-------
TABLE 2
AVERAGE SEASONAL CONCENTRATIONS OF SOLUBLE PHOSPHORUS (As P)
IN VARIOUS SECTORS OF THE WESTERN BASIN OF LAKE ERIE (yg/l)
Season
Maumee
Bay
Southern
Nearshore
Mid-basin
Northeast
sector
(outlet)
Winter
Spring
Summer
Fall
110
25
95
90
150
50
50
50
55
25
40
30
20
20
20
20
15
-------
during wind-induced sediment resuspension and low utilization by limited
algal populations. Concentrations above 150 pg/l are probably common in
January and February. The abrupt rise in concentration at the beginning
of the winter season is followed by an equally abrupt decline at the end
of the winter season.
Soluble phosphorus data gathered on each of four quarterly cruises
during the year preceding that of the intake data are characterized by
a rather wide variability between stations and between cruises except in
the northeast quarter of the basin (Fig. 4 and Table 2). In this area a
soluble phosphorus concentration of about 20 ug/l appears to prevail
throughout the year. In contrast the Maumee Bay area seems to average
near 100 yg/l in summer, fall and winter, but drops to 25 pg/l in spring
In spring soluble phosphorus may be lower and fairly evenly distributed
throughout the basin. Summer and fall are characterized by a predict-
able decline across the basin from southwest to northeast. In winter
the cross-basin decline also occurs but shows more erratic and higher
values in the central portion of the basin. This characteristic is also
apparent to a less extent in summer.
The somewhat erratic behavior of midlake soluble phosphorus concen-
trations in the western basin is undoubtedly influenced by the mid-channel
flow of the Detroit River. That flow, containing relatively low amounts
of phosphorus, can be expected to meander over a period of time under the
influence of wind and water density differences. Of course the mid-channel
flow is bounded on either side by water of higher phosphorus content.
From the above description emerge some characteristics of seasonal
patterns of phosphorus distribution in the western basin, along with some
16
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17
-------
inferences as to the causes for the observed variability.
In winter, soluble phosphorus concentrations along shore rise rapid-
ly. The rise is not impeded at this time of year by significant biolog-
ical uptake of phosphorus because of low temperature. Low temperatures
also slow the processes of chemical reaction. These conditions allow an
accretion in phosphorus load, due mainly to increased tributary inputs
and to the early winter introduction of interstitial soluble phosphorus
during wind-induced sediment resuspension. The soluble phosphorus ac-
cretion is enhanced in late winter under the disruption reducing con-
ditions of ice cover and the rather stable temperature-density barriers
to mixing. The phosphorus accretion diminishes toward the center of the
basin and does not reach to the northeast part of the basin. The central
and northeastern portions of the basin are occupied largely by low phos-
phorus water from the high-volume main flow of the Detroit River. This
mass^of water also helps to confine the high phosphorus water to the
western and southern parts of the basin.
In early spring, concurrent with the breakup and disappearance of
ice cover3 the high soluble phosphorus content is rapidly reduced and
approaches uniformity throughout the basin. The reduction is accom-
panied by a tremendous increase in diatom population. In general the
areas which had the greatest soluble phosphorus accretion develop the
highest diatom populations. The populations decrease northeastward
across the basin, so that where soluble phosphorus had not increased
significantly neither had diatoms increased greatly.
The preceding description suggests at least a general relationship
between diatom populations and soluble phosphorus in western basin water.
18
-------
However a detailed examination reveals that the expected immediate in-
verse correlation is in fact delayed. The rapid spring reduction of
soluble phosphorus occurs, not simultaneously with a great rise in plank-
ton, but prior to it. The highest plankton populations occur just after
the soluble phosphorus content has been reduced to the average level of
spring and summer. This suggests that one or both of two things have
occurred: (I) luxury consumption of phosphorus by diatoms in their
early bloom stages or (2) the sedimentation of soluble phosphorus at the
time of ice breakup. Examination of particulate phosphorus should reveal
which of these is more likely.
Particulate Phosphorus
The particulate phosphorus as P time-space distribution in nearshore
waters of the western and central basins of Lake Erie is shown in Fig. 5.
Western Basin particulate phosphorus is more erratic and variable over
the short-term than soluble phosphorus although the annual particulate
phosphorus range and average concentration are less.
