WATER POLLUTION CONTROL RESEARCH SERIES
18050 DBM 02/72
Lake Superior Periphyton
in Relation to Water Quality
ENVIRONMENTAL PROTECTION AGENCY
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes the
results and progress in the control and abatement of pollution
in our Nation's waters. They provide a central source of
information on the research, development, and demonstration
activities in the water research program of the Environmental
Protection Agency, through in-house research and grants and
contracts with Federal, state, and local agencies, research
institutions, and industrial organizations.
Inquiries pertaining to Water Pollution Control Research Reports
should be directed to the Chief, Publications Branch (Water),
Research Information Division, R&M, Environmental Protection
Agency, Washington, D. C. 20460
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LAKE SUPERIOR PERIPHYTON
IN RELATION TO WATER QUALITY
by
T. A. Olson
T. 0. Odlaug
University of Minnesota
School of Public Health, Minneapolis
and
Department of Biology, Duluth
for the
Office of Research and Monitoring
ENVIRONMENTAL PROTECTION AGENCY
Project # 18050 DBM
formerly # WP-00828
February, 1972
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402 - Price $2
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EPA Reviev Notice
This report has been reviewed by the Environmental Protection
Agency and approved for publication. Approval does not
signify that the contents necessarily reflect the views and
policies of the Environmental Protection Agency nor does
mention of trade names or commercial products constitute
endorsement or recommendation for use.
ii
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ABSTRACT
Laboratory and field studies were conducted to evaluate the im-
portance of periphyton in western Lake Superior with special reference
to the make-up and distribution of the periphyton growths and to the
overall importance of productive capacity of this assemblage of or-
ganisms .
The taxonomic portion of the investigation indicated that over
90% of the total number of organisms were diatoms and that the phyla
to which these diatoms belonged were the Chrysophyta, the Chlorophyta,
and the Cyanophyta. Predominant genera were Synedra. Achnanthes, Nav-
icula. Cymbella. and Gomphonema.
In many respects, the periphyton of Lake Superior was similar to
that found in streams and there was evidence that the interrelated fac-
tors that affected periphyton growths were temperature, light intensity,
depth of water, water movements, nutrient levels, and the type of sub-
strate.
Artificially denuded rocks demonstrated definite re-growth but
after 46 days this growth level was only 18% of that occurring natural-
ly.
The mean total counts of organisms in the primary sampling area
ranged from 497,000 to 1,470,000 per square centimeter of rock surface.
Studies of the pigment concentrations showed that the biomass of
periphyton along the North Shore of Lake Superior resemble those of
other oligotrophic bodies of water and range from 0.338 to 3.59 mg of
total pigment per 100 square centimeters of rock surface. The average
was 1.36 mg per 100 square centimeters of rock surface. Pigment ratios
indicated that the Lake Superior periphyton was dominated by the Chry-
sophyta. Assimilation values for Stony Point Bay averaged 1.48 grams
of carbon fixed per gram of chlorophyll in 1967. In Stony Point Bay,
the total standing crop in terms of dry weight was 55.5 tons.
In re-growth studies, chlorophyll levels were observed to increase
by an average of 0.057 grams (57 mgs) per square meter per day.
The efficiency of energy utilization in Stony Point Bay was found
to be 0.082%, a typical value for algal communities.
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CONTENTS
Section Page
I Conclusions 1
II Recommendations 3
III Introduction 5
IV Materials and Methods 11
V Periphyton Distribution and 31
Taxonomy — Results and
Discussion
VI Periphyton Pigments and 115
Productivity — Results
and Discussion
VII The Potential of Periphyton 215
Organisms as Components of
Lake Superior Periphyton
VIII Acknowledgements 231
IX Bibliography 233
X Appendix 247
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FIGURES
PAGE
1. WESTERN ARM OF LAKE SUPERIOR, SHOWING THE 13
POSITION OF STONY POINT BAY, SITE OF
PERIPHYTON STUDIES
2. DETAILED MAP OF STONY POINT BAY, 13
LAKE SUPERIOR
3. NORTH SHORE SAMPLING STATIONS - 17
WESTERN ARM LAKE SUPERIOR
4. MEAN COUNTS OF PERIPHYTON 39
STONY POINT BAY, 1966
5. PHOTOMICROGRAPH - ACNANTHES MICROCEPHALA 45
6. PHOTOMICROGRAPH - SYNEDRA ACUS 45
7. PHOTOMICROGRAPH - SYNEDRA ULNA 47
8. PHOTOMICROGRAPH - CYMBELLA VENTRICOSA 47
9. PHOTOMICROGRAPH - CYMBELLA LANCEOLATA 49
10. PHOTOMICROGRAPH - NAVICULA RADIOSA 49
11. PHOTOMICROGRAPH - NAVICULA REINHARDII 50
12. PHOTOMICROGRAPH - COCCONEIS FLEXELLA 50
13. PHOTOMICROGRAPH - COCCONEIS PIACENTULA 51
14. PHOTOMICROGRAPH - GOMPHONEMA SP 51
15. PHOTOMICROGRAPH - GOMPHONEMA OLIVACEUM 52
16. PHOTOMICROGRAPH - AMPHORA OVALIS 52
17. PHOTOMICROGRAPH - ASTERIONELLA FORMDSA 53
18. PHOTOMICROGRAPH - CERATONEIS ARCUS 53
19. PHOTOMICROGRAPH - CYCLOTELLA SP 54
20. PHOTOMICROGRAPH - CYMATOPLEURA SOLEA 54
21. PHOTOMICROGRAPH - DENTICULA THERMALIS 55
vi
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22. PHOTOMICROGRAPH - DIATOMA VULGARE 55
23. PHOTOMICROGRAPH - DIATOMA VULGARE 56
24. PHOTOMICROGRAPH - FRAGILARIA CAPUCINA 56
25. PHOTOMICROGRAPH - FRAGILARIA CROTONENSIS 57
26. PHOTOMICROGRAPH - FRAGILARIA HARISONII 57
27. PHOTOMICROGRAPH - FRUSTULIA VIRIDULA 58
28. PHOTOMICROGRAPH - GOMPHONEIS HERCULEANA 58
29. PHOTOMICROGRAPH - GYROSIGMA ATTENUATUM 59
30. PHOTOMICROGRAPH - NITZSCHIA VERMICULARIS 59
31. PHOTOMICROGRAPH - NITZSCHIA PALEA 60
32. PHOTOMICROGRAPH - MELOSIRA GRANULATA 60
33. PHOTOMICROGRAPH - MELOSIRA VARIANS 61
34. PHOTOMICROGRAPH - PINNULARIA VIRIDIS 61
35. PHOTOMICROGRAPH - RHIZOSOLENIA ERIENSIS 62
36. PHOTOMICROGRAPH - RHOICOSPHENIA CURVATA 62
37. PHOTOMICROGRAPH - TABELLARIA FENESTRATA 63
38. PHOTOMICROGRAPH - TABELLARIA FLOCCULOSA 63
39. PHOTOMICROGRAPH - SURIRELLA ANGUSTATA 64
40. PHOTOMICROGRAPH - SURIRELLA OVATA 64
41. MEAN COUNTS NATURALLY OCCURRING PERIPHYTON, 6?
STONY POINT BAY, 1967
42. PERIPHYTON COUNTS AT 2.5 FEET, 68
STONY POINT BAY, 1967
43. PERIPHYTON COUNTS AT 5 FEET, STONY 68
POINT BAY, 1967
44. PERIPHYTON COUNTS AT 10 FEET, 69
STONY POINT BAY, 1967
vli
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45. PERIPHYTON COUNTS AT 15 FEET, 69
STONY POINT BAY, 1967
46. PERIPHYTON COUNTS AT 20 FEET, 70
STONY POINT BAY, 1967
47. PERIPHYTON COUNTS AT 35 FEET, 70
STONY POINT BAY, 1967
48. PERIPHYTON COUNTS VS ASH-FREE 80
DRY WEIGHTS AT 2.5 FEET,
STONY POINT BAY, 1967
49. PERIPHYTON COUNTS VS ASH-FREE 80
DRY WEIGHTS AT 5.0 FEET,
STONY POINT BAY, 1967
50. PERIPHYTON COUNTS VS ASH-FREE 81
DRY WEIGHTS AT 10.0 FEET,
STONY POINT BAY, 1967
51. PERIPHYTON COUNTS VS ASH-FREE 81
DRY WEIGHTS AT 15.0 FEET,
STONY POINT BAY, 1967
52. PERIPHYTON COUNTS VS ASH-FREE 82
DRY WEIGHTS AT 20.0 FEET,
STONY POINT BAY, 1967
53^ PERIPHYTON COUNTS VS ASH-FREE 82
DRY WEIGHTS AT 35.0 FEET,
STONY POINT BAY, 1967
54. NATURALLY OCCURRING PERIPHYTON 83
ASH-FREE DRY WEIGHTS AT 2.5 FEET,
STONY POINT BAY, 1967
55. NATURALLY OCCURRING PERIPHYTON 83
ASH-FREE DRY WEIGHTS AT 5 FEET,
STONY POINT BAY, 1967
56. NATURALLY OCCURRING PERIPHYTON 84
ASH-FREE DRY WEIGHTS AT 10 FEET,
STONY POINT BAY, 1967
57.,. NATURALLY OCCURRING PERIPHYTON 84
ASH-FREE DRY WEIGHTS AT 15 FEET,
STONY POINT BAY, 1967
58. NATURALLY OCCURRING PERIPHYTON 85
ASH-FREE DRY WEIGHTS AT 20 FEET,
STONY POINT BAY, 1967
viii
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59. NATURALLY OCCURRING PERIPHYTON 85
ASH-FREE DRY WEIGHTS AT 35 FEET,
STONY POINT BAY, 1967
60. AVERAGE LIGHT INTENSITY NEAR 87
MID-DAY, STONY POINT BAY, 1967
61. TOTAL COUNTS OF PERIPHYTON RE- y$
GROWTH, STONY POINT BAY, 1967
62. COUNTS VS ASH-FREE DRY WEIGHTS, 97
REGROWTH STUDY, 10 FOOT SAMPLES,
STONY POINT BAY, 1967
63. COUNTS VS ASH-FREE DRY WEIGHTS, o?
REGROWTH STUDY, 20 FOOT SAMPLES,
1967
64. COUNTS VS ASH-FREE DRY WEIGHTS, 98
REGROWTH STUDY, 35 FOOT SAMPLES,
1967
65. TOTAL COUNTS, NATURALLY OCCURRING 107
PERIPHYTON, LESTER RIVER AREA,
LAKE SUPERIOR, 1967
66. TOTAL COUNTS, NATURALLY OCCURRING 107
PERIPHYTON, KNIFE RIVER AREA,
LAKE SUPERIOR, 1967
67, TOTAL COUNTS, NATURALLY OCCURRING 108
PERIPHYTON, BURLINGTON BAY,
1967
68. TOTAL COUNTS, NATURALLY OCCURRING 108
PERIPHYTON, SPLIT ROCK RIVER BAY,
LAKE SUPERIOR, 1967
69. TOTAL COUNTS, NATURALLY OCCURRING 109
PERIPHYTON, BEAVER BAY,
LAKE SUPERIOR, 1967
70. TOTAL COUNTS, NATURALLY OCCURRING 109
PERIPHYTON, NO-NAME BAY,
LAKE SUPERIOR, 1967
71. TOTAL COUNTS, NATURALLY OCCURRING 110
PERIPHYTON, SUGARLOAF COVE,
LAKE SUPERIOR, 1967
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72. TOTAL COUNTS, NATURALLY OCCURRING 110
PERIPHYTON, TOFTE AREA,
LAKE SUPERIOR, 1967
73. TOTAL COUNTS, NATURALLY OCCURRING HI
PERIPHYTON, LUTSEN AREA,
LAKE SUPERIOR, 1967
74. TOTAL COUNTS, NATURALLY OCCURRING HI
PERIPHYTON, GOOD HARBOR BAY,
LAKE SUPERIOR, 1967
75. TOTAL COUNTS, NATURALLY OCCURRING 112
PERIPHYTON, GRAND MARAIS AREA,
LAKE SUPERIOR, 1967
76. AVERAGE PERIPHYTON PIGMENT CONCENTRATIONS 117
(PER UNIT OF ROCK SURFACE),
STONY POINT BAY, 1966
77. AVERAGE PERIPHYTON PIGMENT CONCENTRATIONS 121
(PER 100,000 ORGANISMS),
STONY POINT BAY, 1966
78. PERIPHYTON TOTAL CHLOROPHYLL CONCENTRATIONS 122
AS MEASURED BY COLORIMETRIC AND
SPECTROPHOTOMETRIC METHODS
79. AVERAGE GROSS PHOTOSYNTHETIC RATES OF 122
PERIPHYTON (PER UNIT AREA) FOR SAMPLES
FROM STANDARD DEPTHS, STONY POINT BAY,
1966.
80. AVERAGE PERIPHYTON GROSS PHOTOSYNTHETIC 128
RATES (PER UNIT TOTAL CHLOROPHYLL) AT
STANDARD SAMPLING DEPTHS,
STONY POINT BAY, 1966
81. AVERAGE PERIPHYTON PIGMENT CONCENTRATIONS 130
(PER UNIT AREA OF ROCK SURFACE) AT
STANDARD SAMPLING DEPTHS,
STONY POINT BAY, 1967
82. AVERAGE PERIPHYTON TOTAL CHLOROPHYLL 131
CONCENTRATIONS (PER UNIT ASH-FREE DRY
WEIGHT) AT STANDARD SAMPLING DEPTHS,
STONY POINT BAY, 1967
83. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 132
(PER UNIT AREA) AT 2.5 FEET,
STONY POINT BAY, 1967
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84. PERIPHYTON CAROTENOID CONCENTRATIONS 133
(PER UNIT AREA) AT 2.5 FEET,
STONY POINT BAY, 1967
85. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 134
(PER UNIT AREA) AT 5.0 FEET,
STONY POINT BAY, 1967
86. PERIPHYTON CAROTENOID CONCENTRATIONS 134
(PER UNIT AREA) AT 5.0 FEET,
STONY POINT BAY, 1967
87. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 135
(PER UNIT AREA) AT 10 FEET,
STONY POINT BAY, 1967
88. PERIPHYTON CAROTENOID CONCENTRATIONS 135
(PER UNIT AREA) AT 10 FEET,
STONY POINT BAY, 1967
89. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 136
(PER UNIT AREA) AT 15 FEET,
STONY POINT BAY, 1967
90. PERIPHYTON CAROTENOID CONCENTRATIONS 136
(PER UNIT AREA) AT 15 FEET,
STONY POINT BAY, 1967
91. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 137
(PER UNIT AREA) AT 20 FEET,
STONY POINT BAY, 1967
92. PERIPHYTON CAROTENOID CONCENTRATIONS 137
(PER UNIT AREA) AT 20 FEET,
STONY POINT BAY, 1967
93. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 138
(PER UNIT AREA) AT 35 FEET,
STONY POINT BAY, 1967
94. PERIPHYTON CAROTENOID CONCENTRATIONS 138
(PER UNIT AREA) AT 35 FEET,
STONY POINT BAY, 1967
95. REGRESSION LINE, COUNTS VS TOTAL 140
CHLOROPHYLL, NATURALLY OCCURRING
PERIPHYTON AT 2.5 FEET,
STONY POINT BAY, 1967
96. REGRESSION LINE, COUNTS VS TOTAL 141
CHLOROPHYLL, NATURALLY OCCURRING
PERIPHYTON AT 5.0 FEET,
STONY POINT BAY, 1967
xi
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97. REGRESSION LINE, COUNTS VS TOTAL 141
CHLOROPHYLL, NATURALLY OCCURRING
PERIPHYTON AT 10 FEET,
STONY POINT BAY, 1967
98. REGRESSION LINE, COUNTS VS TOTAL 142
CHLOROPHYLL, NATURALLY OCCURRING
PERIPHYTON AT 15 FEET,
STONY POINT BAY, 1967
99. REGRESSION LINE, COUNTS VS TOTAL 142
CHLOROPHYLL, NATURALLY OCCURRING
PERIPHYTON AT 20 FEET,
STONY POINT BAY, 1967
100. REGRESSION LINE, COUNTS VS TOTAL 143
CHLOROPHYLL, NATURALLY OCCURRING
PERIPHYTON AT 35 FEET,
STONY POINT BAY, 1967
101. RATIO OF PERIPHYTON CHLOROPHYLL 143
c/CHLOROPHYLL a AT STANDARD
SAMPLING DEPTHS,
STONY POINT BAY, 1967
102. RATIO OF PERIPHYTON NON-ASTACIN 144
CAROTENOIDS/CHLOROPHYLL a AT
STANDARD SAMPLING DEPTHS,
STONY POINT BAY, 1967
103. AVERAGE MID-DAY LIGHT INTENSITY 144
AT STANDARD SAMPLING DEPTHS,
STONY POINT BAY, JUNE-SEPTEMBER, 1967
104. PERIPHYTON AND ASH-FREE DRY WEIGHTS 151
(PER UNIT AREA) AT 2.5 FEET,
STONY POINT BAY, 1967
105. PERIPHYTON AND ASH-FREE DRY WEIGHTS 151
(PER UNIT AREA) AT 5 FEET,
STONY POINT BAY, 1967
106. PERIPHYTON AND ASH-FREE DRY WEIGHTS 152
(PER UNIT AREA) AT 10 FEET,
STONY POINT BAY, 1967
107. PERIPHYTON AND ASH-FREE DRY WEIGHTS 152
(PER UNIT AREA) AT 15 FEET,
STONY POINT BAY, 1967
xii
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108. PERIPHYTON AND ASH-FREE DRY WEIGHTS 153
(PER UNIT AREA) AT 20 FEET,
STONY POINT BAY, 1967
109. PERIPHYTON AND ASH-FREE DRY WEIGHTS 153
(PER UNIT AREA) AT 35 FEET,
STONY POINT BAY, 1967
110. AVERAGE PERIPHYTON GROSS SYNTHETIC 156
RATES (PER UNIT AREA) FOR SAMPLES
FROM STANDARD DEPTHS,
STONY POINT BAY, 1967
111. PERIPHYTON GROSS PHOTOSYNTHETIC 157
RATES (PER UNIT AREA) FOR SAMPLES
FROM 2.5 FEET, STONY POINT BAY, 1967
112. PERIPHYTON GROSS PHOTOSYNTHETIC 157
RATES (PER UNIT AREA) FOR SAMPLES
FROM 5 FEET, STONY POINT BAY, 1967
113. PERIPHYTON GROSS PHOTOSYNTHETIC 158
RATES (PER UNIT AREA) FOR SAMPLES
FROM 10 FEET, STONY POINT BAY, 1967
114. PERIPHYTON GROSS PHOTOSYNTHETIC 158
RATES (PER UNIT AREA) FOR SAMPLES
FROM 15 FEET, STONY POINT BAY, 1967
115. PERIPHYTON GROSS PHOTOSYNTHETIC 159
RATES (PER UNIT AREA) FOR SAMPLES
FROM 20 FEET, STONY POINT BAY, 1967
116. PERIPHYTON GROSS PHOTOSYNTHETIC 159
RATES (PER UNIT AREA) FOR SAMPLES
FROM 35 FEET, STONY POINT BAY, 1967
117. PERIPHYTON GROSS PHOTOSYNTHETIC 160
RATES (PER UNIT ASH-FREE DRY
WEIGHT) STONY POINT BAY, 1967
118. PERIPHYTON GROSS PHOTOSYNTHETIC 162
RATES (PER UNIT CHLOROPHYLL)
STONY POINT BAY, 1967
119. REGRESSION LINE, PHOTOSYNTHETIC 162
RATE VS COUNTS, NATURALLY OCCURRING
PERIPHYTON AT 2.5 FEET,
STONY POINT BAY, 1967
xiii
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120. REGRESSION LINE, PHOTOSYNTHETIC 163
RATE VS COUNTS, NATURALLY
OCCURRING PERIPHYTON AT 5 FEET,
STONY POINT BAY, 1967
121. REGRESSION LINE, PHOTOSYNTHETIC 163
RATE VS COUNTS, NATURALLY
OCCURRING PERIPHYTON AT 10 FEET,
STONY POINT BAY, 1967
122. REGRESSION LINE, PHOTOSYNTHETIC 164
RATE VS COUNTS, NATURALLY
OCCURRING PERIPHYTON AT 15 FEET,
STONY POINT BAY, 1967
123. REGRESSION LINE, PHOTOSYNTHETIC 164
RATE VS COUNTS, NATURALLY OCCURRING
PERIPHYTON AT 20 FEET,
STONY POINT BAY, 1967
124. REGRESSION LINE, PHOTOSYNTHETIC 165
RATE VS COUNTS, NATURALLY
OCCURRING PERIPHYTON AT 35 FEET,
STONY POINT BAY, 1967
125. REGROWTH PERIPHYTON CHLOROPHYLL 170
CONCENTRATIONS (PER UNIT AREA)
AT 10 FEET, STONY POINT BAY, 1967
126. REGROWTH PERIPHYTON CHLOROPHYLL 171
CONCENTRATIONS (PER UNIT AREA)
AT 20 FEET, STONY POINT BAY, 1967
127. REGROWTH PERIPHYTON CHLOROPHYLL 171
CONCENTRATIONS (PER UNIT AREA)
AT 35 FEET, STONY POINT BAY, 1967
128. REGRESSION LINE, COUNTS VS TOTAL 174
CHLOROPHYLL, REGROWTH PERIPHYTON
AT 10 FEET, STONY POINT BAY, 1967
129. REGRESSION LINE, COUNTS VS. TOTAL 174
CHLOROPHYLL, REGROWTH PERIPHYTON
AT 20 FEET, STONY POINT BAY, 1967
130. REGRESSION LINE, COUNTS VS TOTAL 175
CHLOROPHYLL, KEGROWTH PERIPHYTON
AT 35 FEET, STONY POINT BAY, 1967
131. REGROWTH PERIPHYTON SYNTHETIC RATES 175
(PER UNIT AREA) STONY POINT BAY,
1967
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132. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 180
(PER UNIT AREA) AT STANDARD DEPTHS,
LESTER RIVER STATION, LAKE SUPERIOR,
AUG. 16, 1967
133. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 180
(PER UNIT AREA) AT STANDARD DEPTHS,
KNIFE RIVER STATION, LAKE SUPERIOR,
SEPT. 5, 1967
134. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 181
(PER UNIT AREA) AT STANDARD DEPTHS,
KNIFE RIVER STATION, LAKE SUPERIOR,
SEPT. 15, 1967
135. PERIPHYTON CHLOROPHYLL CONCENTRATIONS lgl
(PER UNIT AREA) AT STANDARD DEPTHS,
BURLINGTON BAY, LAKE SUPERIOR, 1967
136. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 182
(PER UNIT AREA) AT STANDARD DEPTHS,
BURLINGTON BAY, LAKE SUPERIOR, 1967
137. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 182
(PER UNIT AREA) AT STANDARD DEPTHS,
SPLIT ROCK RIVER BAY, LAKE SUPERIOR,
AUG. 29, 1967
138. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 183
(PER UNIT AREA) AT STANDARD DEPTHS,
SPLIT ROCK RIVER BAY, LAKE SUPERIOR,
SEPT. 7, 1967
139. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 1S3
(PER UNIT VOLUME) AT STANDARD DEPTHS,
STONY POINT BAY, BEAVER BAY, LAKE
SUPERIOR, AUG. 29, 1967
140. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 184
(PER UNIT AREA) AT STANDARD DEPTHS,
BEAVER BAY, LAKE SUPERIOR,
SEPT. 14, 1967
141. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 184
(PER UNIT AREA) AT STANDARD DEPTHS,
NO-NAME BAY, LAKE SUPERIOR,
SEPT. 1, 1967
142. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 185
(PER UNIT AREA) AT STANDARD DEPTHS,
NO-NAME BAY, LAKE SUPERIOR,
SEPT. 14, 1967
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143. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 185
(PER UNIT AREA) AT STANDARD DEPTHS,
SUGAR LOAF COVE, LAKE SUPERIOR,
AUG. 31, 1967
144. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 186
(PER UNIT AREA) AT STANDARD DEPTHS,
SUGAR LOAF COVE, LAKE SUPERIOR,
SEPT. 7, 1967
145. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 186
(PER UNIT AREA) AT STANDARD DEPTHS,
TOFTE STATION, LAKE SUPERIOR,
AUG. 31, 1967
146. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 187
(PER UNIT AREA) AT STANDARD DEPTHS,
TOFTE STATION, LAKE SUPERIOR,
SEPT. 7, 1967
147. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 187
(PER UNIT AREA) AT STANDARD DEPTHS,
LUTSEN STATION, LAKE SUPERIOR,
AUG. 31, 1967
148. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 188
(PER UNIT AREA) AT STANDARD DEPTHS,
LUTSEN STATION, LAKE SUPERIOR,
SEPT. 7, 1967
149. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 188
(PER UNIT AREA) AT STANDARD DEPTHS,
GOOD HARBOR BAY, LAKE SUPERIOR,
AUG. 31, 1967
150. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 189
(PER UNIT AREA) AT STANDARD DEPTHS,
GOOD HARBOR BAY, LAKE SUPERIOR,
SEPT. 7, 1967
151. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 189
(PER UNIT AREA) AT STANDARD DEPTHS,
GRAND MARAIS STATION, LAKE SUPERIOR,
AUG. 31, 1967
152. PERIPHYTON CHLOROPHYLL CONCENTRATIONS 190
(PER UNIT AREA) AT STANDARD DEPTHS,
GRAND MARAIS STATION, LAKE SUPERIOR,
SEPT. 7, 1967
xvi
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153. PHOTOSYNTHETIC RATES OF PERIPHYTON .g_
FROM STONY POINT BAY AND LESTER
RIVER STATION AT VARIOUS TEMPERA-
TURES, JUNE, 1968
154. CHANGES IN PERIPHYTON CHLOROPHYLL 195
CONCENTRATIONS (PER UNIT ASH-FREE
DRY WEIGHTS) AS LIGHT INTENSITY
IS SEVERELY ALTERED
155. CHANGES IN PERIPHYTON CHLOROPHYLL 197
CONCENTRATIONS (PER UNIT ASH-FREE
DRY WEIGHTS) AS LIGHT INTENSITY
IS MODERATELY ALTERED
156. CHANGES IN PERIPHYTON CHLOROPHYLL 198
CONCENTRATION (PER UNIT ASH-FREE
DRY WEIGHT AS LIGHT INTENSITY IS
REDUCED AND SUBSEQUENTLY INCREASED
157. RATE OF PHOTOSYNTHESIS IN "CONDITIONED" 198
STONY POINT BAY PERIPHYTON AT NINE
LIGHT INTENSITIES
158. RATE OF PHOTOSYNTHESIS IN "CONDITIONED" 201
PERIPHYTON AT NINE LIGHT INTENSITIES
(20° C.)
159. RATE OF PHOTOSYNTHESIS IN "CONDITIONED" 201
PERIPHYTON AT NINE LIGHT INTENSITIES
(15° C.)
160. RATE OF PHOTOSYNTHESIS IN "CONDITIONED" 202
PERIPHYTON AT NINE LIGHT INTENSITIES
(10° C.)
161. RATE OF PHOTOSYNTHESIS IN "CONDITIONED" 202
STONY POINT BAY PERIPHYTON AT NINE
LIGHT INTENSITIES (5° C.)
162. RATE OF PHOTOSYNTHESIS IN STONY POINT 203
BAY PERIPHYTON AT NINE LIGHT INTENSITIES
AND FOUR TEMPERATURES; "CONDITIONED" AT
20° C.; 800 FOOT-CANDLES
163. RATE OF PHOTOSYNTHESIS IN STONY POINT BAY 203
PERIPHYTON AT NINE LIGHT INTENSITIES AND
FOUR TEMPERATURES; "CONDITIONED" AT 10° C.
800 FOOT-CANDLES
xvii
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164. RATE OF PHOTOSYNTHESIS IN STONY 204
POINT BAY PERIPHYTON AT NINE
LIGHT INTENSITIES AND FOUR TEM-
PERATURES; "CONDITIONED" AT 20°
C.; 80 FOOT-CANDLES
165. RATE OF PHOTOSYNTHESIS IN STONY 204
POINT BAY PERIPHYTON AT NINE
LIGHT INTENSITIES AND FOUR TEM-
PERATURES; "CONDITIONED" AT 10°
C.; 80 FOOT-CANDLES
166. RATE OF PHOTOSYNTHESIS IN PERIPHY- 206
TON FROM LESTER RIVER STATION AT
NINE LIGHT INTENSITIES AND FOUR
TEMPERATURES
167. RATE OF PHOTOSYNTHESIS IN STONY 206
POINT BAY PERIPHYTON FROM STANDARD
DEPTHS FOLLOWING A PERIOD OF CLEAR
WEATHER (NINE LIGHT INTENSITIES)
168. RATE OF PHOTOSYNTHESIS IN STONY 208
POINT BAY PERIPHYTON FROM STANDARD
DEPTHS FOLLOWING A PERIOD OF STORMY
WEATHER (NINE LIGHT INTENSITIES)
169. RATE OF PERIPHYTON PHOTOSYNTHESIS 208
AND RESPIRATION MEASURED HOURLY FOR
24 HOURS
170. RATE OF PERIPHYTON PHOTOSYNTHESIS 209
AND RESPIRATION (24 HOURS) FOLLOWING
A 10-DAY PERIOD OF INCUBATION IN
CONTINUOUS LIGHT
171. CALCULATED HOURLY LIGHT INTENSITIES 211
AT STANDARD DEPTHS IN STONY POINT
BAY, AVERAGE FOR JUNE-SEPTEMBER,
1967
xviit
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TABLES
S2t Page
1 Rock Identifications, Stony Point Bay 33
2 Species Check-list, Periphyton Regrowth 35
3 Periphyton - Dry Weights, Stony Point Bay 36
4 Genera of Natural Periphyton, Stony Point Bay 38
5 Natural Periphyton - Counts of Organisms 4Q
6 Quantitation of Seven Most Common Genera ^-»
7 Dry Weights Naturally Occurring Periphyton - 1966 65
8 Species Checklist, Naturally Occurring Periphyton, 72
Stony Point Bay, 1967
9 Naturally Occurring Periphyton Dry Weights, 77
Stony Point Bay, 1967
10 Naturally Occurring Periphyton Ash-Free Dry Weights, 73
Stony Point Bay, 1967
11 Water Temperature, Surface and Bottom, Stony Point Bay, 87
1967
12 Regrowth Organisms on Artificially Denuded Rocks, 91
Stony Point Bay, 1967
13 Phyla and Counts of Organisms, Regrowth Periphyton, g3
Stony Point Bay, 1967
14 Dry and Ash-Free Dry Weights of Periphyton Occurring 96
as Regrowth, Stony Point Bay, 1967
15 Summary of Results, North Shore Stations,
Lake Superior, 1967
16 Periphyton Dry Weights, 2.5 to 35 Foot Depths,
North Shore Stations, Stony Point Bay, 1967
17 Periphyton Ash-Free Dry Weif its, 2.5 to 35 Foot
Depths, North Shore Stations, Lake Superior, 1967
18 Water Temperature, Surface to Bottom, North Shore
Stations, Lake Superior, 1967
xix
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19 Pigment Concentrations of Naturally Occurring 119
periphyton, Stony Point Bay, 1966
20 Chlorophyll Content of Stony Point Bay Peri- 123
phyton (1966) and Other Communities on a Unit
Area Basis
21 Photosynthesis Data for Periphyton Sampled at 125
Different Depths, Stony Point Bay, 1966
22 Periphyton Volume and Dry Weights at Standard 125
Depths, Stony Point Bay, 1966
23 Periphyton Pigment Concentrations in Relation to 126
Ash-Free Dry Weights at Standard Depths, Stony
Point Bay, 1967
24 Seasonal Variation of Periphyton Pigment Ratios, 147
Stony Point Bay, 1967
25 Naturally Occurring Periphyton Dry Weights at 149
Standard Sampling Depths, Stony Point Bay, 1967
26 Naturally Occurring Periphyton Ash-Free Dry 150
Weights at Standard Sampling Depths, Stony
Point Bay, 1967
27 Temperatures at Standard Sampling Depths, 155
Stony Point Bay, 1967
28 Photosynthesis Data for Periphyton Sampled 166
at Different Depths, Stony Point Bay, 1967
29 Dry and Ash-Free Dry Weights of Periphyton 173
Occurring as Regrowth (mg/cm2 of rock surface),
Stony Point Bay, 1967
30 Periphyton Sampling Stations along the North 177
Shore of Lake Superior
31 Summary of Results, North Shore Stations, 178
Lake Superior, 1967
32 Ten Most Commonly Occurring Periphyton Organisms, 193
2.5 Foot Depth, Stony Point Bay, 1967
33 Summary of Water Chemistry, Stony Point Bay, 1968 194
34 Periphyton Production Rates Converted to Expected 211
Rates. Grams Carbon Fixed per Day per Square Meter.
Stony Point Bay, 1967
xx
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35 Castle Danger Studies - 1970. Predominant 216
Organisms in the Phytoplankton and Periphyton
36 Lake Superior Plankton Counts (organisms/liter) - 224
Lakewater Intake Pipe
37 Lake Superior Plankton Counts (organisms/liter) - 225
Control Pool Effluent
38 Lake Superior Plankton Counts (organisms/liter) - 226
Test Pool Effluent
39 Lake Superior Periphyton, Rock Surface Growth 227
(organisms/cm2) - Control Pool
40 Lake Superior Periphyton, Rock Surface Growth 228
(organisms/cm2) - Test Pool
41 Rank of Predominant Organisms 229
(Phytoplankton and Periphyton)
xxi
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SECTION I
CONCLUSIONS
A. Periphyton Taxonomy and Distribution
(1) The plant portion of the periphyton found attached to rocks
consisted almost entirely of representatives from three phyla
of algae, namely the Chrysophyta, the Chlorophyta. and the
Cyanophyta.
(2) The genera of diatoms which were predominant in the periphyton
growth were Synedra. Achnanthes. Navicula. Cymbella. and Gom-
phonema.
(3) The periphyton of Lake Superior was found to be similar, in
many respects, to attached growths found in streams.
(4) The interrelated factors which affect periphyton growth are
light intensity, water movement, temperature, water depth,
water movement, nutrient levels, and type of substratum.
(5) Most abundant in terms of numbers of organisms was the phylum
Chrysophyta, and diatoms made up over 90% of this group.
(6) Mean total counts of organisms in the naturally occurring peri-
phyton of Stony Point Bay, the primary sampling area, ranged
from 497,000 per square centimeter of rock in 1966 to 1,470,000
in 1967.
(7) The biomass of the naturally occurring Stony Point Bay periphy-
ton in terms of dry weight, was 153 grams per square meter in
1965, 104 gr/m2 in 1966, and 156 gr/m2 in 1967.
(8) After 46 days of regrowth on artificially denuded rocks, the
growth level finally reached was approximately 18% of that
occurring naturally.
(9) The daily regrowth production rate in Stony Point Bay averaged
3.6 grams of dry weight per square meter and 0.067 grams of
organic weight (ash-free dry) per square meter.
(10) Mean total counts of organisms from eleven North Shore stations
ranged from 1,466,000 organisms per square centimeter at Sugar
Loaf Cove to 3,798,000 per square centimeter at Split Rock
River Bay.
B. Periphyton Pigments and Productivity
(1) Pigment concentrations showed that the biomass of the periphv-
-------
ton of Lake Superior's North Shore was similar in magnitude to
other oligotrophic bodies of water. Total pigment concentra-
tions ranged from 0.338 to 3.59 milligrams per 100 square cen-
timeters of rock surface, and averaged 1.36 mg/100 cm^.
(2) Pigment ratios indicated that most of the North Shore periphy-
ton was dominated by organisms of the Phylum Chrysophyta.
(3) Assimilation values for Stony Point Bay periphyton averaged 1.48
grams of carbon fixed per gram of chlorophyll in 1967.
(4) The total standing crop of Stony Point Bay periphyton in terms
of dry weight was 55.5 tons, or 156 grams per square meter in
1967.
(5) Regrowth periphyton over a period of 46 days was equivalent to
approximately one-third only of the biomass of naturally occur-
ring periphyton. Chlorophyll levels increased by an average of
0.00057 grams per square meter per day.
(6) Net production by the periphyton in 1967 averaged 1.01 grams
C fixed/M^/day or 3.35 grams glucose per M^/day. The ratio of
gross photosynthesis to respiration averaged 3.17.
(7) In water up to 40 feet deep in western Lake Superior periphy-
ton can be five to six times as important in primary production
as the phytoplankton.
(8) Laboratory experiments showed that alteration of light inten-
sity (below 800 foot-candles) caused a rapid change in the
chlorophyll content of the periphyton. The maximum rate of
chlorophyll reduction in response to a substantial increase
in light intensity was shown to be 12.7 per cent per day for
eight days. The most rapid increase in chlorophyll concentra-
tion in response to a severe reduction in light intensity was
7.5 per cent for six days.
(9) Short-term "conditioning" of periphyton to different combina-
tions of light intensity and temperature caused a variety of
responses when the photosynthetic rate was measured in crossed
gradients of light intensity and temperature.
(10) For conditioned samples at light saturation Q^Q ranged from
1.24 to 2.48. The compensation point varied from 80 to 130
foot-candles.
(11) Naturally occurring periphyton was shown to exhibit typical
"light-adapted" or "shade-adapted" photosynthetic reaction de-
pending on the prevailing level of light intensity.
(12) The efficiency of energy utilization by Stony Point Bay periphy-
ton was found to be 0.82 per cent, a typical value for algal
communities.
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SECTION II
RECOMMENDATIONS
The study which has been carried out has opened up a number of
avenues which should be explored if the future welfare of Lake Superior
is to be kept in mind:
(1) What role, if any, does the periphyton play in the transfer of
energy to the second trophic level?
(2) Do any animals actually feed directly on Lake Superior periphy-
ton?
(3) What is the general level and seasonal variation of phaeophyton
in naturally occurring periphyton at various depths?
(4) What are the effects of increased nutrient concentrations and
increased temperature on the periphyton?
(5) Is periphyton a source of phytoplankton?
(6) How much time is required for regrowth periphyton to reach the
level of naturally occurring biomass?
(7) What is the level of radioactivity in the periphyton mass? The
answer to this question would be of particular interest should
a nuclear-fueled power plant be located on the North Shore of
Lake Superior.
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SECTION III
INTRODUCTION
Lake Superior, with a surface area of 31,820 square miles, is
the largest body of fresh water on earth. It lies at the head of the
chain of Great Lakes which include, in addition to Lake Superior, Lake
Michigan, Lake Huron, Lake Erie and Lake Ontario. Lake Superior is
350 miles long with a maximum breadth of 160 miles. It lies 602 feet
above sea level and has a maximum depth of 1333 feet.
Lake Superior, despite its vast size and relatively dramatic for-
mation, is in many ways ecologically similar to a one-half acre farm
pond. Both bodies of water, for instance, depend upon the sun as their
original energy source and, through a complex series of energy transfers,
maintain their own characteristic ecosystem. To accomplish this, both
require populations of algae, which Gilbert M. Smith (1933) defines as
"simple plants with an autotrophic mode of nutrition". In an aquatic
environment, algae may be either attached or free-floating. When algae
are attached to aquatic plants or other surfaces projecting above the
bottom, they constitute a part of the periphyton. Free-floating algae
are known collectively as phytoplankton and along with minute organisms
such as rotifers and crustaceans, called zooplankton, constitute the
plankton. The latter term may be defined as the assemblage of micro-
scopic or near-microscopic plants and animals which are non-motile or
weakly motile and whose transport is, therefore, dependent upon the
wind, waves, or current.
Since algae are ubiquitous in the euphotic zone of a body of water,
their available habitats are almost endless, as are the descriptive terms
applied to them. For example, when algae are found at the air-water in-
terface, they are part of the neuston. In beach sand, they would be
referred to as psammon. When periphyton algae break loose from their
substratum and are found unattached as a part of the phytoplankton, they
become tychoplankton. Wherever they occur, their primary function is
the photosynthetic fixation of carbon. By this process of photosynthe-
sis, algae produce organic matter from basic inorganic components and
may, therefore, be referred to as primary producers. As such, they
form the first link in the aquatic food chain.
Algae, regardless of their habitat, are fed upon by consumers
(heterotrophs), such as zooplankton and immature insects. These forms
are fed upon by small fish which, in turn, may be eaten by larger fish.
Ultimately, the larger fish may be fed upon by man. Each group of
consumers has a definite position, or trophic level, in the so-called
food pyramid. Ecologists have long used this concept. It was origin-
ally proposed by Charles Elton in 1927 as a simple graphic representa-
tion of the food chain or web. Producer organisms constitute the base
of the Eltonian pyramid, consumers the remainder. Each successive tier,
-------
in units of biomass, numbers, or energy, becomes smaller and smaller.
At the apex one finds man, or some other dominant carnivorous species.
The precise organisms, of course, will depend on the ecosystem under
scrutiny.
In addition to the free-floating or attached organisms mentioned
above, producers and consumers may also be found in or on the bottom.
The animals usually feed upon settled or settling organic debris and
consist of forms such as nematodes, annelids, protozoans, molluscs,
et cetera. The plants, consisting chiefly of algae, grow as a thin
layer on the surface of the sediment.
For the proper functioning of an ecological community, organisms
other than producers and consumers are needed. These are the decom-
posers, which consist primarily of bacteria and fungi. Such organisms
are found in all habitats. Their function consists of breaking down
organic matter, usually in the form of dead animals and plants, into
their inorganic constituents so that they may be utilized once again
by the autotrophs.
Thus, it can be seen that algae, in both the periphyton and the
plankton, are the fundamental units of any aquatic environment. Lake
Superior, with its approximately three thousand cubic miles of water,
supports vast quantities of phytoplankton. However, its irregular shore-
line area, which is even larger than the lake's breadth and width would
suggest, is virtually completely covered by periphyton. While water
from the open lake must be concentrated before the phytoplankton can be
counted, periphyton scraped from a small rock must be diluted before a
satisfactory count can be made. Periphyton organisms, due to their
need for light, are most abundant near the shore. Here they are washed
by shore currents and water movements induced by wind. In view of this
constant exposure to ever-changing masses of water, this community
should reflect certain characteristics of the lake, particularly the
quality of the water. In the report which follows, this important com-
ponent of the biota of Lake Superior will be defined qualitatively as
well as quantitatively. In addition, certain ecological aspects of the
periphyton and its possible role in the economy of Lake Superior will
be considered.
Although periphyton has been briefly defined in the preceding des-
cription of an aquatic ecosystem, the confusion that exists in the lit-
erature over the precise meaning of this term points out the need for
a more exact definition. Alena Sladeckova (1962), in her excellent
monograph on the investigation of the periphyton community, discusses
in some detail the terminology of this attached, aquatic association.
Our use of the term "periphyton" follows the generally accepted defi-
nition proposed by Young (1945) and quoted by Sladeckova and Welch (1948),
"By periphyton is meant that assemblage of organisms growing
upon free surfaces of submerged objects in water, and cover-
ing them with a slimy coat. It is that slippery brown or
-------
green layer usually found adhering to the surfaces of water
plants, wood, stones, or certain other objects immersed in
water and may gradually develop from a few tiny gelatinous
plants to culminate in a wooly, felted coat that may be slipp-
ery, or crusty with contained marl or sand."
The German word "aufwuchs" may be considered essentially synony-
mous with Young's definition of periphyton. Ruttner (1963) defines
"aufwuchs" as those organisms that are firmly attached to a substrate
but do not penetrate into it." As the translator (Frey and Fry) of
Ruttner*s text point out, the term "aufwuchs" has a broader connotation
than does the term periphyton as used by some English-speaking authors.
Prescott (1957), for example, defines periphyton as "organisms which
form associations on the stems and leaves of aquatic plants." "Auf-
wuchs", as delineated by Ruttner, includes all the attached organisms
except the macrophytes, as well as the unattached forms living free
within the mat of attached organisms. Up to this point, "aufwuchs" and
Young's definition of periphyton are synonymous. Ruttner's definition
of "aufwuchs", however, does not contain the word aquatic. "Aufwuchs"
may, therefore, exist in a terrestrial habitat with an adequate mois-
ture content while periphyton, as defined by Young, is necessarily
aquatic. With this exception, periphyton and "aufwuchs" are synonyms.
Other authors prefer not to use either term and refer to this community
as benthic algae (Blum, 1956 and Round, 1964), benthos (Lund and Tailing,
1957), or other similar terms. However, the terms "benthos" or "benthic"
usually refer to those unattacked organisms living in or on the bottom
sediments.
Strictly speaking, periphyton includes both plants and animals.
Although the previously cited definitions use only the work "organisms",
Odum (1959) defines periphyton as "organisms (both plant and animal)
attached or clinging to stems or leaves of rooted plants or other sur-
faces projecting above the bottom." The vast majority of the periphy-
ton community, however, is composed of plant material. This investiga-
tion, therefore, deals only with the members of the periphyton belong-
ing to the plant kingdom. The term "epilithic", as used in this re-
port, refers to the fact that the periphyton studied was growing upon
rocks.
In his book on the algae of the western Great Lakes area, G. W.
Prescott (1962) states that "although convenient, the term algae has
been applied to such a great variety of plant groups and has been given
so many interpretations that it has no very precise meaning." It
is not surprising, therefore, that basic algal taxonomy has long been,
and remains, a subject of controversy among botanists. The details of
algal taxonomy, therefore, will depend upon the authority consulted.
Fuller and Tippo, in their 1949 textbook, for example, divide the algae
into seven separate phyla under the subkingdom Thallophyta. Prescott
(1962) solves the problem of taxonomy in a somewhat similar fashion,
placing the algae in eight phyla, or divisions, as he calls them.
Robbins, Weier, and Stocking (1967) suggest six phyla, with the blue-
-------
green algae included in the phylum Schizophyta along with the bacteria,
class Schizomycetes. G. M. Smith (1933), on the other hand, divided
the algae into nine classes under the phylum Thallophta. In 1950,
he reorganized his algal groupings and raised most of the classes to
division (phylum) status. This resulted in seven divisions. For
reasons of simplicity, we have adopted in this report the conservative
taxonomic system proposed by Fuller and Tippo (1949), whose seven
phyla are, for practical purposes, identical to those of Smith (1950).
The productivity of a periphyton or plankton community may be
measured by either of two general methods, each with its own special
applicability. One is the evaluation of the "standing crop", or the
determination of biomass, which is quite significant when attention is
paid to the rate of establishment and "turnover" of the communities.
The other method involves the investigation of the dynamics of energy
transfer through the communities, or more specifically, the determina-
tion of photosynthetic rates. The estimation of "standing crop" may
include taxonomic studies, the determination of numbers of organisms,
the measurement of weight or volume of the communities, or the quanti-
tative analysis of some component of the organisms, such as carbon,
nitrogen, photosynthetic pigments, or DMA. The measurement of photo-
synthetic and respiratory rates may be used to calculate gross primary
productivity (the total rate of photosynthesis including the organic
matter used up in respiration) and net primary productivity (the rate
of storage of organic matter in plant tissues in excess of respiratory
utilization). The latter may also be termed "apparent photosynthesis"
or "net assimilation." When both "standing crop" and assimilation rates
for all communities of primary producers have been determined the true
basic productivity of an ecosystem may be calculated.
The overall objective of the study being reported here is to fill
in some of the gaps of knowledge relating to periphyton in general.
