EFFECTS OF FERTILIZATION AND .
AERATIQN ON THE ECOLOGY 0F PONDS

Thesis for the Degree of M. S.
MICHIGAN STATE UNIVERSITY
HOWARD ALAN SIMONIN
1973

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ABSTRACT

EFFECTS OF FERTILIZATION AND AERATION
ON THE ECOLOGY OF PONDS

BY

Howard Alan Simonin

Two farm ponds were fertilized, one (Pond C) with both phosphates
and nitrates to approximate a secondary sewage effluent, and the other
(Pond D) only with nitrates. Each pond was divided into two sections
by a black plastic divider, and half of each pond was aerated. We
expected that as a result of fertilization, the plant community would
increase and result in increased demands on the dissolved oxygen in
the system. In an unaerated situation we expected that dissolved
oxygen levels would drop to critical levels at night, due to the in-
creased plant respiration. In the aerated system, however, an adequate
dissolved oxygen level would be maintained.

The project was divided into two phases, with aeration continuing
throughout the summer. During the first phase, the ponds were fer-
tilized once, and the biological and chemical changes were monitored.
During the second phase, high nutrient concentrations were maintained
by fertilizing every fourth day. Again, the chemical and biological
changes which occurred were measured.

The dissolved oxygen concentrations in pond C were continuously
monitored and showed little difference between the aerated and unaerated

sections. Supersaturated conditions occurred during the day, and the

Howard Alan Simonin

lowest recorded value at night was 5.7 mg/l. Greater fluctuations in
the diurnal dissolved oxygen curve were noted as a result of continued
fertilization of pond C with nitrates and phosphates. ‘

The ortho-phosphate and nitrate concentrations decreased rapidly,
shortly after fertilization. Pond D, which showed relatively little
increase in plant growth, exhibited a rapid nitrate decline, similar to
that of pond C. The plant community of pond C increased as a result
of fertilization with nitrates and phosphates, and as a result the
concentrations of these nutrients declined rapidly. The rapid decline
of phosphate was due most likely to a combination of factors including
bacterial activity, adsorption, uptake by plants, and precipitation
with Ca4-+

The'phytoplankton in both sections of both ponds C and D responded
similarly to fertilization. Increases in the absorbance of plant pig-
ments at 665 nm were noted approximately seven days after fertilization.
During the second phase of the project, this value remained at a high
level.

A definite increase in periphyton was noted in pond C as a response
to fertilization with nitrates and phosphates. The periphyton coloni-
zation rates of the aerated section Cl were significantly greater than
those of unaerated C2. This was thought to be due to the aeration

system bringing CO into the system and acting as an additional carbon

2

source“
Filamentous algae became very abundant in pond C by the end of

the summer, but not in pond D. Oedogonium was the dominant alga and

Howard Alan Simonin

appeared first along the aeration hose in section Cl. This was attrib-
uted to the carbon dioxide being brought into the system by aeration.

The macrophyte Najas flexilis in pond D died as a result of fer-

 

tilization with nitrate fertilizer, whereas populations in pond C
remained relatively healthy. Different species of macrophytes in pond
C behaved differently over the summer period. Whether the responses
were due to the fertilization or to normal seasonal changes could not

be determined.

EFFECTS OF FERTILIZATION AND AERATION

ON THE ECOLOGY OF PONDS

BY

Howard Alan Simonin

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Fisheries and Wildlife

1973

ACKNOWLEDGMENTS

I extend my sincere thanks and appreciation to Dr. Robert C. Ball,
for his assistance and guidance throughout my graduate program. Also,

I would like to thank Drs. Niles R. Kevern and Clarence D. McNabb for
their assistance and for serving as committee members.

I greatly appreciate the help that numerous graduate students have
been to me throughout this project. I am especially grateful to Phillip
DeVore, John A. Janssen, and John P. Giesy. I would also like to thank
Sue Blaisdell for her help in identifying the aquatic plants.

Finally, I am very grateful to the Agriculture Experiment Station
of Michigan State University for their financial support throughout

my graduate program.

ii

TABLE OF CONTENTS

INTRODUCTION .
DESCRIPTION OF STUDY AREA
TECHNIQUES AND MEASUREMENTS

Pond Fertilization

Aeration System .

Physical and Chemical Parameters
Temperature .
Dissolved Oxygen .
pH . . . . .
Phosphate Concentrations
Nitrate Concentrations

Biological Parameters
Phytoplankton
Periphyton .

Macrophytes
Zooplankton
Fish

RESULTS AND DISCUSSION .

Physical and Chemical Parameters
Temperature and Weather Conditions
Dissolved Oxygen .
pH .

Phosphorus Concentrations and Uptake by Plants
Nitrate Concentrations

Zooplankton .

Primary Production
Phytoplankton
Periphyton .

Macrophytes . .

Macrophyte - Algal Interactions

SUMMARY

LITERATURE CITED .

iii

Page

11

ll
12
13
l3
13
15
l6
17
18
18
19
20
23
24

25

25
25
25
33
35
40
44
46
46
63
67
75

79

82

Table

LIST OF TABLES

Summary of the various treatments used on the four pond
sections.

Dissolved oxygen (mg/liter) recorded for Lake City ponds
C and D during the summer of 1971. . . . . . .

Percent composition by number of invertebrates collected
by light traps from the four Lake City pond sections

during the summer of 1971.

The genera of phytoplankton observed in the Lake City
ponds on September 16, 1971. . . . . .

The major aquatic plants observed in the Lake City ponds
during the summer of 1971.

iv

Page
14

34

48
55

69

Figure

8a.

8b.

10a.

10b.

LIST OF FIGURES

A map of the Lake City ponds C and D.

The daily maximum and minimum air and water temperatures
for the summer of 1971.

The change in dissolved oxygen concentration observed in
pond section Cl on September 4, 1971.

The changes in dissolved oxygen concentrations observed
in pond C during the summer of 1971.

Phosphorus concentrations observed in Lake City pond C
during the summer of 1971.

Nitrate concentrations observed in Lake City ponds C
and D during the summer of 1971.

Percent composition by number of invertebrates collected
by light traps from the four Lake City pond sections
during the summer of 1971. . . .

Phytoplankton abundance in Lake City pond C during the
summer of 1971 as indicated by the relative absorbance
at 665 nm of extracted plant pigments.

Phytoplankton abundance in Lake City pond D during the
summer of 1971 as indicated by the relative absorbance
at 665 nm of extracted plant pigments._

Photographs of pond section C1 showing filamentous algae
growing along the aeration hose. Bubbles on the water
surface indicate the aeration. The submerged macrophyte
is Potamogeton berchtoldii Fieber.

