ALGAE - TEMPERATURE
NUTRIENT
RELATIONSHIPS
AND DISTRIBUTION
IN LAKE ERIE
1968
ENVIRONMENTAL PROTECTION AGENCY
WATER QUALITY OFFICE
REGION V
LAKE ERIE BASIN
MAY 1972
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ALGAL-TEMEERATURE-NUTRIENT RELATIONSHIPS
AND DISTRIBUTION IN LAKE ERIE
By
Robert P. Hartley
and
Chris P. Potos
ENVIRONMENTAL PROTECTION AGENCY
WATER QUALITY OFFICE
REGION V
LAKE ERIE BASIN
MAY 1972
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TABLE OF CONTENTS
Page
SUMMARY AND CONCLUSIONS 1
INTRODUCTI ON 8
PHOSPHORUS DISTRIBUTION IN LAKE ERIE II
Western Basin
Soluble Phosphorus 12
Particulate Phosphorus 19
Central Basin
Soluble Phosphorus 26
Particulate Phosphorus 28
NITROGEN DISTRIBUTION IN LAKE ERIE 30
Western and Central Basins
Organic Nitrogen 31
Ammon i a N i trogen 36
Nitrate Nitrogen 40
Organic-Inorganic Nitrogen Ratios 45
WATER TEMPERATURE 46
AIR TEMPERATURE 50
SUNSHINE AND SOLAR RADIATION 50
WIND 52
PHYTOPLANKTON 52
DISSOLVED OXYGEN 58
CHEMICAL OXYGEN DEMAND 61
CORRELATION OF FACTORS AFFECTING ALGAL PRODUCTIVITY 61
Centric Diatoms
Water Temperature 62
Soluble Phosphorus and Temperature 63
Inorganic Nitrogen 64
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TABLE OF CONTENTS
Pennate Diatoms
Water Temperature 70
Soluble Phosphorus and Temperature 70
Inorganic Nitrogen and Temperature 72
Green Coccoid Algae
Water Temperature 73
Soluble Phosphorus and Temperature 75
Inorganic Nitrogen and Temperature 76
Blue-green Coccoid Algae
Water Temperature 78
Soluble Phosphorus and Temperature 80
Inorganic Nitrogen and Temperature 80
Blue-green Filamentous Algae
Water Temperature 82
Soluble Phosphorus and Temperature 82
Inorganic Nitrogen and Temperature 84
FUTURE INVESTIGATIONS 86
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LIST OF TABLES
Table No. Title Page
I Summary of Water Intake Physical Data 10
2 Average Seasonal Concentration of Soluble Phosphorus 15
in Various Sectors of the Western Basin of Lake Erie
3 Average Seasonal Concentrations of Partlculate 22
Phosphorus in Various Sectors of the Western Basin
of Lake Erie
4 Average Seasonal Concentrations of Soluble Phosphorus 27
in Various Sectors of the Central Basin of Lake Erie
5 Average Seasonal Concentrations of Partlculate 29
Phosphorus in Various Sectors of the Central Basin
of Lake Erie
6 Average Seasonal Concentrations of Organic Nitrogen in 34
Various Sectors of the Central Basin of Lake Erie
7 Average Seasonal Concentrations of Organic Nitrogen in 37
Various Sectors of the Central Basin of Lake Erie
8 Average Seasonal Concentrations of Nitrate Nitrogen in 43
Various Sectors of the Western Basin of Lake Erie
9 Average Seasonal Concentrations of Nitrate Nitrogen in 43
Various Sectors of the Central Basin of Lake Erie
10 Concentrations of Inorganic Nitrogen and Phosphorus 68
Required to Produce Various Populations of Centric
Diatoms during Warming Months
II Concentrations of Inorganic Nitrogen and Phosphorus 73
Required to Produce Various Populations of Pennate
Diatoms during Warming Months
12 Concentrations of Inorganic Nitrogen and Phosphorus 75
Required to Produce Various Populations of Green
Coccoid Algae during Warming Months
13 Concentrations of Inorganic Nitrogen and Soluble 82
Phosphorus Required to Produce Various Populations
of Blue-green Coccoid Algae
14 Concentrations of Inorganic Nitrogen and Soluble 86
Phosphorus Required for Various Populations of Blue-
green Filamentous Algae
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LIST OF FIGURES
Figure No. Title
I Lake Erie Surveillance Stations 9
2 Nearshore Soluble Phosphorus Distribution in Lake Erie 13
" Nearshore Seasonal Distribution of Soluble Phosphorus 14
4 Mid lake Seasonal Distribution of Soluble Phosphorus 17
5 Nearshore Participate Phosphorus Distribution in Lake 20
Erie
6 Nearshore Seasonal Distribution of Particulate 21
Phosphorus
7 Mid lake Seasonal Distribution of Particulate 23
Phosphorus
8 Nearshore Organic Nitrogen Distribution 32
9 Midlake and Nearshore Seasonal Distribution of Organic 33
N i trogen
10 Nearshore Ammonia Nitrogen Distribution in Lake Erie 38
II Nearshore and Midlake Seasonal Distribution of 39
Ammonia Nitrogen
12 Nearshore Nitrate Nitrogen Distribution in Lake Erie 41
13 Nearshore Seasonal Distribution of Nitrate Nitrogen 42
14 Midlake Seasonal Distribution of Nitrate Nitrogen 44
15 Comparison of Organic and Inorganic Nitrogen in 47
Central Basin Nearshore for One-year Cycle
16 Comparison of Organic and Inorganic Nitrogen in 47
Western Basin Nearshore for One-year Cycle
17 Nearshore Temperature Distribution In Lake Erie 48
18 Water Temperature at Put-In-Bay 49
19 Monthly Averages of Various Physical Factors 51
Affecting Lake Erie
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LIST OF FIGURES
Figure No. Title Page
20 Nearshore Centric Diatom Distribution in Lake Erie 53
21 Nearshore Pennate Diatom Distribution in Lake Erie 54
22 Nearshore Coccoid Green Algae Distribution in Lake Erie 55
23 Nearshore Coccoid Blue-green Algae Distribution in Lake 56
Erie
24 Nearshore Filamentous Blue-green Algae Distribution in 57
Lake Erie
25 Nearshore Dissolved Oxygen Distribution in Lake Erie 59
26 Nearshore COD Distribution in Lake Erie 60
27 Centric Diatoms vs. Temperature in Lake Erie Central 65
Basin Nearshore
28 Centric Diatoms vs. Temperature in Lake Erie Western 65
Basin Nearshore
29 Centric Diatoms as Related to Water Temperature, 67
Soluble Phosphorus and Inorganic Nitrogen in Lake Erie
Nearshore Waters
30 Estimated Requirements of Solar Radiation at Lake Erie 69
Water Temperature for Centric Diatoms
31 Pennate Diatoms as Related to Water Temperature, 71
Soluble Phosphorus and Inorganic Nitrogen In Lake Erie
Nearshore Waters
32 Green Coccoid Algae vs. Water Temperature In Nearshore 74
Waters of Central Basin
33 Green Coccoid Algae vs. Water Temperature In Nearshore 74
Waters of Western Basin
34 Green Coccoid Algae as Related to Water Temperature, 77
Soluble Phosphorus, and Inorganic Nitrogen In Lake Erie
Nearshore Waters
35 Blue-green Coccoid Algae vs. Water Temperature In 79
Nearshore Waters of Central Basin
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LIST OF FIGURES
Figure No. Title Page
36 Blue-green Coccoid Algae vs. Water Temperature in 79
Nearshore Waters of Western Basin
37 Blue-green Coccoid Algae as Related to Water 81
Temperature, Soluble Phosphorus and Inorganic
Nitrogen in Lake Erie Nearshore Waters
38 Blue-green Filamentous Algae vs. Water Temperature 83
in Nearshore Waters of Central Basin
39 Blue-green Filamentous Algae vs. Water Temperature 83
in Nearshore Waters of Western Basin
40 Blue-green Filamentous Algae as Related to Water 85
Temperature, Soluble Phosphorus and Inorganic
Nitrogen in Lake Erie Nearshore Waters
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SUMMARY AND CONCLUSIONS
Data gathered In the Lake Erie surveillance program by the Federal
Water Quality Administration Lake Erie Basin Office provide the basis
for discussion of the distribution of algal types and some of the physi-
cal and chemical factors which control algal populations in the western
and central basins of the lake. Sufficient data are not available to
include the eastern basin.