Specifically, it will deal with the characteristics of naturally occurr-
ing periphyton growths in a relatively unpolluted and very large body
of fresh water, the western arm of Lake Superior. Although the future
role of Lake Superior in the overall water economy of this continent
cannot be exactly predicted, it is generally agreed that any change that
occurs in this large body of water will have important and far-reaching
effects on the entire "heart-land" of America. Therefore, it may be
expected that a consideration of the periphyton and its importance as a
part of the ecosystem will provide data on the general character of the
lake which can be used as a reference or base-line in future years to
estimate tendencies toward eutrophication. The rationale involved in
this concept, fixed as it is in a region of the lake where it is constan*
tly swept by waves and currents, might be expected to develop in ways
which would reflect the characteristics of the water.
Specifically the study was directed toward the determination of;
1. The extent of natural periphyton growths in certain selected
areas of Lake Superior, quantitatively determined.
-------
2. The make-up of the periphyton mass in terms of its animal
and plant components with special attention to the algae, a taxonomic
analysis.
3. The speed and the phases of growth demonstrated by periphy-
ton in re-establishing itself on an artificially denuded substrate.
4. The primary productivity potential of the periphyton and its
relation to the typical productivity of the water in the open lake.
5* The possible interrelationship existing between plankton and
periphyton.
6. A study of the nature of the photosynthetic pigments and their
relationship to environmental factors such as depth and light.
The measurement of photosynthetic pigments has been long recog-
nized as a fast and relatively easy method for estimating the produc-
tivity of plankton populations. According to Richards and Thompson
(1952), the analysis of plankton pigments, when extended to include
the various chlorophylls and carotenoids, should yield "(a) a measure
of the potential of the plankton for absorbing radiant energy for photo-
synthesis, (b) some measure of the extent and stage of development of
the phytoplankton, and (c) a possible measure of the presence of animals
grazing on the crop". The relative concentrations of chlorophylls
a_, jb and £ also reflect to a certain degree the composition of an algal
community, since members of the various phyla contain different ratios
of these pigments. The use of pigment analysis can logically be ex-
tended to the determination of the standing crop of epilithic periphy-
ton, and further, to the estimation of the rate of carbon fixation,
when assimilation values are known or assumed.
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SECTION IV
MATERIALS AND METHODS
A. Occurrence, Regrowth, and Taxonomy of Periphyton
The area from which the majority of samples were obtained was
a small bay at the western end of Lake Superior which is known locally
as Stony Point Bay (Figs 1 & 2). It is situated approximately fifteen
miles northeast of the Duluth, Minnesota city limits and University of
Minnesota Limnological Research Laboratory at Lester River. Lying
two miles south of Knife River Harbor, where the thirty-foot motor-
ized research vessel, the Oneota. is moored, the study area is bounded
by the Little Sucker River on the southwest and Rocky Point on the
northeast.
The investigations began during the summer of 1965 (July 19 -
September 1) with a general survey of the study area. Conventional
surveying techniques were employed, utilizing a baseline, stadia
readings and a professional transit. For the purpose of establishing
the contour of the shoreline of the bay, a base station was selected in
the approximate center of the arc formed by the water's edge. This
base station was located directly below a tourist observation point on
a hill above the bay. A line, which extended from this station to a
point on the shoreline 427 ft. away at an angle of 84°30* east of south,
was then established. The transit was used to determine the angle of
this baseline while a stadia rod was employed to ascertain the distance.
Points along the shoreline from the Little Sucker River to Rocky Point
were then marked with fluorescent paint. The exact position of each
of these marked points with relation to the baseline was determined by
triangulation and plotted on the master map, thus providing an accurate
delineation of the water margin.
The second phase of the survey was the determination of the
depth profile of the bay. The Oneota was used to place an initial
reference buoy at a point 2336 feet from shore and in a southerly di-
rection from the establihsed base station. With the stadia rod aboard
the boat and the transit ashore, it was possible, by knowing the distance
of the vessel from shore and its angle from the base station, to deter-
mine the exact position of the Oneota at each sounding. Depth readings
were made with an electric fathometer. At the depths encountered, the
instrument was accurate to within six inches. Depth readings were re-
layed to shore by hand signals so that each depth determination could be
related to the position of the boat as it traversed the bay.
When depth permitted, the type of bottom was determined by water
glass observations. When the water was too deep for this procedure,
SCUBA-diving procedures were employed to ascertain the bottom type.
A small dinghy was used to survey shallow areas less than ten
11
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feet in depth. The Qneota could not be used here due to the presence
of occasional protruding boulders. The position of the dinghy at
each depth reading was determined by the triangulation method used to
locate the larger boat. Depth readings from the dinghy were made with
a marked sounding pole. A water glass or simple visual observation was
used to determine the type of bottom. The depths established by these
procedures were then plotted on the master map. Points of the same
depth were connected, thus providing a depth contour. Intermediate
depths were established by interpolation. These contours are included
in the map of the bay which also indicates the type of bottom. The
bottom area not designated by the word sand was covered with rocks.
It should be pointed out that small sand patches were encountered in
predominantly rocky areas while the sand patch contained small areas
of rock bottom.
In sampling, an imaginary line extending from the reference buoy
2336 feet from shore to the base station was used for orientation.
Whenever possible, samples were collected along this line. The same
line was used for the placement of the rocks used in the regrowth
studies.
The study began during the summer of 1965 with an evaluation of
the regrowth capabilities and the taxonomy of the periphyton. This was
a qualitative study. The substrata chosen for the regrowth study were
rocks already present and supporting periphyton growth in Stony Point
Bay. By choosing these rocks, we hoped to minimize any deviations
from the naturally occurring periphyton populations that might occur
if rocks foreign to the area were used as substrata. Artificial sub-
strata were not used for the same reason. In addition, unpublished
preliminary studies made by Olson and Odlaug in which glass slides,
tile, fish net, wood, and other materials were used, showed that the
type of substratum material affected periphyton growth. For the re-
growth studies, therefore, medium-sized rocks (eight to twelve inches in
diameter) were taken from shallow water in the bay and returned to the
laboratory in plastic buckets. There the rocks were thoroughly scrubbed
with a stiff-bristled plastic fingernail brush and rinsed with tap water.
A three-eighths inch wooden dowel was driven into the hole. The
rocks, with attached pegs, were then autoclaved at fifteen pounds per
square inch (250°F.) for twenty minutes and after sterilization, were
replaced in the lake. The rocks were lowered to the bottom by ropes
attached to the pegs at designated stations and depths. Styrofoam
buoys attached to the ropes marked the locations of the rocks. In
water depths greater than ten feet, SCUBA diving techniques were em-
ployed to determine the nature of the bottom and to make sure that the
experimental rocks were in a suitable position for regrowth to occur.
After an "incubation" period which ranged from three to twenty-
seven days, the rocks were retrieved by slowly pulling them back up
by the buoy ropes. This simplified technique was permissible because
this was a preliminary qualitative study. At the surface, the rocks
12
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DULUTH
KNIFE RIVER HARBOR
ROCKY POINT
STONY POINT BAY
LITTLE SUCKER RIVER
048
I i i
STATUTE MILES
FIGURE I. WESTERN ARM OF LAKE SUPERIOR, SHOWING THE
POSITION OF STONY POINT BAY, SITE OF PERIPHYTON
STUDIES.
ROCKY
POINT
BUOY
BASE STATION
LITTLE
SUCKER
- X RIVER
LOOKOUT
_L_J SCALE
LIMIT OF
STUDY AREA
FIGURE 2. DETAILED MAP OF STONY POINT BAY, LAKE
SUPERIOR.
13
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were carefully placed in individual plastic buckets which were then
transported to the laboratory. There the rocks were scrubbed clean
with a brush and rinsed with distilled water to remove the surface
growth. A small funnel was then inverted in the periphyton-water sus-
pension and rapidly moved in a vertical direction. During this thorough
mixing, two fifty milliliter samples were removed by dipping. One of
these samples was placed in a seventy-five milliliter amber bottle and
preserved by bringing the aliquot to a five per cent formalin concentra-
tion. This aliquot was retained as a reference sample. The other re-
mained unpreserved and was subjected to a prompt microscopic examination.
The microscopic examination was carried out at magnifications of
430 and 970 diameters. Drops of the sample were placed on a standard
microscope slide and a standard square cover slip was used. Organisms
were identified to genus and, when possible, to species. Each slide
was examined until no "new" organisms were observed.
In addition to this microscopic examination of the regrowth peri-
phyton, determinations were made of the dry weight of naturally occurr-
ing populations of periphyton. For this purpose, three rocks (four to
six inches in diameter) were obtained at each of three depths. Waders
were used to retrieve samples from the two foot depths near shore while
rocks from depths of ten and twenty feet were obtained by SCUBA div-
ing techniques. At these deeper depths, as determined by the fathometer
aboard the Oneota. divers, each with his right hand and forearm in an
inside-out clear plastic bag, reached out and grasped a sample rock
with his right hand. With the left hadn, he then pulled the bag down
over his forearm and hand, entrapping the sample rocks, as well as
a small quantity of the surrounding water. The same plastic bag proce-
dure was used at the two-foot depth. Each bag was knotted, brought to
the surface and placed in a labelled plastic bucket with two other rocks
from the same depth. The samples were returned to the laboratory within
three hours.
At the laboratory, rocks were removed by slitting each bag open
with a scalpel. Periphyton clinging to the bag was removed by rinsing
with distilled water. The area on which growth occurred was marked by
scraping an outline on each rock with a dull scalpel. Next, the periphy-
ton was completely removed by scrubbing and rinsing with distilled
water. The final sample from each depth consisted of the combined peri-
phyton and rinse water from all three rocks. After each suspension of
periphyton had been thoroughly agitated, using the funnel method des-
cribed earlier, aliquots were removed, measured and filtered through
Whatman filter paper. In order to insure a reasonable filtration time,
the aliquot size was determined on the basis of the turbidity of each
sample. In general, the sample sizes ranged from six to fifty milli-
liters. The filter papers were dried for one hour in an oven at 103°C.,
cooled in a desiccator and weighed.
In order to determine the extent of the surface upon which growth
had occurred, the previously outlined area of each rock was lubricated
14
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with a thin layer of automobile grease and coated with paraffin. The
paraffin was heated and applied with a paint brush until the rock was
covered with a one-eighth to one-fourth inch coat. The wax was removed
after it had solidified, but before it had become brittle, by cutting
slits in the coating covering the vertical surfaces of the rock. The
flaps created by these slits were then freed from the rock with a
scalpel and the portion of the paraffin coat still attached to the
horizontal surface was peeled off. By using this method, the coating
could be removed as one intact piece. The paraffin was then gently
pressed flat on a piece of white paper and its outline traced. A
previously calibrated polar planimeter was used to determine the area
enclosed by the tracing. Areas of the three rocks from each depth were
combined.
During the summer of 1966 (August 9 - September 6), rocks were
retrieved from depths of 2.5, 5, 10, 15, 20 and 35 feet. The depths
of the deep water stations (ten feet and greater) were determined by
t he fathometer aboard the Oneota. Buoys were placed at these stations
as permanent markers. The Oneota was used to transport divers and equip*
ment to Stony Point Bay from Knife River Harbor and upon arrival at the
bay, the vessel was anchored near the thirty-five foot buoy. Divers
retrieved sample rocks using the plastic bag procedure earlier described,
Again, three rocks were obtained from each depth. Laboratory procedures
used for preparing the periphyton-water suspension followed those de-
vised the previous summer.
A twenty-five milliliter aliquot to be used for counting, was
removed and transferred to a seventy-five milliliter amber bottle.
Twenty-five milliliters of ten percent formalin were then added. The
mixture was thus preserved in five percent formalin and diluted two-
fold. A graduated dropper was used to transfer one milliliter of the
sample into a Sedgwick-Rafter counting cell. After allowing ten minutes
for settling, a binocular compound microscope was used to count ten ran-
dom fields under a magnification of 200 diameters. The organisms were
identified to genus. A Whipple disc, previously calibrated with a
stage micrometer, was used to convert the ten random field counts into
a count per milliliter. By knowing the total volume of the periphy-
ton-water suspension, the dilution factor due to preservation and the
rock area, it was possible to determine the number of organisms per
square centimeter of rock surface. When the preserved sample was too
turbid for accurate counting, an additional twofold dilution with
distilled water was made.
For the determination of dry weights, a four milliliter sample
was removed from the periphyton-water suspension, filtered through a
pre-weighed Millipore membrane filter, dried for one hour in an oven at
103° C. and weighed. Results are expressed in milligrams per square
centimeter of rock surface.
During the summer of 1967 (June 9 - September 15), the analysis
15
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of the naturally occurring periphyton in Stony Point Bay continued.
A sampling run consisted of collecting three rocks from depths of 2.5,
5, 10, 15, 20 and 35 feet. At the time of each sampling run, light
readings and water temperatures were taken. Light readings were made
with a GM submersible photometer, which consists of two separate photo-
meters, a deck and a sea cell. At the 35-foot station, readings were
made at each meter from the water surface to the bottom. A standardized
laboratory thermometer was used to determine the water temperature at
the surface and at the bottom. A diver read the thermometer directly
above the bottom at each sampling depth.
In addition to the studies of the naturally occurring periphyton
of Stony Point Bay, denuded, autoclaved rocks were placed into the bay
and retrieved at predetermined time intervals in order to quantitative-
ly study the regrowth capabilities of the periphyton. Following the
methods used during the summer of 1965, the rocks to be denuded and auto-
claved were obtained by the use of waders from shallow, near-shore areas
of Stony Point Bay. As described earlier, these rocks were returned
to the laboratory where they were thoroughly scrubbed with brushes and
autoclaved. Since this study was to be quantitative, the methods of
necessity differed somewhat from those used the first summer. In-
stead of inserting pegs into the rocks and raising and lowering them in
the lake by buoy lines, these rocks, after being lowered in a wire
basket, were carefully placed in a circular configuration directly on
the bottom. SCUBA divers placed the rocks at 10, 20, and 35 feet. A
buoy marked each location. After the proper time interval had elapsed,
three of the rocks were picked up by divers. The plastic bag technique
was employed.
During the summer of 1967, samples of naturally occurring per-
iphyton were collected from areas other than Stony Point Bay. A 107
mile segment of the north shore of the western arm of Lake Superior
was sampled at intervals of approximately ten miles (Fig. 3). Begin-
ning with the Lester River as the southernmost point, samples were co-
llected as far north as Grand Marais, Minnesota. A fourteen-foot
aluminum skiff with a five horsepower outboard motor was towed by
car to each sampling location. Again, SCUBA diving procedures were
used to collect three rocks from each depth sampled. The actual
field techniques were the same as those used during the summer of
1966. Depths, however, were determined with a pitot-tube type depth
gauge carried by the individual diver. These depth gauges had been
calibrated against the electric fathometer aboard the Oneota. Tem-
peratures were taken at the bottom and at the surface. Whenever pos-
sible, rocks were collected from each of the six standard sampling depths
(2.5, 5, 10, 15, 20, and 35 feet) at each station. Each station
was sampled on two different days. Collections were made at the
locations shown below:
16
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PERIPHYTON SAMPLING LOCATIONS,
NORTH SHORE, LAKE SUPERIOR.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
II.
LESTER RIVER
KNIFE RIVER
BURLINGTON BAY
SPLIT ROCK RIVER BAY
BEAVER BAY
NO-NAME BAY
SUGAR LOAF COVE
TOFTE
LUTSEN
GOOD HARBOR BAY
GRAND MARAIS
0 MILES
13.8 MILES
22.1 MILES
39.4 MILES
48.0 MILES
53.9 MILES
69.9 MILES
78.8 MILES
86.3 MILES
100.9 MILES
106.9 MILES
FIGURE 3.
NORTH SHORE SAMPLING STATIONS AND
THE WESTERN ARM OF LAKE SUPERIOR.
17
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1. Lester River 0 miles
2. Knife River 13.8 miles
3. Burlington Bay 22.1 miles
4. Split Rock River Bay 39.4 miles
5. Beaver Bay 48.0 miles
6. No-Name Bay (near Little Marais) 53.9 miles
7. Sugar Loaf Cove 69.9 miles
8. Tofte 78.8 miles
9. Lutsen 86.3 miles
10. Good Harbor Bay 100.9 miles
11. Grand Marais 106.9 miles
In the laboratory, all the rocks collected during 1967 were
prepared for examination by the standard procedures adopted in 1966.
An aliquot consisting of 152 milliliters was removed for counting
and identification. The sample was brought to a concentration of five
percent formalin by adding eight milliliters of pure formalin. The
counting procedure remained the same. Organisms were identified to
genus and, when possible under a magnification of 200 diameters, to
species. When samples were too turbid for examination, appropriate
dilutions were made with distilled water.
After the counts were made, several drops of each sample were
placed on a glass microscope slide which was then placed in a muffle
furnace at 300° C. for ten minutes. After cooling, the ashed sample
was covered with a glass cover slip, using Hyrax as the mounting me-
dium. The ashing process incinerated all the material except the
siliceous diatom frustules which were then examined microscopically und-
er magnifications of 430 and 970 diameters. By using this procedure,
many of the diatoms could be identified to species. These permanent
diatom slides, from each depth and from each station, are now on file,
as are the duplicate aliquots which were preserved in formalin.
For the determination of dry weights, twenty-five milliliter por-
tions of the suspension were filtered through pre-weighed four-centime-
ter filter paper. Each filter was then placed in a weighed procelain
crucible, dried for one hour in an oven at 103°C., cooled and reweighed.
The samples were then ashed in a muffle furnace for fifteen minutes at
600°C. After cooling, they were again weighed in order to calculate
ash-free (or organic) dry weights. Results are expressed as milligrams
of total and ash-free weight per square centimeter of rock surface.
The remaining determinations, which included the pigment and the
photosynthesis-respiration analyses, were made using the procedures of
1966.
B. Pigment, Productivity, and Physiology Studies of Periphyton
The first phase of the productivity study involved field studies
18
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in which the biomass, production rates and regrowth capabilities of
naturally occurring periphyton in selected areas of Lake Superior were
quantitated and analyzed on the basis of pigment concentrations, photo-
synthetic rates, and other parameters. The second phase was a labora-
tory study in which the effects of light intensity and temperature on
pigment concentrations and photosynthetlc rates of periphyton were
determined experimentally. Most of the samples for both phases of the
investigation were taken from a selected area within the confines of
Stony Point Bay. This bay, as pointed out earlier, is situated on the
western arm of Lake Superior near Duluth, Minnesota, fifteen miles
northeast of the University of Minnesota Llmnological Research Station
at Lester River, The northeastern boundary of the study area is Stony
Point, while the mouth of the Little Sucker River serves as the south-
western boundary. Two miles to the north is Knife River Harbor where
the research vessels Oneota and Jacobs are moored.
In addition to its favorable location and configuration Stony
Point Bay which earlier had been surveyed to establish depth contours
and to determine the total area of the bay provided a basis for quan-
titative calculations of productivity in the periphyton community.
Routine sampling of the natural periphyton in Stony Point Bay
began during the summer of 1966. The samples were taken at depths of
2.5, 5, 10, 20 and 35 feet along a course perpendicular to the shore-
line; each sampling station was marked permanently with an anchored
buoy. Divers and sampling equipment were transported on the Oneota
from Knife River Harbor to Stony Point Bay, where the vessel was an-
chored at the thirty-five foot station. Divers employing SCUBA tech-
niques obtained three rocks of four to six inch diameter from each of
the six sampling depths.
Details of the collection technique and laboratory method for
quantitation have been described earlier. In the pigment studies,
aliquots from the combined periphyton slurry from the total surface
area of three rocks were used as a basis for calculations.
For the analysis of periphyton pigments in samples taken during
1966, twenty-milliliter aliquots of suspension were removed from each
sample. When the suspension appeared less turbid than usual, a forty-
milliliter aliquot was used. These aliquots were processed according
to modification of a pigment extraction method suggested by Creitz
and Richards (1955) for the analysis of phytoplankton. The detailed
procedure is as follows. Each portion of periphyton suspension was
filtered through a glass fiber filter (Gelman, Type A), and the col-
lected material was fixed by washing with fifteen roilliliters of satur-
ated magnesium carbonate solution. The purpose of this washing was to
provide buffering and thus prevent the conversion of chlorophyll to
phaeophytin. Each filter was ground in a tissue grinder along with five
roilliliters of ninety percent reagent-grade acetone to effect pigment
extraction. The material was transferred to a graduated centrifuge tube
and the volume was adjusted to ten milliliters with acetone. The sus-
pension was then centrifuged in a stoppered tube for ten minutes to
19
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produce a clear supernatant solution from which a five-milliliter
aliquot was pipetted into a cuvette. Total chlorophyll was first es-
timated on the basis of readings made with a Klett-Summerson colorimeter,
using a No. 66 Klett-Summerson filter (640-700 millimicrons) and ninety
percent acetone as the zero absorption standard. The following formula
was used to calculate total chlorophyll concentrations;
Chlorophyll (Mg/cm2) »
(0.28) (Klett units) (2) (L. of sample)
10J (L. of aliquot) (cm^ surface area)
Results are expressed in terms of milligrams of chlorophyll per 100
square centimeters of rock surface and as milligrams of chlorophyll
per 100,000 organisms.
Each of the pigment solutions tested in the K-S colorimeter was
then transferred to an absorption cell and its spectrum from 350 to
700 millimicrons was scanned and plotted with the Beckraan DK-2A spec-
trophotometer, again using ninety percent acetone as the reference.
The ratio of reference to sample absorbance (R/S) of a split-beam single
light source is plotted by the instrument, thus removing any error ac-
countable to unexpected power modulation. Sample temperature was held
constant at 30°C. by means of a control device mounted on the instru-
ment. Absorbance values at wavelengths of 480, 510, 630, 645, and 665
millimicrons were taken from the charted data and used for calculation
of chlorophyll a_, b and £ concentrations, as well as for calculation
of astacin and non-astacin carotenoids. The formulas developed by
Richards and Thompson (1952), which were used in these calculations,
are shown below.
Chlorophyll £ (mg/L) » 15.
Chlorophyll b (mg/L) » 25.4Dg45 - 4.4D&65 - 10.3D630;
Chlorophyll £ (MSPU) - 109D630 - 12.5D665- 28.7D645;
where D is absorbance at a given wavelength.
Dres> 51° = D510 " •°°26Ca - .0035Cb - .0021CC;
Dres, 480 = D480 - .0019Ca - .0136Cb - .0054CC;
where Dres is the residual absorbance at a given wavelength
after subtraction of the absorbancies of the chlorophylls.
Astacin carotenoids (MSPU/L) - 2(4.45Dreg, 510 - D , 480)
Non-ast. carotenoids (MSPU/L) - 7.6 (Dres, 480 - 1.49Dres, 510)
Results are converted to milligrams (or MSPU) of pigment per 100 square
centimeters of rock surface, and to milligrams (or MSPU) per 100,000
organisms at various sampling depths.
20
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As used above MSPU refers to milltspecifted pigment unit. It
represents a specific, but undetermined weight of the pigment which
should be about one milligram, based on the weights and absorption co-
efficients of related compounds (Richards and Thompson, 1952).
A Gilson differential-volumetric respirometer was used to deter-
mine the gross photosynthetic rate of the periphyton. This instrument
measures volume changes as a gas is absorbed or evolved under constant
temperature and pressure, producing a digital reading directly in micro-
liters. A special cover of black plastic sheeting was constructed for
the respirometer so that the respiration rate of periphyton organisms
could be determined in total darkness. The instrument was equipped
with a bank of floodlights to facilitate photosynthesis measurements.
Four-milliliter aliquots of the periphyton-water suspension were pipet-
ted into acid-cleaned Warburg flasks together with 1.92 milliliters of
carbonate-bicarbonate buffer solution (Warburg Number 11). This solu-
tion is composed of 0.1 molar sodium bicarbonate (95 percent) and 0.1
molar potassium carbonate (five percent). The buffer insures a constant
pH (8.2), provides an adequate carbon dioxide source for photosynthesis,
and incorporates carbon dioxide evolved during respiration into the
carbonate-bicarbonate system. The reaction flasks were attached to
individual manometers, each of which was connected to a common reference
flask. A mixture of five per cent carbon dioxide in air was introduced
into the gas spaces above the samples. The flasks were shaken in a
20°C. water bath while manometer readings were made during alternate
ten minute light (1500 foot-candles) and dark periods. A ten-minute
equilibration interval was allowed before each light or dark test.
During the light periods, both photosynthesis and respiration
occur, and manometer readings reflect net photosynthesis (oxygen evo-
lution less oxygen absorption, or "P-fR"). In the dark, only respira-
tion occurs. The manometer readings, therefore, indicate oxygen ab-
sorption, or "R". The assumption was made that oxygen absorption (res-
piration) in the dark is volumetrically equal to absorption in the light.
Therefore, gross photosynthesis rate could be determined on the basis
of the formula P (ten minutes) « -£R - (P+R)3 (from Umbreit, et aU,
1964), A correction factor involving barometric pressure and water
vapor pressure was applied to yield microliters of dry gas at 760
millimeters of mercury. The results of three separate runs on each
sample were averaged and expressed as microliters of oxygen produced per
hour per 100 square centimeter of rock surface, and as microliters per
hour per milligram of total chlorophyll.
Dry weights were determined by filtering four-milliliter portions
of the periphyton suspensions through pre-weighed membrane filters;
each filter, with its collected material, was dried for one hour in an
oven at 103°C. and weighed again. Results are expressed as milligrams
per square centimeter of rock surface,
Periphyton volume was estimated by settling the material from for-
ty milliliters of suspension for three hours in a narrow graduated
21
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cylinder. Thus the recorded volumes included small and varying amounts
of sand and clay. Results are reported in terms of milliliters of peri-
phyton per square centimeter of rock surface.
To calculate pigment concentrations on the basis of a standard
number of organisms, a twenty-five milliliter aliquot was transferred to
a sample bottle along with twenty-five milliliters of ten percent for-
malin. One milliliter of this suspension was pipetted into a Sedgwick-
Rafter counting cell and allowed to settle for ten minutes. A binocular
compound microscope fitted with a Whipple disc was used to count ten
random fields at a magnification of 200 diameters. The total numbers
of organisms per square centimeter of rock surface was used for cal-
culation of milligrams of pigment per 100,000 organisms.
Field studies were continued during the summer of 1967 (June 9
to September IS) with accelerated routine sampling of the naturally
occurring periphyton of Stony Point Bay. Three rocks were taken twice
each week from sampling stations at 2.5, 5, 10, 15, 20 and 35 foot depths,
Water temperature and light intensity readings were also recorded during
each sampling run. The temperature of water near the bottom at each
sampling station was determined by a diver carrying a standardized lab-
oratory thermometer. Light intensity at each depth was measured with
a GM submersible photometer. In addition, daily incident radiation was
continually recorded during the summer by a photometer situated on the
roof of the laboratory.
A study of the rate of establishment of periphyton in Stony Point
Bay was initiated in June, 1967. In order to present natural conditions
for growth, rocks from the bay itself which were already supporting per-
iphyton growth were chosen for use as a substrate in the regrowth ex-
periment. This natural substrate was chosen to avoid the deviations
in growth which may be expected with the use of an artificial substrate.
Rocks four to six inches in diameter were obtained from shallow water
in the bay and transported to the laboratory, and rinsed with tap water.
The rocks were then autoclaved for twenty minutes at a pressure of fif-
teen pounds per square inch (250°F.). After sterilization, the rocks
were replaced in Stony Point Bay at depths of 10, 20, and 35 feet by
SCUBA divers. The rocks were lowered in a wire basket to the divers,
who placed them on the bottom in a circle around the anchor of a mark-
er buoy. After predetermined "incubation" periods, ranging from eight
hours to 101 days, three rocks were retrieved from each depth by divers
employing the plastic bag technique.
In addition to the regular sampling of Stony Point Bay, an inves-
tigation of the periphyton of other north shore areas was carried out
during the summer of 1967. Eleven stations approximately ten miles a-
part along a 107 mile segment of the north shore of Lake Superior were
selected for sampling of the periphyton community. These stations rang-
ed from the southernmost at Lester River to the northernmost at Grand
Marais, Minnesota. Three rocks were taken from depths of 2.5, 5, 10,
15, 20 and 35 feet except in certain cases where no rocks were encoun-
tered at the 35 foot depth.
22
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Samples collected from Stony Point Bay and the other north shore
stations during the summer of 1967 were prepared for laboratory exami-
nation by the same basic procedures as described previously. Pigment
analyses were performed on all samples in the same manner as in 1966,
except that the K-S colorimeter was not used to estimate total chloro-
phyll. Photosynthetic rate under standard conditions was again deter-
mined for each sample from Stony Point Bay. Since the addition of car-
bon dioxide to the reaction flasks seemed to pressurize the system and
produce high results, none was added during the 1967 measurements. Due
to the large number of samples collected in a short period of time from
the other north shore stations, photosynthetic rates of only a limited
number of these samples could be determined.
In addition to the determination of total dry weights, the samples
were analyzed for ash-free (organic) dry weight. A twenty-five milli-
liter aliquot of each periphyton suspension was drawn through a pre-
weighed four-centimeter filter paper. The filters were placed in pre-
weighed porcelain crucibles and dried for one hour in an oven at 103°C.
After the crucibles had been cooled in a desiccator and reweighed, they
were placed in a muffle furnace at 600°C. for fifteen minutes. After
cooling in the desiccator, the ashed samples were weighed again for
the calculation of ash-free dry weights. Results are expressed as mill-
igrams of total dry weight and ash-free dry weight per square centimeter
of rock surface.
The second phase of the investigation began in June, 1968. It
was designed to provide information regarding the effects of short-
term changes in light intensity and temperature on the productivity
of Lake Superior periphyton. The general procedure was to "condition"
or acclimate, natural periphyton samples to various light intensities
and temperatures for short periods in the laboratory and then to de-
termine the photosynthetic rates of the conditioned samples in crossed
gradients of light intensity and temperature. Analysis of photosynthe-
tic pigment concentrations in conditioned samples provided a basis for
the calculation of assimilation values for periphyton organisms under
a variety of conditions. The rate of change of pigment concentrations
following an increase or reduction of light intensity was also examined.
To facilitate the conditioning of periphyton organisms in a simu-
lated lentic situation, special incubators were designed for use in the
laboratory. Each of four Precision B.O.D. incubators with variable
temperature control was modified to enclose a ten-liter plastic tub
which served as a sample container. Two banks of fluorescent lamps
(General Electric daylight white, 20 inch) were mounted in a vertical
position along the inside walls of the incubators. The light intensity
within the incubators could be altered by adding, removing or masking
lamps in the lighting system. A Weston light meter reading directly
in foot-candles was used to measure light intensity in the incubators.
A continual-flow water circulation system was installed in each incuba-
tor for the purpose of maintaining a steady, slow flow of water through
the sample container. A variable-speed peristaltic pump mounted on the
top of the incubator circulated water through the sample container by
23
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means of 3/8-inch Tygon tubing. The inlet and outlet tubing reached
from the pump to the sample container through two small holes drilled
in the side of the incubator. The inlet tube reached slightly be-
low the surface of the water in the container, while the outlet tube
was anchored to the bottom in the opposite corner of the container.
A four-liter plastic aspirator bottle was suspended above the sample
container inside the incubator and tied into the inlet line. This bot-
tle could be disconnected and removed at selected intervals and replaced
with another bottle full of fresh water, thus serving as a means for
maintaining a rather constant level of nutrients in contact with the
samples.
Rocks with well established growths of periphyton were carefully
collected by hand from Stony Point Bay and placed in buckets of water
for transport to the laboratory. The rocks were transferred to the
sample containers in the incubators. Water from Stony Point Bay was
collected daily in a large carboy and used as the medium for sustaining
growth of the samples in the containers; the rocks were submerged in
seven liters of water. To simulate the lentic situation, the pumps
were arbitrarily set to recirculate the water at a rate of 350 milli-
liters per minute. This rate allowed a retention time of twenty minutes
in the sample container. During all experiments, the medium was par-
tially changed each day by replacement of the aspirator bottle. Water
pumps and individual ballasts for each fluorescent lamp were located
outside the incubators to disperse the heat developed during operation.
Four different sets of conditions for incubation could be provided
at one time by selecting various combinations of temperature and light
intensity within the incubators. After a specified time period, the
rocks were usually removed from the incubators and the attached periphy-
ton removed for analysis as previously described. Pigment analyses
and ash-free dry weight determinations were performed as in the field
study. Organisms were microscopically examined, counted and identified
to species if possible. For the determination of photosynthetic rates
under different conditions, it was necessary to alter the respirometer
so that various light intensities could be produced. This was accom-
plished by removing certain lights from the apparatus and positioning
the flasks in such a way as to provide different light intensities at
nine flask locations (20, 60, 80, 180, 300, 400, 600, 900 and 1500
foot-candles). These intensities were determined with the Weston
light meter. Photosynthetic rates of conditioned samples were measured
at the nine light intensities and at a variety of temperatures by em-
ploying the automatic water bath temperature control on the respirometer.
Several experiments were run each designed to examine a separate problem
and each employing the general procedures just described.
In 1969 and 1970 the study was expanded to include observations
on periphyton growth in Lake Superior water which had been pumped into
holding pools where certain environmental controls could be imposed
to modify the normal lake water while adequate controls were being
maintained. This also presented an opportunity for a study of the con-
24
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tributions periphyton might make to the lake plankton.
To provide an aquatic environment for periphyton growth which
would be both natural and yet capable of experimental modification, a
field station consisting essentially of two rock-basin pools, a piping
system and a small building to house the pumping, metering and other
necessary equipment was established on a relatively isolated stretch
of shoreline near Castle Danger, Minnesota. This particular section
of shoreline comprises part of a 50-acre tract of lakeshore property
owned by the University of Minnesota (UMD) and is located about 40
miles from the base laboratory (Lake Superior Limnological Research
Station) at the Lester River in Duluth.
In order to determine the best site for pool construction, a
preliminary survey was made covering approximately one-third mile of
shoreline within this area. A specific site was eventually found which
met all of the predetermined criteria used in the survey: (1) The
rock stratum was to be sufficiently level and large enough to assure
exposure of both pools to sunlight of equal intensity; (2) The elevation
above lake level had to be high enough to prevent ordinary or moderate-
ly-sized waves from splashing excessive water into the pools; (3) The
bank above the pools should have a slope which would minimize the pos-
sibility of seepage and surface runoff; (4) The area should be fairly
well protected from the effects of periodic storms; (5) The rock
substrate, itself, had to be solid and not excessively "granular" or
full of fissures; and lastly, (6) The pools had to be near a source
of electricity to provide power for the pumps.
Construction of the pools began in the middle of July, 1969.
Using air-hammers, two basins were excavated in the solid gabro rock
bed, one with an approximate capacity of 3,000 gallons and the other
with a slightly smaller capacity of 2,500 gallons (Figs. 1, 2). The
entire bottom and as much as possible of the side surfaces were formed
of the natural rock. Concrete blocks reinforced with iron rods were
used only where necessary to fill in irregularities and to form the
rims of the pools. To minimize leaching of calcium from the cement
blocks, the walls were scrubbed with a solution of technical grade hy-
drochloric acid and, as a final chore, any cracks or fissures present
were patched with an inert hydraulic cement sealer known commercially
as "Thoroseal".
The exact capacity of each pool, when filled with water to a level
about two inches below the rim, was calculated by measuring the flow
rate of the incoming water and the time required to fill the pools. For
this preliminary determination, flow meters were temporarily installed
on each branch of the single intake pipe. The pool with the larger
capacity, designated as the "control pool", contained 394 cubic feet
(2,950 gallons) of water; the "test pool" was of slightly smaller cap-
acity and contained 337 cubic feet (2, 520 gallons) of water. The wat-
er level in both pools was regulated and maintained at the previously
mentioned height by means of 2" overflow pipes on the outside of the
25
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front walls.
As shown in Plate 1, the control pool was built at a slightly
higher elevation than the test pool. This higher level coupled with
a greater volume was intentionally designed to eliminate or, at least,
substantially reduce any diffusion which might occur between the two
pools through their common center wall. If diffusion were to occur it
would, therefore, be directed from the control pool to the test pool
due to the greater water pressure in the former. This is an important
consideration since the water in the test pool was experimentally en-
riched and any diffusion in the reverse direction would alter the natural
quality of the lakewater in the larger pool and, thus, invalidate its
use as a control.
Using a %**hp pump, lakewater was drawn into a single T-shaped in-
take pipe and continually cycled through both pools, resulting in an
average of six overturns per day. An "American series" flow meter in-
stalled on each arm of the inlet line indicated that the flow through
the control and test pools was approximately 18,000 gallons/day and
15,000 gallons/day, respectively.
Solutions containing 0.163 ppm phosphate as PO^-Pand 1.96 ppm
nitrate as N03-N were added to the test pool with a £-hp American Meters
Co. Proportioning pump. Any change in concentration of these ions was
monitored by chemical analysis of water samples collected daily from
both pools. Phosphate concentration was measured by the stannous chlo-
ride method (APHA Standard Methods, 1965) and nitrate nitrogen was de-
termined by both the phenoldisulfonic acid method (APHA Standard Methods,
1965) and an Orion Ion-Analyzer equipped with a nitrogen-specific elec-
trode. Since the amounts of phosphorus and nitrogen added to the test
pool were always maintained in a 1:15 ratio, the concentration of phos-
phate could also be calculated from the nitrate analyses.
In 1969, periphyton-covered rocks lying 2-3 feet below the surface
were initially collected from a relatively sheltered area along the shore.
However, it was subsequently found that many of these rocks were extreme-
ly jagged and irregular in outline and therefore would not be suitable
to the study because of the uncertainty involved in determining the sur-
face area and the difficulty of completely removing the natural growth
as would be later required. For this reason, another survey was begun
along the entire shoreline within the boundaries of the University-owned
property to find an area in which the rocks would be more uniform in
shape, size and degree of periphyton growth. The use of SCUBA gear al-
lowed underwater exploration at considerable distances outward from the
shore and, thus, a much greater area of the lake bottom was able to be
examined at depths ranging from three to twenty feet.
Rocks of adequate size were frequently noted at depths of 5-9
feet but their surface was usually covered with patches of green fila-
mentous forms and rather uneven periphyton distribution. A suitable
area was finally located at a depth of 12 feet in a small bay about
26
-------
•
Plate 1. Experimental pools for perlphyton studies on North
Shore of Lake Superior at Castle Danger, Minnesota.
Note the lower level of the test pool in the fore-
ground.
-------
! >
Plate 2. Experimental pools for periphyton studies on the
North Shore of Lake Superior, Castle Danger, Minn-
esota, showing piping arrangement to control pool
(left) and test pool (right).
-------
one-quarter mile trom the tield station. In contrast to the patchiness
observed previously, the periphyton at this depth appeared to be more
uniform and the rocks were heavily coated with the wooly brown growth
characteristic of diatoms.
Rocks from this site were collected by the underwater method des-
cribed for Stony Point Bay. Within a period of two hours, a total of
120 rocks, similar in shape and approximately 7-9 inches in diamter,
were selected and repositioned in the experimental pools. At the field
station, the plastic bags were carefully removed and 60 rocks were a-
ligned in north-south rows in each of the half-filled pools. The rocks
in each pool were individually placed in a position similar to their
original orientation on the lake bottom and at a sufficient distance
from the walls to prevent unequal shading and, consequently, any dis-
crepancies which could be attributable to differences in length of ex-
posure to sunlight. The pools were then filled with lakewater and, af-
ter a one-week period of stabilization, phosphorus and nitrogen were
added to the test pool.
At weekly intervals thereafter two sample rocks were removed
from each pool and placed in individual plastic bags. The rocks were
gathered either by using hip waders and stepping directly into the pools
to remove the specimens or by temporarily spanning the pools with a
16-foot board from which, by lying face downward, it was possible to
retrieve the rocks from any desired depth or location. Following the
method of Fox and Stokes, as cited previously, the samples were random-
ly collected from various areas of both pools with as little as pos-
sible discrimination regarding visible growth. Collections were usu-
ally made in the late morning and the samples were promptly returned to
the base laboratory where they were processed no later than four hours
afterwards.
Biological and chemical analyses were done in the laboratory at the
Lake Superior Limnological Research Station in Duluth. Procedures for
periphyton recovery and delineation of rock surface area were the same
as those which have been described previously.
A microscopic examination was made of both the periphyton and the
phytoplankton in the experimental pools. After the growth outline had
been scratched onto the rock surface, the periphyton were scraped off
with a stiff plastic brush and, together with a small amount of dis-
tilled water used in rinsing the rock and the plastic bag, the total
fluid suspension was measured in a graduated cylinder and transferred to
a small plastic pail from which the samples for identification and enu-
meration were obtained.
Although a large, inverted funnel was immersed and rapidly agita-
ted in the liquid periphyton suspension, the mixture remained fairly
thick and dilutions ranging from 2:1 to 8:1 were made prior to examina-
tion. Due to the abundance of filamentous algae in the sample a cut-
off 10-ml pipette, instead of the 1-ral pipette normally employed, was
29
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used to transfer a one-railliliter aliquot to the Sedgewick-Rafter count-
ing cell. Organisms were examined with a binocular microscope at 200X
magnification and ten random fields were counted.
For phytoplankton examination, 4-liter water samples were collec-
ted twice a week from (a) the lakewater intake pipe, (b) control pool
effluent pipe, and (c) test pool effluent pipe. The samples were qual-
itatively and quantitatively examined using the drop method developed
by Lackey during his investigations of the Scioto River, Ohio (APHA
Standard Methods, 1965). In this method, most of the supernatant liq-
uid from the centrifuged sample is removed and the concentrate is re-
suspended in the small amount of fluid remaining. After having estab-
lished the ratio between the number of drops in the concentrate and the
volume of the original sample, one drop is transferred to a glass slide
and a coverslip is immediately applied. In this study, the organisms
ware counted in four microscopic traverses using a medium-power 20X
objective (4 strips at this magnification (200X) being considered equiv-
alent to 8 strips at 44X or 2 strips at 100X).
The temperature of the water in both pools and that of the lake-
water from the intake pipe was monitored daily with an electronic ther-
mometer coupled to a recording chart unit. General environmental con-
ditions which could possibly influence the nature of the results, such
as storms or high winds, were also noted and recorded. Since, for
Lake Superior, lists of periphyton species are not available, a special
study was undertaken during the summer of 1970 to provide such a refer-
ence. This list is based on the Castle Danger Studies and the accumu-
lated observations (1965-1970) on the near-shore periphyton along the
North Shore. Dr. Alan J. Brook, R. Colingsworth and other experts were
consulted. On the basis of their assistance and the personal judge-
ment of the senior investigators a species list has been prepared.
30
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SECTION V
RESULTS OF PERIPHYTON DISTRIBUTION
AND TAXONOMY STUDY
For the sake of simplicity findings are reported here in chron-
ological order, and to avoid unnecessary repetitions, the results and
the discussion of results have been combined. In this section there-
fore, one will find the presentation and summation of data obtained over
the entire four year period of study, namely, 1965, 1966, 1967, and 1968.
Stony Point Bay was the primary sampling area. Its location and
a detailed presentation of the sampling area are shown in Figures 1 and
2. As may be seen from Figure 2, the study area is triangular, bounded
by Rocky Point on the northeast, the Little Sucker River on the south-
west, and a reference buoy in the lake 2,236 feet from shore. The
total area enclosed by these three points is approximately 321,000
square meters. The straight line distance from Rocky Point to the
Little Sucker River is about one half mile.
Initial observations made of the bay showed that the surrounding
land area was very sparsely populated. The only spectators noticed du-
ring the course of our operations were an occasional tourist or commer-
cial fisherman. Permanent cribs for holding fish were noted in the bay.
One fisherman complained of the slimy growth which often fouled his nets
and pointed out periphyton on some nearby rocks as the cause. Earlier
unpublished studies made by one of the authors (Olson, 1960) support
the hypothesis of the fisherman. In microscopic examinations of the
growths on fish nets from other areas of Lake Superior, Olson found dia-
toms attached by gelatinous stalks. The organisms were primarily mem-
bers of the genus Cymbella.
The water of Stony Point Bay appeared either blue, green, gray,
tan, or intermediate shades, depending on the cloud cover, the nature
of the bottom, and the turbidity produced by living or non-living
suspended materials. Secchi disc readings likewise varied, with the max-
imum being about eight meters. The bottom type could usually be deter-
mined visually in depths of up to twenty feet. Maximum visibility in
the bay, as reported by SCUBA divers, was about thirty feet. In general,
water temperatures, in the early summer were about 6°C. just under the
surface and 4.5°C. at thirty-five feet.
In preparing a report on the nutrients of the western arm of Lake
Superior, Putnam and Olson (1960) obtained their data from a large num-
ber of samples collected from the Larsmont-Knife River area, which is
approximately two miles from Stony Point Bay. The mean values that
they obtained for several chemical parameters (from July 15 - Septem-
ber 10, 1959 are as follows:
31
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Epilironion Hypolimnion
Silica (ppm) 2.04 2.13
Carbon dioxide (ppm) 1.28 2.33
Nitrate (ppm) 0.36 0.42
Organic nitrogen (ppm) 0.14 0.13
pH 7.9 7.7
Phosphorus, total (ppm) 0.01023 0.0136
Oxygen saturation (%) 105 97
Alkalinity (ppm) 38.5
Routine analyses performed during each of the summers, 1964 to 1968,
by School of Public Health students show that these values have remained
essentially the same. In fact, when even slight variations from these
values were obtained, the deviation could almost invariably be traced
back to faulty laboratory technique.
In 1960, the predominant genera of phytoplankton taken in the
Larsmon-Knife River area were Asterionella. Cyclotella. Fragilaria.
Melosira, Synedra. Tabellaria, Dinobryon, and Ankistrodesmus (Putnam
and Olson, 1961). Counts made in 1968 showed that the same organisms
were predominant and that in August, Dinobryon sertularia was the most
common organism in the phytoplankton.
Periphyton was visible generally throughout the Stony Point Bay
area, on the rocks appearing as a thick, tan, wooly growth containing
entrapped gas bubbles (presumably oxygen) causing them to rise to the
surface. It was observed that wave action occurring as a result of a
storm would dislodge the periphyton from the rocks in the shallow areas
of the bay. The resulting suspension imparted a distinct tan color to
the water and sometimes reduced x'isibility to zero. Sculpins (genus
Cottus). ranging in size from one to four inches, were the only fish
observed. Occasionally, Mysis relicta. a species of minute crustacean
was seen swimming in groups of ten to twenty individuals near the bot-
tom. On one occasion, several clumps of an attached, filamentous,
macroscopic green alga, Nitella. were observed.
In general, the bay floor was uniformly covered with a tan mat of
periphyton, on both the sand and the rocks. The rocks on which the
growth occurred ranged in size from less than an inch in diameter to
boulders projecting as much as six feet above the bottom. Animal forms
sometimes seen in this periphyton were leeches, snails, nematodes,
caddisfly larvae, and mayfly nymphs.
When the rocks were scrubbed clean in the laboratory, it was noted
that they differed markedly in appearance. An analysis of one hundred
representative rocks indicated that there were about twenty -two lithic
types in Stony Point Bay (see Table I). The majority (fifty-six per
cent) of the rocks were basalt, with twenty-four per cent of these pos-
sibly being wither andesite (sixteen per cent) or diabase (eight per
cent). The next most common rock type was diabase, with fourteen posi-
32
-------
tive identifications. Seven per cent of the rocks were porphyritic
trachyandesite to mafic quartz latite.
The 1965 regrowth study, in which denuded, autoclaved rocks were
replaced in the lake, provided the first qualitative periphyton data.
Nineteen different rocks were recovered from depths of from two to
nineteen feet. "Incubation" times ranged from three to twenty-seven
days. Thirty-four different genera from three phyla of algae were
found in the regrowth on these rocks, they are listed in Table II.