 

Photograph of pond C on August 30, 1971. Section C1
(aerated) is on the right of the divider, section C2
(unaerated) on the left.

Photograph of pond C on September 6, 1971. Section
Cl (aerated) is on the right of the divider, section
CZ (unaerated) on the left.

Page

10

27

3O

32

37

43

50

53

53

57

60

60

LIST OF FIGURES
Figure Page
11a. Photograph of pond C on September 13, 1971. Section

Cl (aerated) is on the right of the divider, section

C2 (unaerated) on the left. . . . . . . . . . . . . . . . . 62
11b. Photograph of pond C on September 20, 1971. Section

Cl (aerated) is on the right of the divider, section

C2 (unaerated) on the left. . . . . . . . . . . . . . . . . 62

12. Periphyton colonization rates for Lake City pond C as ,
determined by chlorophyll 3 measurements. . . . . . . . . . 66

13a. The observed relative abundance of macrophytes in Lake
City pond section Cl during the summer of 1971. . . . . . . 73

13b. The observed relative abundance of macrophytes in Lake
City pond section C2 during the summer of 1971. . . . . . . 73

vi

INTRODUCTION

The effects that our society has had on the natural world are
many. In regard to aquatic environments, perhaps the most important
of these concerns the process of eutrophication. The adding of nutri-
ents to our lakes and streams and the resulting increases in plant
growth have lead to problems of every sort and dimension. The complex-
ity of the various relations and interactions involved in the aquatic
environment make dealing with these problems difficult. It is this
same complexity, however, which helps to maintain the stability of
the natural ecosystem.

The many factors which affect the growth of aquatic plants are an
integral part of eutrophication. Even though a lake may be rich in
nutrients, it may not be able to support a large plant population be-
cause certain of these conditions are not met. Some of the physical
factors involved include temperature, light, depth of the water,
suitable substrate, percent littoral zone, and the degree of circula-
tion. Chemical factors would include dissolved oxygen levels, pH,
presence or absence of toxicants, concentrations of essential nutrients,
and carbon dioxide concentrations. These factors are of course not the
only ones involved, but they do help to show the interactions involved
in the eutrophication process.

Oxygen is one of the most critical components in regard to life

in the aquatic environment. When abundant dissolved oxygen (D.O.) is

l

present, and other conditions are adequate, then a diverse biota can
exist. However, when this oxygen is not present, then most forms of
aquatic life cannot survive, and the anaerobic forms become dominant.
Eutrophication is exemplified by abundant plant growth, and this in-
creased biomass in the system results in increased demands on the oxygen
balance. Edwards and Owens (1965) have summarized much of the work
concerning the effects of plants on the oxygen balance of rivers.
Owens, Knowles, and Clark (1969) showed that at high plant densities
and low light intensities the average dissolved oxygen concentration
decreased to about 1 mg/l. With low plant densities and low light
intensity, however, the average dissolved oxygen level remained at
about 6 mg/l.

The overall effect of plant life in the water results in a diurnal
change in oxygen concentration. During the daylight hours, the plants
photosynthesize and release oxygen, therefore increasing the D.O. of
the water. At night, however, oxygen production stops, and the D.0.
of the water decreases, due to the respiration of the biotic community.
In a eutrophic environment with its abundant plant growth, we would
expect both greater demands and greater fluctuations in the oxygen
balance than in a less eutrophic environment.

The problem of nutrient concentrations and the limiting nutrient
concept have been the topic of many discussions. Whether or not a cer-
tain nutrient is present in adequate supply or not is critical to the
growth of a plant. Part of the discussion concerns the fact that dif-
ferent species of plants, both algae and macrophytes, may require
nutrients in different quantities. This variation in species require-

ments results in certain species being present when conditions are

3
not adequate for others. This also is shown by seasonal changes in
plant communities.

It is generally accepted that phosphorus is the nutrient most
frequently limiting plant growth in freshwater environments. There are
of course lakes in which one of the micro-nutrients such as molybdenum,
cobalt, manganese, or iron may be limiting to plant growth (Goldman,
1972), but this is not saying that these are phosphorus-rich lakes.
Cultural eutrophication in lakes has often resulted when, by man's
activity, the input of phosphorus to a lake increased, perhaps by sew-
age effluents or by agricultural or urban drainage.

When the demand for a limiting nutrient such as phosphorus is met
by an increase in the supply, then plant growth increases. This growth
would then, however, become limited by other factors in the environment,
such as light, temperature, or other nutrients. Carbon is an important
nutrient in the growth of plants and is oftentimes in great demand.
When the phosphorus and nitrate concentrations in the water are increased,
this nutrient may very well become limiting to many of the plants. In
fact, Kerr et a1. (1972) suggest that the phosphorus and nitrogen
stimulation of algal growth may be indirect and mediated by the avail-
ability of carbon dioxide. King (1970) and Kuentzel (1969) have pre-
sented arguments that carbon and not phosphorus is the nutrient most
important in limiting algal growth.

Innumerable methods have been developed for controlling or treat-
ing the problems of eutrophication. The tremendous variety in methods
is in part a reflection of the tremendous variety in aquatic environ-
ments. Biological, chemical, and mechanical schemes have been applied

to different situations.

One of the methods used in water treatment is aeration. Aeration
of sewage and wastewater has been common practice to reduce the bio-
chemical oxygen demand. By bubbling air through the water column,
oxygen is made more available to the biota of the system. One of its
uses in farm ponds is to reduce the chance of a winterkill by creating
an oxygen supply adequate for fish. Aeration systems also have been
used in the management of larger bodies of water (Symons, 1969).

In eutrophic lakes and reservoirs which stratify during the summer
months, very low dissolved oxygen levels may occur in the hypolimnion.
This puts a stress on the deep water aquatic life and may force fish
into warmer shallow waters and result in the death of other aerobic
organisms. Another problem resulting from the reducing conditions in
the hypolimnion is that nutrients formerly trapped in the sediments are
now released to the water, and may become available to plant growth
when the lake overturns in the fall.

Aeration is often used to destratify reservoirs or lakes where
eutrophication problems arise. This destratification theoretically
results in a homothermal condition with oxygen present at all depths,
and the nutrients remaining locked in the sediments. Symons (1969)
has reported some of this work in regard to reservoirs. Leach and
Harlin (1970) studied the effects of induced aeration on a small moun-
tain reservoir which was used as a rainbow trout lake. In a study
quite similar to the one reported here, Malueg et al. (1973) recorded
the effects of induced aeration on stratification and eutrophication
processes in an Oregon farm pond.

Fast (1971) reported the results of two aeration projects. In

one, the hypolimnion of a eutrophic lake was aerated while thermal

stratification was maintained. In the other study, an oligotrophic
lake was aerated and destratified. In both of these projects the
aeration resulted in changes in the oxygen and temperature regimes of
the lakes, and consequently changes in the animal and plant populations
were observed.