In spring nearshore particulate phosphorus (Fig. 6 and Table 3)
averages about 30 yg/l, and is considerably less than soluble phosphorus.
The concentration drops steadily across the lake to about 10 yg/l in the
northeast quarter of the basin (Fig. 7). Particulate phosphorus rises
in summer in the nearshore area to greater than 50 ug/l. Toward midlake
it falls-off rapidly to values of 10 to 15 pg/l and these values are
characteristic of most of the basin. The fall distribution of particulate
phosphorus is similar to that of summer with only a slight decline in
nearshore waters. In winter however midlake values rise to more than 30
pg/l while nearshore concentrations remain essentially unchanged at an
average of 50 yg/l. As with soluble phosphorus, particulate phosphorus
19
-------
20
FIGURE 5
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21
-------
TABLE 3
AVERAGE SEASONAL CONCENTRATIONS OF PARTICIPATE PHOSPHORUS (As P)
IN VARIOUS SECTORS OF THE WESTERN BASIN OF LAXE ERIE (pg/l)
Season Maumee Southern Mid-basin Northeast
Bay Nearshore sector
(outlet)
Winter 45 50 30 20
Spring 55 30 25 10
Summer 40 55 \5 20
Fa I I 70 50 15 20
22
-------
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O
Q.
(0
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23
FIGURE 7
-------
in the northeast quarter of the basin does not change substantially
throughout the year.
Integrating the distribution of soluble and particulate phosphorus
leads to several possible conclusions. During the winter soluble phos-
phorus increases dramatically while particulate phosphorus does not.
This indicates that particulate phosphorus from tributary inputs and
sediment resuspension settles quickly while soluble phosphorus from the
same two sources remains in solution and rapidly accretes. Lack of
plankton uptake and limited chemical activity involving phosphorus most
likely allows the accretion.
At the end of winter more than half of the dissolved phosphorus and
at least one-third of the particulate phosphorus disappear from the
waters of the western basin. Flushing from the basin can be discounted
because of the seasonal uniformity of the basin phosphorus discharge and
because inputs of phosphorus via runoff have probably increased. It is
indicated that in great part phosphorus is precipitated to the western
basin bottom sediments through a biological intermediary. However since
the loss appears to occur slightly before the height of the spring diatom
pulse, the possibility exists, that simultaneous with the luxurious con-
sumption of nutrients by algae, phosphorus removal from water to the sed-
iments may be additionally accomplished by physical adsorption on clay
and silt particles in suspension. The lake turbidity at this time of year
is especially high due to a combination of much runoff and wave stirring
of bottom sediments. Apparently physical adsorption and biological util-
ization account for an efficient, natural, phosphorus removal process.
In fact the removal mechanism is so efficient that in spring the total
-------
phosphorus content of western basin waters reaches Its lowest level.
Again it should be emphasized that phosphorus is not lost from the
basin in unusual quantities as indicated by its stability of concentra-
tion at the main outflow in the northeast corner of the basin. Rather
it is stored in the sediments through the mechanisms described above.
A moderate accretion in waterborne total phosphorus, both soluble
and particulate, occurs in summer, while a slight reduction occurs in
the fall. The summer increase is correlative with a reduction in plankton
populations, while the fall decrease most likely is the result of an in-
crease in plankton. It would appear that a fair balance is maintained
in summer and fall, and also late spring, between inputs to the basin
and precipitation to the lake bottom.
Although not completely documented in the intake data, but based
on many individual observations, in late summer blue-green algae pop-
ulations increase dramatically throughout the basin and even in places
such as the northern island area, far removed from tributary Inputs.
This suggests recycling of nutrients, including phosphorus, from the
bottom sediments. The suggestion is supported by a temporary increase
in midlake phosphorus without a concomitant increase near shore. How-
ever, the increase is short-lived and.phosphorus returns to moderate
levels, remaining there throughout the fall and until the beginning of
the winter phosphorus accretion in December.
CENTRAL BASIN
The central basin phosphorus distribution, both soluble and par-
ticulate, Is more easily described because concentrations are generally
less, short-term and long-term variations are more subdued, and area I
-------
differences are diminished. The tendency toward uniformity can be as-
cribed to the damping effects of a larger less easily disturbed basin
and the smaller input to the basin. The general annual distribution of
soluble phosphorus in the central basin is shown in Fig. 2.
