United States
Environmental Protection
Agency
Great Lakes National
Program Office
536 South Clark Street
Chicago, Illinois 60605
EPA-905/3-85-004
August 1985
vvEPA
Phytoplankton
Composition
Abundance And
Distribution
In Lake Huron
Do not WEED. This document
should be retained in the EPA
Region 5 Library Collection.
-------
EPA-905/3-85-004
August 1985
PHYTOPLANKTON - COMPOSITION, ABUNDANCE AND DISTRIBUTION
IN LAKE HURON
by
R. Jan Stevenson
Department of Biology
University of Louisville
Louisville, Kentucky 40292
Grant No. R005767-01
Project Officer
David DeVault
Great Lakes National Program Office
United States Environmental Protection Agency
Chicago, Illinois 60605
GREAT LAKES NATIONAL PROGRAM OFFICE
GREAT LAKES FISH MONITORING PROGRAM
U. S. ENVIRONMENTAL PROTECTION AGENCY
CHICAGO, ILLINOIS 60605
V.S. Environmental Protection
Region 5. yt»afy{Pl.UJ)
77 West Jackson Boutevard, Itf& fte*
ChtcagMi 60604-3590
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ABSTRACT
The phytoplankton of Lake Huron were studied to assess the water quality
of this Great Lake. The phytoplankton species were counted in integrated and
discretely collected water samples from all of Lake Huron except Saginaw Bay.
Cell abundances and biovolumes of the algae were studied seasonally and
spatially in the Lake.
Patterns of phytoplankton indicated that Lake Huron waters were generally
oligotrophic. Diatoms with broad ecological ranges, Tabellaria flocculosa and
Fragilaria crotonensis, dominated the phytoplankton year-round. Abundance and
biovolume were not great during the spring bloom. Algal biovolumes were low
during the summer. Small, coccoid blue-green algae were common, but
heterocystis, nitrogen-fixing blue-greens were never abundant. Only a slight
increase in phytoplankton abundance occurred during the fall.
Regional variation in water quality was indicated by the highest standing
crops of phytoplankton commonly occurring in the nearshore regions of the
southern basin and the lowest in the Georgian Bay. Slight enrichment along the
western shore of Lake Huron and near Cheboygan was indicated by high and
persistent standing crops of phytoplankton during spring.
Little evidence was observed that the water quality of Lake Huron had
changed during the last decade. There were some signs that continued loading
of nutrients to the southern basin was causing some degradation of those
waters. But, low standing crops of algae near Saginaw Bay indicated that
nutrient loading through Saginaw Bay had been reduced.
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ACKNOWLEDGEMENTS
Completion of this study of Lake Huron would not have been possible
without the assistance of many scientists. The staffs of Mar, Inc., Bionetics,
and Great Lakes Research Division, who counted the algae, deserve recognition
for their efforts in generating this data. I would also like to thank Joe
Makarewicz for assembling the raw data into computer files. I would
particularly like to thank Russ Moll and Russ Kreis for making available copies
of drafts of their reports of Lake Huron water quality. Dr. Kreis was
especially helpful in gathering background information about Lake Huron. A
special note of appreciation is given to Dr. E. F. Stoermer, who encouraged me
to do this project. Dr. Stoermer made materials in his library available to me
and also helped me develop a perspective of conditions in the Lake.
ii
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TABLE OF CONTENTS
PAGE
ABSTRACT i
ACKNOWLEDGEMENTS ii
TABLE OF CONTENTS iii
LIST OF FIGURES iv
LIST OF TABLES vii
LIST OF APPENDICES viii
INTRODUCTION 1
CONCLUSIONS AND RECOMMENDATIONS 2
METHODS 3
Sampling 3
Sample Preparation and Algal Enumeration 3
Data Analyses 3
RESULTS , 8
Seasonal Variation in Algal Division Biovolumes 8
Spatial Patterns in Phytoplankton — April 12
Spatial Patterns in Phytoplankton — May 20
Spatial Patterns in Phytoplankton — June 24
Spatial Patterns in Phytoplankton — July 29
Spatial Patterns in Phytoplankton — September 32
Spatial Patterns of Phytoplankton — October through February 36
Statistical Summary of Seasonal and Spatial Patterns 41
Vertical Patterns in Algae 41
Correlations Between Lake Huron Water Chemistry Characteristics 44
Correlations Between Algal Division Biovolumes and Water Chemistry.. 44
Autecologies of Common Diatoms 49
—Asterionella formosa 49
—Cyclotella comensis & C. michiqaniana 52
—Cyclotella ocellata 54
—Cyclotella stelliqera 54
—Fragilaria capucina 54
—Fraqilaria crotonensis 54
—Melosira islandica 57
—Tabellaria fenestrata 57
—Tabellaria flocculosa 59
DISCUSSION 61
Seasonal Phytoplankton Patterns in Lake Huron 61
Georgian Bay 61
North Channel 62
Offshore Regions in North and Central Basin 62
Offshore Region in Southern Basin. 63
Nearshore Regions of Lake Huron 63
SUMMARY 65
REFERENCES 66
APPENDIX 1 68
iii
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LIST OF FIGURES
FIGURE PAGE
1. Sampling locations in Lake Huron during April 1980 to March 1983
study 4
2. Regions of Lake Huron from which phytoplankton and water chemistry
averages were calculated. These regions were similar to the
regions delineated in the 1974 segmentation scheme by IJC (1976a,
1976b) 9
3. Seasonal patterns in phytoplankton biovolume at selected locations
(numbered at right edge of each figure) around the Lake. Unmarked
area under curve indicated diatom biovolume and dotted area
indicated dinoflagellate biovolume. Biovolumes of other algal
divisions could not be distinguished graphically 9
4. Seasonal patterns in phytoplankton abundance at selected locations
(numbered at right edge of each figure) around the Lake. Unmarked
area under curve indicated diatom abundance; dotted area indicated
blue-green algal abundance; area marked by horizontal lines
indicated microflagellate abundance; and area marked by vertical
lines indicated chrysophyte abundance 10
5. Seasonal biovolume patterns of all algae in different regions (Fig.
2) of Lake Huron. "0" marks missing samples 10
6. Seasonal biovolume patterns of diatoms in different regions (Fig.
2) of Lake Huron. "0" marks missing samples 11
7. Seasonal biovolume patterns of green algae in different regions
(Fig. 2) of Lake Huron. "0" marks missing samples 11
8. Seasonal biovolume patterns of blue-green algae in different
regions (Fig. 2) of Lake Huron. "0" marks missing samples 13
9. Seasonal biovolume patterns of chrysophytes in different regions
(Fig. 2) of Lake Huron. "0" marks missing samples.. 13
10. April spatial pattern of total algal biovolume 14
11. April spatial pattern of diatom biovolume 14
12. April spatial pattern of blue-green algal abundances 15
13. April spatial pattern of unidentified flagellate abundances 15
14. April spatial pattern of diatom abundances 16
15. April clusters of similar planktonic diatom assemblages 16
16. April spatial pattern of diatom diversity 19
17. May spatial pattern of total algal biovolume 21
18. May spatial pattern of diatom abundances. 21
19. May spatial pattern of blue-green algal abundances 22
20. May spatial pattern of cryptomonad abundances 22
21. May spatial pattern of unidentified flagellate abundances 23
22. May clusters of similar planktonic diatom assemblages 23
23. May spatial pattern of diatom diversity 25
24. June spatial pattern of total algal biovolume 25
25. June spatial pattern of diatom abundances 26
26. June spatial pattern of unidentified flagellate abundances 26
27. June spatial pattern of blue-green algal abundances 27
28. June spatial pattern of diatom diversity 27
29. June clusters of similar planktonic diatom assemblages 28
iv
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LIST OF FIGURES
FIGURE PAGE
30. July spatial pattern of total algal biovolume. 28
31. July spatial pattern of diatom abundances 30
32. July spatial pattern of blue-green algal abundances 30
33. July clusters of similar planktonic diatom assemblages 31
34. July spatial pattern of diatom diversity 31
35. September spatial pattern in total algal biovolume 33
36. September spatial pattern in diatom abundances 33
37. September spatial pattern in unidentified flagellate abundances.... 34
38. September spatial pattern in blue-green algal abundances 34
39. September clusters of similar planktonic diatom assemblages 35
40. September spatial pattern in diatom diversity 35
41. October-November spatial pattern in total algal biovolume 37
42. October-November spatial pattern in diatom diversity 37
43. January 1981 spatial pattern in total algal biovolume 38
44. January 1981 spatial pattern in diatom abundance 38
45. Jaunary 1981 spatial pattern in blue-green algal abundance 39
46. February 1981 spatial pattern in total algal biovolume 39
47. February 1981 spatial pattern in diatom abundance 40
48. February 1981 spatial pattern in blue-green algal abundance 40
49. Spatial pattern in seasonal variation of algal divisional
biovolumes. Dotted lines were used at stations where integrated
samples were not collected during one or more of the first four
cruises 42
50. Regions of Lake Huron that were used to study differences in algal
division biovolumes with analysis of variance procedures 42
51. Depth profiles of algal division biovolumes at various stations
(numbered in lower right hand corner of figures) during ftpril.
Unmarked area indicated diatoms & the dotted area indicated
dinoflagellates 45
52. Depth profiles of algal division biovolumes at various stations
(numbered in lower right hand corner of figures) during May.
Unmarked area indicated diatom biovolumes 45
53. Depth profiles of algal division biovolumes at various stations
(numbered in lower right hand corner of figures) during June.
Unmarked area indicated diatom biovolumes. 46
54. Depth profiles of algal division biovolumes at various stations
(numbered in lower right hand corner of figures) during July.
Unmarked area indicated diatoms; area marked by cross hatching
indicated chrysophytes; and the area marked by diagonal lines
indicated green algae 46
55. Depth profiles of algal division biovolumes at various stations
(numbered in lower right hand corner of figures) during September.
Unmarked area indicated diatoms and the area marked by diagonal
lines indicated green algae 47
56. Depth profiles of algal division biovolumes at various stations
(numbered in lower right hand corner of figures) during
October-November. Unmarked area indicated diatom biovolumes 47
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LIST OF FIGURES
FIGURE PAGE
57. Seasonal abundance patterns of Asterionella formosa in
different regions (Fig. 2) of Lake Huron. "0" marks missing
samples 51
58. Seasonal abundance patterns of Cyclotella comensis plus
C. michiqaniana in different regions (Fig. 2) of Lake Huron.
"0" marks missing samples 51
59. Seasonal abundance patterns of Cyclotella gcellata in different
regions (Fig. 2) of Lake Huron. "0" marks missing samples 55
60. Seasonal abundance patterns of Cyclotella stelliqera in
different regions (Fig. 2) of Lake Huron. "0" marks missing
samples 55
61. Seasonal abundance patterns of Fraqilaria capucina in different
regions (Fig. 2) of Lake Huron. "0" marks missing samples 56
62. Seasonal abundance patterns of Fraqilaria crotonensis in
different regions (Fig. 2) of Lake Huron. "0" marks missing
samples 56
63. Seasonal abundance patterns of Melosira islandica in different
regions (Fig. 2) of Lake Huron. "0" marks missing samples 58
64. Seasonal abundance patterns of Tabellaria fenestrata in
different regions (Fig. 2) of Lake Huron. "0" marks missing
samples 58
65. Seasonal abundance patterns of Tabellaria flocculosa in
different regions (Fig. 2) of Lake Huron. "0" marks missing
samples 60
vl
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LIST OF TABLES
TABLE PAGE
1. The cruise dates and types of samples collected at locations in Lake
Huron 5
2. Common diatoms species that were used in cluster analysis of
planktonic diatom assemblages during each cruise 18
3. Average relative abundances of common diatoms in Lake Huron during
each cruise. 19
4. Ranks of the biovolumes of algae in segments of Lake Huron. The
lowest is 1 and 10 is the highest 43
5. Correlation coefficients between physicochemical conditions in Lake
Huron. This data was reported by Moll et al. (in press) 48
6. Partial correlation coefficients between divisional biovolumes ad
physicochemistry of waters in regions of Lake Huron 50
7. Partial correlation coefficients for diatom species' biovolumes and
physicochemistry of waters in regions of Lake Huron 53
V1T
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LIST OF APPENDICES
APPENDIX PAGE
I. Stations used to calculate average phytoplankton and average water
chemistry for regions in correlation and regional biovolume and
abundance studies 68
viii
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INTRODUCTION
Lake Huron is the main body of water connecting Lakes Superior and
Michigan to Lake Erie in the chain of Laurentian Great Lakes. It is a valuable
natural resource for the citizens of the United States and Canada. The waters
of Lake Huron provide a source of water for most commercial and private
activities for the millions of people that live along the eastern border of
Michigan and the southwestern border of Ontario. Lake Huron is a shipping
waterway, assimilates wastes from agricultural, municipal and industrial
sources, and is a source of recreation for millions of Americans each year.
The water quality of Lake Huron varies from region to region. The greatest
water quality problems in the lake have been associated with high nutrient
concentrations which have caused large standing crops of phytoplankton and
taste and odor problems in Saginaw Bay (Vollenweider e_t al. 1974, Smith et al.
1977, Stoenner e_t al. 1982), one of the two large embayments of Lake Huron.
Low standing crops of phytoplankton in the waters of the Georgian Bay, the
North Channel, and the north and central basins of Lake Huron indicate that
they have been oligotrophic. Nutrient enrichment in the nearshore waters in
regions of the Georgian Bay (Veal and Michalski 1977, Nicholls et al. 1977) and
the central basin (Lowe 1976, and Ladewski ejb al. 1982) have been detected.
This study of the phytoplankton of Lake Huron was part of the Great Lakes
surveillance program, during which the five Great Lakes are monitored on a
rotational basis. In particular, this study was part of an intensive research
program conducted during 1980 to survey the water quality of Lake Huron. Other
parts of the intensive 1980 research program were: surveillance of nutrient
chemistry and physicochemical characteristics of Lake Huron waters (Moll et al.
in press), surveillance of zooplankton patterns (Evans 1983), and a detailed
study of phytoplankton in the southern basin of Lake Huron (Kreis e_t al. in
press). Whereas, the primary objectives of all three studies were to assess the
water quality of Lake Huron and estimate changes in water quality that have
occurred after implementation of measures to reduce phosphorus loading into the
lake, each study focused on different aspects of the limnology and ecology of
Lake Huron.