Whereas the aeration research discussed above was concerned with
a stratified environment, the work reported in this paper is concerned
with aeration of a shallow, unstratified environment. The shallow
nature of the study ponds meant that plant growth was possible even at
the deepest point. Littoral communities of this nature are character-
istically rich in both plant and animal life.

In a typical eutrophic pond we would expect several changes in
the environment to occur as a result of the plant activity. As a
result of photosynthesis during daylight hours, the amount of C02
and bicarbonate in the water would be expected to decrease.
Because of its relationship to the hydronium ion concentration, this
decrease in C02 and bicarbonate would coincide with a rise in the pH
of the water. In ponds with dense plant populations the pH may rise
above 10, where it may have adverse effects on the biota of the system.

As was discussed previously, a second environmental change result-
ing from an increase in plant populations is an increase in the fluctu-
ations of dissolved oxygen. A condition of abundant plants would result
in higher daytime dissolved oxygen levels, and lower nighttime levels.
In very eutrophic situations these low D.O. levels at night may greatly
stress the biota of the system. In fact, it is not uncommon that after

a period of hot, calm, cloudy days, where photosynthesis is low, the

level of dissolved oxygen at night may drop to critical levels. At
such levels intolerant animal life dies and a summerkill results.

An objective in managing a eutrophic pond environment would be
to eliminate or decrease the possibility of adverse effects from pH
and oxygen changes. Aeration was thought to be a reasonable method of
eliminating the high pH and low dissolved oxygen levels. By bubbling
air through the water column, a certain amount of C02 would be added.
This would act to balance some of the CO2 removed by plants and would
in effect decrease the possibility of a high pH. The oxygen being
added to the water by aeration would then eliminate the chance of
oxygen depletion occurring at night.

The research reported in this paper was focused on the effects
of fertilization and artificial aeration on the plant communities of
two small ponds. As a result of fertilization, the plant community
was expected to increase, and the dissolved oxygen concentrations at
night were expected to drop to levels that would be critical to the
pond biota. In an aerated system, however, these oxygen deficiencies

would be eliminated.

DESCRIPTION OF STUDY AREA

This study was carried out during the summer of 1971 at the Water
Quality Laboratory of the Lake City Agricultural Experiment Station.
The experiment station is run by Michigan State University and is
located about two miles south of Lake City, Michigan in Missaukee
County.

The Department of Fisheries and Wildlife maintains the Water
Quality Laboratory which includes four experimental ponds and adequate
laboratory facilities. A 2.6 hectare (6.5 acre) reservoir formed by
the damming of Mosquito Creek is the water source for the ponds. The
outlets of the ponds connect with the downstream section of Mosquito
Creek. The four ponds are designated A, B, C, and D from west to east.
Only ponds C and D were used in this study.

Both study ponds were divided into two sections by a large black
plastic divider. This resulted in two ecologically similar but separate
units, where the effects of aeration or no aeration could be determined.
The plastic divider was supported by a rope running the length of each
pond and by posts driven into the pond bottom. The bottom of the wall
was sealed with the sediments by extending the excess plastic along
the pond bottom and weighting it down with rocks and gravel. The
dividing walls in both ponds C and D were set up to give an inlet and
outlet for each section. Chicken wire was used to cover the inlet and

outlet areas to keep the fish populations of each section from mixing.

A relatively static condition was maintained during the summer, with
a small inflow and outflow being unavoidable. Figure 1 shows the
layout of the ponds and the pond sections.

The surface area of pond C was 0.07 hectare (0.17 acre) and of
pond D was 0.07 hectare (0.18 acre). Both ponds were quite shallow,
having an average depth of 1.1 meters (3.5 feet) and a maximum depth
of 1.5 meters (5 feet). The volumes of water in the pond sections

were as follows:

Cl - 349,800 liters
C2 - 386,000 "
D1 - 363,000 "
D2 - 416,300 "

Sections Cl and D1 were the aerated sections.

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TECHNIQUES AND MEASUREMENTS

Pond Fertilization

 

The increase in nutrients in ponds C and D was carried out in
two phases. During the first part of the summer, the ponds were fer-
tilized once, and the declines in phosphate and nitrate concentrations
were measured, along with the effects of this fertilization on the
biotic community. During the second phase of the project, which began
at the end of August, the ponds were fertilized every fourth day.
During this phase, high concentrations of phosphate and nitrate were
maintained in the system. Again, the effects on the biotic community
were measured.

The levels of nutrients in pond C were brought up to 6 mg/l P04
as P and 15 mg/l N03 as N. The nitrate concentration of pond D was
likewise brought up to 15 mg/l, but this pond was not fertilized with
phosphates. These nutrient levels were chosen in order to approximate
levels found in secondary sewage effluent. This was done because we
wanted to approximate expected conditions at the MSU Water Quality
Project. In this project secondary sewage effluent will flow through
a series of four ponds (Ball and Tanner, 1972).

The nitrate levels of ponds C and D were measured the day before
each fertilization. From these values, and the known volumes of each

pond, it could be determined how much fertilizer had to be added in

11

12

order to bring the nitrate concentration to 15 mg/l. The nitrate form
used was KN03 and was 33.3 percent by weight of the powdered fertilizer.

The phosphate fertilizer was 46 percent available P205 and is
referred to as triple superphosphate. The phosphate levels in the
ponds were measured the day before application of the fertilizer, as
was done with the nitrates. The ambient phosphate level and volume
of each pond section were then used to calculate the amount of phosphate
fertilizer to be added. As was mentioned before, only pond C was
fertilized with phosphates.

In order to increase the mixing of the powdered fertilizer with
the water, the fertilizer was first dissolved in buckets of pond water
on the shore. This solution was then sprayed over the pond from the
back of a rowboat, using a hand pump. The boat was then rowed around
the pond until the fertilizer appeared evenly distributed.

During the first phase of the project, the ponds were fertilized
with nitrates on July 23, and with phosphates on July 24. During the
second phase, the ponds were fertilized on August 27 and 31, and

September 4, 8, 12, and 16.

Aeration System

 

A one-half horsepower oil-less air compressor distributed by
Hinde Engineering Co. was used as an air source for this project. The
compressor was set up on the dike separating ponds C and D. From the
compressor, tubing lead to a tee and from there to sections Cl and D1,

the sections nearest the compressor (Figure 1). In each of these

13

sections was 200 feet of Air—aqua aeration tubing. This tubing is
weighted and has small air openings at frequent intervals.