Although not shown in the table, some genera were represented by more
than one species. Of the thirty-four genera, twenty-five, or seventy-
four per cent, were members of the phylum Chrysophyta and twenty-four
of these were diatoms. The one remaining genus, Dinobryon. belongs to
the class Chrysophyceae. Next in order of abundance was the phylum
Chlorophyta. Seven genera of these green algae were found. Blue-green
algae were represented by only two genera.
TABLE I
ROCK IDENTIFICATIONS, STONY POINT BAY, LAKE SUPERIOR.
Number of
Samples
Lithic Description
medium to coarse grained granite
porphyritic andesite
massive graywacke
laminated hornfels, pelitic
fine grained, porphyritic, red granophyre
aphanitic to fine grained basalt, aphyric
very fine grained basalt with small amygdules
very fine grained porphyritic basalt or andesite
very fine grained porphyritic trachyandesite
to mafic quartz latite (intermediate)
fine grained porphyritic trachyandesite
very fine grained porphyritic felsite
fine to medium grained amygdaloidal basalt
aphanitic to very fine grained ophitic basalt
fine grained ophitic basalt
fine to medium grained basalt or diabase
fine grained diabase
fine to medium grained diabase
anorthositic gabbro
anorthositic olivine gabbro
porphyritic gabbroic anorthosite
arkosic sandstone (one red, one white)
red siltstone
Total
33
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Although in 1965 the study was limited to qualitative observations,
it was observed that the number of genera increased with increased
"incubation" time. In the shallow area, only Cymbella. Diatoma. Gom-
phonema, Melosira. and Synedra occurred. These same groups plus thir-
teen additional genera were observed in the sample from deeper water.
Several factors may be responsible for this phenomenon. Wave action in
the shallower water may make the attachment process difficult for some
genera. Certain genera may be more capable of withstanding rough water.
Also, waves undoubtedly knock periphyton from the rocks into the water,
thereby reducing both numbers and kinds of organisms. Finally, selec-
tive grazing by insects and other organisms may also be a contributing
factor in preventing the establishment of certain genera on rocks in
shallow water.
The results of Douglas (1958) support the latter hypothesis.
She found a negative correlation between populations of Achnanthes and
the caddisfly larvae, Agapetus fuscipes, in studying the periphyton of
an English stream. She stated that her findings suggest a grazing
effect. In Stony Point Bay, Achnanthes is a common diatom and caddis-
fly larvae occur, especially in shallow water. Douglas also noted
shifts in the populations of Gomphonema and Synedra which could be
attributed to grazing. It is interesting to note that these forms
are also common in Stony Point Bay.
It was not felt that the varying rock types affected the growth
of the periphyton in any way, inasmuch as two different types of rock
from the same depth "incubated" for a like amount of time seemed to
support similar numbers of the same genera of organisms. Although no
specific experiments were conducted to verify this observation, later
quantitative findings supported the hypothesis.
In 1965, another pertinent find was that a growth made up of
eighteen genera of algae could be produced on rocks "incubated" for
only three days in the lake. This information suggested that initial
colonization of a denuded, autoclaved rock could take place in a very
short time and provided the basis for planning future studies, in which
rocks were examined as early as eight hours after being replaced in the
lake.
Although quantitation was not the objective of this preliminary
study, a purely subjective estimation of abundance indicated that
Achnanthes and Synedra were predominant in the majority of samples.
In addition to the microscopic examination, dry weight determina-
tions were also made on the periphyton of Stony Point Bay. Samples
came from depths of two, ten, and twenty feet and weights were expres-
sed as milligrams per square centimeter of rock surface. The results
are presented in Table III. Each depth was sampled on seven different
days in July and August. It will be noted that the weights are quite
variable and that no seasonal trends are apparent. In terms of mean
weights for the seven days, the ten foot samples were the highest, the
34
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TABLE II
A CHECKLIST OF LAKE SUPERIOR PERIPHYTON OCCURRING
AS REGROWTH ON ARTIFICIALLY DENUDED ROCKS,
STONY POINT BAY, LAKE SUPERIOR, 1965.
Phylum Chrysophyta
Class Bacillariophyceae
Achnanthes mlcrocephala
(Kuetzing) Cleve
Amphora ovalls
Kuetzing
Amphora normanl
Rabenhorst
Asterionella formosa
Hassall
Ceratonets arcus
(Ehrenberg) Kuetzing
Cocconeis flexella
(Kuetzing) Cleve
Cocconeis spp.
Cyclotel La spp.
Cymatopleura solea
(Brebisson) W. Smith
Cymbella lanceolata
(Ehrenberg) Van Heurck
Cymbella spp.
Denticula thertnalis
Kuetzing
Diatoma elongatum
C.A. Agardh var. tenuis
(Agardh) Van Heurck
Diploneis elliptica
(Kuetzing) Cleve
Fragilaria capucina
Desmazieres
Fragilaria crotones is
Kitton
Gomphonema geminatum
(Lyngbye) C.A. Agardh
Gomphonema spp.
Melosira granulata
(Ehrenberg) Ralfs
Melosira sp.
Navicula spp.
Nitzschia spp.
Pinnularia sp.
Rhizosolenia eriensis
H.L. Smith
Rhoicosphenia curvata
(Kuetzing) Grunow
Surirella spp.
Stauroneis spp.
Stephanodiscus sp.
Synedra acus
Kuetzing
Synedra rumpens
Kuetzing
Synedra ulna
(Nitzsch) Ehrenberg
Tabellaria fenestrata
(Lyngbye) Kuetzing
Tabellaria flocculosa
(Roth) Kuetzing
Class Chrysophyceae
Dinobryon sertularia
Ehrenberg
Phylum Chlorophyta
Actinastrum sp.
Cosmarium sp.
Closterium sp.
Coelastrum sp.
Oedogonium sp.
Scenedesmus quadricauda
(Turpin) Brebisson
Tetraedron minimum
(A. Brown) Hansgirg
Phylum Cyanophyta
Anacystis sp.
Merismopedia convoluta
Brebisson
35
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twenty foot samples the lowest, and the two foot samples were inter-
mediate. Although the variation between these three means is relative-
ly small, the figures reported are logical. For instance, it is pos-
sible that the two foot mean is lower than that for ten feet because
of the fact that wave action dislodges more periphyton at the shallower
depth. The lower weight at twenty feet may be explained by the fact
that in deeper water there is less light penetration and therefore
fewer photosynthetic organisms. Also, lower temperatures exist in deep-
er water and could be expected to retard growth rate.
On the basis of the mean dry weight figure for the three depths
(July 27 to August 23) and the area of the bay, a rough estimate of the
average total dry weight, or the standing crop, of the periphyton on
the floor of Stony Point Bay was 54.4 tons (153 g/m^).
TABLE III
NATURALLY OCCURRING PERIPHYTON DRY WEIGHTS AT SEVERAL
DEPTHS, STONY POINT BAY, LAKE SUPERIOR, 1965.
MILLIGRAMS PER SQUARE CENTIMETER
OF ROCK SURFACE.
Depth in feet
Date 2 10 20
7-27 12.8 28.5 25.5
8-3 39.2 18.1 6.4
8-9 3.1 10.1 3.5
8-12 8.4 8.0 8.4
8-16 17.2 14.4 20.1
8-19 20.2 36.8 19.1
8-23 5.1 5.0 13.3
Mean 15.1 17.3 13.8
The marked reductions in dry weights that occurred on August 9
and 23 (Table III) are compatible with the theory that a counterclock-
wise current is produced within Stony Point Bay during the time of a
strong northeast wind. An east wind would have the same effect, only
to a lesser degree. The current thus produced could then loosen and
dissipate the periphyton, thereby reducing its volume. The depth at
which the periphyton could be affected would depend on the velocity of
the current. U.S. Department of Commerce climatological data, obtained
from the Duluth International Airport, strongly support this hypothesis.
During August of 1965, northeast winds were recorded for only three
days. They occurred on August 7, 8, and 23. These dates all corres-
pond with those on which the low weights were obtained.
36
-------
In 1966, samples were examined quantitatively as well as qualita-
tively. From August 9 to September 6, twenty-seven samples of three
rocks each were obtained from Stony Point Bay at depths of 2.5, 5,
10, 15, 20 and 35 feet. The results are presented in Figure 3 and
Tables IV to VI.
The numbers of naturally occurring periphyton organisms found
per square centimeter of rock surface, plotted against the six standard
sampling depths, are shown in Figure 3. Numbers are means of the to-
tals found at each depth for the five sampling days. The mean at the
2.5 foot depth was 490,000 per square centimeter, which was lower than
the five foot mean of 587,000 per square centimeter. This was possibly
due to the dislodgement of the organisms by wave action. The ten foot
mean of 433,000 per square centimeter and the fifteen foot mean of
365,000 per square centimeter showed that there was a downward trend.
This could be explained on the basis of lower temperatures and less
light penetration in the deeper water. Because of these two factors,
the twenty foot mean of 468,000 per square centimeter and the thirty-
five foot mean of 637,000 per square centimeter were unexpectedly high.
The only plausible explanation is that the unusually rough weather
which occurred during the summer of 1966 dislodged the periphyton up
to depths of at least twenty feet, and possibly affected growth be-
yond that point to a lesser degree. In discussing these counts, the
numbers have been rounded off to the nearest thousand, A mean of
the counts at all depths is 497,000 organisms per square centimeter
of rock surface.
A list of the genera observed while making the counts is presen-
ted in Table IV. Of the twenty-four genera listed, nineteen, or seven-
ty-nine percent, are members of the phylum Chrysophyta. Only one of
these, Dinobryon. is not a diatom. Four genera of green algae (Chloro-
phyta) were observed. The phylum Cyanophyta was represented by only
one blue-green alga, Merismopedia.
It would be logical to expect more genera of organisms to be
present in the naturally occurring periphyton sampled during 1966 than
in the 1965 regrowth periphyton. This was not the case. In 1965,
thirty-four genera were found occurring as regrowth, while only twenty-
four genera were observed in the naturally occurring periphyton of 1966.
This difference in the number of genera is probably a result of the
differing procedures used in examining the two sets of samples. In
1965, periphyton was examined qualitatively, with the desired result be-
ing identification to species. For this reason, a good deal of time
was spent on each sample and many organisms were examined. In 1966,
the goal was to identify the organisms to genus and quantitate them.
A ten random field counting method was used. By using this method,
fewer organisms were encountered than during the 1965 examinations. In
addition, the total number of samples examined during 1966 was relative-
ly small. All but one of the genera, Ankistrodesmus, observed in the
naturally occurring periphyton in 1966 had been found in the 1965 re-
growth samples. Genera of organisms encountered during 1965 and not
37
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reported for 1966 include: Chrysophyta - Ceratonels. Diploneis.
Pinnularia. Rhoicosphenia. Stauroneis. and Stephanodiscus; Chlorophyta -
Actinastrum. Cosmarlum, Coelastrum. and Oedogonium; Cyanophyta -
Anacystls.
The numbers of organisms from each of the three phyla which
characterize the periphyton of Stony Point Bay and the total counts of
each sample are presented in Table V. It can be seen that diatoms were
found in all of the twenty-seven samples, while one or more of the
genera of Chlorophyta were found in eleven samples. Merlsmopedia. the
only blue-green, was observed in ten samples. Dlnobryon. the only
member of the phylum Chrysophyta that is not a diatom, was found in low
numbers in thirteen of the samples. This organism, therefore, can be
considered an insignificant contributor to the total numbers of Chrys-
ophytes. The distribution of phyla according to depth is interesting,
although possibly not significant. All three phyla were observed at
2.5, 5, 10, and 20 feet. At fifteen feet, however, no greens or blue-
greens were found. At thirty-five feet, no greens were observed. Be-
cause of the narrow time span over which the sampling occurred and the
rough weather, it would be unrealistic to intimate that these organisms
were responding to seasonal changes.
In Table VI, seven genera, all diatoms, are listed in the order
of abundance. This listing has been done on the basis of the average
of the means of the percentage compositions of each organism at all
six depths. These results confirm the earlier judgement that Achnanthes
and Synedra were the most common organisms. The average of the mean
percentages for all depths of Achnanthes is 32.1 per cent, while a com-
parable figure for Synedra is 26.4 per cent. At every depth on all
sampling days, these two organisms together comprised greater than fifty
per cent of the total count.
TABLE IV
GENERA OF ORGANISMS OBSERVED IN NATURALLY
OCCURRING PERIPHYTON, STONY POINT BAY, LAKE SUPERIOR, 1966.
Phylum Chrysophyta Melosira
Navicula
Class Bacillariophyceae Nitzschia
Achnanthes Rhizosolenia
Amphora Surirella
Asterionella Synedra
Cocconeis Tabellaria
Cyclotella Unidentified
Cymatopleura Class Chrysophyceae
Cymbella Dinobryon
Dlatoma-Denticula Phylum Chlorophyta
Fragilaria Ankistrodesmus
Gomphonema Closterium
38
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TABLE IV (Continued)
Phylum Chlorophyta (Continued)
Scenedesmus
Tetraedron
Phylum Cyanophyta
Merismopedia
600
400
-S
c
O
200
0
Figure
Depth in Feet
30
Mean total counts of naturally occurring periphyton
at the standard sampling depths, Stony Point Bay,
Lake Superior, 1966.
39
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TABLE V
PHYLA. AND COUNTS OF ORGANISE OBSERVED IN
NATURALLY OCCURRING PERIPHYTON, STONY POINT BAY,
LAKE SUPERIOR, 1966. ORGANISMS x 103 PER SQUARE
CENTIMETER OF ROCK SURFACE.
Date
Depth
in Feet Phylum
Chrysophyta
Chlorophyta
2.5 Cyanophyta
Total
Chrysophyta
5 Chlorophyta
Cyanophyta
Total
Chrysophyta
Chlorophyta
10 Cyanophyta
Total
8-9
N.S.*
N.S.
568.1
5.0
5.0
578.1
8-17
319.9
4.6
2.3
326.8
710.1
5.2
2.6
717.9
271.8
1.8
...
273.6
8-23
417.5
...
...
417.5
592.3
2.6
...
597.5
523.5
2.8
...
526.3
8-25
562.3
...
...
562.3
551.0
...
...
551.0
419.6
3.2
...
422.8
9-6
641.2
3.4
6.7
651.3
470.8
9.0
...
479.8
360.4
...
3.4
363.8
Chrysophyta 703.9 172.7 N.S. 193.9 389.7
15 Chlorophyta — — —
Cyanophyta — — -•— —
Total 703.9 172.7 193.9 389.7
Chrysophyta 699.6 355.3 321.8 504.4 446.0
20 Chlorophyta — 2.8 5.4 — —
Cyanophyta _IH_ _I^L_ _1II_ 2.6 —
Total 699.6 358.1 327.2 507.0 446.0
Chrysophyta 778.7 759.6 491.9 525.4 623.1
35 Chlorophyta — — —-
Cyanophyta 3.0 _n^_ —-. 2.6 1.9
Total 781.7 759.6 491.9 528.0 625.0
*N.S. means no sample was collected because of rough weather. Three
dashes mean zero.
40
-------
TABLE VI
COUNTS AND PERCENTAGE CONTRIBUTION TO THE TOTAL OF
THE SEVEN MOST COMMON ORGANISMS OBSERVED IN THE
NATURALLY OCCURRING PERIPHYTON, STONY POINT BAY,
LAKE SUPERIOR, 1966. ORGANISMS x 103 PER SQUARE
CENTIMETER OF ROCK SURFACE AND PERCENTAGE.
Depth
Organism in Feet 8-9
8-17
Achnanthes 2.5 N.S.*
N.S.
5 N.S.
N.S.
10 259.
44.
15 274.
38.
20 148.
21.
35 323.
41.
Synedra 2.5 N.S.
N.S.
5 N.S.
N.S.
10 134.
23.
15 150.
21.
128.9
42.8%
356.5
49.7%
1
8%
1
9%
3
2%
4
4%
5
3%
9
4%
60
22
52
30
147
41
238
31
76
25
174
24
83
30
54
31
.4
.1%
.7
.9%
.3
.1%
.9
.5%
.0
.2%
.0
.2%
.5
.5%
.8
.7%
8-23
133.0
31.9%
248
41
124
23
N.S
N.S
119
36
122
25
99
23
97
16
166
31
N.S
N.S
.7
.6%
.3
.6%
•
•
.1
.4%
.9
.0%
.4
.8%
.9
.4%
.8
.7%
•
•
8-25
121.
21.
224.
40.
123.
29.
40.
21.
113.
22.
147.
28.
208.
37.
81.
14.
116.
27.
5
6%
9
7%
0
1%
9
1%
0
3%
9
0%
0
0%
8
8%
7
6%
73.2
37.8%
9-6
175.
26.
172.
35.
115.
31.
133.
34.
108.
24.
129.
20.
185.
28.
96.
20.
71.
19.
5
9%
1
9%
6
8%
1
2%
5
3%
1
7%
6
5%
6
1%
4
6%
109.7
28.1%
Mean
139.
30.
250.
42.
136.
30.
125.
31.
127.
29.
192.
29.
142.
28.
112.
18.
7
8%
5
0%
4
3%
2
2%
2
1%
4
3%
2
6%
5
9%
114.5
26.5%
97.1
29.8%
*N.S. means no sample was collected. Three dashes mean zero.
41
-------
TABLE VI (Continued)
Depth
Organism in Feet 8-9 8-17 8-23 8-25 9-6 Mean
20 257.4 78.4 56.8 168.0 112.4 134.6
36.8% 21.9% 17.4% 33.1% 25.2% 26.9%
35 206.6 156.2 127.7 126.8 177.8 159.0
26.4% 20.6% 26.0% 24.0% 28.4% 25.1%
Unidentified 2.5 N.S. 25.3 65.9 78.2 148.5 79.4
Diatoms N.S. 8.4% 15.8% 13.9% 22.8% 15.2%
N.S. 71.3 84.7 163.6 105.7 106.3
N.S. 9.9% 14.2% 29.6% 22.0% 18.9%
10 64.8 33.8 90.5 72.5 74.8 67.2
11.2% 12.4% 17.2% 17.1% 20.6% 15.7%
15 73.2 12.6 N.S. 38.8 79.4 51.0
10.4% 7.3% N.S. 20.0% 20.4% 14.5%
20 69.8 44.0 59.5 95.0 104.7 74,6
10.0% 12.3% 18.2% 18.7% 23.5% 16.5%
35 80.9 125.6 78.0 105.7 134.7 104.9
10.3% 16.5% 15.9% 20.1% 21.6% 16.9%
Cymbella 2.5 N.S. 25.3 25.4 86.5 27.0 41.0
N.S. 8.4% 6.1% 15.4% 4.1% 8.5%
5
N.S.
N.S.
7.9
1.1%
66.1
11.1%
24.5
4.4%
27.2
5.7%
31.4
5.6%
10 34.9 26.7 48.1 22.1 27.2 31.8
6.0% 9.8% 9.1% 5.2% 7.5% 7.5%
42
-------
TABLE VI (Continued)
Depth
Organism in Feet 8-9
15 64
9
20 21
3
35 26
3
Nevicula 2.5 N.S
N.S
5 N.S
N.S
10 34
6
15 36
5
20 48
6
35 21
2
Cocconeis 2.5 N.S
N.S
5 N.S
N.S
10 5
.0
.1%
.9
.17.
.9
.4%
•
•
•
•
.9
.0%
.6
.2£
.0
.9%
.0
.7Z
*
•
*
•
.0
.9%
8-17
8.
4.
19.
5.
33.
4.
27.
9.
29.
4.
12.
4.
19.
11.
19.
5.
21.
2.
2.
*
18.
2.
12.
4.
4
97.
3
47.
7
4%
6
27.
0
0%
4
5%
0
0%
3
42
4
8%
3
8%
5
6%
4
5%
8-23
N.S.
N.S.
16.
5.
26.
5.
42.
10.
42.
7.
23.
4.
N.S.
N.S.
2
0%
0
3%
8
3%
3
1%
2
4%
N.S.
0%
35.
7.
1.
*
7.
1.
22.
4.
5
2%
2
3%
9
3%
6
3%
8-25
17.
8.
23.
4.
13.
2.
37.
6.
32.
5.
18.
4.
6.
3.
28.
5.
34.
6.
4.
*
2
9%
1
6%
2
57.
1
6%
7
97.
9
57.
5
4%
3
67.
3
5%
1
77.
«•«•••
0%
12.
3.
6
0%
9-6
28
7
23
5
26
4
84
13
33
6
27
7
11
3
7
1
39
4
6
1
9
1
10
2
Mean
.0
.2%
.3
.2%
.2
.2%
.4
.0%
.2
.9%
.2
.5%
.7
.0%
.8
.7%
.9
.8%
.7
.0%
.0
.97.
.2
.8%
29
7
20
4
25
4
48
9
34
6
23
5
1
5
20
3
28
4
3
8
1
12
3
.4
.5%
.8
.77.
.2
.07.
.0
.87.
.3
.07.
.2
.47.
.8
.77.
.7
.9%
.4
.8%
.6
.7%
.9
.57.
.6
.11
43
-------
TABLE VI (Continued)
Depth
Organism in Feet 8-9
15 45.7
6.5%
20 91.7
13.1%
35 24.0
3.1%
Gomphonema 2.5 N.S.
N.S.
5 N.S.
N.S.
10
0%
15 18.3
2.6%
20 4.4
.6%
8-17
8.4
4.9%
12.4
3.5%
91.9
12.1%
9.2
3.1%
31.7
4.4%
1.8
.7%
0%
11.0
3.1%
8-23
N.S.
N.S.
13.5
4.1%
14.2
2.9%
39.3
9.4%
18.5
3.1%
10.5
2.0%
N.S.
N.S.
18.9
5.8%
8-25
0%
2.6
.5%
21.1
4.0%
16.5
2.9%
12.3
2.2%
3.2
.8%
0%
23.1
4.6%
9-6
11.7
3.0%
23.3
5.2%
43.0
6.9%
10.1
1.6%
3.0
.6%
0%
2.3
.6%
11.6
2.6%
Mean
16.5
3.6%
28.7
5.3%
38.8
5.8%
18.8
4.3%
16.4
2.6%
3.1
.7%
4.1
.8%
13.8
3.3%
35 47.9 15.3 28.4 18.5 18.7 23.8
6.1% 2.0% 5.8% 3.5% 3.0% 4.1%
44
-------
Figure 5. Achnanthes microcephala
Figure 6. Synedra acus
45
-------
According to Smith (1950) Acnanthes is found in both salt and
fresh water and is usually attached by means of a gelatinous stalk to
some firm object. About a dozen species have been reported for the
United States. In 1966 on August 17, this genus reached its maximum
in Stony Point Bay in terms of absolute numbers (356,500/cm2) and
percentage of the total growth (49.7 per cent). The species was
Acnanthes microcephala.
Synedra (Figures 5 and 6) was the second most common organism
and it reached a maximum of 257,400 per square centimeter on August 9
at a depth of twenty feet. At five feet, the percentage contribution
of Synedra to the total remained low throughout the season in comparison
to the other depths. The fact that Achnanthes was higher than normal
at this depth suggests an upset in the balance evidently existing be-
tween these two genera. Smith (1950) states that Synedra occurs in a
variety of habitats. The smaller species are usually sessile and form
a brownish-green layer on stones and woodwork in running water while
the larger species are either free-floating or occur epiphytically in
lakes. Twenty-five species occur in the United States. The predominant
species of Synedra found in the Stony Point Bay periphyton is shown in
Plate 2.
The unidentified organisms category listed in Table VT include
small pieces of broken organisms, atypical forms which were impractical
to identify, and a number of organisms which were "naviculoid" in
appearance but which could not with certainty be assigned to the genus
Navicula.
The remaining diatoms in Table VI, Cymbella. Navicula. Cocconeis.
and Gomphonema. each comprise an average of less than seven per cent
of the total at all depths. Figures 8 through 15 are photomicrographs
of common species from these four genera.
Cvmbella. with an average mean percentage for all depths of 6.3 per
cent, was the fourth most common organism. Smith (1950) states that
this organism may be either free-floating or sessile. The sessile spe-
cies may be found singly at the tip of a stout gelatinous stalk or may
occur grouped seriately within branched gelatinous tubes. A typical
Cvmbella ventricosa tube and its incii ded organisms are shown in
Figure 8. Cymbella lanceolate (Figure 9) typically grows at the tip of
a stalk, which, in this case, has been incinerated. Cymbella. like
Navicula. Cocconeis. and Gomphonema. shows no marked seasonal variations
in Stony Point Bay. However, the means of the numbers and percentages
at each depth indicate that Cymbella decreases with increasing depth.
Navicula (Figures 10 and 11) comprises on the average 6.1 per
cent of the total at all depths and is the only one of the seven organ-
isms listed which is usually free-floating. Navicula is motile and
probably moves at will among the other members of the attached periphy-
ton. Strictly speaking, organisms that are not attached but live with
the periphyton constitute a part of the merophyton. Navicula. like
Cvmbella. seemed to decrease as the depth of the water increased.
46
-------
Figure 7. Synedra ulna
Figure 8. Cymbella ventricosa
-------
Cocconeis. with an average mean percentage at all depths of 3.7
per cent, was the sixth most abundant organism. Four species of this
predominantly marine genus occur in fresh water. All grow attached,
with the hypotheca flattened against the substratum. Figures 12 and 13
show two species commonly found in Stony Point Bay. Cocconeis. unlike
Cymbella and Navicula. was more common in samples from deeper water.
Gomphonema comprised on the average 2.6 per cent of the total
count at all depths. According to Smith (1950), the frustules "are
usually epiphytic and borne at the tips of a dichotomously branched
system of gelatinous stalks." This method of attachment is illustrated
by Figure 14. Here, the organisms appear in girdle view. Figure 15
represents the valve view. Gomphonema occurred in highest percentages
at 2.5 and thirty-five feet. The minimum occurred at ten and fifteen
feet.
The dry weights of the 1966 samples are presented in Table VII.
Results are expressed as milligrams of dry weight per square centimeter
of rock surface. Because the samples used for counting and those used
for the weight determinations were taken from the same periphyton-water
suspension, each weight is representative of a corresponding count.
The weights, according to the mean weight at each depth, were lowest
at 2.5 feet and gradually reached their peak at fifteen feet. The var-
iations of the weights, if viewed alone, would be expected on the basis
of the factors already discussed, namely, dislodgement of the periphyton
by waves in the shallow water and lower numbers due to the decrease in
light and temperature in the deeper water. The fact that the counts
(Figure 4 and Table V) do not correlate with their corresponding dry
weights (Table VII) may be due to the variation in the sizes of the in-
dividual organisms at each depth. Thus, if the total count at a par-
ticular depth is high and the corresponding dry weight is low, one
could surmise that the individual organisms were of a small size. By
the same token, larger organisms in smaller numbers could cause a high-
er dry weight. This disparity might also be explained by the presence
of varying amounts of sand in the periphyton-water suspensions or by
the presence of empty diatom frustules. Both of these factors could
cause fluctuations in the dry weights.
It is most probable that rough water dislodged and suspended
both periphyton and sand in Stony Point Bay. The sand, of course,
would settle rapidly on the rocks and is probably included in the dry
weights, while some of the periphyton, which would take longer to
settle out, was carried away by the current. This theory explains why
tiie weights were high when the counts were low and vice versa. In an
attempt to determine why the counts did not correlate with the dry
weights the methods were modified in 1967. In that year, the ash-free
dry weight, or organic weight, of the periphyton was determined.
On the basis of the average of the 1966 mean dry weights for all
of the depths, the total biomass, or standing crop, of the Stony Point
Bay periphyton was calculated to be 37.1 tons (104 g./m.2). The fact
48
-------
Figure 9. Cymbella lanceolata
Figure 10. Navicula radiosa
49
-------
-.1
I v
Figure 11. Navicula reinhardii
* *
Figure 12. Cocconeis flexella
50
-------
*£^
• ;£
^
1*
V
Figure 13. Cocconeis placentula
>*
Figure 14. Gomphonema sp.
51
-------
Figure 15. Gomphonema olivaceum
f
Figure 16. Amphora ovalis v. pediculus
52
-------
N\
Figure 17. Asterionella formosa
Figure 18. Ceratoneis arcus
53
-------
Figure 19. Cyclotella sp.
Large Cyclotella bodanica
•m
Small Cyclotella antiqua
Figure 20. Cymatopleura solea
54
-------
€*-. , r
figure 21. Denticula thermalts
«fc*
Figure 22. Diatoma vulgare
55
-------
•"2
n
,- 4
Figure 23. Dtatoraa vulgare
Figure 24. Fragilaria capucina
:.
-------
* ^
.
-
Figure 25. Fragilaria crotonensis
* «* . •
I J
n\
I)
Figure 26. Fragilaria harrisonii
57
-------
*
'£
Figure 27, Frustulia viridula
Figure 28. Goraphoneis herculeana
-------
Figure 29. Gyrosigma attenuatum
Figure 30. Nitzschia vermicularis
59
-------
o
•
* /
Figure 31. Nitzschia palea
Figure 32. Melosira granulata
60
-------
Figure 33. Melosira varians
t r
Figure 34. Pinnularia viridis
61
-------
%
•>*
Figure 35. Rhizosolenia eriensis
Figure 36. Rhoicosphenia curvata
62
-------
Figure 37. Tabellaria fenestrata
Figure 38. Tabellaria flocculosa
63
-------
I
Figure 39. Surirella angustata
•
Figure 40. Surirella ovata v. pinnata
64
-------
that this figure is lower than the comparable figure (54.4 tons or 153
g./m.2) for 1965 is probably due to the rough weather of 1966. Even
though six depths were sampled during 1966, as compared to three for
1965, the average depth sampled was just about the same for the two
years.
The results of 1967 are presented in three sections. The first
deals with the naturally occurring periphyton of Stony Point Bay. The
second section is concerned with regrowth studies made in the same
area while the third includes the results of studies conducted in areas
other than Stony Point Bay along Lake Superior's north shore.
TABLE VII
NATURALLY OCCURRING PERIPHYTON DRY WEIGHTS AT THE STANDARD
DEPTHS, STONY POINT BAY, LAKE SUPERIOR, 1966
MILLIGRAMS PER SQUARE CENTIMETER
OF ROCK SURFACE.
Date
8-9
8-17
8-23
8-25
9-6
Mean
2.5
N.S.*
7.5
2.5
10.0
6.0
6.5
5
N.S.
15.1
4.8
3.1
5.4
7.1
Depth
10
19.7
5.1
7.3
6.0
13.0
10.2
in Feet
15
30.0
6.0
N.S.
10.0
10.2
14.0
20
32.0
12.4
2.1
11.0
9.5
13.4
25
9.9
24.3
5.3
9.2
9.7
11.6
*N.S. means no sample was collected.
Naturally occurring periphyton. Stony Point Bay.
During 1967, routine sampling was carried on between July 11 and
September 15. An additional sampling trip was made on November 10.
From July 11 to November 10, samples were collected on seventeen days.
On each day, three rocks were obtained from each of the six standard
sampling depths (2.5. 5, 10, 15, 20 and 35 feet). A total of 306
rocks was collected.
The numbers of organisms found at each depth are presented in Fig-
65
-------
ure 41. Each point represents the mean count of seventeen samples col-
lected from one particular depth during the sampling season. The means,
rounded off to the nearest ten thousand, range from a maximum of
2,116,000 per square centimeter at 2.5 feet to a minimum of 1,034,000
per square centimeter at thirty-five feet. The downward trend in the
counts as the depth increases is logical in view of certain facts.
With increasing depth, light penetration is diminished and the temper-
ature drops. The decrease in these two factors results in the general-
ly lower periphyton populations which are shown in Figure 41. A mean
of the counts at all depths is 1,470,000 organisms per square centi-
meter of rock surface. The mean of the 1967 counts for all depths was
three times as high as the comparable figure for 1966. This three-
fold differential did not hold true at each depth, thus accounting for
the difference in the shape of the curves. The greatest differences
occurred in shallow water. At 2.5 feet, the 1967 mean count was more
than four times as high as the 1966 mean count at the same depth. At
five and ten feet, the 1967 means were greater than three times those
of the comparable 1966 means. At fifteen and twenty feet, the 1967
mean counts were less than three times those of 1966, while the 1967
count at thirty-five feet was less than twice as high as the 1966
thirty-five foot mean count. These findings further substantiate the
hypothesis that bad weather adversely affects periphyton growth, par-
ticularly in shallow water. The summer of 1967 was characterized by
ideal weather conditions. High numbers of organisms were present that
year because violent storms did not dislodge the periphyton nor stir
up the bottom to produce deleterious turbidity. Climatological records
show that during the 1967 sampling season (sixty-seven days) east
winds occurred on only eleven days, or sixteen per cent of the time.
No northeast winds occurred. In contrast, east and northeast winds
occurred during thirty-nine per cent of the 1966 sampling season.
While it is felt that the differing weather conditions which occurred
during the two years are primarily responsible for the variations in
the counts, the twofold decrease in the counts at thirty-five feet may
have been caused by factors other than, or in addition to, the weather.
The variations in the total counts of organisms according to date
are presented in Figures 42 through 47. Since, in this case, each
count is an actual count and not a mean these curves show greater var-
iation than does Figure 41. However, the figures reflect the general
decrease with depth shown by Figure 41. This can readily be seen if
the graphs are superimposed and the area below each curve is inspected.
The greatest variation is shown in the counts from samples obtained
from shallow water.
While it is impossible to explain precisely the causes for each
dip and rise in these six curves, it is possible to surmise the reason
for the similarity between the curves for the four relatively shallow
depths (2.5, 5, 10, and 15 feet). A plausible explanation can also
be offered for the similarity between the twenty and the thirty-five
foot curves. The variability exhibited by the shallower water counts
(Figures 42-45) is probably due to the effect of wave action upon the
66
-------
-------
380}
2700
1800
c
? 900
o
•J
o.
\.
0 ~
CO 00 00
Date
it. 15
» ...
OOOOOOODOlO)
Figure 42. Naturally occurring periphyton, total counts at
2.5 feet, Stony Point Bay, Lake Superior, 1967.
3600
«N
E 2700
D
a
Ul
in
'£
reoo
MO
0 L
aoaoaoO)
Figure 43. Naturally occurring periphyton, total counts at
5 feet, Stony Point Bay, Lake Superior, 1967.
68
-------
3600]
-------
E 27001
X
in
£
WOO
c
?' 900
o
ts CD 00 00
Date
Figure 46. Naturally occurring periphyton, total counts at
20 feet, Stony Point Bay, Lake Superior, 1967.
3GOO
2700
o
L.
01
Q.
? 1800
c
iJJitJ
Do/c
Figure 47. Naturally occurring periphyton, total counts at
35 feet, Stony Point Bay, Lake Superior, 1967.
70
-------
A checklist of the organisms encountered while making the above
counts is presented in Table 8. The total number of genera observed
was thirty-eight. Sixty-eight per cent, or twenty-six genera, be-
long to the phylum Chrysophyta. Only one of these twenty-six genera,
Dinobryon, is not a diatom. There were seven genera of green algae
and five blue-green algae. Only these three phyla were represented.
The checklist can be broken down further into sixty-one recognized
species. Of the sixty-one species, forty-seven (seventy-seven per
cent) were diatoms. Eight species of Chlorophyta and five species of
Cyanophyta are reported.
Fourteen more genera of naturally occurring periphyton were en-
countered during 1967 than were found in the 1966 samples. In both
years, however, the proportion of diatom genera to greens and blue-
greens remained constant. The twenty-four genera encountered during
1966 (Table IV) were also present in 1967. The fourteen additional
genera found in 1967 were: Chrysophyta - Ceratoneis, Frustulia.
Gomphoneis. Gyrosigma. Pinnularia. Rhoicosphenia. and Stauroneis;
Chlorophyta - Cladophora. Pediastrum. and Spirogyra; Cyanophyta -
Anabaena. Lyngbya. Oscillatoria. and Raphidiopsis.
The number of organisms found is indicated by the mean total
counts as shown in Figure 41. It will be noted that the means of the
totals are used as points on the curve in this figure whereas the means
of the total at each depth are plotted in Figures 42 through 47*
In all cases, Chrysophytes were by far the most abundant organisms,
ranging from a minimum of 88.2 per cent of the total at twenty feet on
September 15 to 100 per cent of the total in samples collected on Nov-
ember 9 at 2.5, 15 and 35 feet and on July 17 at 2.5 feet. With the
one exception indicated, Chrysophytes always comprised at least 90% of
the total population.
Chlorophytes, or green algae, were found in only 73 of 102 samples,
or 71 per cent of the time. Blue-greens were more abundant and occurred
in 87 per cent of the samples.
Hhen results from the years 1966 and 1967 were compared it was
found that the Chrysophytes were the predominant forms during both years.
This was true for every sample from every depth. In many instances dia-
toms comprised the entire population and Dinobryon was the only genus
of the Chrysophyta observed which was not a diatom.
The phyla Chlorophyta and Cyanophyta showed some variations in
frequency of occurrence for the two year period. In 1966, greens were
found in forty per cent of the samples, as contrasted with sixty-seven
per cent in 1967. A similar rise in the blue-greens occurred during
1967. In 1966, the Cyanophytes were represented only by Merismopedia.
which was present thirty-seven per cent of the time, whereas five genera
of blue-greens occurred in 1967. Cyanophytes, in that year, were seen
in eighty-seven per cent of the samples.
71
-------
TABLE VIII
ORGANISt-E OBSERVED IN NATURALLY OCCURRING
PERIPHYTON, STONY POINT BAY, LAKE SUPERIOR, 1967.
Phylum Chrysophyta
Class Bacillariophyceae
Achnanthes mlcrocephala
(Kuetzing) Cleve +
Amphora oval is
Kuetzing *+
Amphora normani
Rabenhorst *
Asterionella formosa
Hassall +
Ceratonels arcus
(Ehrenberg) Kuetzing
Cocconeis group:
•
~" (Kuetzing) Cleve +
C. pediculus
Ehrenberg
£. placentula
Ehrenberg +
Cvclotella antiqua
Wm. Smith * +
Cvclotella group:
C_. bodanlca
Eulenstein var.
michiganensis Skvortzow +
C. menegfainiana
Kuetzing
£. michiganiana
Skvortzow
Cvmatopleura solea
(Brebisson) Win. Smith* +
Cymbella group A:
C. cistula
"" (Hemprich) Grunow
£. lanceolata
"" (Ehrenberg) Van Heurck +
Cymbella group B:
£. vent ri cos a
Kuetzing +
C. amphicephala
Naegeli
Denticula thermalis
Kuetzing +
Diatoma elongatum
C.A. Agardh var. tenuis
(Agardh) Van Heurck
Fragilaria capucina
Desmazieres +
Fragilaria crotonensis
Kitton * +
Fragilaria harrisonii
(Win. Smith) Grunow* +
Frustulia viridula
(Brebisson) DeToni +
Gomphoneis herculeana
(Ehrenberg) Cleve * +
Gomphonema group +
Gyrosigma attenuatum
(Kuetzing) Cleve * +
Melosira granulata
(Ehrenberg) Ralfs 4-
Melosira yarians
C. A. Agardh * 4-
Navicula group:
N. dicephala
(Ehrenberg) Wm. Smith
N. radiosa
Kuetzing +
N. reinhardtii
"~ (Grunow) Van Heurck+
N. rfayncocephala
Kuetzing
Nitzschia denticula
(Grunow) *
Nitzschia palea
(Kuetzing) Vta. Smith*+
Nitzschia sigmoidea
(Nitzsch) »n. Smith *
*0rganisms found on less than eight of the seventeen sampling days
-t-Refer to List of Plates in Table of Contents for location of photo-
micrograph of this organism.
72
-------
TABLE VIII (Continued)
Nltzschia vermicularIs
(Kuetzing) Hantzsch +
Pinnularia virldis
(Nitzsch) Ehreaberg * +
Rhizosolenia erlensis
H. L. Smith +
Rhoicosphenia curvata
(Kuetzing) Grunow * +
Stauroneis producta
Grunow *
Surirella group:
S. angusta
Kuetzing +
£>. ovalis
Brebisson
S. ovalis
Brebisson var. pinnata
Wn. Smith +
Synedra acus
Kuetzing +
Synedra ulna
(Nitzsch) Ehrenberg+
Tabellaria fenestrata
(Lyngbye) Kuetzing +
Tabellaria flocculosa
(Roth) Kuetzing +
Class Chrysophyceae
Dinobryon sertularla
Phylum Chlorophyta
Ankis trodesmus falcatus
(Corda) Ralfs *
Cladophora glomerata
(Linmaeus) Kuetzing*
Closterium sp. *
Pediastrum duplex
Meyen *
Scenedesmus acuminatus
(Lagerheim) Chodat*
Scenedesmus quadrlcauda
(Turpin) Brebisson
Spirogyra sp. *
Tetraedron sp. *
Phylum Cyanophyta
Anabaena sp.
Lyngbya sp.
Merismopedia convoluta
Brebisson
Oscillatoria sp.
Raphidiopsis curvata
Fritsch *
73
-------
The eight groups of organisms which were commonly found and whose
average mean percentage composition at all depths was greater than one
per cent were:
1. Synedra acus
2. Achnanthes microcephala
3. Navicula group
4. Cymbella group
5. Gomphonema group
6. Cocconeis group
7. Blue greens
8. unidentified Diatoms
On the average these 8 groups comprised 93 per cent of the count
at all depths. With the exception of the "blue-greens", which were not
satisfactorily identified, all were diatoms. The blue-greens appeared
to be a very small species of Oscillatoria. Synedra acus and Achnanthes
microcephala were the outstanding organisms in each sample. For exam-
ple, the average of the mean percentages at all depths for Synedra acus
was 47.2 per cent, while a comparable figure for Achnanthes microcephala
was 28.1 per cent. On the average, therefore, these two diatoms com-
prised seventy-five per cent of any one sample.
Synedra acus (Figure 6),reached its maximum of 2,523,000 per
square centimeter at a depth of 2.5 feet on July 27. On the basis of
mean counts, it can be seen that Synedra acus. in both absolute numbers
and percentages of the total, decreased as the depth increased. In
general, however, the counts at the twenty and thirty-five foot depths
rose seasonally.
Achnanthes microcephala (Figure 5), the second most common or-
ganism of 1967, reached its maximum (l,002,000/cm.2) on August 25 at
a depth of twenty feet. As with Synedra acus. a marked variation
according to depth occurred. In this case, however, the means of Ach-
nanthes microcephala rose with increasing depth.
In comparing the per cent contribution to the total at each depth
on each day for Achnanthes microcephala and Synedra acus. a balance
was found between these two organisms. When the percentage of one
was low, the other was high, and vice versa. In most instances, the
combined percentage of these two diatoms was somewhere between seventy
and eighty per cent.
In 1966, the genus Achnanthes was the predominant organism, with
an average mean percentage contribution to the total of 32.1 per cent,
while Synedra was second with a comparable figure of 26.4 per cent.
Together, therefore, they averaged about fifty-nine per cent of the
total. In 1967, on the other hand, these two diatoms comprised seventy-
five percent of the total, with Synedra acus averaging 47.2 per cent
of the total and Achnanthes microcephala 28.1 per cent. The changes
74
-------
that occurred in the individual order of predominance of these two and
their combined contribution to the total in 1967 were probably due to
several interrelated factors. The genus Achnanthes grows at the tips
of gelatinous stalks which are attached to rocks by means of specialized
holdfasts. Synedra. on the other hand, attached itself with a small
amount of adhesive material secreted from one end of its frustule.
These organisms are often found free-floating, while Achnanthes is
rarely found unattached. The rough weather that had occurred during
1966, therefore, probably dislodged a proportionately greater number
of Synedra than Achnanthes because of Achnanthes' superior mode of
attachment. The counts reflected this in showing more Achnanthes than
Synedra,
In 1967, calm weather prevailed and both organisms were subjected
to optimal growth conditions. The results of 1967 show that Synedra
acus "prefers" shallow water, for here the greatest numbers occurred.
Achnanthes, in contrast, was proportionately more common in the deep
water. Since bad weather in 1966 caused a great amount of turbulence
in the shallow water, Synedra was adversely affected and, in that
year, was exceeded in numbers by Achnanthes.
In 1967, the third most commonly occurring organism in the natur-
ally occurring periphyton of Stony Point Bay was Navlcula. with an av-
erage mean percentage of the total of 5.8 per cent. Two of the common-
ly occurring species are shown in Figures 10 and 11. The species in-
cluded in this group are presented in Table VIII. In general, it was
observed that Navlcula increased with increasing depth. The maximum
reached by this organism was 436,000 per square centimeter. In 1966,
Navicula was the fifth most abundant organism and comprised, on the
average, 6.1 per cent of the total at all depths.
The fourth most numerous organism in 1967 was Cymbella (group B,
Table VIII). This group is made up of the smaller species of Cymbella
and was most frequently represented by Cymbella ventricosa ( Figure 8 ).
The average mean percentage contribution to the total for all depths
was 5.4 per cent. If all the species of Cymbella observed in 1967 had
been grouped together, as they were in 1966, their average mean percen-
tage contribution to the total would have been 6.0 per cent. In 1966,
the genus Cymbella averaged 6.3 per cent of the total and was the fourth
most common genus. In both 1966 and 1967, Cymbella decreased, in abso-
lute numbers and percentage of the total, with increasing depth. The
1967 maximum for CyrobeHa group B was 262,000 per square centimeter,
Numberically, the fifth most common organism in 1967 was Gompho-
nema (Figures 14 and 15), which constituted an average of 2.5 per cent
of the total at all depths. In 1966, this genus ranked seventh and
averaged 2.6 per cent of the total. In the first year, no definite
depth "preference" was noted for this organism, although the highest
percentages occured at 2.5 and thirty-five feet. In 1967, the thirty-
five foot counts were the highest, in both absolute numbers and percen-
tage of the total.
75
-------
The sixth most abundant organism for both years was Cocconeis
(Figures 12 and 13). It averaged 3.7 per cent of the total for all
depths in 1966 and 1.5 per cent in 1967. In both years, this organism
was more common in the deeper water.
The last two groups, the unidentified blue green (probably
Oscillatoria) and unidentifiable diatoms occupied the seventh and
eighth positions in terms of abundance. The average mean percentage
contribution to the to the total was 1.5 per cent for the blue-greens
and 1.0 per cent for the diatoms.
The photomicrographs (Figures 16 through 40), show representative
species of diatoms found as a part of the 1967 naturally occurring per-
iphyton in Stony Point Bay. The photomicrograph of Rhizosolenla erien-
sis (Figure 35) is somewhat unusual, inasmuch as its delicate frustules
usually do not survive the incineration process used in preparing per-
manent slides.
The dry and ash-free (organic) dry weights of all the 1967 Stony
Point Bay samples are presented in Tables IX and X. The ash-free dry
weights are shown graphically by Figures 48 through 53. Each weight
is representative of a corresponding count, since samples for both de-
terminations were taken from the same periphyton-water suspension.
The dry weights (Table IX), in terms of mean weights for each depth,
were highest at 2.5 feet and lowest at thirty-five feet. With the ex-
ception of the fifteen and twenty foot means, which were almost identi-
cal, the dry weights decreased with increasing depth. The mean ash-
free dry weights (Table X) were highest at 2.5 feet and dropped regular-
ly to their minimum at fifteen feet.
On the basis of the average of the 1967 mean dry weights for all
depths, the total dry weight of the Stony Point Bay periphyton was cal-
culated to be 55.5 tons (156 g./m.2). The corresponding figure for the
ash-free dry weights is 4.4 tons (12 g./m.2) or 7.9 per cent of total
dry weight.
