v>EPA
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Duluth MN 55804
EPA-600/3-80-074
July 1980
Research and Development
Limnological
Conditions in
Southern Lake Huron,
1974 and 1975
EP 600/3
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' I , • \,t i v, ;.
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development. U S Environmental
Protection Agency have been grouped into nine series These nine broad cate-
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This document is available to the public tnrough the National Technical Informa-
tion Service Springfield Virginia 22161
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EPA-600/3-80-074
July 1980
LIMNOLOGICAL CONDITIONS IN
SOUTHERN LAKE HURON, 1974 AND 1975
by
Claire L. Schelske, Russell A. Moll,
and Mila S. Simmons
Great Lakes Research Division
University of Michigan
Ann Arbor, Michigan 48109
Grant No. R803086
Project Officer
Nelson A. Thomas
Large Lakes Research Station
Environmental Research Laboratory - Duluth
Grosse He, Michigan 48138
ENVIRONMENTAL RESEARCH LABORATORY-DULUTH
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
DULUTH, MINNESOTA 55804
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DISCLAIMER
This report has been reviewed by the Environmental Research Laboratory-
Duluth, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or recommendation
for use.
ii
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FOREWORD
Limnology of the Great Lakes is a very complex subject and requires the
cooperative studies of many investigators to develop an overall under-
standing. This understanding of how the systems are interrelated is required
in the development of pollution management scenarios.
This report brings together many observations and data systhesis
resulting from a large field experiment conducted as part of the Upper Lakes
Reference Study. The data and interpretations contained in this report have
aided greatly in the protection of Lake Huron.
Norbert Jaworski, Ph.D.
Director
Environmental Research Laboratory
Duluth, Minnesota
111
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ABSTRACT
la 1974 and 1975, several studies were conducted on southern Lake Huron
and outer Saginaw Bay to obtain seasonal data on limnological conditions.
In 1974, 44 stations were sampled on each of eight cruises conducted from
April to November. Each station was sampled at multiple depths so that more
than 200 samples were taken on each cruise. Data obtained for each sample
included water temperature, pH, specific conductance, chloride, total
phosphorus, soluble reactive silica, nitrate plus nitrite nitrogen, ammonia
nitrogen, chlorophyll _a, and phaeopigments. In 1975, five special cruises
were conducted. Four of these were used to compare phytoplankton
productivity and nutrient dynamics in the frontal zone between highly
enriched Saginaw Bay and the relatively low productivity waters of southern
Lake Huron. One cruise was used to study the effect of the spring thermal
bar on the distribution of nutrients and nearshore phytoplankton standing
crops. These studies confirm that Saginaw Bay and the nearshore zone of
southern Lake Huron have larger concentrations of total phosphorus (the major
growth limiting nutrient in the system) and greater standing crops of
phytoplankton than the offshore waters. They also show that the nearshore
zones, especially on the Canadian shore, differ from the offshore waters to a
greater degree during the period of the spring thermal bar than at other
times of the year.
vi
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CONTENTS
Foreword
Abstract
Figures ,
Tables . ,
1.
2.
3.
4.
5.
6.
7.
Introduction
Conclusions
Descriptive physical-chemical limnology
Statistical inferences from southern Lake Huron — 1974
Euclidean distances
Phytoplankton dynamics in outer Saginaw Bay
Influences of spring nearshore thermal bar
, .. iii
iv
vi
. . . x
1
6
8
64
89
, . . 104
. .. 140
References 3, 62, 87, 103, 139, 163
Appendix A 165
Appendix B 171
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FIGURES
Number Page
3.1 Proposed stations for study of southern Lake Huron, 1974 .... 9
3.2 Major stations sampled during study of southern Lake Huron .. 10
3.3 Flow chart illustrating sample processing for study of
southern Lake Huron, 1974 17
3.4 Surface water temperature (°C) in southern Lake Huron,
1974 (a, b, c, d, e, f, g, and h) 21
3.5 Surface concentrations of chloride (mg/1) in southern
Lake Huron, 1974 (a, b, c, d, e, f, g, and h) 25
3.6 Surface values for pH in southern Lake Huron, 1974
(b, c, d, e, f, and h) 29
3.7 Surface concentrations of silica (mg/1) in southern
Lake Huron, 1974 (a, b, c, d, e, f, g, and h) 33
3.8 Surface concentrations of nitrate nitrogen (mg/1) in
southern Lake Huron, 1974 (a, b, c, d, e, g, and h) 36
3.9 Surface concentrations of chlorophyll ^a (yg/1) in
southern Lake Huron, 1974 (a, b, c, d, e, f, g, and h) .... 41
3.10 Secchi disc transparency (m) in southern Lake Huron,
1974 (a, b, c, d, e, f, g, and h) 44
3.11 Seasonal changes in surface water temperature (°C)
for selected stations in southern Lake Huron, 1974 47
3.12 Seasonal changes in surface concentrations of chloride
(mg/1) 48
3.13 Seasonal changes in surface concentrations of silica
(mg/1) 50
3.14 Seasonal changes in surface concentrations of nitrate
nitrogen (mg/1) 51
vi
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Number Page
3.15 Seasonal changes in surface concentrations of chlorophyll
£ (yg/1) 53
3.16 Seasonal changes in Seechi disc transparency (m) 54
3.17 Nutrient concentrations in the epilimnion of Lake
Huron in 1974 59
3.18 Map of southern Lake Huron showing relationship
between 1974 stations sampled by Great Lakes
Research Division and segmentation used by the
International Joint Commission 60
4.1 Stations sampled during study of southern Lake Huron 65
4.2 Correlations between particulate and soluble silica
and l^C and chlorophyll 84
5.1 Example of stations plotted in arbitrary temperature and
specific conductance coordinates 90
5.2 Contours of multivariate euclidean distances from the
reference station for cruise 2 95
5.3 Contours of multivariate euclidean distances from the
reference station for cruise 3 96
5.4 Contours of multivariate euclidean distances from the
reference station for cruise 4 97
5.5 Contours of multivariate euclidean distances from the
reference station for cruise 5 98
5.6 Contours of multivariate euclidean distances from the
reference station for cruise 6 99
5.7 Contours of multivariate euclidean distances from the
reference station for cruise 7 101
5.8 Contours of multivariate euclidean distances from the
reference station for cruise 8 102
6.1 Area sampled (between stations 36-40 and 41-45)
during study of Saginaw Bay, 1975 105
6.2 Vertical distribution of chlorophyll at station 38
from '+-6 August, 1975 108
6.3 Contour maps from cruise 1 of 1975 study (6 May) 109
vii
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Number Page
6.4 Contour maps from cruise 1 of 1975 study (8 May) 110
6.5 Results of the early May 14C uptake profiles 113
6.6 Contour maps from cruise 2 of 1975 study (29 May) 116
6.7 Contour maps from cruise 2 of 1975 study (1 June) 117
6.8 Results of the late May 14C uptake profiles 120
6.9 Contour maps from cruise 3 of 1975 study (1 August) 121
6.10 Contour maps from cruise 3 of 1975 study (4 August) 122
6.11 Results of the early August ^C uptake profiles 126
6.12 Contour map from cruise 4 of 1975 study (15 October) 127
6.13 Contour map from cruise '+ of 1975 study (17 October) 128
6.14 Results of the October 14C uptake profiles 132
7.1 Station locations for the 1974 southern Lake Huron
cruises 143
7.2a One meter underway map of temperature (°C) near
Bayfield, Ontario, 30 April 1975 149
7.2b One meter underway map of chloride (mg/1) near
Bayfield, Ontario, 30 April 1975 150
7.2c One meter underway map of nitrate nitrogen (yg/1) near
Bayfield, Ontario, 30 April 1975 151
7.2d One meter underway map of silica (mg/1) near
Bayfield, Ontario, 30 April 1975 152
7.3a One meter underway map of temperature (°C) near
Harbor Beach, Michigan, 1 May 1975 154
7.3b One meter underway map of chloride (mg/1) near
Harbor Beach, Michigan, 1 May 1975 155
7.3c One meter underway map of nitrate nitrogen (yg/1) near
Harbor Beach, Michigan, 1 May 1975 156
7.3d One meter underway map of silica (mg/1) near
Harbor Beach, Michigan, 1 May 1975 157
viii
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Number Page
7.3e One meter underway map near Harbor Beach, Michigan,
1 May 1975 - chlorophyll fluorescence 158
7.4 Temperature distribution at 8 stations on a 5 km
east-west transect 10.5 km south of Harbor Beach,
Michigan 159
7.5 Chemical parameters and chlorophyll a_ at selected
stations along the Harbor Beach transect 160
ix
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TABLES
Number
3.1
3.2
3.3
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
5.1
5.2
6.1
Sampling Depths (for Primary Stations Occupied in
Southern Lake Huron)
Dates and Thermal Periods of Cruises on Southern Lake
Huron, 1974
Correlation Matrix from Cruise 2
Factor Analysis of Cruise 2 and Cruise 3 Data
Correlation Matrix from Cruise 3
Correlation Matrix from Cruise 4
Factor Analysis of Cruise 4 and Cruise 5 Data
Correlation Matrix from Cruise 5
Correlation Matrix from Cruise 6
Factor Analysis of Cruise 6 and Cruise 7 Data
Correlation Matrix from Cruise 7
Correlation Matrix from Cruise 8
Factor Analysis of Cruise 8 Data
Mean Concentrations (and Their Standard Errors) of Four
Nutrients from Southern Lake Huron, 1974
Stations and Reference Used for the 1 m Plots
Descriptive Statistics for the Euclidean Distance Used to
Produce the Contour Plots by Cruise and Depth
Descriptive Measures, Cruise 1, 1975, Southern Lake Huron ...
Page
11
14
20
68
69
70
72
73
74
76
77
73
80
81
83
92
93
111
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Number Page
6.2 Product-Moment Correlations Among Variables from Cruise 1,
1975, Southern Lake Huron 112
6.3 Average Values Observed During 1975, Incubation Series 115
6.4 Descriptive Measures, Cruise 2, 1975, Southern Lake Huron ... 118
6.5 Product-Moment Correlations Among Variables from
Cruise 2, 1975, Southern Lake Huron 119
6.6 Descriptive Measures, Cruise 3, 1975, Southern Lake Huron ... 124
6.7 Product-Moment Correlations Among Variables from
Cruise 3, 1975, Southern Lake Huron 125
6.8 Descriptive Measures, Cruise 4, 1975, Southern Lake Huron ... 130
6.9 Product-Moment Correlations Among Variables from
Cruise 4, 1975, Southern Lake Huron 131
6.10 Descriptive Measures, Bay Stations, 1975,
Southern Lake Huron 133
6.11 Descriptive Measures, Interface Stations, 1975,
Southern Lake Huron 134
6.12 Descriptive Measures, Open Lake Stations, 1975,
Southern Lake Huron 135
6.13 Comparison of Means from Bay, Interface, and Open Lake
Waters by t-Tests 136
7.1 Water Chemistry and Phytoplankton Parameters at Selected
Stations for the First Two Southern Lake Huron Cruises,
1974 144
7.2 Population Abundance of Predominant Diatom Species in
Southern Lake Huron, Cruise 1, 28 April-3 May 1974 145
7.3 Population Abundance of Predominant Diatom Species in
Southern Lake Huron, Cruise 2, 14-17 May 1974 146
7.4 Average Values for the Upper 10 m Along a Transect Due
West of Bayfield, Ontario, 30 April 1975 148
xi
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SECTION 1
INTRODUCTION
Studies on southern Lake Huron were conducted in 1974 and 1975 as part
of the investigations of Lake Huron and Lake Superior by the Upper Great
Lakes Reference Group. These studies, including results we are presenting in
this report, have been summarized in previous publications (International
Joint Commission, 1976; International Joint Commission, 1977a; International
Joint Commission, 1977b). Results obtained as part of our investigation of
southern Lake Huron were included in the reports by the Upper Great Lakes
Reference Group and are referred to as data from the Great Lakes Research
Division (GLRD) which is a division in the Center for Great Lakes and Marine
Waters, University of Michigan.
We conducted two different types of research activities: in 1974, eight
cruises were scheduled from April to November to sample a variety of
physical, chemical, and biological variables, and in 1975, two special
projects were undertaken. In the first 1975 study, processes were compared
in the interface region between Saginaw Bay, a highly enriched area, and open
Lake Huron (Moll et al., In press). The second 1975 study was used to
determine the influence of the spring thermal bar on nearshore chemical and
biological conditions. Results of the 1974 investigations are presented in
Sections 3-5 and those for the 1975 studies in Sections 6 and 7.
A number of reports compiled as part of the studies by the Upper Great
Lakes Reference Group have been published. Two of these reports resulted from
data collected at the same stations we occupied in 1974; one deals with the
rotifers of Saginaw Bay and southern Lake Huron (Stemberger et al., 1979), and
the other deals with the phytoplankton in southern Lake Huron (Stoermer and
Kreis, In press). During 1974, stations in Saginaw Bay were sampled
extensively by Smith et al. (1977) and water circulation was studied by Danek
and Saylor (1975). Zooplankton collected during this study of Saginaw Bay have
been examined (Stemberger et al., 1979), as have the phytoplankton (Stoermer
et al., In prep.). Bierman et al. (In press) have utilized some of these data
to develop and calibrate a phytoplankton model for Saginaw Bay that predicts
changes in phytoplankton composition at the class level. Several papers
dealing with atmospheric inputs of phosphorus to southern Lake Huron have been
published (Delumyea and Petel, 1977; Delumyea and Petel, 1978; Delumyea and
Petel, 1979). Reports of the chemical limnology of Georgian Bay (Warry, 1978a)
and the North Channel (Warry, 1978b) of Lake Huron and on the phytoplankton of
Georgian Bay (Nicholls et al., 1975) have been published. These papers provide
an extensive amount of data on physical, chemical, and biological conditions in
Lake Huron during 1974 and 1975.
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In addition to obtaining data, on water quality characteristics in southern
Lake Huron, our study was designed with two specific purposes. First, we were
interested in the effect of transport of water and materials from Saginaw Bay
on water quality in southern Lake Huron. As a consequence, three transects of
stations across Saginaw Bay were established so spatial relationships could be
studied. Second, we wanted to study dynamics of environmental processes prior
to and during the period of spring warming and thermal bar formation. To
attain this objective the eight cruises were unequally spaced in time with the
first four cruises being scheduled between the end of April and mid June.
Several additional studies that include valuable background information on
Saginaw Bay and Lake Huron should be cited. These include studies on physical
and chemical limnology (Ayers et al., 1956; Johnson, 1958; Beeton et al., 1967;
Sloss and Saylor, 1975), chlorophyll and primary production (Glooschenko and
Moore, 1973; Watson et al., 1976), historical conditions (Freedman, 1974;
Goodell, 1977), and biological, chemical and physical limnology (Schelske and
Roth, 1973).
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REFERENCES
Ayers, J. C., D. V. Anderson, D. C. Chandler, and G. H. Lauff. 1956.
Currents and Water Masses of Lake Huron. Pub. No. 1, Great Lakes Res.
Div., Univ. of Mich., Ann Arbor, Michigan, 101 pp.
Beeton, A. M., S. H. Smith, and F. F. Hooper. 1967. Physical Limnology
of Saginaw Bay, Lake Huron. Technical Report 12, Great Lakes Fishery
Comra., 56 pp.
Bierman, V. J., Jr., E. F. Stoermer, J. E. Gannon, and V. E. Smith.
In press. The Development and Calibration of a Spatially-Simplified,
Multi-Class Phytoplankton Model for Saginaw Bay, Lake Huron.
U.S. Environmental Protection Agency, Duluth, MN.
Danek, L. J., and J. H. Saylor. 1975. Saginaw Bay Water Circulation.
NOAA Technical Report SRL 359-GLERL 6, U.S. Department of Commerce,
51 pp.
Delumyea, R. G., and R. L. Petel. 1977. Atmospheric Inputs of Phosphorus
to Southern Lake Huron, April-October 1975. Ecol. Res. Series,
EPA-600/3-77-038, U.S. Environmental Protection Agency, Duluth, MN.
54 pp.
^^ . 1973. Wet and Dry Deposition of Phosphorus into Lake Huron.
Water, Air and Soil Pollution 10:187-198.
. 1979. Deposition Velocity of Phosphorus-Containing Particles
over Southern Lake Huron, April-October 1975. Atmospheric Environment
13:287-294.
Freedman, P. L. 1974. Saginaw Bay: An Evaluation of Existing and
Historical Conditions. National Technical Information Service,
PB-232 440, U.S. Department of Commerce, 137 pp.
Glooschenko, W. A., and J. E. Moore. 1973. Surface Distribution of
Chlorophyll a and Primary Production in Lake Huron, 1971. Fish. Res.
Board Canada~Tech. Rep. No. 406.
Goodell, C. J. S. 1977. Bay City, Michigan, Water Intake Data, January,
1962 through April, 1976. M.S. thesis, Univ. of Mich., Ann Arbor,
Michigan, 68 pp.
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International Joint Commission. 1976. The Waters of Lake Huron and Lake
Superior. Vol. I, Summary and Recommendations. Report of the Internat.
Joint Comm. Upper Lakes Reference Group, Windsor, Ont. 236 pp.
. 1977a. The Waters of Lake Huron and Lake Superior. Vol. II
(Part A), Lake Huron, Georgian Bay and the North Channel. Report of the
Internat. Joint Comm. Upper Lakes Reference Group, Windsor, Ont. 292 pp.
. 1977b. The Waters of Lake Huron and Lake Superior. Vol. II
(Part B), Lake Huron, Georgian Bay and the North Channel. Report of the
Internat. Joint Comm. Upper Lakes Reference Group, Windsor, Ont.
pp. 295-743.
Johnson, J. H. 1958. Surface-Current Studies of Saginaw Bay and Lake
Huron, 1956. Spec. Sci. Rep., Fish 267, U.S. Fish and Wildlife Service,
84 pp.
Moll, R. A.., C. 0. Davis, and C. L. Schelske. In press. Phytoplankton
Productivity and Standing Crop in.the Vicinity of the Lake Huron-
Saginaw Bay Front. J. Great Lakes Res.
Nicholls, K. H., E. C. Carney, and G. W. Robinson. 1975. Phytoplankton of
an Inshore Area of Georgian Bay of Lake Huron Prior to Reductions in
Phosphorus Loading from Local Sewage Treatment Facilities. Ontario
Ministry of the Environment. 33 pp.
Schelske, C. L., and J. C. Roth. 1973. Limnological Survey of Lakes
Michigan, Superior, Huron and Erie. Pub. No. 17, Great Lakes Res. Div.,
Univ. of Mich., Ann Arbor, Michigan, 108 pp.
Sloss, P. W., and J. H. Saylor. 1975. Measurements of Current Flow During
Summer in Lake Huron. NOAA Technical Report ERL 353-GLERL 5,
U.S. Department of Commerce, 39 pp.
Smith, V. E., K. W. Lee, J. C. Filkins, K. W. Hartwell, K. R. Rygwelski, and
J. M. Townsend. 1977. Survey of Chemical Factors in Saginaw Bay
(Lake Huron). Ecol. Res. Series, EPA-600/3-77-125, U.S. Environmental
Protection Agency, Duluth, MN. 143 pp.
Stemberger, R. S., J. E. Gannon, and F. J. Bricker. 1979. Spatial and
Seasonal Structure of Rotifer Communities in Lake Huron. EPA-600/3-
79/085, U.S. Environmental Protection Agency, Duluth, MN. 160 pp.
Stoermer, E. F., and R. G. Kreis, Jr. In press. Phytoplankton Composition
and Abundance in Southern Lake Huron. U.S. Environmental Protection
Agency, Duluth, MN. 382 pp.
Stoermer, E. F., L. Sicko-Goad, and R. G. Kreis, Jr. In prep. Phyto-
plankton Dynamics in Saginaw Bay.
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Warry, N. D. 1978a. Chemical Limnology of Georgian Bay, 1974. Scientific
Series No. 91, Inland Waters Directorate, Water Quality Branch,
Burlington, Ont. 13 pp.
1978b. Chemical Limnology of the North Channel, 1974.
Scientific Series No. 92, Inland Waters Directorate, Water Quality
Branch, Burlington, Ont. 12 pp.
Watson, N. H. F., L. R. Gulp, and H. F. Nicholson. 1976. Chlorophyll a_
and Primary Production in Georgian Bay, North Channel, and Lake Huron,
April to December, 1974. Fisheries and Marine Service Technical Report
600, Canada Centre for Inland Waters, Burlington, Ont., 40 pp.
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SECTION 2
CONCLUSIONS
Water quality in the open waters of southern Lake Huron is very good,
although inputs from shoreline sources in the United States and Canada affect
water quality in adjacent nearshore zones. Most of the nearshore loading
from the shoreline in the United States originates from Saginaw Bay, and from
the Canadian shoreline, the sources appear to be the Maitland and Bayfield
Rivers. Effects of nutrient loading in the Canadian nearshore zone are most
pronounced during and after the period of the spring thermal bar.
Transboundary (international) movement of water masses with low water
quality is not likely to occur as a result of shoreline inputs from either
the United States or Canada. Identifiable water masses have been traced
moving north, south, and lakeward from outer Saginaw Bay, but these slugs of
water ordinarily will be mixed and diluted greatly with open lake waters
prior to crossing the international boundary.
Although transboundary movement is not readily identifiable as discrete
parcels of water, there is no question that nutrient inputs from shoreline
sources in both the United States and Canada contribute to the subtle
long-term changes in water quality that have occurred in southern Lake Huron.
Inputs from the southern part of Lake Huron probably have little effect on
water quality in northern Lake Huron, primarily because predominant
circulation patterns tend to minimize this type of transport and,
additionally, allow long periods of time for mixing and dilution of nutrients
and other substances and for utilization and loss of nutrients by biological
and physical processes-
Comparisons of our data from 1974 with those from the northern part of
the lake are not ideal because few data were collected in the northern part
during 1974. Our data cannot be used to represent conditions in the entire
lake. Phasing differences in seasonal cycles that can be caused by
latitudinal and morphometric effects make it difficult to compare lake-wide
data other than those collected synoptically. Year-to-year comparison of
data from the same location can be confounded by year-to-year variations in
meteorological conditions and associated seasonal cycles in the lake.
Our limited sampling of Saginaw Bay (restricted to stations in the outer
part of the bay) indicates that Saginaw Bay is highly eutrophic compared to
the open waters of southern Lake Huron. Saginaw Bay water was readily
identifiable by greater chloride and total phosphorus concentrations and by
an order of magnitude greater standing crops of chlorophyll a_ in comparison
to the open lake.
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Conditions in outer Saginaw Bay were variable from station to station
and from cruise to cruise. This variability is a function of complex current
patterns and water movement, which are strongly influenced by short-term
meteorological events.
Although data collected in our study and by other workers suggest that
transport from Saginaw Bay follows several different general patterns, it is
likely that the predominant transport pattern is movement of water along the
south shore of outer Saginaw Bay, around the thumb, and then southward along
the shoreline. Significant movement of water out of the bay must be
accompanied by a compensating intrusion of water into the bay. (At certain
times of the year, the net exchange of water is from the lake to the bay.)
Seasonal factors play an important part in environmental processes in
the southern part of Lake Huron. During the period of the spring thermal
bar, water movement and biological processes are different from those that
occur in the thermally stratified lake during the summer. Winter conditions
would also be different (but these were not studied) in that during this
period of the year, the system is either homothermous or partially
ice-covered, which would affect currents and water movement.
Our studies and those by others show that phosphorus is the major
nutrient that limits phytoplankton growth and controls the standing crop of
algae. The results also show that excessive inputs of phosphorus have
stimulated diatom growth to the extent that soluble reactive silica levels
were reduced to limiting concentrations in and near outer Saginaw Bay during
1974 and 1975. This result is substantive evidence that phosphorus
enrichment is excessive and indicates that such an effect in the future may
expand over larger areas of southern Lake Huron unless phosphorus inputs can
be controlled.
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SECTION 3
DESCRIPTIVE PHYSICAL-CHEMICAL LIMNOLOGY
by Claire L. Schelske, David D. Dow, and Laurie E. Feldt
In this section, data on physical-chemical variables and chlorophyll a_
are presented for the samples collected in 1974 at a depth of 1 m. These
data and data for other depths have been utilized also in the analyses
presented in Sections 4 and 5.
METHODS
Data presented in this section were collected in 1974 and analyzed
according to the methods listed below. In addition, as discussed in the
Introduction, these methods and procedures were utilized for specialized
studies conducted during 1975. All cruises in both years were conducted from
the R/V ROGER R. SIMONS, a vessel provided by the Environmental Protection
Agency.
In 1974, eight cruises were conducted on southern Lake Huron, beginning
April 28 and ending November 14. There was a cruise each month, with the
exception of June when there were two and September when there was none.
Originally, 62 station locations were selected for sampling (Figure 3.1).
After the first two cruises, it was obvious that it would not be possible to
sample all stations on each cruise because the time on station and time to
steam between stations were too great. A revised sampling strategy was then
adopted that included 44 stations that could be sampled in five days (Figure
3.2). Most of these stations were sampled on the last six cruises — a list
of stations sampled on each cruise is presented in Table 3.1. Vessel
operations and scientific activities were designed for a one-shift operation,
and consequently, sampling and research operations were terminated each day
and started again the following day.
Water samples were taken with 8-liter Niskin bottles at predetermined
depths of 1 and 5 m and at 5-, 10-, or 20-m intervals to the bottom; deeper
depths were adjusted so that 10 was the maximum number of Niskin bottles used
per station (Table 3.2). Water transparency was measured with a white Secchi
disc. Temperature at depth was measured with a bathythermograph, and in
addition, surface temperature was measured with a mercury thermometer on
shipboard.
All methods used on the southern Lake Huron cruises are described in a
manual of field and laboratory procedures (Davis and Simmons, 1979). Water
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13
-------
TABLE 3.2. SAMPLING DEPTHS FOR PRIMARY STATIONS
OCCUPIED IN SOUTHERN LAKE HURON
Station r
Day 1
63
64
65
06
07
09
10
11
58
Day 2
57
56
20
21
23
24
25
26
Day 3
36
37
38
39
40
41
42
43
44
47
46
45
10.
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
J
1,
7
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
1,
5
5,
5,
5,
5,
5
5,
5,
5,
5
5,
5,
5,
5,
5,
5,
5
5
5,
5,
5,
5
5,
5,
5,
5,
5,
5
5,
10,
10,
10
10,
10,
10,
10,
10,
10,
10,
10,
10,
10,
10,
10
10
10
10,
10,
10,
10,
10
15
15
15,
15
15,
15,
15,
15,
15,
j
15,
15,
15,
15
15,
15,
15,
15,
Sampling depths (m)
20, 25
20, 30, 40, 50, 60
20, 30 Total samples = 40
20
20, 30, 40
20, 30, 40, 60, 80, 90
20, 30, 40, 50
20, 30, 40, 50, 60
20, 30, 40, 50
Total samples = 51
20
20, 25
20
20, 30, 40
Total samples = 45
(continued.)
14
-------
TABLE 3.2. (continued).
Station no.
Sampling depths (m)
Day 4
48
49
50
51
16
55
54
53
52
Day 5
15
14
67
13
66
60
1, 5, 10, 15, 20, 30, 40
1, 5, 10, 15, 20, 30, 40
1, 5, 10, 15
1, 5, 10, 15, 20, 30
1, 5, 10, 15, 20, 30
1, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80
1, 5, 10, 15, 20, 30, 40, 50, 60
1, 5, 10, 15, 20, 30, 40
1, 5, 10, 15, 20
1, 5
1, 5, 10
1, 5, 10, 15, 20, 25
1, 5, 10, 15, 20, 25
1, 5, 10, 15, 20, 30, 40, 50
1, 5, 10, 15, 20, 30, 40
Total samples = 62
Total samples = 32
15
-------
samples were processed as illustrated in the flow chart (Figure 3.3).
Samples for soluble chemical analyses were filtered through 47-mm HA
Millipore filters that were previously soaked and rinsed several times with
distilled-deionized water. These were stored in Nalge conventional
polyethylene bottles that were rinsed at least once with excess sample before
filling (Schelske et al., 1975).