The ojectives of the study described in this report were:
1. to characterize phytoplankton standing crop and species
composition in Lake Huron;
2. to characterize the water quality of regions of Lake
Huron by studying the abundance and the autecology
of phytoplankton;
3. to provide data with which future assessments of the
changes in water quality of Lake Huron can be made;
4. to compare the phytoplankton communities of Lake Huron
with those found in the past and to assess
changes in water quality that have occurred during
the period in which phytoplankton has been monitored.
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CONCLUSIONS AND RECOMMENDATIONS
Patterns of phytoplankton indicated that the waters of Lake Huron were
generally oligotrophic. The phytoplankton was dominated by the eurytopic
diatoms year-round. Abundance and biovolume of algae was not large during the
spring bloom. Algal biovolumes were low during the summer. Nitrogen-fixing
blue-green algae were never abundant. Only a slight increase in phytoplankton
abundance occurred during the fall.
Regional variation in water quality was indicated with relatively large
standing crops of algae in the nearshore waters of the southern basin and with
low standing crops in the Georgian Bay. Higher and more persistent standing
crops of phytoplankton than in most regions of the Lake were also observed
along the western shore of Lake Huron and near Cheboygan, which indicated that
these waters were slightly enriched at different times of the year.
Little change in the water quality of Lake Huron waters was indicated by
studying reports of algal abundances during the last 20 years. There were some
signs that loading of nutrients to the southern basin was still causing some
degradation of these waters. But, lower standing crops of algae near Saginaw
Bay, than in the past, indicated that loading of nutrients had been reduced
there.
Recommendations for future monitoring address the problems of identifying
trends in the water quality of Lake Huron. It was difficult to assess
long-term trends in water quality without knowing what annual variation in
phytoplankton standing crops was. Seasonal sampling of nearshore and offshore
waters would be desirable. Such studies have been done by studying algae at
water intake stations and with seasonal cruises running transects through the
Great Lakes. The spring bloom should be studied thoroughly by starting
sampling earlier in the winter, rather than ending then. Patterns of algal
biovolume by division, and abundances of algal species causing those patterns
should be studied as complimentary information.
Interpretation of the significance of large standing crops of algae in
nearshore areas of the Lake were difficult. The importance of entrainment of
nutrients within a thermal bar area and then transport into offshore waters is
poorly understood in Lake Huron. Intensive studies of nearshore waters in the
southern basin and at discharges of several northern Michigan rivers is
recommended to study the loading of nutrients in these regions.
The combination of data that was collected during the three 1980 studies
of water chemistry, phytoplankton, and zooplankton was a particularly large and
well integrated set of data on a lake that has not been thoroughly studied, but
which is a very valuable resource. These data should be studied further as a
synthesized data set so that we can learn more about the limnology and ecology
of Lake Huron.
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MATERIALS AND METHODS
Sampling
Phytoplankton samples were collected from Lake Huron aboard the CSS
LIMNOS, R/V ROGER R. SIMONS, and USCGS BRAMBLE. Nine cruises were conducted,
three 1891 "winter" cruises, when a skeleton of locations were sampled, and six
other 1980 cruises when more thorough sampling occurred. The location and
number of samples collected varied substantially from cruise to cruise. For
example, no samples were collected with the CSS LIMNOS in the Georgian Bay
during Cruise 5 and most of the samples of Cruise 6 were discrete depth samples
from offshore locations in northern Lake Huron. Winter samples were collected
aboard the USCGS Bramble, but only from the southern basin. Most sampling
locations were located in the nearshore regions of the main body of Lake
Huron (Fig. 1). The cruise dates and number and location of samples are
listed in Table 1.
Two sampling methods were used. Integrated samples were collected with a
20 m integrating sampler at most nearshore sampling locations and sometimes at
offshore locations. Discrete samples were collected with Niskin bottles and
usually from 1, 5, 10, 15, 20, 25, 30, and 50 m and at larger intervals to the
bottom of the Lake. Samples were fixed with 10 ml of Lugol's solution/1.
Sample Preparation and Algal Enumeration
Samples from different cruises were processed in different laboratories.
Samples collected during Cruises 1 to 3 were prepared and counted by Mar, Inc.
Samples collected during Cruises 4 to 6 and "winter" cruises were prepared and
counted in the laboratories of Bionetics. A few of the samples collected
during Cruise 6 were prepared and counted by Great Lakes Research Division at
The University of Michigan.
Samples were prepared for observation with inverted microscopes by using
the modified Utermohl method. At least 250 algae were counted from a sample.
The number of live diatoms was determined from these enumerations, but the
taxonoraic composition of diatom phytoplankton was determined from a second set
of counts of at least 500 frustules that had been acid cleaned and mounted in
HYRAX on microscope slides. The number of algae of a species observed and
the proportion of samples that were counted, were recorded on benchsheets. In
addition, the dimensions of algae were recorded so that the biovolumes of algae
could be determined.
Data Analyses
The cell volume of each species was computed by applying average
dimensions to the geometrical shapes that most closely resembled the species
form, such as: sphere, cylinder, prolate spheroid, etc. During enumeration,
cell shape was determined and appropriate (e.g. length, width, depth, diameter)
dimensions of at least 10 specimens of each species were measured. When fewer
than 10 specimens were present, those present were measured as they occurred.
For most organisms, the measurements were taken from the outside wall to
outside wall. With loricated forms, the protoplast was measured, while the
individual cells of filaments and colonial forms were present.
Analyses of data treated integrated samples differently than discrete
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Fig. 1. Sampling locations in Lake Huron during April 1980 to
March 1983 study.
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Table 1. The cruise dates and types of samples collected at locations in Lake
Huron. Integrated samples are indicated by a "0-7" notation, where ? is equal
to the lower depth (m) of the depth range from which the sample was collected.
Numbers separated by commas indicate the depth from which discrete samples were
collected. "HC" stands for "winter" cruise and an "X" simply indicates that a
sample was taken. "b2" stands for a sample collected 2 m from the bottom.
Loca-
tion
1
3
4
5
7
9
10
13
15
16
17
19
21
25
30
33
I4,
40
43
47
50
53
58
63
66
71
78
84
101
104
117
125
130
133
137
Cruise
1
0-20
0-20
0-20
0-20
1,5,10,
15,26,36
50
0-20
0-20
0-20
0-20
5
0-20
0-20
1,5,10,
15,26,36
56.75,
106, 142
0-20
0-20
0-20
0-20
0-20
1,5.10.
15,26,36
50,64
0-20
0-20
0-20
1,5,10.
15,26,56
78
0-20
0-20
0-20
2
0-20
0-20
0-20
0-20
1,5,10,
15,26,36
50,58
0-20
0-20
0-20
0-20
0-20
8:38
0-20
1,5,10,
15,20,36
56,75,
106, B-2
0-20
0-20
0-20
0-20
0-20
1,5.10.
15,26,36
50
0-20
1,5,10,
15,26,36
b2
0-20
0-20
0-20
1 5 10
* f -' f *u f
15,26.36
15:26,36
0-20
0-20
0-20
0-20
3
0-20
0-20
0-20
0-20
1,5,10,
15,26,36
50,57
0-20
0-20
0-20
0-20
0-20
0-20
0-20
0-20
0-20
1,5,10.
20,25,36
56 75
100 '156,
174
0-20
0-20
0-20
0-20
0-20
0-20
1,5.10,
15,26,25
30,50,68
6-26
0-20
1,5,10,
15,26,25
30,43
0-20
0-20
0-20
5.10,15.
26,25,36
fcf) 7C
J\J , / 3
0-13
0-20
0-20
4
0-20
0-20
0-20
0-20
1,5.10.
15,26,36
50
0-20
0-20
0-20
0-20
1
1
1,0-20
15:26,36
56,75,
100,156,
i.60
0-10
0-20
0-20
1,5,10,
15,26,26
30,50,b2
0-20
1,5,10,
15,26,36
bZ
0-20
0-20
1 (j * I"?M *^i\
50, &2
15 '26. 36
§0,62
0-20
0-20
0-20
5
0-9
0-20
0-20
0-9
0-10
0-20
1,5,10.
20,25,36
40,59
0-10
0-16
0-20
0-20
1,5,10,
15,26,25
30,50'75
6-26
0-15
0-20
0-20
0-8
0-20
0-20
1,5.10,
15,26,25
30,50,75
106, 150,
iso
0-18
0-20
0-13
0-14
0-20
1,5.10,
15,26,25
30,50,68
6-26
0-20
1,5,10,
15:26, 2§
30,45
6
0-20
1,10,15,
20,25,30,
50,75
0-20
1,5,10,
15,26,25
30,50,75
106,150,
180
0-20
0-20
1,5,10,
15,26,25
30,50,67
6-26
0-20
1,5,10,
15,26,25
30,44
we we
1 2
X X
X X
X
X X
9x 3x
X
X X
x llx
X X
X X
X X
-------
samples. Patterns in algal division biovolume with depth were studied by
plotting data from the stations where discrete samples were collected. In
this analysis, algal biovolumes from all depths were studied. In most other
analyses, the average of algal standing crops in discrete samples from the
surface to 20 m was calculated and compared to algal standing crops in
integrated samples.
The standing crop data of algae have been analyzed in a variety of
different forms. Algal abundances (cells/ml) were studied when a more cellular
interpretation of patterns of algal genetic diversity and cell numbers was the
objective. Algal biovolumes (um3/ml) were studied when interpretation of
patterns with respect to the ecology of algal biomass and sequestering of
resources was more important. Hhen competition between species of algae for
resources was a priority or when parametric statistical analyses of data were
performed, algal abundances and biovolumes were transformed with a natural
logarithm function and were considered to be an indication of algal
reproductive rates. When the standing crops of algae were not transformed, the
objective of study was more in the context of how much or many were present. Of
course, all analyses were not performed with all forms of the data that have
just been listed, but the forms of data used in analyses have been selected in
accordance with the above criteria.
Standing crops of phytoplankton divisions were the data studied from
Cruises 1 to 6. Abundances and biovolumes of numerically or volumetrically
dominant algal divisions in integrated samples from Cruises 1 to 6 have been
plotted to analyze seasonal trends in standing crop and divisional composition
of phytoplankton at selected locations. In addition, histograms of the
abundances and biovolumes of dominant algal divisions were spatially plotted
within an outline of Lake Huron to illustrate the spatial variation in algal
standing crop within the lake. The statistical significance of spatial
variation in standing crop of algal divisions in different segments of Lake
Huron (segmentation scheme modified slightly from that of Moll et al., in
press) was assessed by using two-factor analyses of variance with cruise and
regions of the lake as factors. The number of replicates per region during
each cruise varied and was equal to the number of locations in a region in
which integrated samples were collected during a cruise.
Another spatial pattern in the seasonal standing crops of algal divisions
that was studied was seasonal variation in algal biovolumes. Seasonal
variation has been used in this report as an indicator of resource
availability, probably nutrient availability, at various locations in the lake.
The theory behind using seasonal variation in algal standing crop as an
indicator of resource availability is: that abundances of opportunistic algae
will vary more in locations where resources are abundant and they can reproduce
rapidly, than in locations where resources are scarce and, consequently
reproduction and turnover rates of algae are slower. The seasonal variation
in phytoplankton was measured as the change in biovolumes of algal divisions
from one sampling date to the next. The change in biovolume was calculated
with the following Euclidean distance (difference) formula:
where, D is equal to the number of divisions, and By and B^ were the
biovolumes of the ith division on the jth and kth sampling dates. Of course.
the seasonal variation in standing crop of phytoplankton may be the result of
-------
environmental factors other than resource availability, such as current
patterns in the lake. This measure was studied because it could be an easily
calculated and could be a valuable indicator of eutrophication.
The spatial variation in diatom assemblages around Lake Huron during
Cruises 1 to 6 Has studied to delineate water masses in the lake. Water masses
were delineated by using cluster analyses to group locations where diatom
reproduction rates were similar. The cluster analyses were computed using
BMDP software on a DEC-10 computer at the University of Louisville.
Log-transformed abundances of the dominant diatoms, those with an average
abundance greater than 2% or a maximum abundance that was greater than 10% of
the total diatom abundance at a location, were used as variables in the
cluster analyses. In these analyses, clusters of locations were grouped
based on the Euclidean difference in log-transformed diatom abundances
between locations. Initially, each case is considered to be a cluster; and
then the two clusters with the least difference (amalgamation distance) between
them are grouped. This process continued until all cases were combined
into one cluster by using an algorithm called average distance or average
linkage.
Results of cluster analyses were used to assess the spatial integrity of
regions of the Lake that were discussed in this report. The location of water
masses with similar diatom communities will be compared to several nearshore
regions around the Lake and offshore regions in the North Channel, the Georgian
Bay, and the north, central, and southern basins. Since the Euclidean
difference between assemblages was calculated with log-transformed abundances
of diatoms, it was an integrated estimate of the similarity of net reproductive
rate of the dominant diatoms in two assemblages (assuming grazing and sinking
rates were the same in the two assemblages). Thus, low distance, i.e. high
similarity, between diatom assemblages indicated similar physicochemistry and
similar water qualities at the two locations.
The species that characterized a water mass were determined by studying
tables of the species' averages within clusters. The tables were part of the
output generated by the BMDP-1M program.
The correlations between physicochemical conditions of the Lake and algal
division biovolumes plus abundances of the many common diatoms were studied
with water chemistry data from Moll et al. (submitted). The average of
log-transformed algal division biovolumes and of log-transformed diatom
species' abundances were calculated for each region during each cruise. The
segmentation scheme (Fig. 2) used to calculate average water chemistry of a
region by Moll et al. (submitted) and average phytoplankton characteristics in
this analysis closely corresponded to the 1974 segmentation scheme of the IJC
(1976a, 1976b). The identification number of stations that were located in
each segment are listed in Appendix I. Water chemistry and average algal
statistics in eight segments of Lake Huron during the six cruises were
correlated using Pearson correlation and partial correlation procedures (SPSS
software). Partial correlations between water chemistry and algae were studied
while accounting for the variation in algae that was due to seasonal changes.
The seasonal time variable used was simply cruise number (determining the exact
time of collection of each sample was impractical). Since seasonal changes in
algae are usually not linear, partial correlation, while holding time and
time-squared constant, was used so that non-linear changes in algae with season
could be accounted for.