For three seasons of the year, spring, summer, and fall, soluble
phosphorus is remarkably uniform at any one place In Lake Erie, although
there are occasional substantial variations. Concentrations generally
decrease from shore lakeward and from west to east in the lake. It can
be stated for generalization that for those three seasons mldlake western
basin soluble phosphorus as P averages about 30 ug/l compared to 50 ug/l
near shore. The central basin nearshore averages 30 ug/l, about the
same as the western basin mid lake, while In the central basin mid lake
soluble phosphorus drops to about 15 ug/l.
In winter, a season when adequate data have not previously been
available, soluble phosphorus more than doubles in all nearshore areas
and in the western basin mid lake. Limited non-nearshore data show very
little winter rise in soluble phosphorus at the outlet end of the western
basin and in the western portion of central basin midlake. This indicates
considerable winter tributary* input, nearshore sediment resuspension,
limited dispersion, and low utilization by algae in winter.
Particulate phosphorus exhibits an erratic distribution throughout
the year and at any one time in the nearshore area, although It generally
* In this text the word tributary refers to totalinputs, municipal,
industrial, and agricultural.
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Is less than soluble phosphorus. The erratic nearshore distribution,
not so evident In mid lake waters, most likely Is controlled by variability
in productivity and by variability in runoff and wind-induced sediment re-
suspension. ParticuI ate phosphorus shows no definable seasonal pattern
except for a slight rise in winter.
Organic nitrogen, which should reflect fluctuations in biological
productivity is remarkably uniform on the average throughout the lake
during all seasons at 300-400 ug/l. An exception is a slightly higher con-
centration In nearshore waters of the western basin in spring. Organic
nitrogen does not correlate with algal numbers although it may with total
blomass, a parameter not being determined In the present program.
Ammonia nitrogen shows no clear seasonal pattern and concentrations
in midlake are not far from those in the nearshore area, generally at
200 jjg/l or less. Since nearshore short-term nutrient dispersion Is
minimal, it is indicated that the sediments are an Important source of
midlake ammonia, although it is not Implied that sediment inputs neces-
sarily cause the approach to uniformity.
Nitrate nitrogen, however, does show a clear seasonally changing
annual pattern in both nearshore and midlake waters. Nearshore area
nitrate nitrogen is generally more than twice that of midlake. During
winter and spring there is a significant decrease from west to east
throughout the lake.
Nitrate nitrogen climbs to levels greater than 1,500 pg/l in winter
in the nearshore waters of the western basin, most likely due to higher
tributary inputs, the introduction of interstitial ammonia during sed-
iment resuspension with subsequent conversion to nitrate, and low
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nutrient utilization by limited algal populations. The winter rise is
progressively less eastward until at Conneaut, Ohio, it is insignificant.
A conspicuous drop In nitrate nitrogen occurs in spring, correla-
tive with high algal populations. However, in the east half of the
centra! basin, nitrate nitrogen Increases in f.rring, Summer and fall
are characterized by low concentrations of rJv-ot^ m t-cgen (200 jjg/l or
less/ after strong algai uptake in both nearr'I'^o and midlake waters.
Organic nitrogen exceeds inorganic between July and November in
Lake Erie. The excess of organic nitrogen indicates that inorganic
nitrogen is being biologically converted faster than it is being supplied.
The sustenance of such a condition would eventually result In the com-
plete depletion of ambient Inorganic nitrogen and thus create the poten-
tial for nitrogen limitation of certain algal genera. Blue-green algae,
certain species being nitrogen fixers, are dominant during this period.
Nearshore data correlations with respect to nutrients and algae
have been made at various temperatures. During the year of concern
(1968-69) an investigation of physical factors revealed that water tem-
perature, air temperature, solar radiation, and percent of possible sun-
shine were above average in early spring, below average in late spring
and early summer, and at or above average for the remainder of the year.
Precipitation was below average the first half of the year and above
average the last half. The winds throughout were lighter than normal ana
lake levels were above normal. All nutrient-aIgai relationships most
likely are affected by the variations in the physical factors described
above, however, except for wa+er temperature these effects are not de-
fined In this report.
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Various types of algae show preference for particular temperature
ranges, and within those ranges there are optimum growth temperatures.
There are no important Lake Erie algal types which prefer freezing tem-
peratures. Diatoms prefer temperatures between 2°C (36°F) and IO°C
(50°F), green algae between IO°C and 20°C (68°F) and blue-green algae
prefer temperatures in excess of 20°C. The following observations are
based on ambient water nutrient concentrations and phytoplankton popu-
lations at the time of sample collection. The measurement of algal
metabolic rates was never attempted, consequently any and all correlations
are indirect, and can only be considered indications. In general and in
opposition to what one might normally expect, it is indicated that for
any algal species nutrient requirements increase as temperatures depart
from the optimum. In addition increases in temperature do not necessarily
result in increases in populations of algae. In fact, except for the
occasional and sometimes massive blue-green bloom, which Is not fully
documented by the present biweekly sampling program but based on many
individual observations, lower populations are characteristic of the
warmest season of the year. However, total algal biomass during both
spring and summer may be equivalent as suggested by the comparable organic
nitrogen concentrations during both seasons.
Diatoms, the first algae to appear In great numbers In late winter
or early spring, appear to require relatively low concentrations of nitro-
gen and phosphorus at their optimum temperature although these nutrients
generally are at or near their highest concentrations. As temperatures
increase the nitrogen and phosphorus requirement appears to increase while
the actual nutrient concentration Is diminishing. Thus it appears that
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control of the nutrient supply is most critical at optimum temperatures.