A Corning pH meter, Model 110 equipped with a digital expanded scale and
an automatic temperature compensator, was used on shipboard to measure pH
immediately after the samples were taken.
Specific conductance was measured on shipboard with a Leeds and Northrup
Model 4866-60 conductivity bridge, corrected to 25°C (Schelske et al., 1974).
Samples for measurements of carbon fixation were obtained at 1 m at all
stations and at 1 and 5 m at selected stations. Water samples (265 ml) were
collected in glass-stoppered Pyrex bottles, injected with 2.0 yCi^-+C, and
incubated in a shipboard incubator with 0, 1, or 2 layers of plastic window
screen. The screens reduced light intensity, simulating depth in the water
column. Surface lake water was pumped through the incubator, and fluorescent
lights were used as the light source. The samples were incubated for 3 to 4
hours after which they were filtered through 47-mm HA Millipore filters. The
filters were mounted with rubber cement on 52-mm-diameter aluminum planchets
and stored for counting. A Low Beta Beckman Planchet Counter was used for
counting. Efficiency of this counter and the absolute activity of C was
determined with a Nuclear Chicago Liquid Scintillation Counter (Wolfe and
Schelske, 1967).
Alkalinity was determined from pH measurement on 20-ml samples that were
added to 4 ml of 0.01N HC1. Measurements were made only on samples from 1
and 5 m where ^C productivity was measured.
A Technicon AutoAnalyzer II basic Dual-Channel System was equipped to
measure four nutrients — nitrate plus nitrite nitrogen, ammonia nitrogen,
soluble reactive silica, and chloride, on shipboard using unfrozen samples
(Figure 3.3). Samples for total phosphorus, total soluble phosphorus, and
sulfate were frozen and returned to Ann Arbor for analyses. Methods for
chemical analyses have been used previously (Schelske et al., 1976) and are
described by Davis and Simmons (1979).
Nitrate was reduced to nitrite with a copper-hydrazine solution at 54°C.
The nitrite produced and the nitrite initially present in the sample were
then determined by a diazotization-coupling reaction using sulfanilamide and
N-1-naphthyl-ethylene diamine. The resulting red-violet colored complex was
measured at 520 my (Kamphake et al., 1967). Nitrite was not analyzed
separately, as quantitatively insignificant values would be expected in
non-polluted oxygenated waters.
Ammonia was oxidized to nitrous acid by hypochlorite, which reacts with
phenol to give a blue color. The reaction was catalyzed by nitro-prusside
and buffered by EDTA. The color produced was measured at 630 mp. A special
sampling chamber was used in which acid-scrubbed air was constantly purged to
16
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minimize ammonia contamination from the atmosphere.
Silica was determined by the heteropoly-blue method. la this method,
silica is complexed with acidified molybdate to form a silicomolybdate
complex that is reduced to an intense heteropoly blue. Oxalic acid was added
with ascorbic acid prior to the reduction to destroy any phosphomolybdate.
The color produced was measured at 630 my.
Chloride was determined from its reaction with mercuric thiocyanate that
forms mercuric chloride. The released thiocyanate reacts with ferric
ammonium sulfate to form a red complex, Fe(SCN)3. The resulting color was
measured at 480 my.
Chemical analyses for total phosphorus, total soluble phosphorus, and
sulfate were performed in the laboratory on thawed samples with the Technicon
AutoAnalyzer.
Samples for total phosphorus and total soluble phosphorus were
concentrated by evaporation and then digested with potassium persulfate for
one and a half hours in an oven at 110°C, as modified from Menzel and Corwin
(1965). The samples were then treated with an acidic solution of ammonium
molybdate to give phosphomolybdate that was then reduced by ascorbic acid to
give a blue color. This was measured at 530 my.
An automated turbidimetric method was used for the determination of
sulfate. The turbidity produced by the reaction of BaCl2 in HC1 with sulfate
was measured at 420 my. \n NH^-OH-EDTA rinse was used to prevent the coating
of the 83804 precipitate on the walls of the manifold system and the flow
cells (Santiago et al., 1975).
Samples for chlorophyll a_ (250 ml) ware filtered on 47-mm HA Millipore
filters that were then extracted in 90 percent acetone buffered with
magnesium carbonate. Samples were stored in amber vials in the dark at 0°C
for a minimum of 12 hours. On the earlier cruises, some chlorophyll
determinations were made on the ship. Otherwise, they were done in our
laboratory in Ann Arbor. Samples were centrifuged, and then 5 ml were
transferred to sample cuvettes and read in a modified Turner Model 111
fluorometer. The samples were subsequently acidified with 50 percent V/V HC1
and read in the fluorometer for phaeopigment determination (Strickland and
Parsons, 1968). All results were corrected for phaeophytin. Th^ phaeophytin
fraction generally represented a small proportion of the chlorophyll a_, so
possible errors resulting from the addition of excess amounts of hydrochloric
acid (Riemann, 1978) would probably be small.
There are limitations to our experimental design in addition to the
changing station pattern and to omitting stations on the first three cruises
and on cruise 7 (Table 3.1). One limitation was that 5 days were required to
sample the 44 stations, or under normal conditions, about 100 hours elapsed
from the time the first station was sampled until the last station was
sampled. A second limitation was that our sampling design included only the
southern part of the lake so that no data are available for northern Lake
Huron or only limited data that were collected in 1974 by the Canada Centre
18
-------
for Inland Waters. Finally, our sampling program did not include stations
from the inner part of Saginaw Bay, but three transects of stations (Stations
36 to 59) did provide good coverage of outer Saginaw Bay. Saginaw Bay,
however, was sampled rather intensively by Smith et al. (1977) at the same
time as our 1974 studies. Combined, our study and Smith's provide good
coverage of Saginaw Bay that can be used to verify the extreme range of
environmental conditions and determine the exchange of materials between the
two water masses.
In interpreting the data, the reader should be aware of the limitations
outlined above. Lack of synoptic coverage and the fact that adjacent
stations may have been sampled on different days may in some cases make the
interpretation of data rather difficult. Persons working with the data,
which are on file in STORET, should be aware of these limitations and if
their particular applications warrant, should determine when data were
collected.
A final caution to the user of the data, particularly those who might
use the data filed in STORET. The quality of the data is not uniform among
various variables or within variables among the different cruises. In the
text, we have pointed out inconsistencies; for example, many of the pH
measurements were not considered reliable and have either been omitted or
given little weight in our discussion. Also, in our discussion of the data
we have adjusted our interpretations to reflect the quality of data where
such adjustments are needed.
THERMAL CONDITIONS
The eight cruises on Lake Huron can be divided into four periods,
according to thermal characteristics: thermal bar, spring warming, summer
stratification, and autumnal cooling. The presentation of physical-chemical
data is organized according to these thermal periods (Table 3.3).
Thermal Bar
On the first two cruises conducted in April and May, the thermal bar was
obvious over the study area with water temperatures being >4°C offshore and
<4°C nearshore (Figures 3.4a and b). The major differences in surface water
temperatures between the two cruises were that the 4°C isotherm was farther
offshore during the May cruise (Figure 3.4b) than during the first cruise
(Figure 3.4a), and the nearshore area of the lake encompassed by the 8°C
isotherm was much larger on the second cruise, extending all along the east
and west shores of the lake and into Saginaw Bay.
As would be expected, the area of the lake that was <4°C was related to
the depth profiles in the lake, with the shallower areas warming faster than
the deeper areas. As a consequence, the area with water temperatures >4°C
was larger in the shallow southern part of the study area than in the deeper
northern part.
19
-------
TABLE 3.3. DATES AND THERMAL PERIODS OF CRUISES
ON SOUTHERN LAKE HURON, 1974
Cruise number
Time of cruise
Thermal period
1
2
3
4
5
6
7
8
April 28-May 3
May 14-17
June 4-8
June 17-21
July 17-22
August 26-31
October 8-12
November 10-14
Thermal bar
Spring warming
Summer stratification
Autumnal cooling
20
-------
to
21
-------
' o
22
-------
Spring Warming
By mid-June, the thermal bar was no longer present. The retardation of
wanning was still obvious, however, in the northern and deeper parts of the
study area where surface water temperatures were <6°C during the first week
in June (Figure 3.4c) and <10°C by mid-June (Figure 3.4d). In contrast,
nearshore temperatures were 4-8C° warmer than the offshore temperatures on
both cruises.
On the two June cruises, strong vertical thermal stratification was
evident only in nearshore areas and in Saginaw Bay. Considerable warming of
surface waters occurred in the 2 weeks between the two June cruises, so that
by the third week in June, water temperatures south of a line between Harbor
Beach and Goderich were about 12°C or greater (Figure 3.4d).
Summer Stratification
Strong vertical thermal stratification developed after the second June
cruise and was present during the July and August cruises. In July, surface
water temperatures ranged from 17-19°C in the open lake with a gradient of
increasing temperature from the northeast to the southwest (Figure 3.4e).
The pattern of isotherms observed may have been caused by transport of cold
water from the north along the east shore of Lake Huron or by weak upwelling
along the eastern shore in the vicinity of Port Albert and Kincardine.
Maximum temperatures observed during the study occurred during the last
week of August when surface water temperatures ranged from 20 to 22°C. The
warmest temperatures were present in the southern part of the lake near the
outflow to the St. Glair River and along the eastern shore (Figure 3.4f).
Autumnal Cooling
By early October, the surface waters of the lake had cooled from the
20-22°C range observed in late August to 11-13°C. The warmest temperatures
were found along the east coast south of Goderich (Figure 3.4g). Surface
temperatures along the west coast were cooler than in the open lake, and as a
consequence, surface temperature decreased generally from east to west.
In November, the lake had cooled so that the surface waters ranged from
9-ll°C with temperatures >10°C being present only in the southeastern part of
the lake (Figure 3.4h). The effect of depth on the rate of cooling was
apparent from examination of the data collected because colder water (<9°C)
was found in Saginaw Bay, which is shallow, and warmer water was present in
the deeper main lake. Warmer waters at mid-lake may reflect, in part,
transport of waters from the northern deeper parts of the lake, which because
of a larger mass, cool at a slower rate than shallower'waters.
CHLORIDE
In contrast to the major plant nutrients, chloride, being a conservative
substance, would not be expected to vary seasonally. Variations in chloride
23
-------
concentration seasonally and spatially on any given cruise, therefore, can be
related to inputs primarily from shoreline sources. In southern Lake Huron,
the two major shoreline sources are Saginaw Bay on the United States side of
the lake and the area near Goderich on the Canadian side of the lake.
Thermal Bar
During the first cruise of the thermal bar period, chloride
concentrations were quite uniform over the study area, with concentrations in
Saginaw Bay being only slightly greater than in the open lake (Figure 3.5a).
Other areas of "high" chloride concentrations along the western shore of the
lake south of Harbor Beach and on the eastern shore of the lake near Goderich
vere limited in extent with chloride concentrations ranging to 8 mg/1 near
Goderich, about 2 mg/1 greater than the open lake. Concentrations in outer
Saginaw Bay were only 6 mg/1, indicating that the effect of the thermal bar
on water transport was quite pronounced, holding water with larger
concentrations within the area of Saginaw Bay, which was not sampled. By the
second cruise, however, water with higher chloride concentration was present
in the sampling area, as indicated by concentrations of 13 mg/1 and by the
7-mg/l isopleth that was found in Saginaw Bay (Figure 3.5b). The only other
area of relatively high concentration was off Goderich where the water
contained 7 mg/1 of chloride. Mid-laka concentrations of chloride on the
second cruise did not change from the first cruise, being 5.5 mg/1.
Spring Warming
Chloride distributions during the spring warming cruises were
characterized by two features not found during the thermal bar period.
First, water with relatively high chloride concentrations was found across
the mouth of Saginaw Bay (Figures 3.5c and d), and second, the high chloride
concentrations along the east shore near Goderich had disappeared, presumably
because of the breakdown of the thermal bar. However, water along the
eastern shore did have chloride concentrations >6 mg/1, a concentration
slightly greater than the open lake.
Chloride concentrations >11 mg/1 were found in early June along the
northern part of outer Saginaw Bay (Figure 3.5c). Chloride isopleths at this
time indicated that water was being transported out of the bay along the
northern shore, but on the second cruise in June, high chloride
concentrations, >17 mg/1, were found along the southern shore near the thumb
(Figure 3.5d), indicating that water was being transported into the open lake
on the opposite shore.
Mid-lake concentrations on both June cruises were <6 mg/1, or
essentially the same as on the first two cruises. Patterns of isopleths on
both cruises indicated chloride input from Saginaw Bay to the open lake
because concentrations >6 mg/1 were found in the area off Harbor Beach. The
observed pattern of isopleths is interpreted as being the result of transport
of high chloride water from Saginaw Bay, which was mixed and diluted with
open lake water of lower chloride concentration, producing water masses
offshore from Harbor Beach with chloride concentrations >6 mg/1. There was
also some indication of input from the Canadian shore, because on both
24
-------
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a
o
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60
e
01
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•H
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r-l
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26
-------
cruises concentrations >6 mg/1 were found along the eastern shore of the lake.
Postulating transport of water from Saginaw Bay to the open lake along
the northern shore of Saginaw Bay based on chloride concentrations on
cruise 3 is also supported by the pattern of temperature isotherms
(Figure 3.4c); likewise, postulating easterly and southerly transport of high
chloride water along the southern shore of Saginaw Bay during cruise 4 is
also supported by the pattern of isotherms (Figure 3.4d).
Summer Stratification
On the July cruise, high chloride water was most pronounced in the
southern part of Saginaw Bay (Figure 3.5e). This water appears to have been
transported from inner Saginaw Bay toward the open lake in a northeasterly
direction. The transport of high chloride water was accompanied by an
intrusion of low chloride water, <6 mg/1, along the northern shore of the bay
in the vicinity of East Tawas. Water with elevated chloride concentrations
extended into the lake to the northeast rather than being confined to the
nearshore area east and south of the thumb.
On the August cruise, chloride concentrations in outer Saginaw Bay were
much less than in July, but the area with the greatest concentration was in
Saginaw Bay along the northern shore near Tawas Bay where concentrations
exceeded 8 mg/1 only in a limited area (Figure 3.5f). Concentrations in most
of outer Saginaw Bay ware <7 mg/1, which suggests that at least in the area
sampled, Saginaw Bay water had been displaced by intrusions of open lake
water.
Main lake concentrations on the July and August cruises ranged from
<6 mg/1 to 7 mg/1 over most of the study area (Figures 3.5e and f). The
distribution of chloride on the August cruise indicates extensive horizontal
transport and mixing prior to this cruise because chloride concentrations in
outer Saginaw Bay were relatively low and because our data show pockets of
high chloride water, >7 mg/1, off Harbor Beach and some 100 km east of
Saginaw Bay near Kincardine (Figure 3.5f).
The fact that mid-lake chloride concentrations increased to >6 mg/1
during the summer stratification period from concentrations <6 mg/1 on the
previous cruises is interpreted as being the result of inputs from shoreline
sources, primarily from Saginaw Bay. Chloride concentrations increased
because high chloride water was transported from Saginaw Bay into southern
Lake Huron where it was mixed with relatively low chloride water from the
northern part of the lake, increasing the concentration of lake water prior
to its discharge through the St. Glair River.
Autumnal Cooling
On the two cruises during this period, high chloride water was present
only along the southern shore of Saginaw Bay, indicating water from Saginaw
Bay was transported out of the bay along the southern shore and into the open
lake (Figures 3.5g and h). On both cruises, there was evidence of intrusion
of low chloride water, <6 mg/1, into Saginaw Bay from the northeast and
27
-------
extending into the bay to the south of East Tawas. This pattern is much more
pronounced on cruise 7, when the <6 mg/1 zone extended through the study
area, than on cruise 8.
Mid-lake concentrations remained relatively low at approximately 6 mg/1
on both cruises. The fact that water with <6 mg/1 covered a greater area on
cruise 8 (Figure 3.5h) than on cruise 7 (Figure 3.5g) and that concentrations
on both cruises were smaller than during summer stratification indicates that
Saginaw Bay water was diluted with open-lake water to a greater degree on
cruise 8. From October to November, the depth of the epilimnion increased
significantly, thereby providing a greater volume in which to dilute high
chloride water from Saginaw Bay.
HYDROGEN ION CONCENTRATION
Data for pH are limited; none were obtained on cruise 1 or on cruise 7.
In addition, some of the remaining data are difficult to interpret. For
example, surface pH, in general, decreased 0.1 or 0.2 units from cruise 3 to
cruLse 4, indicating first, either a systematic error in measurement
techniques, or second, a large change in surface water chemistry. Because
these cruises were only two weeks apart, the latter explanation hardly seems
logical. However, one explanation for the chemical change might be that,
because epilimnetic depth increased between cruise 3 and cruises 4 and 5,
mixing of deep water with low pH with surface water of greater pH reduced the
epilimnetic pH' values between the two cruises.
Another interesting aspect of the data is the low mid-lake pH values on
cruises 4 and 5. These values taken in mid-June and mid-July were lower at
mid-lake than the values obtained on cruise 3 in early June, indicating a
decrease in pH (Fig. 3.6). Sufficient time elapsed between the July and June
cruises so that advection of water from the north or epilimnetic entrainment
of deep water may be plausible explanations for the decrease in pH. The most
interesting feature of the pH data for cruise 5, however, is seen on
examination of vertical profiles. At stations where surface pH values ranged
from 3.3-8.4, a subsurface maximum in pH can be found. In some cases, the
value of this subsurface maximum, usually found at 15-25 or 30 m, is about
8.5. One would have to interpret this increase in pH as resulting either
from increased photosynthetic activity at depth or to high pH water that
originally was present on the surface and had sunk to thermocline depths as
it was being transported within the lake. This feature of maximum pH at
thermocline depths also persists to a limited extent in the data obtained on
cruise 6 in the latter part of August.
Thermal Bar
On the second cruise when the thermal bar was present, there was little
definition in the structure of pH in the surface waters (Figure 3.6b). The
pH was >8.4 in Saginaw Bay and around the tip of the thumb, but in most of
the lake it was very close to 8.4. Areas with high pH were on the landward
side of the thermal bar and were found both on the north and south shores of
Saginaw Bay.
28
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Spring Warming
On the two cruises in June, there are two major points related to pH.
First, there is the large differences between pH values for the two cruises;
much higher values for pH were found, as discussed above, on the early June
cruise then on the cruise conducted 2 weeks later. The second feature is the
very large values for pH found to the south of Saginaw Bay where pH was >8.6
and in a limited area represented by two stations where pH was >8.7
(Figure 3.6c). The large values for pH were associated with water
temperatures in Saginaw Bay that were 6-10C° greater than in the open lake.
In the open lake waters, pH ranged from 8.3 to 8.45. On the second cruise in
June, however, pH values were less in the study area, ranging from 7.9 to
8.2, with the exception of a small area near the southern part of the lake
where values were >8.5. Possible explanations for these differences were
given above.
Summer Stratification
On the first cruise during the summer stratification period, pH varied
little over the study area, ranging generally from 8.3 to 8.5 (Figure 3.6e).
Higher values were found in Saginaw Bay and along the east and west shores of
the lake. Low values in the center of the lake, <8.3 in some cases, were not
expected, and explanations have been discussed above.
In the 6 weeks between the two summer stratification cruises, pH
increased greatly over a large part of the central area of the lake, being
>8.55 and ranging to as high as >8.65 at one station (Figure 3.6). Likewise,
in Saginaw Bay, pH was elevated, being >8.6 and ranging to >8.7 at the mouth
of the bay. One value, <8.4, was obtained in the southeastern part of the
lake. Whether this is a true value or not is questionable.
Autumnal Cooling
In November (the only cruise during autumnal cooling for which pH data
are available), pH was much less than during the latter part of summer
stratification and ranged generally from 8.2 to 8.3 (Figure 3.6h). Lowest
values for pH were found at midlake south of Goderich. The limited data
available from our cruise Indicate that low pH water, <8.2, was present north
of the area that was sampled.
DISSOLVED REACTIVE SILICA
Dissolved reactive silica (silica) varies seasonally, the primary
mechanism for its loss being utilization by diatoms. Diatoms have an
obligate silica requirement for growth, so the growth of diatoms depletes
silica in the surface waters during summer stratification. Silica in the
surface waters is replenished during the fall and winter circulation periods
when silica from the bottom waters is mixed into the water column. During
stratification, bottom waters are enriched with silica released from the
sediments and regenerated from diatoms.
31
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Thermal Bar
At the end of April, the horizontal variation in silica over the study
area was quite small. The largest concentrations, ranging from 1.7 to
1.8 mg/1, were found at the mid-lake stations (Figure 3.7a). Smaller
concentrations, from 1.4 to 1.5 mg/1, were found in the open waters of the
southern part of the lake, along the western shore south of Harbor Beach and
in a small area of Saginaw Bay. The lowest concentration, 1.0 mg/1, was
found along the western shore south of Harbor Beach.
By mid-May, silica concentrations had been reduced to 1.2 mg/1 or less
over much of the study area, with the exception of a small parcel of water
containing 1.4 mg/1 at the mouth of Saginaw Bay (Figure 3.7b). Compared with
the open lake, silica concentrations were lower in nearshore areas. The area
of most extreme silica depletion was in the southern part of Saginaw Bay
where silica concentrations were reduced to 0.1 mg/1 at one station, probably
approaching the minimum level that could be detected by our methodology. On
the eastern shore near Goderich, a considerable area had silica
concentrations <0.5 mg/1. These areas of reduced silica concentration
probably ring the lake inside the thermal bar, but because of the sampling
grid employed in this study it was not possible to verify such a structure.
Spring Warming
Two areas had relatively low silica concentrations on both cruises
during the period of spring warming. First, along the eastern shore near
Goderich, the silica concentration was <0.5 mg/1, and second, in Saginaw Bay,
the concentration was lower, <0.2 mg/1 (Figures 3.7c and d). On both
cruises, there is some indication that the low silica water from Saginaw Bay
was either being transported (Figure 3.7c) or had been transported
(Figure 3.7d) out of Saginaw Bay along the western shore of the lake, a
pattern also suggested by the distribution of chloride. The distribution on
cruise 3 also indicates transport of water with 0.2 mg/1 to the north
alongshore near East Tawas.
Open lake concentrations on the first cruise in June generally ranged
from 1.2 to 1.5 mg/1; however, little of the area had concentrations
>t.4 mg/1 (Figure 3.7c). The 1.5 mg/1 isopleth at the northern end of the
study area probably indicates the limit of intrusion of northern Lake Huron
water with higher silica concentrations than those found in the southern part
of the lake. On the second June cruise the relatively high silica
concentration water from northern Lake Huron contained 1.3 mg/1
(Figure 3.7d). At the time of this cruise in late June, most of the
remaining open lake waters had silica concentrations between 1.0 and 1.2 mg/1
or less. The reduction in silica concentrations of approximately 0.7 mg/1 in
the open lake between late April and the latter part of June indicates a
relatively rapid growth of diatoms in the surface water.
Summer Stratification
Surface waters on the two cruises during the period of summer
stratification were marked by a continued decline in silica concentrations so
32
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33
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34
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that by the end of August, silica concentrations over much of the study area
had been reduced to the range of 0.6 to 0.8 mg/1 (Figure 3.7f). Water with
higher concentrations found in the northern part of the study area probably
delimits the zone in which Saginaw Bay influences open lake chemistry.
Higher concentrations to the north result from intrusion of relatively high
silica water from the north mixing with low silica water from Saginaw Bay.
On both summer stratification cruises (Figures 3.7e and f), there was
relatively little difference in silica concentrations between outer Saginaw
Bay and open Lake Huron. As this represents an increase in silica
concentration in Saginaw Bay from the period of the thermal bar, these
results indicate that there was a relatively large amount of mixing or
exchange between outer Saginaw Bay and open Lake Huron between these two
periods of the study.
Autumnal Cooling
From late August, the last cruise during the summer stratification
period, to early October, the first cruise during the autumnal cooling
period, there was a general and continued decrease in silica concentrations
in the surface waters, particularly in the northern part of the study area.
During early October, most concentrations in the study area were <0.7 mg/1
(Figure 3.7g). In the southeastern part of the lake and in Saginaw Bay,
areas with <0.6 mg/1 were present. In October, there was a north-south
gradient in silica concentration that was also present in late August.
October concentrations ranged from >0.7 mg/1 in the northern part of the
study area to <0.6 mg/1 in the southern end of the lake.
Concentrations of silica in the surface waters in November (Figure 3.7h)
increased in relation to concentrations present in October (Figure 3.7g)
because of epilimnetic entrainment of subsurface waters relatively rich in
silica as the epiliranion cooled and deepened. Concentrations over much of
the study area ranged from 0.8 to 1.2 mg/1, except in nearshore areas and in
Saginaw Bay where concentrations were 0.8 mg/1 and less. The reduced
concentrations in the southern part of Saginaw Bay and along the east coast
near Goderich were caused by either a period of high diatom growth or the
lack of a source of silica-rich waters in these shallow waters, or both.
NITRATE NITROGEN
Nitrate, like silica, varies seasonally as a function of growth of
phytoplankton, but unlike silica, its concentration may be reduced by the
growth of phytoplankton other than diatoms because all phytoplankton require
nitrogen for growth, but not all phytoplankton are diatoms.
Thermal Bar
During the first cruise of the thermal bar period, concentrations of
nitrate nitrogen ranged generally from 0.3 to 0.4 mg/1. The major feature
that was different was relatively large nitrogen concentrations off Goderich
(Figure 3.8a) on the first cruise. These concentrations, exceeding 1.3 mg/1,
35
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have been traced to the flow of the Maitland River into the lake at Goderich.
High, nearshore nitrogen concentrations near Goderich persisted until
mid-May. The distribution of large nitrate concentrations near shore has
been directly related to the presence of the thermal bar (see Section 7).
On the second cruise of the thermal bar period, nitrate nitrogen
concentrations over most of the study area again ranged from 0.3 to 0.4 mg/1,
with much of the open lake being <0.35 mg/1 (Figure 3.8b). In addition to
the area with high nitrate nitrogen off Goderich, there was a small area of
relatively high nitrogen concentration, >0.6 mg/1, on the southern shore of
Saginaw Bay that may have been caused by land runoff in the general area or
may have been caused by transport from Saginaw Bay.
During mid-May, the effects of the thermal bar on the distribution of
nitrate nitrogen in Saginaw Bay were evident because concentrations were
<0.3 mg/1 in Saginaw Bay (Figure 3.8b). This lower concentration probably
resulted from utilization of nitrate for the growth of phytoplankton within
Saginaw Bay.
Spring Warming
The relatively high nitrate concentrations in the nearshors zone off
Goderich, observed during thermal bar conditions, persisted during the spring
warming period (Figures 3.8c and d), presumably resulting from continued high
nitrate loading from the Maitland River.
On the early June cruise, isopleths of nitrate in Saginaw Bay were
parallel, running generally southwest-northeast (Figure 3.8c). This
distribution would seem to indicate that low nitrate water is being
transported out of Saginaw Bay along the northern shore and that high nitrate
water is being transported into the bay along the southern shore.
Distributions of chloride and silica also suggest that this type of transport
has occurred.
On the second cruise in June, the distribution of nitrate with
concentrations >0.35 mg/1 corresponds roughly with temperatures >12°C in
Saginaw Bay (Figure 3.8d). These data indicate that water from Saginaw Bay
is being mixed with water lower in nitrate from the open lake and along the
northern shore and is then being transported eastward to the open waters of
the lake, at concentrations between 0.33 and 0.35 mg/1.
Summer Stratification
Only one set of data is available from the summer stratification cruises
because data from the August cruise could not be used as a result of
technical difficulties with the nitrate analysis.
During late July, nitrate nitrogen concentrations were much less
variable than during any of the previous cruises and ranged generally from
0.25 to 0.30 mg/1 (Figure 3.8e). At this time of the year, nitrate
concentrations in lower Saginaw Bay were apparently less than those in the
open lake, and the pattern of isopleths indicated that this low nitrate water
38
-------
with concentrations <0.25 mg/1 was being transported out of Saginaw Bay along
the southern shore.