-------
RESULTS
One thousand forty-nine algal taxa, grouped into nine divisions
and two categories of unidentified taxa, were recorded from Lake Huron
samples. More than half, 540, of those taxa were forms, varieties, and
species of diatoms. Most of the unidentified taxa were small phytoflagellates.
A list of these taxa is available from the author or project officer.
Seasonal Variation in Algal Division Biovolumes
Algal biovolume was usually greatest during the late spring (Fig. 3),
even though cell numbers were usually lowest then (Fig. 4). Most of the
phytoplankton biomass in Lake Huron was diatoms. With few exceptions, diatoms
comprised the greatest proportion of algal biovolume at stations around the
lake and during all seasons (Fig. 3). Biovolumes of dinoflagellates and
green algae were occasionally great. Blue-green algae were numerically most
common during most of the year at most locations, but the cells were generally
so small that they seldom represented important proportions of the biovolume.
The seasonal pattern in algal biovolumes varied around the Lake (Fig.
5). Large biovolumes of diatoms occurred during the spring, greater than 1.0 x
106 um3/ml in the Lake Huron proper (region 1), but less than those near the
St. Mary's River, in the North Channel, and in the Georgian Bay (regions 3, 4,
& 2; Fig. 6). The patterns in total algal biovolume were very similar to
patterns in diatom biovolume (Figs. 3, 5, S 6). In general, diatom biovolume
decreased from spring through early summer highs to summer and fall lows. This
pattern was observed in all areas of the lake except near the St. Mary's River
in the North Channel (region 3; Fig. 6) where diatom biovolumes were low and
variable throughout the field season, and near the Straits of Mackinac (region
7) where a second, fall peak was observed. The greatest diatom biovolumes
during the spring-early summer peak period were along the wlfetern shore of
southern Lake Huron (region 6). The large diatoms responsiWe for most of the
biovolume peaks were Tabellaria fenestrata and T. flocculosa.
In addition to biovolumes of algae, the length of time that the large
standing crops of spring persisted into summer seemed to be related to
suspected nutrient loading (Fig. 5). The bloom period was shortest in the
North Channel and Georgian Bay (regions 2 & 4). Biovolumes of algae did not
decrease to below 500.0 x 103 um^/ml until July or September in the nearshore
and offshore regions of the central and southern basins of Lake Huron (regions
1, 5, 6, & 8; Fig. 5).
Substantial seasonal variation was observed in the biovolumes of the
other, non-diatom algae, although their biovolumes usually peaked later than
diatoms during June, July, and/or September. Green algae (Fig. 7) in offshore
waters of the central basin of Lake Huron (region 1) and Georgian Bay (region
2) increased throughout the latter part of the field season, often because of
an increase in chlorococcalean algae, such as Oocystis. A similar pattern was
indicated in the offshore waters of the southern basin, except that a very high
July maximum was followed by a decrease in green algal biovolumes; however, the
July maximum was an artifact of observing one large Staurastrum cell. High
green algal biovolumes, mostly unidentified coccoid forms, were observed during
April along the western shore of the southern basin. The April peak near the
Straits of Mackinac may have been overestimated because of the observation of a
-------
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Cruises
1 2 3 4 5~~6 7 8"
Regions
FIT. 6 . Seasonal biovclumc pat t^rn = zf diatoms in -ii f f ev"r:'"r
regions ( Ficr. 2 ^ of Lake Huron . " n " "larks missina sa
e
1 61 61 61 61 61 6
2 3 4 56
Regions
7 8
Fi-T. 7. Seasonal biovolume patterns of crreen alqae in different
regions Tier. 2) of Lake Huron. "6" marks missing samples.
-------
large Pedlastrum colony. The only area where a May or June minimum was not
found was near the St. Mary's River. So there is an indication that diatoms
outcompete green algae for inorganic nutrients supplied by spring turnover,
except in areas where enough nutrients may be entrained that green algae can
also bloom.
Blue-green algal biovolume was lowest in all regions of the Lake during
June (Fig. 8). Again, high spring biovolumes were followed by late summer-fall
maxima in areas where substantial nutrient loading would be suspected, near the
mouth of Saginaw Bay (region 5) and the western nearshore and offshore regions
of the southern basin (regions 6 and 8). Chroococcalean algae, small coccoid
forms, comprised much of the spring and fall peak.
Chrysophyte biovolumes peaked during July in all regions of the Lake
except the North Channel (Fig. 9). A steady increase in chrysophyte biovolume
through July was only observed in the Georgian Bay region. June lows were
observed in many parts of the main body of Lake Huron. Dinobrvon statospores
and D. sertularia typically comprised most of the biovolume during April-May
periods, whereas other Dinobryon spp., Chrysosphaerella lonqispina, and
Qchromonas spp. comprised the July-September chrysophyte assemblage.
Dinoflagellate biovolumes were variable seasonally, as were biovolumes of
cryptomonads and unidentified flagellates. Their biovolumes were generally
less than 1.0 x 104 umS/ml. The only regularities observed in seasonal
patterns of these algae were the July minima in unidentified flagellate
biovolumes.
Cell numbers of diatoms, on the other hand, were relatively constant from
cruise to cruise (Fig. 4), while being as high as 1500 cells/ml, but usually
between 100 and 500 cells/ml. Unidentified flagellates were most abundant
during the spring (Fig. 4) and blue-green algae were most abundant during the
summer, fall, and winter. Blue-green algal abundances were commonly 5000
cells/ml and as great as 20,000 cells/ml during these seasons, whereas peak
abundances of unidentified flagellates were between 500 and 1000 cells/ml.
Spatial Patterns in Phytoplankton — April
Diatoms comprised such a large proportion (> 90%) of the algal biovolume
during the first three cruises that illustrations of algal biovolume and
diatom biovolume look the same (Figs. 10 S 11). During the April cruise
algal biovolume commonly exceeded 1.0 x 106 um3/ml in the western nearshore
regions of Lake Huron. High algal biovolumes were also observed in the north
basin (S 53) and along the eastern shore of Lake Huron at S 40. Tabellaria,
primarily T. fenestrata, comprised most of the biovolume along the western
shore of Lake Huron, whereas Melosira islandica was also an important
species, if not the dominant (> 40%) species of the phytoplankton communities
in other parts of the lake. The greatest abundances of blue-green
algae and unidentified flagellates were in nearshore regions of the southern
basin and along the western shore of Lake Huron in April (Figs. 12 S 13).
Algal standing crops were generally lowest in the Georgian Bay and North
Channel. The greatest biovolumes and abundances of algae were at S 7 along the
western shore of the southern basin, where diatom abundances were also the
highest (Fig. 14).
The April differences in phytoplankton from the Georgian Bay, S 7, and
most of the rest of Lake Huron were also evident in the patterns of similarity
in diatom assemblage composition (Fig. 15). Sixteen species of diatoms with
12
-------
10000
1000<
500<
co
O 100
r-
X 50
CO
5<
1 61 61 61 61 61 61 61 6
Cruises
1 2 3 4 5 6 7 8~
Regions
Fig. 8. Seasonal biovolume patterns of blue-green algae in
different regions 'Fig. 2) of Lake Huron. "0" marks missina
samples.
10000.*
500<
CO
O
X 50
CO
10
5
•A'
16 16 16 16 16 161616
1234 5678
Regions
Fig. 9. Seasonal biovolume patterns of chrysophytes in different
regions (Fig. 2) of Lake Huron. "0" marks missing samples.
-------
[um3x106/ml|
Fig. 10. April spatial pattern of total algal biovolurae.
[um3x106/ml]
Fig. 11. April spatial pattern of diatom biovolume.
-------
[103 cells/mil
Fig. 12. April spatial pattern of blue-green alaal abundances.
Lo
[103 cells/ml)
Fig. 13. April spatial pattern of unidentified flagellate
abundances.
-------
HO3 cells/ml)
Fig. 14. April spatial pattern of diatom abundances.
Ficr. 15. April clusters of similar planktonic diatom assemblacres.
-------
relative abundances greater than 10 percent or averaging greater that 2 percent
were used in the cluster analysis of April diatom assemblages (Table 2).
Fragilaria crotonensis and Tabellaria fenestrata were the most common with
average relative abundances of 18.0 and 16.8 percent, respectively (Table 3).
Asterionella formosa and two Cyclotella spp., C. glomerata and C. ocellata had
relative abundances averaging about 6 percent. A fourth subdominant species,
Melosira islandica, had an average relative abundance of 5 percent during
April. Regions of the lake with similar diatoms were delineated when the
amalgamated Euclidean difference within a cluster was between 2.5 and 4.0, or
when an assemblage at an individiual station was distinctly different from
those in the rest of the lake (distance greater than 9.0).
Except for the assemblage at S 53 in the north basin, offshore diatom
assemblages in Lake Huron in April were quite similar. The offshore assemblage
was characterized by higher abundances of an unidentified centric diatom and
Stephanodiscus subtilis (which may have actually been Stephanodiscus pan/us;
see Stoermer and Hakansson 1984) and with lower abundances of Nitzschia palea
and F. crotonensis than elsewhere. By increasing the amalgamation distance
from 2.5 to 3.5, many northern and eastern nearshore assemblages were included
in the big Lake Huron cluster. Nearshore assemblages, generally, had more
Fragilaria pinnata and N. palea and fewer centric diatoms than offshore
stations.
High abundances of C. qlomerata and C. ocellata and few M. islandica and
S. subtilis characterized diatom assemblages in the Georgian Bay.
If the April amalgamation distance was 3.6, the diatom assemblages of the
large Lake Huron and Georgian Bay clusters were grouped. Cyclotella qlomerata
and Cyclotella michiganiana were more abundant in the Georgian Bay cluster than
in the large Lake Huron cluster; whereas, Fragilaria capucina and T. fenestrata
were more abundant in the Lake Huron cluster. The remaining assemblages were
different than this large cluster because they generally had higher diatom
abundances, but in particular, lower abundances of the unidentified centric
(known as #1).
Diatom abundances were low in water from the St. Mary's River also. In
particular, abundances of C. michiqaniana, S. subtilis, and T. fenestrata were
lower and abundance of Diatoma elongatum was higher at S 71 than in the rest of
the Lake.
Two unusual diatom assemblages occurred in offshore waters at S 53 and S
133. Low diatom abundances, about 200 cells/ml, at S 133 in the Georgian Bay
were dominated by N. palea. Higher than average abundances, about 800
cells/ml, were observed at S 53 in the north basin where spring plankton
diatoms were most common. Unusually, a typically benthic diatom, Gomphonema
parvulum var. micropus, was uniquely most abundant at both stations S 53 and S
133.
With 3400 cells/ml, the diatom assemblage at S 7 along the southwestern
shore was more abundant than anyplace else in the Lake. Log-transformed
abundances of F. pinnata, F. capucina, D. elongatum. and A. formosa increased
more rapidly from Lake to S 7 than other species. Even though abundances of
diatoms in general were greatest at S 7, abundances of Tabellaria flocculosa
and the unidentified centric were less abundant at S 7. Despite the high
abundances of diatoms at S 7, species diversity was relatively high (H'>4.0)
there (Fig. 16). In general, species diversities of diatom assemblages were
highest in April, ranging from 3.0 to 5.0.
17
-------
Table 2. Common diatom species that Here used in cluster analysis of
planktonic diatom assemblages during each'cruise. Use of a species was
indicated with an "X". "1-2" and "2-2" indicate the first and second species
of two that were added together and used as one species.
Species
Cruise
3 4
Achnanthes minutissima
Asterionella formesa
Cvclotella comensis
Cyclotella comta
Cvclotella qlomerata
Cvclotella michiqaniana
Cyclotella ocellata
Cvclotella stelliqera
Diatoma elongatum
Fraqilaria capucina
Fraqilaria rrotonensis
Fraqilaria pinnata
Gomphonema parvulum
var. micropus
Helosira islandica
Melosira italica
Mitzschia palea
Rhizosolenia eriensis
Rhizosolenia lonqiseta
Stephanodiscus subtilis
Svnedra radians
Tabellaria fenestrata
Tabellaria flocculosa
Unidentified centric #01
X
X
X
X
X
X
X
V
v
X
X
X
XXX
1-2 1-2
X X
X X
X X 2-2 2-2
X X X X
XXX
X X
X X X X
X
X X
X X X
XXX
18
-------
Fig. 16. April spatial pattern of diatom diversity.
Table 3. Average relative abundance of common diatoms in Lake Huron during
each cruise. Relative abundance was calculated as the percent of the diatoms
observed in a sample that Has represented by one of the common species.
Species
Cruise
Astenonella formosa
Cyclotella comensis
Cvclotella qlomerata
Cvclotella michiqaniana
Cvclotella ocellata
Cvclotella stelliqera
Fraqilaria capucina
Fraqilaria crotonensis
Melosira islandica
Tabellaria fenestrata
Tabellarla flocculosa
6.5
-
5.7
2.1
5.9
2.0
3.3
16.8
4.9
18.0
3.1
6.2
-
10.5
2.2
7.1
3.0
3.3
13.1
4.4
21.5
4.4
7.5
1.6
6.3
4.8
4.6
2.2
2.2
11.7
3.2
38.5
4.0
8.8
11.6
-
32.9
4.5
5.1
0.6
11.1
0.5
5.4
3.2
1.2
14.6
-
12.0
2.1
1.8
0.6
17.0
0.2
1.8
0.3
10.1
11.0
-
1.2
7.2
0.6
0.4
43.2
1.2
3.7
5.2
-------
Spatial Patterns in Phytoplankton — May
During the May cruise algal standing crops were again greater along the
western shore of Lake Huron and eastern shore of the southern basin than
along the North Channel and in Georgian Bay (Fig. 17). Algal biovolumes
commonly exceeded 3.0 x 106 um3/tnl in the nearshore regions of the southern
basin. Most of that biovolume was still due to T. fenestrata with
substantial quantities of M. islandica at S 5. Again abundances of diatoms
were highly correlated to algal biovolumes (Fig. 18). In addition, locally
high abundances of blue-green algae along the eastern shore of the southern
basin contributed to high algal biovolumes there (Fig. 19). Cryptomonads and
unidentified flagellates were also abundant along the eastern shore of the
southern basin (Figs. 20 & 21).