According to Hinde Engineering Company, the compressor was supply-
ing about 4 ft3/min. There would therefore be 2 ft3/min of air being
supplied to each of the aerated sections Cl and D1. The compressor
was run continuously from July 15 until September 20, except for
repairs and replacing the compressor itself on September 5.

A summary of the various pond treatments is shown in Table 1.

Physical and Chemical Parameters

 

Temperature

Water temperature was measured daily using Taylor maximum-minimum
thermometers, which were left in pond sections Cl and D2. Temperature
readings were recorded at 9:00 A.M. daily, therefore giving the previous
day's high and nighttime low. Air temperature, rainfall, and general
weather conditions were recorded at the weather station of the Lake

City Agricultural Experiment Station.

Dissolved Oxygen

Since the level of dissolved oxygen in the ponds was a critical
part of this project, a continuous sensor was used to record the diurnal
oxygen curves. On August 13, a submersible electric pump was placed
in pond Section C2. The pump was inside a wire basket designed to

keep fish and debris from clogging the intake. Water was pumped from

14

Table 1. Summary of the various treatments used on the four pond
sections.

 

 

 

Pond SECtiOI'l Fertilizer FertIEIIzer Aeration
Cl x x x
c2 x x
D1 x x
D2 x

 

 

15

a depth of about 0.8 meter into the lab and into a large plexiglass
cylinder where the oxygen probe was suspended. The water was then
returned to the pond section through a plastic hose.

The oxygen levels were measured with a Beckman Model 777 dissolved
oxygen meter, which was calibrated daily during the morning hours. The
dissolved oxygen meter was connected to a Sargent recorder, which ran
continuously.

In order to also monitor the diurnal oxygen curve of pond section
Cl, the submersible pump unit was moved to section C1 on September 1.

On September 9 the unit was returned to section C2. Because of the
relatively small response to fertilization shown in pond D, a continuous
monitor of the dissolved oxygen was not made.

Chemical measurements of dissolved oxygen were made before and
after the monitoring system was set up, and to calibrate the D.O.
meter. These measurements were made by using the azide modification
of the Winkler method (American Public Health Association et al., 1971),

however, phenylarsene oxide was used in place of sodium thiosulfate.

pH

Measurement of hydrogen ion activity was made several times during
the project after a Beckman pH meter was set up on August 17. The

pH levels before and after fertilization were particularly watched.

16

Phosphate Concentrations

The measurement of orthophosphate in both sections of ponds C and
D was made at regular intervals. The stannous chloride method as de-

scribed by Standard Methods for the Examination of Water and Wastewater

 

 

(APHA et al., 1971) was used for these determinations. This is a A
photometric method and involved measuring the color development at
690 nm on a Beckman Model B spectrophotometer.

The water samples were not filtered or digested, so the measure—
ments of orthophosphate include the total dissolved and suspended ortho-
phosphate. A preliminary acid hydrolysis step was included during
several measurements. By boiling the sample with acid, the condensed
polyphosphates are converted to orthophosphates which can then be
measured with the stannous chloride test. This additional step in the
analysis resulted in orthophosphate values only slightly greater than
those obtained without the hydrolysis. It was therefore decided to
eliminate this step in subsequent determinations.

After the initial fertilization of the ponds on July 23 and 24,
water samples were taken every two hours from pond C, and phosphate
determinations were made as soon as possible. This was done to monitor
any rapid decline in orthophosphate concentration in the water. From
July 26 to August 2 phOSphorus determinations were made daily, to
monitor the changing concentrations in the water. After this period,
the rate of change in orthophosphate concentration had decreased, and
measurements were made every third or fourth day. 3

During the second phase of the project, which began on August 26,

the phosphate concentrations in both sections of ponds C and D were

l7

determined every fourth day. These values then were used to determine
how much phosphate fertilizer was to be added the next day in order to

bring the concentration in the pond back up to 6 mg/l P04 as P.
Nitrate Concentrations

The brucine method for determining nitrate nitrogen (APHA et al.,
1971) was used in this study. The reaction between nitrate and brucine
produces a yellow color, which was then measured at 410 nm on a Beckman
Model B spectrophotometer. Nitrate nitrogen is the main form of
nitrogen in most natural bodies of water, and since the fertilizer
added was in the nitrate form, a measure of this constituent was neces-
sary to examine the change in concentration over a given time period.

Following the initial fertilization of ponds C and D, determinations
of nitrate were made every three days. Several pieces of data were lost,
however, when we encountered problems with the hot water bath on July
30 and August 2. During the second phase of the project, the nitrate
concentrations were determined for both sections of ponds C and D
every fourth day. As with the phosphate, these values were used to
determine how much nitrate fertilizer should be added to each section

to bring the concentration up to 15 mg/l N03 as N.

18

Biological Parameters

 

Phytoplankton

The phytoplankton standing crop in each section of ponds C and D
was measured spectrophotometrically by a method modified from Talling
(1969). A 250 ml water sample was filtered on an HA 0.45 p Millipore
filter. This filter was then placed in a mortar and ground for 2
minutes in about 2 ml of 90% acetone. The mixture was then diluted to
10 m1 and centrifuged for 5 minutes, after which the optical density
was determined at 665 nm on a Beckman Model B spectrophotometer. It
was hoped that by using a background reading at 750 nm and also readings
for each sample after acidification, we would be able to arrive at a
value for chlorophyll 3. However, because the phytoplankton populations
were very low, only relative values could be obtained. These values
are the optical densities of each sample at 665 nm.

During the first phase of the project, phytoplankton samples were
taken daily, and later every second day. During the second phase,
phytoplankton determinations were made every third day.

A qualitative sample to determine the species present in the
phytoplankton was made at the end of the summer by passing buckets of
water through a plankton net. The abundant filamentous algae in pond
C eliminated the possiblilty of towing the net behind the boat. These

samples were preserved in alcohol and identified later in the laboratory.

19

Periphyton

The term periphyton as used in this study includes both epiphytic
and epilithic algae. In his discussion of this community, Ruttner
(1963) uses the term aufwuchs, which includes both plants and animals
living attached to a substrate. The term periphyton is more restrictive
and is a more accurate description of the community being measured in
this part of the project.

To measure the response of periphyton to the conditions in the
ponds, artificial substrates were used. These substrates were left in
the pond for a given period of time and then removed. The amount of
periphyton colonization which had occurred was then measured spectro-
photometrically and the amount of chlorophyll a per unit area was
determined.

The artificial substrates used were plexiglass plates having an
exposed surface area of 140 cm2. The Substrates were mounted horizon-
tally in the water on a cross bar 0.5 meter below the water surface.
This was held up by a metal post driven into the pond bottom. Eight
substrates were used in each series in each of the four pond sections.
During the first phase of the project, these periphyton substrates were
left in the water for five days. Upon collecting the colonized sub-
strates, clean substrates were started. During the second phase of
the project, the substrates were replaced every four days.