When the means for the dry and ash-free dry weights are compared
to the mean total counts for the six depths (Figure 4), it can be seen
that both the dry and the ash-free dry weights, with one exception,
vary with depth as do the mean counts. This apparent correlation be-
tween counts and weights is in distinct contrast to the situation ob-
served in 1966. In that year, the relationship between the mean dry
weights and the mean counts at the standard depths was inverse. When
the cdunts rose, the weights dropped, and vice versa. The lack of
correlation was attributed to the presence of sand in the samples.
The 1967 data support this hypothesis, for in that year storm-caused
turbulence was at a minimum and the mean ash-free and dry weights, in
general, varied directly with the mean counts at each depth. The fac-
tors causing variations in the counts, therefore, can also be cited
as causing variations in the weights. These factors were primarily the
76
-------
TABLE IX
NATURALLY OCCURRING PERIPHYTON DRY WEIGHTS AT THE
STANDARD SAMPLING DEPTHS, STONY POINT BAY, LAKE SUPERIOR, 1967.
MILLIGRAMS PER SQUARE CENTIMETER OF ROCK SURFACE.
Depth in Feet
Date
7-11
7-13
7-17
7-20
7-26
7-27
8-2
8-4
8-8
8-10
8-14
8-17
8-25
8-28
9-5
9-15
11-10
Mean
2.5
28.8
30.0
19.7
33.3
39.8
38.9
28.9
14.8
21.2
12.5
27.9
21.4
21.9
23.3
52.0
39.5
21.3
27.9
5
7.4
8.7
26.1
10.7
18.4
17.2
14.4
5.9
19.8
20.3
11.7
13.6
36.0
29.6
21.5
28.8
20.3
18.2
10
9.0
4.4
9.6
10.5
16.5
17.7
16.2
12.7
10.4
9.0
9.2
14.3
44.3
10.5
12.1
10.7
17.5
13.8
15
7.8
6.2
6.1
10.8
14.5
15.2
17.6
18.8
11.3
10.6
16.7
17.9
14.0
14.8
4.8
3.1
13.4
11.9
20
3.3
9.2
7.4
4.7
8.1
7.2
8.5
13.8
27.8
11.5
15.8
12.1
20.3
9.3
13.7
17.5
17.0
12.1
35
6.0
7.9
..*
8.1
8.4
7.3
11.0
9.0
10.5
10.4
10.9
10.5
13.9
13.6
19.6
17.2
13.8
10.4
Sample was lost
77
-------
TABLE X
NATURALLY OCCURRING PERIPHYTON ASH-FREE DRY WEIGHTS AT THE
STANDARD SAMPLING DEPTHS, STONY POINT BAY, LAKE SUPERIOR, 1967.
MILLIGRAMS PER SQUARE CENTIMETER OF ROCK SURFACE.
Depth in Feet
Date
7-11
7-13
7-17
7-20
7-26
7-27
8-2
8-4
8-8
8-10
8-14
8-17
8-25
8-28
9-5
9-15
11-10
Mean
2.5
2.58
1.86
0.72
1.95
3.43
1.99
1.66
0.85
1.71
0.68
1.15
1.46
1.39
1.90
3.48
1.90
0.33
1.70
5
1.44
0.97
1.38
1.26
2.64
1.60
1.50
0.70
1.88
1.36
0.88
1.02
1.92
2.35
2.37
1.82
0.73
1.51
10
1.23
0.58
0.98
1.03
2.00
1.38
2.07
1.12
1.19
0.71
0.52
1.01
2.25
1.38
1.50
0.81
0.85
1.21
15
1.02
0.63
0.46
0.85
1.22
1.11
1.29
1.22
1.10
0.55
0.93
0.77
1.01
1.81
0.88
0.33
0.44
0.91
20
0.64
0.63
0.84
0.47
1.05
0.30
0.97
0.97
1.97
0.72
1.08
0.72
1.66
1.04
1.82
1.25
0.55
0.98
35
1.14
0.63
— *
0.69
1.07
0.96
1.09
1.04
1.58
0.80
0.82
1.61
1.18
1.48
2.32
1.65
1.17
1.20
Sample was lost
78
-------
weather, temperature and light intensity. The optimal weather conditions
of 1967 probably explain why the total weight figure (55.5 tons or 156
g/m2) for that year was higher than the 1966 figure (37.1 tons or 104
In order to eliminate inconsistencies caused by the presence of
sand, determinations of ash-free dry weights were made in 1967 even
though this factor was minimal that year. If one consults Figures 42
through 47 and compares the findings with those presented in Figures 54
through 59, it will be seen that at each depth, the individual ash-free
dry weights and the counts show an apparent positive correlation which
extends over the entire sampling season.
To test this observation, regression lines were constructed using
the least squares method. See figures 48 through 53. In constructing
these figures counts were placed on the x axis and plotted against ash-
free dry weights on the y axis. The correlation coefficients (r) and
probability values (P) are presented with the regression lines. The
correlation coefficients were positive for all depths, ranging from
.492 at fifteen feet to .775 at ten feet. Probability values ranged
from 0.05 at fifteen feet to 0.001 at ten and thirty-five feet. From
these figures, it can be stated that to predict total counts from ash-
free dry weights, one would be safest in choosing samples from ten and
thirty- five feet. At these two depths, the correlations were the best
and the probability values were lowest. The other depths also showed
positive correlations between counts and weights, but were accompanied
by slightly higher probability values.
79
-------
torn
y - 1,167,632 + 555,317x
r « .598, P • 0.02
7.0 2.0 3.0
Mg Ash-Free Dry Weight per cm2
Figure 48. Counts versus ash-free dry weights, naturally
occurring periphyton, 2.5 foot samples,
Stony Point Bay, Lake Superior, 1967.
fiBS]
V.
0.
c
3000
20V
WOO
y = 904,608 + 673,821x
r = .602, P - 0.02
I
1.0
2.0
3.0
Mg Ash-Free Dry Weight per cm2
Figure 49. Counts versus ash-free dry weights, naturally
occurring periphyton, five foot samples,
Stony Point Bay, Lake Superior, 1967.
80
-------
4000
y = 17,645 + l,240,121x
r = .775, P = 0.001
1.0
I
2.0
3.0
Mg Ash-Free Dry Weight per crrr
Figure 50,
Counts versus ash-free dry weights, naturally
occurring periphyton, ten foot samples,
Stony Point Bay, Lake Superior, 1967.
4000
—
5 3000
l_
II
Q.
-------
4000!
1= —
5 3000
«joo
y - 180,252 + 981,199x
r - .650, P = 0.005
2.0
3\0
\
t.O
Mg Ash-Free Dry Weight per cm2
Figure 52.
Counts versus ash-free dry weights, naturally
occurring periphyton, twenty foot samples,
Stony Point Bay, Lake Superior, 1967.
4000
S 3000
*•>
o
w
2000
c
I row
o
y = -83,482 + 968,704x
r • .756, P - 0.001
1.0
2.0
\
3.0
Mg Ash-Free Dry Weight per cm2
Figure 53. Counts versus ash-free dry weights, naturally
occurring periphyton, thirty-five foot samples,
Stony Point Bay, Lake Superior, 1967.
82
-------
o>
Q.
O)
£
4.0
3.0
10
\
4
/
/
*•• (*> tx fj ^b S?* ^"4 ^^ ^o *^ ^* ^
*^ ^* ^* ^^ ^^ ^^ iii *P i* i*
i!. tl ti. el cv (J. oo to eo "a to oo
00 O) O)
Date
Figure 54. Naturally occurring periphyton ash-free dry weights
at 2.5 feet, Stony Point Bay, Lake Superior, 1967.
i.O
<~
01
Q.
- 3.0
.0)
0>
Oo/e
Figure 55. Naturally occurring periphyton ash-free dry weights
at five feet, Stony Point Bay, Lake Superior, 1967.
83
-------
*fe
4.0
Q.
£ 10
0>
£
si"
1.0
Date
Figure 56. Naturally occurring periphyton ash-free dry weights
at 10 feet, Stony Point Bay, Lake Superior, 1967.
u
c.
01
s ^
.01
0)
1.0
O^T"
/•
Date
Figure 57. Naturally occurring periphyton ash-free dry weights
at 15 feet, Stony Point Bay, Lake Superior, 1967.
84
-------
T:
o
Q.
0)
tj 01
4.0
**
—I
Ci
Date
Figure 58. Naturally occurring periphyton ash-free dry weights
at 20 feet, Stony Point Bay, Lake Superior, 1967.
o
1.
b
O.
5 3.0
O)
10 JC
o o
2.0
1.0
V
el.
Figure 59.
Date
05 O)
~-i
s
Naturally occurring periphyton ash-free dry weights
at 35 feet, Stony Point Bay, Lake Superior, 1967.
85
-------
Several times reference has been made to the fact that as the
depth of the water increases in Lake Superior, the temperature drops
and the amount of light reaching the bottom decreases. This is general-
ly true even in the relatively shallow areas studied during this period
of investigation. These assumptions relative to depth, temperature
and light are substantiated by the findings presented in Table XI and
Figure 60. Table XI, for example, shows the water temperatures of
Stony Point Bay on all the collection days at each sampling depth (just
above the bottom) as well as immediately below the surface. Two trends
are obvious. The water temperatures decreased with increasing depth
and increased at all depths as the summer progressed, reaching a max-
imum around August 14. For the whole season, the highest temperature
(19.5°C.) was encountered by SCUBA divers at a depth of thirty-five
feet on July 11, twenty and thirty-five feet on July 13, and thirty-
five feet on November 10.
The light intensities reaching depths of water corresponding to
the sampling depths are presented in Figure 60. Each point on the curve
is an average of the light intensities in foot candles recorded at that
particular depth cm the seventeen sampling days. The average intensity
of the sunlight striking the deck photometer was 7,275 foot candles.
This figure was reduced to 5,600 foot candles by six inches of water.
As expected, the intensity of the sunlight diminished gradually with
depth, reaching a minimum of 265 foot candles at thirty-five feet. In
general, readings were made near mid-day.
The hypothesis that decreased light intensity is responsible for
the fact that the counts were lower in deeper water is supported by
results reported by Ryther (1956b). In studying the effect of light
on cultures of marine diatoms (Skeletonema costaturn, Nitzschia clos-
terium. and Navicula sp.), Ryther found that these organisms photo-
synthesized most effectively at light intensities of 1,000 to 2,200
foot candles. Below 1,000 foot candles, photosynthesis dropped rapidly.
At 500 foot candles, for instance, a fifty per cent reduction occurred.
From Figure 60, it can be seen that in Stony Point Bay at depths great-
er than about seventeen feet the light intensity is less than 1,000
foot candles. The minimum readings were taken at thirty-five feet
and averaged 265 foot candles. At thirty-five feet, the total counts
were, on the average, fifty per cent of the counts from 2.5 feet.
Whether or not a reduction in photosynthesis is directly related to
reduction of total counts was not determined. It seems logical to
assume, however, that a reduction in photosynthesis would retard growth
rate and, over a period of time, result in populations consisting of
fewer organisms. In this study, Ryther also found that light inten-
sities greater than 2,200 foot candles had an inhibitory effect on the
photosynthesis of the diatoms. The deleterious effect of high light
intensity on photosynthesis was less marked than the low intensity
effect. At 5,000 foot candles, relative photosynthesis was reduced
fifty per cent. The high counts of organisms from the shallow depths
of Stony Point Bay, where light intensity was probably the greatest, do
86
-------
TABLE XI
WATER TEMPERATURES AT THE SURFACE AND THE
BOTTOM AT THE STANDARD SAMPLING DEPTHS, STONY
POINT BAY, LAKE SUPERIOR, 1967. DEGREES CENTIGRADE.
Date
0.5
2.5
Depth in Feet
10 15
20
in feet
Figure 60. Average light intensity near mid-day,
Stony Point Bay, Lake Superior, 1967.
35
7-11 6.5
7-13 6.0
7-17 6.5
7-20 7.5
7-26 8.0
7-27 9.5
8-2 11.0
8-4 12.5
8-8 16.5
8-10 18.0
8-14 19.5
8-17 17.7
8-25 . 16.5
8-28 15.5
9-5 16.0
9-15 15.5
11-10 7.5
9000
^
§ 7000
(j
-io
^*M
T
c
V
-Ci
^C 3000
^ Jodo
6.5
6.0
6.5
7.5
8.0
9.5
10.5
12.5
16.0
18.0
19.5
17.0
16.0
15.5
15.5
15.0
6.5
6.0
6.0
6.5
7.0
7.5
9.0
10.5
12.5
15.0
17.5
19.0
17.0
15.5
15.5
15.0
14.5
5.5
5.5
6.0
5.5
7.0
6.5
7.5
10.5
12.0
15.0
15.0
17.5
16.0
15.5
15.0
15.0
14.5
5.0
5.5
5.0
5.5
6.0
5.5
6.0
9.5
10.0
15.0
14.5
16.0
11.0
12.0
13.5
14.0
14.5
4.5
5.0
4.5
5.5
5.5
5.0
5.0
6.5
8.0
10.0
13.5
14.0
11.0
11.0
12.5
13.5
14.0
4.5
4.5
4.5
5.0
5.0
5.0
5.0
5.5
7.0
8.5
9.5
9.5
8.3
9.5
9.5
9.5
7.0
4.5
4 — Tncidfrd Radiation
\
\
\
\
^
o & h
-
10 15
~~ — • .
20
.
i lo
i
87
-------
not indicate that Lake Superior periphyton is inhibited by high light
intensity. One explanation is that near shore, where the samples were
taken, wave-caused turbidity probably filtered out harmful light.
The kinds and numbers of organisms found in the naturally occur-
ling periphyton of oligotrophic waters have been determined only infre-
quently. Foerster and Schlicting (1965) studied the epiphytic periphy-
ton growing upon leaves of rooted aquatic plants in an oligotrophic
Texas lake. Their methods were similar to those used in this study.
SCUBA diving procedures were employed to snip leaves from submerged
plants. The leaf surfaces were washed free of periphyton and measured
for area. Foerster and Schlicting found that most of the organisms
growing on the leaves were diatoms, although five phyla of algae were
represented. On the average, the counts obtained were from 300,000 to
500,000 organisms per square centimeter of leaf surface. These counts
are comparable to those found for Lake Superior periphyton, especially
those made in 1966, when a relatively lower growth level occurred. The
diatoms found by Foerster and Schlicting included many genera observed
in Lake Superior periphyton. Examples are Achnanthes. Synedra. Navicula.
Nitzschia. Gomphonema. and Diatoma. The phyla they encountered were
the three found in Lake Superior (CJirysophyta, Chlorophyta, and Cyanophy-
ta), as well as Euglenophyta and Pyrrophyta.
Douglas (1958), in a quantitative study of naturally occurring
periphyton, dealt with the periphyton of a stream in England. She
concluded that her sampling apparatus was practical only for the collec-
tion of diatoms. Since this was a stream study, the organisms found
could be expected to differ from those found in Lake Superior. This
was not so, for the diatoms Douglas found were primarily Achnanthes, which
usually varied in numbers from 100,000 to 500,000 per square centimeter
of permanent rock surface. She recorded over a million per square cen-
timeter several times. On stones in the stream, however, the maximum
Achnanthes count was 270,000 per sqaure centimeter. The other common-
ly occurring genera were Synedra. Gomphonema. Cocconeis. Eunotia. Cer-
atoneis. and Cyrobella. Douglas concluded that the substratum and the
weather affect the number of organisms that occur. More diatoms were
present on permanent rock than on stones. Rainstorms caused high water
which scoured the substratum and removed the periphyton. The latter
finding was also made by Mclntire (1966), who observed that increased
velocity adversely affects the periphyton growth in a laboratory stream.
Lake Superior findings indicate that currents produced by storm winds
scour the rocks, particularly in shallow water, and thereby reduce
periphyton populations. Additional findings of Douglas showed that there
did not seem to be a relationship between temperature or light intensity
and growth of diatoms. In a shallow stream, however, light and tempera-
ture are not reduced by depth as they are in Lake Superior.
The general similarity between Douglas* findings and ours indicate
that the periphyton environment in Lake Superior is not entirely un-
like that of a stream. Moving masses of lake water constantly supply
88
-------
the attached growth with nutrients and flush away harmful metabolic
by-products. The analogy is especially valid for the shallow water
area of Lake Superior, for here the temperature and light intensity
probably approach levels found in streams.
Duffer and Dorris (1966), like Douglas, concluded that the sub-
stratum affects the amount of periphyton growth that is produced. In
studying the Blue River in Oklahoma, they found that "aufwuchs" pro-
ductivity was higher on a granite stustratum than it was on limestone
or sand. They concluded that a major factor in determining the magn'i- .
tude of a stream's productivity is a favorable attachment surface for
"aufwuchs". Genera of organisms found in Blue River periphyton included
Leptodictyon. Diatoma. Melosira. Synedra. Spirogyra. Rhizoclonium.
Schizothrix, and Cladophora. Duffer and Dorris also point out the fact
that high productivity is not limited to organically enriched waters.
The Blue River, Florida artesian springs, and Pacific coral reefs are
examples of oligotrophic areas with high productivity.
The fact that the bodies of flowing water just discussed support
genera of periphyton identical to Stony Point Bay genera emphasizes the
ecological similarity between the bay and a stream* Furthermore, the
findings of Douglas (1968) and Duffer and Dorris (1966) were not atypical.
In her 1948 article, Ruth Patrick states that "in fast flowing streams
only those forms which can attach themselves by gelatinous mass(es) or
stalks can survive. Thus the typical genera of such habitats are Ach-
nanthes. Cocconeis. Cymbella. and Gomphonema, Ceratoneis arcus is also
considered a typical stream species." All of these organisms were found
in Stony Point Bay periphyton, some in quite high numbers,
To classify a lake solely on the grounds of its algal components
(either phytoplankton or periphyton) would be, at best, risky. The
status of many of the so-called indicator species is uncertain. Raw-
son (1956), in a paper dealing with the phytoplankton of the Great Lakes
and large oligotrophic lakes in western Canada, discusses several of
these and questions species generally thought to be indicative of eutro-
phy. Patrick (1948), for instance, calls Asterionella formosa an indi-
cator of eutrophic water while Rawson places the same species at the
head of his list of indicators of oligotrophic waters. Often, the ab-
sence of certain groups of organisms may be as, or more, indicative
of water quality than the presence of others. Thus, in Lake Superior,
the fact that large numbers of Cyanophytes are not present is indica-
tive of oligotrophy, for blue-greens grow best in water with a high
nutrient content.
Many of the species of diatoms have a wide range of requirements
and may occur under almost any conditions. Need (1953), for instance,
found Diatoma. Nayicula, Gomphonema. Rhoicosphenia, Synedra, and Cymbel-
la_ in the periphyton of what he considered a polluted irrigation stream.
All these forms are also present in Lake Superior periphyton. It might
be added that Neel also found large numbers of blue-greens.
89
-------
As long as it is realized that the presence or absence of parti-
cular species of organisms is the result of a great variety of physical,
chemical and biological factors, biological indicators may be used to
draw certain conclusions regarding a particular body of water. The
validity of the conclusions depends a great deal on the number of phy-
sical and chemical factors known. The similarity between the abundant
forms in Lake Superior periphyton and the forms present in oligotrophic
streams and lakes suggests that the water of Stony Point Bay is relative-
ly clean. Rawson (1956) lists species of the following genera as be-
ing indicators of oligotrophy: Asterionella. Tabellaria, Dinobryon.
Fragilaria. Stephanodiscus. Staurastrum, and Melosira. In the oligo-
trophic lakes he studied, diatoms comprised eighty to ninety per cent
of the phytoplankton populations. Rawson concludes by stating that only
a few algal species can be used to indicate oligotrophy, whereas many
species are limited to eutrophic waters. Thus, some organisms need,
while others only prefer, high concentrations of nutrients. Very few,
however, prefer low nutrient concentrations. This latter group would
be indicators of oligotrophy. It is not surprising that there are so
few of them. Although Rawson was discussing only phytoplankters, it
seems logical to assume that his conclusions would also apply to or-
ganisms in the periphyton.
Regrowth of Periphyton
In 1967 studies on regrowth of periphyton on denuded rocks were
carried out during the period of July 31 to November 9. In this time
interval, eighty-four denuded, autoclaved rocks were replaced in the
lake exposed for given period and then recovered for careful examination
and quantitative measurements. The depths of exposure were ten, twenty
and thirty-five feet. "Incubation" times ranged from eight hours to
101 days. The total counts at the time of each collection for all three
depths is shown in Figure 61. In general, the counts increased with in-
creased "incubation" times. Counts of samples from ten feet were higher
than counts of twenty foot samples "incubated" for the same amount of
time. Accordingly, the twenty foot counts were higher than the thirty-
five foot counts. At ten feet, the counts reached 30,000 per square
c entimeter after forty-six days of "incubation". These ten foot counts
always remained higher than counts of samples from the other two depths
"incubated" for the same period of time. In the same forty-six day time
interval, the twenty foot counts went from 16,000 per square centimeter
to 340,600 per sqaure centimeter. The thirty-five foot samples ranged
from 8,000 organisms per square centimeter after eight hours of "in-
cubation" to 215,500 per square centimeter after forty-six days. By
November 9, the count had dropped to 129,200 per square centimeter.
In general, the counts rose fairly regularly with time at all depths.
A checklist of the organisms occurring as regrowth is given in
Table XII. A total of at least forty-seven species representing
thirty genera and three phyla were found. Forty of the species (eighty-
five per cent) and twenty-three of the genera (seventy-seven per cent)
90
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TABLE XII
ORGANISMS OCCURRING AS REGROWTH ON ARTIFICIALLY
DENUDED ROCKS, STONY POINT BAY,
LAKE SUPERIOR, 1967.
Phylum Chrysophyta
Class Bacillariophyceae
Achnanthes mlcrocephala
(Kuetzing) Cleve
Amphora ovalis
Kuetzing
Amphora normani
Rabenhorst
Asterionella formosa
Hassall
Ceratonels arcus
(Ehrenberg) Kuetztng
Cocconeis group*
Cvclotella group*
Cvmat op1eura solea
(Brebisson) Wm. Smith
Cvmbella group A*
Cymbella group B*
Denticula thermalis
Kuetzing
Diatoma elongatum
C.A. Agardh var. tenuis
(Agardh) Van Heurcl
Fragilaria capucina
Desmazieres
Fragilaria harrisonii
(Sm. Smith) Grunow
Frustulia viridula
(Brebisson) DeToni
Gomphoneis herculeana
(Ehrenberg) Cleve
Gomphonema group
Melosira granulate
(Ehrenberg) Ralfs
Navicula group*
Nitzschia palea
(Kuetzing) Wm. Smith
Nitzschia vermicularis
(Kuetzing) Hantzsch
Pinnularia viridis
(Nitzsch) Ehrenberg
Rhizosolenia eriensis^
H. L. Smith
Stauroneis producta^
Grunow
Surirella group*
Synedra acus
Kuetzing
Synedra ulna
(Nitzsch)Ehrenberg
Tabellaria fenestrata
(Lyngbye) Kuetzing
Tabellaria flocculosa
(Roth) Kuetzing
Class Chrysophyceae
Dinobryon sertularia
Ehrenberg
Phylum Chlorophyta
Cosmarium sp.
Scenedesmus quadricauda
(Turpin) Brebisson
Phylum Cyanophyta
Anabaena sp.
Lyngbya sp.
Merismopedia convoluta
Brebisson
Oscillatoria sp.
* See Table VIII for the species comprising this group.
91
-------
were diatoms. Dinobryon sertularia was the only "non diatom" Chry-
sophyte observed. Two species of greens and four species of blue-
greens were found.
The numbers of organisms in each of the three phyla, as well as
the total counts of all the regrowth samples, are shown in Table XIII.
No averages are presented, for they would be meaningless in this type
of study. In all but one of the samples, the phylum Chrysophyta com-
prised over ninety per cent of the total number of organisms. The
vast majority of the Chrysophytes were diatoms. Dinobryon sertularia
was present in low numbers and appeared only near the end of the samp-
ling season. Since most of the organisms were diatoms, their variation
may be seen graphically in Figure 61, which shows the total counts for
each depth versus "incubation" time.
By looking at Table XIII, it can be seen that the greens and blue-
greens do show a rising trend with increased "incubation" times. Be-
cause of the fact that they occurred in such small numbers, however,
any conclusions that might be drawn by looking at these figures would
be highly speculative. It can only be pointed out that greens and blue-
greens did appear as regrowth, but in relatively low numbers.
In these regrowth studies the two predominant organisms were
Synedra acus and Achnanthes microcephala. Together, these two diatoms
comprised an average of sixty-eight per cent of the total counts at
all three depths. In terms of percentage contribution to the total,
Achnanthes microcephala climbed regularly at all depths with increas-
ing "incubation" time, as did Synedra acus. For the whole study,
Synedra acus was predominant. Among the initial colonizers, on the
other hand, Achnanthes microcephala was the predominant form. In terms
of percentage of the total, Achnanthes microcephala, with one exception,
was higher than Synedra acus after eight and forty-eight hours of
"incubation" at all depths. The exception was at ten feet after eight
hours. Graphically, the order of predominance (in absolute numbers
and percentage contribution to the total) of Achnanthes microcephala (A)
and Synedra acus (S) according to incubation time and depth may be pre-
sented as follows:
8 hrs. 48 hrs. 96 hrs. 8 days 14-46 days
10 feet S A S S S
20 feet A A S S S
35 feet A A A A S
The fact that Achnanthes microcephala was the initial colonizer
supports the conclusion that one of the reasons Achnanthes was predom-
inant in 1966 (when much rough weather occurred) was its superior mode
of attachment.
The two other primary colonizers at all depths in the 1967 re-
growth study appeared to be Navicula spp. and Gomphonema spp. Fairly
substantial numbers of Cymbella spp. (group B) appeared early at ten
feet. After a week of regrowth, Asterionella formosa. Cocconeis spp.,
Cyclotella spp., Cymbella spp. (group B), Melosira granulate and the
unidentified blue-greens appeared regularly at all depths.
92
-------
vO
U>
TABLE XIII
PHYLA AND COUNTS OF ORGANISMS OBSERVED IN REGROWTH PERIPHYTON, STONY POINT BAY, LAKE SUPERIOR 1967,
ORGANISMS X 103 PER SQUARE CENTIMETER OF ROCK SURFACE.
*Date and "Incubation Time"
Depth
in
Feet
10
20
35
Phylum
Chrysophyta
Chlorophyta
Cyanophyta
TOTAL:
Chrysophyta
Chlorophyta
Cyanophyta
TOTAL:
Chrysophyta
Chlorophyta
Cyanophyta
TOTAL:
Jul 31
8
hrs
28.8
0.5
1.0
30.3
16.1
...
16.1
8.0
8.0
Aug 2
48
hrs
76.0
1.0
3.0
80.0
60.1
...
0.7
60.8
25.3
25.3
Aug 4
96
hrs
55.7
4.5
60.2
21.4
...
1.6
23.0
38.4
1.1
39.5
Aug 8
8
days
184.7
2.7
187.4
57.0
3.4
60.4
8.4
1.4
9.8
Aug 14
14
days
212.5
3.7
12.3
228.5
146.9
5.3
8.4
160.6
66.0
66.0
Aug 25
25
days
345.7
5.9
5.9
357.5
190.8
3.9
9.6
204.3
173.6
3.3
5.5
182.4
Aug 28
28
days
278.1
0.9
5.5
284.5
177.1
0.7
4.8
182.6
102.2
4.2
3.4
wv'.s
Sep 5
36
days
338.7
5.1
7.7
351.5
193.4
0.6
20.5
214.5
149.9
1.0
6.9
157.8
Sep 15
46
days
368.3
2.2
370.5
314.2
1.8
24.6
340.6
208.3
2.4
4.8
215.5
Nov 9
101
days
N.S.
N.S.
123.9
5.3
129.2
*Dash indicates zero; N.S. indicates no sample was collected.
-------
t>
Q.
400
^ —J
o 300
X
(o
6
c
D
200
100
*- 10 Feet
*-20 Feet
0 — 35 Feet
7-31 8-2 8-4 8-8 S~14 8~25 8~28 9~5 9~15 1f-9
8hr. 48hr. 96hr. fBdays Kdays 25days28days 36days 46daysW1days
Date and" Incubation Time"
n. Total
Bearing as regr^th, Stony Point B,,,
-------
The dry and the ash-free dry weights of the regrowth periphyton are
shown in Table XIV. In general, the weights increased with prolonged
"incubation" time and decreased with depth. Since the weights of two
groups of samples collected after different "incubation" times are not
comparable, means for these weights are not presented. When the weights
obtained on the last regular day of sampling (September 15) are divided
by their "incubation" time (forty-six days), a daily production rate
can be calculated. For the dry weights at ten, twenty, and thirty-five
feet the rates are 5.76, 2.26, and 2.77 grams per square meter per
day. On the basis of the ash-free dry weights, comparable figures for
the three depths are 0.09, 0.05, and 0.06 grams per square meter per
day.
Figures 62 through 64 show the regression lines obtained when one
attempts to predict total counts from ash-free dry weights. Correla-
tion coefficients and probability values are presented with the regres-
sion lines. The best correlation coefficient (.803) and the lowest
probability value (0.01) were obtained with the data from ten feet.
Although the correlation coefficients for the twenty and thirty-five
foot data (.574 and .605) were not exceedingly low, their corresponding
probability values were quite high (0,1 for both) because of the low
number of samples.
TABLE XIV
DRY AND ASH-FREE DRY WEIGHTS OF PERIPHYTON
OCCURRING AS REGROWTH, STONY POINT BAY, LAKE SUPERIOR, 1967.
MILLIGRAMS PER SQUARE CENTIMETER OF ROCK SURFACED
Dry Weight
Depth in Feet
Ash-Free Dry Weight
Depth in Feet
Date
10
20
35
Date
10
20
35
7-31
8-2
8-4
8-8
8-14
8-25
8-28
9-5
9-15
11-9
.68
.54
1.65
1.92
5.03
13.8
16.53
7.97
26.49
N.S.*
.28
.27
.80
1.83
6.96
7.49
11.71
9.48
10.41
N.S.
.62
.30
.59
.78
5.36
12,82
6.10
4.22
12.75
7.02
7-31
8-2
8-4
8-8
8-14
8-25
8-28
9-5
9-15
11-9
.06
.17
.23
.45
.64
1.21
.49
1.03
.43
N.S.
.02
.01
.18
.18
.57
.52
.37
.40
.24
N.S.
.04
.09
.17
.13
.54
.77
.26
.75
.29
.13
N.S. means no sample was collected.
96
-------
"fe
91
Q.
Ul
6
c
o
o
2000
1500
1000
500
y » 69,583 + 280,989x
r - .803, P « 0.01
I
0.5
1.0
\
1S
Mg Ash-Free Dry Weight per err?
20
Figure 62. Counts versus ash-free dry weights, regrowth
study, ten foot samples, Stony Point Bay,
Lake Superior, 1967.
u.
Q.
-------
2000
E K/in
t.
b
Q.
in
row1
C
O
£> 500
o
y - 42,095 + 164,610x
r = .605, P = 0.1
l
as
i
1.0
1J5
l
20
Mg
Ash-Free Dry Weight per cm*
Figure 64.
Counts versus ash-free dry weights, regrowth study,
thirty-five foot samples, Stony Point Bay, Lake
Superior, 1967. -
Since only qualitative regrowth data was obtained during 1965, quan-
titative comparisons to the 1967 data cannot be made. The organisms in
the checklists for these two summers, however, are comparable. In 1965
(Table II), thirty-four genera of Chrysophytes, Chlorophytes, and Cyano-
phytes were found. In 1967, the same three phyla were represented by
thirty genera. Genera observed in 1965 and not seen in the 1967 regrowth
samples were: Chrysophytes - Diplonels. Rhoicosphenia. and Stephanodis-
cus; Chlorophytes - Actinastrum. Closterium. Coelastrum. Oedogonium and
Tetraedron. The four genera observed in the 1967 counts and not seen in
1965 included one diatom, Gomphoneis. and three blue-greens: Anabae-
na. Lyngbya. and Oscillatoria. With these exceptions, the genera on
both checklists were seen both summers. From this comparison, it can be
seen that the organisms in the regrowth for 1965 and 1967 were quite sim-
ilar, at least qualitatively.
In order to see how close the 1967 regrowth approximated the natura-
lly occurring growth, the following comparison was made. The regrowth
counts reached their maximum at all depths after forty-six days of "incu-
bation". If the September 15 regrowth counts are compared to the 1967 nat-
urally occurring counts for the same date, it will be seen that the re-
growth level reached was approximately fourteen per cent of the naturally
occurring growth level at ten feet, twenty-eight per cent at twenty feet,
and eleven per cent at thirty-five feet. From this comparison, it is clear
that the quantity of regrowth that occurs after forty-six days of "in-
cubation" is far below the amount of naturally occurring periphyton.
98
-------
In the forty-six day growth pertod, thirty genera of algae appear-
ed on the rocks. In contrast, thirty-eight genera were found in the nat-
urally occurring periphyton in 1967. The only genus that appeared as re-
growth and was not seen in the naturally occurring periphyton was Cos-
mariuqi. which appeared in very low numbers and in one sample only. Gen-
era of naturally occurring periphyton that did not appear in the re-
growth in 1967 were: Chrysophyta - Gyrosigma and Rhoicosphenla; Chloro-
phyta - Ankistrodesmus. Cladophora. Closterium. Pedtastrum, Spiroeyra,
and Tetraedron; Cyanophyta - Raphidlopsis. All of these genera, most
of which are greens, appeared in relatively low numbers. The fact that
they did not appear as regrowth is probably not significant. The most
common genera in the naturally occurring periphyton of 1967 were also the
most numerous regrowth forms. On the basis of the means of the Septem-
ber 15 counts from the three depths for each organism, the most abundant
forms in the regrowth, in order, were Synedra acus, Achnanthes microce-
phala. Navicula spp., Cymbella spp. (group B), and Gomphonema spp.
These werealso the five most commonly occurring organisms in the 1967
naturally occurring periphyton. Even the order of abundance was almost
identical. In the naturally occurring periphyton, Gomphonema spp. was
more common than Cymbella spp. (geoup B). The naturally occurring
periphyton populations and those occurring as regrowth both showed a
preponderance of diatoms in all samples; low numbers of greens and blue-
greens showed no marked trends, either seasonally or according to depth,
and a decrease in counts with increasing water depth. The primary dif-
ference between the two communities was one of quantity.
Most of the past studies encountered in the literature have dealt
with periphyton occurring as regrowth on some artificial substratum.
Gumtow (1955) was one of the few workers who used a natural substratum
in studying periphyton regrowth. He cleaned cobblestones taken from the
bank of the West Gallatin River in Montana by rinsing them in formalin.
After placing them in the river for varying periods of time, he found
that the most common genera of diatoms appearing as regrowth were
Navicula. Diatoma. Cymbella^ Cocconels. Synedra. and Ceratoneis.
Plexiglas and glass have been the most common materials used as
artificial substrata. Jackson (1967) used plexiglas plates in studying
the periphyton of the eastern end of Lake Ontario. He identified the
organisms occurring as regrowth to genus and estimated their abundance.
He also determined their monthly biomass in terms of organic weight per
square decimeter of plate surface. The most common organisms found
were diatoms. Of the seventeen genera recorded, Melosira and Stephano-
discus were always common. The most abundant of the ten genera of greens
observed was Cladophora. an organism which has created nuisance prob-
lems in Lakes Erie and Ontario since the early nineteen-thirties (Neil
and Owen, 1964). None of the five genera of Cyanophytes were considered
abundant by Jackson. All of the diatom genera reported were also obser-
ved in Lake Superior periphyton.
Kevern et, al. (1966) and King and Ball (1966) also used plexiglas
99
-------
plates as a substratum for regrowth. Kevern et al. used this method to
determine the periphyton production in a laboratory stream. Their aver-
age estimate for daily net production was 0.6 grams of organic (ash-
free dry) weight per square meter per day. King and Ball arrived at a
comparable figure of about 0.3 grams per square meter per day. In their
study of the Red Cedar River in Michigan, they found that almost all the
organisms occurring as regrowth were diatoms. The most common genera
were Gomphonema. Navicula, Fragilarja. Cymbella^ Cyclotella. and Synedra.
Castenholz (1960) used glass slides as a substratum in studying
the periphyton of lakes in the state of Washington. Common diatoms
appearing as regrowth were Achnanthes. Amphora, Cocconeis, Cymbella,
Gomphonema. Navicula. Nitzschia. and Stephanodiscus. A typical high
production rate was 0.5 grams per square meter per day of organic weight.
Castenholz felt that glass was not unduly selective and that a two week
period of submergence was sufficient for determining production rates.
Foerster and Schlicting (1965), on the other hand, came to a different
conclusion. After comparing the natural periphyton growth in a Texas
lake to regrowth on glass slides, they stated that "the artificial
barren surface gave a false impression of the productivity trends and
indicated only some of the significant genera present in the ecosystem."
In looking at these regrowth results from other bodies of water,
most of which were streams, it can be seen that the genera of organisms
found are remarkably similar to those found in Lake Superior periphyton.
The production figures, however, are a good deal higher than those found
for Lake Superior periphyton. The average daily production rate for the
three depths sampled in Stony Point Bay was 0.066 grams per square meter
while others reported figures from streams of as high as 0.6 grams per
square meter per day. Whether or not regrowth on glass or other artifi-
cial substrata is comparable to regrowth on a natural substratum is
debatable, as has been shown. It must also be remembered that the Lake
Superior regrowth study was conducted at depths of ten, twenty, and
thirty-five feet. Had regrowth production rates been determined for the
very shallow water area of Stony Point Bay, figures comparable to those
reported for streams may have resulted.
Naturally Occurring North Shore Perlphvton
This study included eleven sampling areas along the North Shore
of Lake Superior extending approximately 107 miles from the zero station
at Lester River. The points involved are listed in the tabulation
given below.
PERIPHYTON SAMPLING LOCATIONS,
NORTH SHORE, LAKE SUPERIOR.
1. Lester River 0 miles
2. Knife River 13.8 miles
3. Burlington Bay 22.1 miles
100
-------
Periphyton Sampling Locations (Cont'd)
4. Split Rock River Bay 39.4 miles
5. Beaver Bay 48.0 miles
6. No-Name Bay (near Little Marais) 53.9 miles
7. Sugar Loaf Cove 69.9 miles
8. Tofte 78.8 miles
9. Lutsen 86.3 miles
10. Good Harbor Bay 100.9 miles
11. Grand Marais 106.9 miles
The geographic locations of each of these sampling points can be
obtained by reference to the accompanying map (Figure 3).
The results of the North Shore study has been summarized in Tables
XV, XVI, XVII, and XVIII. Table XV for example deals with organisms
found and their abundance and mean weights. In preparing the latter
table, counts from all depths on the two sampling days for each station
were averaged to give the mean total count. This figure was rounded off
to the nearest ten thousand organisms per square centimeter of rock sur-
face. The individual total counts for all depths on the two sampling
days for each north shore station are shown in Figures 65 through 75.
In Table XV, the dry and ash-free dry weights, expressed as milligrams
per square centimeter of rock surface, are also expressed as means.
Individual weights are shown in Table XVI.
The five most common organisms in Table XV were calculated on the
basis of their total numbers per square centimeter of rock surface at
a particular station, regardless of depth or day collected. They are
presented in their order of abundance.
The water temperatures recorded while sampling the north shore
stations are shown in Table XVII.
The 1967 total counts, with only a few exceptions, were higher at
the north shore stations than were counts for the same year at Stony
Point Bay (1,470,000 per square centimeter). The exceptions were sam-
ples from the Lester River area, the Knife River area, and Sugar Loaf
Cove. These stations were similar to Stony Point Bay.
The lowest mean count (1,466,000/cm.2) was recorded at Sugar Loaf
Cove. This area has been and still is the site of a large logging oper-
ation. At times, the entire cove was filled with floating logs, which
undoubtedly diminished the sunlight reaching the bottom. Also, large
amounts of wood chips were noted covering the rocks, again, causing a
reduction in available sunlight.
Counts of over three million organisms per square centimeter were
recorded at Split Rock River Bay, Good Harbor Bay, and Grand Marais.
Only the Grand Marais sampling area was near a relatively large popula-
101
-------
TABLE XV
SUMMARY OF RESULTS, NORTH SHORE STATIONS, LAKE SUPERIOR, 1967
Mean Total Mean Weights**
* Organisms per square centimeter of rock surface
** Milligrams per square centimeter of rock surface
Study Area Count* Dry Ash-Free
Lester River 1,693,000 19.5 1.46
Knife River 1,526,000 9.5 1.16
Burlington 2,890,000 16.6 1.50
Bay
Split Rock 3,798,000 12.5 1.35
River Bay
Beaver Bay 2,964,000 31.5 2.31
No-Name Bay 2,294,000 5.65 0.84
Sugar Loaf 1,466,000 2.72 0.61
Cove
Tofte 2.291,000 5.5 0.97
Lutsen 2,497,000 9.5 0.89
Good Harbor 3,020,000 10.5 1.51
Bay
Grand Marais 3,309,000 16.0 1.60
Five Most Common Organisms
Achnanthes microcephala, Synedra acus, Cymbella spp.,
Navicula spp., Nitzschia spp.
S_. acus , A. microcephala .
unidentified blue-green
S. acus, A. microcephala,
blue-green, Cymbella spp.
S. acus, A. microcephala,
Synedra ulna
S. acus, A. microcephala,
Gomphonema spp.
S. acus. A. microcephala,
Gomphonema spp.
A. microcephala. S. acus,
Gomphonema spp.
S. acus. A. microcephala,
Gomphonema spp.
S. acus. A. microcephala.
unidentified blue -green
£. acus. A. microc^ephala .
Synedra ulna
S_. acus, A. microcephala,
Navicula spp., Cymbella spp.,
Navicula spp., unidentified
Cymbella spp., Navicula spp.,
Cymbella spp., Navicula spp..
Navicula spp., Cymbella spp..
Cymbella spp., Navicula spp.,
Cymbella spp., Navicula spp.,
Cymbella spp., Navicula spp.,
Cymbella spp., Navicula spp.,
Cymbella spp., Navicula spp.,
Ceratoneis arcus
-------
TABLE XVI
PERIPHYTON DRY WEIGHTS AT SEVERAL DEPTHS, NORTH SHORE STATIONS,
LAKE SUPERIOR, 1967. MILLIGRAMS PER SQUARE CENTIMETER OF ROCK SURFACE.
Depth in Feet
Date 2.5 5 10 15 20 35
8-16
9-6
9-5
9-15
8-22
9-1
8-29
9-7
8-29
9-14
9-1
9-14
8-31
9-7
8-31
9-7
8-31
9-7
8-31
9-7
8-31
9-7
2.9
2.6
2.8
1.1
7.7
17.8
4.8
7.7
4.5
15.1
4.5
3.6
2.0
3.5
2.7
4.1
9.5
0.9
4.0
8.4
4.9
2.1
10.1
5.0
5.0
1.1
3.7
9.5
7.6
9.6
11.0
29.9
2.8
3.3
1.9
1.9
4.3
3.7
7.5
13.5
9.1
9.1
19.3
21.7
Lester River
47.5 76.5
5.4 11.6
Knife River
3.6 4.3
3.5 3.2
Burlington Bay
13.9 20.5
35.2 19.6
Split Rock River
7.6 22.6
13.8 9.7
Beaver Bay
9.4 13.1
45.4 56.4
No-Name Bay
13.2 3.2
12.6 5.7
Sugar Loaf Cove
1.7 1.5
4.5 2.4
Tofte
3.6 3.9
4.9 10.5
Lutsen
6.2 8.0
8.4 7.5
Good Harbor Bay
6.1 17.5
6.2 19.4
Grand Mara is
12.9 22.2
21.1 21.9
13.9
13.9
6.8
35.8
...
22.0
Bay
25.1
14.4
49.8
51.8
4.1
3.5
5.5
2.3
2.6
2.6
11.3
2.5
16.7
11.1
28.6
24.7
...
...
36.3
9.8
...
t*m
-------
TABLE XVII
PERIPHYTON ASH-FREE DRY WEIGHTS AT SEVERAL DEPTHS,
NORTH SHORE STATIONS, LAKE SUPERIOR, 1967.
MILLIGRAMS PER SQUARE CENTIMETER OF ROCK SURFACE.
Depth in Feet
Date 2.5 5 10 15 20 35
8-16
9-6
9-5
9-15
8-22
9-1
8-29
9-7
8-29
9-14
9-1
9-14
8-31
9-7
8-31
9-7
8-31
9-7
8-31
9-7
8-31
9-7
0.38
0.90
0.34
0.23
1.03
1.39
0.55
0.57
0.50
0.84
0.76
0.59
0.27
0.29
0.43
0.76
0.49
1.43
0.53
0.81
0.65
0.31
1.23
1.25
0.70
0.42
0.63
0.98
0.81
0.87
0.82
2.62
0.46
0.42
0.14
0.41
0.72
0.82
0.49
1.89
0.97
0.98
1.61
1.90
Lester River
3.33 3.54
0.63 0.91
Knife River
0.73 0.66
0.59 0.31
Burlington Bay
1.47 1.95
2.45 1.54
Split Rock River
1.04 1.02
2.13 1.64
Beaver Bay
0.72 2.32
4.07 3.75
No-Name Bay
1.75 0.56
1.75 0.80
Sugar Loaf Cove
0.42 0.60
1.04 1.17
Tofte
0.66 0.89
1.14 1.80
Lutsen
0.27 0.65
0.97 1.14
Good Harbor Bay
1.16 2.44
0.67 3.21
Grand Mara is
2.09 3.74
1.76 2.73
0.95
0.90
2.81
...
2.07
Bay
2.04
2.27
4.25
3.55
0.60
0.69
0.94
0.79
0.57
0.50
1.22
0.39
2.67
1.85
0.91
2.50
...
3.84
2.40
...
...
...
1.88
2.80
3.58
•••»••
...
...
M«B
1.24
1.95
0.91
1.13
1.32
0.59
0.55
0.57
104
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TABLE XVIII
WATER TEMPERATURES AT THE SURFACE AND THE BOTTOM
AT THE STANDARD SAMPLING DEPTHS, NORTH SHORE STATIONS,
LAKE SUPERIOR, 1967. DEGREES CENTIGRADE.
Depth in Feet
Date 0.5 2.5 5 10 15 20 35
8-16
9-6
9-5
9-15
8-22
9-1
8-29
9-7
8-29
9-14
9-1
9-14
8-31
9-7
8-31
9-7
8-31
9-7
8-31
9-7
8-31
9-7
21.5
23.0
15.0
15.5
13.0
13.0
10.0
8.0
8.0
12.5
11.0
13.0
7.0
7.5
11.0
10.8
12.5
13.0
11.5 ,
11.5
9.5
10.5
21.5
22.5
15.0
15.5
13.0
13.0
10.0
8.0
8.0
12.5
11.0
13.0
7.0 i
7.5
11.0
10.8
12.5
13.0
11.5
11.5
9.5
10.5
Lester River
20.0 9.0
21.0 20.0
Knife River
14.5 14.0
14.5 14.0
Burlington Bay
12.5 12.0
13.0 13.0
Split Rock River
10.0 10.0
8.0 7.0
Beaver Bay
7.5 7.0
12.5 12.5
No-Name Bay
11.0 10.5
13.0 13.0
Sugar Loaf Cove
6.5 6.0
7.5 6.5
Tofte
11.0 9.5
10.5 10.5
Lutsen
12.5 12.0
12.5 12.5
Good Harbor Bay
11.0 9.0
11.0 10.0
Grand Marais
9.5 9.0
10.0 10.0
8.0
11.0
11.0
8.0
10.0
13.0
Bay
10.0
6.5
6.5
12.5
9.5
13.0
6.0
6.5
9.5
9.5
11.5
10.0
8.5
10.0
9.0
10.0
9,0
6.0
7.5
13.0
10.0
6.0
5.5
12.5
9.5
13.0
5.5
6.1
9.0
8.6
11.5
10.0
8.5
9.5
8.5
9.2
6.0
7.0
•»•»*•>
•*••••
5.5
8.5
—
__„
8.5
8.0
10.0
9.0
7.8
9.5
8.5
9.0
105
-------
tion center. It is possible that sewage effluent found its way into
Grand Marais Bay. Rather extensive growths of Ulothrix sp. were noted
in very shallow water. This green alga also appeared in the counts.