Patterns in the similarity of diatom assemblages in Lake Huron were large
mosaics in the North Channel, Georgian Bay, and north and central basins of
Lake Huron (Fig. 22). The southern basin was a spatially finer mosaic than in
the rest of the Lake. Twelve species of diatoms with relative abundances
greater than 10 percent or averaging greater than 2 percent were used in the
cluster analysis of May diatom assemblages (Table 2). Tabellaria fenestrata
and Fraqilaria crotonensis were again most common while averaging 21.5 and 13.1
percent, respectively, of the diatoms in samples (Table 3). The same
subdominant species as in April were again subdominant during May. Regions of
the Lake with similar diatoms were delineated when the amalgamated Euclidean
distance was less than 3.0, except for the offshore assemblages in the north
and central basins which had a distance of less than 1.3 between them.
The diatom assemblages at offshore stations in the north and central
basins of Lake Huron were characterized by low abundances. Fewer Cyclotella
spp. and more Melosira islandica distinguished diatom assemblages in this
cluster from assemblages in the rest of the Lake. The assemblage at S 38 was
very different than at S 43, S 53, and S 66 or elsewhere in the Lake because:
1) it was the only assemblage without Asterionella formosa and 2) more
Cyclotella stelliqera occurred at this site than at any other site.
Actually, diatom assemblages throughout most of the northern, central, and
southern basins were very similar during May. High abundances of Tabellaria
spp. (both T. fenestrata and T. flocculosa), A. formosa, and M. islandica and a
low abundance of Cyclotella michiqaniana characterized the diatom assemblages
of most of Lake Huron.
There were three clusters of diatom assemblages in the Georgian Bay and
North Channel. One near the St. Mary's River (S 71) and at S 125 was
characterized by low abundances of C. stelliqera. North Channel assemblages
were notable because of low abundances of Tabellaria spp.and high abundances of
Melosira italica. Georgian Bay assemblages were characterized by their higher
than average abundances of Cyclotella spp. and lower than average abundances of
other species.
The fine-scale mosaic in the southern basin was the result of great
dissimilarity between diatom assemblages at S 3, S 5, and S 7. The amalgamated
distance within the cluster containing all three assemblages would have to be
greater than 4.5 to include them. Assemblages at S 5 and S 7 had less C.
michiqaniana and C. stelliqera and higher abundances of other species,
particularly Fraqilaria pinnata. When considering all algae, algal assemblages
at S 5 were distinguished from S 7 by having more of the cryptomonad Rhodomonas
minuta and unidentified flagellates and much more chroococcalean blue-green
20
-------
[um3x106/ml|
Ficr. 17. May spatial pattern of total algal biovolume.
(103 cells/ml)
Fig. 18. May spatial pattern of diatom abundances.
-------
N5
|103 cells/ml)
I103 cells/ml)
Fig. 19. May spatial pattern of blue-green algal abundances.
Fig. 20. May spatial pattern of cryptomonad abundances.
-------
NJ
CO
L0
[103 cells/ml)
Fig. 21. May spatial pattern of unidentified flagellate
abundances.
Fig. 22. May clusters of similar planktonic diatom assemblages.
-------
algae (Figs. 19, 20, & 21). The greatest abundance of diatoms occurred at S 3.
With an amalgamated distance of 7.0, the S 3 assemblage with particularly high
abundances of C. ocellata and F. pinnata clustered with the rest of the
assemblages observed in May.
Diatom diversity was as high in May as in April (Fig. 23), ranging from
3.0 to 5.0. Diatom species diversity was high in low abundance assemblages of
the North Channel and Georgian Bay as well as in the assemblages of the
nearshore of the southern basin. The greatest diversity was found at S 3, where
the highest diatom abundance was also observed.
Spatial Patterns of Phytoplankton — June
During June, when diatom biovolume still comprised most of the algal
biovolume in the lake, diatom biovolume was again high, usually greater than
3.0 x 106 um3/ml in the southern basin. But unlike earlier in the spring,
algal biovolumes were also shown to be higher in the central basin of the lake
(Fig. 24). Diatom biovolume, as well as total algal biovolume was again
low in the North Channel and Georgian Bay. As far as the biovolume of algae
was concerned, Tabellaria fenestrata was more exclusively dominant
around the lake during June than earlier in the spring. Abundances of diatoms
and unidentified flagellates were generally greater in the nearshore
areas of the southern basin (Figs. 25 & 26), whereas blue-greens were again
concentrated along the eastern shore of the southern basin (Fig. 27). As in
May, diatom biovolumes were greater at S 7 than elsewhere in the Lake; and
as throughout the spring cruises, diatom biovolumes were consistently greater
at S 7 than S 13, and greater at S 5 than S 10 along the two shores of
the southern basin. Diatom diversity was low in this region in June
-------
Ln
(um3x106/ml|
Fig. 23. May spatial pattern of diatom diversity.
Fig. 24. June spatial pattern of total algal biovolume.
-------
N3
ON
[103 cells/mil
[103 cells/ml)
Fig. 25. June spatial pattern of diatom abundances.
Fig. 26. June spatial pattern of unidentified flagellate
abundances.
-------
[103 cells/ml]
Fig. 27. June spatial pattern of blue-green algal abundances.
Fig. 28. June spatial pattern of diatom diversity.
-------
NJ
00
L0
Ium3x106/ml|
Fig. 29. June clusters of similar planktonic diatom assemblages.
Fig. 30. July spatial pattern of total algal biovolume.
-------
analysis. Synedra radians Has only abundant at S 71, and was the reason that
the region around the mouth of the St. Mary's River was separated from others.
The diatom assemblage in the central basin and most of the northern and
southern basin during June was characterized by having more Asterionella
formosa and Melosira ialandica and less Cyclotella spp., particularly C.
glomerata and C. michiqaniana, than other assemblages.
The Georgian Bay - North Channel diatom assemblage had more Cyclotella
spp. and less Fraqilaria capucina, M. islandica, and Tabellaria spp. (both
species) than other clusters of diatom assemblages.
Assemblages east of Saginaw Bay were characterized by having high
abundances of F. capucina.
Diatoms were again most abundant at S 7 along the western shore of the
southern basin, and most different from other assemblages as well. High
abundances of T. fenestrata and C. glomerata and low abundances of Cvclotella
stelligera and M. islandica characterized the assemblage at S 7.
As far as miscellaneous assemblages around the Lake were concerned, again
more C. stelligera occurred at S 125 than other localities in the Lake. Low
abundances of F. crotonensis and A. formosa occurred at S 50 and S 58 along the
north shore.
Spatial Patterns in Phytoplankton —- July
Spatial patterns in standing crop of algal divisions were not clearly
evident during the rest of the cruises. Two reasons seemed to be
responsible for this. First, it is probable that no patterns existed during
the July cruise. Second, the Georgian Bay was not sampled during the September
cruise, 5, few nearshore stations were sampled during cruise 6, and only
stations in the southern basin of Lake Huron were sampled during the
winter cruises.
During July, algal biovolumes in the nearshore regions of the southern
basin were substantially lower than in the spring and were not very
different from the biovolumes of algae that were in the other parts of the
Lake (Fig. 30). Algal biovolumes in the North Channel and Georgian Bay were
similar to spring biovolumes. Algal biovolume seldom exceeded 1.0 x 106
um3/ml and was usually less than 0.5 x 106 um3/ml. Algal biovolumes were
again highly correlated to diatom abundances (Fig. 31), which were
generally 500 cells/ml or less. The correlation between algal biovolumes
and diatom abundances was maintained despite the fact that blue-green algal
abundances were starting to increase from previous dates (Fig. 32).
Blue-green abundance, most of which was Anacystis marina, exceeded 1.0 x 104
cells/ml at S 71 in the North Channel and at several stations in the
nearshore regions of the southern basin.
The composition of July diatom assemblages was similar in the Georgian Bay
and many areas of Lake Huron, but small offshore and regional nearshore
differences were evident (Fig. 33). Eleven species of diatoms with relative
abundances greater than 10 percent or averaging greater than 2 percent were
used in the cluster analysis of diatoms assemblages in July (Table 2). The
relative abundances of Cyclotella michiqaniana increased from 4 to 33 percent
from June to July (Table 3). The sudden increase in C. michiqaniana was
probably the result of different personnel identifying algae in June and July.
Fraqilaria crotonensis and Cyclotella comensis were subdominant taxa with 11
and 12 percent relative abundances, respectively. Relative abundance of
29
-------
U>
o
HO3 cells/ml]
/
s r-«tf-h3 *•
40
30
20
10
•0
„!!
Fig. 31. July spatial pattern of diatom abundances.
Fig. 32. July spatial pattern of blue-green algal abundances.
-------
Fig. 33. July clusters of similar planlctonic diatom assemblages.
Fig. 34. July spatial pattern of diatom diversity.
-------
Tabellaria fenestrata had decreased to an average of 5.4. The amalgamated
Euclidean distances among assemblages in the clusters discussed Here no greater
than 3.0.
The large assemblage in the Georgian Bay and many nearshore areas of the
Lake were characterized with less Svnedra radians and more Tabellaria
flocculosa and Cyclotella spp., particularly C. comta, C. ocellata. and C,
stelliqera, than in the rest of the lake. When amalgamation distance was
increased from 2.8 to 3.0, the offshore assemblage in the central basin
clustered with the Georgian Bay and the nearshore regions of most of Lake
Huron. The offshore region had less C. comta and more C. ocellata, Rhizosolenia
eriensis, Rhizosolenia longiseta, and T. fenestrata than most other
assemblages.
The most different assemblage, clustering with the rest of the Lake with
an amalgamation distance of 6.4, was at S 71 near the St. Mary's River. This
assemblage was unusually rich in S. radians, T. flocculosa, and Asterionella
formosa. Less T. fenestrata was observed here than elsewhere.
Species diversity of diatoms was lower than usual, ranging from 1.0 to 4.0
(Fig. 34).
Spatial Patterns in Phytoplankton — September
During September algal biovolume was usually less than 0.5 x 106 um3/ml,
but a couple of curiously high biovolumes occurred at S 50 along the north
shore of the central basin and at S 2 in the southern basin (Fig. 35).
Abundances of 10 cells/ml of the dinoflagellate Ceratium hirundinella were
responsible for the peak in the southern basin, whereas a single
observation of a frustule of the large diatom, Cymbella lanceolate, was
responsible for the peak at S 50. Diatom abundances were again usually 500
cells/ml or less (Fig. 36), as were unidentified flagellate abundances
(Fig. 37). Higher than average diatom abundances were again observed at S 7.
Unidentified flagellates were also common at S 7, but also at other locations
in the southern basin. Alternatively, high abundances of blue-green algae were
more widespread during September than during July (Fig. 38). Although
blue-green abundances greater than 2.0 x 104 cells/ml were most common in the
southern basin, high abundances also occurred in other areas of the
lake. Coccochloris peniocystis, as well as Anacystis marina, were the
numerically dominant blue-green algae.
Diatom assemblages were very similar throughout the Lake during September,
perhaps because abundances were so low. Only seven taxa of diatoms were
considered to be numerically dominant forms for use in the cluster analyses of
September diatom assemblages (Table 2). Regions of the Lake with diatom
assemblages having differences between them of less than 2.0 were delineated,
and an assemblage at a station with a difference greater than 3.0 was
distinguished from other assemblages (Fig. 39). Three cluster analyses
were computed to study regions with similar diatom assemblages because
some taxonomic difficulties were encountered with three of the dominant
taxa that were small species of Cvclotella. In these analyses,
Cyclotella comensis, C. michiqaniana, and C. comensis var. #1 were
combined in different ways. Irregardless of which clustering scheme was
studied, similar regions were delineated.
Cvclotella comensis (with var. #1) accounted for an average of 40 percent
of the diatoms observed in samples (Table 3). Cyclotella michiqaniana and
32
-------
LO
Lo
[um3x106/ml)
Lo
[103 cells/ml)
Fia. 35. September spatial pattern in total alcral biovolume.
Fig. 36. September spatial pattern in diatom abundances.
-------
OJ
1
1 II
/
I
1
ll
(103 cells/ml]
Fig. 37. September spatial pattern in unidentified flagellate
abundances.
Lo
[103 cells/ml)
Fig. 38. September spatial pattern in blue-green algal abundances.
-------
FW-
ptember dusters
Fig-
40.
spatial
rn
in diatom
diversity-
-------
Fraqilaria crotonensis remained subdominants with 12 and 17 percent relative
abundance averages, respectively.
Diatom assemblages in the central basin and most of the southern basin
were very similar. Assemblages in this region formed a cluster with an
amalgamated distance less than 2.3. Diatom abundances in this region were
lower than average. Cyclotella comensis (and related morphotypes) were
unusually sparse here.
Diatom assemblages in the North Channel, near the Straits of Mackinac, and
the nearshore regions of the north basin were also similar. The diatom
assemblage at 5 7 was again different from others in the southern basin, but
during September was similar to assemblages in the northern end of the
lake. Hith a 2.34 distance, abundances of Achnanthes minutissima were lower
and abundances of Cyclotella comta were greater in this cluster than in most
other assemblages.
Diatom assemblages with high abundances of A. minutissima at S 10, along
the eastern side of the southern basin, and at S 50, in the nearshore region
near the Georgian Bay, were very similar to one another, and different from
assemblages in the rest of the lake.
The diatom assemblage at S 19, at the eastern end of Saginaw Bay, was the
most different from other assemblages in the lake. It was grouped with the
rest of the assemblages in the Lake if amalgamated distance of the cluster was
4.0. This assemblage was characterized by lower abundances of A. minutissima,
and in particular, higher abundances of F. crotonensis than elsewhere.
Diatom diversities were again in the range of 1.0 to 4.0 during September
(Fig. 40). No spatial pattern in diversities was evident.
Spatial Pattern of Phytoplankton — October through February
Few integrated samples were collected during the late October cruise.
Standing crops of algae at the stations that were sampled were not different
than those observed in July and September cruises (Fig. 41). Fraqilaria
crotonensis accounted for 43 percent and Asterionella formosa accounted for 10
percent of the diatoms in samples from the northern regions of the Lake during
October and November. No cluster analyses of diatom assemblages were
studied. Diatom diversity again ranged from 1.0 to 4.0 (Fig. 42).