Soluble Phosphorus
Central basin nearshore average soluble phosphorus is remarkably
stable for seven months of the year, including the spring and summer
seasons and part of the fall (Fig. 3 and Table 4). The average concen-
tration during this period is about 30 yg/l - only 60 percent of the
nearshore concentration in the western basin. During this period near-
shore soluble phosphorus is similar from one end of the basin to the
other.
In midlake central basin, from spring through fall, soluble phos-
phorus averages 10 to 15 yg/l or less than one-half that of nearshore
(Fig. 3 and Table 4). There is little change areally except in spring
when concentrations are lowest in the western part of the basin.
In October, centra! basin nearshore soluble phosphorus begins to
rise and by January I is averaging 40 yg/l. A relatively rapid rise
then occurs, reaching more than 100 yg/l at the beginning of March. This
peak is followed by a rapid decline to 30 yg/l again at the advent of
spring. The winter increase in soluble phosphorus is less than half the
concurrent increase in western basin nearshore waters. The high winter
period in the central basin nearshore is also characterized by a general
west to east decrease which is not apparent throughout the remainder of
the year.
Winter phosphorus data from midlake central basin is scarce but it
26
-------
TABLE 4
AVERAGE SEASONAL CONCENTRATIONS OF SOLUBLE PHOSPHORUS (As P)
IN VARIOUS SECTORS OF THE CENTRAL BASIN OF LAKE ERIE (yg/l)
Season Southwest Southeast Western Eastern
Nearshore Nearshore Mfdlake Mid lake
Winter 80 55 25
Spring 30 25 10 15
Summer 35 25 15 10
Fall 30 30 20 15
27
-------
appears that an increase in soluble phosphorus occurs, although relatively
insignificant (Fig. 4 and Table 4). The average concentration in midlake
may never exceed 25 vg/l3 that value being approached only in winter.
Particulate Phosphorus
In central basin nearshore, as in the western basin, particulate phos-
phorus is much more erratic in its time and space distribution (Figs. 5 and
6). The average concentration, except in midsummer, is comparable in both
western and central basin nearshore areas.
In the central basin nearshore, particulate phosphorus averages about
20 yg/l in spring and summer, considerably less than in the fall and winter
when an average of about 40 yg/l prevails (Fig. 6 and Tesble 5). Fall and
winter levels however are much more variable. They range from 30 to 80 yg/l
in fall and from 20 to 65 ug/l in winter. In winter there is a west to east
decrease in particulate phosphorus, not apparent during the other seasons.
In central basin midlake particulate phosphorus apparently averages
less than 10 pg/l the year-round with perhaps slightly higher values in
spring than during the other seasons (Fig. 7 and Table 5). Compared to
nearshore, the midlake has a remarkably narrow range in particulate phos-
phorus content. Central basin midlake also differs radically in this
respect from the widely variable western basin midlake.
The areal and time distribution of soluble and particulate phosphorus
in the central basin roughly parallels the distribution in the western
basin but with considerably lower values. This indicates that the same
factors of biological uptake, wind-induced sediment resuspension, and inputs
are operating in a manner similar to that In the western basin, but on a
reduced scale. One important difference is the lack of variation in
28
-------
TABLE 5
AVERAGE SEASONAL CONCENTRATIONS OF PARTICIPATE PHOSPHORUS (As P)
IN VARIOUS SECTORS OF THE CENTRAL BASIN OF LAKE ERIE (yg/l)
Season Southwest Southeast Western Eastern
Nearshore Nearshore Mfdlake Mldlake
Winter 50 35 10
Spring 15 20 10 5
Summer 20 20 5 <5
Fall 50 50 5 5
29
-------
phosphorus in summer, In the central basin, indicating perhaps a general
damping effect on all phosphorus input factors.
The winter soluble phosphorus accretion In both the central basin
nearshore and mldlake is depleted very rapidly near the beginning of spring,
As in the western basin more than half is lost to the bottom sediments.
The western part of the central basin seems to "over-react" in spring
(Fig. 4) when compared to ,,ie other portions of the basin, and concentra-
tions reach their annual low. As in the western basin the loss of soluble
phosphorus in the western portion of the central basin, accompanied also
by a loss of more than half the particulate phosphorus, indicates rapid
biological utilization or adsorption on eroded or resuspended clays, or
both, followed by rapid precipitation to the sediments.
