though nutrient conditions for the
experiments with natural assemblages and unialgal populations are identical.
Changing the medium and changing other environmental conditions from those
existing in nature (including isolation of species into unialgal culture) to
those existing in the laboratory therefore may affect the growth rates of
phytoplankton species.
                                      58

-------
                                SECTION  4

                      CONCLUSIONS AND RECOMMENDATIONS
     Although results of this seasonal study on the effects of nutrient enrich-
ment on the growth of natural phytoplankton assemblages did not single out one
limiting nutrient throughout the year, they do clearly point to the critical
role of phosphorus enrichment on phytoplankton growth.  During part of the year
additions of phosphorus alone increased phytoplankton growth, but during July,
August and September Lake Huron water had to be enriched with phosphorus plus
EDTA and possibly iron or Fe-EDTA to increase the growth of phytoplankton.  The
importance of increased phosphorus loadings in degrading water quality, however,
is not obviated by these results because many sources of phosphorus to lakes,
particularly sewage effluents, would include substances that could perform the
function of EDTA in stimulating phytoplankton growth if phosphorus concentra-
tions in the receiving waters were increased.  Materials such as chelators and
vitamins probably enhance the effects of phosphorus on phytoplankton so effects
evaluated from addition of phosphorus alone would necessarily be smaller than
those from the same quantity of phosphorus in a sewage effluent.  Therefore,
for realistic evaluation of phosphorus enrichment effects on phytoplankton
production it is essential to consider the simultaneous enrichment of multiple
limiting nutrients.

     In the present study growth of phytoplankton in ALL treatments generally
increased with phosphorus additions ranging from 1 to 10 yg P/liter.  All these
additions represent significant increases over lake levels.  An addition of
10 yg P/liter would more than double the total phosphorus concentration in the
waters.  It is significant that additions of 1 and 3 yg P/liter caused
increased standing crops of phytoplankton, further indicating the extreme
sensitivity of the system to phosphorus loading, particularly when nutrients
and other growth promoting substances are supplied with the phosphorus inputs.
Caution is needed in interpreting the above results, because they have been
compared to maximum responses, of very large chlorophyll standing crops.
Maximum responses produced in many treatments were chlorophyll concentrations
obviously in the range which would be considered highly eutrophic.  Maximum
chlorophyll standing crops were as large as 60 yg/liter or were 50 to 60
times greater than the initial values in lake water.  Therefore relatively
small increases in these experiments could be quite significant in oligo-
trophic lakes from the standpoint of water quality problems.

     These results of the nutrient enrichment experiments can be extrapolated
to events which now occur in Lake Huron.  Blooms of phytoplankton are related
proportionately to the magnitude of phosphorus loading in southern Lake Huron
including Saginaw Bay.  With moderate phosphorus enrichments the blooms are
dominated by diatoms, but with greater enrichments the proportion of diatoms
decreases, particularly during periods of silica depletion in the lake.  At
higher levels of phosphorus enrichment supplies of other nutrients for phyto-
                                       59

-------
 plankton become  limiting,  creating  conditions  conducive  for  shifting  species
 composition.

      There  is  some  evidence  from  the results indicating  trace metals  added  in
 low concentrations  may  inhibit  the  growth of phytoplankton.  Additional
 experiments designed  to test  this effect would be needed to  verify this rela-
 tionship.   In  addition,  the  effects of  trace metals in natural water, like
 other anthropogenic inputs,  should  not  be evaluated completely from experiments
 with pure spikes as environmental inputs normally are complex mixtures.  The
 role of  trace  metals  like  other nutrients cannot be evaluated in the  absence
 of  data  on  chemical forms  and availability of  these forms to phytoplankton.
 Inputs of trace metals  would be expected to have a relatively minor effect  on
 water quality.

      In  these  experiments  with natural  phytoplankton conducted under  conditions
 which simulated seasonal changes in light and  temperature, responses  of phyto-
 plankton in the winter  were much smaller than  during the summer.  Smaller re-
 sponses  during the  winter  are due to slower growth rates under the winter con-
 ditions.  Greater responses would be expected  if experimental periods had been
 extended  beyond the eight  days used throughout the study.

      Responses of natural  phytoplankton under  experimental treatments were
 species  specific and  there were 100 species identified throughout the seasons.
 These responses are complex, partly due to seasonal changes  in species compo-
 sition and  partly due to concomitant changing  environmental conditions.  The
 results  indicate that differential responses by species must be considered  in
 evaluating  the effects  of  nutrient enrichment.