At the end of each exposure period the periphyton was scraped
from two of the substrates and preserved in 95% alcohol for later iden-
tification. The other six substrates were each placed in a plastic bag

and frozen. This freezing procedure not only allowed for later analysis

20

at a convenient time, but also served to help rupture the algal cells
and release the plant pigments.

After allowing the sample to thaw, the periphyton was scraped from
the plate into a mortar. The plate and scraper were rinsed with 90%
acetone, and the material was ground for two minutes. The volume of
the extract was then brought up to 20 m1, and a subsample was then
centrifuged for five minutes. Next, the absorbance of the sample was
determined at 665 nm and 750 nm on a Beckman Model B spectrophotometer.
The sample was then acidified with 0.1 ml 4N HCl, recentrifuged and
measured again at 665 nm and 750 nm. The values at 750 nm are used
to correct for background absorption by materials other than plant
pigments. The acidification step is to correct for the presence of
non-photosynthetic plant pigments. The chlorophyll a per square meter

was then determined as explained by Standard Mathods (APHA et al., 1971).

 

Macrophytes

The measurement of primary production of the higher aquatic plants
has always created problems to the aquatic biologist. Wetzel (1965)
and Westlake (1969) have discussed these factors and the methods of
dealing with them. Depth of the water, sediment type, amount of peri-
phyton covering the macrophyte, and the diversity of the plant community
all affect the methods of measuring the primary production.

In this study only the primary production of the submerged aquatic
vegetation was measured. Emergent vegetation and floating leaved
macrophytes were present in some of the pond sections, but not abundant

enough to accurately determine production rates.

21

As explained by Westlake (1969), the primary production rate can
be determined from the change in biomass. This method does have several
deficiencies, however, in that loss of biomass due to dying or decaying
vegetation may balance the gain in biomass due to the growth of young
plants. Also, different plant species may have their greatest growth
rate at different times of the year. Therefore, the measurements of
the biomass of a plant community should be made during the main growing
season and flowering period of the species being measured, and not
during the time period when parts of the plant decay and drop off.

Another factor to be considered is the amount of plant biomass
in the sediments as roots, rhizomes, or various anchoring devices.

This is particularly important when dealing with emergent vegetation

and plants having large rhizomes. When determining the amount of biomass
per unit area, as in primary production studies, it is important that
this underground biomass is included.

One method used to determine the change in biomass of the macro-
phyte community was to harvest and dry representative samples. One
means of harvesting used was to place a 10 cm X 10 cm wooden square
over the plant community and then remove all the plant material within
the square. This was done at a depth of about 0.7 meter using a mask
and snorkel. The sample was then carefully washed to remove detritus
and periphytic algae. Edwards and Owens (1965) showed that the weight
of epiphytic algae may be on the same order of magnitude as the weight
of the macrophytes. Washing of the plants proved to be a time consuming
job and limited the number of samples that could be processed.

Whereas the wooden squares were used in the sampling of relatively

small plants in shallow water, a 15.2 cm X 15.2 cm Ekman dredge was

22

used for sampling in the deeper water. Again, the samples were washed
to remove detritus and periphyton. The washed plants were then placed
in white enamel pans and dried for 18 hours at 80C. The dried plants
were then placed in sealed, air tight plastic bags for transport to
East Lansing where they were weighed.

Sampling was done three times during the summer: before fertili-
zation, at the end of the first phase, and at the end of the second
phase. As was mentioned, the process of washing the samples limited
the number that could be collected in a reasonable time. -

A second method used to monitor any changes in the macrophyte
community was to periodically examine quadrats in each of the pond
sections. Three 0.5 m X 0.5 m quadrats were established in each of
the four pond sections and were marked by a wooden stake at each of
the corners. Observations and measurement of plants in the quadrats
were made every two weeks throughout the project, using a mask and
snorkel.

By using a quadrat technique, it was possible to measure the change
in height of the plants, and also to observe the colonization and growth
of new plants in the quadrat. This was done by visually dividing the
quadrat into 16 equal units and then from each unit recording the
species and height of the tallest plant. From these data, which repre-
sent only the tallest plants in the sections, an average value for each
species was determined. Also, the percentage of the 16 units where a
given species was tallest was determined. Sections which were barren
or covered with filamentous algae were recorded as such.

The quadrat method does not measure the primary production or

biomass of an area, but it is a very useful tool in monitoring the

23

community structure and the ecological changes which occur over a
period of time.

Specimens of the various plant species found in the Lake City
ponds were collected and pressed about midway through the summer.

These were later identified to species.
Zooplankton

Zooplankton samples were taken four times during the project, at
four week intervals. A light trap used at night was the method of
sampling. The trap consisted of an amber light mounted in a small jar
under a wooden float. Under the light was a funnel leading to a col-
lecting chamber. One trap was set out in each of the four pond sections
from 9:00 P.M. until 10:00 P.M. The samples were then preserved in
95% ethanol for later measurement and identification.

Baylor and Smith (1953) and Ervin (1969) have shown that light
traps used for zooplankton sampling are very effective and deserve
further study. Both found that yellow light attracted cladocerans,
copepods, water mites, ostracods, and various aquatic insects. Since
the light source may result in different responses or rates of response
among various organisms, the light trap is most likely best used as a
qualitative sampling method. Assuming that these different responses
and rates of response are generally constant, we may still use the data
collected to make approximate comparisons between ponds.

The biomass of each sample was measured volumetrically in a

graduated cylinder. Then, one milliliter subsamples were examined in

24

a Sedgwick-Rafter counting cell, and the percent composition of

organisms by count was determined.

Fish

The effects of fertilization and aeration on the fish life in
the ponds were not determined. However, since fish play an important
role in the aquatic environment, an attempt was made to have equal
numbers and types of fish on each side of the plastic divider. Fish
from ponds C and D were not mixed, however. To keep the fish from
mixing between the two sections of each pond, chicken wire extended
from the end of the plastic divider to the shore.

The fish species found in the Lake City ponds included golden

shiners, Notemigonus crysoleucas; pumpkinseed sunfish, Lepomis gibbosus;

 

 

green sunfish, L; Eyanellus; largemouth bass, Micropterus salmoides;

 

yellow perch, Perca flavescens; and brown bullheads, Ictalurus nebulosus.

 

RESULTS AND DISCUSSION

Physical and Chemical Parameters

 

Temperature and Weather Conditions

Findings in regard to temperature showed that ponds C and D did
not differ appreciably. The maximum water temperature recorded during
the time of this study was 29C (85F) while the minimum temperature was
16C (61F). The average diurnal change from nighttime low to afternoon
high was 3.60 (6.4F). Figure 2 shows the daily maximum and minimum
air and water temperatures for the summer of 1971.