During the first winter cruise in January 1981, algal biovolume
was nearly the same as during the July and September cruises, about 0.5 x
106 um3/ml, in the nearshore regions and less than that in the offshore
regions of the southern basin (Fig. 43). Diatom abundance, about 500
cells/ml, was again responsible for algal biovolume (Fig. 44). Similar
species of diatoms were common during January as were common during the rest of
the year. Blue-green algae were quite abundant, commonly exceeding 1.5 x
104 cells/ml (Fig. 45). Diatom and especially blue-green algal abundances
were generally lower near Saginaw Bay than elsewhere in the southern basin.
During the second winter cruise in February 1985, algal biovolume
was generally the same in the southern basin as during January, but unusually
high quantities of biovolume were observed at S 7 and 1 (Fig. 46). The high
peaks at S 7 and 1 were due to observation of a few cells of an unidentified
species of the desmid Staurastrum. Diatom cell abundances were again about
500 cells/ml (Fig. 47). Similar species of diatoms were common during
February as were common during the rest of the year. A bloom of Anacvstis
marina was evident in blue-green algal abundances at S 5 (Fig. 48). Again,
36
-------
CO
[um3x106/ml]
Fig. 41. October-November spatial pattern in total algal
biovolume.
Fig. 42. October-November spatial pattern in diatom diversity.
-------
U)
00
um3x106/ml|
|103 cells/ml)
Fig. 43. January 1981 spatial pattern in total algal biovolume.
Fig. 44. January 1981 spatial pattern in diatom abundance.
-------
|103 cells/mil
Fig. 45. January 1981 spatial pattern in blue-green algal
abundance.
L0
Ium3x106/ml)
Fig. 46. February 1981 spatial pattern in total algal biovolume.
-------
Lo
1103 cells/ml]
Fig. 47. February 1981 spatial pattern in diatom abundance.
(103 cells/mil
Fig. 48. February 1981 spatial pattern in blue-green algal
abundance.
-------
diatom and blue-green algal abundances were not as high as average near Saginaw
Bay. During January and February, abundances of diatoms were greatest at
S 7, and blue-green algal abundances were greater at 37 than S13.
Statistical Summary of Seasonal and Spatial Patterns
Algae at S 7 were also distinguished by the fact that changes in algal
division biovolume from cruise to cruise were greatest there (Fig. 49).
Generally, changes in algal division abundances between successive cruises were
greatest in the nearshore regions of the southern basin. Unusually high
changes were observed at S 21 near Saginaw Bay and S 84 in the North Channel.
These great changes were probably related to the irregular sampling schedule
at these stations such that times between successive samples were greater.
The results of the analysis of regional variation in algal biovolumes were
highly significant. Statistically significant (P<0.001) differences in
total algal biovolume and diatom, chlorophyte, chrysophyte, cyanophyte, and
unidentified flagellate biovolume occurred between cruises and between
segments of the lake. The regions of the lake that were used in this
analysis were modified from those outlined in the EPA segmentation scheme
from the 1980 Lake Huron study by Moll ejb al. (submitted for publication) and
are illustrated in Fig. 50. The segmentation scheme was modified to examine
differences in algal biovolumes in nearshore regions along the western
shore of the southern basin and along the eastern coast of the lake. The
nearshore region along the western shore was divided between S 16 and S 13 so
that changes in algal abundance due to effects of waters from Saginaw Bay
could be separated from effects of water quality degradation that could be
occurring along the southwest shore of the lake. The nearshore region
along the eastern shore of the lake was divided between S 30 and S 10 for
a similar reason, so that changes in water quality along the southeastern
shore of the lake could be distinguished from conditions farther north.
Interactive effects between season and region were also statistically
significant, and probably biologically significant as well, so detailed
comparisons of differences between regions would not have been appropriate. In
addition, the number of samples collected during each cruise within a
region varied from cruise to cruise. The following discussion, then, is based
upon the most pronounced differences between segments.
Offshore biovolumes of all algae in the north and central basin,
segment 8, and in the Georgian Bay, segment 7, were generally the lowest
in the lake (Table 4). Highest algal biovolumes were found in either
the nearshore region on the eastern side, western side, or southern end of
the southern basin. Biovolumes of all algal divisions were higher in segment
10 than segment 3, farther north along the eastern shore of the lake.
Biovolumes of all algae except blue-greens were higher in segment 11, on the
western shore of the southern basin than east of Saginaw Bay in segment 2.
The highest total, diatom, and green algal biovolumes were found along the
western shore of the southern basin in segment 11. Biovolumes of diatoms and
green algae were also high in segment 5, along the western shore of the north
basin and near the Straits of Mackinac.
Vertical Patterns in Algae
The seasonal pattern of high algal biovolumes during the spring and
41
-------
Fig. 49. Spatial pattern in seasonal variation of algal division
biovolumes. Dotted lines were used at stations where
integrated samples were not collected during one or more of
the first four cruises.
Fig. 50. Regions of Lake Huron that were used to study differences
in algal division biovolumes with analysis of variance
procedures.
-------
Table 4. Ranks of the biovolumes of algae in segments of Lake
Huron. The lowest is 1 and 10 is the highest.
Segment
1
2
3
4
5
6
7
8
9
10
11
Total
Algae
q
7
6
2
5
3
4
1
A
10
8
Diatoms
7
4
6
2
8
5
1
3
*
9
10
Green
Algae
7
6
3
5
9
4
2
1
A
8
10
Blue-Green
Algae
10
8
6
4
5
3
2
1
A
9
7
Chryso-
phytes
9
7
6
2
5
3
4
1
A
10
8
Unident .
flag.
8
7
5
3
6
4
1
1
A
10
9
Only one integrated sample collected in region 9.
43
-------
early summer was also evident in plots of depth profiles of algal
biovolume at stations 9, 43, 66, 78, 104, and 117 (Figs. 51 to 56). Algal
biovolume in surface waters was lowest during July, September, and October;
however, great biovolumes of diatoms were observed at deeper depths during
July. The great predominance of algal biovolume by diatoms was again evident
throughout the year.
The regional pattern in algal biovolume was also evident. Algal biovolume
was generally greatest in the southern basin at S 9, and was regularly lowest
in the North Channel and Georgian Bay at S 78, S 104, and S 117. Of course,
this pattern was particularly evident when algal biovolumes were seasonally
higher during April, May, and June (Figs. 51, 52, S 53) than during July,
September, and October-November cruises (Figs. 54, 55, S 56).
It was also noted that peaks in algal biovolume occurred between 25
and 30 m at station 9 (Figs. 51 to 55), whereas unusually high algal
biovolumes at significant depths were not clearly evident at other locations
except during July. Some evidence for diatom blooms at 20 m was apparent
near the Straits of Mackinac (S 66) in April, but diatom biovolumes were
also high at 5 m (Fig. 51).
The deep-water peaks in algal biovolume were the result of many different
species. Unidentified flagellates were responsible for the deep-water peak in
the southern basin during April. The September peak in the southern basin at S
9 was due to observation of a couple cells of the green alga Staurastrum, as
was also the case at 10 m at S 9 in July. The remaining deep-water peaks of
algal biovolume in July were due to high abundances of the Rhizosolenia spp.
Most of the 30 m peak in biovolume a S 9 in July was accounted for by R.
lonqjseta, as was the small peak at S 78 in the North Channel. Deep-water
peaks in the Georgian Bay were the result of high abundances of R. eriensis.
Both species of Rhizosolenia were important in deep-water biovolume peaks at S
43 and S 66 in the central and northern basins of Lake Huron.
Correlations Between Lake Huron Water Chemistry Characteristics
Nutrient levels were generally poorly correlated to conservative ion
concentrations and pH in the Lake Huron waters (Table 5; raw chemistry data
from Moll e_t al. in press). Phosphorus, nitrogen, and silica concentrations
were positively correlated to each other, and to ammonia and oxygen
concentrations. Total and dissolved phosphorus concentrations were the most
closely correlated nutrients (r=.74). Conductivity, chloride, and alkalinity
were more closely related to each other (.97>r>.57) than to sulfate. The
strongest negative correlations were between silicate and pH, conductivity,
chloride, and alkalinity (-.60>r>-.74).
Nutrient concentrations decreased from spring to fall. Cruise number was
negatively correlated to phosphorus concentrations and nitrate-nitrite, and
silica concentrations. The strong negative correlation between cruise number
and oxygen indicated the importance of the decrease in algal biovolume from
spring to fall. However, little correlation was observed between conservative
ion concentrations (conductivity, chloride, sulfate, and alkalinity) and cruise
number.
Correlations Between Algal Division Biovolumes and Water Chemistry
Total algal biovolume was positively correlated to phosphorus and nitrogen
44
-------
BIOVOLUME Ium3x106/ml]
BIOVOLUME [urn3 x 106/ml)
25
50-
75-
10°J
20 1
20
43 J
78
t-
CL
HI
Q
B-2-
100J
117
25
SO-
TS-
100J
66 J
117
104
Fig. 51. Depth profiles of algal division biovolumes at various
stations (numbered in lower right hand corner of figures)
during April. Unmarked area indicated diatoms & the dotted
area indicated dinoflagellates.
Fig. 52. Depth profiles of algal division biovolumes at various
stations (numbered in lower right hand corner of figures)
during May. Unmarked area indicated diatom biovolumes.
-------
BIOVOLUME (urn3 x 106/ml|
I
Q.
LU
Q
2 0
2 0
BIOVOLUME (urn3 x 106/mlJ
0 1 20 1 20 1 2
100J
150-
174-
43
78,
78
a.
LU
Q
150-- -\
160 »
25
50-
75-
100-1
66
117
25
50
75
100J
66
117
104
Fig. 53. Depth profiles of algal division biovolumes at various
stations (numbered in lower right hand corner of figures)
during June. Unmarked area indicated diatom biovolumes.
Fig. 54. Depth profiles of algal division biovolumes at various
stations (numbered in lower right hand corner of figures)
during July. Unmarked area indicated diatoms; area marked by
cross hatching indicated chrysophytes; and the area marked by
diagonal lines indicated green algae.
-------
BIOVOLUME (um3x106/ml)
2 0
2 0
BIOVOLUME [urn3 x 106/ml]
0 1 20 1
25-
50-
75-
100J
.057-
43
78
Q.
^> IK
-J Q
150-
180
25
50-
75-
X 100J
H ;
Q. 150 ••' —
LU
43 J
78
ISO
25-
50-
75-
100-"
66
117
25-
50-
75-
100-J
66
117
Fig. 55. Depth profiles of algal division biovolumes a.t various
stations (numbered in lower right hand corner of figures)
during September. Unmarked area indicated diatoms and the
area, marked by diagonal lines indicated green algae.
Fig. 56. Depth profiles of algal division biovolumes at various
stations (numbered in lower right hand corner of figures)
during October-November. Unmarked area indicated diatom
biovolumes.
-------
CD
Table 5. Correlation coefficients between physicochemical conditions in Lake Huron.
This data was reported by Moll et al.r>0.30)
CHEMICAL
PARAMETER DP
TP .74
DP
OP
N23
NH3
Si04
02
PH
COND
CL
S04
OP N23 NH3
.53 .29 .36
.53 .21 .36
.35 .21
.21
Si04
.44
.20
.30
.52
.53
02
.37
.52
.31
.63
.22
.41
PH
-.37
-.35
-.15
-.42
-.33
-.60
-.42
COND
-.23
-.03
-.07
-.24
-.53
-.69
.13
.57
CL
-.26
.08
.13
-.24
-.36
-.73
.06
.63
.96
S04
-.06
.18
-.34
-.12
.14
-.25
.12
.13
.19
.25
ALK
-.24
-.03
-.08
-.39
-.54
-.74
.00
.61
.97
.93
.20
-------
concentrations as Nell as conservative ion concentrations (Table 6). Total
algal biovolume was also positively correlated to oxygen concentrations. Total
algal biovolume was negatively correlated to ammonia and silicate
concentrations.
Diatom biovolume was more closely correlated to total phosphorus and
nitrate-nitrite concentrations than total algal biovolume, but was more poorly
correlated to dissolved and ortho- phosphorus than total biovolume. Diatom
biovolume was also more poorly correlated to conservative ion concentrations
than total biovolume.
Green algal biovolume was negatively correlated to nutrient
concentrations, especially nitrate-nitrite concentrations. Green algae were
also negatively correlated to oxygen and positively correlated to pH, which was
a pattern opposite the correlation pattern of diatoms.
Blue-green algal biovolume was also negatively or poorly correlated to
nutrient concentrations as well as pH. Two reasons could explain the negative
correlations between blue-green or green algal biovolume and nutrient levels.
One was that these algae were most abundant during the summer, so that their
negative correlations with nutrients could simply be an artifact of when they
typically bloom. However, only the negative correlations between green, and to
some extent, blue-green algae and dissolved and orthophosphorus can be
accounted for if variation in biovolumes with cruise is accounted for. A
stronger negative correlation between these algae and nitrate-nitrite developed
if variation in biovolumes with cruise is accounted for in analyses of partial
correlations. A second reason may have been that these algae were more
efficient at sequestering phosphorus and nitrogen than diatoms when those
nutrients were in low concentrations. They have been generally classified as
facultative heterotrophs, so perhaps they could use organic sources of
nitrogen. The latter reason more completely explained the strong negative
correlation between green and blue-green algae and nutrient concentrations.
Chrysophyte and dinoflagellate biovolumes were also negatively correlated
to orthophosphate, nitrate-nitrite, and silica concentrations, and oxygen
concentrations. These correlations also became stronger when seasonal
variation in chrysophyte concentrations were accounted for. Facultative
heterotrophy was again indicated.
Autecologies of Common Species of Diatoms
—Asterionella formosa
Abundances of this species were generally greatest during the spring (Fig.
57) in most regions of the Lake. Lowest abundances regularly occurred during
September, except near the Straits of Mackinac (region 7) where abundances
increased from April to November. Increases during cruise 6, the fall,
indicated that abundances again increased, although high abundances were not
observed during the winter in the southern basin. Similar seasonal abundance
patterns have been observed in Lake Ontario (Stoenner et al. 1974) and in
studies of the southern basin of Lake Huron (Stoenner and Kreis 1980, Kreis et
al. in press).
However, Stoermer and Yang (1970) reported the highest relative abundances
of this species during the late summer and fall in Lake Michigan. Although
August samples were not collected in this Lake Huron study, its relative
abundance in Lake Huron was lowest in September (Table 3), when small
Cyclotella were most abundant in samples. These discrepancies may have been
49
-------
Table 6. Partial correlation coefficients* between divisional biovolumes and physicochemistry of waters in
regions of Lake Huron while holding the variation in biovolume with time and time2 constant. Physicochemical
data and section designations from Moll et al. (in press).