To reduce the population of green algae at their preferred temper-
ature range it appears that any reduction of nutrients would be somewhat
effective. If the objective were to keep populations below 200 organ-
isms/ml, about 25 percent reduction of inorganic nitrogen or 80 percent
reduction of soluble phosphorus, at the time of green algal dominance,
would be required. Unlike diatoms, it appears that the duration of green
algae dominance would not change but that the amplitude (maximum popu-
lation) of the pulse would be decreased.
At temperatures above 20°C (68°F) blue-green populations most likely
would not be reduced by the control of inorganic nitrogen, since blooms
occur at present after this nutrient has all but disappeared from the
lake in summer. It appears however that maximum populations, but not
the period of dominance, can be limited by soluble phosphorus control.
If concentrations of soluble phosphorus as P can be maintained below 40
ug/l it appears that blue-green populations can be controlled to less
than 500 organisms/ml. This would be essentially a 25 percent reduction
in soluble phosphorus. However the control of blue-green algae Is com-
plicated by the fact that these organisms, possibly more than any other
algae, apparently are largely stimulated by nutrients regenerated from
bottom sediments. Since the regeneration process is not presently con-
trollable, compensation for this nutrient source must be accomplished
by further tributary input reduction. The necessary additional reduction
is not known, but a total of 80 to 90 percent does not seem unreasonable to
effectively reduce blue-green populations.
Based on limited environmental relationships, of the two nutrients
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which are or may be controllable, phosphorus appears to be the one of-
fering the most feasibility and practicality. Furthermore blue-green
algae cannot be controlled by nitrogen tributary Input limitation.
Diatoms also cannot be controlled effectively with less than extreme
nitrogen limitation. The probable effective nitrogen control of green
algae may extend blue-green dominance for even longer periods due to
minimized ecological competition and since as mentioned above, blue-
greens cannot be controlled by waterborne nitrogen limitation. The blue-
green algal ability to fix atmospheric nitrogen precludes dependence on
waterborne nitrogen. Finally, if as indicated by this study a 90 per-
cent input phosphorus reduction can be made to limit diatoms, apparently
there is little doubt that with that same control, all algae can be lim-
ited greatly in their abundance. An 80 percent reduction of soluble
phosphorus will limit the duration but not the maximum population of the
diatom pulse. This reduction will also reduce the magnitude but not the
duration of the green pulse, and may reduce the magnitude of the blue-
green pulse but unfortunately not the duration.
The limited correlation analysis made for this report is only a
beginning but it has shown that an adequate algal response prediction
system can be made for Lake Erie with perhaps considerably less effort
than apparently first thought possible. The model most likely will not
have optimum practicality since the effected correlations do not consider
exact algal nutrient use as measured by metabolic uptake, nor do they
consider nutrient storage in cell bodies, a most likely cause for any de-
layed ambient algal-nutrient response. As previously mentioned correla-
tions were made using ambient water nutrient concentrations and prevalent
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algal populations. However a comparison of organic and inorganic nutri-
ent forms does not reveal significant luxuriant consumption allowing for
some degree of confidence in the nutrient concentration versus biological
populations approach. Thus, it is indicated that a working model formu-
lated with the technique described in this report can be made somewhat
less than optimumly effective with but slight "over-engineering" to com-
pensate for any undefined biological vagaries.
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DISTRIBUTION OF CHEMICAL, PHYSICAL, AND
BIOLOGICAL FACTORS IN LAKE ERIE
INTRODUCTI ON
The following report describes the time and space distribution of
measured chemical, physical, and biological factors for a one-year
cycle in the western and central basins of Lake Erie. The nearshore
descriptions are based upon data gathered in a biweekly sampling program
at 17 Ohio domestic water supply intakes from March 1968 through March
1969. It should be emphasized that the Cleveland area sampling locations
are relatively a great distance from shore3 up to 203000 ft.t and for
this veason the water quality in this area is of higher quality espec-
ially when compared to other Ohio nearshore areas where samples were re-
trieved as little as I3l00 ft. from shore. The mid lake descriptions are
based upon data gathered at 20 mid lake stations sampled four times be-
tween May 1967 and January 1968. Sampling locations, depths and distance
from shore are shown on Fig. I and Table I. Although the sampling times
for nearshore and mid lake were one year apart, for the purposes of this
report the data are assumed to be comparable.
The data are certainly not so abundant nor so precise that the con-
clusions are indisputable. Conclusions drawn from data gathered over a
one-year period are subject to argument on several grounds, not the least
of which are sampling frequency, measurement technique, living systems
idiosyncrasies and even the unique whims of nature during any one year.
Even further danger exists in comparing mid lake data for one year with
nearshore data for the following year, not only for The above reasons
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but because the overall quality of lake waters may change noticeably
from one year to the next. For the purposes of this report however it
will be assumed that no significant changes occurred between 1967 and
1968.
In addition to describing a one-year distribution of various fac-
tors an attempt has been made herein to describe the interrelationships
of these factors. Although much has been written on the general bio-
chemical relationships in a lake system, the applicability of these
relationships to the general pollution control effort in Lake Erie has
nearly always been questionable. The correlation of any two analytical
measurements, such as algal population and phosphorus content, more
often than not leads to erroneous or conflicting conclusions, thus week-
ening the defensibiIity or justification for pollution control expendi-
tures. This report attempts to point out the fallibility of some two
parameter correlations. Also it demonstrates with a few examples of
multiple-parameter correlations that it is possible to predict an ade-
quate biological response to a given set of physical and chemical factors.
It is difficult to clearly describe the details of parameter dis-
tributions in the lake and their changes with time. For this reason
some rather novel graphic approaches have been devised to simplify ex-
planations. Most of the illustrations attempt to show three related
factors simultaneously. Scales have been arbitrarily chosen, with graph-
ics showing distance, not necessarily to scale.
PHOSPHORUS DISTRIBUTION IN LAKE ERIE
The most important nutrient by reason of rapidly increasing ac-
cumulation in Lake Eries is phosphorus. An abundance of phosphorus is
11
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generally considered as the cause for the remarkably high biological
productivity in Lake Erie. The acceptance of this as fact does not lead
to the unequivocal conclusion that cessation of phosphorus inputs will
produce a predictable result. Not only are the mechanics of phosphorus
utilization by biological systems still unclear, but the temporal and
spatial distribution have been largely undetermined. Without a basic
knowledge of phosphorus distribution in Lake Erie the mechanics of its
quantitative utilization offer little hope of being fully understood,
much less predictable.
Phosphorus is described herein as soluble phosphorus and particu-
late phosphorus. Particulate phosphorus is simply the difference be-
tween the soluble phosphorus and total phosphorus forms. It is that
portion of total phosphorus retained on fluted Whatman filter paper No.
12 while soluble phosphorus is that portion which passes. Particulate
phosphorus is assumed to be either chemically or biologically bound to
inorganic or organic particulate matter.
WESTERN BASIN
Soluble Phosphorus
The time - space distribution of soluble phosphorus as P in near-
shore waters for one year is shown in Fig. 2. The distance axis from
Toledo to Conneaut is not to scale.