NITROGEN DISTRIBUTION IN LAKE ERIE
Nitrogen in Lake Erie has been measured in three forms, organic
nitrogen, ammonia, and nitrate. Nitrite is normally present in insig-
nificant quantities, and therefore has not been measured as such, but is
included as part of the total nitrate analysis.
Organic nitrogen is that portion of the total nitrogen .combined in
organic compounds. Organic nitrogen should be more or less proportional
to the total biological mass. Data from Lake Erie indicate that time and
spatial variations are not as great as one might expect.
Although organic nitrogen should reflect biological productivity in
Lake Erie, it is the inorganic nitrogen forms which are essential to
promote that productivity. The inorganic forms, particularly nitrate
nitrogen, follow a more predictable pattern of concentration throughout
the year and are more easily relatable to plankton abundance than is
30
-------
organic nitrogen. However the classical materials balance, relating one
form to the other, is not read!ly apparent.
Nitrogen is vital to algal productivity, its deficiency in a marine
environment often being a limiting factor to algal biomass. Although
both ammonia and nitrate are utilized as nutrients the content of nitrate
normally shows greater depletion characteristics. It is not clear however
that nitrate is the preferred nutrient since during high algal use periods,
ammonia is continually being replenished from the sediments while nitrate
is not. In addition, the conversion of ammonia to nitrate most likely is
hampered by the lower oxidation-reduction potentials prevalent during the
summer high nutrient use periods.
WESTERN AND CENTRAL BASINS
Organic Nitrogen
The time-space distribution of organic nitrogen for one year in the
nearshore waters of the western and central basins of Lake Erie is shown
in Fig. 8.
In the western basin nearshore area, organic nitrogen in winter, sprlm
and summer averages approximately 700 yg/l but drops to about 400 yg/l in
the fall (Fig. 9 and Table 6). In western basin midlake organic nitrogen
in spring and summer averages about one-half those of the nearshore area
or about 350 yg/l. Fall and winter concentrations in western basin midlake
average about 300 yg/l. In the fall organic nitrogen approaches uniformity
throughout the basin at relatively low concentrations. Occasional rather
precipitous rises in organic nitrogen in the nearshore throughout the year
are probably due mainly to stirring and resuspension of bottom sediments
during periods of higher wind velocity and precipitation.
-------
FIGURE 8
-------
I/*" N39081IN D1NV9WO
FIGURE 9
-------
TABLE 6
AVERAGE SEASONAL CONCENTRATIONS OF ORGANIC NITROGEN
IN VARIOUS SECTORS OF THE WESTERN BASIN OF LAKE ERIE (ug/l)
Season
Winter
Spring
Summer
Fall
Maumee
Bay
500
550
500
500
Southern
Nearshore
750
700
650
400
Mid-basin
300
350
400
250
Northeast
sector
(outlet)
250
400
250
250
-------
Limited available data indicate that the concentration of organic
nitrogen in the northeast part of the basin, in the Pelee Passage outlet,
is relatively low and uniform at near 250 to 400 yg/l (Fig. 9 and Table
6). This suggests since inorganic nitrogen is also lower in these areas,
that nitrogen is accumulating significantly in western basin sediments.
When examined as averages of all stations during each sampling per-
iod, central basin nearshore organic nitrogen has a rather stable annual
pattern, averaging 500 Vg/l in spring, and decreasing steadily throughout
the summer to less than 200 yg/l in November (Fig. 9 and Table 6). It
then begins to rise and continues to rise gradually until the beginning
of spring.
The pattern of organic nitrogen in nearshore waters is more complex
when examined as variations between sampling sites during a season and
from one season to the next. For example in spring nearshore organic
nitrogen west ot Lorain averages about 700 ug/l or approximately the same
as western basin nearshore. At Lorain and eastward however, organic
nitrogen averages less than 500 yg/l and at Conneaut about 400 yg/l. In
summer nearshore organic nitrogen drops even more quickly from 600 yg/l at
Sandusky, again near the level in western basin nearshore, to about 350
yg/l at Vermilion. This concentration prevails relatively well throughout
the Cleveland area in summer but rises dramatically east of Cleveland to
700 yg/l at Madison. It then decreases again eastward.
In fall organic nitrogen Is more consistent throughout central basin
nearshore at between 300 and 400 yg/l. The extremes are in the Cleveland
area with a high averaging 600 yg/l at the westernmost Crown intake and a
low of 200 yg/l at the Baldwin intake.