Split Rock River Bay and Good Harbor Bay, on the other hand, were quite
isolated and their high counts cannot be explained on the same basis as
those of Grand Marais.
Neil and Owen (1964), in their paper on Cladophora in the Great
Lakes, state that this green alga causes nuisance problems in Lake Erie
and Lake Ontario. In this study, Cladophora was observed only at the
Lester River. This growth may have been stimulated by the intermittent
discharges of raw sewage directly into the lake near the sampling area.
Such discharges have been observed following storms. Neil and Owen
feel that increased nutrient levels, often as a result of added sewage,
cause excessive growths of Cladophora. At Lester River, however, the
growth could not be considered to be of nuisance proportions.
106
-------
6000
u
*• —
a <000
in
E
10
c
D
—8-16-67
— 9-6-67
T"
10
Depth in Feet
T
IS
—I
20
Figure 65. Naturally occurring periphyton, total counts,
Lester River area, north shore, Lake Superior, 1967,
600d\
fc 4000]
a
7,
A- 9- S-67
o-9-fS-67
2.5 5
to
T"
is
~r
20
25
Depth in Feet
30
35
Figure 66. Naturally occurring periphyton, total counts,
Knife River area, north shore, Lake Superior, 1967.
107
-------
6000
0.
•?>
4000
c. 2000
o
&-B-22-67
0-9- 7-57
2.5
\
5
JO
Depth in Feet
T
75
20
Figure 67. Naturally occurring periphyton, total counts,
Burlington Bay, north shore, Lake Superior, 1967.
8000
*> asi
01
Q.
-------
.1/1
°c
o
O)
8000
6000
tool
2000
35
Figure 69. Naturally occurring periphyton, total counts,
Beaver Bay, north shore, Lake Superior, 1967.
o
0000
6060
£boo
6
2000
o
&—9-1-67
o -9-U-67
2.5
S
I
70
Depth in Feet
I
75
20
Figure 70. Naturally occurring periphyton, total counts,
No-name Bay, north shore, Lake Superior, 1967,
109
-------
6000
Q.
«*)
10
s
10 ,
c 200C
e>
*—8-31-67
0-9-7-67
2.5
\
S
\
10
Depth in Feet
I
15
I
20
Figure 71. Naturally occurring periphyton, total counts,
Sugar Loaf Cove, north shore, Lake Superior, 1967.
600C
in
A -9- 7-67
0 -8-3h67
2.5 5
T
10
'T-
IS
20
25
30
~r
35
Depth in Feet
Figure 72. Naturally occurring periphyton, total counts,
Tofte area, north shore, Lake Superior, 1967.
110
-------
6000
o
I*
Ql
^
*^
x
4000
2000}
2.5 5 10 15 20 25
Depth in Feet
A - 9- 7-67
° -8-31-67
30
35
Figure 73. Naturally occurring periphyton, total counts,
Lutsen area, north shore, Lake Superior, 1967.
f\l
a
%
8500
SOW
4000
to
'£
§> 200^
O
2J5 5
10
15 20
Depth in Feet
25
* - 9-7-67
°- 8-31-67
30
T
35
Figure 74. Naturally occurring periphyton, total counts,
Good Harbor Bay, north shore, Lake Superior, 1967,
111
-------
BOOC
food
20$
- S-37-S7
/O /5 20
Depth in Feet
~r
25
30
35
Figure 75. Naturally occurring periphyton, total counts,
Grand Marais area, north shore, Lake Superior, 1967.
At Beaver Bay, which is close to the taconite operation at Silver
Bay, black magnetic particles (ten to twenty microns in diameter) were
observed. These did not seem to interfere with periphyton growth, for
the counts were quite high (2,964,000/cm.2). Interestingly enough, the
highest periphyton productivity, in terms of weight, occurred at Beaver
Bay.
At all eleven stations, four of the five most common organisms were
Synedra acus. Achnanthes microcephala. Cymbella spp., and Navicula spp.
The predominant organisms were always Synedra acus and Achnanthes micro-
cephala. At the Lester River and at Sugar Loaf Cove, Achnanthes microce-
phala was the most common. At all other points, Synedra acus pre-
cominated. Occasionally appearing among the five most common organisms
were Nitzschia spp., an unidentified blue-green (probably a small species
of Oscillatoria). Synedra ulna. Gomphonema spp., and Ceratoneis arcus.
The five most common organisms in 1967 samples from Stony Point
Bay were, in order, Synedra acus. Achnanthes microcephala. Navicula spp.,
Cymbella spp., and Gomphonema spp. Thus it can be seen that the organ-
isms comprising the periphyton remain practically the same for a 107
mile segment of the north shore.
It is felt that the same factors which affect periphyton growth in
Stony Point Bay influence growth at any other point in the lake. These
are primarily water movement (regardless of cause), light intensity,
temperature, available nutrients, and the type of substratum. While it
112
-------
is true that all of these factors are variable, the similarity found
between the periphyton at Stony Point Bay and the eleven north shore
stations indicate that these factors did not, at the time of this survey,
differ drastically from point to point in the stretches of Lake Superior
shoreline studied.
Summary and Conclusions
Taxonomy and Distribution of Periphyton
On the basis of the results obtained in this, the first portion
of our Periphyton Study in the westem arm of Lake Superior, it is con-
cluded that the organisms found in the periphyton of the western arm
of Lake Superior are indicative of clean water. The extensive shallow
water area of Lake Superior supports large quantities of attached al-
gae, which, as primary producers, form the first link in the food chain.
It is felt that the results of this study will be of practical value in
the future. Since the periphyton is fixed in one place, it reflects the
quality of water masses with which it comes into contact. By using the
results of this study as baseline data, it will be possible in the fu-
ture to determine the qualitative and quantitative changes that occur in
the periphyton as a result of eutrophication. It is hoped that, in this
way, subtle changes in water quality brought about by chemical or ther-
mal pollution can be detected.
Some of the specific observations which can be reported here in
the nature of a summary are:
(1) The plant portion of the periphyton found attached to rocks con-
sists almost solely or representatives from three phyla of algae namely
the Chrysophyta. the Chlorophyta and the Cyanophyta.
(2) Most abundant in terms of numbers of organisms is the phylum
Chrysophyta. and diatoms make up over ninety per cent of this group.
(3) The genera of diatoms which were predominant in the periphyton
growth were Synedra. Achnanthes. Navicula. Cvmbella and Gomphonema.
(4) Mean total counts of organisms in the naturally occurring periphy-
ton of Stony Point Bay, the primary sampling area, ranged from 497,000
per square centimeter of rock surface in 1966 to 1,470,000 per square
centimeter in 1967.
(5) The biomass of the naturally occurring Stony Point Bay periphyton,
in terms of dry weight, was 153 grams per square meter in 1965, 104
g./m.2 in 1966, and 156 g./m.2 in 1967.
(6) After forty-six days of regrowth on artificially denuded rocks in
Stony Point Bay, the growth level reached finally was approximately
eighteen per cent of that occurring naturally.
113
-------
(7) The daily regrowth production rate in Stony Point Bay averaged
3.6 grams of dry weight per square meter and 0.067 grams of organic
weight (ash-free dry) per square meter.
(8) Mean total counts of organisms from eleven north shore stations
ranged from 1,466,000 organisms per square centimeter at Sugar Loaf
Cove to 3,798,000 per square centimeter at Split Rock River Bay.
(9) The interrelated factors which affect periphyton growth are light
intensity, water movement, depth, temperature, nutrient levels, and
type of substratum.
(10) The periphyton of Lake Superior was found to be similar, in many
respects, to attached growths found in streams.
114
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Section VI
The Photosynthetic Pigments of Periphyton and Periphyton Productivity
Results and Discussion
Since this portion of the study was carried out over a period of
three consecutive summers, we have, in the interest of simplicity and
clarity chosen to present the results of the investigation in a chron-
ological order. In 1966 for example, while some quantitative data were
accumulated, time was spent largely in the development of methods.
The 1967 season, on the other hand, represents the period devoted pri-
marily to a sampling program, and 1968 was the year for special studies
intended to provide answers for special problems which had become ap-
parent in the course of our 1966 and 1967 studies. The results of
the 1968 laboratory experiments were needed to convert the data collec-
ted earlier under standard conditions to a form more nearly approxima-
ting the actual situation in the lake.
In the interest of brevity and clarity, this chapter includes
discussion of results along with the presentation of data. The data
have been combined and summarized in various ways and are presented
in the form of figures and tables. The discussion involves general in-
terpretation of the data, comparisons between results of the three
summers and between various sampling areas, and correlations between
the several parameters employed in the study of periphyton. When
possible, results will be compared with data reported from other studies-
of periphyton communities. An attempt also will be made to establish
the relative importance of the periphyton community as a primary produc-
er in Lake Superior when a comparison is made with the productivity of
the phytoplankton.
The area in which the major part of the study was concentrated
was Stony Point Bay which has been described in detail in an earlier
section of this report. As will be remembered most of the bottom in
this bay was covered by rocks, with very small and scattered sand pat-
ches breaking up the rocky areas. Portions of the bay floor are, to be
sure, designated on maps by the word "sand" but even here patches of
rocks were encountered. In general the rocks ranged in size from one
inch to five or six feet in diameter, but most of the bottom was covered
by rocks ranging from four to twelve inches in diameter. The triangular
sampling area, bounded by a reference buoy 2336 feet from shore, the
Little Sucker River on the southwest, and Stony Point on the northeast,
was found to encompass 321,000 square meters.
Stony Point Bay is located in a sparsely populated area and is not
easily accessible from the adjacent land because the banks leading to
the water's edge are very steep. The only persons encountered in the
bay area were commercial fishermen who cane by boat to tend small fish-
net cribs which were permanently located in the bay. Because of past
115
-------
experiences with net fouling these fishermen expressed considerable
interest in the project and welcomed the technicians who carried out
the field work.
Turbidity in the water of the bay was quite variable and was con-
siderably affected by flow from the Little Sucker River. During and
following stormy periods, heavy suspensions of silt were carried into
the bay from the mouth of the river, whereupon the materialwas often
carried across the bay in an easterly direction.
Ruschmeyer and Olson (1957) have shown the general circulation
of water in the western arm of Lake Superior to be counterclockwise.
However, winds and eddy effects can cause a reversal of flow near shore
in certain areas.
Under more normal conditions periphyton organisms and silt from the
shore area were also suspended in the bay by water agitation when wave
action was severe. Secchi disc readings varied considerably, the max-
imum being approximately eight meters. Occasionally, the water was clear
enough that the bottom could be viewed from the surface in depths up
to twenty feet. Water color as viewed from shore was usually greenish,
but atmospheric conditions and turbidity sometimes accounted for a tan
or grey appearance.
A heavy, brown layer of periphyton was usually apparent on the rocks
and sand in the bay. Where the periphyton was not disturbed by wave ac-
tion, small gas bubbles could be seen entrapped in the wooly growth.
Occasionally, divers reported viewing small fish near the bottom of the
bay; these fish were found to be sculpins. Small groups of crustaceans,
identified as Mysis relicta. were sometimes present. Mayfly nymphs,
midge larvae, caddisfly larvae, nematodes, snails and leeches also were
found in association with the periphyton on the rocks. A few clumps
of the macroscopic, filamentous green alga, Nitella. were encountered
on rare occasions.
The rocks taken from Stony Point Bay differed somewhat from one
another in appearance when the periphyton was removed. An analysis of
one hundred of these rocks revealed that twenty-two lithic types were
represented in the bay. The predominant type was found to be basalt,
of which twenty-four per cent were andesite and diabase. Fourteen of
the one hundred were diabase, while seven were porphyritic trachyandesite
to mafic quaryz latite.
Findings in 1966
Data presented represent that portion of the study which was car-
ried out between August 9 and September 6. During this twenty-nine day
sampling period, east or northeast winds occurred on eleven days, or
thirty-eight per cent of the time. The average velocity was fifteen
miles per hour. These winds caused very rough water, making it impos-
sible to safely navigate the two miles from Knife River Harbor to Stony
Point Bay. For this reason, only five sampling trips were completed.
116
-------
However, in the course of these five trips, a total of eighty-one rocks
were obtained from depths of 2.5, 5, 10, 15, 20, and 35 feet.
The average periphyton pigment concentrations per unit area of
rock surface are plotted against sampling depth in Figure 76. Maximum,
minimum, and mean concentrations are presented in Table XIX. Since the
quantity of phytoplankton pigments, in the small amounts of water collec-
ted along with the rocks in the plastic bags, proved to be negligible
when compared with that of the periphyton, no correction for this fac-
tor was necessary. All pigments of the periphyton collected from depths
of ten through thirty-five feet decreased considerably during the sampling
period; this trend was not shown by samples taken at depths of 2.5 and
five feet. From Table XIX and Figure 76, it can be seen that chlorophyll
a_ was the predominant pigment in nearly all samples. The minimum mean
concentration was 0.190 milligrams per 100 square centimeters of rock
surface at a depth of 2.5 feet, while the maximum mean concentration rea-
ched 0.510 milligrams per 100 square centimeters at a depth of thirty-
five feet. Chlorophyll _c and non-astacin carotenoids were present in
somewhat lower concentrations, attaining minima at the same depth and
maxima at different depths (see Figure 76). The minimum mean chloro-
phyll c_ concentration, 0.068 MSPU per 100 square centimeters, appeared
at a depth of 2.5 feet and the maximum, 0.340 MSPU per 100 square cen-
timeters, at a depth of thirty-five feet. The lowest mean concentration
of non-astacin carotenoids was encountered at 2.5 feet (0.132 MSPU/100 cm2)
and the highest at twenty feet (0.311 MSPU/100 cm2).
E
o
S? 0.3
en
E
D
V
2
0.1-
Chlorophyll
0
Ast. Carotenoids
Non-astacin
Carotenoids
10
25
30
Figure 76
15 20
Depth in Feet
Average Periphyton Pigment Concentrations (per
unit area of rock surface) at Standard Sampling
Depths, Stony Point Bay, Lake Superior, 1966.
117
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The observed ratio of chlorophyll a_ : chlorophyll £ : non-astacin
carotenoids, approximately 5:3:3, is to be expected because of the over-
whelming preponderance of diatoms in the samples. In Section V
reference was made to the fact that six genera. Achnanthes. Synedra.
Cymbella. Navicula. Cocconeis. and Gomphonema. accounted for over nine-
ty per cent of the organisms in samples from all depths. The ratio
of chlorophyll c/chlorophyll a at the 2.5-foot depth was 0.35; at five
feet, 1.10; at ten feet, 0.61; at fifteen feet, 0.51; at twenty feet,
0.64; and at thirty-five feet, 0.67. No trend is apparent. The ratio
of non-astacin carotenoids/chlorophyll a_ was more constant with depth.
At a depth of 2.5 feet, the ratio was 0.67; at five feet, 0.76; at ten
feet, 0.73; at fifteen feet, 0.74; at twenty feet, 0.63; and at thirty-
five feet, 0.58. The ratio seems to decrease slightly as depth increas-
es. The sampling period was not long enough to indicate any seasonal
trends as far as the pigment ratios are concerned.
Chlorophyll b_ and astacin carotenoids were present in smaller
amounts. Chlorophyll £ reached a minimum of 0.036 milligrams per 100
square centimeters at a depth of 2.5 feet and a maximum of 0.158 milli-
grams per 100 square centimeters at a depth of ten feet; the minimum
astacin carotenoid value, 0.015 MSPU per 100 square centimeters, appear-
ed at 2.5 feet and the maximum, 0.061 MSPU per 100 square centimeters,
at thirty-five feet. The chlorophyll b^ peak corresponds to a drop in
chlorophyll £ concentration (Figure 76), possibly indicating the presence
of a relatively higher number of periphytic green algae at depths of
ten and fifteen feet than at other depths. This hypothesis was not
borne out by the routine microscopic examination, as little difference
was seen in the numbers of green algae at the various depths; however,
it is possible that with the use of a random field counting method and
a 200X magnification, some small green algae might be missed in a heavy
sample. After careful re-examination of several samples, it was con-
cluded that the reported percentage of green algae was, in fact, low.
The minute but persistent astacin carotenoid values observed may
be attributable to the presence of animal grazers in the samples. Lit-
tle difference can be seen in the concentrations at various depths;
the minimum and maximum concentrations during the sampling period cor-
respond in general with those of the other pigment groups. Part of
the apparent astacin carotenoid value may be the result of an error
in the formulas of Richards and Thompson (1952). This possible error
(suggested by Parsons and Strickland, 1963) is due to the production
of a positive animal carotenoid value by the plant xanthophyll, fucoxan-
thin.
Further inspection of Figure 76 reveals that all of the periphyton
pigments tend to increase on a unit area basis from the shallow to the
deeper parts of the bay. However, this increase is not due to a pro-
portional rise in numbers of organisms with depth (see Figure 77).
Although peaks occur at fifteen or twenty feet, it will be seen that
when the amount of each pigment per 100,000 organisms is plotted
against depth, the same general increase in concentration occurs with
118
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TABLE XIX
PIGMENT CONCENTRATIONS OF NATURALLY OCCURRING PERIPHYTON
FROM STANDARD DEPTHS, STONY POINT BAY. LAKE SUPERIOR,
1966. MILLIGRAMS OR MSPU PER 100 CM2 ROCK SURFACE
Chlorophyll a_
Max?
Min.
Mean
Chlorophyll b_
MaxT
Min.
Mean
Chlorophyll £
MaxT
Min.
Mean
Non-astacin
carotenoids
Max.
Min.
Mean
Astacin
carotenoids
Max.
Min.
Mean
2.5
0.232
0.125
0.191
0.054
0.012
0.040
0.091
0.027
0.066
0.152
0.110
0.130
0.027
0.001
0.015
5
0.275
0.120
0.198
0.094
0.001
0.058
0.517
0.010
0.197
0.211
0.089
0.153
0.096
0.001
0.044
Depth in
10
0.729
0.136
0.328
0.430
0.010
0.158
0.733
0.010
0.199
0.530
0.091
0.237
0.143
0.010
0.046
feet
15
0.803
0.096
0.338
0.421
0.015
0.149
0.404
0.011
0.171
0.520
0.090
0.255
0.076
0.008
0.032
20
1.399
0.139
0.491
0.450
0.017
0.134
0.778
0.091
0.316
0.860
0.088
0.312
0.130
0.017
0.053
35
0.969
0.277
0.510
0.304
0.001
0.090
1.060
0.103
0.340
0.595
0.152
0.297
0.183
0.020
0.061
119
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depth. Therefore, higher pigment concentrations in the individual
organisms were found to correspond directly to decreasing light intensity.
The peaks observed at fifteen or twenty feet could be explained on the
basis that larger aliquots were used to compensate for a relative scar-
city of organisms present on the rocks from these depths. Such aliquots,
when fine colloidal clay is present, may lead to slightly increased ab-
sorption readings, as centrifugation of the colloidal clay is difficult.
If an adjustment is made for this factor, the amount of pigment per or-
ganism when plotted against increasing depth will approximate a sigmoid
curve which reaches an asymptote at fifteen or twenty feet. It was as-
sumed that the higher pigment concentrations in deeper water were a re-
sult of conditioning to a lower light intensity. This "sun and shade"
reaction has been reported on several occasions as a phenomenon occurring
in phytoplankton populations (Kozminski, 1938; Burkholder and Sieburth,
1961); however, the conditioning is much more apprent in the Stony
Point Bay periphyton, because organisms attached at one depth must re-
main at that depth unless broken loose by violent currents, and are not
continually mixed as phytoplankton organisms are. Thus the periphyton
growing at a certain depth has a greater opportunity to adjust to light
intensity than does the phytoplankton.
In order to compare the results of chlorophyll analyses performed
with a broad spectrum instrument with those based on readings from a
narrow-band spectrophotometer, the observed chlorophyll a_, b_ and £ con-
centrations (DK-2A) were added together and plotted against depth along
with the Klett-Summerson total chlorophyll concentration values (Figure
78). The chlorophyll results based on readings with the Klett-Summerson
colorimeter were considerably lower than the corresponding total chloro-
phyll concentrations obtained with the DK-2A method. This discrepancy
may be due to the fact that the Klett #66 filter allows the passage of
light only in the 640 to 700 millimicron range, thus effecting no measure-
ment of chlorophyll £, which does not absorb visible light of wavelength
greater than 635 millimicrons. Therefore, these observations do not
lend support to the contention by Parsons and Strickland (1963) that
Richards' formulas yield chlorophyll values which are too high. The
data from the six standard sampling depths show that the narrow-band
instrument produced total chlorophyll figures which averaged 1.7 times
as high as those from the broad spectrum instrument. This factor, when
calculated on the basis of data from each depth, varied from 1.49 to
1.90. It is interesting to note that the two methods agreed best on
samples from 2.5 and fifteen feet, where the amounts of chlorophyll £
were lowest in relation to the other pigments.
Many investigators have reported chlorophyll concentrations on a
unit area basis as a reflection of the general magnitude of biomass.
In order to compare the data from Stony Point Bay with those reported
for certain other ecosystems, the total chlorophyll values obtained by
the DK-2A method were converted to grams per square meter (see Table XX).
These values ranged from 0.0297 at the 2.5-foot depth to 0.0941 at the
twenty-foot depth. The average from the entire bay was 0.0660. Table
XX includes values calculated for some ecosystems studied by other
120
-------
120O-
-------
(0
2000-
9 1
* DI 1500
**"•» L.
I o
E o"
c __
o
>„ 10OO-
500-
-I 1 1 1
5 10 15 2O
Depth in Feet
—T"
25
30
35
Figure 78. Periphyton Total Chlorophyll Concentrations as Meas-
ured by a Broad-Spectrum Colorimetric Method, and
by a Narrow-Band Spectrophotometric Method.
o
CM
CM
O
c
o
V
80-
E 60
u
40-
20-
Run at 20 C , 1500 ft-c.
1O 15 20 25
Depth in Feet
30
35
Figure 79. Average Gross Photosynthetic Rates (per unit area)
for Samples from Standard Depths, Stony Point Bay,
Lake Superior, 1966; Run at 20° C., 1500 Foot-
Candles.
122
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TABLE XX
CHLOROPHYLL CONTENT OF STONY POINT BAY PERIPHYTON
(1966) AND OTHER COMMUNITIES ON A UNIT AREA BASIS
Investigator Ecosystem
Stony Point
Bay Periphyton
2.5'
5'
10'
15'
20'
35'
Average
Chlorophyll (G/M2)
.0297
.0453
.0685
.0658
.0941
.0940
.0660
Riley (1956)
Long Island Sound
phytoplankton
O.I - 0.6
Odum and Odum
(1955)
Coral reef
0.5
Ichimura (1954) Japanese lake
McConnell and Rocky stream
Sigler (1959)
0.006
0.05 - 1.0
123
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sampling period. This probable error is borne out by the photosynthesis/
respiration ratios (Table XXI). The ratio for the five-foot sample
(4.40) is inconsistent with the values calculated for samples from the
other depths (3.03 to 3.43),and the 1967 data subsequently showed that
no significant peak occurs at five feet. The P/R ratio for the five
foot samples during that year was 3.46, while the ratio for the other
depths ranged from 2.96 to 3.36.
The overall mean P/R ratio for Stony Point Bay periphyton under
the test conditions was found to be 3.39. Published data relating the
photosynthetic and respiration rates of periphyton are rare. However,
a striking comparison may be made between the average P/R ratio for Stony
Point Bay periphyton (3.39) and that calculated from the data of Jack-
son (1966) for Cladophora fracta in Lake Ontario (3.42). Riley's (1957)
data for the algae of the Sargasso Sea yield a P/R value of 3.06. A
value of 2.91 has been calculated for the photosynthetic organisms of
Silver Springs, Florida (Odura, 1957).
Since the P/R ratios for samples from all depths in Stony Point Bay
are similar except for the five-foot samples, the net photosynthetic
rates follow nearly the same pattern as the gross rates (Table XXI).
The net rates ranged from 27.5 microliters of oxygen evolved per square
centimeter of rock surface per hour for the samples from 2.5 feet to 67.9
microliters of oxygen per square centimeter per hour for the five-foot
samples. Values for the remaining depths varied between 35.9 and 45.3.
The overall mean rate for net photosynthesis in samples from all depths
was 43.3 microliters of oxygen evolved per square centimeter per hour.
Assuming fifteen hours of daylight per day, the photosynthetic
rates were converted to production rates in terms of carbon fixed
(Table XXI). Net production varied between 1.62 grams of carbon fixed
per square meter per day at a depth of 2.5 feet and 4.49 grams of car-
bon fixed per square meter of rock surface per day at five feet; the
average value for all sampling stations was 2.63 grams of carbon fixed
per square meter per day. These values take into account losses due to
daytime and nighttime respiration, and represent true net production fig-
ures under the test conditions. The figures were again converted to re-
flect net production in terms of organic matter. For purposes of cal-
culation, it was assumed that all carbon was fixed in the form of glucose
(see Table XXI). Thus the production rates ranged from 4.05 grams pro-
duction (as glucose) per square meter per day to 11.22 grams per square
meter per day; the average rate for samples from all depths was 6.58
grams (as glucose) per square meter per day. Again, these values are
corrected for respiration losses and are net production rates for the
test conditions (20° C., 1500 foot-candles)
124
-------
TABLE XXI
PHOTOSYNTHESIS DATA FOR PERIPHYTON SAMPLED AT
DIFFERENT DEPTHS, STONY POINT BAY, 1966;
RUN AT 20° C., 1500 FOOT-CANDLES
Sampling depth in feet
2.5
10
15
20
Gross Photosynthesis
ul 02/cm2/hr
Respiration
ul 02/cm2/hr
Net Photosynthesis
ul 02/cm2/hr
P/R
Net production
Grams carbon
fixed per M*
per day
Grams (as glu-
cose) per M
per day
35 Mean
+39.7 +87.9 +66.3 +53.6 +61.5 +55.6 +60.7
-12.2 -20.0 -21.0 -17.7 -17.9 -16.0 -17.3
+27.5 +67.9 +45.3 +35.9 +43.6 +39.6 +43.4
3.26 4.40 3.14 3.03 3.43 3.10 3.39
1.62 4.49 2.63 2.03 2.64 2.41 2.63
4.05 11.22 6.57 5.07 6.60 6.02 6.53
TABLE XXII
PERIPHYTON VOLUMES AND DRY WEIGHTS AT THE STANDARD
DEPTHS, STONY POINT BAY, LAKE SUPERIOR, 1966
2.5
Depth in feet
10 15 20
Dry Weight
(Mg. per cm^ rock
surface) Max. 10.0
Min. 2.5
Mean 6.5
15.1 19.7
3.1 5.1
7.1 10.7
35
30.0 32.0 24.3
6.0 2.1 5.3
14.0 13.4 11.6
(continued next page)
125
-------
TABLE XXII (continued)
Depth in feet
2.5 5 10 15 20 35
Volume
(Ml. per 100 cm2) 3.35 2.98 9.27 8.55 A.89 6.74
2.62 2.20 2.29 1.72 2.80 1.85
3.00 2.56 4.05 3.71 3.36 3.98
An interesting relationship between oxygen yield, chlorophyll con-
centration and sampling depth is suggested by Figure 80. The volume of
oxygen evolved per milligram of total chlorophyll begins at 13.5 x 10^
microliters per hour at 2.5 feet, rises to 22.3 x 103 microliters per
hour at five feet, and then falls off asymptotically through the remain-
ing depths. If the five-foot value is ignored (this figure is probably
too high), a smooth, slowly descending curve is produced. If photosyn-
thetic rate increases proportionately with increased pigment concentra-
tion, then the oxygen:pigment ratio should approximate a constant value
in all samples, regardless of their source, when the samples are exposed
to excess light. However, recalling that pigment concentrations were
shown to increase with depth, and noting from Figure 80 that the oxygen:
pigment ratio is not constant for organisms taken from different depths,
one may assume that once a certain low light level is reached, the fur-
ther addition of pigments by an algal cell in decreased light will not
necessarily maintain the expected photosynthetic rate. Apparently, cond-
itioning to a certain light intensity affects the photosynthetic capacity
of a pigment unit as well as influencing pigment concentrations. This
factor is important in the consideration of the effects of short-term
and long-term increases in turbidity on periphyton productivity, whether
such turbidity is caused by natural runoff from the land or by advancing
water pollution.
The photosynthesis and chlorophyll data from Figure 80 were also
calculated as grams of carbon fixed per gram of chlorophyll so that com-
parisons of these "assimilation numbers" could be made with those re-
ported elsewhere for other communities. The assimilation value de-
termined for Stony Point Bay at a depth of 2.5 feet was 7.2 grams of
carbon fixed per hour per gram of chlorophyll; at five feet, 11.9;
at ten feet, 4.8; at fifteen feet, 3.7; at twenty feet and thirty-five
feet, 3.2. The average of these figures is 5.7 grams of carbon fixed
per hour per gram of chlorophyll. Discarding the five-foot value,
uhich is probably in error as previously explained, the average becomes
4.4. This figure compares quite well with the 3.7 reported by Ryther and
Yentsch (1957) for marine phytoplankton. It is, however, considerably
higher than assimilation numbers calculated for various ecosystems by
certain other workers. For example, Ichimura (1954) reported 2.36 grams
126
-------
of carbon fixed per hour per gram of chlorophyll in Lake Suwa, Japan.
Odum and Odum (1955) found the value for a coral reef to be 1.5, while
the data of McConnell and Sigler (1959) show 0.75 grams of carbon fix-
ed per hour per gram of chlorophyll in a rocky stream in Utah.
The dry weights of the 1966 periphyton samples are presented in
Table XXII. The average weights correlate rather well with the pigment
concentrations, but this relationship may be purely coincidental.
Since the relationship between pigment concentrations and numbers of
organisms has been shown to depend on the depth from which the sample
was taken, there is reason to believe that the amount of pigment per
unit of dry weight would also vary from one depth to another. The mean
dry weight was lowest at the 2.5-foot depth (6.5 milligrams per square
centimeter of rock surface) and highest at the fifteen-foot depth (14.0
milligrams per square centimeter). The total number of organisms was
lowest at fifteen feet (Fox _et_ a.1., 1967). The weight of the periphyton
was less at thirty-five feet than at the intermediate depths. This
pattern can be explained on the basis that the organisms near shore are
sometimes removed from the rocks by wave action while the organisms
in the deeper areas are not affected. The lower biomass at thirty-five
feet is probably due to relatively low light intensity and temperature.
Varying amounts of sand and silt accompanied the organisms in the sam-
ples; apparently, a larger proportion of sand and silt was present in
the samples from the fifteen-foot depth than those from other depths.
This point was borne out by visual examination of the samples. On
the basis of the 1966 mean dry weights for all depths, the standing
crop of periphyton in Stony Point Bay was calculated to be 104 grams
per square meter or 37.1 tons for the entire bay.
The volumes of the settled periphyton samples are also shown in
Table XXII. The mean values range from 3.00 milliliters of periphyton
per 100 square centimeters of rock surface at the five-foot depth to
4.05 milliliters per 100 sqaure centimeters at the ten-foot depth.
These results compare reasonably well with the dry weights, inasmuch
as the volume determinations were also subject to the influence of sand
and silt in the samples. Dry weight and volume determinations would
appear to be useful in the estimation of the general magnitude of bio-
mass in the periphyton community.
Enough quantitative data were gathered during the summer of 1966
to allow the formulation of certain tentative conclusions regarding
the biomass of Stony Point Bay periphyton and the relationships between
the various parameters which were observed. The periphyton pigments
were dominated by chlorophyll a_, with chlorophyll £ and non-astacin
carotenoids approximately equal as secondary pigments. Low chlorophyll
b_ concentrations indicate the presence of a relatively low proportion
of green algae to diatoms. It is apparent that the organisms increased
their pigment concentrations in deeper water, probably in response to
lower light intensity. Chlorophyll per square meter and carbon fixed
per square meter were shown to be of the same order of magnitude as
127
-------
I- >
Bi
-c o
O o
21 -
14-
7-
0
Figure 80.
Run at 2O C., 15OO ft-c.
10
—I—
15
—I—
20
25
30
35
Depth in Feet
Average Periphyton Gross Photosynthetic Rates (per
unit total chlorophyll) at Standard Sampling Depths,
Stony Point Bay, Lake Superior, 1966.
for other ecosystems. Astacin carotenoid values, while quite low,
probably reflect the association of certain animal forms with the peri-
phytic algae. The data indicate that any single measurement, such as
pigment analysis, enumeration of organisms, or the determination of
weight, volume or photosynthetic rate, will probably now show the true
productivity of the periphyton.
It was deemed necessary to confirm the 1966 results by obtaining
more data on the same bay with similar techniques. In addition, the
1966 data raised a number of questions which could be answered only by
a more extensive sampling program. Among these questions were the
following: Are periphyton pigment concentrations actually so variable
with depth as indicated by the 1966 data? Are there seasonal changes
in concentration on an area basis, and do consistent differences
in pigment ratios occur with depth? What is the relationship between
organic weight, total dry weight and other parameters of biomass?
Would further sampling confirm the apparent decrease in efficiency of
the pigment unit as the pigments become more concentrated?
128
-------
Findings 1967
The experience gained in sampling procedures and analysis during
the 1966 season made a much more comprehensive program possible in
1967. Furthermore general observations in the field relative to con-
ditions of growth and a multitude of other ecological factors provided
a basis for better judgement relative to the interpretation of the
findings made. The weather, too, during the summer of 1967, was more
favorable and the sampling program was not seriously interrupted by
storms. Greater emphasis should therefore be given to the data ob-
tained during that year. For simplicity and hence for greater effec-
tiveness, this chapter has been divided into three parts. The first
section is concerned with the naturally occurring periphyton of Stony
Point Bay, and the second with the regrowth study conducted in the same
bay, while the third part deals with an investigation of the periphyton
communities of north shore areas other than Stony Point Bay.
Naturally Occurring Periphyton. Stony Point Bay
Routine samples were collected in Stony Point Bay from July 11 to
September 15, 1967. An additional sampling trip was made on November
10. The same procedures were used as in 1966 and during each sampling
run three rocks were taken from each standard depth, namely 2.5, 5, 10,
15, 20 and 35 feet. Sampling was done twice a week and a total of
306 rocks were collected.
The pigment concentrations, on a unit area basis, for each depth
are shown in Figure 81. Each point represents the average concentration
of one pigment type at one depth during the entire sampling period.
Chlorophyll a, was the predominant pigment at all depths, ranging from
a minimum mean concentration of 0.330 milligrams per 100 square cen-
timeters of rock surface at a depth of fifteen feet to a maximum of
0.976 milligrams per 100 square centimeters at a depth of 2.5 feet.
The mean concentration for samples from the thirty-five foot depth was
0.583 milligrams per 100 square centimeters. The same pattern
was exhibited by the other plant pigment groups. The chlorophyll £
concentration began at 0.386 MSPU per 100 square centimeters at a ~~
depth of 2.5 feet, fell to 0.163 MSPU per 100 square centimeters at
fifteen feet, and then rose to 0.298 MSPU per 100 square centimeters
at thirty-five feet. The non-astacin carotenoid values were similar
in magnitude, varying from 0.475 MSPU per 100 square centimeters at
the 2.5 foot depth to 0.132 MSPU per 100 square centimeters at fifteen
feet. At the thirty-five foot depth, the mean concentration was
0.201 MSPU per 100 square centimeters. Chlorophyll b_ was present at
all depths in considerably lower concentrations than the other plant
pigments. The maximum chlorophyll b_ concentration appeared at a
depth of 2.5 feet (0.146 milligrams per 100 square centimeters) while
the minimum concentration occurred at fifteen feet (0.064 mg./lOO cm.2).
The concentration at the thirty-five foot depth was intermediate in
magnitude (0.096 mg./lOO cm^). Astacin carotenoids were present in
129
-------
small amounts, but did not follow the pattern of concentration exhibited
by plant pigments in terms of sampling depth. The highest mean concen-
tration of astacin carotenoids was found in samples from a depth of
thirty-five feet (0.035 MSPU/100 Cm2) and the lowest in samples from
2.5 feet (0.015 MSPU/100 cm2).
Chlorophyll a — A
Chlorophyll b— *
Chlorophyll c— o
Astacin Carotenoids
Non-Astacin Carotenoids
25
10 ~7s Jo 3"
Depth in Feet
f
Figure 81. Average Periphyton Pigment Concentrations (per
unit area of rock surface) at Standard Sampling
Depths, Stony Point Bay, Lake Superior, 1967.
The curves representing the relationships between periphyton
concentrations on an area basis and sampling depth in 1967 (Figure 81)
bear little resemblance to those of 1966 (Figure 76). Differences in
both shape and magnitude are obvious; however, it will be noted that
the major differences occur only at depths from 2.5 feet to ten feet.
The mean chlorophyll a_ concentration found at the 2.5 foot depth in
1967 (0.976 milligrams per 100 square centimeters) was more than five
times as high as the corresponding figure for 1966 (0.191 mg./lOO cm^).
The amounts of chlorophylls Ja and £ and non-astacin carotenoids were
four to five times higher at 2.5 fe"et in 1967 than in 1966. At the
five foot depth, all plant pigment groups were two to three times
higher in 1967. The mean chlorophyll a_ concentration at the ten foot
depth was thirty per cent higher in 19?7 than in 1966, but the other
plant pigment concentrations were not significantly different at that
depth. At the remaining depths (15, 20 and 35 feet), chlorophylls
£, b_ and £, and non-astacin carotenoids occurred in approximately the
same concentrations in 1967 as in 1966. Although the mean concentra-
tion of astacin carotenoids was low for both summers, the averages for
130
-------
1966 were somewhat higher than those for 1967 at all depths except
2.5 feet, vjhere the values were identical. The pigment concentration
values of 1967 are considered to be more accurate than those obtained
in 1966, because a correction was made for turbidity in the acetone-
pigment solutions. This correction was accomplished by subtracting
the absorbance reading at 750 millimicrons, a wavelength at which none
of the pigments absorbs any light, from the absorbance values at 480,
510, 630, 645 and 665 millimicrons, before these readings are used for
calculation of pigment concentrations.
As in 1966, the pigment concentrations calculated on an area
basis do not directly reflect the amount of periphyton growth at
each depth in the bay. This point is illustrated by the relationship
between total chlorophyll and ash-free dry weight of periphyton at the
standard depths (see Figure 82). The amount of total chlorophyll rose
from 5.58 x 10~3 milligrams per milligram of ash-free dry weight at
2.5 feet to 8.14 x 10"-* milligrams per milligram of ash-free dry weight
at thirty-five feet. The major increase in concentration occurred be-
tween the fifteen and twenty foot depths (6.12 x 10" 3 mg. chlorophyll/
mg. ash-free dry weight to 7.85 x 10*3 mg. chlorophyll/mg. ash-free
dry weight). The relationship between chlorophyll concentration and
biomass is further established by consideration of the total numbers of
organisms at each depth. A continuous downward trend in the counts as
depth increased was obvious. The organisms in deeper water apparently
had increased their pigment concentrations in response to lower light
intensity as in 1966. However, the relationship between total chloro-
phyll and ash-free dry weight (Figure 82) indicates that this increase
was not so marked in 1967 as the pigment per organism ratios of 1966
would suggest.
fe 8-
n 2
'o .?
x | 6-
:hlorophy
-free do
^
232
5 E
01
i
0
© «
/
© — ®-
2*5 5 10 15 2O 25 3O 35
Depth in Feet
Figure 82. Average Periphyton Total Chlorophyll Concei
(per unit ash-free dry weight) at Standard
Sampling Depths, Stony Point Bay, Lake Superior,
1967.
131
-------
The increased periphyton biomass in the shallow x<7ater of Stony
Point Bay in 1967 (indicated by pigment concentrations) may be explain-
ed on the basis of weather. Very few violent storms arose during the
summer of 1967; the organisms growing in the shallow waters were dis-
turbed less often by currents and wave action than in 1966. East and
northeast winds cause the most severe turbulence along the north shore
of Lake Superior because their course parallels the long axis of the
lake. United States Department of Commerce local climatological data
show that no northeast winds occurred in the general area during the
1967 sampling period. East winds occurred on only eleven of the sixty-
seven days, or sixteen per cent of the time. During the summer of 1966,
east and northeast winds prevailed thirty-nine per cent of the time.
These data reinforce personal observations which indicated that the wa-
ters of Stony Point Bay x*ere much calmer during the 1967 season than in
1966. The hypothesis is that many periphytic organisms were washed
away from the shallow areas in 1966, x^hile those in relatively deep
water were not affected by wave action. Thus the biomass in deep x^ater
was of approximately the same magnitude both summers.
The variations in pigment concentrations at each depth (on a
unit area basis) according to sampling date are presented in Figures
83 through 94. The points represent the individual measurements from
which the average concentrations at each depth (Figure 81) were calcu-
lated. While the general pattern of Figure 81 may be seen by superim-
posing the individual graphs and observing the area under each curve,
it is obvious that the variation in terms of time is not the same at
each depth. In discussing these variations, the sample taken on Nov-
ember 10 will be considered separately.
g
f
o
5
I
I1
Chlorophyll a — A
Chlorophyll b— O
Chlorophyll c— *
050
Dale
Figure 83. Periphyton Chlorophyll Concentrations (per unit
area) at 2.5 feet, Stony Point Bay, Lake Superior,
1967.
132
-------
20
1 "
•to
3
QJ
D
o
^
£ 0.5
Non-Asfacin —
Astacin —
A
A
I I
\ A
\ / A —
\l
ti.tl.tC
0
^
v~.
ti. oL o, ol
y
*O NJ
£ I
A
V-"\
^- jo fc if> &> ei
03 03 0) 0) jl
Date
Figure 84. Periphyton Carotenoid Concentrations (per unit
area) at 2.5 Feet, Stony Point Bay, Lake Superior,
1967.
At the 2.5 foot depth (Figures 83 and 84) the maximum concentra-
tions of all five pigment groups occurred early in the season; all
of the pigments peaked on July 13, except the astacin carotenoids,
which were highest on the first sampling day (July 11). The minimum
values for each pigment type at 2.5 feet were obtained near the end of
August. The maximum concentrations were about three times as high as
the minimum concentrations. For example, the maximum chlorophyll a_
value was 1.863 milligrams per 100 square centimeters on July 13,
while the minimum was 0.547 milligrams per 100 square centimeters on
August 28. While major peaks in the curves appeared on July 20,
August 17 and September 15, the general downward trend of each of the
pigment groups during the season is apparent.
There is no suggestion of a downward trend in pigment concentra-
tions during the summer at the five foot depth (see Figures 85 and 86).
The concentration of total pigments per unit area remained rather con-
stant throughout the sampling period. The maximum concentration of
chlorophyll <± (0.930 mg./lOO cm2) and non-astacin carotenoids (0.465
MSPU/100 cm2) occurred on July 27. Slightly lower peaks appeared on
August 10 and 28. The concentrations of chlorophylls b_, c^, and asta-
cin carotenoids reached their highest levels on August 28. The most
obvious depression in the major plant pigment curves occurred on
August 4.
133
-------
o
§
d.
o
I.
o
I
050
Chlorophyll a— A
Chlorophyll b- O
Chlorophyll c— *
ft I O—
*N ** OD o N» tv
co co oo oo oo OD
Date
oo 01
Figure 85. Periphyton Chlorophyll Concentrations (per unit
area) at Five Feet, Stony Point Bay,
Lake Superior, 1967.
;.a
SP X"*1 *N "^ ^ N* ^ st 5D lo trt cr»
T**rV'Tl'^i^iiT'i*rT^^i ^
P«» ts. ^v ^^ t*x. PS, ^o ^Q CD CD CD CD CD CD o) en ts
Figure 86. Periphyton Carotenoid Concentrations (per unit
area) at Five Feet, Stony Point Bay,
Lake Superior, 1967.
134
-------
Two major peaks were observed in the concentrations of all the
periphyton pigments in samples from a depth of ten feet (Figures
87 and 88). The maximum values for chlorophyll a_ (1.102 mg./lOO cm2),
chlorophyll £ (0.472 MSPU/100 cm2), and non-astacin carotenoids
(0.463 MSPU per 100 cm2) occurred on August 2. Chlorophyll b_ and as-
tacin carotenoid concentrations were highest on August 25. Between
these two dates, the level of all the pigment groups remained quite
low. No general trend during the sampling period is apparent.
200
a
o
1.
.0
5
1
Wo
oso
Chlorophyll a — &
Chlorophyll b — O
Chlorophyll c - *
tl.
.
«D
, TT
00 00 00
Date
nHij,
Figure 87
Periphyton Chlorophyll Concentrations (per unit area)
at Ten Feet, Stony Point Bay, Lake Superior, 1967.
0.5
Non-Astacin
Astacin
Date
Figure 88. Periphyton Carotenoid Concentrations (per unit area)
at Ten Feet, Stony Point Bay, Lake Superior, 1967.
135
-------
The pigment concentrations at fifteen feet were lower and less
variable than at all other depths during most of the summer (Figures 89
and 90). The chlorophyll a_ curve includes two peaks of nearly equal
magnitude (0.468 rag. per 100 cm2 on July 27, and 0.490 mg./lOO cm2 on
August 17). The non-astacin carotenoid values show a very similar
pattern, peaking on the same two days. Chlorophyll £, however, peaked
on July 20, while chlorophyll b reached its maximum level on August 28.
The concentrations of all the pigment types were lowest in September.
"6
u
o
ea
Q.
o
7.00
075
02
Chlorophyll o- A
Chlorophyll b- O
Chlorophyll c- *
o
5
Dofe
Figure 89. Periphyton Chlorophyll Concentrations (per unit area)
at Fifteen Feet, Stony Point Bay, Lake Superior, 1967.
0.5
o
c
o
O
03
02
I rt
Non-Astacin —
Astacin
o— ° — o— o— o
0 1 ^ i. i t
I £ 2: 3! £
*!** V ^ »2
ao oo oo 03
Dale
j j
J
Figure 90. Periphyton Carotenoid Concentrations (per unit area)
at Fifteen Feet, Stony Point Bay, Lake Superior, 1967.
136
-------
Figures 91 and 92 show that the periphyton pigments generally
increased on a unit area basis at a depth of twenty feet during the
sampling period. Chlorophyll a_ rose from 0.201 milligrams per 100
square centimeters on July 11 to a maximum of 0.784 milligrams per
100 square centimeters on August 25. In similar fashion, the non-asta-
cin carotenoid level increased from 0.036 MSPU per 100 square centimet-
ers on July 11 to 0.319 MSPU per 100 square centimeters on Septebmer 5.
The maximum chlorophyll £ value (0.473 MSPU/100 cm2) appeared on August
25, as did the highest chlorophyll b level (0.142 mg./lOO cm2). The
major pigments underwent a series of continuous increases and decreases
between August 10 and September 15.