Examination of soluble phosphorus data from Toledo and Port Clinton
water intakes has revealed a remarkable consistency at near 50 yg/l for
much of the year (Fig. 3 and Table 2). Winter* houever departs dramati-
cally from the previous three seasons, apparently affected by higher
tributary inputs, the introduction of interstitial soluble phosphorus
12
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13
FIGURE 2
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TABLE 2
AVERAGE SEASONAL CONCENTRATIONS OF SOLUBLE PHOSPHORUS (<\s P)
IN VARIOUS SECTORS OF THE WESTERN BASIN OF LAKE ERIE (ya/l)
Season
Maumee
Bay
Southern
Nearshore
Mi d-basi n
Northeast
sector
(outlet)
Winter
Spring
Summer
Fa I I
I 10
25
95
90
150
50
50
50
55
25
40
30
20
20
20
20
15
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during wind-induced sediment resuspension and low utilization by limited
algal populations. Concentrations above 150 yg/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 yg/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 vg/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
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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 x>f 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 cover, 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
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However a detailed examination reveals that the expected immediate in-
verse correlation is in fact delayed. The rapid spri-ng reduction of
soluble phosphorus occurs, not simultaneously uith 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 pg/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 mid lake
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
yg/l while nearshore concentrations remain essentially unchanged at an
average of 50 yg/l. As with soluble phosphorus, particulate phosphorus
19
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-------
TABLE 3
AVERAGE SEASONAL CONCENTRATIONS OF PARTICIPATE PHOSPHORUS (As P)
IN VARIOUS SECTORS OF THE WESTERN BASIN OF LAKE ERIE (pg/l)
Season
Maumee
Bay
Southern
Nearshore
Mid-basin
Northeast
sector
(outlet)
Winter
Spring
Summer
Fall
45
55
40
70
50
30
55
50
30
25
15
15
20
10
20
20
22
-------
(O
3
CL
fO
O
O
0.
O
c
O
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. Bather
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 mid lake 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 areal
25
-------
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 ug/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 jjg/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, central 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 ug/l at the beginning of March. This
peak is followed by a rapid decline to 30 ug/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 (ug/l)
Season Southwest Southeast Western Eastern
Nearshore Nearshore Mfdlake Midlake
Winter 80 55 25
Spring 30 25 10 15
Summer 35 25 15 10
Fa I I 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/l, 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 Table 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 yg/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 vg/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 (gg/l)
Season Southwest Southeast Western Eastern
Nearshore Nearshore Mfdlake Mfdlake
Winter 50 35 10
Spring 15 20 10 5
Summer 20 20 5 <5
Fa I I 50 50 5 5
29
-------
phosphorus in summer, in the central basin, indicating perhaps a general
damping effect on a I 1 phosphorus input factors.
The winter soluble phosphorus accretion in both the central basin
nearshore and midlake 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 tf\ 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. Ahhougi
both ammonia and nitrate are utilized as nutrients the content of nirraie
normally shows greater depletion characteristics. It is not clear however
that nitrate is the preferred nutrient since during high algal use periocs,
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, sprint
and summer averages approximately 700 ug/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 mid lake-
average about 300 pg/l. In the fall organic nitrogen approaches up'form'tv
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
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FIGURE 9
-------
TABLE 6
AVERAGE SEASONAL CONCENTRATIONS OF ORGANIC NITROGEN
IN VARIOUS SECTORS OF THE WESTERN BASIN OF LAKE ERIE (yg/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 wg/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 of Lorain averages about 700 yg/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 ug/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
ug/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 yg/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 (ug/D
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
-------
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 in 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-
ical ly 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 ritrate
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
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FIGURE 12
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TABLE 8
AVERAGE SEASONAL CONCENTRATIONS OF NITRATE NITROGEN
IN VARIOUS SECTORS OF THE WESTERN BASIN OF LAKE ERIE (pg/l)
Season
Winter
Spring
Summer
Fal 1
IN
Season
Winter
Spring
Summer
Fal 1
Maumee
Bay
1,500
800
<50
100
AVERAGE SEASONAL
VARIOUS SECTORS OF
Southwest
Nearshore
600
600
100
100
Southern
Nearshore
1,700
800
250
200
TABLE 9
CONCENTRATIONS OF
THE CENTRAL BASIN
Southeast
Nearshore
250
400
150
175
Mid-basin
600
300
75
175
*
Northeast
sector
(outlet)
350
200
<50
175
NITRATE NITROGEN
OF LAKE ERIE (pg/l)
Western
Midlake
250
200
<50
<50
Eastern
Midlake
-
<50
<50
<50
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FIGl'RE 14
-------
concentration at the northeast corner of the basin being about 300 ug/l.
Central basin nearshore nitrate nitrogen follows a reasonably smooth
annual curve, highest in late winter, (600 ug/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 pg/l at Sandusky
to less than 200 ug/l at Conneaut. In spring it is relatively constant
from Sandusky to Cleveland where it declines. Then it rises to its highest
level (600 pg/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 ug/l.
A similar west to east nitrate nitrogen distribution but at lower
levels, exists in central basin midlake (Fig. 14 and Table 9). In wjnter
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 vg/t) 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 ug/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. 485 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
-------
1900 •
1000
5OO
Dashed, line - inorganic N
Solid line - organic N
Shaded - organic > inorganic
4/l/*8 5/1 6/1 7/1 8/1 9/1 K>/l I I/I 12/1 1/1/69 2/1
FIG. 15 COMPARISON OF ORGANIC AND MORGANC NITROGEN N
CENTRAL BASIN NEARSHORE FOR ONE-YEAR CYCLE
3/1
3500
3OOO
2500
— 2000
O>
1500 i
IOOO
500 •
Dashed line - inorganic N
Solid line - organic N
Shaded - organic » inorganic
j\
4/1/68
3/1
6/1
T/l
8/1
W/l
H/l
12/1 1/1/69 2/1
FIG. 16 COMPARBON OF ORGANIC AND MORGANS NITROGEN IN
WESTERN BASM NEARSHORE FOR ONE-YEAR CYCLE
-------
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FIT RE 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
-------
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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90
2»
20
£
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s
10
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\
AMJJASONDJ F
1968 1969
A. MONTHLY AVERAGE AIR TEMPERATURE
7O
MAM
D, MONTHLY AVERAGE WIND VELOCITY
MONTHLY AVERAGE PRECIPITATION
B. MONTHLY AVERAGE % POSSIBLE SUNSHINE
600
§40
2OO-
lOOr
U»J
MAMJJASONOJF
1968 1969
C. MONTHLY AVERAGE SOLAR RADIATION
111 I
iu '
0 N D J f
1968 I9M
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 alt Cleveland unless otherwise noted.