Autumnal Cooling
By early October, phytoplankton growth within Saginaw Bay apparently had
reduced nitrate concentrations to low levels compared to previous cruises or
to the open lake on this cruise. The lowest concentration was <0.08 mg/1 at
one station, with a more extensive area of concentrations <0.15 mg/1 being
found along the southern shore of Saginaw Bay (Figure 3.8g). The
distribution of nitrate on this cruise indicates that Saginaw Bay water was
moving out of the bay along the southern shore into the open part of the lake
and that open-lake water with relatively high nitrogen concentrations, >0.26
mg/1, was being transported into the outer bay from the northeast.
With the exception of the relatively low nitrate water in Saginaw Bay,
concentrations over the rest of the study area were uniform, ranging
generally from 0.25 to 0.27 mg/1 (Figure 3.8g).
On the second autumnal cooling cruise, nitrate concentrations within
Saginaw Bay were still low, ranging to <0.13 mg/1, but as was observed on the
preceding cruise, concentrations over the remainder of the lake were
relatively uniform, ranging generally from 0.25 to 0.27 mg/1 (Figure 3.8h).
Differences in nitrate nitrogen concentrations between the southern and
northern parts of the lake are evident in data from the November cruisa.
Concentrations in the southern end of the lake as great as 0.25 mg/1 were
found in contrast to concentrations as large as 0.30 mg/1 in the northern
part of the study area (Figure 3.8h). Along the western shore and extending
into the open part of the lake was a large area with concentrations ranging
from <0.23 to 0.25 mg/1 that undoubtedly represents a water mass influenced
by inputs from or mixing with water originating in Saginaw Bay.
CHLOROPHYLL a_
Chlorophyll a results are of interest because this variable can be
measured quite readily on large numbers of samples and can be used as a
measure of phytoplankton standing crop. Chlorophyll concentration is a
community parameter that provides little insight into the dynamic aspects of
phytoplankton productivity because as a static estimate of biomass it does
not reflect changes in standing stock or phytoplankton species composition.
Thermal Bar
In late April and early May, chlorophyll a concentrations over much of
the study area were relatively constant with concentrations ranging generally
from 2 to 3 pg/1. Although low, these concentrations probably represent
maximum concentrations obtained in the open waters during the spring bloom.
Lin and Schelske (1978) reported a maximum value of 3.0 pg/1 during 1975 from
an area near Station 13.
39
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At the end of April, there were two areas with relatively high
chlorophyll concentrations. The greatest concentrations existed off Goderich
in the area of the high nitrate concentrations where chlorophyll exceeded
16 yg/1 and south of Harbor Beach along the western shore where 6 yg/1 were
found (Figure 3.9a). There also was an area near East Tawas with
concentrations exceeding 3 yg/1.
By mid-May, chlorophyll a_ concentrations in Saginaw Bay had increased to
6 yg/1 along the northern shore near East Tawas, and water with 4 yg/1 was
found along the southern edge of Saginaw Bay extending along the western
shore nearly to Harbor Beach (Figure 3.9b). These areas with elevated
chlorophyll a_ concentrations were presumably the result of nutrient input
from Saginaw Bay and possibly to the influence of nearshore conditions,
because the largest concentrations were located on the landward side of the
thermal bar. Along the eastern shore, concentrations >14 yg/1 were observed
near Goderich in the area of high nitrate concentration.
Spring Warming
On the early June cruise, chlorophyll a^ concentrations over most of the
study area ranged from <1 to 2 yg/1 (Figure 3.9c). One station south of
Harbor Beach had concentrations >4 yg/1; it was part of an area along the
western shore of the lake extending to Saginaw Bay with concentrations
>2 yg/1 . By the third week in June, concentrations at mid-lake were all
<2 yg/1 and in some areas had been reduced to <1 yg/1 (Figure 3.9d).
Relatively large phytoplankton blooms were present in the area near Goderich
on the eastern shore and in Saginaw Bay along the southern shore where
concentrations ranged from 4 to 6 yg/1.
Summer Stratification
During the summer stratification period, open-lake chlorophyll a^
concentrations were quite low, ranging from <0.4 yg/1 to 0.6 yg/1. In July,
there was a small area in Saginaw Bay with chorophyll a_ concentrations
>2 yg/1 that also was the only area where concentrations exceeded 1 yg/1
(Figure 3.9e). This same pattern of low chlorophyll ji concentrations existed
during the August cruise, and the only areas in which concentrations exceeded
1 yg/1 were along the northern shore of Saginaw Bay, extending north of East
Tawas where a cruise maximum of 4 Vg/1 was observed (Figure 3.9f).
Autumnal Cooling
Chlorophyll a concentrations in mid-lake on the October cruise ranged
from 1.0 to 1.5 yg/1, which represents the fall bloom as we sampled it
(Figure 3.9g). Concentrations >1.5 yg/1 were present along the western
shore of Saginaw Bay and in Saginaw Bay; however, in most areas,
concentrations did not exceed 2 yg/1, with only a small area having
concentrations >4 yg/1.
By mid-November, concentrations had decreased to the range of 0.5 to
1.0 yg/1 over most of the open lake (Figure 3.9h). Even in Saginaw Bay,
concentrations in general were <1.5 yg/1, so that during this cruise, most of
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the chlorophyll a concentrations ranged from 0.5 to 1.5 yg/1. Transport of
water along the southern shore of Saginaw Bay and then south on the western
shore of the lake that was observed on the previous cruise was evident again
from chlorophyll a distributions on the November cruise.
SECCHI DISC TRANSPARENCY
Thermal Bar
During the period of thermal bar, the patterns for Secchi disc
transparency were essentially the same as those for water temperature, with
the greatest transparencies occurring in the middle of the lake on the
lakeward side of the thermal bar and lower transparencies being found
shoreward of the thermal bar along both shores of the lake and in Saginaw Bay.
In mid-May, the pattern of transparency was related to thermal
structure, but Secchi disc transparency in the nearshore zone on both sides
of the lake was reduced, being less than it had been on the first cruise
(Figure 3.10a and b). This difference was especially pronounced in the area
along the eastern shore of the lake.
Spring Warming
In June during the period of spring warming, the inshore-offshore
differences in Secchi disc transparency persisted even though the thermal bar
was no longer present (Figures 3.10c and d). In June, however, Secchi disc
transparency was much less at the mouth of Saginaw Bay than it had been
during the cruises in April and May. The area of low transparency water
extended south and west of Saginaw Bay along the western shore of Lake Huron.
Transparency over much of the open lake ranged from 6 to 7 m, which was
not greatly different than that which had been observed during the previous
two cruises during the period of the thermal bar.
Summer Stratification
During July and August, water transparency in Saginaw Bay was much less
than in the open waters of the lake (Figure 3.10e and f). Transparency in
the open lake increased greatly in comparison to values on the previous
cruise. In July the area of low transparency water observed in Saginaw Bay
extended farther into the lake than it did in August. Low transparency water
was also observed on both cruises in the nearshore area near Goderich.
The open waters of the lake, particularly during July, were very
transparent with Secchi disc readings being close to maximum for this study.
One value of 16 ra and one value of 15.5 m were observed during this cruise.
Transparency decreased by the end of August when Secchi disc readings were
10 m or less in the open waters. However, these August readings reflected
greater water transparency than had been observed in either the thermal bar
or spring warming periods.
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Autumnal Cooling
A very sharp gradient in Secchi disc transparency was found during the
October cruise at the mouth of Saginaw Bay where transparencies ranged from 3
to >18 m (the maximum transparency during this study) over a distance of
about 30 km (Figure 3.10g). Some of the low transparency water was being
transported to the east and south and was present along the western shore
near Harbor Beach. This pattern of transparencies at the mouth of Saginaw
Bay persisted on the November cruise (Figure 3.10h) although the gradients
were not as sharp.
SEASONAL CHANGES
Averages of selected variables for Saginaw Bay and open Lake Huron were
plotted to show seasonal variation. In general, there was a distinct
difference between the stations in Saginaw Bay and those in the open lake;
however, the differences between stations in the northern and southern parts
of our study area were small.
Temperature
A distinct seasonal cycle in the surface water temperature was obvious
for the three areas. The expected relationship of water temperature to depth
of the water column was observed; water temperature in Saginaw Bay was warmer
during the warming period and cooler during the cooling period than in the
deeper waters of the open lake (Figure 3.11). Maximum temperatures for the
three groups of stations exceeded 20°C during cruise 6 at the end of August,
and temperatures may have been greater in September when no samples were
obtained.
Sampling did not begin early enough in the spring to obtain data during
the entire warming period, especially in Saginaw Bay, and did not continue
long enough in the autumn for water to cool to the temperature of maximum
density. On the last cruise (November 10-14), water temperatures averaged 9
to 10°C.
Chloride
Average concentrations of chloride were larger at the Saginaw Bay
stations than at stations in the open part of the lake (Figure 3.12). In
addition, chloride concentrations in the bay were greater on cruises 3, 4,
and 5 (early June to mid-July) than at other times of the year. Whether this
increase in concentration in outer Saginaw Bay resulted from a buildup of
chloride in the bay during the winter and spring is not known. Data for
water temperature and chemistry indicate that exchange between Saginaw Bay
and the open part of the lake is limited during the thermal bar period.
Another explanation for large concentrations in the spring is that this is
the period of maximum loading from runoff.
46
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Dissolved Reactive Silica
A seasonal cycle in dissolved reactive silica is apparent both for
Saginaw Bay and open Lake Huron (Figure 3.13). The two regions differ in
that the rate of decrease in Saginaw Bay is much greater than that in the
open lake and in that the minimum concentration in Lake Huron is larger than
the minimum concentration in Saginaw Bay.
The decrease in concentration of silica in Saginaw Bay during the spring
amounted to 0.9 mg/1 and occurred over a period of about 40 days from the end
of April to early June. The average rate of this decrease was
0.022 mg/l/day. In the open lake, the silica concentration decreased a
comparable amount, but the time required to reach the minimum found in
October was about 160 days. The average rate of decrease in the open lake
was, therefore, only 0.0057 mg/l/day.
On the first analysis, the rates of silica decrease in outer Saginaw Bay
and open southern Lake Huron appear to be very different. Different physical
processes in the two environments, however, would tend to reduce these
differences if calculations were considered on an areal basis instead of a
volumetric basis. In the 40 days in which silica decreased in Saginaw Bay,
the volume of the epilimnion would have changed little compared to the volume
of the epilimnion in the open lake. In fact, the open lake was not
stratified until early June (Figure 3.4c) when silica concentrations in
Saginaw Bay were the lowest observed during our study. Therefore, until
early June, diatoms in the open lake undoubtedly were utilizing silica and
decreasing concentrations throughout the water column. In addition, after
the lake stratified, the epilimnion in the open lake would have increased
proportionately much more than that in Saginaw Bay.
Nitrate Nitrogen
The seasonal cycle in concentration of nitrate nitrogen was not as
pronounced as it was for silica. In the open lake, concentrations decreased
gradually during the entire period of sampling (Figure 3.14). The expected
autumn increase in concentration resulting from entrainment of nitrate rich
hypolimnetic water was not observed. In outer Saginaw Bay, data did not fit
the expected seasonal pattern because the largest concentrations occurred on
cruise 4 during mid-June.
Part of the explanation for the lack of a seasonal cycle in outer
Saginaw Bay is the lack of nitrate data for the August cruise when the lowest
nitrate nitrogen concentrations would have been expected. The absence of the
expected seasonal pattern was in part the combination of two factors. First,
Saginaw Bay warmed much faster than the open lake, so one would not
necessarily expect the seasonal pattern to be the same for the two
environments. Second, the largest nitrate concentrations were found on
cruise 4 when maximum chloride concentrations also were observed (Figure
3.12), indicating that the proportion of inner Saginaw Bay water was greatest
for this cruise during June. Smith et al. (1977) have shown that
concentrations of nitrate nitrogen were greater in inner Saginaw Bay than in
the outer bay during this period in 1974.
49
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Chlorophyll a
In both outer Saginaw Bay and In the open lake, maximum chlorophyll a_
concentrations were found in mid-May during cruise 2 (Fig. 3.15). After
cruise 2, concentrations decreased generally until cruise 7 in October when
there was an obvious increase in concentration in Saginaw Bay and an
indication of an increase at the open lake stations. Detecting seasonal
differences in absolute concentrations for the open lake stations is
obviously more difficult than in Saginaw Bay because the summer
concentrations in the open lake were <1.0 yg/1. Although small, minimum
concentrations in outer Saginaw Bay were <1.5 yg/1 or several times larger
than those at the open lake stations. Data for the one station sampled in
outer Saginaw Bay in mid-June indicate elevated chlorophyll a levels,
possibly the result of intrusion of inner Saginaw Bay water.
It is also obvious that the standing crop of chlorophyll a in outer
Saginaw Bay was greater than that found at the open lake stations (Figure
3.15). Average concentrations for the stations in Saginaw Bay ranged from
1.5 to 5.0 yg/1, a range in concentrations that overlapped with those in the
open lake only for cruises 1 and 2. In the open lake, average concentrations
ranged from 0.3 to 3.8 yg/1, but if the first two cruises or the spring
maximum values are excluded, the average concentrations ranged only from 0.3
to 1.5 yg/1.
Secchi Disc Transparency
Secchi disc transparency varied seasonally at the open lake stations,
but the variation was not strictly the inverse of that observed for
chlorophyll a_ concentrations. If the one large value for the north lake
stations is excluded, transparency values generally were greatest when
chlorophyll concentrations were least and were smallest when the chlorophyll
concentrations were greatest (Figure 3.16). A similar relationship between
transparency and chlorophyll a concentrations also was found at the Saginaw
Bay stations.
Transparency, as measured with the Secchi disc in our studies, was
compared with data collected in 1954 by Ayers et al. (1956). Data in 1954
were collected in June, July, and August. Compared with our data collected
in 1974, transparencies in 1954 were generally greater. The largest
differences between the 2 years occurred when the June data were compared;
in 1954, tranparencies greater than 8 m occurred over a large part of
southern Lake Huron whereas during 1974, transparencies were generally 7 m or
less in the same areas. The biggest difference was in maximum values that
were 13 m in 1954 and only 7 m in 1974. In addition, the area in which
transparency was >12 m in 1954 only had a transparency of >6 m in 1974. In
July 1974, a large area had transparencies >12 m with the value at one
station being 16 m, but in 1954 the transparency was >14 m over a large area
with a maximum value of 19 m. In August 1974, transparencies in the open
lake south of Saginaw Bay ranged from 8 to 10 ra, but in 1954, values as large
as 11 m were observed.
52
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54
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TRANSPORT FROM SAGINAW BAY
One of the objectives of our study was to assess the importance of
transport of materials from Saginaw Bay to Lake Huron. This objective was
accomplished by studying the distribution of water masses in the vicinity of
the mouth of Saginaw Bay. Although we did not study currents directly during
our cruises, it is obvious that the distribution of water masses is the
direct result of water movement. During 1974, at the same time our data were
collected, Danek and Saylor (1975) studied the currents in Saginaw Bay and
reviewed results of previous studies of the currents of Saginaw Bay and Lake
Huron, including those by Ayers et al. (1956), Johnson (1958), and Beeton
et al. (1967).
Previous conclusions from studies of currents in Saginaw Bay generally
have been that current patterns are complex and are highly dependent on local
winds. Some of the complexity in current patterns at the mouth of Saginaw
Bay may be caused by rapid response to winds because one would not expect an
effect on circulation patterns in the main part of the lake to be as rapid.
The typical pattern of transport from Saginaw Bay around the thumb and then
southward has been observed many times; but other patterns of currents are
also quite common, leading to the general conclusion that current patterns
are complex in and near the mouth of Saginaw Bay.
Influences of the wind on surface currents and water transport would
have been relatively less during the thermal bar cruises than on subsequent
cruises. During the thermal bar period, surface water temperatures vary
horizontally, and in addition, during periods of warm weather, a thermal
atmospheric inversion frequently occurs near the water's surface. As a
result, the effective wind energy at the water's surface varies greatly
depending on the difference between the air and water temperatures;
therefore, wind velocities on land may be much greater than those near the
lake surface. The distribution of temperature (Figures 3.4a and b), chloride
(Figures 3.5a and b), and other variables during the first two cruises
indicates little or no surface transport of water from Saginaw Bay.
On 2 of the 3 days preceding the third cruise, winds were moderate from
the south to southeast, averaging about 2 knots at the Selfridge station
(Appendix A) and were stronger about 4 knots at the Wurtsmith station
(Appendix B). On the second and third days before the cruise, the wind
velocity at Wurtsmith averaged only 4 knots from the ESS. During the cruise,
winds averaged from 6-11 knots from the SSE to SSW. Water transport from
Saginaw Bay apparently occurred along the north shore as indicated by the
intrusion of a water mass with Saginaw Bay water characteristics, high
chloride (Figure 3.5c) and low silica (Figure 3.7c), toward the main lake.
This pattern of water masses conforms with the current pattern proposed by
Danek and Saylor (1975) for southwest winds.
The fourth cruise was preceded by SSW winds of 6 knots or less.
During the cruise, velocities ranged from 3 to 6 knots at Selfridge
(Appendix A) and from 6 to 9 knots at Wurtsmith (Appendix B). These winds
were generally S to SW, shifting to N at Wurtsmith on the last day of the
55
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cruise. On cruise 4, there was some indication of intrusion of Saginaw Bay
water along the northern shore near East Tawas, but the most pronounced
feature was the presence of Saginaw Bay water along the southern shore
extending around the thumb toward Harbor Beach. Isopleths for temperature
(Figure 3.4d), chloride (Figure 3.5d), silica (Figure 3.7d), and
chlorophyll a_ (Figure 3.9d) indicate extensive transport from Saginaw Bay.
The best indicator of this transport is the presence of the 15-mg/l isopleth
for chloride across the mouth of Saginaw Bay (Figure 3.5d).
Northerly winds, averaging as large as 8-9 knots, preceded the fifth
cruise. During the 6 days of the cruise, winds were quite variable in
velocity and direction. On July 17, the first day of the cruise, winds
shifted to the south at Selfridge and averaged about 5 knots. On the second
day, the direction shifted to WSW, and the velocity increased, averaging 9 to
10.5 knots. On the next two days, the wind shifted to W and N, but average
wind velocity decreased to 6 to 8 knots. Wind velocities decreased on the
last 2 days, and the direction shifted to N to NNE. Velocities were 1.5 and
2.7 knots at Wurtsmith (Appendix B), but were much greater at Selfridge
(Appendix A) averaging 3.5 and 5.0 knots. Current patterns expected from the
variable wind conditions would be complex. The distribution of water masses
shows a slight intrusion of Saginaw Bay water near the thumb toward the
northeast to the open lake (Figures 3.5e, 3.6e, and 3.8e) rather than around
the thumb. In addition, there is evidence for a slight intrusion of open
lake water into Saginaw Bay near the northern shore (Figures 3.5e-3.8e). The
transport is obviously weak but is the type expected from current patterns
shown by Danek and Saylor (1975) for northeast winds that occurred during
part of the cruise.
Prior to the sixth cruise, winds were northerly and moderate with
velocities averaging 4 knots. On the day before the cruise started, winds
shifted to the east. On the first day of the cruise, winds were moderate,
averaging about 6 knots from the SW. During the next 3 days, the velocity
decreased, generally averaging <4 knots, and the direction was variable
ranging from the west to the northeast. Winds then shifted to the south at
<4 knots and to the west on the last day of the cruise when the velocity
increased to 7 to 8 knots. With these variable wind conditions, current
patterns are probably not predictable. There was an intrusion of water with
elevated chloride (Figure 3.5f) and high chlorophyll a_ (Figure 3.9f) from
Saginaw Bay along the northern shore near East Tawas toward the open lake.
The distribution of isopleths, however, does not suggest transport of water
out of the bay.
The seventh cruise was preceded by several days of winds, from 7 to 11
knots from the SW shifting to NW on the day before the cruise started.
During the first 4 days of the cruise, wind velocity averaged from 3 to 5
knots, and the direction varied from S to W. On the last day of the cruise,
the direction shifted to NW, and the velocity increased to 6 to 7 knots.
On cruise 7, there appears to have been an intrusion of open Lake Huron water
in the middle portion of Saginaw Bay and strong transport of Saginaw Bay
water to the northeast along the southern shore around the thumb area toward
Harbor Beach (Figures 3.5g, 3.3g, and 3.9g) Isopleths for chloride (Figure
3.5g) and chlorophyll a_ (Figure 3.9g) also indicate a lesser but pronounced
56
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transport of water along the northern shore from Saginaw Bay. The intrusion
of water in the middle part of the bay indicates a different current pattern
than that suggested by Danek and Saylor (1975) for southwest winds.
Prior to the last cruise, winds were W to SW and were moderate, being 2
to 3 knots. On the first day of the cruise, winds shifted to the south and
increased in velocity to 7 to 10 knots on the second day of sampling. During
the last 3 days, wind direction ranged from southwest to west, and velocity
increased to 9 to 12 knots on the last day. The distribution of water masses
was similar to that for cruise 7 in that there was an intrusion of open lake
water in the mid portion of Saginaw Bay and also evidence for transport along
the south shore around the thumb with weaker transport to the open lake along
the north shore.
DISCUSSION
It has been recognized in many investigations that there is a great
amount of variability in most environmental parameters within the Lake Huron
system, especially if values from Saginaw Bay are compared with any other
area in the lake (Beeton et al., 1967; Schelske and Roth, 1973). Saginaw Bay
is different than other parts of Lake Huron because the Saginaw River carries
large loads of many materials, increasing concentrations in inner Saginaw Bay
in comparison to those found in the open parts of the lake. As shown by
Smith et al. (1977), the Saginaw River in 1974 carried loads of chloride,
total phosphorus, and total nitrate nitrogen that were large enough to
increase concentrations in lower Saginaw Bay in comparison to those found
either in outer Saginaw Bay or in the open lake. Concentrations of the
conservative ions, sodium, calcium, and magnesium, were also greater in
Saginaw Bay than in the open lake.
The large nutrient loads from the Saginaw River produced favorable
conditions for large phytoplankton standing crops in Saginaw Bay. Average
yearly chlorophyll a_ concentrations in lower Saginaw Bay were 30 yg/1 with
maximum concentrations during the summer ranging to more than 70 yg/1. Smith
et al. (1977) also reported concentrations of total phosphorus in lower
Saginaw Bay that averaged more than 35 yg/1.
In contrast to the relatively highly polluted waters in Saginaw Bay are
the other major sources of surface water inputs to the main body of Lake
Huron. Waters from Lake Superior, the North Channel, and Georgian Bay have
very high quality compared to Saginaw Bay or to any other area or part of the
Great Lakes. The other important source of surface water to Lake Huron is
the outflow from Lake Michigan, which also is high quality water but has
larger concentrations of total phosphorus than either Lake Superior or Lake
Huron and differs chemically from these waters in several other respects
(Schelske et al., 1976).
The Upper Great Lakes Reference Group segmented the main part of Lake
Huron, the North Channel, and Georgian Bay into nine areas to reflect
variability in environmental parameters. Nearshore zones, areas <3 km from
shore or with depths <15 m, were excluded in the segmentation as was Saginaw
57
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Bay (International Joint Commission, 1977). It is surprising to note how
little average values for nutrients differed among the segments in 1974
(Figure 3.17). For example, average total phosphorus concentrations among
the segments, excluding those for the North Channel, ranged only from 4.8 to
5.7 pg/1. The lowest average concentration of total phosphorus was 4.8 yg/1
in Segment 6. Without this value, average concentrations for 7 to 15 cruises
among the remaining segments ranged from 5.3 to 5.7 yg/1.
Differences among the segments in the average concentrations of silica
and nitrate were larger than those for average total phosphorus concentra-
tions (Figure 3.17). If the maximum and minimum concentrations as well as
the average concentrations are compared for different segments, it is
possible to distinguish differences among the segments. The range in
concentrations of silica and nitrate nitrogen is mainly attributable to
seasonal changes, as shown in Figures 3.13 and 3.14.
The report by the International Joint Commission (1977) utilized
Segment 6 to establish average conditions for the lake. Data we collected
for this report do not reflect conditions in Segment 5 because most of our
stations were in Segments 7 and 8 and in Saginaw Bay (Figure 3.13). The
average values for open lake stations in Figures 3.11-3.16 represent
conditions in Segment 8. No attempt was made to plot seasonal averages for
the data collected in Segment 7 because of crulse-to-cruise variability in
data at each station. Conditions at our stations in Segment 7 were
influenced most by current patterns and water transport from Saginaw Bay;
therefore, water quality at any given time is greatly influenced by the
proportion of Saginaw Bay water at any given station. This type of
variability is obvious for the data from Stations 36-40, which were averaged
to reflect variable conditions in outer Saginaw Bay.
Horizontal variations in physical, chemical, and biological variables in
our study area were strongly influenced by the presence of readily
identifiable water masses. These water masses with distinct characteristics
were either transported from Saginaw Bay to the open lake or from the open
lake into Saginaw Bay. One general pattern that was observed on several
cruises was the movement of water out of Saginaw Bay near one shoreline and
the compensating transport of water into Saginaw Bay along the opposite
shoreline. Differing patterns of transport are undoubtedly dependent on
meteorological conditions, particularly wind direction and velocity for the
several hours to several days prior to the time data were collected.
As one aid in interpreting patterns of water masses, we compiled
meteorological information from two shore locations near our study area. A.t
both locations, Selfridge Air Force Base and Wurtsmith Air Force Base, wind
speed and direction were recorded hourly during 1974. This set of data has
been reduced to daily averages that are presented in Appendices A and B.
Presenting data in this manner may introduce some bias, but it does identify
storm periods that have greater than average wind velocities and that affect
water currents more than periods with smaller inputs of wind energy.
The transport of Saginaw Bay water to the open lake was only apparent
from the distribution of water masses on two or three of our eight cruises.
58
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SEGMENT 4
NAME
Tot P
NO
SiO
MEAN
57
261
165
MAX
82
293
225
MIN
35
198
096
N
8
8
8
SEGMENT 5
NAME
Tot P
NO
SiO
MEAN
56
192
090
MAX
75
260
159
MIN
49
140
036
SEGMENT 9
NAME
Tot P
NO
SiO
MEAN
54
268
118
MAX
96
331
191
MIN
33
230
066
N
8
8
8
SEGMENT 7
NAME ' MEAN
SEGMENT 6
NAME
Tot P
NO
MEAN
48
266
MAX
77
322
MIN
24
142
SiO J_ 137_[ 199 1 099
N
13
13
13
NUTRIENT CONCENTRATIONS IN THE EPILIMNION OF
LAKE HURON IN 1974. Units: Total Phosphorus in
ygP/X,; Nitrate in UgN/£; Reactive Silicate in mg Si02/&
Data are cruise averages; N = number of cruises. The
open waters do not include nearshore areas, harbours,
and embayments. Open waters are generally defined as
those waters more than about 3 km offshore or with a
depth greater than about 15 m.
8
SEGMENT 8
NAME
Tot P
NO
SiO
MEAN
53
276
1 18
MAX
87
378
214
MIN
36
186
058
N
15
15
15
MILES
10 20 30
40
20 40 60
KILOMETRES
Figure 3.17. Nutrient concentrations in the epilimnion of Lake Huron in 1974.
(International Joint Commission, 1977)
59
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60
-------
The most obvious transport was the previously reported typical pattern of
transport out of the bay along the southern shore around the thumb, then
southward toward Harbor Beach. Lakeward transport was also evident, although
to a lesser extent, along the northern shore near East Tawas. Current
patterns reported by Sloss and Saylor (1975) for 15-day periods show that
currents flow outward to the lake from the bay along both the southern and
the northern shores, so the presence of Saginaw Bay water moving out of the
bay along the northern shore is not unexpected. Currents have been reported
to be complex and strongly influenced by short-term meteorological events at
the mouth of and in Saginaw Bay, so one would expect that water transport
would also be complex.
61
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REFERENCES
Ayers, J. C., D. V. Anderson, D. C. Chandler, and G. H. Lauff. 1956.
Currents and Water Masses of Lake Huron. Pub. No. 1, Great Lakes Res.
Div., Univ. of Mich., Ann Arbor, Michigan, 101 pp.
Beaton, A. M., S. H. Smith, and F. F. Hooper. 1967. Physical Limnology of
Saginaw Bay, Lake Huron. Technical Report 12, Great Lakes Fishery Comm.,
56 pp.