Ul
o
Division
Bac i 1 lar iophy ceae
Chlorophyta
Cyanophyta
Chrysophyceae
Colorless Flag.
Cryptomonads
Euglenoids
Dinoflage Hates
Unideterm. Flag.
Total biovolume
Co-
Var
_
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
TP
.45
.59
.54
-.19
-.28
-.21
-.07
-.17
-.37
-.19
-.00
-.09
.58
.62
.56
.45
.47
.32
.39
.25
.12
.00
-.12
.17
.16
.00
-.01
.39
.50
.46
DP
.40
.46
.39
-.02
.07
.19
-.05
.20
.07
-.21
.20
.14
.40
-.12
-.21
.23
.31
.11
-.21
-.13
-.29
-.07
-.08
.18
.04
.18
.18
.39
.52
.48
OP
.32
.20
.34
-.31
.09
.02
-.15
-.02
.09
-.56
-.08
-.02
-.12
-.03
.11
.26
.16
.41
.08
-.14
.10
-.02
.27
.14
.45
.32
.35
.30
.28
.39
N23
.47
.36
.28
-.40
-.53
-.50
-.33
-.27
-.42
-.48
-.52
-.63
-.05
.03
-.26
.25
.38
.25
-.01
.51
.43
-.27
-.35
-.20
.29
.08
.08
.39
.25
.19
NH3
-.13
-.21
-.24
-.15
.04
.06
-.25
-.14
-.17
-.15
-.03
-.05
.16
.20
.02
-.03
-.05
-.10
-.17
-.10
-.23
.03
-.13
-.11
-.08
.01
.01
-.19
-.28
-.30
Si04
.14
-.00
-.12
-.44
-.41
-.37
-.27
-.24
-.38
-.40
-.26
-.34
.31
.36
.20
.30
.21
.05
.35
.36
.24
-.30
-.32
-.17
.01
-.20
-.23
-.02
-.21
-.31
02
.71
.54
.49
-.50
-.64
.67
-.44
-.20
-.54
-.49
-.42
-.71
.18
.21
-.31
.28
.43
.16
-.20
.44
.34
-.37
-.53
-.33
.08
-.21
-.30
.61
.38
.35
PH
-.04
.21
.46
.30
.11
-.01
.10
-.22
-.07
.21
-.14
-.06
-.24
-.06
-.05
-.14
-.21
.09
-.13
-.29
-.15
.20
.17
-.17
.16
.28
.35
.10
.33
.55
COND
.31
.38
.40
.19
.05
.05
.12
.11
.12
.13
.07
.07
-.23
-.07
-.10
-.07
.02
.02
-.35
-.07
-.02
.10
.09
.08
.17
.06
.06
.41
.48
.49
CL
.21
.36
.41
.15
.16
.14
.12
.20
.24
.07
.09
.10
-.35
-.23
-.20
-.11
.01
.07
-.27
-.15
-.06
.23
.19
.14
.27
.24
.25
.36
.52
.55
304
-.03
.27
.28
.07
.04
.04
.06
.24
.26
.27
.12
.13
-.15
-.36
-.36
-.23
-.04
-.03
-.29
-.09
-.04
.19
.11
.09
-.02
.19
.19
-.02
.39
.40
ALK
.19
.22
.27
.27
.18
.17
.20
.19
.22
.20
.15
.17
-.18
-.06
-.01
-.12
-.08
-.03
-.44
-.28
-.22
.17
.16
.11
.14
.05
.06
.31
.35
.38
* The Probability that the correlation coefficient was equal to 0.00 was generally less than 0.05 if the correlation
coefficient was greater than 0.25 or less than -0.25, however that varied somewhat depending upon sample size.
-------
00
10000<
50001
1000<
5OO<
1001
501
1 61 61 61 61 61 61 61 6
Cruises
1 2 3 4 5 6 7 8~
Regions
Fig. 57. Seasonal abundance patterns of Asterionella formosa
in different regions (Fig. 2) of Lake Huron. "0" marks
missing samples.
Trrm mrTT rrTTn mm MUM mm rrmr rmrr
1 61 61 61 61 61 61 61 6
Cruises
2 3 4 5 6
Regions
7 8
Fig. 58. Seasonal abundance patterns of Cvclotella comensis
plus C. michiqaniana in different regions (Fig. 2) of Lake
Huron. "0" marks missing samples.
-------
the result of unsuccessful competition for nutrients during low nutrient
periods or predation (grazing) pressures which could be highly variable in
different waters.
This species has been commonly referred to as a eurytopic species because
of its widespread occurrence. To some extent that may be due to the great
variablility in its seasonal occurrence between habitats (Fig. 57). However,
correlations between its log-transformed abundance and nutrient concentrations
suggested that it did well in transitional environments where most of the
phosphorus had been sequestered by organisms, but nitrate-nitrite nitrogen and
silica concentrations were higher than average (Table 7). This species, more
than any of the common diatoms, had the strongest contrast in its positive
correlation with total phosphorus and its negative contrast with
orthophosphorus; which suggested that it was a good competitor for
orthophosphorus as phosphorus was recycled from organic to inorganic form.
Thus, the greatest abundances of this species would be expected at the end of
the spring bloom, which was the case in many regions of Lake Huron. Cholnoky
(1968) reported that lab studies indicated that A. formosa was a long-day
species, which was not when it had been found abundant in small lakes. The
periods of long days and cool water temperatures do not coincide in small
lakes. Stoermer and Yang (1970) suggested that long-day characteristics and
thermal inertia of the Great Lakes may allow this species to function near its
optimum in the Great Lakes. The suggestion by correlation, that it was a good
competitor for orthophosphorus when other nutrients were in abundance, may have
also complimented the coincidence of light and temperature optima in the Great
Lakes with nutrient optima.
—Cyclotella comensis & C.. michiqaniana
Since these Cyclotella spp. are small it can be difficult to distinguish
between them. Cyclotella qlomerata was probably also a problem taxon in this
group. Counts from one lab to another exhibited marked discontinuites in the
reports of abundances in these taxa. As many as four morphological entities of
C. comensis were recorded in counts from one lab, whereas no C. qlomerata were
reported then. Relative abundances of all three taxa were listed in Table 3.
At the time when data was accessible for correlation, the great abundance of C.
qlomerata and its role in taxonomic problems was not realized; thus, it was not
studied further. The good data that were studied were C. corneasis and C.
michiqaniana data. The combined abundances of these two taxa were illustrated
in Fig. 58. Correlations between physicochemical conditions and abundances of
each of the taxa and both together were presented in Table 7.
The reason that these taxa were studied, despite taxonomic problems, was
because they were so abundant during the summer through fall period (Fig. 58),
which was rather unique for the diatoms. Although, Stoermer and Yang (1970)
reported that C. michiqaniana was an ephemeral offshore species in Lake
Michigan, both taxa were most common during the summer in Lake Huron (Table 3,
Stoermer and Kreis 1980, Kreis et al. in press).
Although abundances of C. comensis and C. michiqaniana were correlated,
some niche separation was evident because of differences in correlations
between physicochemical conditions. The strong negative correlations between
log-transformed abundances of both taxa and nitrate-nitrite nitrogen indicated
that they were both good competitors for nitrogen (Table 7). However,
contrasts in whether the taxa were positively or negatively correlated to
orthophosphorus, ammonia, and pH especially, indicated autecological
differences. For example, the more negative correlation between C.
52
-------
Table 7. Partial correlation coefficients* for diatom species' biovolumes and physicochemistry of waters in
regions of Lake Huron while holding the variation in biovolume with time and time2 constant. Physicochemical
data from Moll et al. (in press) using 1974 Lake Huron Segmentation scheme (IJC 1976a,b).
Division
Asterionella
f ormosa
Cyclotella
comensis &
C. michiganiana
Cyclotella
comensis
Cvclotella
michiganiana
Cvclotella
ocellata
Cvclotella
stelligera
Fragilaria
capucina
Fragilaria
crotonensis
Melosira
islandica
label laria
fenestrata
Tabellaria
f locculosa
Co-
Var
.
t
t2
-
t
t2
_
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
-
t
t2
TP
.28
.48
.39
-.11
-.04
.41
.26
.10
.42
-.13
.04
.36
.19
.36
.23
-.09
-.23
-.03
.57
.48
.50
.50
.60
.53
.42
.46
.34
.25
.38
.47
.28
.50
.40
DP
.12
.13
-.02
-.21
-.23
.11
.15
.03
.20
-.07
-.14
.12
.10
.25
.10
.02
-.22
-.01
.43
.47
.47
.23
.42
.33
.34
.21
.04
.14
.03
.09
.16
.27
.12
OP
-.15
-.21
-.11
-.37
.11
-.17
.02
.39
.14
-.36
-.02
-.23
-.05
.00
.15
-.18
-.42
-.62
.34
.04
.08
.11
-.05
.07
.32
.05
.20
.37
.39
.37
.02
.08
.23
N23
.26
.33
.24
-.64
-.54
-.36
-.56
-.62
-.48
-.35
-.38
-.20
.20
.18
.05
-.18
-.39
-.24
.13
-.22
-.26
-.04
.01
-.12
.33
.19
.06
.62
.55
.62
.03
.07
-.06
NH3
.21
.15
.14
-.05
.02
.16
-.52
-.50
-.37
.12
.03
.11
-.19
-.20
-.24
.15
.30
.36
-.03
-.22
-.22
-.23
-.07
-.11
-.03
.03
.00
-.04
-.11
-.11
-.21
-.29
-.34
Si04
.30
.33
.25
-.36
-.24
.03
-.00
-.15
.06
-.29
-.13
.08
.01
.04
-.10
.06
-.12
.01
-.11
-.43
-.49
.04
.10
-.02
.34
.37
.28
.22
.16
.20
.08
-.03
-.16
02
.51
.59
.52
-.67
-.48
-.08
.53
.35
.29
.22
-.29
.06
.41
.47
.32
.20
-.36
-.14
.31
-.07
-.17
.04
.39
.24
.65
.55
.43
.63
.32
.52
.46
.53
.42
PH
.01
.10
.36
.41
.41
.05
-.35
-.06
-.10
.34
.36
.11
-.21
-.16
.05
-.11
.17
-.18
.07
.33
.52
.21
.12
.39
-.10
.00
.29
-.10
.18
.14
.10
.24
.57
COND
-.02
.08
.07
.05
.19
.21
-.07
.17
.30
.20
.16
.16
.25
.33
.36
-.08
-.02
-.05
.32
.41
.41
.30
.32
.34
.23
.17
.18
.23
.01
.02
.28
.46
.49
CL
-.11
-.06
-.04
.12
.21
.16
-.08
.22
.23
.19
.10
.03
.13
.24
.30
-.19
-.09
-.15
.36
.39
.40
.16
.22
.26
.07
.09
.13
.07
.09
.09
.14
.36
.41
S04
.12
-.09
-.10
.19
.10
.08
-.21
.24
.26
.34
.02
-.00
-.05
.34
.37
-.17
-.11
-.14
-.04
.14
.13
.04
.17
.18
-.12
.12
.13
-.12
.06
.06
.02
.27
.28
ALK
-.09
-.03
-.01
.13
.24
. 19
.03
.28
.31
.20
.16
.09
.17
.23
.29
-.09
.03
-.03
.29
.39
.40
.26
.20
.25
.17
.10
.14
.17
-.13
-.14
.23
.38
.44
* The probability that the correlation coefficient was equal to 0.00 was generally less than 0.05 if the
correlation coefficient was greater than 0.25 or less than -0.25, however that varied somewhat depending upon
sample size.
-------
michiqaniana and orthophosphorus suggested that this species was a better
competitor for phosphorus than C. comensis. Independent corroboration of this
suggestion was found in the Stoermer and Kreis (1980) study of southern Lake
Huron where both taxa reached very high abundances near Saginaw Bay; but, C.
michiqaniana was more abundant than C. comensis on the eastern shore of the
southern basin of Lake Huron, where nutrient supply was probably not as great
(phosphorus and nitrogen limitation more likely) as along the western shore.
—Cyclotella ocellata
This taxon has been repeatedly reported as an oligotrophic species which
is common in offshore waters (Stoermer and Yang 1970, Stoermer and Kreis 1980,
Kreis et al. in press). Perhaps its ability to compete well in nutrient-poor
waters was the reason that few consistent patterns with season, region, or
water physicochemistry were observed. Its relative abundance was more constant
seasonally that most of the other common diatoms (Table 3). Its abundance was
highly variable in each region of Lake Huron, but was highest most often in the
offshore waters of the Georgian Bay and central basin of Lake Huron (regions 1
and 2, Fig. 59). Its abundances were poorly correlated to inorganic nutrient
concentrations, but were positively correlated to conservative ion
concentrations and conductivity (Table 7).
—Cyclotella stelliqera
Abundance of this species was highly variable throughout the spring-fall
period in different regions of Lake Huron (Fig. 60). In both the 1974 and 1980
studies of southern Lake Huron (Stoermer and Kreis 1980, Kreis et al. in
press), its abundance was greatest during July.
More than any of the other common taxa, C. stelliqera was negatively
correlated to all nutrient concentrations (Table 7), total as well as
orthophosphorus and nitrate-nitrite nitrogen; thus, it probably was a good
indicator of oligotrophic conditions. This conclusion was corroborated by the
fact that it was one of the few taxa to have its lowest average abundances in
region 6, nearest Saginaw Bay and along the western shore of the southern basin
(Fig. 60). Plus, Hohn (1969) reported that its abundance had decreased
dramatically in western Lake Erie during the recent period of its
eutrophication.
—Fraqilaria capucina
This taxon was most abundant during the spring (Fig. 61), except in
regions where nutrient loading was suspected (region 5 near Saginaw Bay and
region 7 near Mackinac City). Other reports indicated its commonness in spring
and fall collections in Lake Michigan (Stoermer and Yang 1970) and Green Bay
(Stoermer and Stevenson 1979). However, summer blooms have been observed in
nearshore regions of Lake Ontario (Stoermer et al. 1974).