Dashed lines - longterm averalge. 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 forms, numerically speak-
ing, 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 earlrj
summer when the lake temperature is rising and between 10°C and 15°C, 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
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FIGURE 20
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FIGURE 21
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FIGURE 22
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i i i I I i
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57
FIGURE 24
-------
generally are dominant for a longer time in the western basin than in the
central basin. Blue-green algae -peach their greatest populations when
nitrate is nearly absent, when water temperature is above 20°C, and after
the lake has begun to cool.
Flagellates are not dominant in nearshore waters at any time of the
year.
All phytoplankton forms appear to decrease quite significantly in
population from west to east in the lake. By far the largest population
is found in the western basin at all times of the year.
The attached green filamentous alga Cladophora was not considered
in this report. Cladophora grows profusely in Lake Erie, a suitable sub-
strate for "hold-fast'1 attachment being the only limiting factor. Cursory
agency study indicates that the eastern basin, because of appropriate
substrate produces the largest Cladophora biomass.
DISSOLVED OXYGEN
Figure 25 shows the time and spatial distribution of dissolved oxygen
at the intake sampling stations. Early spring is characterized by con-
sistently higher percentages of oxygen saturation while summer is char-
acterized by the lowest. Fall and winter show intermediate percentages
of oxygen saturation. Dissolved oxygen is apparently related to phyto-
plankton populations, particularly diatoms, see Figs. 20 and 21. Acute
low oxygen saturation in summer in the Cleveland area primarily results
from incursions of hypolimnion water into the intake sampling areas. In
areas not affected by the hyoolimnion less acute low oxygen saturation is
most likely the result of chemical deoxyqenation from nearshore resuspended
sed iments.
-------
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FIGURE 25
-------
60
FIGURE 26
-------
CHEMICAL OXYGEN DEMAND
Figure 26 shows the distribution of chemical oxygen demand In the
nearshore waters of the western and central basins. A clear, relation-
ship between this distribution and that of dissolved oxygen does not exist,
If there is a relationship, it is a direct one. Low dissolved oxygen
concentrations in summer are associated with lower COD while higher DO
concentrations in fall and winter are associated with relatively high COD.
CORRELATION OF FACTORS AFFECTING ALGAL PRODUCTIVITY
The relationships described herein deal only with the factors de-
scribed in the previous discussion. It is fully realized that algae re-
quire many kinds of nutrients in addition to nitrogen and phosphorus. It
is assumed however that trace elements and vitamins necessary for sustain-
ing primary productivity are always in adequate supply and that they do
not become limiting at any time. Two other elements, silicon and carbon,
necessary in relatively large quantity, have not been measured in this
study. Silicon is required by diatoms in shell formation but is not a
significant nutrient for other algae.
Many typical general relationships are apparent in Lake Erie. For
example, various Kinds of algae show preference for different temperature
ranges. Populations decrease from west to east in Lake Erie correlative
with a general decrease in nutrient content in that direction. Popula-
tions are higher in nearshore and other shallow waters correlative with
higher nutrient content. Shifts in dominance with time are characteristic
of all parts of the lake. The time shifts may not be relatable to water
temperature alone. Most likely variations in solar radiation (energy)
due to earth position are significant. Finally populations of planktonic
61
-------
algae are generally Inversely correlatable with water depth.
The following discussion examines the five main groups of algae
prevalent in Lake Erie, centric diatoms, pennate diatoms, green coccoid
algae, blue-green coccoid algae, and blue-green filamentous algae, and
their relationship to various physical, chemical, and biological factors.
A glaring omission involves the enumeration of zooplankton. As phyto-
plankton grazers, zooplankton can have a prpnounced effect on phyto-
plankton and consequently on the relationships to be presently described.
CENTRIC DIATOMS
Water Temperature
Centric diatoms show a definite correlation with water temperature
in both the central basin nearshore (Fig. 26) and the western basin near-
shore (Fig. 27). Populations increase very rapidly at the time of ice
breakup following a winter period of relative dormancy. Maximum popula-
tions in both basins occur before the temperature reaches 3°C (37°F).
Above this temperature the central basin population (>6,000 organisms/ml)
declines rapidly to less than 1,000 organisms/ml at a temperature of about
7°C (45°F). In the western basin the high populations (>IO,000 organisms/
ml) persist longer, leveling off at less than 2,000 organisms/ml) when a
temperature of about I0°C (50°F) is reached. Populations in the western
basin remain fairly stable until a temperature of 20°C (68°F) is reached,
then drop rapidly to less than 500 organisms/m!. In the central basin
stability persists through I2.5°C (54°F) when populations drop to 200 or
fewer organisms/ml.
Centric diatoms decrease to or near their minimum populations when
the lake is warmest, thus showing an inverse correlation with temperature
62
-------
while the lake is warminq. After cooling begins, one might expect another
inverse correlation; however the cooling season rise in centric diatoms is
non-existent in the central basin and greatly subdued in the western basin.
Maximum western basin populations occur again at between IO°C (50°F) and
3°C (37°F) in fall but they are less than 10 percent of the populations in
spring. This suggests that some factor other than temperature has a greater
population controlling influence in fall, as will be discussed presently.
Soluble Phosphorus and Temperature
The plot of centric diatoms and soluble phosphorus reveals a varia-
bility difficult to explain. At times higher populations are associated
with lower phosphorus concentrations following the classical tendencies
toward depletion shown by silica and nitrate. At other times the reverse
is true, suggesting the biological mechanisms of nutrient storage and de-
layed phytoplankton response.
A plot of centric diatoms, soluble phosphorus, and temperature (Fig.
29) reveals quite a different picture. Although the detailed interpreta-
tion remains difficult, a definite general trend is shown duping the warm-
ing season indicating that, as the water warms, progressively more phos-
phorus is required to maintain similar populations. For example, to
maintain a population of centric diatoms greater than 1,000 organisms per
mi Mi liter at temperatures less than 5°C (4I°F), less than 10 ug/l solu-
ble phosphorus is required, while at 20 t (68°F) the requirement increases
to greater than 50 yg/l. In these types of correlation, ambient water
nutrient concentration is inferred to mean a concentration associated with
a specific algal population. It is not meant to mean algal metabolic
requi rement.
-------
It appears that above 20°C (68°F) both temperature and soluble phos-
vhorus are severely limiting to diatom growth in Lake Erie. This does
not mean that other factors are not also limiting, but does mean that re-
duction of other prevailing non-1imitinq factors at this time is not
necessary for diatom control.
After the lake begins to cool the relationship between diatoms, sol-
uble phosphorus, and temperature becomes obscure, indicating that some
other factor becomes more important to diatom production.
Although a relationship between soluble phosphorus and diatoms is
apparent during the warming season, in the early part of this period the
relationship in detail is not altogether clear. Below a temperature of
IO°C (50°F) it appears that a concentration of about 30 jjg/l soluble
phosphorus is sufficient for continued diatom growth. If this is fact,
it may be difficult to establish, for at this time soluble phosphorus is
rapidly decreasing. The possibility exists that during this period,
diatom populations are regulating soluble phosphorus rather than the
reverse.