Danek, L. J., and J. H. Saylor. 1975. Saginaw Bay Water Circulation.
NOAA Technical Report ERL 359-GLERL 6, U.S. Department of Commerce, 51 pp.
Davis, C. 0., and M. S. Simmons. 1979. Manual for Field and Laboratory
Procedures. Spec. Rep. 70, Great Lakes Res. Div., Univ. of Mich., Ann
Arbor, Michigan. Pages unnumbered.
International Joint Commission. 1977. The Waters of Lake Huron and Lake
Superior. Vol. II (Part B), Lake Huron, Georgian Bay, and the North
Channel. Report of the Internat. Joint Cotnm. Upper Lakes Ref. Group,
Windsor, Ont. pp. 295-743.
Johnson, J. H. 1958. Surface-Current Studies of Saginaw Bay and Lake Huron.
1956. Spec. Sci. Rep., Fish 267, U.S. Fish and Wildlife Service, 84 pp.
Kamphake, L. J., S. A. Hannah, and J. M. Cohen. 1967. Automated Analysis for
Nitrate by Hydrazine Reduction. Water Res., 1:205-216.
Lin, C. K., and C. L. Schelske. 1978. Effects of Nutrient Enrichment,
Light Intensity and Temperature on Growth of Phytoplankton from Lake
Huron. Spec. Rep. 63, Great Lakes Res. Div., Univ. of Mich., Ann Arbor,
Michigan, 61 pp.
Menzel, D. W., and N. Corwin. 1965. The Measurement of Total Phosphorus in
Seawater Based on the Liberation of Organically Bound Fractions by
Persulfate Oxidation. Limnol. Oceanogr., 10:280-282.
Riemann, B. 1978. Carotenoid Interference in the Spectrophotometric
Determination of Chlorophyll Degradation Products from Natural Populations
of Phytoplankton. Limnol. Oceanogr., 23:1059-1066.
Santiago, M. A., S. Fielek, and C. L. Schelske. 1975. Automated Method for
Sulfate Determination in Lake Water. ASTM STP 573. Water Quality
Parameters, Amer. Soc. for Testing and Materials, pp. 35-46.
62
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Schelske, C. L., L. E. Feldt, M. S. Simmons, and E. F. Stoermer. 1974.
Storm Induced Relationships Among Chemical Conditions and Phytoplankton in
Saginaw Bay and Western Lake Huron. Proc. 17th Conf. Great Lakes Res.,
Internat. Assoc. Great Lakes Res., pp. 78-91.
Schelske, C. L., and J. C. Roth. 1973. Limnological Survey of Lakes
Michigan, Superior, Huron and Erie. Pub. No. 17, Great Lakes Res. Div.,
Univ. of Mich., Ann Arbor, Michigan, 108 pp.
Schelske, C. L., E. F. Stoermer, J. E. Gannon, and M. S. Simmons. 1976.
Biological, Chemical and Physical Relationships in the Straits of
Mackinac. Ecol. Res. Series, EPA-600/3-76-095, U.S. Environmental
Protection Agency, Duluth, MN. 266 pp.
Sloss, P. W., and J. H. Saylor. 1975. Measurements of Current Flow During
Summer in Lake Huron. NOAA Technical Report ERL 353-GLERL 5, U.S.
Department of Commerce, 39 pp.
Smith, V. E., K. W. Lee, J. C. Filkins, K. W. Hartwell, K. R. Rygwelski, and
J. M. Townsend. 1977. Survey of Chemical Factors in Saginaw Bay (Lake
Huron). Ecol. Res. Series, EPA-600/3-77-125, U.S. Environmental
Protection Agency, Duluth, MN. 143 pp.
Strickland, J. D. H., and T. R. Parsons. 1968. A Practical Handbook of
Seawater Analysis. Bull. Fish. Res. Bd. Canada No. 167. 311 pp.
Wolfe, D. A., and C. L. Schelske. 1967. Liquid Scintillation and Geiger
Counting Efficiencies for Carbon-14 Incorporated by Marine Phytoplankton
in Productivity Measurements. J. Cons. perm. int. Explor. Mer., 31:31-37.
63
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SECTION 4
STATISTICAL INFERENCES FROM SOUTHERN LAKE HURON — 1974
by Russell A. Moll
Water quality in southern Lake Huron during 1974 was characterized by
large contrasts. Conditions vary from nearly pristine waters in the center
of the lake to highly eutrophic waters in Saginaw Bay and along the Ontario
shoreline. Because of the large, complex database compiled for southern Lake
Huron, multivariate statistics were employed to aid in the interpretation
of the data. The purpose of this chapter is to present the results of
several statistical analyses and the ecological interpretation that follows
those analyses.
The approach used in the analyses was not without precedent in that we
successfully analyzed data collected in 1973 from the Straits of Mackinac
(Moll et al., 1976). But, the Lake Huron data differed from the Straits data
in that eight cruises were conducted as compared to three, a larger area was
sampled, a larger portion of the year was sampled (April to November), and
more variables were measured. Because of the larger spatial and temporal
range of the Lake Huron data, different techniques were necessary than were
used in the Straits of Mackinac data.
METHODS
Forty-four stations (Figure 4.1) were sampled for fifteen variables on
eight cruises. Although all stations were not visited on every cruise, the
data set was relatively complete. Missing stations were primarily the result
of poor weather during sampling, while missing variables were the result of
failure of a technique where immediate sample analysis was necessary,
although both were not particularly common.
The sampling grid covered Lake Huron from Oscoda to the southern end of
the lake near Port Huron (Fig. 4.1). Stations were concentrated in the mouth
of Saginaw Bay, as this area is known for highly contrasting water quality.
Samples were not collected farther in the bay than Charity Island, since our
intent was to reveal the influence of bay water on the open lake.
The fifteen variables measured included chemical, physical, and
biological variables with a bias toward explaining the function of
phytoplankton in the lake. Many of the samples were analyzed on board the
research vessel; however, some samples were brought to our Ann Arbor
64
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65
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laboratories when shipboard processing was not feasible. A more complete
description of the sampling techniques is found in Section 3.
Statistical Methods
After simple statistics were calculated for each variable, the data were
prepared for multivariate analysis by standardization. This meant that each
variable had a mean set equal to 0.0 and a standard deviation set equal to
1.00 (Sokal and Rohlf, 1969). This transformation had the effect of putting
all variables in the same numerical range or intercomparison. No other
transformations were performed, as the multivariate analyses used were not
particularly sensitive to non-normality (Van de Geer, 1971). Correlations
(simple product-moment) were calculated between all standardized variables;
all possible pairs of measurements were used to find the correlation between
two variables rather than using only pairs of variables found in complete
data cases. Correlations were computed between variables for each cruise
separately. All statistical analyses were performed by existing computer
programs found in the University of Michigan statistical software package,
MIDAS (Michigan Interactive Data Analysis System).
Factor analyses were run using the correlation matrices from each
cruise. The number of factors extracted was based on the somewhat arbitrary
criterion that only factors with eigenvalues greater than or equal to 1.00
should be used (Rummel, 1970). The values of the communalities for each
variable were estimated using the iterative principal axis factor solution as
described in Harman (1967). Convergence of communalities was deemed
sufficient when succeeding estimates differed by less than 1.0 x 10~3 or
after twenty iterations. An orthogonal varimax rotation was performed on the
factor matrix.
In addition to the correlation analyses, cluster analysis was used to
graphically display the similarity between sampling stations. The approach
was similar to the Straits of Mackinac analysis (Moll et al., 1976), in that
data from one depth of one cruise were clustered and these clusters then
circled on a map of the sampling stations. The clustering techniques were
identical to those used in the Straits of Mackinac analysis: euclidean
distances were calculated between all sets of variables, and these distances
were then clustered using an average weighted algorithm (UPGMA) (Sneath and
Sokal, 1973). The only associations that were considered in the cluster
analysis were those in the lower half of the hierarchy based on the number of
branchings. In other words, only the closely related clusters were
considered. This hierarchy was displayed by circling the clusters of
stations on a map of the sampling area.
RESULTS
Correlation Analysis
The correlations were initially calculated on a cruise-by-cruise basis
to look for changes in the relationships of variables to one another
66
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throughout the 1974 sampling season. Data from the first cruise (April 1974)
were not analyzed because the number of stations sampled and the number of
variables measured were considerably fewer than on the other cruises.
The second cruise (May 14-17) occurred when a thermal bar was found
close along the shore. The thermal bar is a condition created by warming of
the lake from the shore toward the center (Boyce, 1974). Thus, a band of
warm water is found along the shore, while the center of the lake remains
cold. The correlation matrix from this cruise (Table 4.1) reflects the
thermal bar condition; almost all correlations were high, indicating the well
mixed, unstratified water column beyond the thermal bar in the center of the
lake. The spring diatom bloom was evident between the thermal bar and the
shore (Stoermer and Kreis, In press) contributing to the high correlation
between ^4C uptake (primary production) and chlorophyll a_. Diatom growth
appears to have been sufficiently advanced to reduce silica levels (Section
3) such that correlations between soluble silica and chlorophyll a and ^4C
uptake were highly negative.
The factor analysis of the cruise 2 data separated the data into three
factors (Table 4.2). These factors are:
1) Open lake water with high loadings for temperature, silica, Secchi
depth, pH, and chlorophyll a_ (Secchi depth and silica negative),
2) water between the thermal bar and the shore with high loadings for
particulate silica, total phosphorus, nitrate nitrogen, silica, and
Secchi depth silica and Secchi disc negative),
3) Saginaw Bay water with high loadings for chloride, total phosphorus,
and chlorophyll a.
Between cruises 2 (May 14-17) and 3 (June '+-8), a period of rapid spring
warming occurred in that surface water temperatures <4° C were not observed
in the survey area. Similar to cruise 2, the correlations from cruise 3
showed that many variables were highly correlated (Table 4.3). Although the
majority of stations sampled were in stratified water, most of the samples
came from hypolimnetic waters in that the newly formed epilimnion represented
only a small volume of southern Lake Huron.
Sufficient phytoplankton growth occurred between the mid-May and early
June cruises to change the relationships between many of the measured
variables. These changes are evident by comparing the correlation matrices
from cruises 2 and 3; many of the correlations among nutrients were lower
during cruise 3. An example is the change in the chlorophyll a_ silica
correlation from -0.829 in mid-May to -0.308 in early June. The largest
shifts in correlations involved correlations among temperature,
chlorophyll a, and Secchi depth.
The factor solution for cruise 3 (Table 4.2) was similar to cruise 2 in
that three factors were extracted and ammonia had a very low communality.
The three factors are:
67
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TABLE 4.2. FACTOR ANALYSIS OF 12 VARIABLES MEASURED DURING 1974
CRUISES IN SOUTHERN LAKE HURON
CRUISE 2
Factor
% Variation
Explained
24.9
29.6
20.3
Variable
Secchi disc
Temperature
pH
Chlorophyll
Si02
NO 3
NH3
T-P04
Conductivity
Chloride
S04
P-3i02
Communality
.801
.879
.614
.888
.812
-.893
.051
.828
.600
.980
.732
.910
Factor Loadings
-.660 -.604 .009
.843 .289 .292
.657 -.004 .426
.531 .505 .592
-.640 -.515 -.369
-.097 -.849 -.403
.037 -.004 .223
.230 .826 .294
.502 .387 .446
.499 .251 .817
.273 .376 .716
.265 .912 -.088
CRUISE 3
Factor
% Variation
Explained
30.9
18.6
9.6
Variable
Secchi disc
Temperature
PH
Chlorophyll
Si02
NO 3
NH3
T-P04
Conductivity
Chloride
SO 4
P-Si02
Communality
.820
.553
.896
.343
.825
.397
.057
.152
.625
.698
.734
.990
Factor Loadings
-.430 -.686 .405
-.648 .130 -.340
.633 -.115 -.694
.117 .529 -.224
-.780 -.326 .333
.075 .532 .328
.021 -.043 .234
.358 .113 -.104
.737 .233 .166
.334 .050 .006
.818 .195 -.166
.200 .974 -.017
69
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1) Nearshore water with high loadings for chloride, conductivity,
sulfate, pH, and silica (negative loading),
2) offshore waters with high loadings for particulate silica,
nitrate-nitrogen, and temperature (negative loading),
3) hypolimnetic waters with high temperature and pH loadings.
Surface waters continued to warm between cruises 3 (June 4-7) and 4
(June 17-21). The relationship among variables continued to change as
thermal stratification developed further and plankton growth proceeded in the
surface waters. The largest changes in correlations among variables from
cruise 3 to cruise 4 involved chlorophyll a_, temperature, pH, ammonia, and
total phosphorus (Table 4.4). The chlorophyll a to ^C uptake correlation
increased from +0.437 in early June to +0.794 by mid-June; the reason for
this increase is not apparent.
The factor solution for cruise 4 (Table 4.5) again yielded three
factors. This solution produced factors for the same three water types as
did the cruise 3 solution, but the ammonia communality vastly increased.
These factors are:
1) Nearshore and Saginaw Bay water with high loadings for ammonia,
chloride, total soluble phosporus, sulfate, and total phosphorus,
2) hypolimnetic water with high loadings for temperature, pH, and silica
(tiegative loading),
3) offshore epilimnetic waters with high loadings for particulate
silica, chlorophyll a^, and Secchi disc (negative loading).
The fifth cruise (July 17-21) occurred during typical summer thermal
stratification with a well developed 15-20 m thermocline (Section 3). The
depletion of nutrients in the epilimnion had apparently caused a lowering of
the level of ^*C uptake and a shift in the plankton crop from mid-June.
These events were reflected in the decrease in the correlation between
particulate silica, ^*C uptake, chlorophyll a_ and silica (Table 4.6). The
high correlations between temperature and nutrients observed throughout the
first four cruises were absent from the cruise 5 correlation matrix,
a further indication of epilimnetic nutrient depletion.
The factor analysis for cruise 5 yielded three factors (Table 4.5).
These factors were identified with the same three water types as the
solutions from earlier cruises, but, the factors for Saginaw Bay are now the
least important of the three (smallest sums of squares) rather than the most
important. The cruise 5 factors are:
1) Hypolimnetic water with high loadings for silica, nitrate nitrogen,
temperature, and pH (negative loadings for the nutrients),
2) epilimnetic water high loadings for chlorophyll a^, particulate
silica, total phosphorus, and conductivity,
71
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72
-------
TABLE 4.5. FACTOR ANALYSIS OF 12 VARIABLES MEASURED DURING 1974
CRUISES IN SOUTHERN LAKE HURON
CRUISE 4
Factor
% Variation
Explained
34.4
14.2
21.8
Variable
Secchi disc
Temperature
PH
Chlorophyll
Si02
NO 3
NH3
T-P04
Conductivity
Chloride
S04
P-Si02
Communality
.644
.827
.305
.688
.900
.208
.692
.731
.748
.996
.823
.885
Factor Loadings
.362 -.339 -.631
.424 .778 .205
.144 .530 .062
.310 .149 .755
.435 -.724 -.431
.295 .048 .344
.805 -.061 .201
.723 .148 .431
.789 .074 .347
.940 .200 .268
.842 .202 .271
.196 .200 -.898
CRUISE 5
Factor
% Variation
Explained
22.3
21.9
17.3
Variable
Secchi disc
Temperature
pH
Chlorophyll
SiO?
~
NH3
T-P04
Conductivity
Chloride
304
P-Si02
Communality
.582
.757
.360
.656
.900
.398
.476
.484
.577
.798
.689
.707
Factor Loadings
,494 -.490 -.313
.723 -.351 .333
.569 .107 .157
.166 .792 -.036
.930 .172 -.075
,619 .087 -.080
,210 .485 .444
.141 .589 .342
,132 .591 .454
.306 .100 .334
.255 .089 .785
,256 .301 -.029
73
-------
m
CRUISE
1
RRELATION MATRI
o
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o fNin voin *fN fncN I*>CN o
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O 0>CN VOP* P"P* OfN ^^ OCN O
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o ^ p" m in 9 ^^ o *"^ en 9 ft ro ^* in
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o _ r- ^ |M ^(s, ^-, u-, ^m (N| IN OfN fNIN O
•- 1 1 1 1 1 1
o cr.-.p».-»cnAm.~.tf p- fN^.^«^vo^^
o P-CN cNen or- inin co«^ os^. inf^i 90 aoin IN
O 9«on^^fO'H«os
voao \o "~ oco P*vo vo9 ^-*^ p*^^ osfN 9en asv O
P-IN ININ fNOn OCN mcN enr» P-P' oncN » «- OOIN *l
CNCN >-CN i»i^ miN »IN fNin ooin OfN OCN VOCN as
p**-»<*r)*«.r-.-«9«-««r^.cn 9 in«^p-»-»ao*-»
oon a-cN oncn inp» p»m CN^^ en-*. CNro mo *-«i
CNCN CNO( men C~CN mcN mp- cop- ^CN WCN VOCN
VOCN CNCN O»* «— IN CNIN OU) rim I*>CN fnfN OO* 03
III 1
VO*M. as.-* f*><^ 9^-. *-^^ in in vo-« oo<^ vo-^
cncn »-CN »on »- p. coin to—. CN-. von mo «om a.
S»CN OIN aron CNCN p^cN or* a*r* »CN ^CN 9fN •;
P-CN infN •• •- OIN OfN »m »in »CN »CN »CN M
i i i i i i
M
p*«~ vo^^ m^« to ~* CN«-« *- tn p»«-« v> ~* »— — * ca
roan cncN non ^p- cnm in«^ ot-^ inf) fNo *in o
OIN infN onon INCN OCN OOP- en P" C-CN OOCN fncN u
eflN rnfN inr- affN »fN INin inin 9IN nfN i*»CN W
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1 1 1 1 1 1 1 1
fN » 0 » O
Oi'lfnoasftc** »H
HOXA'UM) 1 bJO
-------
3) Saginaw Bay water with high loadings for chloride and sulfate.
Nutrient depletion in the epilimnion was particularly evident during
cruise 6 (August 26-31). Water temperatures approached their annual maximum
while nutrients, silica in particular, reached their annual minimum. This
highly stratified condition resulted in a slight lowering of all correlations
among variables on cruise 6 (Table 4.7). The correlations between
particulate silica, ^-4C uptake, and chlorophyll a_ were lower in August than
in July, while the correlation between silica and ^C uptake went from
negative to positive. Despite the five weeks between cruises 5 and 5, the
change in correlations among the different variables changed less than
between other cruises.
Only two factors were extracted from the factor analysis for cruise 6
(Table 4.8) and these were attributed to hypolimnetic and epilimnetic waters.
Saginaw Bay water was apparently mixed into the epilimnion and circulating
throughout the southern half of Lake Huron. The moderately high chloride
loading on the epilimnion (second) factor would support this hypothesis. The
cruise 6 factors are:
1) Hypolimnetic water with high particulate silica, conductivity, pH,
and temperature loadings (pH and temperature negative loadings),
2) epilimnetic waters with high chlorophyll a_ and total phosphorus
loadings.
Significant cooling and mixing had occurred during the month between
cruise 6 (August 26-31) and cruise 7 (October 8-12), dropping surface
temperatures to 10-20°C and lowering the thermocline to 40 m. The cooling
and mixing induced several changes in the correlations among variables from
cruise 6 to cruise 7 (Tables 4.7 and 4.9). A large increase was observed in
the correlations between chlorophyll ji and silica and chlorophyll a and
nitrate-nitrogen. The correlation between silica and *-^C uptake went from
positive to negative. Some of the changes in the correlations between
cruises 6 and 7 were most likely precipitated by a shift in phytoplankton
assemblages from summer to fall (Stoermer and Kreis, In press).
The factor solution for cruise 7 (Table 4.8) was composed of three
factors. Although the factor solution separated the lake into hypolimnetic
and epilimnetic waters as in cruise 6, the communalities in the cruise 7
solution were higher. These higher communalities imply an overall higher
interrelationship of the variables to one another (Mulaik, 1972), perhaps a
result of the well-mixed water column. The cruise 7 factors are:
1) Epilimnetic waters with high chlorophyll a_y total phosphorus,
chloride, Secchi disc, and nitrate nitrogen loadings (Secchi disc and
nitrate nitrogen negative loadings),
2) hypolimnetic water with high temperature and silica loadings (silica
a negative loading),
75
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I
-------
TABLE 4.8. FACTOR ANALYSIS OF 12 VARIABLES MEASURED DURING 1974
CRUISES IN SOUTHERN LAKE HURON
CRUISE 6
Factor
7 Vari aM nn
'<> VCLL L d U. 1. U 1. 1
Explained
Variable
Secchi disc
Temperature
PH
Chlorophyll
Si02
NH3
T-P04
Conductivity
Chloride
P-Si02
1
34.9
Communality
.255
.812
.842
.847
.724
.120
.387
.694
.244
.373
.072
-.886
-.873
.278
.847
.327
.182
.814
-.116
.567
2
18.0
Factor Loadings
-.500
.133
.267
.877
-.080
.115
.595
.179
.480
.227
CRUISE 7
Factor
% Variation
Explained
34.5
19.2
7.2
Variable
Secchi disc
Temperature
PH
Chlorophyll
Si02
NO 3
NH3
T-P04
Conductivity
Chloride
SO 4
P-Si02
Communality
.585
.917
.478
.623
.841
.855
.202
.768
.533
.854
.334
.313
Factor Loadings
.659 -.356 -.155
.064 .934 .199
.119 -.032 -.681
.713 .304 -.146
.241 -.882 .061
.835 -.397 .010
.071 .312 .316
.832 .045 -.270
.663 -.251 -.172
.917 .115 -.018
.511 .090 .253
.430 .304 .188
77
-------
r-
RUISE
u
§
Pd
'
i— i
5s
o
M
H
W
&
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•
<}•
pa
^(
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o m f OD w
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o r^^ r~ m" eno" o m*
O CN Cn cn 00 m cn v OO
o •*•" 01 *- oo *• w •-
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o sr ~* OD ~* m — .. 09 ** IN — .,
o m 01 o 01 mm mo «•• m
o ocn ocn moo ol en » o>
o w »• o »- m*~ ar •- vo t—
f— 1 1
M
i-l
M H
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a) u B i-l O m
•ft w w x a: H o
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0
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o oo N «- m »-
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r* o cn «••« cn ~^
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m «- o) w OD w
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•- f- r-
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cr
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-------
3) the third factor had no apparent significance.
Cruise 8 in mid-November (November 10-14) was conducted when the water
column was mixed to 50 m. There were few large changes in the correlation
coefficients between cruises 7 and 8, although the correlations between
variables were generally higher for cruise 8 than during the summer (Table
4.10). The correlation matrix for cruise 8 was somewhat similar to the
matrices of cruises 2 and 3. This similarity was interpreted as a return
toward non-stratified conditions in southern Lake Huron. The correlations
for cruises 6 and 7 indicate nutrient replenishment in the surface waters had
begun during cruise 6 but was not complete by November.
Four factors were extracted from the cruise 8 solution with the
communalities somewhat higher than the summer cruise solutions (Table 4.11).
The four factors identified three types of water. The three water types are:
1) Open lake epilimnetic water with high loadings for Secchi depth,
chlorophyll _a, and parttculate silica (chlorophyll a_ and particulate
silica negative),
2) nearshore and Saginaw Bay water with high chloride, sulfate, and
total phosphorus loadings,
3) hypolimnetLc waters on two factors (3 and 4) with high loadings for
silica, nitrate nitrogen, pH, chlorophyll a^ and temperature.
Cluster Analysis
Similar to the Straits of Mackinac analysis, station-to-station
relationships were analyzed with cluster analysis (Moll et al., 1976). The
results were not as useful in defining water mass relationships in southern
Lake Huron as they were for the Straits area. Areas of similar water quality
were often observed on opposite shores of the lake and long, meaningless
lines were necessary to connect stations of one cluster. As a result of this
unsatisfactory solution from the cluster analysis, a different technique was
pursued and is discussed in Section 5.
DISCUSSION
Nutrient Succession
Schelske and Stoertner (1971), Schelske et al. (1972), Kilham (1971),
Munawar and Burns (1976), and others have pointed out the importance of
differential uptake of nutrients in phytoplankton annual succession. By the
same token, differential regeneration rates of nutrients have a profound
effect on plankton species succession (Schelske and Stoermer, 1971; Schelske
et al., 1974; Lean, 1973). The sampling program for 1974 showed offshore
southern Lake Huron displayed nutrient depletion typical of oligotrophic or
nutrient-poor waters. An analysis was conducted of the changes in nutrient
ratios in southern Lake Huron during the summer of 1974. This analysis
provided several insights into phytoplankton growth strategy, and these
insights are presented below.
79
-------
oo
w
CO
od
0
1
X
M
BE
o
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1
g
O
O
r-l
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W
CO
H
o
o
g
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0 " ~
o co r-
o r- fM
o m CM
-
o m — o -.
o m c» o r»
O CB rM CM (M
O " fM O fM
" i
O " — « — . 0> ,—
o o w w en en r-
O >O tM 0 fM en (M
O " fM fM fM m fM
• • "• « •• t —
"III
H
a H
<« B a
MUD, O
« 0 B ,4
•* M M 22 ffl
> CO H CU (J
O
0
Q
o
-
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r- a
o " "
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o \e o en en
O fM fM fM "
0 in (M O fM
—
o 5" " ST m r-"
Oh IN OB " „ r- -~
9 fM fM fM O fM
1 1 1
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ID XI CO " O> (X
fO o m " in <7
IN
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M O =0
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O V)
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0 0 fM 0
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o r- fM m rM
o m (M " fM >J
o o> • fM
o ve ,-. CM — o — »
o in in m fMfM otM mtM a
i
«»r-»m oo fn — a -, vo — .
" tM en 91 m «•» r^ ^^ m fM 4 fM o co
CMfM WfM COO> ODCn "(M OfM VfM
OIM fMfM Otfl *-m OfM OfM fM IN r- cr> ocn o IN in IN oo IN B
OfM "fM "in »«1 "fM fMfM OfM M
I I i
M
oofM cnc* fM^^ o,-. cntM SOIN moo {j
mfM moi ocn men mcN vcfM mrM u
fMfM mfM Om »m fMfM OrM >CfM M
1 1 1 1 1 1 1
« Q » O
U SB SB " » M
Oj O i-J 1 i-l O "1
H U « 'J '-J tO "•
80
-------
TABLE 4.11. FACTOR ANALYSIS OF 12 VARIABLES MEASURED DURING 1974
CRUISES IN SOUTHERN LAKE HURON
CRUISE 8 Factor
Explained
Variable
Secchi disc
Temperature
PH
Chlorophyll
Si02
NO 3
NH3
T-P04
Conductivity
Chloride
804
P-Si02
Communality
.723
.906
.277
.741
.651
.592
.035
.257
.396
.835
.529
.641
1
13.1
.749
.016
-.151
-.507
.131
.234
.161
-.149
-.186
.018
.070
-.759
2
9.6
Factor
-.248
.107
-.030
.140
-.164
-.073
.079
.468
.378
.903
.655
.152
3
9.6
Loadings
.022
-.885
-.092
.243
.336
.037
-.028
.032
.327
.041
-.275
-.038
4
17.5
-.315
.335
.494
.636
-.703
-.728
-.041
.123
.334
.135
-.139
.202
81
-------
Table 4.12 shows the mean concentrations of four nutrients measured in
central southern Lake Huron. The seasonal pattern of these four nutrients
was similar to patterns observed in other Great Lakes (Schelske et al., 1975;
Burns, 1976). Silica and nitrate nitrogen, with their slow regeneration
rates, steadily decreased throughout the summer. Ammonia peaked in mid-June
(cruise 4) when zooplankton activity was maximal, and total soluble
phosphorus concentrations remained near the limit of detection throughout the
summer. The phytoplankton community in Lake Huron has developed a strategy
which accommodates the seasonal patterns of nutrient succession. Diatoms and
certain chrysophytes which require silica for growth are most productive
early in the summer when silica levels are at their highest. But plankton
that require silica for growth may not have a large competitive advantage if
they developed an ability to take up ammonia over nitrate as a nitrogen
source. The reason these silica-requiring species may not have an enhanced
ability to take up ammonia over nitrate is that nitrate levels are normally
high when silica is also high. Ammonia, on the other hand, is not
particularly abundant in the spring when silica levels are not limiting for
diatom growth; ammonia is normally most abundant during the mid-summer (Table
4.15), when silica levels are becoming limiting for those phytoplankton which
require silica (Schelske and Stoermer, 1971). Organisms which do not require
silica but require nitrogen and phosphorus face a different scheme. The
ratio of soluble phosphorus relative to nitrate nitrogen was low in June and
July, times when high growth is possible because of high light intensity
(Table 4.15). On the other hand, ammonia concentrations appeared highest
during June of 1974. Analysis of trends in the growth of individual
phytoplankton species by Stoermer and Kreis (In press) for southern Lake
Huron in 1974 showed non-silica requiring phytoplankton followed the ammonia
peak. In 1975, a study was conducted comparing phytoplankton dynamics in
Lake Huron to dynamics in Saginaw Bay, an area where normal seasonal nutrient
succession is disrupted by eutrophication. The results of this study are
presented in Section 6.
