-------
BIOLOGICAL RESULTS
Introduction
A study of the biological conditions in Lake Huron was
initiated in 1965 t>y the FWPCA. Major surveys were made in June
and August of the deepwater areas of Lake Huron, and three surveys
of the nearshore areas and Saginaw Bay were made in the summer of
1965• A November deepwater survey of southern Lake Huron sampled
the phytoplankton of that area. In all, j6 different stations
were sampled for biology data during the 1965 studies. The
following samples were collected in the biological study of Lake
Huron: benthic macroinvertebrate samples - 157; phytoplankton
population counts - 2Lh; and chlorophyll concentration analyses -
9^. Field observations on the water transparencies and bottom
characteristics were also routinely noted.
The purpose of this study was to obtain information on general
biological conditions of the lake; locate areas of biological
degradation; and supplement bacteriological, physical, and chemical
data collected during the same period of study.
For comparative and descriptive purposes, Lake Huron was
divided into six areas: North Channel, Georgian Bay, Northern
Lake Huron, Saginaw Bay, the mouth of Saginaw Bay, and southern
Lake Huron. The range of stations that extended from Tawas Bay
to Port Austin was considered the mouth of Saginaw Bay. The sta-
tions located in the main body of Lake Huron, north of and including
the stations in the AuSable range, were considered as northern
260
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Lake Huron. Stations "below this range in Lake Huron were listed as
southern Lake Huron.
Benthic Macroinvertebrates
Three zones of biological activity characterize the floor of
lakes. These include the littoral zone from the edge of the water
to the limit of rooted aquatic vegetation; the sub-littoral zone
from the littoral zone to the upper boundary of the hypolimnion;
the profundal zone all of the lake bottom up to the hypolimnion.
The region of the lake where there is a rapid change in tempera-
ture per unit of depth is known as the thermocline.
Factors such as the characteristics of the substratum, the
quality of the water, and certain physical features such as depth,
light, currents, wave action, temperature, and morphometry of the
basin determine the kinds and numbers of benthic fauna. The littoral
zone generally contains a variety of species, whereas the profundal
zone supports only a few species. The number of species and indi-
viduals decreases with increasing depth. The benthic fauna of the
profundal zone in the Great Lakes is usually composed of sludge-
worms (Oligochaeta), fingernail clams (Sphaeriidae), scuds (Amphipoda),
bloodworms (Tendipedidae), and opposum shrimp (Mysis relicta).
Benthos preferring organic sediments are known as pollution-
tolerant; those which require an unpolluted habitat are considered
pollution-sensitive. Pollution-tolerant benthic fauna include
aquatic sow bugs(lsopoda), lung-breathing snails (Pulmonata), leeches
(Hirudinea), sludgeworms, fingernail clams and bloodworms.
261
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Pollution-sensitive benthos include scuds, opposum shrimp, gill-
breathing snails (Prosobranchia), pearl button clams (Unionidae),
mayfly larvae (Ephemeroptera) caddisfly larvae (Trichoptera), and
aquatic beetles (Coleptera)o
Phy toplankton
Phytoplankton are suspended or slightly motile microscopic
plants existing near natural buoyancy. Under suitable conditions
of water movement, temperature, and light, phytoplankton popu-
lations increase, with an increase in nutrients. For cell growth,
algae need phosphorus, nitrogen, potassium, iron, calcium, and
organic substances such as vitamin B12 and thiamine,. Algal growth
is stimulated as phosphorus increases, however, nitrogen and other
nutrients must also be present if algal production is to continue.
Phosphorus can be recycled within a lake for several years without
being replenished, enabling crops of algae to succeed themselves.
The kinds of algae that inhabit a body of water are important
indices of the general water quality. In nutrient-poor lakes such
as Lakes Michigan and Superior, the diatoms - Tabellaria, Aster-
ionella, Synedra, and Fragilaria - are predominant. In contrast,
other diatoms, blue-greens and euglenoids, prefer nutrient-enriched
waters of eutrophic lakes. Anacystis, Oscillatoria, Stephanodiscus,
Cyclotella, and Melosira are often the dominant genera. Plankton
algae rarely exceed 500 organisms/ml in oligotrophic waters. Stand-
ing crops in excess of 1,000 organisms/ml are considered indicative
of enrichment.