June proved to be the warmest month of the summer, with July and
August being colder than average. The summer months were fairly dry
in relation to previous years. Only August had more precipitation

than normal.

Dissolved Oxygen

Fish kills have occasionally been observed during the summer
months in ponds or shallow lakes with abundant plant growth. These
summerkills have been observed to occur after a period of several days
with warm temperatures, cloudy skies and little or no wind. Bennett

(1962) records that under these weather conditions, the dissolved

25

26

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27
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28

oxygen normally abundant in the daytime, may become completely used up
during calm, hot nights. High water temperatures, darkness, and rapid
organic decay of shallow weed-filled ponds are also thought to contrib-
ute to the occurrence of summerkills.

Considering the nutrient rich shallow nature of the ponds in this
study, it was expected that dissolved oxygen levels would drop to fairly
low levels during the night. Filamentous algal mats floating on the
pond surface would also tend to block sunlight and decrease the amount
of oxygen produced during daylight hours. These low oxygen levels
were expected to create an unfavorable environment for the animal life
of the pond.

Conditions during the summer of 1971, however, did not result in
low dissolved oxygen levels. The lowest recorded value was 5.7 mg/l
oxygen on August 15 in pond Cl. Figures 3 and 4 show the changes
which occurred in dissolved oxygen levels over a one day period and
over the entire summer period. Considerable fluctuations can be seen
between the daytime and nighttime levels, but it is not likely that
animal life was stressed by any of the low levels.

Figure 4 shows clearly that the diurnal fluctuations of dissolved
oxygen in pond section Cl during September were greater than the fluc-
tuations in C2 during August. It should be pointed out that a large
amplitude of fluctuation also was observed in section CZ during Septem-
ber. The greater fluctuations are not due to the aeration of Cl, but
to the continued fertilization of the pond. The greater fluctuation
in diurnal oxygen concentrations is a characteristic of eutrophic

conditions. It is interesting to speculate that if a high nutrient

29

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TIME

Figure 3

31

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SEPTEMBER

AUGUST

Figure 4

33

level had been maintained from the beginning of the project, perhaps
greater fluctuations in diurnal D.O. curves would have occurred.

Since the concentration of dissolved oxygen in the water was
usually quite high, the efficiency in adding more oxygen to the system
was very low. It also appeared that the aeration system was not reduc-
ing the supersaturated conditions as it had been expected to do. It
is possible that a larger aeration system may be necessary under con-
ditions like these. In deeper water, or water with a lower D.0.
level, the efficiency of an aeration system would increase.

As is discussed later, the plant production in pond C was much
greater than that in pond D. This was attributed to the abundant
supply of phosphorus. As a result of this more productive plant com-
munity in pond C, the daytime oxygen levels were also higher than in
pond D. Table 2 shows the dissolved oxygen concentrations for one

pre-fertilization date and three post-fertilization dates.

pH

The water in the Lake City ponds has been found in other studies
to be relatively hard and alkaline, with total alkalinity values
ranging between 55 and 75 ppm (Sohacki et a1, 1969). The normal pH
of the ponds ranges from 8.0 to 9.0 during the summer months. The
range of pH values in pond C during the summer of 1971 was from 6.9
to 9.2.

Abundant plant growth in a pond environment has a definite effect
on the water pH. During the process of photosynthesis, plants often

use up all the free C02 in the pond and much of the bicarbonate,

34

Table 2. Dissolved oxygen (mg/liter) recorded for Lake City ponds C
and D during the summer of 1971.

 

 

 

. Date
P°nd seetlon 7/6 7/29 7/31 8/4
c1 12.68 11.71 17.12
9.99
oz 12.98 14.57 16.90
D1 9.45 8.85 11.38
10.25

D2 9.50 9.03 11.65

 

35

resulting in a rise in pH (Bennett, 1962). Free CO2 is returned to
the system at night due to respiration, resulting in a diurnal change
in pH values.

A definite drop in pH values was observed following fertilization
with phosphorus. This fertilizer was in a phosphoric acid form.
Before fertilization of C2 on August 28, the pH was 7.7 and after
fertilization this value had dropped to 6.9. A pH value of 7.7 was
recorded the next day again and it appears that the adding of this acid
had no long lasting effects on the pH of the pond. Similar results
were found in section C2 on August 31 with a drop in pH from 8.0 to
7.4. On September 16, the pH of section Cl dropped from 8.8 to 8.3

following fertilization.
Phosphorus Concentrations and Uptake by Plants

The concentration of orthophosphate in both ponds C and D prior
to fertilization was less than 0.003 mg/l P04 as P. This is a fairly
common level for natural bodies of water. Following fertilization of
sections Cl and C2, the uptake of phosphorus was rapid (Figure 5).
Rigler (1956) and Hepher (1958) have shown that phosphorus may be
rapidly taken up by various components of the aquatic community. This
rapid uptake and the process of mixing the fertilizer with the pond
water make it very difficult to determine when to measure the phos-
phorus concentration. As is shown in Figure 5, measurements taken
every two hours after fertilization on July 27 showed variations from

4.0 to 6.8 mg/l P04.

36

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37

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38

The values of orthophosphate concentrations obtained during the
second half of the project are connected by lines in Figure 5. Between
each of the measurements, however, the actual concentration was theo-
retically increased to 6 mg/l P04. Measurements on September 16 show
that the actual values were fairly close to the theoretical values
after fertilization.

Also shown in Figure 5 is the fact that sections Cl and C2
behaved similarly in regard to change in phosphorus concentration.

One difference which could be pointed out, however, is that during the
second phase of the project, Cl values were consistently below C2
values. As is discussed later, the periphyton community of Cl was
more abundant than that of C2, and if we assume that this community is
taking up much of the phosphate, this would explain the difference in
concentrations. Periphyton communities may be very important in
eutrophic situations and this explanation would seem reasonable.

In looking at the overall effects of fertilization with phosphorus
on pond C as compared with pond D, it appears that phosphorus is the
major factor limiting plant growth in these ponds. Pond D, which
received only nitrate fertilizer, showed relatively little increase
in plant activity.

Many environmental and physiological factors may influence the
uptake of phosphorus by plants. Gerloff (1969) has reported two zones
in regard to algal growth and phosphorus concentration in the water.

A phosphorus deficient condition is indicated when the concentration
of phosphorus in the plant tissue is below a specific critical level.

In this deficient zone, plant growth is directly dependent on the

39

phosphorus concentration in the water. The algae of the Lake City
ponds were most likely in this phosphorus deficient zone prior to
fertilization.