Phytoplankton Successional Events
Phytoplankton succession in southern Lake Huron was carefully monitored
during the summer of 1974 (Stoermer and Kreis, In press). The correlation
analysis of nutrient succession (Fig. 4.2) showed that major shifts in
phytoplankton crop (observed by Stoermer and Kreis, In press) could be
related to changes in silicon form (from soluble silica to particulate
silica) and concentration. In addition, the correlations between silica,
uptake, and chlorophyll a_ also indicated a shift in algal crop.
The correlation and factor analyses reflect the changes in relationships
between nutrients and other variables throughout the summer of 1974. Some of
the changes can be interpreted as differential uptake of one nutrient,
although cause and effect cannot be inferred from correlations. The period
of most rapid change in correlations was between cruises 3 and 5, during the
onset of thermal stratification. The correlations among soluble and
particulate silica, chlorophyll a, and *-^C uptake confirms the rapid changes
between cruises 3 and 5. Figure 4.3 shows that while the ^-4C uptake to
particulate silica and chlorophyll a to particulate silica correlations
change little throughout the summer7 this is not true for correlations with
82
-------
TABLE 4.12. MEAN CONCENTRATIONS AND STANDARD ERRORS
OF FOUR NUTRIENTS FROM SOUTHERN LAKE HURON, 1974
Cruise 1
Cruise 2
Cruise 3
Cruise 4
Cruise 5
Cruise 6
Cruise 7
Cruise 8
Soluble
Silica
(tag S102/D
1.86 + .03
1.17 4- .02
1.26 + .03
1.21 -1- .02
1.06 4- .02
1.03 + .03
0.72 4- .01
1.03 + .02
Nitrate
(kg N/l)
348 4-8.2
348 4- 6.0
306 4- 3.1
339 4- 3.5
291 4- 2.4
299 + 4.0
241 4- 3.7
261 + 2.9
Ammonia
(yg N/l)
11.9 + .40
12.8 + .22
10.4 4- .38
25.9 4- 1.6
12.4 4- .54
8.8 4- .32
5.0 + .25
8.57 4- .52
Total Soluble
Phosphorus
(yg P/i)
2.48 f .12
2.51 + .06
3.33 4- .14
3.25 4- .12
2.49 + .09
2.99 4- .14
2.53 + .11
3.81 4- .20
83
-------
X
o
I
cvJ O
g g>
(/) Q-
*> T
s I
5
Vvi
o
'(75
I
O
>
o
o
o
Q_
U
CO
e>
<
o:
a.
IO O IQ
o o
4 I
!N3IOIdd3-00 NOIiVGddOO
CO
T)
c
(fl
r-l
-------
soluble silica. These results can be interpreted as follows: the relative
proportion of chlorophyll a_ biomass containing particulate silica did not
change dramatically throughout the sampling season (particulate silica to
chlorophyll £ correlations ranged from -1-0.756 to +0.383). But, the
proportion of l^C uptake associated with particulate silica changed
considerably (particulate silica to ^C uptake correlation ranged from +0.773
to +9.188). The inference is that the fraction of chlorophyll a_ containing
particulate silica contributed only a small amount to the ^C uptake pool by
late summer of 1974. The chlorophyll a_ to *-4C uptake correlations change
very little throughout the entire sampling season.
The correlations among soluble silica, chlorophyll £, and '•^C uptake
changed touch more than did correlations with particulate silica. The
correlations between soluble silica and chlorophyll a were large and negative
early in the summer of 1974, but by July were small and positive. The *4C
uptake to soluble silica correlations follow a similar pattern, moving from
large and negative to small and positive. The inference from these results
is not clear. Prior research indicates that diatoms predominate in the late
spring and early summer (Schelske and Stoermer, 1971). The results from Lake
Huron seem to confirm those earlier studies; in the early summer productivity
and biomass are high, silica levels are low and rapidly decreasing. By
mid-summer, soluble silica levels are very low and much less tied to l^C
uptake and chlorophyll a concentrations implying more production by
non-silica requiring species.
Several aspects of the sampling program may place a limit on the
validity of the results discussed above. The ^C uptake values during all
the Lake Huron cruises came from 1 to 5 m samples and were incubated on-deck
in an artificial light incubator. A better understanding of phytoplankton
successional events may be possible with In situ ^C uptake profiles that
include samples from the deep chlorophyll layer, normally a major portion of
summer phytoplankton ecology in the Great Lakes (Moll, 1978).
General Limnological Succession
The sampling frequency in 1974 (at least one cruise per month except
September) allowed an analysis of limnological succession from thermocline
formation to fall mixing. The limnology of Lake Huron was dominated in the
spring of 1974 by the thermal bar. The thermal bar had the effect of holding
the high nutrient runoff water nearshore (Section 7). This effect was
particularly interesting in that Saginaw Bay water, readily identified by
high chloride content, was prevented from mixing with open lake water by the
thermal bar. The cruise 2 factor analysis showed the most important factor
was for thermal bar waters. As the thermal bar moved offshore the spring
phytoplankton bloom followed. This intense bloom used a considerable portion
of the surface nutrient pool. As a result, the relationships between
variables changed quickly during the late spring. Thermal stratification,
which separates surface and deep waters, was more static in that large
changes in correlations were not evident between summer cruises. In
addition, Saginaw Bay water moved more readily across southern Lake Huron, so
the factor analysis extracted just two factors by late summer — hypoliranion
and epilimnion. Cooling and mixing processes of the fall reduced the
85
-------
differences between surface and deep waters, and the correlations changed
again.
CONCLUSION
Southern Lake Huron in 1974 was a system dominated by three limnological
periods: homothermous, thermal bar, and thermally stratified. The
transition between these periods was brief in 1974 while conditions during
each period were noticeably different from the other two. Large shifts in
the relationships of variables among one another marked the transition
between two periods. These shifts were evident in the correlation and factor
analyses. The results of the analysis for cruises 3 and 4 were quite
different despite the fact that only two weeks separated the two.
Although homothermous conditions were never fully reestablished during
the fall sampling, the correlations and factor analyses implied a return to
winter conditions. The transition between stratified summer conditions and
homothermous winter conditions did not occur as rapidly as the reverse
process, the onset of spring thermal stratification. Nevertheless, the data
analysis showed a large amount of change between the October and the November
cruise.
86
-------
REFERENCES
Boyce, F. M. 1974. Some Aspects of Great Lakes Physics of Importance to
Biological and Chemical Processes. J. Fish. Res. Bd. Canada, 31:689-730.
Burns, N. M. 1976. Nutrient Budgets for Lake Erie. 1970. J. Fish. Res.
Bd. Canada, 33(3):520-536.
Harman, H. H. 1967. Modern Factor Analysis. Univ. Chicago Press, Chicago.
474 pp.
Kilham, P. 1971. A Hypothesis Concerning Silica and the Freshwater
Planktonic Diatoms. Limnol. Oceanogr., 16:10-18.
Lean, D. R. S. 1973. Phosphorus Dynamics in Lake Water. Science,
179:678-680.
Moll, R. A. 1978. An Alternate Hypothesis of General Phytoplankton
Ecology Considering the Subsurface Chlorophyll Layer. Presented at the
41st ASLO meeting, Victoria, British Columbia.
Moll, R. A., C. L. Schelske, and M. S. Simmons. 1976. Distribution of
Water Masses in and Near the Straits of Mackinac. J. Great Lakes Res.,
2(l):43-59.
Mulaik, S. A. 1972. Foundations of Factor Analysis. McGraw-Hill,
New York. 453 pp.
Munawar, M., and N. M. Burns. 1976. Relationships of Phytoplankton Biomass
with Soluble Nutrients, Primary Production, and Chlorophyll a in Lake
Erie, 1970. J. Fish. Res. Bd. Canada, 33(3):601-611. ~~
Rummel, R. J. 1970. Applied Factor Analysis. Northwestern Univ. Press,
Evanston. 617 pp.
Schelske, C. L., L. E. Feldt, M. A. Santiago, and E. F. Stoermer. 1972.
Nutrient Enrichment and its Effect on Phytoplankton Production and
Species Composition in Lake Superior. Proc. 15th Conf. Great Lakes
Res., Internat. Assoc. Great Lakes Res., 149-165.
Schelske, C. L., L. E. Feldt, M. S. Simmons, and E. F. Stoermer. 1974.
Storm Induced Relationships Among Chemical Conditions and Phytoplankton
in Saginaw Bay and Western Lake Huron. Proc. 17th Conf. Great Lakes
Res., Internat. Assoc. Great Lakes Res., 78-91.
87
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Schelske, C. L., M. S. Simmons, and L. E. Feldt. 1975. Phytoplankton
Responses to Phosphorus and Silica Enrichments in Lake Michigan. Verh.
Int. Verein. Limnol., 19:911-921.
Schelske, C. L., and E. F. Stoermer. 1971. Eutrophication, Silica
Depletion, and Predicted Changes in Algal Quality in Lake Michigan.
Science, 173:423-424.
Sneath, P. H. P., and R. R. Sokal. 1973. Numerical Taxonomy: The
Principles and Practices of Numerical Classification. W. H. Freeman,
San Francisco. 359 pp.
Sokal, R. R., and F. J. Rohlf. 1969. Biometry, The Principles and
Practices of Statistics in Biology Research. W. H. Freeman, San
Francisco. 571 pp.
Stoermer, E. F., and R. G. Kreis, Jr. In press. Phytoplankton Composition
and Abundances in Southern Lake Huron. U.S. Environmental Protection
Agency, Duluth, MN. 382 pp.
Van de Geer, J. P. 1971. Introduction to Multivariate Analysis for the
Social Sciences. W. H. Freeman, San Francisco. 293 pp.
88
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SECTION 5
EUCLIDEAN DISTANCES
by T. Dennis Berry
INTRODUCTION
Analysis of large data sets consisting of data from many stations and
variables measured at each station is complicated by the presence of large
spatial and temporal variations that can obscure general trends and make
interpretation difficult. One of the roles of multivariate statistical
techniques is to find unifying principles that help explain the observed
variation.
Some statistical techniques (for example, multivariate analysis of
variance, MANOVA) require a well-balanced database to be applicable. Such
analyses applied to the southern Lake Huron data sat would require a subset
of observations so small that inferences about spatial and temporal variation
would be impossible. The application of such techniques also requires
several assumptions such as randomness, independence, and normality, which
may not be justified in this instance. Because of these limitations, other
methods of analysis were pursued.
It has long been recognized that graphical techniques in data analysis
are a great aid in data interpretation. For example, a contour map of
surface temperature is often easier to interpret than a table of numbers.
However, the southern Lake Huron data set includes eight cruises with
nineteen variables measured at a series of depths on each cruise from which a
total of 152 contour maps could be prepared for surface samples alone. Even
in graphical form, this is a lot of information to assimilate in a short
time. In order to reduce the number of plots, I have integrated all the
variables from each depth by calculating the euclidean distance Ln a
multi-variable space between each station and a reference station. These
distances were then contoured for each cruise at depths of 1 and 5 m,
reducing the total number of plots from a maximum number of 304, if all
variables were plotted individually, to only 16 plots of euclidean distance
contours for these two depths.
METHODS
The method is based on the calculation of the euclidean distance between
a given station and a reference station in multi-dimensional space. To
illustrate the method it is assumed that two variables, temperature and
specific conductance, have been measured and plotted as shown in Figure 5.1.
Arbitrarily choosing point A (with coordinates Xa.Ya) as the reference, the
89
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0)
o
c
cd
•U
o
3
O
u
u
•H
U-l
•H
O
0)
CU
CO
A
E
B
Temperature
Figure 5.1. Example of stations plotted in arbitrary temperature and
specific conductance coordinates.
90
-------
euclidean distance between point A. and any other point (with coordinates X,Y)
can be calculated using the formula
euclidean distance = [(Xa - X)2 + (Ya - Y)2]1/2.
From Figure 5.1 several things are evident. First, the smaller the
euclidean distance, the more closely a given point resembles the reference
for all variables measured. Second, two points such as C and D could have
the same euclidean distance (from A) and be very different from each other.
Points C and F, however, have the same euclidean distance (from A) and are
closely related. The euclidean distance indicates only the degree of
similarity between a given point and the reference, measured in arbitrary
units, and gives little information about the relationship between points
having the same euclidean distance. Therefore, as euclidean distance
increases, the variability among points with the same distance has the
potential to increase; but, points having small euclidean distances are all
closely related to the reference and thus one another. Third, Figure 5.1
demonstrates that the magnitude of the euclidean distance calculated will
depend on the choice of units used on the axis. In the calculations used for
this analysis, each variable was normalized to a mean of zero and a standard
deviation of one so that all variables would be weighted equally in the
analysis.
The choice of a reference station is important because of its effect on
the interpretation of the results. Since the greatest amount of information
is obtained about stations that have a small euclidean distance from the
reference, the reference station should be chosen in the area of prime
interest. For the purposes of this analysis, a reference station (Table 5.1)
characteristic of the open lake was chosen so that stations that were very
different from the open lake would have large euclidean distances.
Euclidean distances were calculated for cruises 2 through 8 at depths of
1 m and 5 m. The stations and reference used varied as a result of missing
data and are shown in Table 5.1. Twelve variables were used in the analysis:
temperature, Secchi transparency, pH, soluble silica, particulate silica,
nitrate, chloride, ammonia, total phosphorus, specific conductance, and
sulfate. The only exception to this was cruise 6 which does not include
nitrate data because of a large number of missing values for this variable.
Calculated euclidean distances were contoured using an interactive
computer contouring program. The program superimposed a rectangular grid of
points over the sampling area and calculated a euclidean distance for each of
these points using a weighted (by distance) average of the six nearest
stations. This grid was then contoured using the algorithm of Cottafava and
LeMoli (1969).
RESULTS
The percentage of the observed variation explained by the contouring
algorithm as shown in Table 5.2 was calculated by squaring the difference
between the observed and predicted values, summing these, and dividing by N
(the number of stations). Many of the contours fit the observed data poorly,
91
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TABLE 5.1. STATIONS AND REFERENCE USED FOR THE 1 M PLOTS1
Station
06
07
09
10
11
13
14
15
16
20
21
23
24
25
26
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
60
63
64
65
66
67
Cruise
2
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
3
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
4
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
5
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
6
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
7
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
8
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
Lx
stations used in analysis
* = reference station
92
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TABLE 5.2. DESCRIPTIVE STATISTICS FOR THE EUCLIDEAN DISTANCES
BY CRUISE AND DEPTH
Cruise Depth
N
Mln.
Max.
Mean
Std. Dev,
2
2
3
3
4
4
5
5
6
6
7
7
3
8
1
5
1
5
1
5
1
5
1
5
1
5
1
5
30
29
40
38
34
36
30
33
43
47
34
36
42
41
42
40
51
31
69
72
53
51
33
33
73
72
61
41
0.345
0.403
0.415
0.476
0.675
0.641
0.642
0.711
0.496
0.651
0.456
0.369
0.377
0.659
3.469
3.289
3.039
3.083
3.481
3.453
2.149
2.530
3.491
3.340
2.437
2.822
2.834
2.772
1.060
1.067
1.202
1.187
1.368
1.361
1.280
1.286
1.201
1.431
1.047
1.168
1.068
1.280
0.637
0.677
0.555
0.548
0.665
0.650
0.321
0.374
0.567
0.543
0.438
0.520
0.504
0.409
Information tabulated is: number of stations included in the analysis,
percentage of variation in the data explained by analyses, and the minimum,
maximum, mean, and standard deviation of the euclidean distances.
93
-------
explaining less than 50 percent of the variation. While these contours imply
a synoptic picture of the lake, it took several days to collect the data.
During this period, the conditions were not static, especially when the
sampling was interrupted by bad weather. A major wind event, for example,
could cause considerable mixing across existing gradients, move surface
waters, and deepen the epilimnion (if the lake were stratified). It is
obvious that any combination of these events would change the multivariate
spatial relationships of the stations, both horizontally and with depth.
This could result in anomalous stations with a concomitant decrease in the
percentage of the variation explained by the contours.
Thermal Bar
The euclidean distance contours for the second cruise (Figure 5.2)
showed a strong relationship to the thermal bar in both the 1 m and 5 m
plots. In general the contours were oriented parallel to shore, but the
gradient was more intense along the Canadian shore than along the U.S. shore.
This implied two things: first, that water along the Canadian shore was in
some respects more different from the open lake than water along the U.S.
shore and second, that some factor other than temperature was causing the
increased intensity of the gradient. This other factor was most likely
nitrate, which had a strong gradient along the Canadian shore (see Sections 3
and 7).
Spring Warming
During this period, the plots were similar with gradients across the
mouth of Saginaw Bay and parallel to the U.S. and Canadian shores (Figures
5.3 and 5.4). The euclidean distance contours tended to follow the depth
contours indicating that differences in water quality were primarily the
result of nearshore effects. Again, the gradients were more intense along
the Canadian shore than along the U.S. shore. This pattern of isopleths
corresponds with those observed for several physical-chemical variables
(see Section 3).
Summer Stratification
The euclidean distance contours during this period showed gradients
across the N-S axis of the lake (Figures 5.5 and 5.6) in contrast to the
predominantly E-W gradients observed earlier in the year. This indicated a
change in the relationship between the southern and northern basins of the
lake. The contours from cruise 5 (Figure 5.5) were difficult to interpret
because of the lack of data in the central portion of the southern basin.
The most interesting features of the summer cruise 6 euclidean distance
contours (Figure 5.6) were the strong gradients along the north shore of
Saginaw Bay and the close relationship (small euclidean distances) of the
stations in the central part of the southern basin and stations near the
south shore of Saginaw Bay.
During summer stratification, water circulation patterns in the
epilimnion were dependent on weather (Sloss and Saylor, 1975). Light NNE
winds prevailed during cruise 5, and the euclidean distance contours
94
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CRUISE tt2 1974 1tt
M
X
Y
Z
X
2.3768
2.1912
2.0056
1.8201
1.6345
1.4489
1.2633
1.0777
0.8922
0.7066
0.5210
CRUISE #2 1974 Sfl
M
X
Y
Z
X
»
4
X
+
A
o
2.3592
2.1871
2.0149
1.8428
1.6707
1.4986
1.3264
1.1543
0.9822
0.8101
0.6379
Figure 5.2. Contours of multivariate euclidean distances from the reference
station. For Cruise 2.
95
-------
CRUISE #3 1974 in
K
Y
Z
X
X
•f
A
2.6516
2.4465
2.2413
2.0362
1.8310
1.6259
1.4207
1.2156
1.0105
0.8053
0.6002
CRUISE #3 1974 5M
K
K
Y
Z
X
*
o
2.5981
2.3989
2.1997
2.0005
1.8013
1.6021
1.4029
1.2036
1.0044
0.8052
0.6060
Figure 5.3. Contours of multivarlate euclidean distances from the reference
station. For Cruise 3.
96
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CRUISE H4 1974 1H
M
X
Y
Z
X
2.9184
2.7040
2.4896
2.2751
2.0607
1.8462
1.6318
1.4173
1.2029
0.9884
0.7740
CRUISE #4 1974 5M
x
Y
Z
X
o
2.9626
2.7305
2.4983
2.2661
2.0340
1.8018
1.5697
1.3375
1.1053
0.8732
0.6410
Figure 5.4. Contours of multivariate euclidean distances from the reference
station. For Cruise 4.
97
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CRUISE #5 1974 in
K
X
Y
z
X
1.9250
1.8069
1.6888
1.5707
1.4526
1.3345
1.2164
1.0983
0.9802
0.8621
0.7440
CRUISE «5 1974 5tt
K
K
Y
Z
X
2.1740
2.0351
1.8962
1.7573
1.6184
1.4795
1.3406
1.2017
1.0628
, 0.9239
0.7850
Figure 5.5. Contours of multivariate euclidean distances from the reference
station. For Cruise 5.
98
-------
CRUISE #6 1974 in
M
M
Y
Z
X
*
•
X
•f
A
0
2.6577
2.4454
2.2331
2.0208
1.8086
1.5963
1.3840
1.1718
0.9595
0.7472
0.5349
CRUISE #6 1974 5M
•
M
Y
Z
X
*
•
X
+
A
0
3.0293
2.8200
2.6106
2.4013
2.1913
1.9826
1.7732
1.5639
1.3545
1.1452
0.9358
Figure 5.6. Contours of multivariate euclidean distances from the reference
station. For Cruise 6.
99
-------
indicated that water similar to open lake water was confined to the SW
portion of the lake. SW winds were predominant before and during the sixth
cruise and the euclidean distance contours for this cruise indicated that
Saginaw Bay water had been transported north and was held along the north
shore of the bay.
Autumnal Cooling
The 1 m plots for this period showed strong gradients along the southern
shore of Saginaw Bay. For cruise 7 (Figure 5.7), this was the only gradient
present over the entire sampling area which implied that the lake was
horizontally mixed at this depth. On cruise 8 (Figure 5.8) gradients were
present across the southern portion of the lake and along the Canadian shore
in addition to the gradient in Saginaw Bay.
CONCLUSIONS
Contours obtained from the analysis of euclidean distances do not give a
water quality value to a given point in the lake, but general patterns of
changes in water quality or water mass movement can be traced with the
contours. The area at the mouth of Saginaw Bay illustrates this point.
During periods of SW winds, bay water was situated along the north shore of
the bay as shown in the plots from cruise 6. During periods of northerly
winds, bay water was found along the southern shore of Saginaw Bay as the
plots from cruise 5 show. In these plots, the general water mass patterns
are evident, but the water quality at any given station at the mouth of
Saginaw Bay is probably not predicted by the contours.
Contours of euclidean distances show water mass distribution as areas of
water quality in relation to differences from open lake water quality.
Information concerning the prevailing winds, combined with the contour maps,
imply water mass movement. The first two cruises produced maps dominated by
the thermal bar conditions. An interesting aspect of contours from these
cruises is the similarity of gradients along the Ontario shore of Lake Huron
and the mouth of Saginaw Bay. Apparently, the high nutrient runoff from
Ontario farms in the spring alters the open lake water quality as much as the
highly eutrophic water leaving Saginaw Bay. The thermal bar keeps the
enriched water near the Canadian shore allowing phytoplankton blooms to
develop. A comparable high nutrient situation did not develop along the U.S.
shore south of Saginaw Bay.
Because current patterns and water movements in Lake Huron were
influenced by winds, a consistent water mass pattern was not observed.
East-west contours as well as north-south contours were present during
stratified conditions. Transport of Saginaw Bay to the open lake was subject
to the prevailing winds, and the resulting widely fluctuating water mass
distributions indicate the problem of determining boundaries for the
segmentation of the lake into regions of similar water quality. Certain
parts of the lake tend to have consistently oligotrophic (open northern
waters) or eutrophic waters (inner Saginaw Bay), but in other areas,
differing wind regimes readily shift epilimnetic waters about, complicating
segmentation of the lake into areas of uniform water quality.
100
-------
CRUISE M7 1974 Itt
M
X
Y
Z
X
2.2318
2.0650
1.8982
1.7315
1.5647
1.3979
1.2311
1.0643
0.8976
0.7308
0.5640
CRUISE tt7 1974 5H
M
X
Y
Z
2.4193
2.2374
2.0555
1.8735
1.6916
1.5097
1.3277
1.1458
0.9639
0.7819
0.6000
Figure 5.7. Contours of multivariate euclidean distances from the reference
station. For Cruise 7.
101
-------
CRUISE #8 1974 in
x
Y
Z
X
2.2415
2.0596
1.8776
1.6957
1.5137
1.3318
1.1498
0.9679
0.7859
0.6040
0.4220
CRUISE #8 1974 5M
x
V
Z
X
A
o
2.3105
2.1543
1.9981
1.8419
1.6857
1.5295
1.3733
1.2171
1.0609
0.9047
0.7485
Figure 5.8. Contours of multivariate euclidean distances from the reference
station. For Cruise 8.
102
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REFERENCES
Cottafava, G., and G. LeMoll. 1969. Automatic Contour Map. Communications
of the ACM, 12:386-391.
Sloss, P. A., and J. H. Saylor. 1975. Measurements of Current Flow During
Summer in Lake Huron. NOAA Technical Report ERL 353-GLERL 5,
U.S. Department of Commerce, 37 pp.
103
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SECTION 6
PHYTOPLANKTON DYNAMICS IN OUTER SAGINAW BAY
by Russell A. Moll
The Laurentian Great Lakes have been closely watched in recent years by
both the U. S. and Canadian governments for changes in water quality.
Emphasis has been placed on monitoring the lakes and using the data collected
in preditive models (Thomann et al., 1976; Bierman and Dolan, 1976).
However, research efforts have been stifled by the lack of data in certain
aspects of limnology, primarily rates of biological processes. There are
relatively few places to study phytoplankton in the Great Lakes where point
sources of pollution move into relatively clear water. In these areas, the
high concentration of nutrients and organisms provide ample material for
study while allowing insight as to how the open lake will react to future
nutrient loadings. Areas of the upper Great Lakes suitable for this type of
study include plumes of rivers in Lake Michigan, the mouths of Green and
Saginaw Bays, and a few single point pollution sources in Lake Superior
(International Joint Commission, 1976).
During 1975, studies were conducted in the mouth of Saginaw Bay, an area
where oligotrophic open lake water mixes with eutrophlc bay water (Sections 2
and 3). Four research cruises were conducted between early May and October.
Water quality regions were identified before and after each cruise so that
experiments could be conducted in eutrophic bay water, oligotrophic lake
water, and as close to the interface of the two as possible. Different water
masses were identified by underway sampling conducted in the mouth of the
bay. Once the zones of water quality were located, a series of biological,
chemical, and physical measurements were repeated in each area.
The sampling area was confined to the proximity of the front between bay
and open lake water which was normally between two lines of stations in the
mouth of the bay (stations 36-40 and 41-45) (Figure 6.1). The water in this
area was deep enough to allow thermocline development throughout most of the
summer. The study was restricted to an area which could be sampled by
underway techniques in 6-8 hrs.
METHODS
Four cruises were conducted in the mouth of Saginaw Bay in 1975: 5-9
May, 28 May to 1 June, 31 July to 5 August, and 14-20 October. These cruises
were designed to sample four different parts of the thermal cycle: early
spring homothermous, early stratified, summer stratified, and fall
homothermous.
104
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Initial sampling of each cruise consisted of underway sampling or
mapping. This sampling required drawing water from the ship's sea chest
(about 1 m below the surface) and running a series of analyses while
underway. The following variables were measured: chloride, silica, nitrate
nitrogen, and ammonia nitrogen (all with an Autoanalyzer II system), in vivo
fluorescence, and temperature. The in vivo fluorescence estimated in vivo
chlorophyll a_ levels and is referred to as chlorophyll throughout thTs
Section. A complete description of the underway mapping techniques can be
found in Section 7. A decision was made in the field as to the location of
bay and lake water from the underway data. The data were later fed into a
computer with navigational information and plots of gradients were made. The
gradient plots were made with the same contouring program as described in
Section 5. The underway sampling program was repeated at the termination of
our cruise to learn the extent of movement of the nutrient front during the
three days of sampling.
Identification of water types in the bay mouth allowed the location of a
sampling station in each water type. Sampling at each station included a
bottle cast followed by a 4-hr incubation for ^C uptake both for
phytoplankton and bacteria. The ^ C uptake for phytoplankton was conducted
in situ following the methods described in Hall and Moll (1975).