35
-------
In central basin midlake organic nitrogen appears to average about
300 vig/l throughout the year (Fig. 9 and Table 7). This is not greatly
less than nearshore except in spring. At this time the lowest concentra-
tions are found in the western half of the basin at less than 200 yg/l.
However they rise to the east to more than 400 yg/l and may reach 700
yg/l near the east end of the basin. The west to east pattern in spring
in midlake is the reverse of that in nearshore. Organic nitrogen in mid-
lake, as in the nearshore, is on an average lowest in fall and the most
consistent areally, averaging 250 to 300 yg/l (Table 7).
Ammonia Nitrogen
The distribution of ammonia nitrogen, with distance and time, in
nearshore waters of the western and central basins for one year is shown
in Fig. 10.
Spring ammonia nitrogen in western basin nearshore averages about
200 ug/l and does not show great variability during the season (Fig. II).
In early summer it begins to decline and continues to do so, except for
a brief rise in October, until the middle of November when it reaches its
lowest level of less than 100 yg/l. However ammonia nitrogen then rises
dramatically to more than 400 yg/l in early December, remaining at this
level through January, then declining to spring levels.
In western basin midlake ammonia nitrogen is highest in summer, aver-
aging more than 200 yg/l (Fig. II). It drops to about 100 yg/l in fall,
and rises to about 150 yg/l in winter. It then drops again to about 100
yg/l in spring.
Central basin nearshore ammonia nitrogen Is fairly consistent through-
out the year, varying around the average of about 150 yg/l. It reaches a
36
-------
TABLE 7
AVERAGE SEASONAL CONCENTRATIONS OF ORGANIC NITROGEN IN
VARIOUS SECTORS OF THE CENTRAL BASIN OF LAKE ERIE (yg/l)
Season Southwest Southeast Western Eastern
Nearshore Nearshore Mid lake Mid lake
Winter 400 300 300
Spring 600 450 250 300
Summer 450 500 300 350
Fall 350 350 250 250
37
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FIGURE 10
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FIGURE 11
-------
temporary high In early July of more than 300 yg/l but then decreases to
its annual low of less than 100 yg/l at the end of the summer.
In central basin mid lake ammonia nitrogen is again remarkably con-
sistent throughout the year averaging between 100 and 150 yg/l (Fig. II),
not much less than in nearshore. Its lowest level of less than 100 yg/l
apparently occurs in winter.
Summarizing, it appears that ammonia nitrogen does not show a very
wide variation either areally or temporally throughout the year.
Nitrate Nitrogen
The time-space distribution of nitrate nitrogen i'n nearshore waters
of Lake Erie for one year is shown in Fig. 12.
The annual pattern for western basin nearshore nitrate nitrogen
parallels neither that for ammonia nor organic nitrogen (Fig. 13 and
Table 8). It averages about 1200 yg/l In early spring but drops dramat-
ically at the end of April to about 400 yg/l. Nitrate nitrogen rises
again to about 800 yg/l in early July, then drops sharply to less than
100 yg/l. It virtually disappears In early fall and begins to rise again
in November. The rise In late fall and early winter is remarkable, ex-
ceeding 2500 yg/l by the middle of January. In early February nitrate
nitrogen begins a similar remarkable decline to spring levels.
In western basin midlake, spring nitrate nitrogen averages about
300 yg/l but shows a marked west to east decline, from more than 500 to
about 200 yg/l (Fig. 14 and Table 8). The lowest midlake level of about
50 yg/l occurs In summer and then rises to about 150 yg/l in fall. As in
nearshore a remarkable nitrate nitrogen rise occurs In winter to an average
of about 600 yg/l, but again with a marked west to east decline, the
-------
FIGURE 12
-------
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FIGURF 13
-------
TABLE 8
AVERAGE SEASONAL CONCENTRATIONS OF NITRATE NITROGEN
IN VARIOUS SECTORS OF THE WESTERN BASIN OF LAKE ERIE (ug/l)
Season
Winter
Spring
Summer
Fall
1C
Season
Winter
Spring
Summer
Fall
Maumee
Bay
1,500
800
<50
100
AVERAGE SEASONAL
J VARIOUS SECTORS OF
Southwest
Nearshore
600
600
100
100
Southern
Nearshore
1,700
800
250
200
TABLE 9
CONCENTRATIONS OF N
THE CENTRAL BASIN
Southeast
Nearshore
250
400
150
175
Mid-basin
600
300
75
175
*
Northeast
sector
(outlet)
350
200
<50
175
ITRATE NITROGEN
OF LAKE ERIE (yg/l)
Western
Midlake
250
200
<50
<50
Eastern
Midlake
-
<50
<50
<50
-------
c
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FIGURE
-------
concentration at the northeast corner of the basin being about 300 yg/l.