Gerloff (1969) defines the critical level as the concentration
of phosphorus in the tissue which is just inadequate for maximum
growth. If the algal tissue contains more than this critical concen-
tration, it is in a luxury consumption zone. In this condition
phosphorus is taken up by the plant and stored in the algal cells.

As Gerloff (1969) points out, however, this luxury consumption is not
associated with increases in yield. In this zone growth remains at
a constant maximum.

Light is one of the major environmental factors which may influence
the uptake of phosphorus by plants. Kuhl (1962) found that in most
cases the uptake of phosphorus is increased by light. He reported
research done with the diatom Nitzschia, and the green algae Chlorella,

Ankistrodesmus, Hydrodictyon, and Scenedesmus.. Azad and BorChardt

 

 

 

(1968), however found that whereas Chlorella had a rapid uptake during

darkness, Scenedesmus had no measurable uptake during darkness.

 

Mackereth (1953) reported that the uptake of phosphorus by Asterionella

 

cells occurred at the same rate independent of light or dark. In
regard to macrophytes, light was found to increase the overall uptake

of phosphorus by Elodea densa (Jeschke and Simonis, 1965).

 

The role of bacteria in the phosphorus balance of ponds is also
important. The effect of bacteria is to reduce the rate of exchange
of phosphorus with the plants and to hold most of the phosphorus in
the water column (Phillips, 1964). Bacteria also are known to take up

phosphorus more rapidly than either the algae or aquatic plants.

40

The adsorption of phosphorus onto surfaces may be a very important
consideration in shallow ponds, where there is a large bottom area to
water volume ratio. The presence of macrophytes also increases the
surface area and sites where phosphorus could become adsorbed. Harter
(1968) and Fitzgerald (1970) report that lake sediments are capable of
adsorbing large amounts of phosphorus from the water. Some of this
phosphorus is tightly bound, but the remainder is loosely bonded and
may be released to the water at a later time. Hepher (1958) reports
that in alkaline water with a high calcium content, most of the phos-
phorus fertilizer added to ponds is precipitated as Ca3(PO4)2. An

increase in pH also results in more phosphate being precipitated.
Nitrate Concentrations

Nitrogen can be found in several common forms in aquatic environ-
ments, NH4+, N02-, and N03- being the most common. Most plants can
use any of these three forms as a source of nitrogen for proteins
(McCarty et al., 1970). In natural waters nitrate is the most common
form and is the product of the oxidation of NH4+ and N02-.

The fertilizer added to both ponds C and D was in nitrate form
so was readily available to plants in the water. Chemical determinaf
tions likewise were made only of the nitrate levels. Nitrate is quite
soluble in water and is relatively non-reactive chemically, under
natural water conditions. The major factor influencing the nitrate
concentration is biological action, including incorporation into organic

matter .

41

Figure 6 shows the nitrate concentrations observed during the
summer of 1971 in ponds C and D. As with phosphorus, the nitrate was
taken out of the water quite rapidly. Even in pond D, the concentration
went down rapidly. Lines have been drawn in Figure 6 connecting the
measured nitrate concentrations. However, as was the case with phos-
phorus, the nitrate concentrations were theoretically increased to 15
mg/l between each measurement during the second half of the summer. A
measurement of nitrate in C1 on September 17 showed that following
fertilization the actual concentration was fairly close to the theo-
retical value.

Since the plant populations of pond D did not appear to respond
significantly to the fertilization, the rapid decrease in nitrate
concentration could possibly have been due to bacterial action. The
same mechanism appears to have been operating in both ponds. Kerr et
a1. (1972) found that bacterial populations increased within 12 hours
after fertilization with N, P, and KCl. They also report that the
relative availability of organic carbon and CO2 could regulate the
total bacterial density and the molecular form of nitrogen present in
the water. It would therefore seem possible that bacteria were reducing
NO3-N to another form such as NH4-N. This, however, requires anaerobic
conditions, which were not observed in the ponds.

Because of the increased primary production in both sections of
pond C, the nitrate nitrogen was removed from the water faster than in
pond D. This is shown for both phases of the project. As was noted
also in regard to phosphate concentrations, the nitrate values of sec-
tion Cl were consistently lower than those of C2. This was attributed

to the more abundant periphytic and filamentous algae in section Cl.

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43

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44

Nitrogen is often present in relatively low amounts in natural
systems. The pre-fertilization nitrate concentration for pond C was
0.025 mg/l and for pond D 0.011 mg/l. If phosphate alone had been
added to pond C with no nitrate, it is likely that nitrate would have
become the limiting factor for plant growth. In situations like this,
nitrogen fixing blue-green algae may become the dominant algal form
(Provasoli, 1969).

As was reported concerning phosphorus uptake by plants, the uptake
of nitrate also is dependent on light. Light was found to stimulate

the uptake of nitrate by Chlorella and Ankistrodesmus (Morris and

 

Ahmed, 1969) and also by a Ceratophyllum - periphyton community

 

(Toetz, 1971). The assimilation of NH +, however, was found by Toetz

4

to occur both during the day and at night.

Zooplankton

 

Most zooplankton are primary consumers and in the absence of
predators would be expected to increase in population size in relation
to increases in food supplies. Brooks (1969) and Hall et al. (1970)
have shown, however, that the presence of predators in the system has
a definite effect on the size and composition of the zooplankton pop-
ulation. Both researchers report that fish predation had the effect
of removing the larger zooplankters. This results in the smaller
zooplankton, such as Bosmina, rotifers and small crustaceans increasing
in abundance. Hall et a1. (1970) report that there is an interaction
of nutrients and predation in regulating the zooplankton population.

Although increased nutrients tend to increase the zooplankton biomass,

45

predation by fish at least partly balances this increase by eliminating
the larger zooplankters.

Various species of zooplankton may react in different ways to
increases in primary production. Increases in macrophytes in shallow
ponds, for example, would most likely lead to increases in Chydorus
populations, since this cladoceran is a weed dweller and is more
benthic in habit. Brooks (1969) discusses the possibility of using
Bosmina as an indicator of enriched environments. As a lake is enriched,

Bosmina coregoni longispina has been observed to be replaced by Bosmina

 

longirostris. Observations of zooplankton in the Lake City ponds

 

showed that Bosmina coregoni was the only member of this genus present.

 

It was a major component of the zooplankton even at the end of the
summer.

In using a light trap for sampling zooplankton, the limitations
of this technique must be remembered. Members of the zooplankton
community, for example, swim at different rates and would be expected
to be sampled differently. Also, different organisms collected by
the traps are known to prefer certain habitats in the littoral community,
some being more benthic than others. Another complication in the use
of light traps is that light would travel a considerable distance in
a clear pond, but it would not reach out as far in a phytoplankton
rich pond. In the clear pond, then we would be sampling a larger area
than in the phytoplankton rich pond. Although we would expect a greater
zooplankton biomass in the phytoplankton rich pond, our results may
not reflect the true situation. Caution must be observed in the inter-

pretation of results obtained with light traps.