Phytoplankton were incubated for 4 hr at the depth from which they were
collected; incubation depths ranged from 1 m to 1% of surface light level.
Uptake of *-^C by phytoplankton was corrected for dissolved loss and dark
uptake. All light bottle incubations were run in duplicate. During rough
weather in October, two sets of incubations were run in an on-deck incubator.
Measurement of bacterial activity followed the technique of Wright and
Robbie (1965) as modified by Herbland and Bois (1974). Bacteria were
incubated for 4 hr using ^C glucose as a substrate in 0.45 x 10"^ to 0.36 x
10~^ g/1 concentrations. The technique of Herbland and Bois (1974) includes
a correction in uptake of substrate for respired loss during incubation.
Incubations were carried out in a dark on-deck incubator cooled with running
lake water. Incubation temperatures were kept as close to collection
temperatures as possible. One heterotrophic uptake series was run per
station which served as an indication of bacterial affinity for glucose.
Bacterial and phytoplankton incubations were made from the same water samples.
^-'
Along with samples collected for incubations, additional sample water
was collected for the measurements of chemical, biological, anql physical
variables. These variables included temperature, pH, conductivity, total
alkalinity, corrected chlorophyll a, chloride, silica, nitrate nitrogen,
ammonia nitrogen, soluble phosphorus, and total P04~P. In addition,
measurements were made at each station for Secchi disc transparency, surface
sunlight intensity, and submarine downwelling light.
RESULTS
Underway Sampling
Results from the underway sampling or mapping yielded data that was used
106
-------
to locate broad fronts of changing water quality, determine the range of each
variable measured in the study area, and locate sampling sites. Comparing
maps from the beginning and end of each cruise provided some insight into the
movement of bay and lake water during the cruise. Results of the underway
sampling did not yield detailed maps of variable distribution or information
about the vertical distribution of variables. Although six variables
(temperature, chlorophyll, nitrate nitrogen, ammonia nitrogen, chloride, and
silica) were measured for each map of the bay mouth, many variables showed
only a small range and could not be used to distinguish between bay and
lake waters.
The primary objective of the underway mapping was the location of the
broad nutrient front in Saginaw Bay. Although this objective was achieved,
the maps may suffer from having short-term applicability. Our results show
that rapid, large-scale movements of water masses in the mouth of Saginaw Bay
require several days. The water quality at the bay station (Station 38) did
not change dramatically between two visits to this station within 48 hr. On
the other hand, repeated visits to one station over a 7-day period did show
large changes in chlorophyll £ distribution and concentration (Figure 6.2).
Early May Cruise
Maps from the first cruise of 6 May produced contours (Figure 6.3)
parallel to the mouth of the bay (NW to SE) indicating a broad front between
open lake water and Saginaw Bay water. Contour lines were evenly spaced,
implying a smooth gradient of variables in the mouth of the bay. Underway
sampling on 8 May showad a small change in the surface distribution of
variables from the 6th of May; Figure 6.4 shows that high silica and chloride
water had moved closer to the southern shore of the bay near Hat Point.
Early May 1975 was a period dominated by thermal bar conditions.
Saginaw Bay water was primarily inside the bar, while the open lake station
was still homothermous. Table 6.1, which gives means and other statistics of
the first cruise, showed May was a period of cold water (4.9°), moderate
chlorophyll a_ levels (1.86 jjg/1), moderate silica levels (0.55 mg S102/1),
high !*C uptake (10.7 ygC/l/h), and assimilation ratio (5.04). Simple
product-moment correlation coefficients were calculated between all variables
(Table 6.2). Although many of the correlations were high (>+0.70), as with
the early cruises in 1974 (Section 3), a basic pattern was evident. The
warmer waters behind the thermal bar were also the more productive waters
(correlation between in situ uptake and temperature was +0.86). Silica was
already low in these warm waters (temperature to silica correlation, -0.75)
and likewise low in areas of high 1^>C uptake (14C to silica, -0.84).
Bacterial activity was highly correlated with bay water (high correlation to
temperature, chloride, and conductivity), but these correlations were based
on a small sample size of four. Although there were additional high
correlations most of these were either routine (as chloride to conductivity)
or based on small sample sizes (n <6).
The early May ^C uptake profiles, obtained by In situ incubations in
the bay, showed a high level of uptake from the surface to the bottom (Figure
6.5). Likewise, chlorophyll ^ biomass was distributed evenly throughout the
107
-------
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108
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TAWAS
POINT
N
CHARITY
ISLAND
10 km
Cl 6 MAY 1975
HAT
POINT
TAWA?
POINT
SI02 6 MAY 1975
TEMP 6 MAY 1975
POINT
Figure 6.3. Contour maps from cruise 1 of 1975 study (6 May).
109
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in
in
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110
-------
TABLE 6.1. DESCRIPTIVE MEASURES CRUISE #1 1975 SOUTHERN LAKE HURON
Variable
Depth
Secchi
Water Temp
PH
Chlorophyll a
Silica ~
Nitrate
Ammonia
Total Phosphorus
Total Soluble
Phosphorus
Conductivity
Alkalinity
Chloride
Primary Production
Assimilation Ratio
"max
Surface Light
Extinction
Coefficient
Underwater Light
N
25
22
25
25
24
25
25
25
25
25
25
18
25
32
15
4
22
22
22
Minimum
1.00
4.50
3.10
8.31
.740
.110
180.7
3.80
3.06
2.02
1.82
19.13
2,46
1.48
1.36
.040
69.5
.110
.040
Maximum
40.00
9.000
7.100
8.600
4.390
1.100
368.2
21.84
21.59
12.09
2.481
23.45
11.35
27.80
14.13
3.961
940.0
.3901
574.0
Mean
8.760
6.872
4.960
8.453
1.865
.5486
280.3
11.68
9.745
4.668
2.273
21.30
6.706
10.70
5.038
1.377
669.2
.2495
125.4
Std. Dev.
2.09
1.62
.085
.948
.313
35.48
4.33
5.02
2.38
.146
1.35
1.98
7.75
3.55
1.76
303.3
.076
170.4
111
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nC.T'C.CHLORo 5 10 15 20 25 30
5-
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\ i \ 6 MAY 1975
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LIGHT 100 200 300 400 500 600
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^ 7 MAY 1975
1 ^ BAY
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LIGHT 100 200 300 400 500 600
HLORa 5 10 15 20 25 30
\ \ . • • • '
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1 . • ' ' \
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/ STA 38 A
/ 7 MAY 1975
' INTERFACE
X
LIGHT 100 200 300 400 500 600
HLOR a 5 10 15 20 25 30
1 '• .-••••"
\ ..•••••'"
(
. .-' STA 47
| .' 8 MAY 1975
• / OPEN LAKE
^
PI ii nr? ^n i \ \
vnUUn fl_ l^J fl/ it
i*C UPTAKt ImgO/m-'hJ
1 IfiHT ^,iFin/m2/«V
UlwrF L V^JC.tn / m /9f ' '
r'r.
Figure 6.5. Results of the early May
113
uptake profiles
-------
water column, and the assimilation ratios were high (from 3 to 14). The
samples from the interface zone showed a similar amount of biomass but lower
l4C uptake than bay water (Figure 6.5) even though nutrients in this area
were at higher concentrations than bay water. Bacterial activity was
moderately high at both the interface and bay stations (Table 6.3). The open
lake incubations revealed a small, but productive phytoplankton crop with a
uniform depth distribution (Figure 6.5). Bacterial activity was low in early
May at the open lake location (Table 6.3).
Late May Cruise
The underway sampling conducted on the first day of the second cruise,
29 May, showed a tongue of open lake water extending into Saginaw Bay toward
Charity Island (Figure 6.6). Saginaw Bay water was confined primarily to the
nearshore areas of the outer bay. Winds were light during the second cruise,
and one result of the low wind velocities was very little change in the
surface water distribution between the maps of 29 May and 1 June (Figures 6.6
and 6.7).
The transition between thermal bar conditions and stratified conditions
was made between the early and late May cruises. Water temperatures warmed
considerably from early to late May (increased to 11.7°), chlorophyll a_
biomass increased to 2.76 yg/1, but *-*C uptake, the assimilation ratio, and
silica all decreased to 9.36 ygC/l/hr, 2.81, and .55 mg/1 respectively.
Table 6.4 shows that all nutrient concentrations were lower in late May than
earlier in the month, except ammonia which increased.
The correlations among variables for the late May cruise also reflected
the reduction of nutrient levels, a consequence of phytoplankton growth and
vertical thermal stratification. Large negative correlations were found
between nitrogen (as nitrate and ammonia), silica, and ^C uptake (Table
6.5); these correlations should not be taken to imply cause and effect in
terms of nutrient limitation, but that silica, nitrata, and ammonia were
found at low levels when ^C uptake was high. High positive correlations
were found between l^C uptake and phosphorus as total phosphorus and total
soluble phosphorus.
Chlorophyll a biomass increased between the first two cruises in early
and late May, yet~~^C uptake was lower in bay water yielding a lower
assimilation ratio (Figure 6.8). Bacterial activity was also (lower in late
May than early May (Table 6.3). Chlorophyll a_ concentrations increased at
the open lake station as did *-*C uptake; the assimilation ratio did not
change for the open lake station between the two cruises. The biomass and
l^C uptake values were slightly lower for the interface station in late May.
Bacterial activity was very high at the interface station.
August Cruise
The August maps showed an irregular surface distribution of all
variables in outer Saginaw Bay (Figures 6.9 and 6.10). Bay water, identified
by high chloride content, was found on both sides of a wide tongue of lake
water in the center of the outer bay. During the August cruise gentle SW
114
-------
I TABLE 6.3 AVERAGE VALUES OBSERVED DURING 1975
Incubation Series
Location
Cruise
Variable
Bay
Bay
Interface
Lake
May
May
May
May
Late May
Late May
Late May
Late May
Aug.
Aug.
Aug.
Aug .
Oct.
Oct.
Oct.
Oct.
chlorophyll a
14C uptake
Assim. ratio
^max
chlorophyll a
14C uptake ~
Assitn. ratio
^max
chlorophyll a
1^C uptake
Assim. ratio
"max
chlorophyll a
14C uptake ~~
Assim. ratio
^max
3.02
17 . 34
5.74
0.89
3.62
12.61
3.48
1.12
3.13
5.98
1.91
0.12
4.82
9.19
1.91
0.18
2.07
16.33
7.89
3.96
3.56
9.54
2.68
0.13
7.99
31.46
3.94
0.30
8.77
37.16*
4.24
3.80
2.46
6.73
2.74
0.58
2.00
4.99
2.50
2.93
6.28
6.11
0.97
n.a.
8.25
9.94
1.20
0.47
0.86
1.86
2.16
0.04
1.32
2.91
2.20
0.15
10.98
3.57
0.33
0.05
1.74
8.48*
4.87
0.03
Incubations done in on-deck artificial light incubator
Sample sizes: chlorophyll a
ratio found by dividing *-^
uptake = 8, V
max
1, Assitn.
uptake by chlorophyll a.
115
-------
5.5
Cl 29 MAY 1975
TAWSS
POINT
N
CHARITY
ISLAND
1.13
10 km
Si02 29 MAY 1975
HAT
POINT
X----7
TAWAS
POINT
N
CHARITY
ISLAND
10 km
TEMP 29 MAY 1975
POINT
Figure 6.6. Contour maps from cruise 2 of 1975 study (29 May)
116
-------
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117
-------
TABLE 6.4. DESCRIPTIVE MEASURES CRUISE #2 1975 SOUTHERN LAKE HURON
Variable
Depth
Secchi
Water Temp
pH
Chlorophyll a
Silica ~~
Nitrate
Ammonia
Total Phosphorus
Total Soluble
Phosphorus
Conductivity
Alkalinity
Chloride
Primary Production
Assimilation Ratio
vmax
Surface Light
Extinction
Coefficient
Underwater Light
N
40
25
40
40
40
40
40
29
40
40
40
32
39
32
16
4
19
19
19
Minimum
1.00
3.50
4.40
8.37
.530
.020
200.
.700
3.38
1.63
2.00
19.8
5.43
1.16
.650
.130
340.
.110
4.10
Maximum
24.00
13.00
18.40
8.770
7.100
1.500
293.5
47.17
28.24
10.47
2.450
22.31
8.910
20.09
5.020
2.930
1840.
.4800
1050.
Mean
6.125
7.860
11.74
8.644
2.759
.4495
261.2
18.36
8.101
2.651
2.310
21.33
7.257
7.51
2.811
1.082
1345.
.2768
282.9
Std. Dev.
5.814
3.996
5.109
.1192
1.631
.3841
15.32
13.72
4.696
1.395
.1055
.7978
.9761
5.69
1.431
1.315
341.0
.1003
292.7
118
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LIGHT 100
i«C, T°C,CHLORo 5
200
10
300
15
400
20
5-
10-
500
25
600
30
STA 40
29 MAY 1975
BAY
LIGHT 100 200
nC,T°C,CHLORo 5 10
300
15
400
20
5.
£
a
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25
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840
STA 38A
30 MAY 1975
INTERFACE
'4C,T°C,
LIGHT 100
CHLORo 5
\
200
10
^
300
15
1
400
20
]
500
25
600
30
£L 5
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a
10-
STA 40
31 MAY 1975
BAY
LIGHT 100 200
i«C,T°C, CHLORo 5 10
5-
a-0-
UJ
a
15-
300
15
400
20
500
25
600
30
.55--1050
Figure 6.8. Results of the late May
120
STA 47
31 MAY 1975
OPEN LAKE
CHLOR a (jj g/l)
'«C UPTAKE (mgC/ms/h)
LIGHT OiEin/m2/s)-
T«c_
uptake profiles
-------
TAWAS
POINT
CHARITY
ISLAND
I Okm
Cl I AUG. 1975
HAT
POINT
0.2
TAWAS
POINT
/ _-- 7 2IO/2)S
21.0.
23-5
CHARITY
ISLAND
23.5
23.5
24.0
10km
TEMP. I AUG. 1975
24.O
HAT
POINT
Figure 6.9. Contour maps from cruise 3 of 1975 study (1 August).
121
-------
7°
Cl 4 AUG. 1975
TAWfe
POINT
N
CHARITY
ISLAND
10 km
SI02 4 AUG 1975
HAT
POINT
TAWAS"'
POINT
N
CHARITY
ISLAND
10 km
TEMP 4 AUG 1975
HAT
POINT
Figure 6.10. Contour maps from cruise 3 of 1975 study (4 August).
122
-------
winds apparently had sufficient energy to move warm bay water farther into
the open lake. The differences between the 1 August and 4 August maps
suggest eutrophic bay water moved farther out of the bay on 1 August.
Considerable warming of surface water occurred between late May and
August of 1975. The mean temperature increased to 16°C, while the average
chlorophyll a value was also high at 6.5 g/1 (Table 6.6). Although
chlorophyll a biomass was large in August, much of this chlorophyll was found
10 m and deeper and ^C uptake did not increase comparably (an average of
12.2 yg C/l/hr), yielding a low assimilation ratio (1.8). Dissolved silica
levels continued to fall to where surface values were near analytical zero.
Similar to 1974, in 1975 the August cruise showed a lowering of nearly all
correlations among variables (Table 6.7). Correlations among nutrients,
uptake, and chlorophyll a were lower except for a -0.87 correlation between
l^C uptake and nitrate. The predominant feature of the August 1975 cruise
was high chlorophyll a biomass below 10 m at the open lake station. This
deep, chlorophyll-rich layer occupied a niche not observed during the prior
two cruises, which altered some of the correlations between plankton-related
variables.
The early August cruise, a period of maximum annual temperatures and
fully stratified conditions, was characterized by high chlorophyll a_ biomass
(Table 6.3). Uptake of ^C by phytoplankton which in the bay was high near
the surface, but relatively low below the surface yielded a smaller average
assimilation ratio in August than May or June. Figure 6.11 shows the highest
concentrations of chlorophyll a_ near the bottom, but the highest levels of
l^C uptake near the surface. The interface station also displayed high
chlorophyll a values as did the bay, but *-^C uptake levels were very low; the
average assimilation ratio was close to 1.0 at the interface station (Table
6.3). The open lake station was apparently composed of water from open Lake
Huron at the surface, and from Saginaw Bay below 5 m (Figure 6.11).
Unusually high chlorophyll a^ and chloride levels at 10 m suggest the presence
of bay water at 10 m. The average assimilation ratio was low in open lake
water, but this may have been caused by an early morning incubation with an
overcast sky providing little light at 10 m. Bacterial activity at all
stations in August was fairly low.
October Cruise
The last cruise of 1975 (mid-October) was conducted during strong winds
that shifted 180° between the two sampling dates — from SW to NE. Despite
the wind shift, the sets of maps from the beginning and end of the cruise
were similar, showing a movement of water around the "thumb" of Michigan
(Figures 6.12 and 6.13). The ranges of the three variables sampled were
similar on both sampling dates; this result implied the October winds were
creating a more homogeneous water column by mixing action, but did not cause
any major shift in the distribution of water masses.
The October cruise occurred when shallow waters were homothermous, and a
thermocline existed offshore at 30 m. The strong winds of early and
mid-October had mixed the shallow part of the lake well, but only a moderate
amount of cooling had occurred in that the average temperature was 12° C
123
-------
TABLE 6.6. DESCRIPTIVE MEASURES CRUISE #3 1975 SOUTHERN LAKE HURON
Variable
Depth
Secchi
Water Temp
PH
Chlorophyll a
Silica
Nitrate
Ammonia
Total Phosphorus
Total Soluble
Phosphorus
Conductivity
Alkalinity
Chloride
Primary Production
Assimilation Ratio
"max
Surface Light
Extinction
Coefficient
Underwater Light
N
45
33
43
43
45
45
45
41
44
45
43
29
43
30
15
3
22
2-2
22
Minimum
1.00
3.00
4.10
8.04
2.31
.030
43.1
6.520
3.66
1.77
2.01
19.3
2.83
.560
.060
.050
150.
.170
.100
Maximum
30.00
14.50
25.00
S.850
15.78
1.320
288.8
41.39
24.56
31.47
2.400
26.14
11.97
86.47
7.960
.3000
1650.
.3700
1232.
Mean
7.644
5.851
16.05
8.584
6.539
.2622
175.9^
17.25
9.962
5.865
2.138
20.91
6.284
12.16
1.806
.1565
910.4
.2750
185.1
Std. Dev.
6.146
2.883
6.287
.1481
3.383
.2507
56.69
9.371
4.657
5.002
.088
1.245
1.976
19.79
2.164
.1289
631.1
.0677
289.7
124
-------
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2 AUGUST 1975
INTERFACE
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3 AUGUST 1975
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LIGHT 100
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4 AUGUST 1975
BAY
CHLOR8
i^vn y \jt v i / —
: UPTAKE (mgC/m'/h)
LIGHT OiEin/m2/s)
T«C —
Figure 6.11. Results of the early August *^C uptake profiles.
126
-------
TAW AS
POINT
\
N
\
CHARITY
ISLAND
6.5 /
10km
Cl 15 OCT. 1975
HAT
POINT
Figure 6.12. Contour map from cruise 4 of 1975 study (15 October).
127
-------
6.0
TAWAS
POINT
\
N
CHARITY
ISLAND
5-5
10km
Cl 17 OCT. 1975
HAT
POINT
Figure 6.13. Contour map from cruise 4 of 1975 study (17 October).
128
-------
(Table 6.8). Mixing of the water column had apparently brought sufficient
nutrients and plankton to the surface to stimulate some algal growth.
Average nutrient concentrations were lower in October than August implying
continued phytoplankton growth and nutrient utilization (Table 6.8). The
correlations from the October data set were similar to the August data in
that they were generally lower than the first two cruises (Table 6.9). In
October, all correlations among l^C uptake and nutrients were lower than in
May, June, or August.
Chlorophyll a_ biomass was higher in October than August at all but the
open lake station (Fig. 6.14). There was a comparable increase in ^C uptake
at these stations that increased the assimilation ratio from August (Table
6.3). However, rough seas prevented anchoring the ship for two incubation
series, thus 1*C uptakes were made in an artificial-light incubator onboard
the ship; assimilation ratios from the on-deck incubations are not comparable
to in situ results. The artificial light source approximated 4-5 m in bay
water and 10-12 m in lake water.
Differences Among Water Quality Regions
In addition to the cruise-by-cruise analysis of the chemical, physical,
and biological data, analyses were carried out on the basis of water quality:
bay water, interface water, and open lake water. The analyses did not reveal
any unusual aspects of Lake Huron limnology but did confirm some preconceived
ideas of Saginaw Bay and Lake Huron. Tables 6.10-6.12 give descriptive
measures of the three types of water. Table 6.13 compares the means of some
of the variables measured in the three water types by way of t-tests. These
t-tests show the large differences between lake and bay waters and somewhat
more subtle differences among the lake to interface and bay to interface
comparisons.
Simple means show Saginaw Bay water had the warmest temperatures
(13.3°C), the highest chlorophyll a_ biomass (4.7 yg/l), the highest
uptake (17 ygC/l/hr), the highest assimilation ratio (4.1), and the lowest
silica (.223 mg/1) and nitrate levels (212 yg/l). The lower nutrient levels
were surprising in that bay water is usually characterized by high nutrient
loads (Bierman and Dolan, 1976). But, the area we studied was the outer bay
mouth where inputs of nutrients were low and phytoplankton growth was high.
The interface stations were representative as interface water; these
stations had values of temperature, chlorophyll a, and nutrients in between
the bay stations and open lake stations (Table 6.11). However, for two
variables the interface water was not intermediate in value to the bay and
lake stations: low l*C uptake was found at these stations, producing the
lowest assimilation ratio. Table 6.13 shows the l^C uptake levels were
significantly different between bay and interface waters, while chlorophyll a
levels were not different. Additionally, the bacterial crop at the interface
was very active, almost as active as the bay bacterial crop. We speculate a
posteriori that the interface area was a zone which often received senescent
phytoplankton crops washing out from the bay.
The open lake data appeared representative of the oligotrophic water
129
-------
TABLE 6.8. DESCRIPTIVE MEASURES CRUISE #4 1975 SOUTHERN LAKE HURON
Variable
Depth
Secchl
Water Temp
PH
Chlorophyll a
Silica ~
Nitrate
Ammonia
Total Phosphorus
Total Soluble
Phosphorus
Conductivity
Alkalinity
Chloride
Primary Production
Assimilation Ratio
Vmnv
N
16
16
16
16
16
16
16
16
16
15
16
16
16
32
16
4
Minimum
1.0000
2.00
12.3
8.29
1.49
.030
80.0
4.45
4.41
1.53
2.05
19.3
5.14
1.01
.132
.033
Maximum
30.00
6.000
13.80
8.760
11.28
.2900
203.2
24.62
37.91
16.57
2.490
22.65
10.70
39.51
7.341
3.803
Mean
7.644
3.525
12.67
8.405
5.893
.0969
135.5
15.06
16.58
4.136
2.275
20.92
7.620
16.19
3.216
1.121
Std. Dev.
6.146
1.522
.6708
.1085
3.218
.074
45.10
5.382
10.33
3.890
.1478
.9396
1.836
14.17
2.136
1.797
130
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Figure 6.14.
Results of the October
132
uptake profile's.
-------
TABLE 6.10. DESCRIPTIVE MEASURES BAY STATIONS 1975 SOUTHERN LAKE HURON
Variable
Depth
Secchi
Water Temp
PH
Chlorophyll a
Silica ~
Nitrate
Ammonia
Total Phosphorus
Total Soluble
Phosphorus
Conductivity
Alkalinity
Chloride
Primary Production
Assimilation Ratio
"max
Surface Light
Extinction
Coefficient
Underwater Light
N
78
48
78
73
78
78
78
69
78
73
78
58
77
66
33
09
29
29
29
Minimum
1.00
2.00
5.80
8.29
1.29
.020
43.1
.700
3.66
1.63
2.01
19.3
2.83
1.87
.390
.120
430.
.170
3.10
Maximum
15.00
8.500
25.80
8.850
14.22
.6900
334.2
47.17
28.24
26.10
2.480
23.45
11.97
36.47
14.13
3.960
1840.
.4800
1232.
Mean
5.359
4.431
13.29
3.602
4.722
.2234
209.0
15.95
10.43
4.274
2.259
21.40
7.118
17.15
4.090
1.492
1135.
.3051
239.2
Std. Dev.
4.123
1.580
5.744
.1407
2.856
.1639
71.23
9.921
4.924
3.670
.1414
.9119
1.762
15.33
2.995
1.615
424.3
.073
296.2
133
-------
TABLE 6.11. DESCRIPTIVE MEASURES INTERFACE STATIONS 1975 SOUTHERN LAKE HURON
Variable
Depth
Secchi
Water Temp
pH
Chlorophyll a
Silica
Nitrate
Ammonia
Total Phosphorus
Total Soluble
Phosphorus
Conductivity
Alkalinity
Chloride
Primary Production
Assimilation Ratio
^tnax
Surface Light
Extinction
Coefficient
Underwater Light
N
21
21
21
21
20
21
21
18
20
20
21
19
19
30
14
3
11
11
11
Minimum
1.00
3.00
4.60
8.37
.530
.090
123.
.880
3.49
1.63
2.00
19.1
4.16
1.01
.130
.470
310.
.130
.800
Maximum
20.00
11.00
23.10
8.780
8.660
1.500
293.5
30.69
37.91
18.74
2.490
22.48
10.70
30.58
4.140
2.930
1840.
.3900
840.0
Mean
7.428
5.790
12.19
8.502
4.468
.4881
212.1
14.56
13.54
4.686
2.253
20.78
7.127
7.12
1.863
1.326
1019.
.2809
176.3
Std. Dev.
6.112
2.699
6.022
.1193
2.916
.3775
63.38
7.563
10.49
4.086
.1249
.7773
1.770
7.20
1.355
1.389
673.6
.076
254.9
134
-------
TABLE 6.12. DESCRIPTIVE MEASURES OPEN LAKE STATIONS 1975 SOUTHERN LAKE HURON
Variable
Depth
Secchi
Water Temp
pH
Chlorophyll a
Silica
Nitrate
Ammonia
Total Phosphorus
Total Soluble
Phosphorus
Conductivity
Alkalinity
Chloride
Primary Production
Assimilation Ratio
vmax
Surface Light
Extinction
Coefficient
Underwater Light
N
28
28
26
26
28
28
28
25
28
28
26
19
28
32
16
4
24
24
24
Minimum
1 . 0000
6.0000
3.1000
8.0400
.74000
.030
167.30
3.8000
3.0600
1.5300
1.8200
19.380
2.4600
.56000
.060
.030
69.500
.11000
.040
Maximum
40.000
14.500
22.200
8.7600
15.780
1.3200
368.20
41.390
16.160
31.470
2.3100
26.140
8.5100
9.0200
5.6200
.15000
1470.0
.32000
1050.0
Mean
10.750
9.6964
8.0885
8.4538
3.1743
.63321
251.55
16.437
6.8668
4.4129
2.1650
20.662
5.9529
4.20
2.5437
.0675
750.77
.21458
173.80
Std. Dev.
10.377
2.7633
6.0971
.14037
4.0784
.42581
48.536
10.997
3.6260
5.7032
.10289
1.5359
1.4140
3.03
1.8979
.056
524.87
.063
247.58
135
-------
TABLE 6.13. COMPARISONS OF MEANS FROM BAY,
INTERFACE AND OPEN LAKE WATER BY T-TESTS.
MEANS USED IN COMPARISONS ARE FROM ALL CRUISES.
CHLOROPHYLL A DATA WERE SUBJECT TO A NATURAL LOG TRANSFORMATION
TO CORRECT EXCESSIVE SKEW AND KURTOSIS
T-statistic
Variable
Temperature
Extinction Coefficient
Chloride
PH
Silica
Nitrate
Total Phosphorus
Chlorophyll a
l^C uptake
vmax (glucose)
Bay vs.
Interface
0.707 n.s.
1.212 a.s.
0.238 n.s.
2.787**
2.754**
0.047 n.s.
1.189 n.s.
1.086 n.s.
3.611*
0.163 n.s.
Lake vs.
Interface
2.372*
3.016**
3.154*
0.418 n.s.
0.718 n.s.
1.939 n.s.