262
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The attached algae Cladophora is also encouraged by nutrients,
especially phosphates. Where sufficient light and turbulence are
available,, it can cover all suitable substrates. The long fila-
ments of Cladophora often break off and litter beaches, clog water
intakes, and foul fishing nets. Dense growths are not common to
the oligotrophic Great lakes.
Light Penetration
Water transparencies of less than ten feet in lakes often
occur as a result of algal blooms or excessive turbidities. Oli-
gotrophic lakes are characterized by their exceptionally clean
waters. Secchi disc transparencies of over 20 feet are comiron in
the Great Lakes, and readings of over 50 feet have been found in
many areas. The light penetration characteristics of a lake usually
dictate' the production and distribution of the phytoplankton. The
availability of light energy is important for plant growth and the
primary productivity of a lake.
Chlorophyll
The amount and type of chlorophyll present in the water is an
indicator of the predominant kind of algae and an estimate of the
l
relative productivity. Chlorophyll pigments can be separated into
different types. The most common are chlorophylls a, b, and c.
All types of algae contain chlorophyll a. The green algae have,
in addition to chlorophyll a, chlorophyll b. The diatoms and brown
flagellated algae contain the pigments a and c. Blue-green algae
contain only chlorophyll a. '
263
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Discussion and Results
Physical Observations
Lake Huron is considered to be geologically young and bio-
logically unproductive. The lake basin is deep (average depth -
196 feet) and becomes thermally stratified during the summer and
winter. Its clear waters offer little interference to light
penetration. The lake basin has an unusually long and irregular
shoreline caused by many large islands, peninsulas, and bays.
Water transparency measurements were made by both Secchi
disc and submarine photometric methods. The Secchi disc extinction
depths and one percent surface light penetration depths (euphotic
zone) for the deepwater and nearshore areas are reported in Tables
50 and 51 along with observations on sampling depths and bottom
compositions. Table 52 summarized the Lake Huron Basin physical
observations and noted the mean euphotic zone to be 78 feet in
the deepwater areas. Secchi disc readings averaged between one-
half and one-fifth of the euphotic zone depth during these surveys,
or approximately 22 feet. The August cruise had an average Secchi
disc reading of 27 feet, while June had an average of 20 feet.
Saginaw Bay and the nearshore areas of Lake Huron had much shallower
waters and more turbid conditions (Figure ih). The average Secchi
disc extinction depth for Saginaw Bay was eight feet, while the
nearshore areas averaged twelve feet. Georgian Bay and northern
Lake Huron had the deepest euphotic zones and Secchi disc readings
(Figure 16).
The submarine photometer readings are reportedly more indicative
-------
of the actual water transparency "because of the various human
errors involved in Secchi disc interpretations.
Silt, sand, and clay were the most often reported bottom
types in deep water Lake Huron. The main body of Lake Huron was
sampled between depths of 30 to 700 feet. The average sampling
depth for bottom organism collections was 170 feet in deepwater
areas. Nearshore sampling ranged from 5 to 66 feet and averaged
2k feet. Saginaw Bay was sampled at an average depth of 33 feet.
Benthic Macroinvertebrates
The benthic macroinvertebrates from Lake Huron and Saginaw
Bay were identified and listed in Table 53- Twenty major taxc-
nomic groups of organisms were found.
At the Lake Huron deepwater stations, the predominant benthic
organism was the scud (Pontoporeia affinis). Sludgeworms, finger-
nail clams and bloodworms were the most numerous organisms, in
the order named. This assemblege of aquatic fauna is character-
istic of oligotrophic conditions in the Great Lakes. Scuds
comprised 58 percent of the total benthic population in the main
body of the lake. They were also predominant in the deepest areas
(> 200 feet) where they made up 69 percent of the population.
Table 5^- contains the depth distribution data.
Average benthic population for the 1965 lake surveys was
found to be 78 organisms per square foot (Table 55). Georgian
Bay and southern Lake Huron were the least populous areas for
benthic macroinvertebrates, while the mouth of Saginaw Bay supported
265
-------
over twice the average number found throughout the lake. Table 56
contains the individual deepwater station information for the
various areas. Samples collected in August averaged IT more in-
dividuals per square foot than those collected in June.
Saginaw Bay contained the highest standing crops of benthic
organisms. The average population was over five times as numerous
as those found in Lake Huron and almost three times as great as the
nearshore areas.