1.00
:: 075
a
o
5
I
0.50
Chlorophyll a— A
Chlorophyll t>- o
Chlorophyll c- -*
i
s is i;
«o ao
op
Dale
III
o
I
Figure 91. Periphyton Chlorophyll Concentrations (per unit area)
at Twenty Feet, Stony Point Bay, Lake Superior, 1967.
§
«
c
o
c.
Q.
5
0.5
"67
oJ
"02
Non-Astacin
Aslacin
0 ^.
-------
The pigment concentrations at thirty-five feet also exhibited a
general increase during the summer (see Figures 93 and 94). The mini-
mum chlorophyll £ value, 0.303 mg./lOO cm^, occurred on July 17 and the
maximum, 1.046 mg./lOO cm.2, on September 5. Chlorophylls b_, £, and
non-astacin carotenoids reached their highest levels on September 5 or
15. The seasonal rise in the major pigment concentrations was general-
ly smooth, the only apparent depression occurring on August 28. The
astacin carotenoid values for the thirty-five foot samples, as for those
from all other depths, remained very low and varied little during the
sampling period.
§
I
t.
O
m
ISO
6 wo
050
Chlorophyll a- &
Chlorophyll b- O
Chlorophyll c- *
O^T
f^o—o—°—-o-
CD CD
Date
Figure 93. Periphyton Chlorophyll Concentrations (per unit area)
at Thirty-Five Feet, Stony Point Bay, Lake Superior,
0.5
O
c
tl
t.
o
o
~oJ
0.1
1967.
Non-Astacin — A
Astacin o
o~—r~
I ill
CO
CO
Jb kj
CO CD
Date
* is
ci) d,
Figure 94. Periphyton CarottmoLu Concentrations (per unit area)
at Thirty-Five Feet, Stony Point Bay, Lake Superior,
1967.
138
-------
It is not possible to account for each rise and fall in the pig-
ment concentrations at the various depths throughout the summer. How-
ever, there are reasonable explanations for differences between the
trends exhibited by the pigment concentrations at various depths,
and for some decreased in concentration on specific days. The rather
large variation in pigment concentrations at the shallower depths
(2.5 to 10 feet) during the sampling period probably reflects the ac-
tion of waves on the periphyton. The depressions and peaks represent
removal of organisms as a result of turbulent water and subsequent
regrowth during relatively calm periods. However, the high mean pig-
ment concentrations in the shallow water indicate that the biomass in
these areas was never seriously reduced by wave action. Some of the
variability in biomass in shallow water may also have been due to a
relatively lesser degree of homogeneity in the community in terms of
area than in deeper water. The continual rise in pigment concentra-
tions at the twenty and thirty-five foot depths during the summer is
probably indicative of a true seasonal increase in biomass, which rea-
ched a maximum on September 5. Presumably, the turbulence in shallow
water was more severe than that occurring elsewhere, and sufficient
strength to disturb the periphyton organisms. However, the depression
in pigment concentrations on August 28 at all depths indicates that a
current affecting all parts of the sampling area developed between
August 25 and 28. Such a current might be produced by strong, shift-
ing local winds. Weather data show that rainstorms and winds in ex-
cess of twenty-five miles per hour occurred in the sampling area on
August 26 and 27. During this period, the winds shifted from south
to northwest, and probably produced enough water movement to remove
part of the periphyton at all depths in the bay.
Analysis of samples collected on November 10 revealed that the
pigment concentrations on a unit area basis had decreased considerably
at all depths except ten and fifteen feet, where the concentrations
were never particularly high. The highest concentration of pigments
was present at a depth of thirty-five feet, while the lowest concentra-
tion was encountered at 2.5 feet. For example, chlorophyll a_ ranged
from 0.165 milligrams per 100 square centimeters at 2.5 feet to 0.752
milligrams per 100 square centimeters at thirty-five feet. Part of the
general decrease in pigment concentrations between September 15 and
November 10 may have been due to seasonal reduction in growth; however,
since the pigment concentrations were highest at thirty-five feet, it
is more likely that a severe storm removed much of the periphyton from
the rocks in the shallow water.
The foregoing explanations regarding the variations in pigment
concentrations during the summer are valid only if the pigment values
are correlated well enough with the numbers of organisms to indicate
the general magnitude of biomass at each depth. Correlation coef-
ficients were calculated for total counts and total chlorophyll values
for samples from each sampling depth. In addition, to facilitate fu-
ture estimations of numbers of periphyton organisms based on total
chlorophyll concentration, regression lines were constructed using the
139
-------
least squares method. Counts ( y axis) were plotted against total
chlorophyll values (x axis). The regression lines are presented in
Figures 95 through 100, along with the correlation coefficients (r),
the probability values (P), and the equations for the slope of each
line. The procedures followed in the calculation of correlations and
regressions are described in Appendix D. The two parameters were
found to be positively correlated at all depths, the correlation
coefficients (r) ranging from 0.639 (P=0.01) for samples from the 2.5
foot depth to 0.921 (P=0.001) for samples from a depth of thirty-
five feet. The correlation was generally better for samples from the
deeper water. It should be understood that these rather close corre-
lations do not contradict the findings which show differences in
amount of pigment per unit of ash-free dry weight from one depth
to another. The correlations and regressions were determined for each
depth and do not reflect any differences related to depth. A regression
line based on all counts and pigment concentrations irrespective of
depth would be useless in light of the fact that different relationships
exist between the two values at each depth. However, numbers of or-
ganisms in Stony Point Bay may be predicted from total chlorophyll
data x^hen the sampling depth is known and the proper regression
line is used. The results of such predictions may be expected to be
more accurate for samples from deep water than for those from shallow
water.
4000
in
2000
WOO
Y = 1,108,923 + 667,855 X
r = .639
P = 0.01
1.0
T
2.0
I
3.0
I
4JO
Mg Total Chlorophyll per 100 err?
Figure 95,
Regression Line, Counts Versus Total Chlorophyll;
Naturally Occurring Periphyton at 2.5 Feet, Stony
Point Bay, Lake Superior, 1967.
140
-------
4000
! 3000
10
Ifl
c
2000
;ooo
Y = 279,478 + 1,545,625
r = .739
P = 0.001
7.0
T~
2.0
3.0
4.0
Mg Total Chlorophyll per 100 cm2
Figure 96. Regression Line, Counts Versus Total Chlorophyll;
Naturally Occurring Periphyton at Five Feet,
Stony Point Bay, Lake Superior, 1967.
*
Q.
lo
£
4000
-
300?
2000
> WO
o
Y = 142,211 + 1,911,856 X
r = .818
P •-• 0.001
o.s
]
1.0
\
IS
Mg Total Cftlorophy II per 100 cm2
Figure 97.
Regression Line, Counts Versus Total Chlorophyll;
Naturally Occurring Periphyton at Ten Feet, Stony
Point Bay, Lake Superior, 1967.
141
-------
Q.
%
to
6
.1
4000
3000
.2000
1000
Y = -441,162 + 2,718,284 X
r • .804
P = 0.001
0.5 1.0
Mg Total Chlorophyll per 100 cm*
I
1J5
\
2.0
Figure 98. Regression Line, Counts Versus Total Chlorophyll;
Naturally Occurring Periphyton at Fifteen Feet,
Stony Point Bay, Lake Superior, 1967.
-------
e
to
c
o
01
^000
3000
2000
1000
Y » -571,304 + 1,641,849 X
r = .921
P - 0.001
0.5 1.0
Mg Total Chlorophyll per 100
1J5
Figure 100. Regression Line, Counts Versus Total Chlorophyll;
Naturally Occurring Periphyton at Thirty-Five Feet,
Stony Point Bay, Lake Superior, 1967.
.600
c
D
0)
oo
ct
Q.
to
{.00
.300
25 5
10
T
IS
20
25
30
35
Depth in Feet
Figure 101. Ratio of Periphyton Chlorophyll c/Chlorophyll a_
at Standard Sampling Depths, Stony Point Bay,
Lake Superior, 1967.
143
-------
0.6
Q.
o
| 6
«- o
0 'C
•£ 0.2
o
o
"J>
•<*
c
o
3:
2.5 5
IS 20
Depth in Feet
25
Figure 102. Ratio of Periphyton Non-astacin Carotenoids/Chloro-
phyll a_ at Standard Sampling Depths, Stony Point
Bay, Lake Superior, 1967.
ju
§ 7000
u
o
o
5000-
3000-
1000
-•- Incident radiation
2.5 5 1O 15 2O
Depth in Feet
—I—
25
30
35
Figure 103. Average Mid-Day Light Intensity at Standard Depths,
Stony Point Bay, Lake Superior; June - September,
1967.
144
-------
The mean ratio of chlorophyll c/chlorophyll £ was 0.459 for the
entire bay in 1967. However, the values calculated for each depth range
from 0.395 at 2.5 feet to 0.511 at thirty-five feet (see Figure 101).
In contrast, the ratio of non-astacin carotenoids/chlorophyll a de-
creased with increasing depth, varying from 0.486 at 2.5 feet to 0.344
at thirty-five feet (Figure 102); the mean for the entire bay was 0.415.
The same phenomenon, i.e., a decrease in the ratio of carotenoids/chlo-
rophyll £ as depth increases, has been reported for stratified marine
phytoplankton by Ryther et^ aU (1958). If the species composition of
the periphyton were very similar at all depths in the bay, it could be
assumed that observed differences in pigment ratios in large samples
of the community were a result of differences in the pigment ratios in
individual organisms of the same type. It could be further assumed
that these differences were due to environmental factors. The species
composition of the periphyton community at all depths in Stony Point
Bay was very constant (Fox, 1969), with diatoms making up over ninety
per cent of the population. Percentages of the various types of organ-
isms varied little with depth, so the composition of the community at
different depths is not important in explaining varying pigment ratios.
With this fact established, other possible reasons for differences in
pigment ratios at various depths can be explored. Table XXIII shows that
both chlorophyll a_ and chlorophyll £ increased in relation to ash-free
dry weight as depth became greater; however, the amount of chlorophyll
a_ per unit of organic weight is increased by only thirty-four per cent
from 2.5 feet to thirty-five feet, while chlorophyll £ is increased by
seventy-four per cent. This difference accounts for the rising chloro-
phyll £/a_ ratio as depth is increased. There is virtually no differ-
ence in the concentration of non-astacin carotenoids in relation to
ash-free dry weight at the standard sampling depths ( a decrease of five
per cent from 2.5 feet to thirty-five feet). The decreasing ratio of
carotenoids/chlorophyll £ as depth increased is a result only of the
rising chlorophyll jj concentration.
The rise in pigment concentrations in relation to organic weight
as depth is increased may be viewed as a response to lower light in-
tensity. The average mid-day light intensity at each sampling depth
for 1967 is shown graphically in Figure 103. Each point represents
an average of the readings taken on each of the seventeen sampling
days.
The average intensity at the surface of the water was 7275 foot-
candles. Six inches of water lowered the reading to 5600 foot-candles.
From this point the average readings decreased gradually with depth,
reaching a minimum of 265 foot-candles at a depth of thirty-five feet.
The readings at each depth were quite variable, depending on atmospheric
conditions and the effects of turbidity on the day a measurement was
made. It has been shown that visible light of relatively short wave-
length penetrates deeper into pure water than light of longer wave-
length; the same phenomenon, with certain variations, occurs in water
containing dissolved and suspended solids (Clarke, 1954),, Since the
major absorption peak in the red band for chlorophyll £ is at a lower
145
-------
wavelength than the peak for chlorophyll a_, the preferential increase
in chlorophyll £ by the periphyton as light intensity decreases may be
a response to the greater proportion of shorter wavelength light in
deep water.
TABLE XXIII
PERIPHYTON PIGMENT CONCENTRATIONS IN RELATION TO
ASH-FREE DRY WEIGHT AT STANDARD DEPTHS,
STONY POINT BAY, LAKE SUPERIOR, 1967
Mg pigment x 10~3/mg ash-free dry weight
Depth Chlorophyll Chlorophyll Non-astacin
a c carotenoids
2.5 ft. 3.62 1.42 1.76
5 3.50 1.43 1.64
10 3.79 1.64 1.65
15 3.64 1.79 1.45
20 4.65 1.94 1.64
35 4.86 2.48 1.67
146
-------
TABLE XXIV
SEASONAL VARIATION OF PERIPHYTON PIGMENT RATIOS
STONY POINT BAY, LAKE SUPERIOR, 1967
(ALL DEPTHS COMBINED)
Chlorophyll c Chlorophyll b Non-astacin
Date Chlorophyll a Chlorophyll a carotenolds
Chlorophyll a
7-11
7-13
7-17
7-20
7-26
7-27
8-2
8-4
8-8
8-10
8-14
8-17
8-25
8-28
9-5
9-15
.588
.611
.636
.677
.591
.511
.522
.510
.384
.460
.227
.242
.464
.622
.284
.342
.115
.208
.163
.222
.195
.214
.171
.190
.129
.181
.072
.059
.160
.263
.224
.164
.348
.364
.372
.408
.324
.428
.391
.417
.428
.431
.424
.453
.383
.383
.452
.418
147
-------
In order to determine whether or not the various pigment ratios
changed during the season, the ratios were calculated on the basis of
combined pigment concentrations from all depths for each sampling day.
The ratios of chlorophyll £, chlorophyll b_, and non-astacin carotenoids,
respectively, to chlorophyll a_ for each day are presented in Table XXIV.
The chlorophyll c/a_ ratios exhibit considerable variation, but no seas-
onal trend is apparent. The ratio of non-astacin carotenoids to chlor-
ophyll a_ is quite constant; a slight upward trend during the summer is
indicated. It is reasonable that the chlorophyll c/a_ ratio was much
more erratic on a seasonal basis than the carotenoid/chlorophyll £ ra-
tio, since the concentration of chlorophyll £ seems to be subject to
control by the intensity or spectral composition of light. The changes
in the £/a_ ratio during the sampling period may be indicative of vari-
able light intensity due to turbidity. The ratios of chlorophyll b_ to
chlorophyll a_, which should reflect the relative numbers of green algae
present in the samples, are quite variable and show no particular trend.
The highest ratio occurred on August 28 and the lowest on August 17.
The dry weights and ash-free dry weights of all periphyton samples
collected from Stony Point Bay in 1967 are presented in Tables XXV and
XXVI. The seasonal variation of the ash-free dry weights at each sam-
pling depth is shown graphically in Figures 104 through 109. Each weight
may be compared directly to a corresponding pigment concentration, since
samples for both determinations were taken from the same periphyton
suspension. The mean dry weight per unit area of rock surface was high-
est for samples from a depth of 2.5 feet and lowest for those from
thirty-five feet (Table XXV). The dry weights decreased with increasing
depth, except between fifteen and twenty feet, where the average weights
were nearly identical. The highest mean ash-free dry weight, 2.7 mil-
ligrams per square centimeter occurred at 2.5 feet, while the lowest,
0.91 milligrams per square centimeter, was recorded at fifteen feet
(Table XXVI). The weights increased slightly from fifteen to thirty-
five feet. The ash-free dry weights of the 1967 samples were found to
be well correlated with total counts of organisms. However, as shown
by Figure 82, the relationship between the organic weights and pigment
concentration was not constant at all depths.
148
-------
TABLE XXV
NATURALLY OCCURRING PERIPHYTON DRY WEIGHTS AT THE
STANDARD SAMPLING DEPTHS
STONY POINT BAY, LAKE SUPERIOR, 1967
MILLIGRAMS PER SQUARE CENTIMETER OF ROCK SURFACE
Sampling depth in feet
Date
7-11
7-13
7-17
7-20
7-26
7-27
8-2
8-4
8-8
8-10
8-14
8-17
8-25
8-28
9-5
9-15
11-10
Mean
2.5
28.8
30.0
19.7
33.3
39.8
33.9
28.9
14.8
21.2
12.5
27.9
21.4
21.9
23.3
52.0
39.5
21.3
27.9
5
7.4
8.7
26.1
10.7
18.4
17.2
14.4
5.9
19.8
20.3
11.7
13.6
36.0
29.6
21.5
28.8
21.3
18.2
10
9.0
4.4
9.6
10.5
16.5
17.7
16.2
12.7
10.4
9.0
9.2
14.3
44.3
10.5
12.1
10.7
17.5
13.8
15
7.8
6.2
6.1
10.8
14.5
15.2
17.6
18.8
11.3
10.6
16.7
17.9
14.0
14.8
4.8
3.1
13.4
11.9
20
3.3
9.2
7.4
4.7
8.1
7.2
8.5
13.8
27.8
11.5
15.8
12.1
20.3
9.3
13.7
17.5
17.0
12.1
35
6.0
7.9
_ *
8.1
8.4
7.3
11.0
9.0
10.5
10.4
10.9
10.5
13.9
13.6
19.6
17.2
13.8
10.4
* Sample was lost
149
-------
TABLE XXVI
NATURALLY OCCURRING PERIPHYTON ASH-FREE DRY
WEIGHTS AT THE STANDARD SAMPLING DEPTHS
STONY POINT BAY, LAKE SUPERIOR, 1967
MILLIGRAMS PER SQUARE CENTIMETER OF ROCK SURFACE
Sampling
Date
7-11
7-13
7-17
7-20
7-26
7-27
8-2
8-4
8-8
8-10
8-14
8-17
8-25
8-28
9-5
9-15
11-10
Mean
2.5
3.63
2.53
1.90
2.90
3.39
3.95
2.46
2.88
2.09
2.43
2.77
2.66
2.58
2.72
3.86
2.96
0.33
2.70
5
1.37
1.62
1.75
1.80
2.04
3.04
1.96
1.10
1.70
2.28
1.46
1.28
2.32
2.27
1.72
2.78
1.13
1.92
10
1.23
0.58
0.98
1.03
2.00
1.38
2.07
1.12
1.19
0.71
0.52
1.01
2.25
1.38
1.50
0.81
0.85
1.21
depth in feet
15
1.02
0.63
0.46
0.85
1.22
1.11
1.29
1.22
1.10
0.55
0.93
0.77
1.01
1.81
0.88
0.33
0.44
0.91
20
0.64
0.63
0.84
0.47
1.05
0.30
0.97
0.97
1.97
0.72
1.08
0.72
1.66
1.04
1.82
1.25
0.55
0.98
35
1.14
0.63
_*
0.69
1.05
0.96
1.04
1.09
1.58
0.80
0.82
1.61
1.18
1.48
2.32
1.65
1.17
1.20
*Sample was lost
150
-------
The following figures (104-109) present the detailed information
relative to seasonal variations in ash-free dry weights, and as indica-
ted earlier each weight may be compared directly to a corresponding
pigment concentration inasmuch as samples for both determinations were
taken from the same periphyton suspension.
E
u
1)
Q.
g>
4)
I
x:
ui
0
O
ft!
OOOOODOD (DOO CD o>
Date
Periphyton Ash-Free Dry Weights (per unit area) at
Five Feet, Stony Point Bay, Lake Superior, 1967.
151
-------
OJ
E
u
i.
a
*.»
o
I
.c
m
o
o. 1
O
£ 5 v w ^ ^ ^t?2i6^3SV-
NfJ.Nri.rxr1-
Date
Figure 107. Periphyton Ash-Free Dry Weights (per unit area)
at Fifteen Feet, Stony Point Bay, Lake Superior,
1967.
152
-------
E
u
o
en
0
Date
Figure 108. Periphyton Ash-Free Dry Weights (per unit area)
at Twenty Feet, Stony Point Bay, Lake Superior,
1967.
CM
E
u
L.
0)
CL
Ol
in
O
0.
(b (fa cb db 5i
Figure 109. Periphyton Ash-Free Dry Weights (per unit area)
at Thirty-Five Feet, Stony Point Bay, Lake Superior,
1967.
153
-------
On the basis of the average dry weight of all samples taken dur-
ing 1967, the total dry weight of the periphyton in Stony Point Bay
was calculated to be 55.5 tons (156 grams per square meter). The
corresponding ash-free dry weight was 4.4 tons (12 grams per square
meter), or 7.9 per cent of the total dry weight. The mild weather of
1967 was probably the main reason why the total dry weight (55.5 tons)
was higher than that produced in 1966 (37.1 tons). Since the 1966
samples seemed to contain more sand and clay than the 1967 samples, the
actual difference in weight may have been somewhat greater.
It has been suggested that low temperature may be part of the
reason for less extensive growths of periphyton in the deeper water of
Stony Point Bay. Temperature data for 1967 show that the deeper water
was in fact colder than the shallow water (see Table XXVII). Water
temperatures were taken each sampling day at every sampling depth as
well as at a point just below the surface of the water. It is obvious
that the water temperatures decreased with increasing depth throughout
the summer. The values at 2.5 feet ranged from 6.5° C. to 19.5° C. The
minimum and maximum temperatures were slightly lower at each depth from
five feet to twenty feet. The biggest difference was usually between
twenty and thirty-five feet. The temperatures at all depths increased
continually during the first two-thirds of the sampling period, reading
a maximum on August 14. After that date, the temperatures tended to
decrease slightly at all depths except twenty and thirty-five feet. At
the twenty foot depth, the maximum temperature, 14.0° C., was recorded
on August 14, and again on September 15. The thirty-five foot maximum,
9.5° C., occurred on August 14, 25, 28, and September 5. Even at these
times, the temperatures at 2.5, 5, and 10 feet were about twice as high
as the thirty-five foot value. On November 10, the temperatures at all
depths in the bay were very similar to those recorded on the first day
of the sampling period, July 11.
The average gross photosynthetic rate of periphyton organisms
taken from each depth in Stony Point Bay is presented in Figure 110.
The values are reported in terras of microliters of oxygen evolved per
hour per square centimeter of rock surface and were determined manomet-
rically at 20° C. and at a light intensity of 1500 foot-candles. Samples
from 2.5 feet produced the highest mean rate of oxygen evolution (44.6
microliters per hour per square centimeter). Samples from each succes-
sive depth evolved less oxygen per hour than the preceding ones, except
the twenty foot samples, which produced slightly more than the fifteen
foot samples. The mean production rate for the samples from thirty-five
feet was only 15.3 microliters of oxygen per hour per square centimeter.
The 1967 values were lower than those recorded for Stony Point Bay in
1966. This difference probably occurred because no carbon dioxide was
added to the atmosphere above the reaction flasks in the respirometer.
None was added because it seemed to slow the equilibration of gas phases
in the system rather than to speed the process. It was difficult also,
to add the gas mixture without pressurizing the system. The introduction
of normal atmospheric air to the gas spaces above the samples probably
produced more accurate readings.
154
-------
TABLE XXVII
TEMPERATURES AT THE STANDARD DEPTHS
STONY POINT BAY, LAKE SUPERIOR, 1967
DEGREES CENTIGRADE
Depth in Feet
Date
7-11
7-13
7-17
7-20
7-26
7-27
8-2
8-4
8-8
8-10
8-14
8-17
8-25
8-28
9-5
9-15
11-10
Surface
6.5
6.0
6.5
7.5
8.0
9.5
11.0
12.5
16.5
18.0
19.5
17.7
16.5
15.5
16.0
15.5
7.5
2.5
6.5
6.0
6.5
7.5
8.0
9.5
10.5
12.5
16.0
18.0
19.5
17.0
16.0
15.5
15.5
15.0
6.5
5
6.0
6.0
6.5
7.0
7.5
9.0
10.5
12.5
15.0
17.5
19.0
17.0
15.5
15.5
15.0
14.5
5.5
10
5.5
6.0
6.5
7.0
6.5
7.5
10.5
12.0
15.0
15.0
17.5
16.0
15.5
15.0
15.0
14.5
5.0
15
5.5
5.0
5.5
6.0
5.5
6.0
9.5
10.0
15.0
14.5
16.0
14.0
12.0
13.5
14.0
14.5
4.5
20
5.0
4.5
5.5
5.5
5.0
5.0
6.5
8.0
10.0
13.5
14.0
11.0
11.0
12.5
13.5
14.0
4.5
35
4.5
4.5
5.0
5.0
5.0
5.0
5.5
7.0
8.5
9.5
9.5
8.5
9.5
9.5
9.5
7.0
4.5
155
-------
L.
-c
o
(I
5:
20
10
5
is 20
Depth in Feet
Figure 110. Average Periphyton Gross Photosynthetic Rates
(per unit area) for Samples from Standard Depths,
Stony Point Bay, Lake Superior, 1967; Run at 20o
1500 Foot-Candles.
The variation in oxygen production by the periphyton samples from
each depth during the entire summer may be seen in Figures 111 through
116. While the total amount of pigment per unit area seemed to decrease
during the season at the 2.5 foot depth, the amount of oxygen produced
tends to increase with time. After an initial reading of 58.4 micro-
liters of oxygen per hour per square centimeter on July 11, the rate
dropped to 15.6 microliters/hour/cm2 on July 17 before rising eventually
to the maximum value of 70.6 microliters/hour/cm2 on August 25 (see Fig-
ure 111). Gross photosynthesis also increased during the summer at all
the other depths, even though the counts and pigments increased during
the period only at the twenty and thirty-five foot depths (Figures 112
through 116). This increased efficiency may have been due to an adap-
tation to warmer temperatures as the summer progressed. The test tem-
perature for the determination of photosynthetic rate, 20° C., exceeded
the highest temperature recorded in the bay. However, as the water in
the bay became warmer during the summer, the organisms became accustom-
ed to temperatures more nearly like the test temperature, and therefore
performed the photosynthetic reactions more efficiently at that temper-
ature.
156
-------
80
~W
~GQ
To"
^ 40
~2Q
~W
ei tv cb to ts
Date
Figure 112. Periphyton Gross Photosynthetic Rates (per unit area)
for Samples from Five Feet, Stony Point Bay, Lake
Superior, 1967; Run at 20° C., 1500 Foot-Candles.
157
-------
o"1
80
Jo
"SO
50
To"
Jo
w
Date
Figure 113. Periphyton Gross Photosynthetic Rates (per unit
area) for Samples from Ten Feet, Stony Point Bay,
Lake Superior, 1967; Run at 20° C., 1500 Foot-Candles
t
80
W
~60
"50
30
lo
To"
00 00 09 00
Date
—i 1 i—i i r~
"* ti *" Sj ^ 52
03 OD oo oo o> o>
Figure 114. Periphyton Gross Photosynthetic Rates (per unit area)
for Samples from Fifteen Feet, Stony Point Bay,
Lake Superior, 1967; Run at 20° C., 1500 Foot-Candles
158
-------
L.
-C
80
~7Q
"so
"50
7?
501
20
W
'\
(I.
00 CO CO 00
Dcrfe
> 9 10 >0
T7T i *r
CD CD <» en CT)
Figure 115. Periphyton Gross Photosynthetic Rates (per unit
area) for Samples from Twenty Feet, Stony Point
Bay, Lake Superior, 1967; Run at 20° C., 1500
Foot-Candles.
80
Jo
50
To"
^0
o-
\ 20
To"
Date
Figure 116.
Periphyton Gross Photosynthetic Rates (per unit
area) for Samples from Thirty-Five Feet, Stony
Point Bay, Lake Superior, 1967; Run at 20° C.,
1500 Foot-Candles.
159
-------
When the production rate in terms of oxygen produced per hour per
unit of ash-free dry weight is plotted against sampling depth (Figure 117),
it is seen that photosynthetic efficiency depends on the depth from
which the sample is taken, as well as on the time of year. The photo-
synthetic rate is highest (28.8 microliters of oxygen per hour per milli-
gram of ash-free dry weight) for samples from a depth of 2.5 feet,
and lowest (13.2 microliters/hour/mg. a.f.d.w.) for samples from thirty-
five feet. This trend exactly opposes that exhibited by the amounts of
pigment per unit of ash-free dry weight at each depth. When the amount
of oxygen produced per unit of chlorophyll is plotted against sampling
depth (Figure 118), it may be seen that the values are considerably low-
er at the twenty and thirty-five foot depths than at the shallower sam-
pling depths. The rates remained quite constant from 2.5 feet to fifteen
feet, averaging about 3000 microliters of oxygen per hour per milligram
of total chlorophyll. The twenty foot samples evolved 2516 microliter
02/hour/mg. total chlorophyll, while the thirty-five foot samples pro-
duced only 1566 microliters/hour/mg. total chlorophyll. The amount of
oxygen evolved per hour per unit of chlorophyll a_ produced about the
same pattern when plotted against depth.
For purposes of comparison with other reported assimilation values,
the production rates were also calculated in terms of grams of carbon
fixed per hour per gram of total chlorophyll. The value at 2.5 feet was
1.58; at five feet, 1.59; at ten feet, 1.70; at fifteen feet, 1.65; at
twenty feet, 1.55; and at thirty-five feet, 0.84. These assimilation
numbers are considerably lower than the ones calculated for Stony Point
Bay periphyton in 1966. The differences are probably due to the change
in methodology employed in the determination of photosynthetic rate.
The 1967 mean values represent many more analyses than were run in 1966,
and are therefore considered to be more accurate.
D ;-
£^
"T 3
o c
20
;o
T
. T
Figure 117.
;b 75 20 25 30 35
jDepfh in Peer
Periphyton Gross Photosynthetic Rates (per unit ash-
free dry weight), Stony Point Bay, Lake Superior,
1967.
160
-------
The apparent decreased efficiency in photosynthesis with increas-
ing depth may be due to adaptation to both temperature and light inten-
sity. It has been shown that temperature decreased with depth; there-
fore, the organisms grown in the shallow, warmer water would be more
apt to function at a more rapid rate at the test temperature (20° C.)
than those grown in deep, colder water. Average light intensity has
also been shown to decrease as depth increases in the bay. The aver-
age intensities at fifteen, twenty and thirty-five feet were lower than
in the standard test procedure; the samples from these depths, then,
would not be as accustomed to the test intensity as those taken from
the shallow depths. In order to further determine the magnitude of
variability in the relationship between pigment concentrations and pho-
tosynthetic rate, a correlation coefficient was calculated for these
two parameters of productivity. The correlation coefficient for the
combined data for all depths was 0.573 (P=0.001), indicating a rather
weak positive correlation.
Correlation coefficients were also calculated for total counts and
photosynthetic rate for each sampling depth, to test the seasonal vari-
ation in this relationship. Regression lines were also constructed as
a means for estimating production rates from numbers of organisms.
The regression lines, correlation coefficients (r), and probability val-
ues (P) are shown in Figures 119 through 124). The correlations were
positive at all depths, but were rather poor except for the thirty-five
foot samples, the data for the fifteen foot samples produced the
lowest coefficient (r=0.249, P=0.10); the two measurements correlated
best at thirty-five feet (r=0.844, P=0.001). Generally speaking, one
could not expect very accurate predictions of production rates based on
enumeration of organisms, even when the sampling depth is known. If
the depth were not known, such a prediction would not be at all advis-
able. The relationship between pigments and counts, and between photo-
synthesis and counts are apparently variable with respect to time. There
are obvious differences in the relationships in terms of the depth at
which the organisms grew. These statements should not imply that the
differences occur randomly; work performed in 1968 has shown that these
differences may be ascribed to environmental factors. As will be seen
in a following section, measurements made under standard laboratory con-
ditions may be adjusted to account for existing environmental conditions
at the time of sampling.
161
-------
s
o
I 4000]
c
o
200C
Chlorophyll total — O
Chlorophyll a — A
o—O
0 2.5
10
IS 20
Depth in Feet
25
Figure 118. Periphyton Gross Photosynthetic Rates (per unit
chlorophyll), Stony Point Bay, Lake Superior, 1967.
80
60
o
>
Y = 28.1 + .00000735 X
r » .318; P » 0.10
I I I
1000 2000 3000
Organisms x 10* per cm*
4000
Figure 119. Regression Line, Photosynthetic Rate Versus Counts,
Naturally Occurring Periphyton at 2.5 Feet, Stony
Point Bay, Lake Superior, 1967
162
-------
O
•c
-------
U
O
-C
80
20
Y - 13.4 + .0000033 X
r - .249
P = 0.10
7000 2000 3000
Organisms x 1
-------
The 1967 photosynthesis data are presented in several ways in
Table XXVIII. The average net photosynthetic rate for periphyton sam-
ples from all depths was 17.3 microliters of oxygen evolved per hour
per square centimeter of rock surface. The ratio of gross photosynthe-
sis to respiration ranged from 2.96 for samples from a depth of fifteen
feet to 3.46 for samples from five feet, and averaged 3.17. The pho-
tosynthetic rates were converted to net daily production values, as
carbon fixed per unit area and as glucose produced per unit area. Net
production in terms of carbon fixed varied from 0.57 grams per square
meter per day at thirty-five feet to 1.79 grams per square meter per
day at 2.5 feet; the average value was 1.01. The mean production rate
(as glucose) for all depths was 3.35 grams per square meter per day.
For the purpose of calculating mean production rates for the entire
bay, it was decided that the data for each of the sampling depths would
apply to a strip of the bay as x*ide as half the distance to the next
shallower sampling point plus half the distance to the next deeper sam-
pling point. Since the sampling area was pie-shaped, and since the sam-
pling points were progressively further apart toward the deeper water
(see Figure 2), the area corresponding to each sampling depth was vir-
tually the same size; therefore, each production value wa s given equal
weight in the determination of the mean. All of the net photosynthesis
data was calculated on the basis of a fifteen-hour day, and takes into
account daytime and nighttime respiration.
e
o
3
o
•c
Y = 3.6 + .0000118 X
r = .844
P = .001
2000
103
3000
per c/n'
Figure 124.
1000
Organisms
Regression Line, Photosynthetic Rate Versus Counts,
Naturally Occurring Periphyton at Thirty-Five Feet,
Stony Point Bay, Lake Superior, 1967.
4000
165
-------
TABLE XXVIII
PHOTOSYNTHESIS DATA FOR PERIPHYTON SAMPLED AT
DIFFERENT DEPTHS, STONY POINT BAY, 1967
RUN AT 20°C, 1500 FOOT-CANDLES
Sampling depth in feet
2.5 5 10 15 20 35 Mean
Gross photo-
synthesis +44.6 +31.8 +23.0 +17.2 +19.2 +15.3 +25.2
ul
Respiration
ul 02/cm2/hr -13.9 -9.2 -7.6 -5.8 -5.7 -5.1 -7.9
Net photosyn-
thesis
ul 0,/cra2/hr +30.7 +22.6 +15.4 +11.4 +13.5 +10.2 +17.3
P/R 3.21 3.46 3.03 2.96 3.36 3.00 3.17
Net production
Grams carbon
fixed per M2
per day 1.79 1.36 0.87 0.63 0.81 0.57 1.01
Grams (as
Glucose) per
M2 per day 5.96 4.53 2.90 2.10 2.70 1.90 3.35
The production rates calculated for Stony Point Bay in 1967 may
be compared with those reported for other periphyton communities and
certain phytoplankton communities. In making such comparisons it is
realized that the methodology varies in each investigation and that dif-
ferences or similarities may often be attributed to methodology. The
average rate of carbon fixation by Stony Point Bay periphyton, 1.01
grams/M2/day, compares rather well with the value reported for the per-
iphyton of the Logan River in Utah (0.6 grams/M2/day) by McConnell and
Sigler (1959). Kobayasi (1961) found a production rate of 0.33 grams
of carbon fixed/M2/day in the natural epilithic periphyton of the Ara-
kawa River in Japan. In both of these investigations, the light and
dark bottle oxygen technique was used, possibly producing lower results
166
-------
than would be obtained with a manor.etric method. In addition incuba-
tion of samples by Kobayasi and by McConnell and Sigler was accomplished
by submerging the bottles in water at approximately 11° C., considerably
lower than the test temperature (20° C.) used in the Stony Point Bay
study. On this basis, one might logically invoke Van't Hoff's law,
namely, that the reaction rate doubles for each 10° C. increase in tem-
perature, and raise the Logan River value to 1.2 and the Arakawa River
value to 0.66. The nutrient concentrations in the two rivers were quite
low, as are those found in Lake Superior. Wetzel (1963) has reported a
mean production value of 0.73 grams of carbon fixed/M2/day for the peri-
phyton of Borax Lake, in California. The actual production rates in
the four periphyton communities compared above are probably very similar.
Carbon fixation rates for communities other than periphyton are
quite variable and include a wide range of reported values. For instance,
Odum (1957) has shown the production rates in eleven Florida springs,
including the plankton and the periphyton, to range from 0.17 to 18.1
grams of carbon fixed/M^/day. A value of 0.49 grams of carbon fixed/M2/
day for the phytoplankton of Weber Lake, in Wisconsin, has been reported
by Manning and Juday (1941). Hogetsu and Ichimura (1954) determined the
mean production rate for the phytoplankton of Japan's Lake Suwa to be
0.44 grams of carbon fixed/M2/day. Data provided by Olson and Putnam
(1961) show that the phytoplankton of Lake Superior at Larsmont, not
far from Stony Point Bay, fix an average of 0.17 grams of carbon per
square meter per day during the summer months. Based on this result,
it is concluded that the periphyton of Stony Point Bay can produce five
to six times as much organic matter as the phytoplankton in the area
within one-half mile of shore.
In 1967, the periphyton of Stony Point Bay contained 0.097 grams
of chlorophyll per square meter of rock surface. This value is lower
than the mean yearly chlorophyll concentration in the periphyton of the
Logan River (0.30 grams/M2) as measured by McConnell and Sigler (1959),
and somewhat higher than the 0.040 grams/M2 reported by Kobayasi (1961)
for the Arakawa River periphyton. The periphyton growing in the Arakawa
River at the time of Kobayasi*s investigation was made up primarily of
diatoms. Wetzel (1963) found the mean concentration of chlorophyll in
the periphyton of Borax Lake to be 0.32 grams/M . Values ranging from
0.43 to 2.01 grams of chlorophyll/M2 in laboratory streams have been
recorded as the communtities changed from those dominated by diatoms
to those dominated by Phormidium (Mclntire and Phinney, 1965).
According to Odum (1959), Gessner has stated that the chlorophyll
of diverse communities develops in very similar amounts on a square meter
basis, thus providing an example of "community homeostasis." In light
of this contention, it is interesting to compare the chlorophyll con-
centration of Stony Point Bay periphyton (0.097 grams per M2) with the
concentrations in phytoplankton communities. The concentration of chlo-
rophyll in Lake Superior phytoplankton at the Larsmont station during
the summer of 1961 averaged 0.017 grams/M2 (calculated from data presen-
ted by Putnam and Olson, 1961). According to Hogetsu and Ichmura (1954),
167
-------
the phytoplankton of Lake Suwa also supported less chlorophyll (0.066
grams per M2) than Stony Point Bay periphyton. However, a much higher
value, 0.27 grams/>T, has been reported for the Gerlache Straits of
Antarctica by Burkholder and Sieburth (1961).
Very little information is available regarding assimilation values
for periphyton communities. The mean assimilation value for Stony Point
Bay periphyton was 1.4 grams of carbon fixed per hour per gram of chlo-
rophyll, according to the 1967 data. This figure compares well with
those reported for the epilithic periphyton of the Arakawa River by Ko-
bayasi (1961). When measured at a light intensity of 30,000 lux (2778
foot-candles), the organisms fixed 0.75 grams of carbon/hour/gram of
chlorophyll at 12° C. and 1.9 grams of carbon/hour/gram of chlorophyll
at 26° C. McConnell and Sigler (1959) report an assimilation value of
0.75 grams of carbon fixed/hour/gram of chlorophyll in the periphyton of
the Logan River. These figures agree very well with the assimilation
value calculated for Stony Point Bay periphyton under the test conditions.
Since certain accessory pigments have been shown to be active in photo-
synthesis, an assimilation value based on total pigments should be cal-
culated for all communities studied, so that the photosynthetic effi-
ciencies of diverse communities can be more accurately compared in the
future. For the periphyton of Stony Point Bay this value would be 1.12
grams of carbon fixed/hour/gram of total pigment.
It is difficult to compare the weights of Stony Point Bay periphy-
ton with weights reported for other periphyton communities because most
other investigations have involved the use of suspended glass slides for
the accumulation of organisms. Periphytic communities developing on
these slides do not contain the significant amounts of sand and clay
that are found in natural communities. The periphyton developing on
glass plates in several freshwater lakes in Washington produce an aver-
age dry weight of only 0.15 grams per square meter, compared to 156
grams per square meter for Stony Point Bay periphyton. Corresponding
organic weights were 0.015 and 12 grams per square meter. The organic
weight of the material in the Washington lakes was 34 per cent of the
dry weight, while the organic weight of the Stony Point Bay periphyton
was only 7.7 per cent of the dry weight; this discrepancy emphasizes
the fact that natural communities contain large amounts of sand. New-
combe (1950) reports that the periphyton developing on glass slides in
Sodon Lake, Michigan, produced dry weights ranging from 0.5 to 2.0 grams/
M2 and ash-free dry weights varying between 0.16 and 0.95 grams/M2 (32
to 49 per cent). The average dry weight of the natural epilithic com-
munity in the Logan River was shown to be 25 grams/M2 (McConnell and
Sigler, 1959), while the periphyton community of Sedlice Reservoir, in
Czechoslovakia, weighed 15.9 grams/M2 (Sladecek and Sladeckova, 1963).
According to Atkins and Parke (1951), the chlorophyll of many marine al-
gae makes up from 2.3 to 2.9 per cent of the organic weight. The chlor-
ophyll of Stony Point Bay periphyton accounts for only 0.8 per cent of
the organic weight.
168
-------
Considering the data as a whole, the periphyton of Stony Point
Bay as measured by several parameters seems to be indicative of an
oligotrophic situation. The pigment ratios indicate a community domi-
nated by diatoms. The measures of biomass show that the growths are
of average magnitude when compared with the communities of other bodies
of relatively clean water. The production rate in the bay, based on
photosynthetic activity, is also similar to the rates exhibited by the
periphyton of mountain streams, springs and other cold lakes.
Periphyton Regrowth. Stony Point Bay
From July 31 to November 9, 1967, a study to determine the rate of
establishment of periphyton organisms on denuded, autoclaved rocks was
conducted in Stony Point Bay. In the course of the study, eighty-four
rocks were recovered from the three stations where they had been placed
on July 31. These stations were at depths of ten, twenty and thirty-
five feet. Selected "incubation times" ranged from eight hours to 101
days. On the final sampling day, November 9, samples were collected
only at the thirty-five foot depth, because the marker buoys for the oth-
er two stations had been dislodged by a storm.
The amounts of chlorophylls a_, b_, and £ per unit area of rock sur-
face at each sampling time are presented in Figures 125 through 127.
In general, the chlorophyll concentrations increased continually during
the study period, rising to a maximum at all three depths on September
15, the last day on which all depths were sampled. On any given day,
the amount of chlorophyll per unit area was found to be about equal at
the three depths. At the ten foot depth, chlorophyll £ increased from
0.004 milligrams per 100 square centimeters to 0.165 milligrams per 100
square centimeters during the forty-six day period. The chlorophyll a_
concentration at twenty feet began at 0.004 mg/100 cm2 and rose to 0.213
mg/100 cm2, while at thirty-five feet, the concentration increased from
0.003 mg/100 cm2 to 0.185 mg/100 cm2. The concentration of chlorophyll
a. at the thirty-five foot depth had dropped to 0.108 mg/100 cm2 by Nov-
ember 9 (101 days). The only other depression occurred on August 28,
and was apparent in both the ten and thirty-five foot samples.
Chlorophyll £, chlorophyll b_, and non-astacin carotenoids were
present in about the same relative amounts as in the naturally occurring
periphyton of Stony Point Bay, indicating that the same types of organ-
isms were present. All of the pigment groups increased with time ex-
cept the astacin carotenoids, which varied between 0.002 and 0.015
MSPU/100 cm at all three depths and were as low on September 15 as they
were on August 4 (0.004 MSPU/100 cnr). The varying astacin carotenoid
concentrations are probably indicative of the presence of inconsistent
numbers of Cladocerans in association with the attached algae. The
ratio of chlorophyll £ to chlorophyll ji varied widely during the sampling
period, occasionally exceeding unity when the total concentrations were
very low. On the other hand, the increase in the concentration of
non-astacin carotenoids during the summer closely paralleled that of the
chlorophyll £ concentration; the ratio of non-astacin carotenoids to
chlorophyll £ did not vary significantly from 0.360 at ten feet, 0.312
at twenty feet, and 0.302 at thirty-five feet. Chlorophyll b_ concentra-
tions remained quite low throughout the period, reaching a maximum of
169
-------
0.035 mg. per 100 cm at the twenty foot depth on August 28. Since
the chlorophyll b_ concentration also peaked on the same date at the other
sampling depths, it appears that the relative number of green algae in
the regrowth material reached a maximum on that date.
When the total chlorophyll concentrations obtained on the last
regular day of sampling (September 15) are divided by their "incubation"
time (forty-six days), daily production rates are produced. The daily
rates for accumulation of chlorophyll at ten, twenty and thirty-five
feet are 0.00046, 0.00069, and 0.00056 grams per square meter per day.
No other investigations have been encountered in which the measurement
of chlorophyll has been employed to determine the rate of periphyton
accumulation on a natural substrate in the lentic situation. However,
while observing the growth of periphyton on concrete cylinders in a
river, Waters (1962) found that three to eight weeks were required for
the chlorophyll concentration to reach a maximum level. Past that point,
seasonal variations were shown.
-------
o
1^
o
5 Joo
I
»> .050
Chlorophyll a- A
Chlorophyll t>- o
Chlorophyll c- *
7-31
8hr
8-2
t8 hr
8-4 8-8 8-U 8-25 838 9-5 9-15
96hr 8 days Udays 25days 28days Xdays 46days
Date and 'Incubation Time '
126.
Regrowth Periphton Chlorophyll Concentrations (per
unit area) at Twenty Feet, Stony Point Bay, Lake
Superior, 1967.
.200
.150
8-
o
§
.100
£50
Chlorophyll a—
Chlorophyll b— o
Chlorophyll c- *
7-31
8hr
Figure 127.
8-2 8-4 8-8 8-U 8-25 8-28 9-5 9-15 11-9
48 hr 96 hr 8 days Udays 25days 28days 36days 46days IDIdays
Date and " Incubation Time"
Regrowth Periphyton Chlorophyll Concentration (per
unit area) at Thirty-five Feet, Stony Point Bay,
Lake Superior, 1967.
171
-------
The total dry weights and ash-free dry weights of the regrowth
periphyton are shown in Table XXIX. The weights generally increased
during the regrowth period at all depths. The daily production rate
in terms of total dry weight at ten feet was 5.76 grams/M2/day; at
twenty feet, 2.26 grams/Mz/day; and at thirty-five feet, 2.77 grams/
M2/day. Comparable figures for the rate of ash-free dry weight pro-
duction are 0.09, 0.05, and 0.06 grams/M2/day. It is believed that
the varying types of rocks which made up the substrata did not affect
the growth of periphyton in any way. All rocks "incubated" for a
given length of time at a certain depth supported approximately equal
amounts of biomass per unit surface area.
Several investigators have reported the rate of increase in organ-
ic weight as periphyton accumulated on glass slides or plates. For in-
stance, Kevern et al. (1966) have shown that the communities colonizing
plexiglass plates in their laboratory streams produced an average of
0.6 grams of organic matter per square meter per day. In their study
of the Red Cedar River, in Michigan, King and Ball (1966) found that
growth on plexiglass plates amounted to about 0.3 grams per square meter
per day. Using glass slides as a substrate, Castenholz (1960) reported
production rates up to 0.5 grams of organic weight per square meter per
day for lakes in the state of Washington. He believed that glass was
not too selective as a substrate for growth of periphyton and that sub-
mergence for two weeks was sufficient for the determination of production
rates. Foerster and Schlicting (1965), on the other hand, working with
glass slides, stated that "the artificial surface gave a flase impression
of the productivity trends and indicated only some of the significant
genera present in the ecosystem." Thus, in spite of the fact that in
general, one might expect that artificial media would result in lower
production figures, the production rates reported for stream periphyton
growing on artificial substrata are often higher than those for Stony
Point Bay periphyton. The average increase in organic weight at the
three sampling depths in the bay was 0.066 grams per square meter per
day. It must be remembered, however, that the regrowth substrata were
placed at depths of ten, twenty, and thirty-five feet in Lake Superior;
the light intensities and temperatures at these depths were lower than
those reported for streams in which production was very high.