3.113**
4.228*
1. 164 n.s.
1.547 n.s.
Bay vs.
Lake
3.933***
6.543***
4.951***
3.307***
3.880***
2.599***
5.805***
8.407***
4.319***
2.583*
Significance probability levels: n.s.
* = 9.5, ** = 0.01, and *** = 0.001.
non-significant,
136
-------
found in most of Lake Huron: cold, low in chlorophyll a^ and high in
nutrients (Table 6.12). High ^C uptake was occasionally found producing
moderate assimilation ratios. Bacterial activity was extremely low in the
open lake perhaps due to the low temperatures and/or the low level of biomass
to serve as a substrate.
DISCUSSION
Saginaw Bay appears to behave much like a reactor with an input of
nutrients (at the southern end), dilution, and development of large plankton
crops. Water, which moved toward the open lake, apparently stimulates
phytoplankton blooms, with these blooms rapidly diminishing in the outer
bay. Bay stations, taken near the outer edge of bay water, were readily
identifiable because of high concentrations of conservative tracers as
temperature, chloride, sulfate, and conductivity. But, the biological
reactor (the bay) reduced some of the nutrient levels and increased
chlorophyll a biomass by the time water reached the outer bay. These events
were reflected in the differences between the bay and open lake stations; the
bay water had higher chlorophyll £, ^C uptake, assimilation ratios,
temperature, chloride and pH, but lower nitrate, ammonia, total soluble
phosphorus, silica, and Secchi values than open lake stations (Tables 6.10
and 6.12). Some of the difference between bay and open lake stations may
have been because of the presence of hypolimnetic samples in the lake
stations, but the majority of open lake samples were epilimnetic.
The interface station yielded concentrations of dissolved nutrients
which generally fell between the open lake and bay values, but high
phytoplankton biomass with the low ^4C uptake produced the lowest
assimilation ratio of the three areas studied. These data implied that
plankton in the interface were not actively growing, but, continuing with the
reactor analogy, were in a washout phase. The concept of a washout crop was
further supported by high levels of glucose assimilation by bacteria.
Inactive phytoplankton are known as a suitable and abundant substrate for
bacterial attachment and growth (Paerl et al., 1975). Assuming the interface
between Saginaw Bay and Lake Huron represented a zone of phytoplankton
washout, the question arose as to what extent did bay water influence the
southern end of Lake Huron. This study did not provide enough data to answer
that question, but taken with the 1974 data did allow some speculation. The
high amount of suspended material from the bay does, on occasion, move beyond
the bay around the thumb of Michigan's southern peninsula as was observed at
the lake station during the August cruise. But, wind from the north and east
will hold water in the bay allowing the suspended material to settle out and
phytoplankton to be heavily grazed. The dissolved material, on the other
hand, must eventually leave the bay and mix into the southern end of the
lake. The change in Lake Huron water quality due to the influence of Saginaw
Bay cannot be evaluated in simple terms, but depends on the variable in
question, e.g. whether soluble or particulate in form.
Influence of Seasonal Sampling
Although the effect of seasonal changes was not analyzed statistically,
137
-------
seasonal differences were evident at all sampling locations, with the open
lake stations showing the largest changes (Table 6.3). The coefficient of
variation for the bay station chlorophyll a mean was 60 percent, while the
coefficient of variation for the lake station mean was more than 129 percent.
The conclusion was that the bay represents a more biologically active but
consistent environment. The 1974 data show that much of the variability in
the bay was the result of patchiness rather than seasonality. However, the
1975 sampling effort may have been biased because the onset of thermal
stratification had occurred in the bay just before the first cruise, while
the same event in the open lake was well bracketed by the four cruises. In
addition, the open lake station suffered an intrusion of bay water during the
August cruise which increased the variance of that station.
Vertical Distributions of Phytoplankton-Related Variables
The vertical distribution of *C uptake was, in part, a function of
chlorophyll a biomass and submarine light. Submarine light attenuation was
primarily a function of location; the average extinction coefficient ranged
from 0.21 for the open lake stations, 0.28 for the interface stations, and
0.30 for the bay stations. Thus, we considered the depth distribution of
chlorophyll ji as the more important plankton-related variable.
The trend in the depth distribution of chlorophyll a_ was similar to the
influence of seasonality; the bay station had the most consistent
chlorophyll ^a profile from cruise to cruise, while the open lake station
changed more. All the stations sampled in the first two cruises showed
homogeneous chlorophyll a_ profiles (Figures 6.5 and 6.8). The open lake
station was either homothermous or recently stratified during these early
cruises, thus a homogeneous profile was the expected result. The bay station
provided a uniform chlorophyll a_ profile on almost every occasion. By August
maximum chlorophyll a_ concentrations were found below 5 m at the open lake
station (Figure 6.11). In October this deep layer had disappeared with the
deepening of the thermocline and mixing by strong winds. The interface
station produced chlorophyll ji profiles which were intermediate to the open
lake and bay stations. The shape of these profiles could have been due to
aging plankton populations settling out of the water column as bay water
moved out into the open lake. The sampling frequency in terms of numbers of
cruises in 1975 was -too low to draw many more conclusions than these:
chlorophyll a was generally evenly distributed with depth in bay water, a
definite seasonal depth distribution of chlorophyll a_ was found at the open
lake station, and the chlorophyll a-depth distribution was uneven at the
interface stations.
138
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REFERENCES
Bierman, V. J. Jr. and D. M. Dolan. 1976. Mathematical Modeling of Phyto-
plankton Dynamics in Saginaw Bay, Lake Huron. Proc. Conf. Environmental
Modeling and Simulation. EPA-600/9-76-016, U.S. Environmental Protection
Agency, Cincinnati, OH. pp. 773-779.
Hall, C. A. S. and R. A. Moll. 1975. Methods of Assessing Aquatic Primary
Productivity, pp. 19-53. Iii H. Leith and R. Whittaker (eds), Primary
Productivity of the Biosphere. Springer-Verlag, New York.
Herbland, A. M. and J. F. Bois. 1974. Assimilation et Mineralisation de la
Matiere Organique Dissoute dans la Mer: Me"thode par Comptage en
Scintillation Liquide. Mar. Biol., 24:203-212.
International Joint Commission. 1976. The Waters of Lake Huron and Lake
Superior. Volume I. Summary and Recommendations. Report to the
Internat. Joint Comm. Upper Lakes Ref. Group, Windsor, Ont. 236 pp.
Paerl, H. W., R. D. Thomson and C. R. Goldman. 1975. The Ecological Signifi-
cance of Detritus Formation during a Diatom Bloom in Lake Tahoe,
California-Nevada. Verh. Internat. Verein. Limnol., 19:326-334.
Thomann, R. V., R. P. Winfield, D. M. DiToro and D. J. O'Connor. 1976. Mathe-
matical Modeling of Phytoplankton in Lake Ontario. Part 2. Simulations
Using Lake 1 Model. EPA-600/3-76-065, U.S. Environmental Protection
Agency, Duluth, MN. 87 pp.
Wright, R. T. and J. E. Hobbie. 1965. Use of Glucose and Acetate by Bacteria
and Algae in Aquatic Ecosystems. Ecol., 47:447-464.
139
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SECTION 7
INFLUENCES OF SPRING NEARSHORE THERMAL BAR
by Curtiss 0. Davis, Claire L. Schelske and Russell G. Kreis, Jr.
In 1974, the Great Lakes Research Division conducted eight surveys of
nutrient chemistry and phytoplankton in the southern half of Lake Huron as
part of the Upper Lakes Reference Study for the International Joint
Commission (IJC). During the first two cruises (28 April-3 May and
14-17 May), high nitrate and total phosphorus levels were observed along the
Ontario shore between Point Clark and Kettle Point. The highest values,
nitrate, 1330 yg N/l and total phosphorus, 16.7 yg P/l, were about three
times the open lake values at that time. These levels decreased with time,
and by the fourth cruise, June 22-25, nutrient levels in the Point Clark to
Kettle Point region ware similar to other nearshore areas (Section 3).
In the same year, the Ontario Ministry of the Environment surveyed the
Ontario nearshore regions of Laka Huron and found the Point Clark to Kettle
Point region to have the highest total phosphorus and total nitrogen levels
of any nearshore area studied, particularly during the spring (International
Joint Commission, 1977). They found average values of 29 yg P/l for total
phosphorus and 902 yg N/l for total nitrogen during spring, about twice the
levels observed along the adjacent shorelines.
Physical and chemical characteristics of the Maitland, Bayfield, and
Ausable rivers, which empty into Lake Huron between Point Clark and Kettle
Point were investigated by the Ontario Ministry of the Environment (1978).
These rivers drain 2460, 466, and 865 sq km, respectively, of primarily
agricultural lands. During the first four months of 1975, the Maitland,
Bayfield, and Ausable (via the diversion cut at Port Franks) rivers carried
24.5, 27.7, and 32.3 metric tons of phosphorus and 2160, 973, and 1500 metric
tons of nitrate-nitrogen, respectively, into Lake Huron. Conceivably, If
most of these nutrients were retained in the nearshore zone between Point
Clark and Kettle Point, the river input could account for much of the high
spring nutrient levels observed in that region.
As is typical of large lakes in the temperate zone, the Laurentian Great
Lakes develop a thermal bar in the spring and fall (Rodgers, 1965, 1966;
Huang, 1972). Both Rodgers and Huang note that the spring thermal bar
strongly inhibits exchange between the warm water nearshore and the cold
central lake water mass. Materials entering the lake from rivers or other
discharges are confined to the nearshore zone by the thermal bar. Similarly,
the spring phytoplankton bloom has been observed to initially develop in
nearshore waters and then remain on the nearshore side of the thermal bar
(Nalewajko, 1967; Stoermer, 1968).
140
-------
In 1975, a four-day cruise was conducted from 29 April-2 May to study a
segment of the Ontario nearshore region where high nutrients had been
observed the previous year and a comparable section of the Michigan nearshore
near Harbor Beach where no high nutrient levels had been observed
(Section 3). The objective was to determine how far the elevated nutrient
levels extend into the lake and to examine the role of the thermal bar in
confining phytoplankton and nutrients to the nearshore zone. Some of the
1974 southern Lake Huron survey data are also presented to amplify the
results from the 1975 cruise.
MATERIALS AND METHODS
The 1974 southern Lake Huron surveys and the 1975 nearshore cruise were
conducted on the R/V ROGER R. SIMONS operated by the U.S. Environmental
Protection Agency. Temperature profiles were made using a mechanical
bathythermograph. Discrete water samples were taken with Niskin bottles and
analyzed for pH, specific conductance, and chlorophyll a (extracted in 90%
acetone) by fluorometric analysis (Strickland and Parsons, 1968). Carbon-14
uptake was measured following Schelske and Callender (1970) except that an
artificial light (cool, white fluorescent) incubator was used with a light
intensity of 118 yE/m^/sec. The incubator was cooled with lake water pumped
from a depth of 1 m. Nutrient concentrations were measured using a Technicon
Autoanalyzer system II for nitrate plus nitrite, silica (Armstrong et al.,
1967), ammonia (Slawyk and Maclsaac, 1972), and orthophosphate (Murphy and
Rlley, 1962) and an Autoanalyzer I system for total phosphorus (Menzel and
Corwin, 1965). Chloride was also analyzed using the Autoanalyzer II system
(Technicon, 1972). Phytoplankton cell counts were made according to Stoermer
et al. (1971) except that only two radii were counted instead of six.
During the 1975 nearshore survey, underway "maps" (Kelley, 1976) of
temperature, chlorophyll fluorescence, chloride, nitrate, and silica were
made of the nearshore zones near Bayfield, Ontario, and Harbor Beach,
Michigan. Water from 1 m depth was sampled continuously as the ship steamed
a zig-zag course through the area to be studied. Water was pumped into the
laboratory, passing first through a debubbler containing a thermistor to
measure temperature, then through a Turner model 111 fluororaeter equipped
with a flow-through door to measure in vivo chlorophyll fluorescence
(Strickland and Parsons, 1968). On the outlet side of the fluororaeter, the
water hose was tapped with a small tube that carried the water to the
Autoanalyzer II system. The water was passed through an inline HA Millipore
filter and was analyzed for nitrate plus nitrite, silica, chloride, and in
some cases, orthophosphate and ammonia. All data were recorded continuously
on chart recorders, and values were read at frequent time intervals (3-6
min). Maps were produced by superimposing time series of values for each
parameter on the cruise track and contouring in appropriate units between the
points. The Bayfield nearshore maps were hand contoured, while the Harbor
Beach maps were contoured by computer using a geographical mapping program
(Cottafava and LeMoli, 1969; as modified by W. Tobler, Univ. of Michigan).
141
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RESULTS
1974 Southern Lake Huron Survey Results
The station locations for the 1974 southern Lake Huron survey cruises
are given in Figure 7.1. A comparison of nutrients, chlorophyll £, and l^C
productivity for inshore and offshore stations on the U.S. and Canadian
shores for the first two cruises (Table 7.1) shows high nitrate and total
phosphorus along the Canadian shore. The high nutrient levels in the
nearshore water appear to have induced large phytoplankton standing crops as
evidenced by very high chlorophyll a_ and 1*C assimilation values. The
phytoplankton assemblage was dominated by diatoms that comprised up to 99
percent of the total assemblage (Tables 7.2, 7.3).
Phytoplankton standing crops and species composition were substantially
different in the Ontario nearshore zone as compared with the offshore areas
and the Michigan nearshore zone (Tables 7.2, 7.3). Diatom populations
characteristic of the offshore spring plankton were Tabellaria fenestrata,
Synedra filiformis, Fragilaria crotonensis, Asterionella formosa^
Rhizosolenia gracilis, Cyclotella stelligera, Melosira islandica, Fragilaria
intermedia var. fallax, and Stephanodiscus transilvanicus. These species
predominated or were common at all of the offshore stations as well as the
nearshore zone on the U.S. shoreline. By comparison, the phytoplankton
assemblage during cruise 1 at station 57 on the Canadian shore was dominated
by three species of Stephanodiscus: S. hantzschii, S. minutus, and
S_. alpinus, and a population of Melosira islandica. Melosira islandica was
the only species common throughout the lake during the spring but was most
abundant in the nearshore samples on the Canadian side of the lake. The
Stephanodiscus species were routinely observed in the offshore assemblage but
were only present in low abundance (<4%).
During the second cruise, nearshore populations on the Canadian shore
were again dominated by Melosira islandica and Stephanodiscus species, with
S_. subtilis replacing S_. alpinus in the assemblage (Table 7.3), possibly as a
result of thermal regime restrictions discussed by Stoermer and Ladewski
(1976). As was the case for cruise 1, these populations were not noted in
any large abundance at stations near the Michigan shore. Dominance by this
group of Stephanodiscus species is considered characteristic of enriched
habitats in the Great Lakes, particularly parts of Lakes Erie and Ontario
(Stoermer and Yang, 1970).
One species, Fragilaria capucina, was restricted to the nearshore zone
on both sides of the lake.Stoermer and Yang (1970) note that this is
primarily a littoral form and that it responds well to added nutrients. The
following nearshore periphytic species were also observed at station 57:
Achnanthes lanceolata, Fragilaria brevistriata var. inflata, Fragilaria
vaucheriae var. truncata, Navicula neoventricosa, Nitzschia acuta, Nitzschia
sp.#2, Cymbella minuta var. silesiaca, and Cymbella minuta f. latens.
Meridion circulare and Gomphonema olivaceum were noted at stations 57 and 9;
these species originating from tychoplanktonic and epilithic riverine
habitats, respectively, are indicative of river influence at these stations.
142
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TABLE 7.1. WATER CHEMISTRY AND PHYTOPLANKTON PARAMETERS
AT SELECTED STATIONS FOR THE FIRST TWO
SOUTHERN LAKE HURON CRUISES, 1974. AVERAGE OF 1 AND 5 METER VALUES
1974
Station
Number
Inshore
Canada
Offshore
Canada
Inshore U.S.
Offshore U.S.
Inshore
Canada
Offshore
Canada
Inshore U.S.
Offshore U.S.
57
9
56
10
14
13
57
9
56
10
14
67
Nitrate
ygN/1
Cruise
1331
—
445
—
435
385
Cruise
793
730
356
385
330
326
Total P
ygP/1
Silica
mgSi02/l
Chlorophyll
a
pg/1
Primary
Production
mg C/nrVhr
1, 28 April to 3 May 1974
16.7
—
4.2
—
6.4
3.2
2, 14-17 May
20.4
29.5
8.9
6.6
4.1
3.9
1.81
—
2.36
—
0.89
2.70
1974
0.36
0.42
0.97
0.74
1.14
1.50
14.8
—
3.1
—
5.7
2.1
13.3
8.1
2.7
5.4
3.2
2.2
42.1
—
4.5
—
9.4
3.3
38.6
29.5
3.7
8.3
3.7 •
3.3
144
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High nitrate persisted slightly on the Canadian shore during the third
cruise, 4-8 June, 550 ygN/1 at stations 9 and 57 in the nearshore as compared
with about 400 ygN/1 at stations 10 and 56 farther offshore. Values were
slightly greaterin the nearshore on the 17-25 June cruise, 420 ygN/1 in
contrast to 350 ygN/1 offshore. These differences in nitrate had disappeared
by the 17-24 July cruise.
1975 Nearshore Study
The 29 April to 2 May 1975 cruise focused on the nearshore region around
Bayfield, Ontario and on the Michigan shoreline directly across the lake. An
east-west transect of stations offshore from Bayfield showed higher nitrate
and total phosphorus levels in the nearshore waters (Table 7.4), but nitrate
values were not as high as in 1974 (Table 7.1). Nearshore, the chlorophyll a
concentration was approximately the same as at the offshore stations, but ^C
productivity was twice as high (Table 7.4), indicating a small but very
actively growing phytoplankton population in contrast to the large active
population observed on the same dates in 1974 (Table 7.1). A major storm
passed across southern Lake Huron during the first week of April 1975 and, in
general, greatly retarded the spring warming trend. This could easily
account for the later development of the spring phytoplankton bloom in 1975
compared with 1974. The silica levels also reflect the lack of diatom growth
by the end of April 1975; the silica levels nearshore are still slightly
higher than the offshore values. This indicates that there was a minor
source of silica in the nearshore, either regeneration from the sediments or
runoff.
Underway maps of temperature, nitrate, silica and chloride were also
made on 30 April 1975 (Figures 7.2a, b, c, d). South-southeast winds of
20-24 knots prevailed for 24 hr preceding and during the mapping run. As a
consequence, water from the Bayfield River appears to have been transported
north along the Ontario shore. This is clearly indicated by the temperature
and chloride distribution and indicates that the high nitrate and silica
values observed at the northern nearshore turn can also be attributed to the
Bayfield River plume. The middle nearshora turn, which is 0.7 km offshore
and 0.7 km south of the river mouth, apparently missed most of the river
plume that was close to the shore moving north under the prevailing winds.
As a check that the observed plume north of the river mouth was indeed
Bayfield River water, a comparison was made between the river water and the
observed enrichment of the nearshore waters for chloride and nitrate. These
are the only parameters that were measured in both the underway maps and the
Ontario Ministry of the Environment (1973) river studies (data of 22 April
1975). The center of the observed plume was calculated to be 10 percent and
12 percent river water based on chloride and nitrate concentrations,
respectively. The excellent agreement of these numbers is a clear indication
that the observed plume was Bayfield River water. In addition, water with
temperatures greater than 6°C that flowed north also had enriched silica
concentrations.
The nitrate and to some extent the chloride distribution also showad
high concentrations south of Bayfield. This indicates that either the river
147
-------
TABLE 7.4. AVERAGE VALUES FOR THE UPPER 10 m ALONG A TRANSECT
DUE WEST OF BAYFIELD, ONTARIO, 30 APRIL 1975
Km Chlorophyll Primary
from Nitrate Total P Silica a Production
Station shore T°C ygN/1 ygP/1 mgSi02/l Mg7l mg C/mVhr
Nil
N12
N13
1
7.5
13
5.1
3.1
3.1
636
359
353
29.7
12.5
11.1
1.37
1.27
1.27
1.0
1.2
1.1
4.3
2.5
2.5
148
-------
3.9 4.1 4,3 45 5,0 6.0 65
Figure 7.2a. One meter underway map near Bayfield, Ontario, April 30, 1975.
Contours are based on continuous data taken along the zigzag cruise track
(dashed line), (a) water temperature, (b) chloride (mg/1), (c) nitrate (yg N/l),
(d) silica (mg Si02/l).
149
-------
Cl mg/l
30 APRIL 1975
Figure 7.2b. One meter underway raap of chloride (mg/l) near Bayfield, Ontario,
30 April 1975. See Figure 7.2 for more details.
150
-------
400 500 700
600
N03 jig/I
30APRIL 1975
Figure 7.2c. One meter underway map of nitrate (^gN/1) near Bayfield, Ontario,
30 April 1975. See Figure 7.2 for more details.
151
-------
SILICATE
mg Si 02/1
30 APRIL 1975
D
Figure 7.2d. One meter underway map of silica (mg SiC>2/l) near Bayfield, Ontario,
30 April 1975. See Figure 7.2 for more details.
152
-------
plume was recently transported south along the shore under west or northwest
winds or that there is another nutrient source south of Bayfield and that
water from that source has been transported north along the coast.
A band of lower silica inside the 4°C isotherm (thermal bar) on the
Bayfield transect indicates that a diatom bloom is beginning to develop in
the nearshore waters (Fig. 7.2d). This is the area that had the very large
phytoplankton bloom in April-May 1974, but the bloom was not yet well
developed by 1 May 75. Stoermer (1968) found the largest phytoplankton
populations just inside the thermal bar. This may result, in part, from
physical processes because the thermal bar is a region of downwelling, and
nearshore surface waters move offshore to the bar and sink, tending to
concentrate material there (Rodgers, 1965).
In contrast, on the Michigan shore, even though the thermal bar was
present (Figure 7.3a), high nitrate levels were not observed in the underway
map of the nearshore waters (Figure 7.3c). The nitrate distribution was
fairly uniform with a total variation of only 20 percent over the entire map
as compared with the three times higher values found nearshore on the Ontario
side. On the Michigan shore, the lowest nitrate values were found close to
shore, probably reflecting the phytoplankton growth inshore of the thermal
bar that is also indicated by the chlorophyll distribution (Figure 7.3e).
Silica levels are also reduced inshore reflecting diatom growth (Figure
7.3d). The highest chloride values were found inshore of the thermal bar
(Figure 7.3b), indicating some minor source of runoff or cultural inputs
along the Michigan shore. Possibly this was material transported south along
the shore from Saginaw Bay that has a high chloride content (Ayers et al.,
1956; Section 3).
The Michigan shore underway maps were made during a calm period
following two days of SSE winds at 20-24 knots. The wind reversed on the
evening of 1 May 1975 to WNW at 10-15 knots. Temperature profiles were made
on an east-west transect of eight stations on 2 May (Figure 7.4), which shows
that the thermal bar had moved 5 km inshore under the new wind regime. The
temperature profiles depict the classic thermal bar situation with reverse
thermal stratification offshore of the 4°C water and a positive thermocline
established on the inshore side. The station data indicate that the surface
distributions observed in the underway maps were consistent with depth. At
five of the stations, water samples were taken for chloride, silica,
chlorophyll a_, and nitrate profiles (Figure 7.5a, b, d, c). Chloride was
highest inshore. Chlorophyll a_ was also greater inshore, indicating the
beginning of a phytoplankton bloom in the recently stabilized waters. Silica
was reduced in the nearshore waters, reflecting phytoplankton growth, whereas
the nitrate distribution was relatively uniform, probably reflecting a
balance between consumption by phytoplankton and a minor source(s) along the
shore.
DISCUSSION
The Great Lakes have a persistent year-round coastal boundary layer
(CBL), defined as a band of water approximately 10 km wide, which is
153
-------
Figure 7.3a. One meter underway map near Harbor Beach,
Michigan, 1 May 1975. Dashed line is the cruise track.
(a) water temperature, (b) chloride (mg/1), (c) nitrate (yg N/l),
(d) silica (rag Si02/l), (e) chlorophyll fluorescence:
7 units £ 1 yg Chi a/1.
154
-------
HARBOR
BEACH
43° 50'
43° 40'
Cl mg/l
I MAY T975
B
Figure 7.3b. One meter underway map of chloride (mg/l) near Harbor Beach,
Michigan, 1 May 1975. See Figure 7.3 for more details.
155
-------
HARBOR
BEACH
4 3° 50'
43° 40'
N03 iig/l
I MAY f975
Figure 7.3c. One meter underway map of nitrate (ygN/1) near Harbor Beach,
Michigan, 1 May 1975. See Figure 7.3 for more details.
156
-------
HARBOR
BEACH
43° 50'
43° 40'
SILICATE
mg Si02/l
I MAY 1975
Figure 7.3d. One meter underway map of silica (mg Si02/l) near Harbor
Beach, Michigan, 1 May 1975. See Figure 7.3 for more details.
157
-------
HARBOR
BEACH
43° 50'
43° 40'
CHLOROPHYLL
FLUORESCENCE
I MAY 1975
Figure 7.3e. One meter underway map of chlorophyll fluorescence near
Harbor Beach, Michigan, 1 May 1975. See Figure 7.3 for more details.
158
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dominated by a relatively persistent longshore flow (Csanady, 1975). This
feature serves to trap runoff and domestic inputs from the shore in a narrow
nearshore zone representing perhaps only 1 percent of the water volume of the
lakes. Thus, materials dumped into the lake continue to be a problem until
physical processes, which at this time are poorly understood, mix the
material from the CBL to the midlake water mass (Csanady, 1975). The
nutrient concentrations in the Great Lakes rivers are closely tied to flow
rate, with the highest concentrations being found at times of high runoff
(Ontario Ministry of Environment, 1978; Stephenson and Waybrant, 1971).
Rivers, during winter and spring, therefore may carry a majority of their
nutrient load to the lake; for example, from January to April, and in
December 1975, the Maitland River carried 88 percent of its total annual
nitrate nitrogen load (Ontario Ministry of Environment, 1978). Compounding
the problem is the presence of the thermal bar that effectively prevents the
mixing of the nutrient-rich water from the CBL to the open lake during the
spring. The results of our study confirm this phenomenon, showing that the
nutrients carried by the Bayfield River are retained inside the thermal bar.
Calculations based on the Ontario Ministry of Environment (1978) data
for the Maitland, Ausable, and Bayfield rivers suggest that these rivers may
account for most of the excess nitrate found in the nearshore zone from Point
Clark to Kettle Point. Assuming a nearshore zone of 100 km x 5 km (the
distance offshore to the thermal bar 30 April 1975) x 10 m deep, the nitrate
carried by the rivers in April 1975 was sufficient to add approximately
260 ygN/1 to the entire nearshore. Added to the open lake background of
350 ygN/1 this gives an average of 620 ygN/1 which can be compared to the
observed value near Bayfield of 640 ygN/1 (Table 7.4). This rough
calculation suggests that most of the enrichment of the nearshore zone
observed in late April 1975 was derived from river inputs.
Samples from the 1974 spring cruises indicate that the large
phytoplankton bloom based on river-borne nutrients developed nearshore after
the thermal bar formed. In 1974, this large spring bloom resulted in silica
depletion to 0.4 mg/1 Si02 by 15 May (Table 7.1) even though, as is indicated
in Figure 7.2d, a significant amount of silica was also being carried by the
Bayfield River. Further silica depletion could limit the growth of diatoms
and favor a change to blue-green and green algae (Schelske and Stoermer,
1971, 1972). Although the thermal bar is present only during spring in
southern Lake Huron, the CBL persists throughout the summer and is reasonably
effective at preventing mixing betwaen nearshore and offshore waters. For
example, Holland and Beeton (1972) found that unique phytoplankton
populations were maintained year round in the nearshore zone in Lake
Michigan, which had a different species composition and higher total numbers
than the offshore populations. Conditions that develop in the nearshore zone
and lead to a bloom of diatoms or possibly blue-green and green algae may be
relatively independent of conditions in the offshore waters. The presence of
the thermal bar at the time of spring runoff may thus play a crucial role in
the early development of nuisance algal blooms in nearshore regions.