Central basin nearshore nitrate nitrogen follows a reasonably smooth
annual curve, highest in late winter, (600 yg/l or more) and lowest In late
summer (0-50 yg/l). A short, relatively sharp nitrate nitrogen decline
occurs at the end of April followed by a slight rise, perhaps correspond-
ing to the similar but generally more obvious trend in western basin near-
shore.
At all times nitrate nitrogen shows significantly different areal
patterns in central basin nearshore (Fig. 13 and Table 9). For example
in winter, nitrate nitrogen declines from more than 800 yg/l at Sandusky
to less than 200 yg/l at Conneaut. In spring it is relatively constant
from Sandusky to Cleveland where it declines. Then it rises to its highest
level (600 yg/l) eastward at Mentor, and declines again eastward. In sum-
mer and fall nitrate nitrogen is relatively stable throughout the entire
distance at less than 200 yg/l.
A similar west to east nitrate nitrogen distribution but at lower
levels, exists in central basin midlake (Fig. 14 and Table 9). In winter
nitrate nitrogen decreases from about 350 yg/l at the west end of the basin
to about 50 yg/l at the center of the basin. In spring nitrate nitrogen
reaches its highest level (400 yg/l) at'the center of the basin, declining
eastward to less than 50 yg/l. In summer and fall midlake nitrate nitrogen
is uniformly low throughout - less than 50 yg/l.
Organic-Inorganic Nitrogen Ratios
To determine whether nitrogen is a limiting factor In the biological
productivity of any lake, in addition to actual concentrations, It is nec-
essary to consider the proportion of inorganic to organic nitrogen existing
-------
at any one time. As long as Inorganic nitrogen exceeds organic nitrogen
(assuming organic nitrogen is directly related to biomass) this nutrient
cannot limit biological growth. However when organic nitrogen exceeds
inorganic, it is possible for nitrogen to be a limiting factor, simply
because more inorganic nitrogen is necessary for comparably continuing
growth rates than is available. Obviously such a condition cannot per-
sist for any significant length of time.
The average concentration of inorganic and organic nitrogen for all
samples in central basin nearshore for each sampling period is plotted
on Fig. 15. Fig. 16 shows similar data for the western basin. In the
western basin organic nitrogen exceeds inorganic from the middle of July
through the middle of November. In the central basin organic nitrogen
clearly exceeds inorganic from the middle of July through October. Dur-
ing these times nitrogen is potentially limiting to further algal growth
except possibly for the blue-green nitrogen-fixers.
Averaging all nearshore data for the entire year, the organic and
inorganic portions of the total nitrogen balance fairly well - 52% organic
vs. 4Q% inorganic.
WATER TEMPERATURE
Figure 17 shows the temperature distribution in nearshore waters for
spring 1968 through winter 1968-69. This pattern is probably similar,
except for possible minor variations, for any year.