The ash-free dry weights of the Stony Point Bay regrowth were
lower at twenty and thirty-five feet than at ten feet during the entire
sampling period. Since the chlorophyll concentrations were of virtual-
ly the same magnitude at all depths, the amount of chlorophyll per unit
of ash-free dry weight was higher at the twenty and thirty-five foot
depths than at the ten foot depth. This difference occurred on nearly
every sampling day. In order to test the significance of the chlorophyll
concentration as a measure of biomass accumulation, correlation coeffi-
cients were calculated for total chlorophyll and total numbers of or-
ganisms at each depth. The two parameters correlated very x^ell, the
coefficients ranging from +0.782 (P = 0.02) at the thirty-five foot
depth to 40.992 (P=0.001) at the twenty foot depth. The coefficient
for the ten foot samples was +0.950 (P = 0.001). Regression lines for
172
-------
the estimation of numbers of organisms from the regrowth chlorophyll
concentrations at each depth are shown in Figures 128 through 130.
Good correlation at each depth indicates that chlorophyll concentration
is a good parameter of the biomass of periphyton as long as sampling is
always done at the same depth.
The photosynthetic rates exhibited by the regrowth samples did not
increase smoothly on a unit area basis as did the pigment concentrations
and weights (see Figure 131). For the first five days of incubation, no
oxygen production could be demonstrated by use of the respirometer.
However, on August 8, the photosynthetic rate for the ten foot sample
was 5.54 microliters of oxygen per hour per square centimeter, for the
twenty foot sample, 4.65 microliters/hour/cm2; and for the thirty-five
foot sample, 3.85 microliters/hour/cm2. Corresponding values for August
14 were 23.1, 19.5, and 21.1 microliters/hour/cm2. After August 14,
the rates decreased rather than following the general pattern of increase
exhibited by the parameters of biomass. The rates at ten, twenty, and
thirty-five feet on September 15 were 14.8, 12.6, and 17.6 microliters/
hour/cm 2. Until August 14, the ten foot samples produced the highest
photosynthetic rate; after that date, the thirty-five foot samples showed
the greatest photosynthetic activity. The photosynthetic rates, on a unit
area basis, did not correlate well at all with total numbers of organisms.
In fact, the correlation coefficients were negative at all depths, ranging
from =0.213 (P=0.10) for the twenty foot samples to -0.791 (P=0.01) for
the ten foot samples.
TABLE XXIX
DRY AND ASH-FREE DRY WEIGHTS OF PERIPHYTON OCCURRING
AS REGROWTH, STONY POINT BAY, LAKE SUPERIOR, 1967
MILLIGRAMS PER SQUARE CENTIMETER OF ROCK SURFACE
Dry
Depth
Date
7-31
8-2
8-4
8-8
8-14
8-25
8-28
9-5
9-15
11-9
0
0
1
1
5
13
16
7
26
1
•
0
68
54
65
92
03
18
53
97
49
_*
Weight
in Feet
20
0.28
0.27
0.80
1.83
6.96
7.49
11.71
9.48
10.41
.*
0
0
0
0
5
12
6
4
12
7
35
.62
.30
.59
.78
.36
.82
.10
.22
.75
.02
Date
7-31
8-2
8-4
8-8
8-14
8-25
8-28
9-5
9-15
11-9
Ash-Free
Depth
10
0.06
0.17
0.23
0.45
0.64
1.21
0.49
1.03
0.43
_*
Dry
Weight
in Feet
20
0.02
0.01
0.18
0.1S
0.57
0.52
0.37
0.40
0.24
.*
35
0
0
0
0
0
0
0
0
0
0
.04
.09
.17
.13
.54
.77
.26
.75
.29
.13
* No sample collected
173
-------
Q.
%
c
D
1000
-
750
500
250
Y = 47,281 + 1,539,566 X
r = .950
P = 0.001
I
0.25
0.50
0.75
7.00
Mg Total Chlorophyll per 100 err?
Figure 128.
Regression Line, Counts Versus Total Chlorophyll,
Regrowth Periphyton at Ten Feet, Stony Point Bay,
Lake Superior, 1967.
rooo
750
v 500
in
in
250
Y = 38,859 + 872,453 X
r = .992
P = 0.001
025 0.50 075
Mg Total Chlorophyll per 100 cm2
I
1.00
Figure 129. Regression Line, Counts Versus Total Chlorophyll,
Regrowth Periphyton at Twenty Feet, Stony Point Bay,
Lake Superior, 1967.
174
-------
.
o>
o.
in
_
-------
When the photosynthetic rates were expressed as assimilation val-
ues rather than on a unit area basis, the inconsistency in photosynthetic
efficiency during the regrowth period became obvious. For example, the
assimilation value for the twenty foot sample on August 8 was 3.01 grams
of carbon fixed per hour per gram of chlorophyll; however, by August 14
the value had risen to 8.53 grams C/hour/gram of chlorophyll. The assi-
milation value returned to 3.04 grams C/hour/gram of chlorophyll on Aug-
ust 28, and then fell further to 2.06 grams C/hour/gram of chlorophyll on
September 15. All of these values are higher than those calculated for
naturally occurring periphyton in Stony Point Bay in 1967, although by
September 15, the figures are not significantly different. By comparing
the highest total chlorophyll concentrations attained during the regrowth
study (September 15) with the average concentration for the naturally
occurring periphyton of Stony Point Bay, it is seen that the regrowth
never approached the natural level. At ten feet, the amount of chlorophyll
in the regrowth sample was only twenty-nine per cent of that present in
the naturally occurring growth; corresponding figures for the twenty
and thirty-five foot depths are forty-two and twenty-seven per cent.
However, the photosynthetic rate of the regrowth samples, on a unit area
basis, reached ninety-nine per cent of the rate exhibited by the natural
population at the ten foot level. At the twenty foot depth, the figure
was 101 per cent, and at thirty-five feet, seventy-two per cent. It is
not surprising that the regrowth population reacted in a different manner
to the test conditions than did the natural population. Waters (1961)
stated that developing populations cannot be expected to reflect the
same relationship to external factors as those which have long since
reached a maximum level of biomass. That contention is strongly support-
ed by the apparent discrepancy between the photosynthetic rates of nat-
ural and regrowth periphyton communities under the standard test condi-
tions.
Naturally Occurring Periphyton
Stations other than Stony Point Bay.
In an accessory study, periphyton samples were taken at eleven
points along the north shore other than Stony Point Bay. The stations
used are indicated in Table XXX and Figure 3. Collections were made
from the standard depths and on two separate occasions.
The organisms growing in these areas were studied primarily
to determine whether there are significant local differences in the amount,
type, and activity of the periphyton of Lake Superior's north shore.
In other words, the study was conducted to test the hypothesis that the
periphyton community of the prime sampling area, Stony Point Bay, was
representative of a large segment of the western arm of the lake. The
only data which are discussed in detail are those which appear to be
unusual.
The results of the north shore investigayion are summarized in
Table XXXI. For the purpose of comparing the various periphyton com-
munities, the average amount of total pigment from all depths on the
176
-------
two sampling days was calculated for each station. The individual
concentrations of chlorophylls a_, b, and £ at each sampling depth are
presented in Figures 132 through 152.
The mean dry and ash-free dry weights for each station are in-
cluded in the summary table XXXI. The average photosynthetic rate, on
a unit area basis, at the 2.5 and twenty foot depths may also be seen
in the summary table.
The total pigment concentrations of north shore periphyton ranged
from 0.338 milligrams per 100 square centimeters of rock surface at
Sugar Loaf Cove to 3.590 milligrams per 100 square centimeters at Lester
River. The mean for all of the stations was 1.363 milligrams of pigment
/100 cm2. This value compares well with the average concentration of
pigment in Stony Point Bay periphyton during the same summer (1.181
mg/100 cm2). The area supporting the least extensive biomass, Sugar
Loaf Cove, is the site of an extensive logging operation. The cove is
often used as a storage area for floating logs; during such period, the
light intensity at the bottom of the cove is severely diminished. Low
water temperature also limited the periphyton growth at Sugar Loaf Cove.
Temperatures of 5.5° C. at a depth of twenty feet and 7.0° C. at the sur-
face were recorded on August 31. The ratio of chlorophyll b/chlorophyll
c_ in the periphyton in the cove, 0.143, indicated that diatoms dominated
that community to an even greater extent than in Stony Point Bay. Only
two other sampling areas, Tofte and No-Name Bay, supported significant-
ly less periphyton biomass than Stony Point Bay, as indicated by pigment
concentrations.
TABLE XXX
PERIPHYTON SAMPLING LOCATIONS ALONG
THE NORTH SHORE OF LAKE SUPERIOR
Distance from Lester
Location River in miles
1. Lester River
2. Knife River
3. Burlington Bay
4. Split Rock River Bay
5. Beaver Bay
6. No-Name Bay (near Little Marais)
7. Sugar Loaf Cove
8. Tofte
9. Lutsen
10. Good Harbor Bay
11. Grand Marais
0
13.8
22.1
39.4
48.0
53.9
69.9
78.8
86.3
100.9
106.9
177
-------
00
TABLE XXXI
SUMMARY OF RESULTS, NORTH SHORE STATIONS, LAKE SUPERIOR, 1967
Study Area
Lester River
Knife River
Burlington Bay
Split Rock River
Bay
Beaver Bay
No-Name Bay
Sugar Loaf Cove
Tofte
Lutsen
Good Harbor Bay
Grand Marais
Mean
Mean Total
Pigment Cone.*
3.590
1.033
1.052
1.256
1.264
0.767
0.338
0.665
1.194
1.131
2.700
1.363
* Mg 4- MSPU/100 cmZ
** Me/cm2
Mean Weights**
Dry Ash-free
19.5
9.5
16.6
12.5
31.5
5.6
2.7
5.5
9.5
10.5
16.0
12.7
1.46
1.16
1.50
1.35
2.31
0.84
0.61
0.97
0.89
1.51
1.60
1.29
Production Rate***
Chi. b/c
0.568
0.324
0.359
0.347
0.402
0.413
0.143
0.411
0.331
0.405
0.588
0.390
2.5 feet
18.7
15.4
51.8
63.9
15.2
20.3
18.8
19.4
69.7
28.7
33.3
32.3
20 feet
44.1
23.1
35.8****
20.2
19.0
22.2
15.2
17.2
16.8
21.9
54.5
26.4
*** Microliters O^/hour/cm^
**** 15 feet
-------
The pigment concentrations, on a unit area basis, were consider-
ably higher at both Lester River and Grand Marais than at Stony Point
Bay. In addition, a relatively high ratio of chlorophyll b/chlorophyll
£ at these stations indicated the presence of a substantial percentage
of green algae in the periphyton. The ratios of chlorophyll b_/£ at Les-
ter River (0.568) and Grand Marais (0.588) were much higher than the
ratio at Stony Point Bay (0.366). Microscopic examination of samples
revealed that the Lester River station was the only area which supported
the growth of Cladophora. and that a rather heavy crop of Ulothrix was
present at Grand Marais. Since only the Lester River and Grand Marais
stations are near relatively large population centers, it is possible
that local sewage effluents were partially responsible for the support
of more extensive and more varied periphyton communities at these sta-
tions than in the other areas. The relatively high water temperature
at the Lester River station probably contributed in large measure to
the moderately heavey growth of Cladophora, According to Neil and Owen
(1964), the growth of Cladophora has reached nuisance proportions in
Lake Erie and Lake Ontario. The present study has shown that green al-
gae are of minor importance in the periphyton communities of the western
arm of Lake Superior. Even at the Lester River and Grand Marais stations,
diatoms are the dominant algal type among the attached algae.
The dry and ash-free dry weights of the north shore periphyton were
quite variable. The number of samples taken was not sufficient to allow
the correlation of the weights with other parameters of biomass. The
samples from Beaver Bay contained small (ten to twenty microns) black
magnetic particles which adhered to the periphyton mass on the rocks.
Although the total pigment concentration, on a unit area basis, in the
periphyton of Beaver Bay was less than the average value for all the
north shore stations, the dry weight was the highest encountered any-
where.
The gross production rates at the north shore stations, as measur-
ed by respirometry under standard conditions, were similar to those
exhibited by the periphyton of Stony Point Bay. The average photosyn-
thetic rate for organisms from a depth of 2.5 feet at all stations, 32.3
microliters of oxygen/hour/cm2, was lower than that recorded at Stony
Point Bay (44.6 microliters 02/hour/cm2); however, the samples from a
depth of twenty feet produced 26.4 microliters Og/hour/cn/, compared
with 19.2 microliters 02/hour/cm2 for the twenty foot samples from Stony
Point Bay
The types and numbers of organisms comprising the periphyton are
not drastically different at any point along the 107 mile segment of the
north shore of Lake Superior. Stony Point Bay would seem to qualify as
a representative area for future study of the effects of changes in
water quality on the condition of this community in the western arm of
Lake Superior.
179
-------
o
o
CL
O
i_
O
si
U
0.
l/)
2
en
1.0
O
2.5
Depth in Feet
Figure 132. Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Lester River Station,
Lake Superior, August 16, 1967.
§
g-
ft
s!
2.0
1.5
1.0
Chlorophyll O-A
Chlorophyll 6—*
Chlorophyll C-o
2.5 S
15 20
Depth in Fett
I
25
\
30
I
35
Figure 133. Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Knife River Station,
Lake Superior, September 5, 1967.
180
-------
7.5
§
O
C5
Q.
o
I,
o
O
1.0
0.5
Chlorophyll
Chlorophyll b-*
Chlorophyll c-°
10
!S 20 25
Depth in Feet
30 35
Figure 134. Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Knife River Station,
Lake Superior, September 15, 1967.
u
§
Q.
o
0.
1.0
as
Chlorophyll a—A
Chlorophyll b — *
Chlorophyll c—o
2.5
\
5
\
10
15
Depth in Feet
Figure 135. Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Burlington Bay,
Lake Superior, August 22, 1967.
181
-------
1.0
o
o
a
o
o
si
•
Chlorophyll c—o
\
2.5
\
5
\
10
Depth in Feet
\
15
20
Figure 137. Periphyton Chlorophyll Concentrations (per
unit area) at Standard Depths, Split Rock
River Bay, Lake Superior, August 29, 1967.
182
-------
s
•c
a
2.0
1.5
1.0
0.5
Figure
Chlorophyll a—&
Chlorophyll 6-*
Chlorophyll c—o
2.5 5
10
15
20
Depth in Feet
25
30
T
35
138. Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Split Rock River Bay,
Lake Superior, September 7, 1967.
1.5
§
Q.
o
-------
o
8
Q.
O
w
O
6
Chlorophyll o-A
Chlorophyll b—*
Chlorophyllc— o
2.5 5
10
15 20 25
Dtp//) in Feet
35
Figure 140. Periphyton Chlorophyll Concentrations (per
unit area) at Standard Depths, Beaver Bay,
Lake Superior, September 14, 1967.
w
a
o
I us
o
Chlorophyll a—&•
Chlorophyll b—*
Chlorophyll c—o
0.
i
*
Depth in Feet
Figure 141. Periphyton Chlorophyll Concentrations (per
unit area) at Standard Depths,
No-Name Bay, Lake Superior, September 1, 1967,
184
-------
1.0
§
I
0.5
Chlorophyll a—A
Chlorophyll b—o
Chlorophyll c—*
10
Depth in Feet
IS
20
Figure 142. Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, No-Name Bay,
Lake Superior, September 14, 1967.
a
o
5
5
I
I1
Chlorophyll a A
Chlorophyll b *
Chlorophyll c o
Figure 143.
Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Sugar Loaf Cove,
Lake Superior, August 31, 1967.
185
-------
o
§
I
-35
Chlorophyll a—&
Chlorophyll b~*
Chlorophyll c—°
Figure 144. Periphyton Chlorophyll Concentrations (per unit
area ) at Standard Depths, Sugar Loaf Cove,
Lake Superior, September 7, 1967.
BOO
s
I
^-
I1
.20,
Chlorophyll a- A
Chlorophyll b- O
Chlorophyll c- *
Figure 145. Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Tofte Station,
Lake Superior, August 31, 1967.
186
-------
1.0
-------
o
§
•c
O
Chlorophyll a—&
Chlorophyll i-*
Chlorophyll c-o
OS
Figure 148. Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Lutsen Station,
Lake Superior, September 7, 1967.
w
Chlorophyll a—A
Chlorophyll 6—*
Chlorophyll c—o &.
o
i.
o
g
as
Depth in Feet
Figure 149. Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Good Harbor Bay,
Lake Superior, August 31, 1967.
188
-------
§
I
5
I
s^
I1
7.0
Chlorophyll o—A
Chlorophyll 6—0
Chlorophyll C—*
\ \
2.5 5
10
\
15
20
Depth in Feet
25
30
35
Figure 150.
Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Good Harbor Bay,
Lake Superior, September 7, 1967.
Chlorophyll o-A
Chlorophyll 6-0
Chlorophyll e-*
2.S S
Depth In Feet
Figure 151.
Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Grand Marais Station,
Lake Superior, August 31, 1967.
189
-------
e
o
2.0
Q.
O
v.
O
£
f)
1.0
Chlorophyll a—A
Chlorophyll b—x-
Chlorophyll c-o
/)
Figure 152. Periphyton Chlorophyll Concentrations (per unit
area) at Standard Depths, Grand Marais Station,
Lake Superior, September 7, 1967.
Findings in 1968.
The amount of periphyton biomass along the north shore of Lake
Superior was well documented by the 1967 data, and the relationships
between some of the parameters used to measure the biomass were clari-
fied as a result of the 1967 investigation, However, several questions
relating to the biodynamics of this community remained. Biodynamics
as used here refers to that combination of internal and external factors
which governs the rate and efficiency of energy transfer through a
biological system* Since there seemed to be an inverse relationship
between light intensity and the concentration of pigments in the organ-
isms, it was necessary to determine experimentally whether or not the
concentrations would actually change if light intensity were altered.
If such a change occurred, the rate of change could be measured. This
factor is important in the consideration of the effects of varying tur-
bidity in lake water on the photosynthetic activity of periphyton.
190
-------
Although photosynthetic rates for the periphyton had been determined
in 1967, these measurements were made under standard conditions of light
intensity and temperature, and could not be applied directly to the
community in the lake. It had been shown that the photosynthetic effi-
ciency of the pigment unit under standard conditions depended on the
depth from which the sample was taken. Therefore, in order to calculate
the actual production rates under the variety of conditions to which the
periphyton organisms are subjected, it was necessary to determine photo-
synthetic rates of periphyton in a crossed gradient of light intensity
and temperature after the organisms had been "conditioned" to a particu-
lar set of conditions. Besides facilitating the adjustment of data col-
lected under standard laboratory conditions in 1967, the 1968 experiments
produced basic information about the effects of environmental changes
on the periphyton of western Lake Superior.
Analysis £f Test Communities and Water Chemistry
Periphyton samples were taken from Stony Point Bay during the
summer of 1968 for "conditioning" in the laboratory. For the results
of the experiments to be meaningful, it was imperative that the species
composition of the sample remain constant throughout the summer. There-
fore, the periphyton organisms from a depth of 2.5 feet in Stony Point
Bay, where most of the samples were taken for incubation, were counted
and identified on nine occasions during the summer of 1968. The results
of those counts (Table XXXII) show that the species composition of the
samples remained quite constant during the period of testing. The rel-
ative numbers of the ten most predominant organisms did not vary sig-
nificantly. As in previous years, the community was dominated by
Achnanthes microcephala. Synedra acus, and several species of Navicula.
Thus it was concluded that, for practical purposes, results of experi-
mentation at all times during the summer were comparable and that these
results could be employed for adjustment of data collected in 1967.
On one occasion, a sample was taken from Lake Superior near the
mouth of the Lester River. The periphyton at this point included a large
percentage of Cladophora. For the purpose of further establishing the
nature of the two communities used in the experiments, photosynthetic
rates were determined for samples of each at a variety of temperatures
(see Figure 153). There was no sharply defined optimum temperature for
photosynthesis in either community; the photosynthetic rate for the
Stony Point Bay sample reached a plateau which ranged from 20° to 25° C.,
while the optimum rate in the sample from the Lester River station was
maintained from 20° to 30° C.
Since water from Stony Point Bay was used as the medium for sus-
taining growth of periphyton in the incubators, it was necessary to show
that the quality of the water did not change appreciably during the
course of the experiments. The results of chemical analyses which were
performed on the water during the summer are presented in Table XXXIII.
Techniques described in Standard Methods for the Examination of Water
191
-------
and Wastewater (A.P.H.A., 1965) were employed in the chemical analysis
of water samples. It is apparent that the water quality did not change
significantly throughout the period of experimentation. With this fact
established, it was possible to determine experimentally the effects
of short-term changes in light intensity and temperature on the produc-
tivity of Lake Superior periphyton.
Light Intensity and Chlorophyll Concentrations,
The first series of experiments was designed to demonstrate that
the periphyton organisms of Stony Point Bay actually alter their con«
centration of chlorophyll in response to changes in light intensity,
and to determine the rate at which such an alteration occurs. Six
rocks supporting the growth of periphyton were taken from a depth of
2.5 feet in Stony Point Bay, where the light intensity was about 5000
foot-candles at mid-day. Six rocks were also taken from a depth of
thirty-five feet, where the light intensity was about 100 foot-candles.
The amount of total chlorophyll per milligram of ash-free dry weight in
the 2.5 and thirty-five foot samples was shown to be 0.00571 milligrams
and 0.00916 milligrams, respectively, Three of the rocks from 2.5 feet
were then incubated at a light intensity of eighty foot-candles and
a temperature of 10° C. The rocks from the thirty-five foot depth were
similarly divided and incubated under the same two sets of conditions.
At two day intervals, a portion of the periphyton from each rock in
each incubator was removed for pigment analysis.
The results of the pigment analyses are presented in Figure 154.
The amount of chlorophyll per unit of organic weight in the periphyton
which had been accustomed to a light intensity of 5000 foot-candles,
but incubated at only 80 foot-candles, began to increase within the
first two-day period. The maximum level was reached within six days.
During the six-day period, the amount of chlorophyll in the periphyton
increased at a rate of 0.00043 mg./mg. of ash-free dry weight/day, or
7.5 per cent/day. The final chlorophyll concentration was 45 per cent
higher than the original level. On the other hand, when samples accus-
tomed to 5000 foot-candles were incubated for twelve days at 800 foot-
candles, the amount of chlorophyll in the organisms was not altered.
Apparently the light intensity must be reduced to some point below
800 foot-candles before the organisms respond by increasing their pig-
ments.
192
-------
TABLE XXXII
\o
TEN MOST COMMONLY OCCURRING PERIPHYTON ORGANISMS
STONY POINT BAY, 2.5 FOOT DEPTH, 1968
NUMBER (1000's) PER SQUARE CENTIMETER OF ROCK SURFACE
Organism
Synedra a.cus
Achnanthes, microcephala
Navicula spp.
Cvmbella spp.
Gomphonema spp.
Synedra ulna
Cocconeis. spp.
Dentlcula thermalls
Fragilaria capuclna
Amphora ovalis
7-29
1,390
846
794
166
72
13
8
6
8
2
7-31
1,464
890
644
120
60
6
10
6
6
1
8-6
1,080
660
684
104
66
19
12
3
5
4
8-8
1,440
786
794
95
58
10
14
1
6
4
Date
8-12
1,120
832
540
144
46
16
18
2
2
1
8-14
946
786
465
176
40
5
12
4
2
2
8-20
858
574
480
145
58
10
14
6
6
1
8-27
880
428
386
96
42
12
8
4
5
1
9-5
765
460
324
92
38
9
10
4
3
1
-------
vO
TABLE XXXIII
SUMMARY OF WATER CHEMISTRY, STONY POINT BAY, 1968
Analysis
7-29
Temperature (Degrees C.)
PH
Hardness (mg/L as
Alkalinity (mg/L
Dissolved solids
Total Phosphorus
Nitrate Nitrogen
Dissolved Oxygen
Dissolved Oxygen
CaC03>
as CaCO
-------
0
10 15 20 25 30 35
Temperature (Degrees Centigrade)
40
45
Figure 153.
Photosyrtthetit Rates of Periphyton From Stony
Point Bay and Lester River Station at Various
Temperatures, June, 1968.
t ~
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Time in Days
— ©
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Figure 154.
Change in Periphyton Chlorophyll Concentration
(per unit ash-free dry weight) as Light
Intensity is Severely Altered.
195
-------
The periphyton organisms accustomed to a light intensity of 100
foot-candles, but incubated at 800 foot-candles, decreased the amount
of their total chlorophyll continually for an eight-day period. The
decrease averaged 0.00058 ing. of chlorophyll/mg. ash-free dry weight/
day, or 12.7 per cent/day. The final chlorophyll concentration was
forty-nine per cent of the original value. The level of chlorophyll in
the samples which had been switched from 100 foot-candles to 80 foot-
candles did not change appreciably during the twelve-day test period.
Having established that a light intensity of less than 800 foot-
candles was required to stimulate the addition of chlorophyll in the al-
gal cells of Stony Point Bay periphyton, the next step was to determine
the maximum intensity at which such an addition would be induced. For
this purpose, twelve periphyton samples were taken from Stony Point Bay
at a point where the mid-day light intensity was 825 foot-candles.
The rocks were divided into groups of three, and the chlorophyll concen-
tration per unit of organic dry weight was determined for each group.
Each group of rocks was incubated at 10° C., but at a different light
intensity (100, 250, 400 or 600 foot-candles). The amount of chlorophyll
per unit of ash-free dry weight was determined for each group of samples
at two-day intervals (see Figure 155). The organisms which had been sub-
jected to a reduction in light intensity from 825 foot-candles to 100
foot-candles increased the concentration of their chlorophyll by a total
of fifty-five per cent during an eight-day period, after which the con-
centration remained unchanged for another four days. The daily rate
of increase was approximately 6,9 per cent. The samples whose light in-
tensity had been reduced from 825 foot-candles to 250 foot-candles
also increased their level of chlorophyll, but to a lesser degree than
did the samples incubated at 100 foot-candles. In this case, the increase
totaled thirty-six per cent, or 3.6 per cent per day over a ten-day
period. The reduction from 825 to 400 foot-candles brought about a
total increase in chlorophyll of eighteen per cent over an eight-day
period, or 2.25 per cent per day. There was virtually no response to
the decrease in light intensity from 825 to 600 foot-candles.
These experiments indicate that the light intensity must be reduc-
ed to a point somewhere between 400 and 600 foot-candles before "light-
adapted" periphyton organisms will react by adding chlorophyll to their
cellular material. Below 400 foot-candles, a nearly linear, inverse re-
lationship exists between light intensity and amount of chlorophyll per
unit of organic weight after equilibrium has been reached. Up to this
point in the experimentation, it had been shown only that separate "light
adapted" or'fehade adapted" samples could be stimulated to increase or
decrease their pigment concentration by changing the light intensity to
which they were exposed. It was necessary to determine whether or not
a single sample would respond to decreased light intensity and then to
increased intensity. A sample was taken from shallow water in Stony
Point Bay (about 5000 ft-c. at mid-day) and placed in an incubator at
a light intensity of eighty foot-candles. After twelve days, the light
intensity was changed to 800 foot-candles. The amount of total chloro-
phyll per unit of ash-free dry weight was determined every two days.
196
-------
Figure 156 shows that the chlorophyll concentration increased for about
six days in response to the lowered light intensity, whereupon the con-
centration remained at the same level for the next six days. When the
light intensity was then increased from 80 to 800 foot-candles, the amoun
of pigment per unit of organic weight began to fall back toward the ori-
ginal level. After eight days at the high light intensity, the chloro-
phyll level had returned to a point only slightly higher than that main-
tained at an intensity of 5000 foot-candles. Thus it has been shown that
the periphyton respond quite rapidly to changes in light intensity (be-
tween 80 and 800 foot-candles) with virtually no lag phase in the al-
teration of chlorophyll concentration.
a
+->
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CL TJ
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"B 825 ft-c. »250ft-c. I
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A 825 ft-c. »400ft-c. f
<:> 825 ft-c. »6OOft-c. J time zero
1234 56789 10 11
— ©
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Figure 155.
Change in Periphyton Chlorophyll Concentration
(per unit ash-free dry weight) as Light
Intensity is Moderately Altered.
197
-------
4)
Q.
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6 8 10 12 14 16 18 20 22 24
Time i n Days
Figure 156. Change in Periphyton Chlorophyll Concentration
(per unit ash-free dry weight) as Light
Intensity is Reduced and Subsequently Increased.
24 H
18-
CM <
O "
en
E
0
Conditioned at: 15 C., 800 ft-c. ®
15° C., 80 ft-c. S
No conditioni ng
(from 15°C.,~4000ft-c.) A
Run at 1 5 C
20O 400 600 8OO 1000
Light Intensity (Foot-Candles)
1500
Figure 157. Rate of Photosynthesis in "Conditioned11 Stony
Point Bay Periphyton at Nine Light Intensities;
Samples Conditioned at 80 and 800 Foot-Candles;
Run at 15° C.
198
-------
Conditioned Periphyton Experiment
Six rocks supporting the growth of periphyton organisms were col-
lected from a depth of 2.5 feet in Stony Point Bay, where the light
intensity at the time of sampling was about 4000 foot-candles and the
temperature 15° C. A portion of this non-conditioned periphyton was
removed from each rock and combined for the determination of photosyn-
thetic rate at 15° C. and nine light intensities. The rocks were then
divided into two groups and placed in the incubators. One incubator
was set at a temperature of 15° C. and light intensity of 800 foot-
candles; the other was set at 15° C. and 80 foot-candles. After seven
days, the rocks were removed and the organisms tested for photosynthe-
tic rate at 15° C. and nine light intensities. Figure 157 shows that
conditioning at 800 foot-candles did not alter the pattern of photosyn-
thetic rate with respect to light intensity from that exhibited by the
samples accustomed to 4000 foot-candles. However, the organisms condi-
tioned at 80 foot-candles reached light saturation at a lower intensity
than did the other samples. Light saturation as used here may be defined
as the point at which the photosynthetic rate is no longer increased
significantly in response to increased light intensity. It may also be
seen that the sample conditioned at 80 foot-candles produced a higher
photosynthetic rate from 20 to 400 foot-candles than the other samples;
on the other hand, the maximum rate for the "shade adapted" periphyton
(80 ft-c.) was lower than that for the "light adapted" (800 and 4000
ft-c.).
Having shown that the periphyton organisms would adapt to short
term changes in light intensity, an experiment was designed to test for
adaptation to combinations of light intensity and temperature. Twelve
rocks supporting the growth of periphyton were taken from a depth of
2.5 feet in Stony Point Bay. The rocks were divided into groups of three
and placed in the four incubators. One incubator was set at 20° C.
and 800 foot-candles, one at 10° C. and 80 foot-candles. The samples
were incubated in water from Stony Point Bay for ten days. At the end
of the test period, the samples were removed and processed as usual.
Pigment analyses were run on the four samples and reported in terms of
amount of pigment per unit of ash-free dry weight. Aliquots of the
same samples were used for the determination of gross photosynthetic
rate in crossed gradients of light intensity and temperature.
The results of the photosynthetic rate determinations are presen-
ted in Figures 158 through 161. The same general pattern of "shade
adapted" and "light adapted" photosynthetic rates seen in the prelimin-
ary experiment is exhibited, whether the rates were determined at 10°,
15°, or 20° C. At these temperatures, the samples conditioned at 80
foot-candles produced more oxygen at the lower light intensities than
did those conditioned at 800 foot-candles regardless of the conditioning
temperature. The samples conditioned at 800 foot-candles, however,
reached a higher maximum rate of photosynthesis at light saturation than
did those conditioned at 80 foot-candles. Slight differences due to
199
-------
temperature adaptation are also apparent in samples run at 10°, 15°,
and 20° C. When run at 20° C. (Figure 158), the photosynthetic rate
at light saturation was higher for those samples conditioned at 10° C.
The reverse was true when the samples were run at 15° C. (Figure 159)
and 10° C. (Figure 160). When the photosynthetic rates were determined
at 5° C. (Figure 161), adaptation to temperature was more evident than
adaptation to light intensity. The samples conditioned at 10° C.
produced the same light-saturated photosynthetic rate at 5° C. regard-
less of the light intensity to which they were accustomed. Both of
the samples conditioned at 10° C. exhibited a higher photosynthetic
rate at all light intensities than either of the samples conditioned at
20° C. The compensation point varied somewhat for the different samples,
but usually fell between 80 and 130 foot-candles. Compensation point
is here defined as the light intensity at which gross photosynthetic
rate and respiration rate are equal (net photosynthetic rate - 0).
In order to illustrate another point, the same data were graphed in
a different manner (Figures 162 through 163). These graphs.show the
effects of temperature on the production rates of each sample at the
various light intensities. It is apparent that the test temperatures
produced a wider spread in the photosynthetic rates in the samples
incubated at 20° C. than in the ones incubated at 10° C. Samples
conditioned at 20° C. produced more oxygen when run at 20° C. and less
when run at 5° C. than those conditioned at IQo C. This point is em-
phasized by the temperature coefficients (QIQ) which were calculated
for all of the samples. QIQ calculated for the temperature range of
5° C. to 20° C. for samples incubated at 20° C. and 800 foot-candles was
about 2.0 at light saturation; the value for samples incubated at 20°
and 80 foot-candles was about 2.5 at light saturation. In contrast,
QlO for samples incubated at 10° C. and 800 foot-candles was approximate-
ly 1.7 at light saturation, while the value for samples incubated at
10° C. and 80 foot-candles was about 1.5. QlQ was also calculated for
all samples at all test light intensities for three intermediate tem-
perature ranges (5° - 10° C., IQo - 15° C., 15° - 20° C.). These values
are more variable than the ones calculated for the larger temperature
range, especially at the lower light intensities.
200
-------
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<-y / / o
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/ ' /
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g /®
.O/ Run at 20 C
•¥
-s
O 200 400 600 800 1OOO 1560
Light Intensity (Foot-Candles)
Figure 158. Rate of Photosynthesis in "Conditioned" Stony
Point Bay Periphyton at Nine Light Intensities;
Run at 20° C.
24-
£:
01
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X//0 20°C, 80 ft-c. A
:0f' Run at 15°C
0 200 400 6OO 800 1000
Light Intensity (Foot Candles)
1500
Figure 159. Rate of Photosynthesis in "Conditioned" Stony
Point Bay Periphyton at Nine Light Intensities;
Run at 15° C.
201
-------
-V
-A
10° C , 8OO ft-c. B
20° C., 8OO ft-c. ©
10° C., 80 ft-c. <•>
20°C., 80 ft-c. A
Run at 10 C
2OO 400 600 800 1000
Light Intensity (Foot-Candies)
15'OO
Figure 160. Rate of Photosynthesis in "Conditioned" Stony
Point Bay Periphyton at Nine Light Intensities;
Run at 10° C.
24
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Run at 5 C
£ *>
e/B/l^^'0 A
/El^^'i " " • — -
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200 400 600 800 1000
Light Intensity (Foot-Candles)
1500
Figure 161. Rate of Photosynthesis in "Conditioned" Stony
Point Bay Periphyton at Nine Light Intensities;
Run at 5° C.
202
-------
l_
Q.
\
O*
24-
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o *1
c- £
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X
Run at. 20 C
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Conditioned at 1 0° C., 800 ft-c.
20O 4OO 60O 800 1000
Light Intensity (Foot-Candles)
— ?
15°C
10C
-<3>
5°C
1500
Figure 163.
Rate of Photosynthesis in Stony Point Bay
Periphyton at Nine Light Intensities and
Four Temperatures; "Conditioned" at 10° C.,
800 Foot-Candles.
203
-------
24-
•f
c
Dl
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Run at : 0
20 C
15°C
Q. rn
i_i
10°C
A A
0
^ 5 C
/'/ Conditioned at 2O°C.. 80 ft-c.
O 2OO 4OO 600
Light Intensi
BOO 1OOO 15OO
ty (Foot-Candles)
Figure 164. Rate of Photosynthesis in Stony Point Bay
Periphyton at
Nine Light Intensities and
Four Temperatures ; "Conditioned" at 20° C. ,
80 Foot-Candles.
24-
01
0)
4) ^ 1R
Q.
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AV^
GT / /^"^
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Q Run at: 20 C
. F1— ^___^~~ • ©
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15°C
A
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ys &
-------
Assimilation values were calculated for the four samples at all
light intensities and temperatures. The assimilation values at all test
light intensities are higher for samples incubated at 800 foot-candles
than for those incubated at 80 foot-candles, regardless of temperature,
even though the latter samples had more chlorophyll per unit weight.
This fact confirms the suggestion, first made in 1966, that the chloro-
phyll unit becomes less efficient as an organism adds more chlorophyll
to its cellular material.
Following the conclusion of the experiment, the entire procedure
was repeated, the only difference being that the samples were collected
from a depth of thirty-five feet in Stony Point Bay instead of from 2.5
feet. The purpose of the second experiment was to determine whether or
not samples accustomed to relatively low light intensity and temperature
would be affected by conditioning in the same manner as were those
from an area of high light intensity and temperature. The photosynthe-
tic rates measured in crossed gradients of light intensity and tempera-
ture indicate that the samples from thirty-five feet reacted to the con-
ditioning in the same way as did the samples from 2.5 feet.
In order to determine the effects of conditioning periphyton
samples at intermediate light intensities, samples were collected from
a depth of fifteen feet in Stony Point Bay (825 foot-candles at mid-
day; 15° C.) and incubated for ten days at 100, 250, 400, and 600 foot-
candles and a temperature of 15° C. Photosynthetic rates were then de-
termined for the four samples at nine light intensities and four tem-
peratures. The "shade" reaction was obvious in the rates produced by
the sample which had been incubated at 100 foot-candles, as light satu-
ration is reached at 300-400 foot-candles. This type of reaction was
still present, but less obvious, in the sample incubated at 250 foot-
candles. Light saturation in the sample incubated at 400 foot-candles
was reached at about 600 foot-candles. The curve produced by plotting
photosynthetic rate against light intensity for the sample incubated at
600 foot-candles nearly paralleled that of the original "light adapted"
sample.
Since the periphyton community at the Lester River station in Lake
Superior was one of the few which differed significantly from the commu-
nity at Stony Point Bay, photosynthetic rates of a "non-conditioned"
sample from that s.tation were determined in crossed gradients of light
intensity and temperature. The temperature at the sampling point was
21° C., and the light intensity was about 4500 foot-candles. The purpose
was to see whether or not the rates for a community rich in Cladophora
would differ from those of the diatom community of Stony Point Bay.
The results of this experiment are shown in Figure 166. The general
magnitude of the photosynthetic rates, expressed as microliters of
oxygen produced per milligram of ash-free dry weight, was very similar
to that exhibited by the samples from Stony Point Bay. The slope of
the curves was typical of the "light adapted" reaction, and light sat-
uration was reached at about 900 foot-candles.
205
-------
20
200
Figure 166.
4OO 60O 8OO 1OOO 150O
Light Intensity (Foot Candles)
Rate of Photosynthesis in Periphyton from
Lester River Station (Lake Superior) at
Nine Light Intensities and Four Temperatures,
Sampling depth: 2.5ft.
5 ft.
10 ft.
15 ft.
20 ft.
35 ft.
Run at 20 C
0
2OO 4OO 600 800 10OO
Light Intensity (Foot-Candles)
H
*
A
1500
Figure 167. Rate of Photosynthesis in Stony Point Bay
Periphyton from Standard Depths Following
Period of Clear Weather; Run at Nine Light
Intensities.
206
-------
Photosynthetic Rates of Non-conditioned Periphyton
Several samples of Stony Point Bay periphyton were collected
from the six standard sampling depths during the summer of 1968 for
analysis of photosynthetic rates at various light intensities. One such
group of samples was taken on August 9, following a ten-day period of
very clear weather. During that period, there was little wave action
and very low turbidity in Stony Point Bay. The light intensities at
the six standard depths when the samples were taken were as follows:
2.5' - 5250 foot-candles
5' - 4250
10' - 2330
15' - 910
20' - 475
35' - 250
The photosynthetic rates of these samples at nine light intensities
are shown in Figure 167. There is little difference in the curves for
the samples from 2.5, 5, 10, and 15 feet. These curves are typical of
the "light adapted" reaction; light saturation was reached at about 600
foot-candles. The thirty-five foot sample produced photosynthetic rates
which were typical of the "shade adapted" reaction, reaching light sat-
uration at about 400 foot-candles. At all intensities below 600 foot-
candles, the thirty-five foot sample produced more oxygen per unit of
organic weight than the other samples. Above 600 foot-candles, how-
ever, it produced less than the others. A hint of the "shade" reaction
was exhibited by the sample from twenty feet.
Another group of samples was taken on August 22. During the period
between August 13 and August 22, the weather was cloudy and winds caused
considerable wave action in Stony Point Bay. Turbidity was relatively
high. Light intensities at the standard depths when the samples were
collected were as follows:
2.5' - 2440 foot-candles
5' - 1250
10' - 950
15' - 325
20' - 225
35' - 105
Photosynthetic rate curves for these samples were somewhat diff-
erent than those for samples taken on August 9 (see Figure 168). The
2.5, 5, and 10 foot samples still reacted as "light adapted" communities.
However, the curves for samples from all three of the remaining depths
exhibited the "shade adapted" reaction, reaching light saturation at
about 300 to 400 foot-candles. The periphyton at fifteen and twenty
foot depths in the bay were presumably conditioned to lower light in-
tensity during the stormy period. These results show that the adap-
tations which ware induced in the laboratory can occur naturally in the
lake.
207
-------
20
Sampling depth: 2.5ft. 0
5 ft. a
10 ft. *
15 ft. A
20 ft. <£
35 ft. x
Run at 20 C
200 4OO 60O 800 1OOO
Light Intensity (Foot-Candles)
150O
Figure 168. Rate of Photosynthesis in Stony Point Bay
Periphyton from Standard Depths Following
Period of Stormy Weather; Run at Nine Light
Intensities.
20
.? 16
-------
Diurnal Variation in Respiration Rate
For the purpose of calculating daily net production rates from
the 1967 periphyton data, it was assumed that the respiration rate
remained constant throughout a twenty-four hour period. To test this
assumption, a sample from the 2.5 foot depth in Stony Point Bay was
tested for respiration rate in the dark at hourly intervals for twenty-
four hours. Net photosynthetic rate during alternate light periods was
also determined each hour. Gross photosynthetic rate was calculated
from net photosynthesis and respiration measurements. The results of
these hourly measurements are presented in Figure 169, The net photo-
synthetic rate remained quite constant during the entire twenty-four
hour period. However, the respiration rate and gross photosynthetic
rate both decreased during the nighttime hours, reaching minimum values
at about 4:00 A. M. Between 10:00 P.M. and 7:00 A.M., the rates averag-
ed lower than the daytime readings by about 2.5 microliters of oxygen/
hour/mg. of organic weight. The diurnal reduction in respiration should
be taken into account when net daily production rates are calculated
from instantaneous rates determined in the daytime. As a point of aca-
demic interest, this experiment demonstrated that gross photosynthetic
rate should not be measured in artificial light during the nighttime
hours, because that rate is not a true reflection of photosynthesis in
the daytime.
On another occasion, the same experiment was run using a sample of
Stony Point Bay periphyton which had been incubated in constant light
(800 foot-candles) for ten days (see Figure 170). In this case, no
diurnal variation in respiration rate appeared during the twenty-four
hour period. It is assumed that the long period of constant light
destroyed the respiratory rhythm.
.c
O)
L 5
^>
i_ i_
3 TJ
O
"^ O
"****"% -®-©-0-©-©-©-0-0-®^0_0-'©-©— Q
Gross Photosynthesis
0-©^0-©_0— ©-©'©— ©-©-®-.0— ©-0— 0-0^0— ©'•©^ ^-0-©'S~-0
Net Photosynthesis
o
Run at 20 C., 1500 ft-c.
Respiration
©_©— ®— 0__@^©-0— 0--®-^0_©— ©— 0— ©-©— 0— ©— 0-®— ©-®— ©— ©-©
8 1012 2 4 6 8 1012 2 4 6 8
A.M. P.M. A.M.
Time of Day
Figure 170.
Rate of Periphyton Photosynthesis and Respiration
(24 Hours) Following Ten-Day Period of Incubation
in Continuous Light.
209
-------
Alteration of 1967 Photosynthesis Data
The photosynthesis data collected in 1967 under standard labora-
tory conditions will be useful in comparing the relative production rates
of Lake Superior periphyton with those of communities in other bodies
of water. If future tests on Lake Superior periphyton are run under
the same standard conditions, the results can be used to detect changes
in periphyton activity within the lake. However, if these data are to
be viewed as a reflection of true production rates at different depths
in the lake, alterations must be made to account for the effects of
light intensity and temperature.
The calculated average daily variation in light intensity at each
of the standard depths during the summer of 1967 is shown in Figure 171.
It is obvious that photosynthesis would occur at less than the light-
saturated rate for a different length of time at each station. The
light intensity data from Figure 171, the temperature data from Table
XXVII, and the production rate data have been employed in the conversion
of the 1967 rates to those more nearly reflecting conditions in the lake.
The result of each measurement made during the first two summers could
be altered according to the prevailing conditions at the time of sampling;
however, to provide an example of the conversion process, only the mean
photosynthetic rates for 1967 will be altered.
The mean gross photosynthetic rate of periphyton from the 2.5 foot
depth in Stony Point Bay was 44.6 microliters per hour per square cen-
timeter of rock surface (from Table XXVIII). The respiration rate was
13.9 microliters/hour/cm2. During thirteen daylight hours, the light
intensity at the 2.5 foot depth was at the optimum level or above, so
no correction is made for this factor during that period. However, the
average temperature at 2.5 feet was 12.5° C. On the basis of the dif-
ference between photosynthetic rate at 20° C. and 12.5° C. (interpolated)
the rate for those thirteen hours should be reduced by eighteen per
cent, to 38.6 microliters/hour/era. For two hours of daylight, both
temperature and light intensity (average 600 foot-candles) were below
the optimum level. The difference between photosynthetic rate at 20 C.
with light saturation, and photosynthetic rate at 12.5 C. with a light
intensity of 600 foot-candles, requires a reduction of the measured
rate by twenty-four per cent, to 33.9 microliters/hour/cm2. When these
two figures are properly weighted, the hourly rate becomes 36.2 micro-
liters/hour/cm2, or 543 microliters/cm2 for a fifteen hour day.
The average 1967 respiration rate for the 2.5 foot samples should
be reduced by seven per cent to account for the apparent nighttime var-
iation. The rate must be further reduced by eighteen per cent of the
original value to account for the difference in respiration rate at 20°
C. and 12.5° C. Thus the value is converted to 10.0 microliters/hour/
cm2. During a twenty-four hour day, the respiration amounts to 240
microliters/cm2. Therefore, the resultant net photosynthetic rate be-
comes 303 microliters/day/cm2, which is gross photosynthetic rate (543)
minus respiration rate. This value is equal to a production rate of
210
-------
1.602 grams of carbon fixed per day per square meter. The true mean
production rates for the other five sampling stations were computed in
a similar manner, and are presented in Table XXXIV. The amount of
reduction, in terms of per cent of the original value, increased con-
siderably with increased sampling depth.