Inorganic Nitrogen and Temperature
Inorganic nitrogen appears to show a direct correlation with centric
diatoms when nitrogen averages for each sampling period are plotted against
average plankton numbers. Higher diatom populations are associated with
higher nitrogen values and vice versa. However the correlation becomes
nebulous when inorganic nitrogen and centric diatoms are considered not as
nearshore wide averages but as individual station statistics. For example,
while maximum populations tend to increase eastward, the inorganic nitrogen
associated with these maximums progressively decreases eastward.
-------
10,000
5,000
LU
o
Solid line - warming season
Dashed line - cooling season
10 15
TEMPERATURE °C
20
FIG. 27 CENTRIC DIATOMS VS. TEMPERATURE IN LAKE ERIE
CENTRAL BASIN NEARSHORE
25
20,000
ispoo •
<0 10,000}-
o
5,000 •
Solid line - warming season
Dashed line - cooling season
10 15
TEMPERATURE °C
20
25
FIG. 28 CENTRIC DIATOMS VS. TEMPERATURE IN LAKE ERIE
WESTERN BASIN NEARSHORE
-------
A plot of centric diatoms, inorganic nitrogen and temperature gives
more insight as to cause and effect between the various considered fac-
tors (Fig. 29). It appears that betaeen 0°C (32°F) and 5°C (4l°F)
centric diatoms are virtually independent of the amount of inorganic
nitrogen which exists at the time. Above 5°C (4I°F) the amount of inor-
ganic nitrogen apparently does not greatly affect centric diatom popula-
tions as long as the nitrogen concentrations are below about 800 pg/l and
within the range normally found in nearshore waters. Sporadic signifi-
cant population increases occur above 800 yg/l with progressively larger
ambient nutrient concentrations being required to maintain a certain pop-
ulation at progressively increasing water temperatures. Above 20°C (68°F)
more than 1000 pg/l is needed to produce a significant diatom population
(>IOOO org/ml).
After the lake begins to cool centric diatoms are no longer impor-
tant, showing little relation to either nitrogen or temperature, until
a water temperature of about IO°C (50°F) is reached, then centrics show
a slight increase, but still independent of existing nitrogen concentra-
tions.
Integrating results for temperature, soluble phosphorus, and inor-
ganic nitrogen during the warming season, apparent nutrient requirements
for specified centric diatom populations can be inferred, as shown in
Tabie 10.
66
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TABLE 10
CONCENTRATIONS OF INORGANIC NITROGEN AND PHOSPHORUS REQUIRED TO PRODUCE
VARIOUS POPULATIONS OE CENTRIC DIATOMS DURING WARMING MONTHS
Terno .
(°C)
1
0-5
5-10
10-15
15-20
20-25
000 org/ml
70
Soluble P
(yg/l)
500 org/ml
-------
10 15
WATER TEMPERATURE - °C
zo
FIG. 30 ESTIMATED REQUIREMENTS OF SOLAR RADIATION AT LAKE
ERE WATER TEMPERATURES FOR CENTRIC DIATOMS.
69
-------
any silica deficiency at this time of the year may be controlling diatoms
in general.
PENNATE DIATOMS
Water Temperature
Pennate diatoms shew essentially the same kind of response to tem-
perature as do the centric 'diatoms with the exception that populations
are usually considerably less. The large spring pulse lasts approximately
the same length of time in both the western and central basins, beginning
during the period of ice breakup and essentially disappearing by the time
the water temperature reaches I5°C (59°F).
During the cooling season populations of pennate diatoms rise slight-
ly but do not reach significant numbers, again suggesting, as with centrics,
tha+ they may be subdued by a lack of sufficient sunlight or silica at
preferred temperatures.
Soluble Phosphorus and Temperature
As with centric diatoms, the pennates also show a variable relation-
ship and most likely for the same reasons, with soluble phosphorus alone.
When plotted against soluble phosphorus and temperature some apparently
significant correlations emerge (Fig. 31). During the warming season at
temperatures below 5°C (41°F) and as evidenced by maximum populations,
the pennates appear to prefer soluble phosphorus concentrations of 30 to
40 vg/l, decreasing in numbers when concentrations are above and below
those levels. This correlation prevails somewhat through IO°C (50°F)
when higher concentrations of phosphorus appear to begin to stimulate the
pennates.
From IO°C (50°F) through 20°C (68°F) the correlation becomes clearer
70
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and is direct. However significant populations, more than 500 cells/ml,
require relatively large quantities of soluble phosphorus, in excess of
70 uq/l. Above 20° (68°F) pennate diatoms, because of restricting tem-
peratures, cannot be of great significance regardless of phosphorus con-
centrations.
During the cooling season there is no clear' relationship between
phosphorus and pennate diatoms, indicating that another factor is limiting.
Inorganic Nitrogen and Temperature
Inorganic nitrogen appears to show a direct correlation with pennate
diatoms when nitrogen averages for each sampling period are plotted against
average plankton numbers. Again higher diatom populations are associated
with higher nitrogen values. As with centric diatoms the correlation is
not altogether consistent, with occasional erratic values indicating some
delayed ambient algal-nutrient response.
A plot of pennates, inorganic nitrogen, and temperature however re-
veals the following: Below a temperature of IO°C (^0°F) pennate diatoms
appear to require a concentration of more than 600 vq/l inorganic nitrogen
to produce blooms of more than 500 cells/ml. Above IO°C (50°F) the re-
quirement increases to a'large degree, indicating that temperature is rel-
atively more controlling. Above 20°C (68°F) as with phosphorus, nitrogen
Is no lonaer important to pennate diatoms in Lake Erie, the population
apparently entirely controlled by some other factor, most likely temperature.
During the cooling season, a correlation is not apparent between in-
organic nitrogen and pennates until a temperature of less than IO°C (50°F)
is reached. They then seem to prefer an inorganic nitrogen concentration
of 800-1,000 yg/l. Populations are still relatively small, however,
72
-------
indicating a response to insufficient sunlight or silica.
The results of nutrient-temperature-pennate diatom correlations
provide some insight as to probable pertinent plankton requirements as
shown in Table I I.
TABLE I I
CONCENTRATIONS OF INORGANIC NITROGEN AND PHOSPHORUS REQUIRED
TO PRODUCE VARIOUS POPULATIONS OF PENNATE DIATOMS DURING
WARMING MONTHS
Temp.
(°C)
0-5
5-10
10-15
15-20
20-25
Inorgani
1,000 org/ml 500
1,000
800
1,000
1
-
c N (pg/l)
org/ml 100
800
700
900
,500
1
org/ml
200
200
300
900
,000
Soluble
1 ,000 org/ml 500
30
30
80
-
-
P Cyg/M
org/ml 100
10
30
70
80
-
org/ml
5
10
10
40
-
GREEN COCCOID ALGAE
Water Temperature
The western basin nearshore green coccoid algae temperature plot (Fig.
33 shows a conspicuous rise during the course of lake warming, with maximum
populations of more than 3,000 cells/ml at about 22°C (72°F). A precipitous
decline In population occurs above this temperature. During the lake cooling
period, populations rise again slightly-to about 600 cells/ml at IO°C (50°F)
and then decline again in winter.