      The  dominant species  during the study was Cyclotella oomensis, a diatom
which was abundant  only from the late summer through winter.  It has been
characterized as an oligotrophic organism so its dominance indicates an
oligotrophic environment in the open waters of southern Lake Huron.  Under
experimental conditions, large populations of  this organism  (>8000 cells ml"1)
were  produced.  These large populations were developed under phosphorus
enrichments as small as 3  yg P/liter.   C.  oomensis apparently grows optimally
at about  10°C.

     All  the results point to the essential need to limit the inputs of
phosphorus  if control of eutrophication and maintenance or improvement of
water quality in southern Lake Huron is the desired goal.  There is no
evidence that specific measures for controlling inputs of other nutrients
should be undertaken.   Problems with nitrogen enrichment, limited to experi-
ments with nitrate nitrogen in this study,  would result only as secondary
effects of  increased phosphorus enrichment or loadings,  but specific problems
with nitrogen enrichment would not be  expected  from the results of our study.
                                      60

-------
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                                   TECHNICAL REPORT DATA
                           (Please read Instructions on the reverse before completing)
1. REPORT NO.
 EPA-600/3-79-049
             3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
 EFFECTS  OF  NUTRIENT ENRICHMENT, LIGHT  INTENSITY AND
 TEMPERATURE ON GROWTH OF PHYTOPLANKTON FROM  LAKE HURON
                                                          5. REPORT DATE
                                                             October 1979 issuing date
             6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
 C. Kwei Lin  and  Claire L. Schelske
             8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
 Great Lakes  Research Division
 Great Lakes  and  Marine Waters Center
 University of  Michigan
 Ann Arbor, MI  48109
             10. PROGRAM ELEMENT NO.
             11. CONTRACT/GRANT NO.

              R 800965
12. SPONSORING AGENCY NAME AND ADDRESS
 Environmental  Research Laboratory - Duluth, MN
 Office of Research and Development
 U.S. Environmental Protection Agency
 Duluth, Minnesota   55804
             13. TYPE OF REPORT AND PERIOD COVERED
             Final Report  - 5/1/73-10/31/76
             14. SPONSORING AGENCY CODE
                   EPA/600/03
15. SUPPLEMENTARY NOTES
16. ABSTRACT                                                                 "~~~~~~~~~~~"	~~~~
 This report contains  a seasonal study on effects  of  nutrient enrichment, light  and
 temperature on  the  growth of natural phytoplankton and  three species of cultured  dia-
 toms.  Natural  phytoplankton assemblages collected monthly from April to December
 1975, in southern Lake Huron were used for ten  sets  of  bioassays by adding nutrients
 in 18 combinations  directly to lake water samples.   Nutrients tested were phosphorus,
 nitrogen, silica, EDTA,  trace metals and vitamins.   Responses to different treatments
 evaluated by chlorophyll production and cell counts  were complex and varied seasonal-
 ly.  Nitrogen had the least effect and phosphorus the greatest effect on chlorophyll
 production.  Silica deleted from a complete enrichment  usually had a relatively small
 effect on chlorophyll production but did affect the  proportion of diatoms.  Deletion
 of EDTA and Fe-EDTA reduced chlorophyll production greatly in comparison to the com-
 plete treatment.  Deleting trace metals had a small  effect,  but deleting trace  metals
 and EDTA reduced chlorophyll production significantly during the summer.  Growth  of
 winter phytoplankton  increased with temperature and  light intensity with most species
 being eurythermal,  except Cyolotella comensis and C. stelligera which grew best at
 10°C.  Uptake ratios  of  P,  N and Si varied with temperature  and light.   Specific
 growth rates for three diatoms,  Diatoma tenue var. elongatum,  Fra.g-i'laria erotonensis
 and Asterionella formosa,  isolated from the Great Lakes  were determined in separate
 light and temperature gradient experiments.	
17.
                               KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                             b.IDENTIFIERS/OPEN ENDED TERMS  C. COS AT I Field/Group
   Nutrients, phytoplankton

   Primary Biological Productivity
       Lake Huron
    06
13. DISTRIBUTION STATEMENT
   RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
  Unclassified
21. NO. OF PAGES
      76
                                             20. SECURITY CLASS (Thispage)
                                               Unclassified
                                                                        22. PRICE
EPA Form 2220-1 (9-73)
                                            64
                                                                    •-- U.S. GOVERNMENT PRINTING OFFICE: 1979 -657-146/5477

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