5000
g
(J
o
tb 25OO
1250-
c.
en
0
.2.5
10
15
20'
35
56 789 10 11 12 1 23456789
A.M. Time of Day (CDT) PM.
Figure 171. Calculated Hourly Light Intensity at Standard
Depths in Stony Point Bay; Average for June -
September, 1967.
TABLE XXXIV
PERIPHYTON PRODUCTION RATES CONVERTED TO EXPECTED
RATES UNDER NATURAL CONDITIONS, STONY POINT BAY, 1967
GRAMS CARBON FIXED PER DAY PER SQUARE METER
Depth
2.5'
5
10
15
20
35
Measured value
under standard
lab. conditions*
1.79
1.30
0.96
0.63
0.81
0.57
Calculated value
for average lake
conditions
1.60
1.12
0.73
0.50
0.58
0.17
7.
reduction
10.6
14.0
16.6
21.2
28.0
70.2
* Standard laboratory conditions were 20° C and 1500 ft-c.
211
-------
The corrected photosynthesis data and the light intensity curves
can also be used to determine the efficiency of energy utilization by
the periphyton of Stony Point Bay during the summer of 1967. If the
energy required to form a gram-molecule of glucose is taken to be
676,000 gram-calories and is accompanied by the liberation of 22.4 X 6
liters of oxygen, then one gram-calorie will produce 190 microliters
of oxygen. Since the periphyton organisms cover the substrate completely,
all of the radiation within the range of 380 to 720 millimicrons reaching
a particular depth is available for use in photosynthesis. The light
curves in Figure 171 are based on light reception by a selenium cell,
which is sensitive only to light in the photosynthetic range (Jerlov,
1966). In that range, one foot-candle is equal to 0.00398 gram-calories/
hour/cn>2 (Strickland, 1958). When this conversion has been made, effici-
ency of energy utilization may be calculated by the use of the following
equation.
(net microliters 02/day/cm2) (100)
% eff. =(gram-calories/hour/cmi) (15) (190)
Energy reaching the floor of Stony Point Bay during the summer
of 1967 averaged 6.65 gram-calories per hour of daylight per square
centimeter. Since the average net production rate was 157 microliters
of oxygen produced per day per square centimeter, the efficiency of en-
ergy utilization was 0.82 per cent. This value compares favorably with
the efficiency factor (1%) calculated for phytoplankton in Lake Mendota,
Wisconsin, by Juday (1940). On this basis, it is concluded that peri-
phytic algae are capable of utilizing energy as efficiently as the free-
floating forms.
212
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Summary and Conclusions
Photosynthetic Pigments and Productivity of Periphyton
The study just described in detail was a comprehensive project
designed to measure productivity and explore the biodynamics of Lake
Superior periphyton. It was carried out during the summers of 1966,
1967, and 1968. The biomass, community structure, and photosynthetic
activity of epilithic periphyton from a representative area, Stony
Point Bay, were determined by examination of a variety of parameters.
Naturally occurring periphyton and regrowth organisms were studied.
In addition, the attached communities of other north shore stations were
examined, although to a lesser extent. Data reflecting the effects of
certain environmental conditions on the productivity of periphyton were
acquired in 1968 by laboratory experimentation. These data were employ-
ed in adjusting production rates which had been determined under stan-
dard laboratory conditions during the two previous summers. Some of
the more important findings and conclusions were:
(1) Pigment concentrations show that the biomass of the periphyton
of Lake Superior's north shore is similar in magnitude to other
oligotrophic bodies of water. Total pigment concentrations
ranged from 0.338 to 3.59 milligrams per 100 square centimeters
of rock surface, and averaged 1.36 mg/100 cm2.
(2) Pigment ratios indicate that most of the north shore periphyton
was dominated by organisms of the Phylum Chrysophyta.
(3) Assimilation values for Stony Point Bay periphyton averaged 1.48
grams of carbon fixed per gram of chlorophyll in 1967.
(4) The total standing crop of Stony Point Bay periphyton in terms
of dry weight was 55.5 tons, or 156 grams per square meter in 1967,
(5) Regrowth periphyton over a period of forty-six days, was equiva-
lent to approximately one-third only of the biomass of naturally
occurring periphyton. Chlorophyll levels increased by an average
of 0.00057 grams per square meter per day.
(6) Net production by the periphyton in 1967 averaged 1.01 grams
C fixed/M2/day, or 3.35 grams glucose per M2/day. The ratio of
gross photosynthesis to respiration averaged 3.17.
(7) In water up to forty feet deep in Lake Superior, periphyton can
be five to six times as important in primary production as the
phytoplankton.
(8) Laboratory experiments showed that alteration of light intensity
(below 800 foot-candles) causes a rapid change in the chlorophyll
content of the periphyton. The maximum rate of chlorophyll
reduction in response to a substantial increase in light inten-
sity was shown to be 12.7 per cent per day for eight days. The
213
-------
most rapid increase in chlorophyll concentration in response
to a severe reduction in light intensity was 7.5 per cent per
day for six days.
(9) Short-term "conditioning" of periphyton to different combinations
of light intensity and temperature caused a variety of responses
when the photosynthetic rate was measured in crossed gradients
of light intensity and temperature.
(10) For conditioned samples at light saturation Q10 ranged from 1.24
to 2.48. The compensation point varied from 80 to 130 foot-
candles.
(11) Naturally occurring periphyton was shown to exhibit typical "light-
adapted" or 'shade-adapted" photosynthetic reaction depending on
the prevailing level of light intensity.
(12) The efficiency of energy utilization by Stony Point Bay periphy-
ton was found to be 0.82 per cent, a typical value for algal
communities.
It is believed that the periphyton community will be very useful
in the future as an indicator of water quality, and that the data
collected in the course of this investigation will provide a baseline
for detecting the gradual advance of eutrophication in Lake Superior.
214
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SECTION VII
The Potential of Perlphyton as a Source
of Plankton Organisms
During the period from July 21 through August 19, 1970, periphyton
and phytoplankton of Lake Superior were studied in a miniature replica
of their natural environment, using two simulated "lake basins" of
natural rock located on the shoreline at Castle Danger and immediately
adjacent to the lake. These pools exposed to the same climatic con-
ditions prevailing over the lake in this general area, were furnished
with a constant flow of lakewater. Rocks gathered from the lake bottom
were placed in these pools to provide a natural substrate for periphy-
tic growth. Periphyton from the control and test pool rocks were col-
lected at regular weekly intervals while the phytoplankton population
in both pools and in the lakewater intake was sampled on a bi-weekly
basis.
The types of phytoplankton and numbers of organisms per liter
found in water samples from the lakewater intake, the control pool
effluent and the test pool effluent are summarized in Tables 36 to 38.
Comparable counts of the periphyton could not be made directly since
quantitation of these attached forms must be on the basis of organisms
per square centimeter of rock surface rather than individuals per liter
of water flowing through. Although the phytoplankton and periphyton
are necessarily expressed in different units and are, therefore, amenable
only to direct comparison within each group, their proportionate abun-
dance is nevertheless indicative of analogous and relative magnitudes
between organisms in the two populations. Results of the periphyton
study are presented in Tables 39 to 41.
For practical purposes it had been decided at the outset that
only the most abundant species in each sample would be counted, hence
blank spaces in tables referred to do not of necessity mean that a
given organism was totally absent on a given day. Instead it simply
indicates that not enough individuals of that species were present on
that occasion to qualify it as a member of the predominant group. This
helps to explain, for example, such occasional anomalies as the fact
that both Melosira and Ulothrix were present in samples from the test
pool effluent but were never recorded in the intake.
Except for Sphaerotilus. a filamentous alga-like bacterium, all
organisms included in the counts were algae. They were divided among
the various phyla as follows: thirteen species of Chrysophyta, five
species of Chlorophyta and three species of Cyanophyta. The complete
list of these organisms, in terms of genera and the types of samples
in which they were found, is presented in Table 35.
From this table it will be seen that Chrysophytes constituted the
predominant group of organisms in both the periphyton and the phyto-
215
-------
Table 35
Castle Danger Studies 1970
Predominant Organisms in the Phytoplankton and Periphyton
Phytoplankton
Periphyton
Chrysophyta
Achnanthes
Cymbella
Fragilaria
Gomphonema
Nitzschia
Synedra
Dinobryon
Asterionella
Tabellaria
fenestrata
Tabellaria
flocculosa
Rhizosolenia
Melosira
Denticula
Cyanophyta
Oscillatoria
Lyngbya
Coccochloris
Chlorophyta
Chlamydomonas
Cylindrocapsa
Ulothrix
Staurastrum
Scenedesmus
Schizomycophyta
Sphaerotilus
Intake
Control
Pool
Test
Pool
Control
Pool
Test
Pool
x
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Total species
17
17
19
12
11
present
absent or not sufficiently abundant to list
216
-------
plankton. Eight species, including six diatoms, one Chlorophyte and
one Cyanophyte, were found at all five of the sampling sites. This
information may be further summarized by tabulating the number of
species in each category and the percent this represents of total
number of species present.
Summary of Plankton Samples
Intake and Control Pool Test Pool Effluent
Effluent Species Present
Phylum Species Present
Chrysophyta 11 (65%) 12 (63%)
Cyanophyta 3 (17%) 3 (16%)
Chlorophyta 2 (12%) 3 (167.)
Schizomycophyta 1 (6%) 1 (5%)
Summary of Periphyton Samples
Control Pool Rocks Test Pool Rocks
Phylum Species Present Species Present
Chrysophyta 9 (75%) 7 (64%)
Cyanophyta 1 (8 %) 1 (9%)
Chlorophyta 2 (17%) 3 (27%)
Twelve of the nineteen species of organisms found in the phyto-
plankton were also found in the periphyton. The seven planktonic forms
which did not appear in the periphyton were: Tabellaria flocculosa.
Rhizosolenia griensjLs^ Melosira sp., Lyngbya cpntprta. Cyllndrocapsa
conferta and Sphaerotilus sp.
If the tabulations are examined further, and one considers each
phylum by itself, it will be seen that twelve species of Chrystophytes
were present in the plankton and that five of these were always found
in the intake water and effluent water of both pools. A sixth species
was preseat on every sampling date, excluding one. The organisms
always present were: Nitzschia palea. Synedra sp., Achnanthes mi.cro-
cephala. Dinobryon cylindricum^ and Rhizosolenia eriensis. On the
same basis, it will be found that in the periphyton as well as in the
phytoplankton the Chrysophytes constituted the important part of the
growth. When periphyton organisms are listed by numerical rank as
they were above, for the plankton, the arrangement is as follows:
Nitzschia. Synedra. Achnanthes. Fragilaria capucina. Cymbella and
217
-------
Gomphonema. The ranking used above relates only to the relative
abundance of the organism within the phylum and not to its overall
rank if all organisms are included. The comparative status of each
species at each sampling site with regard to all the organisms counted
is presented in Table 41.
It should be pointed out that Fragilaria. Cymbella and Gomphonema
occurred with much greater frequency in the periphyton than in the phy-
toplankton. In the past (Putnam and Olson 1961), Cymbella and Gom-
phonema found in fish-net slimes from Lake Superior have been associated
with extensive growths of these organisms on rocks along the North
Shore. It was postulated that violent storms had broken portions of
the periphyton masses loose and had swept them out into the lake where
they then became entangled in the nets by the long gelatinous "stalks"
which had served as the anchoring mechanism of the algae along the
shore. All fishnet slimes examined by these investigators showed that
a great part of the bulk of the slimes was made up of Cymbella and
Gomphonema "stalks". At Castle Danger, while Cymbella and Gomphonema
were regularly present in the periphyton they were not seen often in
the plankton effluents from the pools. From Table 41 it will be seen
that they ranked eleventh and sixteenth in the control pool and tenth
and nineteenth in the test pool effluent. Apparently a very strong
agitation of the water is needed to make these attached forms a part
of the plankton and such velocities are never reached by the pool
circulation.
Tables 36 through 40 reveal that Nitzschia. Synedra and Achnan-
thes not only are the most ubiquitous organisms present but also that
they are the only forms which appear consistently in both the phyto-
plankton and periphyton samples at all sampling sites. Moreover it
will be seen that in both periphyton and plankton the order of abundance
at all points was always: Nitzschia. Synedra. Achnanthes. In his open
lake studies of regrowth on artificially denuded rocks Fox (1969)
noted that Synedra and Achnanthes were generally predominant and that
in 1967 they were the only organisms found on all days and at all depths
sampled.
The intake counts for both Nitzschia and Synedra were exceedingly
high on the first sampling date (July 21) and remained, in fact, as
the highest intake values recorded for each of these species. These
particularly high values in the lakewater intake probably resulted
from the effects of a rather severe "northeaster" which had occurred
within this general area of Lake Superior on July 18 and 19 and which
may have caused a detachment of many of the periphytic organisms from
natural periphyton growths which characterize the rock Castle Danger
shoreline. The total count of organisms in the incoming water decreased
one full log cycle from 1,033,000 to 106,000 between July 21 and July
24. Counts in the influent water remained relatively low for the re-
mainder of the season. Between August 4 and August 8 there was a
dramatic drop in the temperature of the incoming lake water from 70° F
218
-------
to 43° F. This drop was accompanied by a corresponding decrease of
the total phytoplankton count from approximately 380,000 to 62,000
organisms. This phenomenon probably represented a shift in the therm-
ocline and the appearance of a new water mass in Lake Superior itself.
Largely because of the exceedingly high value on July 21, the overall
totals for the intake assign first place to Nltzschia while, actually,
it was more abundant than Synedra on only three sampling dates.
Achnanthes was always lowest of the three species in the intake data,
except for July 24 when it ranked second.
If one wishes to test the hypothesis that periphyton can be an
important source of organisms which typify the plankton perhaps the
best approach is to deal with a single species because this approach
is simpler and more readify understood than one which considers all
forms at once. There is always a danger if results are averaged or
"lumped" too greatly. We have already seen that in the experimental
pools at Castle Danger Cymbella and Gomphonema species were not pro-
viding measurable additions to the plankton. This was explained on
the basis that the violent water movements common in the lake itself
did not exist in the sheltered pools. Also it is well known that the
organisms mentioned are very firmly anchored. The alternative is clear.
An organism typical to the periphyton which is not attached must be
found, it must then be stimulated to the fullest growth possible in
order to magnify any small tendencies it may have to join the plankton
assembly. Thus if a given percentage is sloughed off one will, by
increasing the number of individuals in the periphyton, increase the
number of organisms leaving that community to become a part of the
plankton. If this increase is sufficient to be detected by prevalent
counting methods one has a device for checking periphyton contributions
to the plankton.
Nitzschia palea is an organism suited to such a study and the
test pools at Castle Danger provided the means for enrichment and
growth stimulation. Nitzschia palea appears commonly as a benthic
or littoral diatom and although definitely associated with the peri-
phyton it is a motile form and is not attached. It is, furthermore,
tolerant to certain types of fertilization. Its growth in oligotrophic
waters should, therefore, be considerably enhanced by the addition of
chemical nutrients. As the accompanying data show, this theory is am-
ply substantiated by its spectacular growth on rocks in the nitrogen
and phosphorus enriched test pool at Castle Danger. With a dosage of
0.163 ppm phosphate as P04-P and 1.96 ppm nitrate as N03-N, the growth
of Nitzschia on rocks in the test pool was 2.9 times that found in
the control pool. The foregoing figure is based on average results.
If proper allowance is to be made for the pools to come to full
equilibrium a period of time should elapse before the first samples
are taken. In this instance if the first two sampling periods are set
aside as a type of "breaking in" period it will also eliminate any
variations which might have been brought about by the "northeaster"
and the high influent counts mentioned earlier. On this basis the
219
-------
time for experimental observation would include the period from July
30 to August 20th, or a time span of 2/3 of a month. Calculations
made in accordance with this procedure indicated that the Nitzschia
counts in the enriched pool were 2.7 times higher than in the control
pool. This figure, though slightly lower than the first which was
based on all samples is probably more trustworthy.
If one turns to the counts of Nitzschia palea found in the in-
coming water, the control pool effluent and the test pool effluent,
and if the second method of calculation is adopted, the results are
as follows:
Plankton Study 1970
Castle Danger Test Pools
Nitzschia paleaCounts (Organisms/Liter)
Date
July 28
July 31
August 4'
August 8***
August 11
August 13
August 18
Average
Influent water
17,823
43,872
10,968
16,402
7,769
20,108
47,528
23,496
Effluent
Control Pool
75,405
87,744
10,054
10,968
49,813
40,216
72,206
49,486
**
Effluent
Test Pool
1,397,963
1,219,733
65,351
106,481
110,594
97,798
82,717
440,091
* Water coming directly from Lake Superior
** Six overturns of water per day
*** Period characterized by sudden drop in temperature
from 70°F (21°C) to 43°F (6°C)
It will be noted in the above tabulation that effluent waters
were generally higher in organisms than the incoming water, in terms
of Nitzschia palea cell counts. In the control pool the effluent
counts were, on the average, only twice as high, and this might be
considered as inconclusive evidence. However, in the enriched pool
where Nitzschia growths on the rocks was luxuriant, there was an
appreciable difference. On July 28th for example, the effluent con-
220
-------
tained 78 times as many N. palea cells as the influent. Three
days later the difference was much less and the effluent count had
dropped to 28 times that of the incoming water. On an average, the
Nitzschia count was 18 to 19 times as great in the water leaving the
test pool as in incoming waters. A difference of a log cycle can cer-
tainly be considered valid and on this basis the only explanation
which fits the situation, especially since at six overturns a day water
will remain in the pool for a period of four hours only, is that the
"excess" Nitzschia palea observed in the effluent water was derived
from the luxuriant periphyton growth observed on the bottom of the
pool. This demonstrates that periphyton, under experimental conditions
simulating a natural situation, can make contributions to the plankton
and alter its composition.
Cyanophyta and Chlorophyta were only small contributors to the
periphyton and plankton communities. Of the three Cyanophytes ob-
served during this study, Oscillatoria was the only blue-green alga
recorded from both the periphyton and the plankton. Lyn^bya contorta
and Coccochloris sp. were seen only in the plankton and were reported
only once. Lyngbya was recorded in all plankton samples including
the influent on August 4th. Similarly, Coccochloris was reported from
all plankton samples on August 13th. Qsci.llato.ria was found in the
incoming lake water on one occasion only, namely August 4th. It was
found in the control pool effluent on the same day in practically
the same concentrations. During the remainder of the season it was
found only in the test pool effluent where it was abundant during
the whole period, July 31 to August 18.
In the periphyton samples, Oscillatoria was found only once in
the control pool and this was on July 22 before the pools had been
fully equilibrated. After that the periphyton samples from the control
pool never had sufficiently high numbers of this species to be recor-
ded. The enriched test pool on the other hand, in contrast to the
control always had a good growth of Oscillatoria which constantly broke
loose and floated away to become an important part of the plankton
which characterized the effluent of this unit. Counts on the rocks
in the test pool varied from 162,000 to more than five million cells
per square centimeter. Correspondingly, while the influent samples
of plankton were devoid of Oscillatoria (August 9th excepted), the
test pool effluent after the periphyton growth matured, always contained
this organism. The numbers found in the effluait varied from 95,000
to 1,400,000 per liter.
The growths of Oscillatoria sp. like those of Nitzschia palea
demonstrated that the periphyton can be a source of plankton organisms
and that it can greatly influence the composition of the plankton
community.
Considering that the experimental program of this study was de-
signed, in part, to assess the relationship of chemically enriched
221
-------
waters to algal abundance, it is assumed that the considerable differ-
ence in growth of Qscillatoria in the control and test pools is, at
least partially if not largely, a function of the water quality in
these two pools. Furthermore, its response to the enriched environ-
ment of the test pool as opposed to the basically oligotrophic waters
of the control pool is consistent with the fact that this organism is
a typical inhabitant of "polluted waters,"
Chlamydomonag sp., Ulothrix zonata, Cylindrocapsa conferta.
Scenedesmus sp. and Staurastrum sp. comprised the five Chlorophytes
observed during the study period. Scenedesmus and Staurastrum were
recorded for samples taken on August 19 only, and solely from the
periphyton samples. Cylindrocapsa on the other hand was recorded for
plankton samples only and was never listed for the periphyton. Ulothrix
was observed once only in a plankton sample, but was recorded regularly
rrom the periphyton where it was sufficiently abundant to rank fourth,
just below Oscillatoria.
Unlike Ulothrix. the biflagellate vegetative cells of Chlamydo-
monas are highly motile and although it may often adhere to a substrate
in its palmelloid stage it is usually not considered as being truly
periphytic. At Castle Danger this organism was extraordinarily abun-
dant as a member of the periphyton community of the test pool, where its
numbers varied from roughly 700,000 to more than 3,000,000 per square
square centimeter of rock surface. Like Nitzschia palea and Qscilla-
toria sp. the Chlamydomonas organisms became an important part of the
test pool plankton after August 4th. Since this species did not come
in with the influent water, in numbers which were detected by the
counting procedure, its presence in the test pool effluent in concen-
trations ranging from approximately 500,000 to more than 2,000,000
organisms per liter is still another demonstration of the fact that
the periphyton is a source of plankton organisms. During its four
hour stay in the pool, at the temperatures which prevailed, it is not
conceivable that so many organisms could have been produced in the sup-
ernatant water.
Summary and Conclusions
Nitzschia. Synedra. and Achnanthes appeared consistently in both
the phytoplankton and in the periphyton at all sampling sites.
Nitzschia and Synedra counts were extremely high in intake water
from Lake Superior, particularly following severe water movements and
wave action in the lake.
On the average, Nitzschia palea counts were 18-19 time as great
in water leaving the test pool as in incoming water.
The abundant growths of Oscillatoria in the test pool continually
broke free to become part of the plankton community.
222
-------
Fertilization of the test pool water produced a growth of
Nitzschla palea 2.9 times greater than that found in the unfertilized
control pool.
On the basis of the above observations it may be concluded that
periphyton, particularly when it is very heavy in growth, does make
a contribution to the plankton population of a lake.
223
-------
TABLE 36
Lake Superior Plankton Counts [organisms/liter] — Castle Danger,
LAKEWATER INTAKE PIPE
Minn. (1970)
Organism
CHRySOPHyTA
Achnanthes microcephala
Asterionella fornosa
*Asterionella gracillima
Cymbella sp.
Dinobryon cylindricum
Fragilaria capucina
Gomphonema sp.
Nitzschia palea
Rhizosolenia eriensis
Synedra sp.
Tabellaria fenestrata
Tabellaria flocculosa
CYANOPUYTA
Coccochloris sp.
Lyngbya contorts
Oscillatoria sp.
CHLOROPHYTA
Chlamydononas sp.
Cylindrocapsa conferta
SCHIZOMYCOPHYTA
Chlcmydobaateriales
Sphaerotilus sp.
Total
Sampling Date
7/21
20,108
96,884
229,414
573,078
42,044
72,206
1,033,734
7/24
15,995
3,656
27,420
10,968
6,398
35,646
6,398
106,481
7/28
10,511
28,791
3,656
37,474
17,823
18,280
47,528
2,285
166,348
7/31
26,506
13,253
2,285
23,307
43,872
5,941
37,931
21,479
174,574
8/4
11,425
10,054
5,484
8,226
11,425
10,968
7,312
32,904
89,115
191,940
378,853
8/8
3,199
2,742
1,828
6,855
16,402
3,656
10,968
1,828
14,624
62,102
8/11
5,941
6,398
3,199
42,958
7,769
3,656
11,425
67,179
148,525
8/13
10,511
24,221
28,791
20,108
13,710
43,872
5,027
9,140
41,587
20,108
22,393
105,567
345,035
8/18
29,248
15,995
•17,366
47,528
10,054
59,867
44,329
75,862
300,249
Total
133,444
188,741
13,253
9,140
414,042
8,226
18,280
748,516
111,051
352,347
9,140
45,243
41,587
89,115
191,940
20,108
133,901
187,827
* Later re-identified and included with A. formoaa.
-------
TABLE 37
Lake Superior Plankton Counts [organisms/liter] — Castle Danger, Minn. (1970)
CONTROL POOL EFFLUENT
Organism
Achnanthes microcephala
Asterionella formosa
Cymbella sp.
Dinobryon cylindricum
Fragilaria capucina
Gomphonema sp.
Nitzschia palea
Rhizosolenia eriensis
N>
^•j Synedra sp.
Tabellaria fenestrata
Tabellaria flocculosa
CyANOPHNA
Coccochloris sp.
Lyngbya contorta
Oscillatoria sp.
CHLOROPHYTA
Ch lamydomonas sp .
Cylindrocapsa conferta
SCHIZOMXCOPHYTA
Chlamydobaateriales
Sphaerotilus sp.
Total
Sampling Date
7/21
5,941
17,366
49,813
68,550
10,054
10,054
6,855
62,609
231,242
7/24
9,597
10,511
47,985
308,932
5,941
33,361
7,769
424,096
7/28
7,312
23,764
38,845
75,405
21,479
31,076
13,253
11,425
222,559
7/31
37,474
16,452
3,199
36,103
87,744
3,199
22,850
207,021
8/4
4,113
8,226
1,828
1,828
5,941
10,054
4,570
14,624
26,506
115,164
192,854
8/8
914
7,312
914
1,371
6,398
10,968
5,027
12,796
45,700
8/11
40,673
3,656
12,796
18,280
29,248
4,570
49,813
2,285
45,700
62,152
269,173
8/13
14,167
16,452
13,710
40,216
9,597
45,700
11,882
12,796
75,402
239,922
8/18
31,533
13,710
7,769
24,678
15,538
72,206
6,398
79,518
68,093
319,443
Total
151,724
117,449
26,506
232,613
51,184
10, 511
723,888
68,550
295,679
7,769
20,108
11,882
26,506
115,164
12,796
62,152
217,529
-------
TABLE- 38
Lake Superior Plankton Counts [organisms/liter] — Castle Danger, Minn. (1970)
TEST POOL EFFLUENT
Organism
CHRySOPHYTA
Achnanthes microcephala
Asterionella formosa
Cynibella sp.
Dinobryon cylindricum
Fragilaria capucina
Gonphonema sp.
Melosira sp.
Nitzschia palea
Rhizosolenia eriensis
o* Synedra sp.
Tabellaria fenestrata
Tabellaria flocculosa
CyANOPHTTA
Coccochloris sp.
Lyngbya contorta
Oscillatoria sp.
CHLOROPHZTA
Chlamydomonas sp.
Cylindrocapsa conferta
Ulothrix sp.
SCHIZOMyCOPHXTA
Chlamydobacteriales
Sphaerotilus sp.
Total
Sampling Date
7/21
10,511
28,334
86,373
19,651
12,796
15,538
6,855
103,285
283,343
7/24
14,167
8,683
3,199
54,840
17,366
24,678
53,012
2,742
2,742
181,429
7/28
13,253
11,425
37,017
1,397,963
15,081
29,705
2,742
1,507,186
7/31
19,651
10,511
15,995
47,528
1,219,733
2,742
16,909
2,742
369,256
1,705,067
8/4
3,656
5,941
4,113
15,538
5,027
65,351
2,742
17,823
54,383
95,056
269,630
8/8
3,656
16,452
16,909
13,710
11,425
106,481
14,167
25,135
264,603
2,435,810
10,968
56,668
2,975,984
8/11
18,280
23,764
32,447
110,594
4,570
19,194
1,423,098
542,916
100,997
2,275,860
8/13
10,511
19,651
14,167
97,798
12,339
48,899
29,248
1,022,309
704,694
88,658
2,048,274
8/18
21,479
11,882
19,651
4,570
82,717
7,312
53,469
439,177
456,086
20,565
74,948
58,039
1,249,895
Total
115,164
112,879
3,199
272,829
4,570
109,223
16,452
3,117,654
96,427
279,684
5,484
12,339
29,248
54,383
3,613,499
4,139,506
132,530
74,948
306,650
TABLE 39
-------
TABLE 39
Lake Superior Periphyton, Rock Surface Growth [organisms/cm2] — Castle Danger, Minn. (1970)
CONTROL POOL
Organism
CHRYSOPHXTA
Achnanthes microcephala
Asterionella formosa
Cymbella sp.
Denticula sp.
Fragilaria capucina
Gomphoneraa sp.
Nitzschia palea
Synedra sp.
Tabellaria fenestrata
CUNOPHYTA
Oscillatoria sp.
CHLOROPHITA
Chlam/domonas sp.
Staurastrum sp.
Total
Sampling Date
7/22
671,396
114,768
149,199
86,076
837,697
969,663
286,921
74,599
3,190,319
7/29
584,577
135,450
64,160
78,419
121,193
976,673
655,868
135,450
2,751,790
8/5
540,523
15,443
772,177
72,069
1,091,343
797,916
25,739
3,315,210
8/12
707,381
141,475
41,263
70,737
1,456,028
1,019,809
11,789
3,448,482
8/19
665,838
224,526
224,526
38,711
1,014,242
859,396
54,195
69,680
38,711
3,189,825
Total
3,169,715
15,443
616,219
64,160
1,265,584
388,786
5,375,983
4,302,652
54,195
286,921
317,257
38,711
to
to
-J
-------
TABLE 40
Lake Superior Periphyton, Rock Surface Growth [organisms/cm2] — Castle Danger, Minn. (1970)
TEST POOL
Organism
CHMSOPHYTA
Achnanthes microcephala
Cyrabella sp.
Dinobryon cylindricum
Fragilarda capucina
Gomphonema sp.
Nitzschia palea
Synedra sp.
CXANOPHyTA
Oscillatoria sp.
CHLOROPHYTA
Chlamydomonas sp.
Scenedesmus sp.
Ulothrix sp.
Total
Sampling Date
7/22
1,206, 40i*
116,743
45,400
116,743
2,840,763
771,805
162,144
687,490
5,947,492
7/29
366,632
141,012
401,886
3,102,280
867,228
458,291
1,212,709
91,658
6,641,696
8/5
357,882
92,585
405,249
126,311
2,063,092
689,450
263,149
1,278,906
784,184
6,060,808
8/12
1,221,556
325,392
592,108
335,236
5,323,639
1,909,682
5,142,273
3,040,547
4,326,123
22,216,556
8/19
429,313
922,229
2,369,176
1,097,135
755,274
2,043,215
166,954
636,020
8,419,316
Total
3,581,787
675,732
45,400
2,321,472
578,290
15,698,950
5,335,300
6,781,131
8,262,867
166,954
5,837,985
to
ls>
OO
-------
TABLE 41
RttIK OF PREDOMINANT ORGANISMS [PHYTOPLANKTON (, PERIPHYTON]
Eased on Count Totals During the Period: July 21 - August 19, 1970*
Lake Superior Limnological Study — Castle Danger, Minnesota (1970)
RANK
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
PHYTOPLANKTCN
LAKEWATER INTAKE CONTROL POOL EFFLUENT
(17 species) (1? species)
iJitzschia palea j Nitzschia palea
Dinobryon j Synedra sp.
cylindricum ,
Synedra sp.
Asterionella
fomosa
0 Oscillatoria sp.2
(Sphaerotilus sp. )
V Cylindrocapsa
conferta
Achnanthes
microcephala
Rhizosolenia
eriensis
0 Lyngbya contorta2
Tabellaria
flocculosa
9 Coccochloris sp. "*
v Chlamydomonds sp.1*
Gomphonema sp.
Cymbella sp.
Tabellaria
• fenestrata
Fragilaria
capucina2
Dinobryon
cylindricum
(Sphaerotilus sp. )
Achnanthes
microcephala
Asterionella
formosa
9 Oscillatoria sp.2
Rhizosolenia
eriensis
v Cylindrocapsa
conferta3
Fragilaria
capucina
Cynibella sp.
6 Lyngbya contorta2
Tabellaria
flocculosa
v Chlamydomonas sp.1*
6 Coccochloris sp.1*
Gomphonens sp.
Tabellaria
fenestrata1
TEST POOL EFFLUENT
(19 species)
7 Chlamydomonas sp.
6 Oscillatoria sp.
Nitzschia palea
(Sphaerotilus sp. )
Synedra sp.
Dinobryon
cylindricum
V Cylindrocapsa
conferta
,, Achnanthes
microcephala
Asterionella
fornosa
Gomphonema sp.
Rhizosolenia
eriensis
v Ulothrix sp. s
6 Lyngbya contorta2
a Coccochloris sp.1*
Melosira sp.
Tabellaria
flocculosa
Tabellaria
fenestrata
Fragilaria
capucina5
Cymbella sp. 1
PERlPHYTOlt
CONTROL POOL ROCKS
(12 species)
Nitzschia palea
Synedra sp.
Achnanthes
microcephala
Fragilaria
capucina
Cymbella sp.
Gomphonema sp.
? Chlamydoncnas sp.
6 Oscillatoria sp.6
Denticula sp.7
Tabellaria
fenestrata9
" Staurastrum sp.9
Asterionella
fornosa8
TEST POOL ROCKS
(11 speji.es)
Nitzschia palea
v Chlamydomonas sp.
e Oscillatoria sp.
V Ulothrix sp.
Synedra sp.
Achnanthes
microcephala
Fragilaria
capucina
Cymbella sp.
Gomphonema sp.
v Scenedesmus sp. 9
Dinobryon
cylindricum6
* Phytoplankton totals based on 9 sanpling days; periphyton totals based on 5 sampling days.
e Cyanophyta (blue-green algae)
v Chlorophyta (green algae) !.*••>
All other organisms are chrysophytes, except for Sphaerotilua
-------
SECTION VIII
ACKNOWLEDGEMENTS
Dr. Jackson L. Fox and Dr. Lee W. Stokes deserve special recognition
for their painstaking work on photosynthetic pigments, primary pro-
ductivity, taxonomy and general distribution of periphyton in the study
areas of western Lake Superior,
A study of the periphyton organisms as potential components of Lake
Superior plankton and the preparation of a species checklist of near*
shore periphyton organisms should be credited to Drs. Michael L. Adess
and William G. Parkos and to Mr. Robert R. Nelson.
The valuable technical assistance rendered by Patrick T. Trihey and
Loren L. Schlottman contributed greatly to the success of the project.
The support of the project by the Water Quality Office, Environmental
Protection Agency, and the help provided by Dr. Kenneth E. Biesinger,
the Grant Project Officer is acknowledged with sincere thanks.
231
-------
SECTION IX
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SECTION X
APPENDIX A
STATISTICAL PROCEDURES
The regression lines shown in the text were constructed using
the least squares method as presented by Bancroft (1965). Procedures
for determining correlation coefficients were derived from the same
source. The coefficients (r) were calculated by use of the following
formula:
>/n I & - ( I X)2 /n £ Y2 - (
In some cases, Y represents numbers of organisms and X represents chlor-
ophyll concentration. In other correlations, Y represents photos ynthe-
tic rate, while X represents numbers of organisms. The lines were con-
structed to predict Y from X. The number of determinations (n) was
seventeen for regular samples from 2.5, 5, 10, 15 and 20 feet. The n
value for the thirty-five foot samples was sixteen. For the regrowth
study, n was nine for the ten and twenty foot samples, and ten for the
thirty-five foot samples. Probability values (P), which refer to the
probability that r is different from zero, were determined from a cor-
relation coefficient percentage point distribution table (Beyer, 1966).
In a general regression line, Y - a + bX, where a is the Y inter-
cept and b is the slope. To determine b from the data, the following
formula was used:
"y* " n I X2 - ( I X)2
To determine the value of a, the calculated value of b is placed in
the equation
Y - na + b J X
The calculated values of a and b are then inserted into the general
formula Y - a + bX. A known value of X is inserted into the formula
for the determination of the corresponding Y. The regression line is
drawn through the calculated Y and the Y intercept.
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APPENDIX B
SAMPLE CALCULATIONS
A. PIGMENT CONCENTRATIONS
Given:
Absorbance at 665 millimicrons = .345
645 «= .122
630 • .099
510 - .111
480 - .356
Chi a. (mg/L solvent) = 15.6D665 - 2«OD645 ' °'8D6305
.345 .122 .099
x 15.6 x 2 x .18
5.382 - .244 - .792 « 4.346 mg Chi a/L solvent
Chi b (mg/L solvent) - 25.4D645 - 4.4D665 - 10.3D630;
.122 .345 .099
x 25.4 x 4.4 x 10.3
3.0988 - 1.5180 - 1.0197 - 0.5611 mg Chi b/L solvent
Chi £ (MSPU/L solvent) - 109D630 - 12.5D665 - 28.7D645;
.099 .345 .122
x 109 x 12.5 x 28.7
10.7910 - 4.3125 - 3.5014 » 2.8771 MSPU Chi £/L solvent
Dres»510 - D5i0 - ,0026Ca - .0035Cfa - .0021CC;
4.346 .5611 2.8771
x.0026 x.0035 x .0021
Dres,510 - .1110 - .0113 - .0196 - .0060 - .0741
Dres,480 = D480 - .0019Ca - ,0136Cb - .0054CC;
4.346 .5611 2.8771
x.0019 x.0136 x.0054
Dr».,480 - .3560 - .0082 - .0076 - .0011 - .3391
* "• ' • ^
248
-------
Ast. Car. (MSPU/L solvent) - 2(4. 45D 0,510 - D,. 0,480)
.0741
x 4.45
.329 - .3391 x 2 - 0 MSPU Ast. Car./L solvent
Non-ast. Car. (MSPU/L solvent) =
7.6 (Dres,480 - 1.49Dres,510)
.0741
x 1.49
.3391- .1034 x 7.6 = 1.7913 MSPU Non-ast. Car./L solvent
L solvent ^ L sample^
Mg (MSPU) pigment/L solvent x 1000 L aliquot
x JLOO _ - Mg (MSPU) pigment/100 cm2 rock surface
~cm2 rock surface
B. Qio CALCULATION
Given:
Photosynthetic rate at 10° C *• 12.6 microliters Q£ per mg ash-free
dry weight
Photosynthetic rate at 15° C = 16.4 microliters G£ per mg ash-free
dry weight
QlO = (P2/Pl)
Q10 = <16.4/12.6)10/15-10
Q10 = (1.3)2
Qin = I»69 for the temperature range 10-15°
-------
APPENDIX C
LAKE SUPERIOR STUDIES
CHECKLIST OF PERIPHYTON ORGANISE*
SUMMER 1970
Phylum Chrysophyta
Class Bacillariophyceae
Achnanthes lanceolata (Brebisson) Grunow
Achnanthes microcephala (Kuetzing) Cleve
Amphiprora ornata Bailey
Amphora ovalis Kuetzing
Asterionella formosa Hassail
Ceratoneis arcus (Ehrenberg) Kuetzing
Cocconels group:
C. flexella (Kuetzing) Cleve
(J. pediculus Ehrenberg
C. placentula Ehrenberg
Cyclotella antiqua Urn. Smith
Cyclotella bodanica Eulenstein
Cymatopleura solea (Brebisson) Wkn. Smith
Cymbella group:
C. cistula (Hemprich) Grunow
C. lanceolata (Ehrenberg) Van Heurck
C. leptoceros (Ehrenberg) Grunow
.C. parva (Hto. Smith) Cleve
C. prostrata (Berkeley) Cleve
C,. ventricosa Kuetzing
Denticula thermalis Kuetzing
Diatoma hiemale (Lyngbye) Heiberg
Piatoma vulgare Bory
Diploneis puella (Schuman) Cleve
Epithemia turgida (Ehrenberg) Kuetzing
Eunotia monodan Ehrenberg var. major
(Un. Smith) Hustedt
Eunotia pectinalis (Kuetzing) Rabenhorst
var. minor (Kuetzing) Rabenhorst
Fragilaria capucina Desmazieres
Fragilaria crotenensis Kitton
Frustulia viridula (Brebisson) Detoni
Gomphoneis herculeana (Ehrenberg) Cleve
Gomphonema group:
G. angustatum var. obtusatum (Kuetzing) Van Heurck
G. constricturn Ehrenberg
G. geminatum (Lyngbye) C. A. Agardh
G. gracile Ehrenberg var. dicotoma
(Kuetzing) Grunow
* Based on studies of the near-shore areas of Lake Superior's North
Shore and the Castle Danger Control Pool.
250
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G. ollvaceum (Lyngbye) Kuetzing
G. ollvaceum var. calcarea Cleve
Meloslra granulata (Ehrenberg) Ralfs
Melosira varians C. A. Agardh
Navicula group:
N. dicephala (Ehrenberg) Wm Smith
N. dicephala var. elginensis (Gregory) Cleve
N. oblonga Kuetzing
N. pupula Kuetzing
H» radiosa Kuetzing
N. reinhardtii (Grunow) Van Heurck
N. tuscula Ehrenberg
Nitzschia group:
N. denticula Grunow
N. dissipata (Kuetzing) Grunow
N. hungarica Grunow
N. linearis (Agardh) Wm. Smith
N. palea (Kuetzing) Mn. Smith
N.. vermicular Is (Kuetzing) Hatzsch
Pinnularia group:
P. cardinalis (Ehrenberg) Tto. Smith
£• "alo^ (Kuetzing) Vta. Smith
IP. viridis (Nitzsch) Ehrenberg
Rhizosolenia eriensis H. I* Smith
Bhoicosphenia curvata (Kuetzing) Grunow
Stauroneis anceps Ehrenberg var. anceps
Stauroneis obtusa Lagerst
Stephanodiscus sp.
Surirella angusta Kuetzing
Surirella linearis Wte, Smith
Surirella sp.
Synedra group:
£• acus Kuetzing
S_. rump ens Kuetzing
S>. ulna (Nitzsch) Ehrenberg
Tabellaria fenestrata (Lyngbye) Kuetzing
labellaria flocculosa (Roth) Kuetzing
Class Chrysophyceae
Plnobryon sertularia Ehrenberg
Dinobryon sp.
Phylum Chlorophyta
Chlamydoroonas spp.
Cosmarium sp.
Mougeotia sp.
Oedogonium sp.
Pediastrum duplex Meyen
Pithophora sp.
251
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Scenedesmus obllquus (Turpin) Kuetzing
Scenedesmus quadricauda (Turpin) Brebisson
Schizomeris leibleinii Kuetzing
Selenastrum sp.
Staurastrum sp.
Ulothrix tenerrtma Kuetzing
Ulothrix zonata (Weber & Mohr) Kuetzing
Stigeoclonium subsecuntum Kuetzing
Phylum Cyanophyta
Aphanothece microspora (Menegh) Rabenhorst
Chroococcus minor (Kuetzing) Naegeli
Lyngbya martensiana var. calcarea Tilden
Merismopedia convoluta Brebisson
Oscillatorla tenuis C. A. Agardh
Oscillatoria sp.
Plectonema wollei Farlow
252
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Appendix D
Publications of Research Supported
in Part by EPA Project 18050 DBM
Adess, Michael L., Nelson, Robert R., Schlottman, Loren L. and Parkos,
William G. 1971. A study of the potential of periphyton organisms
as components of Lake Superior plankton. Limresta Bulletin, Lake
Superior Research Station, Duluth, Minn. Research Report No. 2.
Fox, J. L., T. A. Olson and T. 0. Odlaug. 1967. The collection, iden-
tification, and quantitation of epilithic periphyton in Lake
Superior. Proc., 10th Conf. on Great Lakes Res.; International
Assoc. for Gt. Lakes Res., Ann Arbor, Michigan, pp. 12-19.
Fox, J. L. 1969. The epilithic periphyton of the western arm of Lake
Superior. Ph.D. thesis, Univ. of Minnesota. 243 pp.
Fox, Jackson L,, T. 0. Odlaug, and T. A. Olson. 1969. The ecology of
periphyton in western Lake Superior. Part I: Taxonomy and distri-
bution. Bulletin 14, Water Resources Research Center, Minneapolis,
Minnesota. 127 pp.
Stokes, L. W., T. A. Olson, and T. 0. Odlaug. 1967. Studies of Chloro-
phyll and Carotenoid Pigments in Lake Superior Periphyton.
Proc., 10th Conf. on Grt. Lakes Res., International Association
for Great Lakes Research, p. 107-114, Ann Arbor, Michigan.
Stokes, L. W. 1969. The productivity of Lake Superior periphyton as
reflected by pigment analysis and respirometry. Ph.D. thesis.
313 pp.
Stokes, L. W., T. A. Olson, and T. 0. Odlaug. 1970. The photosynthetic
pigments of Lake Superior periphyton and their relation to primary
productivity. Bulletin no. 18. Water Resources Research Center
University of Minnesota. 150 pp.
253
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1
5
Accession Number
2
Subject F~U*ld & Group
10A
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Urbanization
University of Minnesota for the Environmental Protection Agency
Title
LAKE SUPERIOR PERIPHYTON IN RELATION TO WATER QUALITY
10
Authors)
Olson, Theodore A.
Odlaug, Theron 0.
16
Project Designation
18050 DBM (formerly WP-00828)
Note
22
Citation
United States Government Printing Office
23
Descriptors (Starred First) ,
*Chlorophyll, *Plant pigments, *Aquatic productivity, *Primary productivity,
*Algae, *Diatoms, *Periphyton, *Phytoplankton, *Sessile algae, Lake Superior,
Limnology, Fertility, Photosynthesis, Respiration, Eutrophication, Plant population,
Classification, Sampling, Chlorophyta, Chrysophyta, Cyanophyta.
25
Identifiers (Starred First)
Lake Superior Periphyton, Productivity
27 Abstract
Laboratory and field studies were conducted to evaluate the importance of periphyton
in western Lake Superior with special reference to the make-up and distribution of the
periphyton growths and to the overall importance of productive capacity of this assemblage
of organisms. The taxonomic portion of the investigation indicated that over 90% of the
total number of organisms were diatoms and that the phyla to which these diatoms belonged
were the Chrysophyta, the Chlorophyta, and the Cyanophyta. Predominant genera were
Synedra, Achnanthes, Navicula, Cymbella, and Gomphonema. In many respects, the periphyton
of Lake Superior was similar to that found in streams and there was evidence that the
interrelated factors that affected periphyton growths were temperature, light intensity,
depth of water, water movements, nutrient levels, and the type of substrate. Artificially
denuded rocks demonstrated definite re-growth but after 46 days this growth level was only
18% of that occurring naturally. The mean total counts of organisms in the primary
sampling area ranged from 497,000 to 1,470,000 per square centimeter of rock surface.
Studies of the pigment concentrations showed that the biomass of periphyton along the
North Shore of Lake Superior resemble those of other oligotrophic bodies of water and
range from 0.338 to 3.59 mg of total pigment per 100 square centimeters of rock.surface.
The average was 1.36 mg per 100 square centimeters of rock surface. Pigment ratios
indicated that the Lake Superior periphyton was dominated by the Chrysophyta.
Abstractor
T.O. Olson and T. 0. Orllaiig
WR:I02 (REV. JULY 19691
Institution
' JsHyV'br^'J-ftR RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF
WASHINGTON. O. C. 20240
CPO: 1869-359-35S
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Title: LAKE SUPERIOR PERIPHYTON IN RELATION TO WATER QUALITY 2
Abstract (continued)
Assimilation values for Stony Point Bay averaged 1.48 grams of carbon fixed per gram of
chlorophyll in 1967. In Stony Point Bay, the total standing crop in terms of dry
weight was 55.5 tons. In re-growth studies, chlorophyll levels were observed to
increase by an average of 0.057 grams (57 mgs) per square meter per day. The
efficiency of energy utilization in Stony Point Bay was found to be 0.082%, a typical
value for algal communities.
(T.O. Olson and T. 0. Odlaug) University of Minnesota
•U.S. GOVERNMENT PRINTING OFFICE:1972 U8ll-ll86/282 1-3
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