Sludgeworms were the most common organisms in Saginaw Bay_,
averaging over 300 per square foot. Scud populations were compari-
tively small and comprised only eight percent of the benthic orga-
nisms in Saginaw Bay. A small area immediately adjacent to the
Saginaw River mouth had an average sludgeworm population of 2,500
per square foot. The pollution-sensitive scuds were restricted
to less than ten per square foot for a distance of fifteen miles
from the Saginaw River mouth.
Sandy bottom areas supported twice the average benthic organism
populations, while clay bottom substrates had one-half the average
number of benthic macroinvertebrates. Silty and rocky areas of
Lake Huron supported approximately the same numbers of organisms.
The higher numbers of scuds and sludgeworms, found in the
North Channel and the channels leading out of the North Channel
into Lake Huron, are of interest. The increase in macroinvertebrate
populations may have been due to the close proximity of productive
nearshore areas and favorable bottom compositions. Scuds numbered
266
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less than ten per square foot in a narrow zone in the middle of the
lake, extending southward from about Rogers City to Port Huron
(Figure 17). Sludgeworm populations of less than ten per square
foot were found in the middle of the lake, in Georgian Bay, and
the northwestern part of the lake (Figure 18).
At the nearshore stations, scuds comprised only k percent and
oligochaetes 6k percent of the total organisms. Table 57 contains
this data. The most populous sample, collected near Rogers City,
contained over 750 organisms per square foot, mostly sludgeworms
and fingernail clams. Hyalella and Gammarus were the predominant
scuds at the majority of stations. Caddisflies or mayflies were
collected in nearly every nearshore area.
A greater variety of organisms was found in the harbor and
nearshore areas than in either the main body of the lake or in
Saginaw Bay, reflecting the shallower waters and increased nutrient
availability. The greatest variety in any of the harbor or near-
shore areas was found near Cheboygan, Rogers City and Alpena where
over ten major taxonomic groups were identified. The least vari-
ety, only three major taxonomic groups, was found in the Straits
of Mackinac and near Au Sable.
The highest scud concentrations, averaging h8 per square
foot, were collected near Cheboygan, while Harbor Beach exhibited
none at all. Sludgeworm concentrations averaging over 620 per
square foot were found near Port Sanilac. Benthic populations
increased slightly at the harbor and nearshore stations in the
267
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summertime, and averaged 153 per square foot for all seasons.
Phytoplankton
Data from the deepwater phytoplankton samples at the surface,
top of the thermocline, euphotic zone, and near the bottom are in
Tables 58, 59> 60 and 6l. The standing crops of phytoplankton in
the deepwater areas of Lake Huron were relatively low, ranging
from 70 to 1,930 organisms/ml at the surface (Table 58) and av-
eraging 650 organisms/ml throughout the lake. The average phy-
toplankton populations were listed according to water depth areas
on Table 62.
Nearshore stations averaged 1,^80 phytoplankters per milliliter,
or over twice that of the deepwater stations. Population increases
between June and August were noted at most nearshore stations, as
well as the deepwater areas. However, population pulses were
found at Rogers City (5,740/ml), Harrisville (4,550/ml), and Oscoda
(ll,780/ml). Rogers City had a bloom of green flagellates; Harris-
ville had a bloom of Navicula near the harbor entrance; and Oscoda
had a spring pulse of green flagellates (Table 63).
The mean number of deepwater phytoplankton taken in June was
520/ml. An increase in the populations was noted during the
August and November surveys. Mean populations in August and Nov-
ember were 760/ml and 720/ml, respectively. In June, the predom-
inant genera found, in order of abundance, were: Rhizosolenia,
Synedra, Cyclotella-Stephanodiscus, various green flagellates,
and Tabellaria. Predominant species in the November samples were
268
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mainly Cyclotella-Stephanodiscus, with fewer numbers of Oscillatoria,
Synedra, and Navicula.
Surface phytoplankton sampled in June found standing crops in
excess of 1,000/ml throughout most of Saginaw Bay and in one small
area of the North Channel (Figure 19)- The average density for
all of Lake Huron was only 520/ml. By August, the area of excess-
ive algal growth had extended to surround the Thumb area of Mich-
igan and parts of the North Channel and Mackinac Straits area.