Of common diatoms in the Great Lakes, F. capucina seems to be one of the
best indicators of eutrophic conditions. Its abundance was highest near
Saginaw Bay and lowest in the North Channel and Georgian Bay (Fig 61). Indeed,
it has been cited repeatedly as an indicator of nutrient-rich conditions in the
Great Lakes (Hohn, 1969, Stoermer and Yang 1970, Stoermer et al. 1974,
Stoermer and Kreis 1980, Kreis et al. in press). Its abundance was highly and
positively correlated to all forms of phosphorus and negatively correlated to
silica, indicating its ability to compete for silica in phosphorus-rich water
(Table 7).
—Fraqilaria crotonensis
This species, one of the two most common in Lake Huron, had spring and
late summer-fall maxima in different regions of the Lake. In the southern
54
-------
/5
o
10000<
50001
1000<
500<
100<
50 <
Ul
Ol
\
1 61 61 61 61 61 61 61 6
Cruises
1 234 5^5 7 8~
Regions
1 61 61 61 61 61 61 61 6
1234 5678
Regions
Fig. 59. Seasonal abundance patterns of Cvclotella ocellata in
different regions (Fig. 2) of Lake Huron. "0" marks missing
samples.
Fig. 60. Seasonal abundance patterns of Cvclotella stelliqera
in different regions (Fig. 21 of Lake Huron. "0" marks
mi s s ing sample s.
-------
10000<
50001
10000<
50001
Ln
CO
V)
0)
O
10001
500<
100<
50<
V
1 61 61 61 61 61 61 61 6
Cruises
1 2 3 4 5~~6 7 8~
Regions
CO
O
10001
5001
1004
50 <
10-
1 61 61 61 61 61 61 61 6
Cruises
1 2 3 4 5 6 7 8~
Regions
Fig. 61. Seasonal abundance patterns of Fraq-jlaria capucina in
different regions (Fig. 2) of Lake Huron. "0" marks missing
samples.
Fig. 62. Seasonal abundance patterns of Fraailaria crotonensis
in different regions (Fig. 2) of Lake Huron. "0" marks
missing samples.
-------
region of the Lake, where nutrient concentrations were greater (regions 5 and
6), abundances were greatest during the spring (Fig. 62). In the northern end
of the Lake (regions 3, 4, and 7), abundances peaked in the early spring and
late summer to fall (regions 1 and 2). The regional variation in seasonal
abundance maxima was also shown by nullification of seasonal patterns in
Lake-wide relative abundances (Table 3). Relative abundances were between 10
and 20 percent until cruise 6, when it was 43 percent of the diatoms in cruise
6 samples (which were all from northern Lake Huron). Mid-summer lows were also
observed in Lake Ontario (Stoermer et al. 1974) and in southern Lake Huron
during 1974 (Stoermer and Kreis 1980).
Although this species was positively correlated to total and dissolved
phosphorus, the lack of negative correlations with nitrogen and silica, which
F. capucina had, indicated that it was not as competitive in phosphorus-rich,
and nitrogen- or silica-poor waters (Table 7). This corroborated the
suggestion of Stoerraer and Yang (1970), that although this is a eurytopic
species, it did not do well in highly polluted waters where high N:P ratios
occur.
—Melosira islandica
This species was a spring bloomer in most of Lake Huron (Fig. 63, Table
3), except near the Straits of Hackinac and the St. Mary's River. It has also
been observed most abundantly during the spring in southern Lake Huron
(Stoermer and Kreis 1980, Kreis et al. in press), Lake Ontario (Stoermer et al.
1974), and Lake Michigan (Stoermer and Yang 1970).
Stoermer and Yang (1970) suggested that it was an offshore species that
responded to nutrient enrichment, but was rapidly displaced in polluted
habitats. Lake Huron data suggested a similar autecology, where its abundance
was most persistent (until June) in offshore waters of the central and southern
basins. It was never abundant in the nutrient-poor Georgian Bay. Although,
abundant during April and May near Saginaw Bay (regions 5 and 6), its abundance
decreased rapidly in June and July.
The positive correlations between this taxon and all nutrients (Table 7),
more than any other common diatom, also indicated that it did well in
nutrient-rich waters, but was not competitive once nutrients became somewhat
limiting.
—Tabellaria fenestrata
This was the most abundant of diatoms in Lake Huron during 1980. Its
large size and abundance made it the dominant component of the phytoplankton
during the spring in many areas of the Lake.
This species was most abundant during the late spring (Fig. 64). Late
summer and fall pulses in abundance occurred in the nutrient-rich area near
Saginaw Bay (region 6) and in the northern regions of the Lake (regions 3, 4,
and 7). Lake-wide, relative abundance of this species increased through June,
then decreased sharply (Table 7). This species has commonly been observed as a
dominant component of spring phytoplankton in the southern basin of Lake Huron
(Stoermer and Kreis 1980, Kreis et al. in press); but, it was also found in
abundance during other times of the year in nutrient-rich areas such as Green
Bay (Stoermer and Stevenson 1979). It was widely distributed in Lake Ontario
(Stoermer et al. 1974).
This species was more strongly and positively correlated to total and
orthophosphorus and nitrate-nitrite nitrogen than any of the common diatoms
studied in Lake Huron (Table 7). The difference between this taxon and
Melosira islandica, which was also positively correlated to nutrient
57
-------
10000
5000-<
CO
o
Ul
00
100<
50
10
5
1
1 61 61 61 61 61 61 61 6
Cruises
~12 3 4 5678
Regions
10000-
50001
1000
500<
CO
50<
0
O
1 61 61 61 61 61 61 61 6
Cruises
~\ 2 3 4 5 6 7 8~
Regions
Fig. 63. Seasonal abundance patterns of Melosira islandica in
different regions (Fig. 2) of Lake Huron. "0" marks missing
samples.
Fig. 64. Seasonal abundance patterns of Tabellaria fenestrata
in different regions (Fig. 2) of Lake Huron. "0" marks
missing samples.
-------
concentrations, was a slightly weaker, but positive correlation between its
abundance and silica concentrations. In Lake Huron, T. fenestrata was most
abundant in the nutrient-rich areas near Saginaw Bay and along the western
shore of the southern basin (Fig. 64); but here its abundance had crashed by
June. Whereas, in most other areas of the Lake, the spring bloom of this
species persisted until July. Thus it, like M. islandica, responded to
nutrient enrichment, but would probably not have competed well in highly
polluted environments where one nutrient or another rapidly becomes limiting.
Stoermer and Yang (1970) also suggested that this species responded to nutrient
enrichment in lower levels, in the form of upwelling. A similar conclusion
could be drawn from Hohn's (1969) observation that its relative abundance
remained unchanged during eutrophication of western Lake Erie.
—Tabellaria flocculosa
Although the seasonal pattern in abundance of this species was variable
from region to region, in most areas of the lake it bloomed in the spring (Fig.
65). Near Saginaw Bay (region 6) and in the North Channel (regions 3 and 4) it
bloomed later in the spring than elsewhere. It also bloomed again during the
fall in the northern regions of the Lake. A September minimum was common. Its
seasonal relative abundance pattern also showed the September minimum. Similar
seasonal patterns were observed in the 1974 study of southern Lake Huron
(Stoermer and Kreis 1980).
The lack of correlation of this taxon with any nutrients, except total
phosphorus, indicated that it did not respond strongly to nutrient enrichment
in Lake Huron (Table 7). Koppen (1978) suggested that this species develops
best in hard water mesotrophic and eutrophic environments. It was strongly
correlated to conservative ion concentrations and conductivity in Lake Huron.
Regionally, abundances of this taxon were greatest near the Straits of
Mackinac and the St. Mary's River. Secondarily, it was abundant in the
southern basin regions (5, 6, and 8), It seemed probable that the alkalinity
of Lake Huron waters was generally not great enough to support large
populations of T. flocculosa.
59
-------
mm mm mm mm mm
1 61 61 61 61 61
Cruises
nrm
61 61
2 3 4 5 6
Regions
Fig. 65. Seasonal abundance patterns of Tabellaria flocculosa
in different regions (Fig. 2) of Lake Huron. "0" marks
missing samples.
60
-------
DISCUSSION
Seasonal Phytoplankton Patterns in Lake Huron
Algal standing crops varied both spatially and seasonally in Lake Huron.
Total algal biovolumes were higher during the spring than other seasons,
however total algal abundances were actually highest during the rest of the
year. Although spatial patterns in algal standing crops tended to be greater
during the spring than during other seasons, generalities in the spatial
patterns persisted. Algal standing crops were generally higher in nearshore
waters than offshore waters and were generally higher in the nearshore
waters of the southern basin than other areas of the lake.
Phytoplankton biovolume generally decreased from April, May, and June
maxima to summer, fall, and winter minima. Diatom and unidentified
phytoflagellate abundances, as well as abundances of most other divisions of
algae, were greater during the spring than other seasons. Alternatively,
Phytoplankton abundances were highest during the summer, fall, and winter
because of large abundances of a small colonial blue-green alga, Anacystis
marina.
No change in overall phytoplankton seasonal standing crop patterns and
species composition was observed during the last decade in Lake Huron. As in
1974, standing crops of algae were greatest in the spring, lowest in the
summer, a weak increase in abundance of eurytopic diatoms was observed in the
fall, and intermediate standing crops during the winter were observed in the
1974 study (IJC 1976b). Diatoms still comprised the major portion of biovolume
throughout the year. Tabellaria fenestrata and Fragilaria crotonensis were
still the dominant diatoms. Small Cvclotella spp. continued to be abundant
during the summer. No significant shifts in common species of blue-green and
green algae, cryptomonads, and chrysophytes were apparent during the last
decade. Thus, Lake Huron generally continued to have the characteristics that
are commonly associated with large oligotrophic lakes.
Georgian Bay
Several characteristics of phytoplankton assemblages in the Georgian Bay
showed evidence that waters there were of the highest quality. Biovolumes of
phytoplankton were lower in the offshore waters of the Georgian Bay than any
other regions of Lake Huron. The spring peak in algal biovolume was lowest and
of the shortest duration in the Georgian Bay, which indicated that nutrient
levels after spring turnover were low and were rapidly exhausted.
The spring composition of diatom assemblages in the Georgian Bay indicated
that water quality of this region was different than the rest of the lake,
apparently because of low nutrient concentrations. More commonly than
assemblages in other regions of the lake, Georgian Bay diatom assemblages were
different than those in the rest of the lake. Higher proportions of small
Cyclotella spp. comprised the spring bloom in Georgian Bay waters. The same
Cyclotella spp. were also the most common taxa in the Bay during the summer and
were commonly associated with low nutrient conditions in other regions of the
Lake.
There were indications of minor nearshore disturbances in the Georgian
Bay. Standing crops were often higher at S 125, near the mouths of the
Wanapitei and French Rivers, and at the southern end of the Bay. Indications
61
-------
of water quality degradation in nearshore waters of the Georgian Bay have been
observed by other investigators (Nichols et al. 1977). Whether the enhanced
standing crops during 1980 were the result of anthropogenic disturbances,
upwelling, thermal bar, or river discharge could not be determined.
There was a slight indication that the offshore waters of the Georgian Bay
had become more enriched in the last decade. A spring pulse in phytoplankton
was observed in 1980, whereas that pulse was not evident in 1974 (IJC 1976b).
Alternatively, other factors indicated that no change occurred. First, no April
sample was collected in the 1974 study, when highest biovolumes were observed
in 1980. Second, the 1980 spring pulse was observed in the average standing
crops for the region, but was not observed in the season pattern at S 130, one
of the offshore stations studied. Third, average biovolumes (biomass) for the
year were the same during 1974 and 1980, varying about 0.5 X 106 um3/ml (or 0.5
g/m3).
North Channel
Phytoplankton assemblages in the North Channel were greater than in the
Georgian Bay, but generally less than in the rest of Lake Huron. Low
biovolumes occurred during the spring peak and the peak was of shorter duration
than in the rest of the Lake, as was the case in the Georgian Bay. However,
small peaks in chrysophytes and blue-greens occurred during the summer. Perhaps
nearshore hydrological influences in this narrow channel contributed to the
slight indications of enrichment. High seasonal variation in algal division
abundance also suggested that the signs of enrichment were artifacts of local
hydrological variations. Nevertheless, the low standing crops of phytoplankton
indicated high quality and low enrichment of waters in the North Channel.
The great seasonal variation in algal standing crops and unusual, often
unique, species composition of phytoplankton in waters at the western end of
the North Channel indicated that discharge of waters from the St. Mary's River
affected the waters of the North Channel. Kreis et al. (1983) have reported
and quantified this phenomenon.
Comparison of 1974 (IJC 1976b) and 1980 phytoplankton patterns indicated
no change in water quality. Again, the lack of a spring peak in 1974 data may
have been an artifact of no April or early May samples in this region where the
spring bloom was so low in abundance and short in duration.
Offshore Regions in North and Central Basin
Low nutrient concentrations were indicated by low phytoplankton standing
crops in these offshore waters. However, lower nutrient levels were indicated
in some parts of the Lake by higher biovolumes and a longer duration of the
spring bloom in the northern and central basins of the Lake than in the North
Channel and Georgian Bay. Alternatively, higher nutrient levels were indicated
in other parts of the Lake by lower biovolumes and shorter durations of spring
blooms in the northern and central basins than in nearshore zones and southern
basin. Spring diatom assemblages in northern and central offshore waters also
indicated lower levels of nutrient replenishment after turnover than in
nearshore waters. Asterionella formosa and Melosira islandica were most
abundant and Tabellaria fenestrata responded more rapidly to moderate levels of
seasonal enrichment than the other two species. High peaks of chrysophytes
during July also indicated some enrichment. Thus the offshore waters of the
62
-------
northern and central basin were classified as oligotrophic, but with minor,
inconclusive indications of enrichment.
Phytoplankton biovolumes were generally greater in the central basin than
in the northern basin.
Comparison of 1971 (Munawar and Munawar 1975, 1982), 1974 (IJC 1976b), and
1980 phytoplankton standing crop indicated that little change had occurred in
the quality of waters in the offshore regions of the northern and central
basins. The same species of diatoms continued to dominate the phytoplankton,
plus biovolumes (biomass) of phytoplankton remained about 1.0 x 106 um3/ml (1.0
g/m3).