The impact of river-borne nutrients on the nearshore zone of Lake Huron
varies greatly with season as a function of river flow, associated nutrient
concentrations, and the presence of the thermal bar. River flow is highest
161
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in December to April averaging 100 times the flow in July to September in
normal years. Nutrient concentration of river water varies, being roughly
proportional to flow rate, with the winter values being roughly 10 times the
late summer values in normal years. Daily inputs of nutrients, therefore,
are often 1,000 times higher in the winter compared to typical summer
loadings. However, if as in 1975, August and September are particularly wet,
the rivers maintain high flow rates and high nutrient levels and the nutrient
load per day to the lakes will be 100 times higher than normal (Ontario
Ministry of Environment, 1978). In moderate to high flow situations, the
nutrients are carried directly into the lake unchanged, while in low flow
situations phytoplankton and macrophytes in the river deplete nutrients to
very low levels, often to levels less than surface values in the lake.
River-borne nutrients have the largest effect on the nearshore zone in
April when the river flow and nutrient levels are high and when the thermal
bar retains the nutrients in the nearshore zone. In addition, the river
water is generally warmer than the nearshore lake water at this time, and
consequently the river water may float as a surface layer inside the thermal
bar. During the nearshore cruise (Figure 7.2a), the thermal bar was only
5 km offshore, and the Bayfield River water was 9°C while the nearshore water
was <6°C. The input of warmer river water increases the temperature and
thermal stability of the water column inshore from the thermal bar and
provides nutrients to the surface layer, all of which are instrumental in
developing large early spring phytoplankton blooms in the nearshore zone.
Clearly, April through May, the period of the thermal bar, is the time
of year when river-borne nutrients should have maximum effect on water
quality in the nearshore zone in southern Lake Huron. In 1975, the 29 April
to 2 May cruise was too early for the spring phytoplankton bloom in the
nearshore zone; however, in 1974 survey data showed a large bloom developing
in April and May in the nearshore zone influenced by the Maitland and
Bayfield Rivers. The 1974 bloom was primarily composed of Stephanodiscus
species that typically bloom only in nutrient enriched areas (Stoermer and
Yang, 1970).
Comparing Michigan and Ontario nearshore regions of southern Lake Huron
points to the important role of the nearshore zone as an extension of the
rivers, particularly during the thermal bar period. On the Ontario shore,
the Bayfield, Maitland, and Ausable Rivers drain large areas of primarily
agricultural lands, resulting in high nutrient loading in the nearshore zone,
particularly during spring runoff, and this apparently causes large spring
blooms such as those observed in 1974 (Table 7.1). At the same latitude, the
Michigan nearshore receives only local runoff, and does not exhibit elevated
nitrate levels or a particularly intense spring bloom. On the Michigan
coast, the majority of the region's runoff enters Saginaw Bay via the Saginaw
River. Saginaw Bay, being highly eutrophic, processes these nutrients so
that little of this material reaches the open lake.
162
-------
REFERENCES
Armstrong, F. A. J., C. R. Stearns, and J. D. H. Strickland. 1967. The
Measurement of Upwelling and Subsequent Biological Processes by Means of
the Technicon AutoAnalyzer and Associated Equipment. Deep-Sea Res.,
14:381-389.
Ayers, J. C., D. V. Anderson, D. C. Chandler, and G. H. Lauff. 1956.
Currents and Water Masses of Lake Huron. Pub. No. 1, Great Lakes Res.
Div., Univ. of Mich., Ann Arbor, Michigan, 101 pp.
Cottafava, G., and G. LeMoli. 1969. Automatic Contour Map. Communications
of the ACM, 12:386-391.
Csanady, G. T. 1975. Circulation, Diffusion and Frontal Dynamics in the
Coastal Zone. J. Great Lakes Res., 1:18-32.
Holland, R. E., and A. M. Beeton. 1972. Significance to Eutrophication of
Spatial Differences in Nutrients and Diatoms in Lake Michigan.
Limnol. Oceanogr., 17:88-96.
Huang, J. C. K. 1972. The Thermal Bar. Geophys. Fluid Dynamics, 3:1-25.
International Joint Commission. 1977. The Waters of Lake Huron and Lake
Superior. Vol. II. Lake Huron Report of the Upper Lakes Reference
Group. Windsor, Ontario.
Kelley, J. C. 1976. Sampling the Sea, pp. 361-387. In_ D. H. Cushing
and J. J. Walsh (eds.), The Ecology of the Seas. W. B. Saunders,
Philadelphia.
Menzel, D. W., and N. Gorwin. 1965. The Measurement of Total Phosphorus in
Seawater Based on the Liberation of Organically Bound Fractions by
Persulfate Oxidation. Limnol. Oceanogr., 10:280-282.
Murphy, J., and J. P. Riley. 1962. A Modified Single Solution Method for
the Determination of Phosphate in Natural Waters. Anal. Chim. Acta.,
12:162-176.
Nalewajko, C. 1967. Phytoplankton Distribution in Lake Ontario. Proc.
10th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res.,
pp. 63-69.
Ontario Ministry of the Environment. Water Res. Br. 1978. Water Quality
Data for Ontario Lakes and Streams. Vol. 10.
163
-------
Rodgers, G. K. 1965. The Thermal Bar in the Laurentian Great Lakes.
Proc. 8th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res.,
pp. 358-363.
. 1966. The Thermal Bar in Lake Ontario, Spring 1965 and
Winter 1965-66. Proc. 9th Conf. Great Lakes Res., Internat. Assoc.
Great Lakes Res., pp. 369-374.
Schelske, C. L., and E. Callender. 1970. Survey of Phytoplankton
Productivity and Nutrients in Lake Michigan and Lake Superior. Proc.
13th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res.,
pp. 93-105.
Schelske, C. L., and E. F. Stoermer. 1971. Eutrophication, Silica Deple-
tion, and Predicted Changes in Algal Quality in Lake Michigan. Science,
173:423-424.
. 1972. Phosphorus, Silica and Eutrophication of
Lake Michigan, pp. 159-171. In; G. E. Likens [ed.], Nutrients and
Eutrophication: The Limiting Nutrient Controversy. Allen Press,
Lawrence, Kansas.
Slawyk, G., and J. J. Maclsaac. 1972. Comparison of Two Automated Ammonium
Methods in a Region of Coastal Upwelling. Deep-Sea Res., 19:521-524.
Stephenson, M. E., and J. R. Waybrant. 1971. Watershed Analysis Relating
to Eutrophication of Lake Michigan. Technical Rep. 11. Institute of
Water Research, Mich. State Univ., East Lansing, Michigan. 118 pp.
Stoermer, E. F. 1968. Nearshore Phytoplankton Populations in the Grand
Haven, Michigan Vicinity during Thermal Bar Conditions. Proc. llth
Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res., pp. 134-150.
Stoermer, E. F., and T. B. Ladewski. 1976. Apparent Optimal Temperatures
for the Occurrence of Some Common Phytoplankton Species in Southern Lake
Michigan. Pub. No. 18, Great Lakes Res. Div., Univ. of Mich.,
Ann Arbor, Michigan. 49 pp.
Stoermer, E. F., C. L. Schelske, and L. E. Feldt. 1971. Phytoplankton
Assemblage Differences at Inshore Versus Offshore Stations in Lake
Michigan, and Their Effects on Nutrient Enrichment Experiments. Proc.
14th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res.,
pp. 114-118.
Stoermer, E. F., and J. J. Yang. 1970. Distribution and Relative Abundance
of Dominant Plankton Diatoms in Lake Michigan. Pub. No. 16, Great Lakes
Res. Div., Univ. of Mich., Ann Arbor Michigan. 64 pp.
Strickland, J. D. H., and T. R. Parsons. 1968. A Practical Handbook of
Seawater Analysis. Bull. Fish. Res. Bd. Canada. No. 167. 311 pp.
Technicon. 1972. Chloride in Sea Water. Autoanalyzer II Industrial
Method No. 217-72W, Technicon Instruments Corp. Tarryton, New York.
164
-------
APPENDIX
Average wind direction and speed at Selfridge AFB,
latitude 42° 36' N, longitude 82° 50' W.
(Wind speed is given in knots)
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
January
Avg. Wind
Direction
not avail.
20.3
32.9
25.8
not avail.
not avail.
25.4
13.7
1.4
2.4
33.9
28.8
19.2
20.9
25.3
February
Avg. Wind
Direction
2.3
5.1
3.6
1.0
5.8
5.1
34.3
30.1
27.0
23.5
24.1
18.3
25.8
1.9
2.8
Avg. Wind
Speed
not avail.
2.9
4.6
4.7
not avail.
not avail .
11.1
5.0
6.7
5.2
6.1
5.9
6.2
10.6
9.6
Avg. Wind
Speed
8.6
13.3
5.0
7.0
5.8
12.3
9.8
3.3
5.9
12.0
11.3
4.4
6.4
10.6
3.3
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
Avg. Wind
Direction
26.4
5.8
8.9
3.6
12.3
22.8
17.8
26.9
23.2
22.5
16.4
25.5
2.3
21.9
21.0
25.9
Avg. Wind
Direction
26.9
31.7
14.6
7.0
26.0
9.2
20.2
30.8
1.8
31.0
24.4
20.7
23.5
Avg. Wind
Speed
8.1
9.0
4.1
6.3
6.6
10.9
3.9
9.3
8.0
8.5
7.6
16.5
3.0
5.7
12.3
16.6
Avg. Wind
Speed
5.3
6.9
9.6
6.5
5.0
4.1
14.4
13.6
8.6
8.8
6.9
9.8
11.9
(continued).
165
-------
APPENDIX A. (continued).
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
March
Avg. Wind
Direction
23.1
14.3
19.0
17.5
26.5
18.0
30.9
7.0
11.4
0.6
10.0
4.3
35.3
22.4
12.4
April
Avg. Wind
Direction
9.1
23.0
13.9
22.0
30.8
28.8
33.8
2.7
2.0
20.8
13.6
17.1
24.0
22.6
32.1
Avg. Wind
Speed
6.9
3.2
12.9
6.2
9.7
6.8
6.6
9.6
4.0
9.4
4.3
11.2
9.2
4.5
7.9
Avg. Wind
Speed
7.1
9.5
7.2
12.4
8.0
7.0
9.1
10.3
10.2
4.7
3.1
9.7
11.5
15.6
11.7
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Avg. Wind
Direction
33.1
30.7
24.3
33.0
6.8
34.0
24.2
29.6
28.8
21.0
28.0
6.7
8.1
8.3
5.8
31.9
Avg. Wind
Direction
27.0
28.3
33.5
5.0
12.4
21.5
24.3
31.6
0.3
24.3
13.0
17.3
22.7
25.0
26.7
Avg. Wind
Speed
7.2
13.5
8.5
8.6
3.5
8.8
11.7
8.7
10.9
8.3
12.4
1.1
9.2
9.6
7.2
9.3
Avg. Wind
Speed
3.5
6.7
7.6
7.2
5.5
10.2
10.6
11.6
11.0
4.8
1.2
4.8
6.9
7.1
6.1
(continued).
166
-------
APPENDIX A. (continued).
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
May
Avg. Wind
Direction
36.0
11.0
27.4
10.2
18.0
32.4
27.5
10.4
35.4
21.0
16.5
22.9
34.6
21.5
27.6
June
Avg. Wind
Direction
16.3
14.5
15.0
20.7
16.8
16.1
16.7
19.5
19.6
23.0
27.3
26.7
19.1
19.5
19.6
Avg . Wind
Speed
8.0
5.6
4.7
3.8
7.9
8.9
4.0
10.0
7.1
4.5
7.6
8.1
8.8
12.3
11.0
Avg. Wind
Speed
2.5
2.0
1.4
6.3
6.2
7.4
10.8
6.8
7.5
11.4
7.6
5.7
6.1
8.3
5.9
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Avg. Wind
Direction
9.8
28.9
3.0
5.0
11.3
11.3
28.2
26.2
28.3
30.0
34.6
17.8
18.3
33.3
3.5
26.1
Avg. Wind
Direction
26.1
23.8
22.4
17.3
18.2
24.5
1.0
0.7
35.8
0.8
3.4
13.0
14.5
23.5
26.5
Avg. Wind
Speed
5.9
5.0
5.4
7.3
5.0
1.7
4.6
7.7
8.7
5.8
3.8
2.3
4.8
4.1
5.0
8.3
Avg . Wind
Speed
5.7
5.9
3.5
2.7
3.3
6.3
5.5
9.9
6.5
5.3
5.0
3.0
2.3
3.3
10.5
(continued).
167
-------
APPENDIX A. (continued).
Month:
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
July
Avg. Wind
Direction
24.3
23.3
22.8
23.3
31.8
8.8
14.8
20.7
26.3
2.3
4.2
9.0
23.8
23.3
0.2
August
Avg. Wind
Direction
23.6
13.3
20.8
24.7
32.3
19.0
12.8
2.1
0.6
10.3
16.6
25.5
33.6
4.6
10.5
Avg. Wind
Speed
6.3
9.1
8.7
9.7
5.2
2.8
2.8
1.7
5.3
7.8
8.8
2.7
3.7
5.5
8.2
Avg. Wind
Speed
3.9
4.4
7.5
9.3
5.7
3.2
2.4
4.0
3.4
6.3
9.4
4.8
5.6
4.8
4.0
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Avg. Wind
Direction
7.0
15.2
24.2
25.3
4.4
14.8
5.9
4.7
4.3
14.0
13.6
28.0
23.6
26.7
26.7
27.5
Avg. Wind
Direction
19.0
29.7
25.7
22.5
16.0
16.5
18.3
31.8
35.2
6.8
20.0
29.8
3.5
9.2
17.7
27.1
Avg. Wind
Speed
1.8
5.7
10.5
6.8
7.0
3.5
5.0
5.5
2.0
2.1
3.0
4.9
4.2
6.0
7.0
5.7
Avg. Wind
Speed
4.0
5.7
3.2
1.3
2.9
4.5
3.7
4.4
4.0
2.3
5.3
5.0
3.2
3.0
2.7
7.3
(continued).
168
-------
APPENDIX A.. (continued).
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month:
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
September
Avg. Wind
Direction
34.8
3.5
1.9
2.8
8.5
10.0
13.5
22.8
23.0
21.4
21.7
23.9
28.3
26.8
27.3
October
Avg. Wind
Direction
29.8
32.7
22.6
19.7
22.0
23.3
31.6
20.5
28.3
26.7
18.8
31.4
10.6
23.1
29.2
Avg. Wind
Speed
2.5
6.9
4.8
3.3
2.5
1.8
1.3
3.1
3.9
3.5
8.1
5.8
9.1
5.7
9.3
Avg. Wind
Speed
9.4
9.2
4.3
7.1
9.8
9.8
7.0
4.7
3.1
2.6
3.7
6.0
6.4
10.2
6.2
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Avg. Wind
Direction
6.0
27.8
4.4
19.4
34.8
31.3
35.0
21.5
19.0
25.7
24.5
19.3
18.5
26.4
28.8
Avg. Wind
Direction
21.0
28.0
1.0
33.8
1.0
22.3
22.3
1.0
20.0
29.4
27.0
22.3
17.5
16.4
20.9
19.5
Avg. Wind
Speed
2.3
7.1
4.4
6.0
5.4
4.3
9.4
3.0
7.8
7.3
5.8
6.8
6.6
8.6
5.5
Avg. Wind
Speed
1.6
10.8
5.0
5.5
5.4
5.7
10.7
2.2
3.3
7.6
5.5
3.5
1.5
3.5
8.0
6.9
(continued).
169
-------
APPENDIX A.. (continued).
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
November
Avg. Wind
Direction
23.4
8.8
22.1
0.7
0.5
31.1
26.3
21.0
15.5
13.3
19.7
29.4
25.6
26.7
23.0
December
Avg . Wind
Direction
5.4
1.1
32.6
28.5
23.0
20.2
16.9
28.9
30.1
22.7
20.3
26.6
8.0
3.7
13.9
Avg. Wind
Speed
7.1
4.1
8.0
7.3
10.3
5.3
2.0
2.8
1.8
4.7
9.8
6.7
9.3
11.6
14.0
Avg . Wind
Speed
16.3
16.1
12.1
5.7
2.7
5.1
4.0
9.4
9.9
7.7
4.4
2.4
2.1
4.6
9.8
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Avg. Wind
Direction
21.5
21.7
21.3
18.9
27.6
32.6
24.7
18.7
28.1
33.9
6.7
19.0
26.9
33.8
6.7
--
Avg. Wind
Direction
20.7
26.3
24.3
20.9
20.0
2.4
21.5
22.7
32.0
28.2
23.1
24.9
23.5
23.4
31.6
16.0
Avg. Wind
Speed
8.2
8.3
5.9
4.7
8.3
14.1
4.9
8.9
12.1
9.8
4.0
7.7
7.6
4.2
12.0
Avg. Wind
Speed
9.7
10.8
10.9
12.2
4.9
4.4
8.3
8.5
1.7
8.3
8.1
7.1
7.3
7.0
4.7
1.8
170
-------
APPENDIX 3.
Average wind direction and speed at Wurtsmith AFB,
latitude 44° 26' N, longitude 83° 22' W.
(Wind speed is given in knots)
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
January
Avg. Wind
Direction
27.8
22.7
23.3
24.1
22.8
23.6
25.4
22.8
32.3
34.1
34.6
28.1
20.6
22.1
13.7
February
Avg . Wind
Direction
32.7
2.4
8.6
0.4
35.1
3.0
36.0
10.5
33.5
23.7
24.7
20.8
32.1
2.9
19.6
Avg. Wind
Speed
7.2
5.5
4.6
6.9
7.8
5.3
10.0
3.8
6.1
4.9
8.4
8.1
9.3
12.0
6.7
Avg. Wind
Speed
4.2
11.7
9.6
8.6
6.4
12.8
6.3
1.2
4.2
9.7
8.1
3.1
8.4
6.5
3.2
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
Avg. Wind
Direction
28.4
6.8
20.6
22.0
10.1
23.7
7.0
26.0
24.1
22.7
13.3
24.0
25.3
21.1
21.0
26.2
Avg. Wind
Direction
23.8
31.8
18.9
31.1
24.7
13.3
2.8
30.2
34.5
31.3
21.0
19.2
22.7
Avg. Wind
Speed
7.3
13.9
5.4
3.9
6.7
9.0
3.1
4.4
7.6
5.4
4.2
5.6
3.6
7.4
10.7
14.5
Avg . Wind
Speed
6.7
6.0
6.0
6.1
4.8
5.9
14.7
9.3
6.1
4.1
3.7
7.5
7.6
(continued)
171
-------
APPENDIX B. (continued).
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
March
Avg . Wind
Direction
4.1
9.3
16.7
21.1
22.6
19.7
31.9
9.6
21.7
35.0
16.8
4.0
0.3
25.8
12.9
April
Avg . Wind
Direction
6.3
31.5
5.9
21.8
32.3
25.4
33.3
3.7
2.0
23.2
8.9
14.9
21.5
1.8
31.5
Avg. Wind
Speed
6.7
1.5
8.4
3.9
7.0
10.8
6.6
13.1
4.7
9.5
4.8
13.1
8.5
5.3
4.3
Avg. Wind
Speed
11.1
9.6
7.6
11.2
10.1
7.1
5.9
11.9
8.5
4.0
5.5
6.6
7.6
9.5
10.4
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Avg. Wind
Direction
2.0
32.0
23.8
31.7
3.7
27.8
20.9
26.3
27.0
20.7
27.9
28.8
6.2
9.7
4.8
31.5
Avg. Wind
Direction
30.3
24.8
1.0
8.3
17.5
19.7
20.7
32.3
35.8
22.3
6.3
19.3
22.1
14.1
9.8
Avg . Wind
Speed
16.1
13.7
8.8
9.0
5.6
7.4
6.6
10.3
8.5
12.3
9.9
4.5
9.0
10.2
10.6
8.3
Avg. Wind
Speed
7.8
10.8
8.7
3.0
6.7
11.7
10.3
9.1
6.0
6.7
2.5
6.8
8.9
3.6
4.1
(continued)
172
-------
APPENDIX B. (continued).
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
May
Avg. Wind
Direction
33.4
15.5
28.7
10.6
2.8
33.9
35.0
11.0
7.4
12.5
17.9
24.8
25.4
19.9
22.4
June
Avg. Wind
Direction
11.0
11.5
14.5
21.2
20.9
15.5
16.3
15.2
11.3
20.6
29.3
24.3
26.3
20.1
20.0
Avg. Wind
Speed
8.7
4.9
8.1
4.5
3.5
9.2
7.2
6.1
14.0
4.8
6.8
12.1
11.9
9.1
10.4
Avg. Wind
Speed
3.7
4.9
3.6
9.5
7.1
6.3
8.4
8.9
7.7
11.3
11.5
8.8
6.1
6.3
4.6
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Avg. Wind
Direction
11.0
1.7
1.6
4.0
10.8
19.5
25.3
24.8
27.8
23.8
3.2
17.5
23.0
2.9
5.6
25.3
Avg. Wind
Direction
22.9
21.6
20.1
17.8
24.0
4.8
0.7
2.0
1.6
1.5
3.2
13.0
10.0
20.3
25.5
Avg. Wind
Speed
6.0
4.1
7.4
8.7
5.2
5.7
7.9
12.5
11.4
7.8
6.7
5.0
7.0
6.6
7.3
9.3
Avg. Wind
Speed
5.9
8.6
6.8
6.4
7.3
6.0
9.8
9.6
8.0
8.3
6.2
2.7
3.3
3.9
9.1
(continued).
173
-------
APPENDIX B. (continued).
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
July
Avg. Wind
Direction
23.5
20.1
25.5
25.5
24.2
22.0
20.2
23.2
16.5
4.6
14.0
20.8
21.3
16.4
0.2
August
Avg. Wind
Direction
15.2
18.4
20.3
23.7
23.3
20.6
22.2
22.3
2.0
8.3
16.0
22.3
2.8
1.8
11.7
Avg . Wind
Speed
7.2
9.8
11.3
8.2
7.6
5.7
5.2
5.5
7.6
7.2
5.2
4.5
6.3
7.1
9.3
Avg. Wind
Speed
3.9
4.1
6.3
5.7
6.7
4.3
3.7
1.1
5.6
5.0
8.0
6.4
4.7
7.2
2.8
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Avg. Wind
Direction
9.2
19.6
25.9
35.7
3.0
10.0
7.2
19.8
3.3
16.2
20.0
25.0
23.7
31.8
26.3
28.0
Avg. Wind
Direction
23.7
27.0
27.0
12.0
19.0
20.3
20.0
34.3
00.0
16.3
23.4
28.2
2.6
28.5
17.8
24.2
Avg. Wind
Speed
4.2
5.5
9.0
7.8
6.2
2.7
1.5
4.3
3.8
3.4
6.9
5.0
8.7 .
6.9
6.5
6.8
Avg. Wind
Speed
3.9
4.6
5.0
3.0
2.8
4.6
6.7
4.5
4.0
3.8
6.2
2.3
3.3
3.2
4.0
8.2
(continued).
174
-------
APPENDIX B. (continued)
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month:
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
September
Avg. Wind
Direction
32.8
26.7
34.2
26.0
11.5
8.3
11.5
21.4
34.3
16.3
20.9
0.7
27.9
23.3
26.6
October
Avg. Wind
Direction
32.8
33.0
25.0
12.0
21.0
18.5
29.6
18.1
29.3
18.9
20.7
32.9
15.3
23.1
27.2
Avg. Wind
Speed
5.0
2.5
5.3
3.5
2.0
2.1
1.1
5.0
4.4
5.4
10.3
3.6
7.9
7.0
11.6
Avg. Wind
Speed
6.9
4.6
4.3
7.2
10.7
7.4
8.9
4.0
3.3
4.2
4.8
7.4
1.4
9.0
5.5
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Avg. Wind
Direction
24.0
28.9
8.0
29.9
34.9
28.1
31.3
20.5
20.8
26.3
18.8
19.7
20.0
29.6
29.5
Avg. Wind
Direction
21.6
29.3
0.7
32.2
34.0
21.8
27.0
29.3
21.0
28.8
23.7
4.5
21.7
17.5
19.7
21.7
Avg. Wind
Speed
5.7
5.3
5.5
7.3
5.3
7.6
7.0
3.2
12.3
8.9
6.9
6.4
3.2
9.8
2.4
Avg. Wind
Speed
5.9
12.3
5.8
2.0
3.7
6.7
9.0
1.3
6.0
8.7
6.0
2.7
4.4
4.4
5.9
5.1
(continued).
175
-------
APPENDIX B. (continued).
Month:
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Month :
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
November
Avg. Wind
Direction
11.3
7.4
28.7
33.0
1.9
27.5
23.1
19.3
20.0
16.1
17.2
25.8
23.4
23.2
23.1
December
Avg. Wind
Direction
6.1
1.8
33.4
26.3
21.8
20.0
14.8
32.3
30.1
22.5
20.9
24.3
2.8
4.6
12.3
Avg. Wind
Speed
6.0
3.2
1.8
1.3
5.9
3.3
4.3
2.2
3.2
2.4
7.3
4.1
8.8
9.1
13.2
Avg. Wind
Speed
11.0
9.0
8.2
4.3
3.4
5.9
2.4
8.9
8.0
6.1
5.3
1.8
3.9
4.3
6.9
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Date
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Avg . Wind
Direction
22.0
22.9
21.0
18.1
26.2
33.1
23.7
20.7
35.1
33.7
25.1
16.8
27.3
33.4
7.0
Avg. Wind
Direction
18.6
24.6
24.1
32.4
22.7
23.7
20.1
21.0
24.8
27.6
23.1
23.7
22.2
22.9
25.9
20.9
Avg. Wind
Speed
8.0
10.1
3.8
3.8
6.4
11.6
5.3
7.7
6.3
7.2
6.3
8.3
5.7
4.0
6.4
Avg. Wind
Speed
7.7
7.1
9.0
3.2
3.0
1.5
6.9
8.9
2.5
8.4
11.7
9.5
8.0
7.0
5.3
2.9
176
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-80-074
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
5. REPORT DATE
Limnological Conditions in Southern Lake Huron,
1974 and 1975
July 1980 issuing date
6. PE'riFCfrfMlNG ORGANIZATION CODE
7. AUTHOR(S)
Claire L. Schelske, Russell A. Moll and
Mi la S. Simmons
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Great Lakes Research Division
University of Michigan
Ann Arbor, Michigan 48109
10. PROGRAM ELEMENT NO.
1BA769
11. CONTRACT/GRANT NO.
R803086
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
Environmental Research Laboratory-Duluth
Office of Research and Development
U.S. Environmental Protection Agency
Duluth, Minnesota 55804
14. SPONSORING AGENCY CODE
EPA/600/03
15. SUPPLEMENTARY NOTES
Large Lakes Research Station, 9311 Groh Road, Grosse He, Michigan 48138
16. ABSTRACT
In 1974 and 1975, several studies were conducted on southern Lake Huron and
outer Saginaw Bay to obtain seasonal data on limnological conditions. In 1974, 44
stations were sampled on each of eight cruises conducted from April to November.
Each station was sampled at multiple depths so that more than 200 samples were
taken on each cruise. Data obtained for each sample included water temperature,
pH, specific conductance, chloride, total phosphorus, soluble reactive silica,
nitrate plus nitrite nitrogen, ammonia nitrogen, chlorophyll a^ and phaeopigments.
In 1975, five special cruises were conducted. Four of these were used to compare
phytoplankton productivity and nutrient dynamics in the frontal zone between highly
enriched Saginaw Bay and the relatively low productivity waters of southern Lake
Huron. One cruise was used to study the effect of the spring thermal bar on the
distribution of nutrients and nearshore phytoplankton standing crops. These studies
confirm that Saginaw Bay and the nearshore zone of southern Lake Huron have larger
concentrations of total phosphorus (the major growth limiting nutrient in the
system) and greater standing crops of phytoplankton than the offshore waters. They
also show that the nearshore zones, especially on the Canadian shore, differ from
the offshore waters to a greater degree during the period of the spring thermal
bar than at other times of the year.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Limnology, Water quality, water chemistry
Lake Huron
08H
B. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
189
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
177
•fy U.S. ijnvERNHFNT PPIMTINP "FFICE•198n--6^7-lK5/008P
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> m c
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