Isolated areas around Goodrich, Ontario, the northern part of
Georgian Bay, and northeast Lake Huron also had standing crops in
excess of 1,000/ml (Figure 20). Huge open water areas in northern
and central Lake Huron had less than 500 organisms/ml during tooth
surveys, and averaged only 380 organisms/ml. Mean'southern Lake
Huron phytoplankton densities ranged between 170 and 310 organisms
higher per milliliter than those in northern Lake Huron. Stations
across the mouth of the Saginaw Bay had average counts of over
1,000 organisms/ml, while Saginaw Bay proper supported mean popu-
lations in excess of 7*000 organisms/ml. Blooms of blue-greens
were found to occur in the late summer in Saginaw Bay; however,
no excessive numbers were discovered in Lake Huron.
Samples taken near the top of the thermocline, one percent
surface light zone, and near the bottom showed very little change
in the population densities (Table 62). Nuisance forms of algae
were never predominant and population blooms were not detected in
the deepwater areas.
269
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Chlorophyll
Chlorophyll analyses in June and August of the surface and
near "bottom vaters of Lake Huron are presented in Tables 6k and
65. Average chlorophyll values are presented "by area in Table 66.
Contrary to phytoplankton population counts, the June sampling
survey showed higher average chlorophyll concentrations than the
August survey. However, the lake-wide distribution of chlorophyll
and phytoplankton concentrations showed a definite correlation
(Figure 15)- Highest values were found in Saginaw Bay, while
Georgian Bay and northern Lake Huron had the two lowest concentra-
tions. There was a slight increase in the amount of chlorophyll
in the bottom-most samples, compared with the surface samples.
The phytoplankton analyses also showed slight population increases
near the bottom. In clear water, it is not uncommon for the high-
est chlorophyll and phytoplankton densities to' occur in shaded
areas well below the surface. Figure 16 shows that the light pen-
etration in Lake Huron is closely related to the density of the
algal populations.
The summary data tables and figures have shown that different
areas of Lake Huron have varying degrees of biological activity.
Phytoplankton and benthic organisms are more dense, chlorophyll
higher, and light penetrations lower in the bay and inshore areas.
Although shallow areas are normally much more productive, pol-
lution-tolerant organisms are not usuaUy predominant. The effects
of water quality degradation on the biota are first noted in areas
of relatively small water volumes.
270
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Saginaw Bay supported the highest populations of both algae and
bottom-dwelling organisms found during this study. Pollution
tolerant sludgeworms and blue-green algae were often the pre-
dominant community forms in Saginaw Bay. Nearshore areas that
supported pollution-tolerant communities include parts of Thunder
Bay near Alpena and Harbor Beach.
The biota of the deepwater areas reflects upon the true
oligotrophic nature of most of Lake Huron. Low numbers of pol-
lution-sensitive organisms inhabited the deep mid-lake areas.
Accelerated eutrophication is beginning in some major bays
and harbors of Lake Huron. These areas are much more important to
the great mass of aquatic life in Lake Huron, and therefore should
be protected from degradation.
Pesticides
Pesticides, necessary to our mass production economy, have
been indicated as despoilers of the environment. Improper use
of pesticides are well documented causes of fish kills. Hot so
well documented are the long-term effects of residual low level
pesticide concentrations which have been observed in waters, plants
and fish. The universality of the pesticide problem is evidenced
by the fact that residues of DDT, in extensive use only since the
end of World War II, have been found in the flesh of animals in
the polar regions many thousands of miles from the nearest known
point of use.
271
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The danger from pesticides lies not in the spectacular fish
kills which make headlines "but in subtle long-term changes to the
total environment.. A silent spring is faced "by Michigan's arobi-
tious Coho salmon planting program. Pesticides have been dis-
covered in the eggs stripped from salmon migrating upstream after
their return from the waters of Lake Michigan. Although pesticide
application rates on land may result in low levels in the surface
waters, the various parts of the aquatic food chain from the once-
celled plants and animals up to man have the ability to concentrate
and retain in their systems the pesticides. Eagle and osprey
nests in parts of the country lie barren because the fish consumed
by the majestic predators contained levels of pesticide sufficient
to cause sterility, if not death. Ducks, too, in eating aquatic
plants ingest pesticides which are taken up in the fatty tissues -
at harmless concentrations - until a cold winter snap requires
the utilization of stored fat creating toxic levels in the blood
stream and sudden death.