In the central basin green coccoid algae are generally about one-half
those in the western basin. The relation to temperature alone is quite
different (Fig. 32). They rise from insignificance at the time of Ice
breakup to a maximum (600 cells/ml) at a temperature of about I2°C (54°F)
then decline rapidly, so that the population minimum occurs at the same
73
-------
1000,
500
UJ
o
Solid line - warming season
Dashed line - cooling season
10 15
TEMPERATURE °C
20
25
FIG. 32 GREEN COCCOID ALGAE VS. WATER TEMPERATURE IN NEARSHORE
WATERS OF CENTRAL BASIN.
zooo
15OO
CO IOOO
o
500
Solid line - warming season
Dashed line - ' cooling season
10
15
20
25
TEMPERATURE °C
FIG.33 GREEN COCCOID ALGAE VS. WATER TEMPERATURE IN NEARSHORE
WATERS OF WESTERN BASIN.
-------
time and same temperature as the population maximum in the western basin.
A secondary maximum in qreen coccoid alqae then occurs in central basin
nearshore just after the lake begins to cool at about 20°C (68°F). This
is followed by a gradual decline to winter populations of less than 100
ce I Is/ml.
Based on the description above it is indicated that temperature is
most influential to green coccoid populations in winter and in the early
part of the warming of the lake in spring. It is also indicated that if
other factors are adequate, as in the western basin the temperature in-
fluence will be extended to the period just prior to lake cooling.
Soluble Phosphorus and Temperature
The plot of green coccoid algae and soluble phosphorus shows no dis-
cernible trend. Adding temperature to the relationship still produces no
clearly defined characteristics. However a few important conclusions can
be drawn. Green coccoid algae increase as the water warns in spring .
through a temperature of about 12°C (54°F)3 while not showing any really
significant preference for higher phosphorus concentrations. Above I2°C
however, green coccoid algae appear to become more phosphorus dependent.
Below I2°C phosphorus concentrations of less than 30 ug/l appear adequate
to sustain populations greater than 400 organisms/ml, whereas above I2°C,
that requirement rises to 50 pg/l or more.
The dependence upon phosphorus continues through maximum water tem-
perature, (25°C (77°F) and into the cooling period. In the cooling period
and below 20°C (68°F) the correlation disappears and does not reappear,
although the green coccoid algae do seem to prefer 50-60 ug/l of soluble
phosphorus for the remainder of the year.
75
-------
Inorganic Nitrogen and Temperature
A plot of inorganic nitrogen temperature (Pig. 34), and green coccoid
algae shovs that belou 10°C (50°F) the green coccoids appear to be more
related to temperature than to nitrogen. Above IO°C the influence of in-
organic nitrogen becomes more apparent, the greater the nitrogen concen-
tration, the higher the populations. As the temperature increases above
IO°C (50°F) larger amounts of inorganic nitrogen are required to produce
similar populations. For example at I2°C (54°F) 700 viq/l inorganic nitro-
gen will produce 300 green coccoid algal cells/ml, but at 22°C (72°F) 600
ug/i is needed for the same population.
Aflor the lake begins to cool, there appears 1o be no clear relation
of preen coccoid algae to inorganic nitrogen, the populations being rela-
tively low regardless of concentration. If there is any preference at
all, it seems to be for lower amounts of inorganic nitrogen.
The relationship between inorganic nitroqen, soluble phosphorus, and
temperature with green coccoid algae is Iis+ed in Table 12.
TABLE I 2
CONCENTRATIONS OF INORGANIC NITROGEN AMD PHOSPHORUS REOUIRED TO
PRODUCE VARIOUS POPULATIONS OF GREEN COCCOID ALGAE DURING WARDING
MONTHS
Temp .
C°C)
0-5
5-10
10-15
15-20
20-25
1 norgani
1,000 org/ml 500
_
-
>900
> 1,000
1,100
c N i'ug/1
orq/ml
_
300
600
850
900
1 )
100 org/ml
400
100
200
400
600
Sol ub le
1 ,000 org/m! 500
_
-
50
60
50
P (uq/l
orq/nl
—
20
10
50
50
)
100 org/ml
10
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BLUE-GREEN COCCOID ALGAE
Water Temperature
Lake Erie water temperature and blue-green coccoid algae are clearly
related (Figs. 35 and 36). It is well-known tiat blue-greens proliferate
above a temperature of 20°C (68°F) and frits rtudy is -further confirmation
of that fact. In Lake Erie however, pisximu'i populations do no* occur
when the water temperature is rising. Rather the maximum nearly alaays
occurs just after the lake reaches peak temperature and begins to aool in
August and September. Apparently when the Sake temperature begins to drop,
some undetermined phenomenon occurs which in turn stimulates or allows in-
creased blue-green growth.
It is possible that during the cooling period the actual water tem-
perature, or even the rate of water temperature decline, may trigger the
extensive blue-green coccoid algal growths, it is also possible that the
algal grazers, the zooplankton which were not considered in this study,
were primarily affected by the temperature downswing killing the grazers
and indirectly allowing the blue-green accretion. Most likely, however,
blue-green blooms are stimulated and sustained by nutrients diffused or
resuspended from the bottom sediments, especially where those blooms occur
at a great distance from tributary inputs, such as the northern island
area or midla'ke. It would appear that sediment nutrient recycling to
overlying waters is enhanced by surface cooling, resulting in top-to-bottom
connective mixing. Under conditions of cooling the lake waters are readily
mixed even without additional wind-induced agitation. Winds however can
induce upwelling, such as commonly occurs in the northwestern part of the
central basin, making the situation even more Ideal for nutrient recycling
78
-------
1500
IOOO
500H
Solid line - worming season
Dashed line - cooling season
IO 15
TEMPERATURE °C
FK3.35 BLUE-GREEN COCCOID ALGAE VS. WATER TEMPERATURE IN
NEARSHORE WATERS OF CENTRAL BASIN.
25
55 OO
5000
4500
4000
350O
2 3000
-^
_J
LU
0 2500
2000
I5OO
IOOO
500
0
I 1 I * I
1
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TEMPERATURE °C
20
FIG.
36 BLUE -GREEN COCCOID ALGAE VS. WATER TEMPERATURE IN
NEARSHORE WATERS OF WESTERN BASIN.
25
79
-------
and blue-green blooms.
Soluble Phosphorus and Temperature
A plot of blue-green coccoid algae and soluble phosphorus also
shows no discernible trend. A relation does develop however when blue-
green coccoids are correlated with phosphorus and temperature together
(Fig. 37). Below a temperature of 25°C (7?°?), when the lake is warming,
blue-green coccoid algae respond neither to temperature nor to phosphorus,
But, as noted previously, when the lake begins to cool, they appear, often
in great numbers and as shown in Fig. 37 are responsive to soluble phos-
phorus. The highest populations appear when soluble phosphorus is 50 ug/l
or more.