Offshore Region in Southern Basin
Poorer water quality in the offshore region of the southern basin than
central and northern basin was interpreted from phytoplankton standing crops in
this region. Phytoplankton biovolume and the spring pulse in blue-green algae
was slightly greater in the southern than central and northern basins. The
frequency and intensity of deep-water peaks in algal biovolume were also
greater and somewhat deeper in the southern than central basin. Deep-water
algal maxima could have indicated that algal growth was great enough in the
surface waters to deplete nutrients, and that those abundant nutrient resources
were being recycled deeper in the water column as the particles settled (Moll
and Stoermer 1982). Thus, the offshore waters of the southern basin were
concluded to be oligotrophic with signs of some enrichment.
Comparison of 1971 (Munawar and Munawar 1975, 1982), 1974 (Stoermer and
Kreis 1980), and 1980 phytoplankton patterns indicated slight degradation in
water quality during the last decade. The seasonal patterns in algal
biovolumes were slightly lower in 1971 when compared to 1980. Blue-green algal
and microflagellate abundance also seemed to be higher in 1980 than 1974.
However, the seasonal patterns in diatom abundance were slightly lower during
1980 than 1974. Kreis et. al. (in press) observed similar patterns in
phytoplankton changes during the past decade. Because of the greater number of
sampling locations in their study of Saginaw Bay regions and the southern basin
than this study of the whole lake, Kreis et al. (in press) made the observation
that the offshore region in the southern basin was less affected by nearshore
regions in 1980 than in 1974. Thus, the data suggested that transport of large
amounts of nutrients from Saginaw Bay had subsided, but that "resident"
nutrient levels in the southern basin had been increased, probably from past
loading from Saginaw Bay.
Nearshore Regions of Lake Huron
Local disturbances in nearshore regions of Lake Huron were common. It was
impractical to determine whether these signs of enrichment were due to
anthropogenic impacts or upwelling events, but it did not seem reasonable to
attribute them completely to nutrient transport from Saginaw Bay.
A variable seasonal pattern in chrysophytes and a significant fall pulse
in diatoms indicated enrichment at S 63, near Chegoygan and the Straits of
Mackinac. Whether this was due to hydrological variations in the channel,
transport from Lake Michigan, or local anthropogenic disturbance could not be
determined. Comparison between 1971 (Munawar and Munawar 1982) and 1980
standing crops indicated no change in the last decade.
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The nearshore region east of Saginaw Bay continued to show signs of
significant nutrient loading, but less than before. High spring abundances of
chroococcalean blue-greens, plus high abundances of the pollution indicator
Fraqilaria capucina during June and pollution-tolerant Fragilaria crotonensis
during September indicated significant enrichment. However, comparison of
biovolumes from 1971 (Munawar and Munawar 1982) and cell numbers from 1974
(Stoermer and Kreis 1980) with 1980 data indicated a reduction in nutrient
levels.
Phytoplankton assemblages in the nearshore region along the eastern shore
of the southern basin showed significant signs of enrichment, second only to
those along the western shore. Algal biovolumes were greater than 3 x 106
um3/ml during May and June on both shores, as well as during April on the
western shore. Algal biovolume was generally lower on the eastern shore, but
blue-green algal, chrysophycean, and flagellate abundances were commonly
greater on the eastern than western shore. This seemed to indicate that
enrichment was more continuous along the western shore than eastern shore
because diatoms were constantly more dominant along the western shore. The
occurrence of a spring bloom of Fraqilaria capucina and greatest annual diatom
and green algal biovolumes also indicated enrichment was greater along the
western than eastern shore. The consistency in the seasonal pattern along the
western shore indicated that the signs of enrichment were probably not the
result of intermittent upwelling events.
Repeated observation of Lake-wide standing crop maxima and unique species
compositions of phytoplankton assemblages and persistence of spring blooms at S
7, south of Sanilac, indicated that local sources of enrichment were probable.
The fact that signs of enrichment were usually greater at S 7 than north at S
13 indicated that all enrichment along the western shore of the southern basin
was probably not from Saginaw Bay. Although the watershed in this region
supported substantial agricultural activity, the watershed was so small that it
seems more probable that local point sources of pollution were responsible for
some enrichment.
Comparison of 1971 (Munawar and Munawar 1982), 1974 (Stoermer and Kreis
1980), and 1980 phytoplankton patterns indicated little change along the
eastern shore of the southern basin, but increased degradation along the
western shore because of higher algal biovolumes in 1980 than 1971.
64
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SUMMARY
The waters of Lake Huron were generally oligotrophic. This conclusion Has
based upon the following observations: first, the phytoplankton of Lake Huron
was dominated by eurytopic diatoms year-round; second, abundance and biovolume
was not great during the spring bloom; third, algal biovolumes were low during
the summer; fourth, nitrogen-fixing blue-green algae were never abundant, only
small chroococcalean forms such as Anacystis marina bloomed; and fifth, only a
slight increase in phytoplankton abundance occurred during the fall. Moll e_t
al. (in press) came to the same conclusion, which was based on a survey of
nutrients, chlorophyll, and particulate materials in Lake Huron during 1980.
Evans (1983) also concluded that zooplankton composition and abundance during
1980 indicated that the waters of Lake Huron were in the oligotrophic range.
Regional variation in water quality was indicated. The most enriched
waters occurred in the nearshore regions of the southern basin, both on the
Michigan and Ontario side of the Lake. Higher and more persistent spring
blooms of phytoplankton along the western shore of Lake Huron and near
Cheboygan than in many regions indicated that these waters continued to be
enriched. Similar conclusions were made by Evans (1983), Kreis et al. (in
press), and Moll et al. (in press).
Measures employed to decrease nutrient loading to Lake Huron through
Saginaw Bay have apparently reduced eutrophication of nearshore and offshore
areas near the mouth of the Bay. However, there were some indications that the
offshore waters of southern Lake Huron had become more enriched, on a long-term
basis, than in the past. Kreis et al. (in press) came to similar conclusions.
Long-term trends in water quality of Lake Huron were difficult to
interpret because of the limited number of phytoplankton studies conducted in
Lake Huron. Agreement with Moll et al. (in press), that there was little
indication of a change in the water quality and level of enrichment of Lake
Huron, corroborated and supported this assessment of trends. There were,
however, some signs that nutrient loading to the southern basin seemed to be
causing slight degradation of these waters.
65
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REFERENCES
Cholnoky, B. J. 1968. Die Okologie der Diatomeen in Binnengewassern. 699 pp.
J. Cramer, Lehre.
Evans, M. S. 1983. Lake Huron Crustacean and Rotifer Zooplankton, 1980:
Factors Affecting Community Structure with an Evaluation of Hater Quality
Status. Great Lakes Res. Div. Spec. Rept. No. 98. 149 pp.
Hohn, M. H. 1969. Qualitative and quantitative analyses of plankton diatoms,
Bass Island Area, Lake Erie, 1938-1965, Including Synoptic Surveys of
1960-1963. Bull. Ohio Biol. Surv., n. s. Vol. 1, No. 3. 208 pp.
International Joint Commission. 1976a. The waters of Lake Huron and Lake
Superior, Vol. I. Summary and Recommendations.
International Joint Commission. 1976b. The waters of Lake Huron and Lake
Superior Vol. II. Lake Huron, Georgian Bay, and the North Channel.
Koppen, J. D. 1978. Distribution and aspects of the ecology of the genus
Tabellaria Ehr. (Bacillariophyceae} in the northcentral United States. Am.
Midi. Nat. 99:383-397.
Kreis, R. G., Jr., Ladewski, T. B., and Stoermer, E. F. 1983. Influence of
the St. Marys River Plume on northern Lake Huron phytoplankton
assemblages. J. Great Lakes Res. 9:40-51.
Kreis, R. G., Jr., Stoermer, E. F., and Ladewski, T. B. in press.
Phytoplankton species composition, abundance and distribution in
southern Lake Huron, 1980: including a comparative analysis with
conditions in 1974 prior to nutrient loading reductions. Univ. Mich,
Great Lakes Res. Div. Spec. Rept.
Ladewski, B. G., Kreis, R. G., Jr., and Stoermer, E. F. 1982. A
comparative analysis of Lake Huron phytoplankton assemblages after
entrainment at selected water intake facilities. Univ. Mich., Great
Lakes Res. Div. Spec. Rept. 92.
Lowe, R. L. 1976. Phytoplankton in Michigan's nearshore waters of Lake
Huron and Lake Superior. Mich. Dept. Nat. Res. Tech. Rept.
Moll, R. A., Chang, H. Y. B., and Rockwell, D. C. in press. Lake Huron
Intensive Survey, 1980. Univ. Mich., Great Lakes Res. Div. Spec. Rept.
Moll, R. A. and E. F. Stoermer. 1982. A hypothesis relating trophic status
and subsurface chlorophyll maxima in lakes. Archiv. Hydrobiol.
94:425-440.
66
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Munawar, M. and I. F. Munawar. 1975. The abundance and significance of
phytoflagellates and nannoplnakton in the St. Lawrence Great Lakes. 1.
Phytoflagellates. Verh. Internet. Verein. Limnol. 19:705-723.
Munawar, M. and I. F. Munawar. 1982. Phycological studies in lakes Ontario,
Erie, Huron, and Superior. Can. J. Bot. 60:1837-1858.
Nicholls, K. H., Carney, E. C., and Robinson, G. W. 1977.
Phytoplankton of an inshore area of Georgian Bay, Lake Huron, prior
to reductions in phosphorus loading. J. Great Lakes Res. 3:79-92.
Smith, V. E., Lee, K. W., Filkens, J. C., Hartwell, K. W., Rygwelski,
K. R., and Townsend, J. M. 1977. Survey of chemical factors in Saginaw
Bay (Lake Huron). USEPA. Office of Res. and Devel., Duluth, Minn.
Stoermer, E. F. 1978. Phytoplankton assemblages as indicators of water
quality in the Laurentian Great Lakes. "Trans. Am. Microsc. Soc.
97:2-16.
Stoermer, E. F., M. M. Bowman, J. C. Kingston, and A. L. Schadel. 1974.
Phytoplankton Composition and Abundance in Lake Ontario during IFYGL.
Great Lakes Res. Div. Spec. Rept. No. 53 373 pp.
Stoermer, E. F. and H. Hakansson. 1984. Stephanodiscus parvus; validation
of an enigmatic and widely misconstrued taxon. Nova Hedwigia 39:497-511.
Stoermer, E. F. and R. G. Kreis. 1980. Phytoplankton Composition and
Abundance in Southern Lake Huron. EPA-600/3-80-061. 384 pp.
Stoermer, E. F., Ladewski, T. B., and Frey, L. 1982. Effects of
phosphorus loading on phytoplankton distribution and certain aspects
of cytology in Saginaw Bay, Lake Huron. USEPA, Office of Res. and
Devel., Duluth, Minn.
Stoermer, E. F. and R. J. Stevenson. 1979. Green Bay Phytoplankton
Composition, Abundance, and Distribution. EPA-905/3-79-002. 104 pp.
Stoermer, E. F. and J. J. Yang. 1970. Distribution and relative abundance of
dominant plankton diatoms in Lake Michigan. Great Lake Research Division,
Publ. No. 16. 64 pp.
Veal, D. M. and Michalski, M. F. P. 1971. A case of nutrient
enrichment in a nearshore area of Georgian Bay, pp. 277-292. In; Proc.
14th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res.
Vollenweider, R. A., Munawar, M, and Stadelmann, P. 1974. A comparative
review of phytoplankton and primary production in the Laurentian Great
Lakes. J. Fish. Res. Bd. Can. 31:739-762.
67
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APPENDIX I
Stations used to calculate average phytoplankton and average water chemistry
for regions in correlation and regional biovolume and abundance studies. These
regions corresponded to stations used by Moll et al. (in press) to calculate
average water chemistry, and closely corresponded to regions delineated in the
1974 segmentation scheme used by the IJC (1976a, 1976b).
Region Station Numbers
1 21, 29, 31-33, 37-38, 43-45, 48, 51-54, 57, 61
2 111, 113-114, 117-118, 121-122, 124, 128-130, 137
3 68, 70-72, 75-76
4 73-74, 77-86
5 16, 18-21, 24, 26
6 7, 13-14, 17, 23, 25, 94
7 56, 62, 63, 64
8 6, 9, 12, 15, 90-93
68
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-905/3-85-004
3. RECIPIENT'S ACCESSIOf+NO.
4. TITLE AND SUBTITLE
Phytoplankton Composition, Abundance
and Distribution In Lake Huron
5. REPORT DATE
August 1985
6. PERFORMING ORGANIZATION CODE
5GL
7. AUTHOR(S)
R. Jan Stevenson
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
University of Louisville
Department of Biology
Louisville, Kentucky 40292
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
ROO5767-01
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Great Lakes National Program Office
536 South Clark Street, Room 958
Chicago, Illinois 60605
13. TYPE OF REPORT AND PERIOD COVERED
Limnology 1980-1983
14. SPONSORING AGENCY CODE
Great Lakes National Program
Office-USEPA, Region V
15. SUPPLEMENTARY NOTES
David De Vault
Project Officer
16. ABSTRACT
The phytoplankton of Lake Huron were studied to assess the water quality of this
Great Lake. The phytoplankton species were counted in integrated and discretely
collected water samples from all of Lake Huron except Saginaw Bay. Cell abundances
and biovolumes of the algae were studied seasonally and spatially in the Lake.
Patterns of phytoplankton indicated that Lake Huron waters were generally oligo-
trophic. Diatoms with broad ecological ranges, Tabellaria flocculosa and
Fraqilaria crotonensis, dominated the phytoplankton year-round. Abundance and
biovolume were not great during the spring bloom. Algal biovolumes were low
during the summer. Small, coccoid blue-green algae were common, but heterocystis,
nitrogen-fixing blue-greens were never abundant. Only a slight increase in
phytoplankton abundance occurred during the fall.
Little evidence was observed that the water quality of Lake Huron had changed
during the last decade, there were sone signs that continued loading of nutrients
to the southern basin was causing some degradation of those waters. But, low
standing crops of algae near Saginaw Bay indicated that nutrient loading through
Saginaw Bay had been reduced.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Phytoplankton
Algae
Lake Huron
Water Quality
Diatoms
3. DISTRIBUTION STATEMENT
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19. SECURITY CLASS (ThisReport)
21. NO. OF PAGES
7R
20. SECURITY CLASS (Thispage)
22. PRICE
EPA Form 2220-1 (9-73)
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