Figure 18 shows the average water temperature curve for the Ohio State
Fish Hatchery at Put-in-Bay for March 1968 through March 1969, superimposed
on the average annual curve (average for 45 years) at the hatchery. Al-
though the 1968-69 curve is not far from the average, it does show departures
-------
0>
I5OO •
1000
500
Dashed line - inorganic N
Solid line - organic N
Shaded - organic > inorganic
7/1
8/1
9/1
ro/i
11/1
e/i
1/1/69 2/1
4/1/158 5/1 6/1
FIG. 15 COMPARISON OF ORGANIC AND INORGANIC NITROGEN IN
CENTRAL BASIN NEARSHORE FOR ONE-YEAR CYCLE
3/1
3500
3OOO >
25OO •
C- 2000 •
o>
1500 /
1000
5OO •
Dashed line - inorganic N
Solid line - organic N
Shaded - organic =- inorganic
/\
4/1/68 5/1
6/1
r/i
8/1
9/1
10/1
ll/l
12/1 1/1/69 Z/\
s/i
FIG. 16 COMPARISON OF ORGANIC AND MORGANS NITROGEN IN
WESTERN BASIN NEARSHORE FOR ONE-YEAR CYCLE
-------
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FTiXRE 17
-------
M'A 'M'J 'J'A'S'O'N'D ' J ' J
FIG. 18 WATER TEMPERATURE AT PUT-IN-BAY
Dashed line 50-year average
Solid line 1968-1969
4-9
-------
which may have been significant in lake biological processes. Spring
water temperatures were above average while in the first half of summer,
water temperatures were below average. From about August I until mid-
December, water temperatures were above average from I to 3°F (0.5 to 2°C),
The curve of average water temperatures for all intake sampling stations
closely parallels, but is slightly lower than that for Put-in-Bay. In
general, nearshore water temperatures rise more slowly in the central
basin than in the western basin. Lower values reflect deeper water and
greater distance from shore. (See Table I).
AIR TEMPERATURE
Figure 19 A indicates that the average air temperature curve at
Cleveland for the year described also closely follows the long-term
average but with slightly cooler temperatures in the spring and warmer
in the early summer of 1968.
SUNSHINE AND SOLAR RADIATION
Figure 19 B, depicting average monthly percent of possible sunshine
for the year of study, superimposed upon the long-term average, indicates
that in this respect the year departed rather far from the average. This
may have had a significant influence upon productivity during the year.
Early spring had a greater than normal amount of sunshine. Late spring
and early summer were rather far below the average as were late fall and
early winter.
Solar radiation, Figure 19 C, was above average in early spring and
below average in late spring and early summer. A particularly non-
characteristic feature of the radiation curve occurred in May when the
radiation was less than in April, coinciding with a significant drop in
50
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»-
S 10
•>
S '
-10
A M
JJASONDJ F
1968 1969
A. MONTHLY AVERAGE AIR TEMPERATURE
MAM
D. MONTHLY AVERAGE WIND VELOCITY
E. MONTHLY AVERAGE PRECIPITATION
B. MONTHLY AVERAGE % POSSIBLE SUNSHINE
600
SCO
2
300
w V
i
zoo
lOo'r
^
—s
MAM
A S 0 N 0 J F
I96B 1969
C. MONTHLY AVERAGE SOLAR RADIATION
0 N 0 J
1968 196*
F. MONTHLY AVERAGE LAKE LEVELS
(U.S. Lake Survey Data)
FIG. 19 MONTHLY AVERAGES OF VARIOUS PHYSICAL FACTORS AFFECTING LAKE ERIE.
All data from U. S. Weather Bureau a|t Cleveland unless otherwise noted.
Dashed lines - longterm averajge. Solid lines - 1968-69.
51
-------
percent of possible sunshine. A concurrent rise in inorganic nitrogen
(Fig. 15 b) may be related. Radiation on the average should, and does,
follow a smooth curve coinciding with seasonal expectations.
WIND
Average monthly wind velocities at Cleveland for the study period
are plotted as an annual curve in Figure 19 D along with the long-term
averages. The year was slightly calmer than normal, December being the
only month when the long-term average was exceeded. September was very
calm which may have been reflected in perhaps higher than normal blue-
green phytoplankton populations.
PHYTOPLANKTON
Figures 20, 21, 22, 23, and 24 show nearshore population distribu-
tion of the dominant phytoplankton in Lake Erie western and central basins.
Diatoms (Figs. 20 and 21) are by far the dominant forms3 numerically speak-
ing j reaching their largest populations in late winter and early spring.
This maximum pulse occurs when water temperatures are 5°C or less and
rising and just after nitrate has reached its maximum. Diatoms reach a
minimum in summer and generally increase through fall.
Although not reaching the extreme populations of other types, green
algae uniquely exist at significant populations throughout the year (Fig.
22). Green algae dominate the phytoplankton in late spring and early
summer when the lake temperature is rising and between 10°C and 15°C3 and
when nitrate levels are intermediate and declining.
The blue-greens, Figs. 23 and 24 are virtually absent much of the
year bu+ may show a growth explosion in late summer and early fall. They
-------
53
FIGURE 20
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FIGURE 21
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FIGURE 22
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56
FIGURE 2J