When the temperature falls, during the cooling season, to below ?0°C
(68°F), blue-green coccoid algae decline. By the time the lake has reached
I5°C (59°F) these algae are no longer significant. Although blue-green
coccoid algae can be found in very small numbers at almost any time of the
year, they are restricted in importance to late summer and very early fall.
Inorganic Nitrogen and Temperature
Fig. 37 shows the correlation of inorganic nitrogen to blue-green
coccoids. If a correlation exists it is inverse, higher populations ex-
isting at low concentrations of inorganic nitrogen.
Since some blue-green algae can fix atmospheric nitrogen, it is assumed
that this nutrient cannot limit all blue-green productivity in Lake Erie.
However the possibility remains that if inorganic nitrogen were plentiful
at this time of the year, green algae might continue to dominate with blue-
greens subordinate. It is indicated that limited populations of green
algae due to nitrogen starvation minimize ecological competition thus
80
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allaying the dominance of nitrogen fixing blue-green algae.
TABLE 13
CONCENTRATIONS OF INORGANIC NITROGEN AND SOLUBLE PHOSPHORUS
REQUIRED TO PRODUCE VARIOUS POPULATIONS OF P.LUE-GREFN COCCOID
ALGAE
Temp .
(°C
0-5
5-10
10-15
15-20
20-25
25-20
Inorganic N (pq/l )
1,000 org/ml 500 orq/nl 100 org/ml
_
_
_
_
_
>200 >200
Soluble p (uc/l )
1,000 org/ml 500 org/ml 100
-
_
- _
50
50 40
org/ml
-
-
-
40
10
BLUE-GREEN FILAMENTOUS ALGAE
Water Temperature
Blue-green filamentous algae show the same general correlation with
temperature as do the blue-green coccoids. That is that maximum populations
occur after the lake begins to cool (Figs. 38 and 39). It is assumed that
this response is for the same reasons as described for blue-green coccoids.
However in the western basin the blue-green filamentous pulse dies out more
slowly than in the central basin persisting at significant populations
(>13000 cells/ml) to a temperature of 10°C (SO°F) in autumn. This probably
is a result of a generally higher nutrient supply in the western basin, per-
haps in turn a result of easier mixing in the basins shallow waters.
Soluble Phosphorus _and Temperature
Fig. 40 shows blue-green filamentous algae plotted against soluble
phosphorus and temperature. From the time of their dominance, at the period
of warmest water, 25°C t, down to a temperature of IO°C (50°n or less, the
82
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3000
20OO
1000
Solid line - warming season
Dashed line - cooling season
A
/\
IO 15
TEMPERATURE °C
FIG.38 BLUE-GREEN FILAMENTOUS ALGAE VS WATER TEMPERATURE IN
NEARSHORE WATERS OF CENTRAL BASIN.
6000
500O
4000 •
(rt 3000 -
UJ
o
2000
1000 -
Solid line - warming season
Dashed line - cooling season
A s
/ vx
10 is
TEMPERATURE °C
20
25
FIG. 39 BLUE-GREEN FILAMENTOUS ALGAE VS. WATER TEMPERATURE N
NEARSHORE WATERS OF WESTERN BASIN.
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blue-aree.n filamentous algae show a rather clear and direct relation to
soluble phosphorus. At concentrations of 30 pg/l or less the filamentous
types are not significant but above this level populations increase greatly.
In fall after the temperature decreases below 10°C (50°F) and until
it reaches above 20°C (C8°F), the follcrjing ^ear, blue-are en filarentou"
alaae are not an important component of t*<:~ algal vorulitt-'on y-ecarSJers of
the phosphorus concentration.
Inorganic Nitrogen and Temperature
Fig. 40 also shows the relation of blue-green filamentous alnae pop-
ulations to temperature and inorganic nitrogen. As with the blue-green
coccoids if a relationship exists, it is inverse, higher populations oc-
curring with lower nitrogen concentrations. Again the ability to fix
atmospheric nitrogen allows the blue-green filaments to proliferate during
periods of water inorganic nitrogen depletion.
As with soluble phosphorus, inorganic nitrogen shows no relation to
blue-green filamentous algae during winter and spring, populations being
insignificant the entire period regardless of nutrient concentration.
Table 14 gives requirements for various blue-green filamentous pop-
ulations.
-------
y.o-r
2.S-O
-------
TABLE 14
CONCENTRATIONS OF INORGANIC NITROGEN AND SOLUBLE PHOSPHORUS
REQUIRED FOR VARIOUS POPULATIONS OF BLUE-GREFN FILAMFNTOUS ALGAE
Temp.
0-5
5-10
10-15
15-20
20-25
25-20
20-15
15-10
10-5
Inorganic N (yq/l )
l,"00 org/ml 500 org/.ml 100
— —
.. _
— _
<500
<200
orq/m i
™
_
_
200
200
200
200
Soluble P (yg/l )
1,000 oro/H 500 org/ml 100 org/ml
— — —
— — —
— — _
50 40
20
45 40 20
55 40
FUTURE INVESTIGATIONS
This study represents the beginning of *he preparation of an algal
response analysis system for Lake Erie. By present-day analytical stan-
dards it is rather crude. However it has demonstrated that such a system
most likely can be designed and at minimum expense. It appears that it can
be designed without an elaborate, sophisticated program of sampling and
ana lysis.
At this point an effective algal response prediction system does not
appear to demand that we determine the part played by trace elements, nor
does it demand that high frequency sampling and analyses be accomplished
during pulses of any particular alga! species,, Such determinations might
refine the system, but presently appears unnecessary as long as the gross
features of the system have not been fully defined.
This study lacks information with respect to the factors governing
algal metabolism. This information deficiency includes the algal capacity
86
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for nutrient storage and subsequent stimulation from dormancy by extraneous
phenomena.
Furthermore some additional parameters presently appear necessary
namely carbon, silica, and zooplankton. It appears that the role of carbon
is important and at times may be limiting to algae. It is possible that
spring diatom repression could limit Lake Erie carbon content especially
in midlake, to the point where green algae and subseouently blue-green algae
would become insignificant.
Silica is necessary for diatom skeletal formation. It may be diatom
limiting during certain parts of the year. Although silica limitation for
winter and early spring diatom repression is a long way from consideration,
a knowledge of the silica cycle could be most useful In understanding other
pertinent chemical and1 biological cycles.
The role of zooplankton must be considered. As algal grazers they
can affect algal populations to the point where phytoplankton-nutrient re-
lationships can be easily misunderstood and subsequently misrepresented.
Perhaps the most difficult segment of a response analysis system, is
the determination of bottom sediment nutrient contribution. Quantification
of recycled nutrients should lead to greater confidence in the prediction
of the results of input control in both immediate and long-term effects on
all algal species.
Future study will involve the refinement of the biological, chemical,
and physical factors so rudimentally presented in this report. In addition
new relationships including carbon, silica, and zooplankton will be studied.
At the same time the second year of data will be added to the one year de-
scribed herein. It is expected also that computer programs will be designed
to facilitate the project.
* U.S. GOVERNMENT PRINTING OFFICE 1972-751 -483
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