Much information is needed. Most critical is an accurate
, !
inventory of pesticide use in the basin - both by, commercial users
and individuals. Research is needed on the effects of pesticides
particularly in such a complex situation as the aquatic food chain.
' i '
Lethal levels of pesticides are reasonably well defined, but sub-
lethal levels which permit lethargic survival or cause genetic
malfunctions or sterility eliminating the species are not as well
known. Synergistic effects of other pesticides, pollutants, or a
variety of water quality indices should be determined to more
272
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adequately predict the effect of pesticide applications in the
basin.
273
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Table 50. BIOLOGICAL DATA - PHYSICAL OBSERVATIONS
Lake Huron Deepwater - 196 5
Bottom Types
Euphotic
Secchi Zone
Station Date
North Channel
H808 6-23
8-30
H809 6-23
8-30
H8lO 6-23
8-29
H812 6-23
8-29
Georgian Bay
H382 6-16
8-23
H381* 6-16
8-23
H386 6-17
8-21*
H388 6-17
Q-2k
Depth
Feet
116
132
66
96
ko
^3
122
125
99
83
86
86
168
178
205
195
Disc
Feet
13
23
15
23
15
18
13
21
30
33
25
31
26
28
23
31
Depth
Feet
ho
56
*5
56
To Bottom
To Bottom
1*6
66
82
To Bottom
82
82
96
99
82
99
Northern Lake Huron
H8l4 6-21
8-29
H530 6-21
8-27
H532 6-21
8-27
H53U 6-22
8-29
116
lit 9
33
30
106
125
320
277
15
20
16
20
18
26
15
25
66
86
To Bottom
To Bottom
76
76
63
82
Silt, clay, ooze
Silt, clay, ooze, sand
Sand
Silt, ooze
Rock, gravel
Silt, clay, gravel
Soft "brown clay, sand
Silt, clay
Silt, ooze
Rock
Clay, rock, gravel
Silt, clay, ooze
-------
Table 50. BIOLOGICAL DATA - PHYSICAL OBSERVATIONS(cent'd)
Lake Huron Deepwater - 1965
Station
Northern
H536
H*l 20
H>*22
Ek2h
Jl4 ^D
TT li Oft
T-fli "5O
H370
H372
H37^
H376
H378
H380
Date
Depth
Feet
Lake Huron (cont
6-22
8-29
6-20
8-27
6 -2k
8-27
6-2h
8-30
6-22
8-30
6-22
8-30
6-22
8-29
6-20
8-26
6-19
8-26
6-19
8-26
6-19
8-26
6-19
8-26
6-19
8-23
73
92
106
99
287
310
479
396
211
218
182
188
106
76
66
73
109
102
5^5
578
627
700
317
300
238
257
Secchi
Disc
Feet
'd)
13
13
16
28
21
26
21
26
15
26
12
21
Ik
25
16 To
30
28
31
33
la
25
35
20
38
20
31
Euphotic
Zone
Depth
Feet
66
5^
86
79
89 '
7^
76
99
76
109
56
76
50
-
Bottom
66
76
82
102
99
99
99
86
82
86
99
Bottom Types
Silt, rock
Silt, clay, ooze
Silt, ooze
Silt, ooze
Silt, sand, gravel
Clay, sand, rock,
gravel
Sand
Bock
Silt, ooze
Silt, hard clay
Silt, clay, ooze
Silt
275
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Table 50, BIOLOGICAL DATA - PHYSICAL OBSERVATIONS (cont'd)
Huron Deepwater - 1965
Euphotic
Secchi Zone
Station
northern
H320
H321
H322
H324
H326
H328
H330
Mouth of
H200
H202
Date
Depth
Feet
Lake Huron (cont
6-15
8-21
11-11
11-18
11-11
11-18
6-15
8-22
11-11
11-18
6-15
8-22
6-15
8-22
6-15
8-22
6-16
8-25
Saginaw
6-14
8-21
11-16
11-23
6-14
8-21
11-16
11-22
175
175
-
221
224
248
280
545
548
185
191
59
66
Bay
66
66
63
86
82
79
86
Disc
Feet
•d)
21
31
20
17
• 20
21
26
31
21
16
26
4l
30
46
21
31
20
23
17
17
20
17
18
17
20
18
Depth
Feet Bottom Types
82 Silt, sand
82
73
73
73
79
86 Silt, clay, sand
82
79
73
86 Silt, clay
132
92 Silt, soft brown clay
132
82 Silt, clay, sand
To Bottom Sand, rock, gravel
To Bottom
To Bottom Silt, sand
To Bottom
To Bottom
To Bottom
76 Silt, sand
To Bottom
To Bottom
To Bottom
276
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TABLE 50. BIOLOGICAL DATA - PHYSICAL OBSERVATIONS (cont'd)
Lake Huron Deepvater -
Euphotic
Secchi Zone
Station
Mouth of
E20k
H206
Southern
H250
H252
H25U
H130
H132
H133
H134
Date
Saginaw
6-14
8-21
11-16
11-22
6-14
8-21
11-16
11-22
Depth
Feet
Bay (cont
106
102
82
66
63
63
63
Disc
Feet
M)
18
23
21
17
18
17
17
20
Depth
Feet Bottom Types
63 Silt, sand
76
To Bottom
86
63 Silt, sand, gravel
To Bottom
To Bottom
To Bottom
Lake Huron
11-11
11-18
11-11
11-18
ll-ll
11-18
6-11
8-20
11-19
6-11
8-20
11-10 •
11-19
6-11
6-10
8-20
11-10
11-21
..
-
_
201
191
182
204
280
206
221
12
7
21
25
22
28
15
28
ko
26
20
23
18
33
20
10
To Bottom
99
89
79 Silt, clay
99
73 Silt, hard clay, sand
99
82
66 Silt
66 Silt, clay, sand
82
56
277
-------
Station Date
Table 50. BIOLOGICAL DATA - PHYSICAL .OBSEKVATIONS (cont'd)
Lake Huron Deep-water - 19°5
Euphotic
Secchi Zone
Depth Disc Depth
Feet Feet Feet Bottom Types
Southern Lake Huron (cont'd)
HI 36
KL02
KL06
6-10
8-20
11-10
11-20
6-10
8-19
11-9
11-21
6-10
8-19
11-9
11-21
33
31
36
38
36
36
37
53
12
12
2
1
25
23
16
13
25
20
15
11
To Bottom Rock
7
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
Sand, rock, gravel
Silt, sand, rock, gravel
278
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Table 51.
BIOLOGICAL DATA - PHYSICAL OBSERVATIONS
Lake Huron Nearshore -
Station
Mean
Depth
Feet
Mean Euphotic
Secchi Zone
Disc
Feet
Depth
Feet
Bottom Types
Straits of Mackinac
H500
Cheboygan
H523
E52k
H525
Rogers City
H^OO
HfcOl
H^02
E&03
Ekok
Thunder Bay
H361,
H362
H366
Harrisville
H351
H352
H353
Oscoda
H301
H303
H30^
66
13
23
10
37
9
28
27
25
23
13
18
20
31
21
20
15
1^
20
10
10
10
27
9
2k
10
9
7
11
7
13
15
15
3
3
k
-
To Bottom
-
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
To Bottom
_
-
_
Clay, rock
Silt, clay,
Silt, clay,
Silt, clay,
Clay, rock
Fine sand
Clay, sand
Silt, clay,
Fine sand
Ooze, sand,
Silt , sand
Silt , sand
Sand
Silt, sand
Rock
. Sand
Sand
Sand
sand, gravel
sand, detritus
sand, gravel
gravel
paper fibers
279
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TalDle 51. BIOLOGICAL DATA - PHYSICAL OBSERVATIONS (cont'd)
Lake Huron Nearshore - 1965
Station
Harbor Beach
ST-1*
ST-2**
KL21
EL23
KL25
EL27
Fort Sanilac
KLL2
HU3
HL15
Mean
Mean Secchi
Depth Disc
Feet Feet
5 3
8 3
25 13
40 17
k3 17
33 1^
18 Ik To Bottom
k6 15 To Bottom
18 13 To Bottom
Euphotic
Zone
Depth
Feet Bottom Types
Silt, ooze, sand
Silt, ooze
Rock, gravel
Rock, gravel
Sand, rock, gravel
Silt, clay, rock
Sand, rock, gravel
Sand, rock, gravel
Silt, sand, rock
*ST-1 500 feet south of Coast Guard Station
**ST-2 2000 feet south of Coast Guard Station
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