46

Table 3 and Figure 7 show the fluctuations in species composition
that the zooplankton were observed to undergo. Definite correlations
or trends are difficult to find in the data. Various species of zoo-
plankton undergo seasonal cycles in regard to population size, and
two neighboring ponds, otherwise quite similar, may be a week out of
sequence with each other (Hall, personal communication). If this is
the case, then samples taken once a month may find a certain species
blooming in one pond but only fairly common in the other pond. Attrib-
uting such differences to different environmental parameters may be
quite incorrect.

The volumes of the various samples are recorded in Table 2 and
show a range of 0.4 to 34.8 ml. The largest sample by volume was

taken in pond C2 on September 14 and was over 90% Cypridopsis

 

(Ostracoda). A sample taken on August 18 in pond D2 measured 9.3 ml

and was about 90% Bosmina coregoni.

 

Primary Production

 

Phytoplankton

The primary productivity of the phytoplankton in ponds C and D
remained at fairly low levels throughout the summer of 1971. Even
though nutrient levels in pond C were high, the water remained clear.
During the summer of 1970, Massey (personal communication) fertilized
the Lake City ponds A, B, and C at various levels: A - 5 mg/l both
phosphates and nitrates, B - 2.5 mg/l both phosphates and nitrates,

and C - 1.25 mg/l both phosphates and nitrates. He found that in pond A,

47

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49

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>0 embomHHoo moumcnmuum>cw mo Honesc nn cowuwmonEoo ucwoumn

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80

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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sasunu A8 NOIlISOdWOO %

 

 

 

 

 

 

6/26 7/25 8/18 9/14 6/26 7/25 8/18 9/14

6/26 7/25 8/18 9/14

50

 

CYCLOPOID COPE PODS

CHYDORIDAE

DAPHNIA
BOSMINA COREGONI

HYDRACAR INA
OSTRACODA

 

 

(D
I
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Figure 7

V
t

 

iW/////////////////%
W 8

 

 

 

 

7/25

 

 

 

 

 

. W/// M, ~
8 8 8 °W

HBBWHN A8 NOILISOdWOO %

 

 

51

which he fertilized daily, large phytoplankton blooms resulted in a
pea-soup character. Pond B was observed to have both large phyto-
plankton and filamentous algal blooms. Since large filamentous blooms
were also observed in 1971 in pond C, this pond appears to have re-
sponded similarly under different nutrient concentrations.

A small, but significant increase in the plankton community of
both ponds was observed about seven days after fertilization, both
during the first phase, and initiation of the second phase of the
project (Figure 8). This increase was much more pronounced in the
second phase, when high nutrient concentrations were maintained. It
would seem possible that some interactions, perhaps involving bacteria,
could release essential micro—nutrients and result in this delayed
response to fertilization. Kerr et a1. (1972) found that following
fertilization with nitrogen, phosphorus and potassium, the bacterial
population increased within 12 hours, whereas the algal population
increased 36-48 hours after fertilization. The bacteria appear to
be able to more rapidly utilize the added nutrients, and the consequences
of this action remain in question.

Even though pond D was fertilized only with nitrates, the phyto-
plankton community responded in the same manner as the community of
pond C. Evidently the fertilization with nitrogen created a chain of
events which in seven days lead to a stimulation of the phytoplankton.
It is not possible to say what effect the added phosphorus in pond C
had on this sequence.

An extensive dieoff of the macrophyte Najas was observed in pond
D during the second week of August. Figure 8b shows that a slight

increase in the phytoplankton population of pond D also occurred during

52

Figure 8a. Phytoplankton abundance in Lake City pond C during
the summer of 1971 as indicated by the relative
absorbance at 665 nm of extracted plant pigments.

Figure 8b. Phytoplankton abundance in Lake City pond D during
the summer of 1971 as indicated by the relative
absorbance at 665 nm of extracted plant pigments.

ABSORBANCE

ABSORBANCE

0.7 1

0.5 ‘

0.4 "

0.3 "'

0.2 “

0.1 "

 

53

POND C —-C1 ° '02

Flgu re Be

A A A
' fl
0 4 UFI‘IT'II'I'I[TlIII'W'fV‘I‘UT'ITUI’TIIIIU'U‘VUrjUUIUI—

 

 

 

  
 

 

24 29 3 8 i3 18 23 28 2 7 i2 l7
JULY AUGUST SEPTEMBER
0 i i i i i i
FERTILIZED inmate
POND D —D1 - '02
0.7 “
0.6 " e
0.5 “
0.4 ‘
0.3 "
0.2 ‘ Figure 8b
0.] ‘1
o u
24 29 3 8 i3 18 23 28 2 7 12 i7
JULY AUGUST SEPTEMBER
i i i i 4 i i
nurmzso reanuzeo

54

this period. It would seem lOgical to assume that this dieoff of
‘Najas resulted in nutrients being released to the water which were then
available for plant growth. Boyd (1970) reports that aquatic macro-
phytes decompose rapidly, and a large quantity of the nutrients in the
plants is returned to the environment during the first few days of
decay.

It must be noted that the chlorophyll extraction technique used
in this study would include chlorophyll extracted from autotrophic
bacteria in the water. If an increase in autotrophic bacteria occurred
as a result of fertilization, the resulting increase in chlorophyll
extracted could be falsely interpretted as an increase in phytoplankton.

The genera of phytoplankton algae found in the ponds on September
16 are given in Table 4. This list undoubtedly does not include all
of the genera present at that time, and is presented only to show the
approximate composition of the phytoplankton.

Filamentous algae present a major problem to the limnologist
attempting to measure primary production in a pond. It is difficult
to measure accurately as phytoplankton or periphyton, although it can
be considered part of both communities. In nutrient rich habitats it
often grows epiphytically, extending in long strands into the water
column. These strands may then break off and float to the surface
forming large cotton candy like mats.

In pond Cl filamentous algae were first observed during the first
week of August growing along most of the aeration hose (Figure 9).

The algae were identified as Oedogonium, Spirogyra, Zygnema, Mougeotia,

 

and Ulothrix, with Oedogonium becoming more dominant as the summer

 

progressed. Since nitrogen and phosphorus were present in adequate

Table 4. The genera of phytoplankton observed in the Lake City
ponds on September 16, 1971.

 

 

Pond

Pond

Pond

Pond

Cl
Microcystis
Lyngbya
Eudorina
Volvox

 

Oedogonium

Zygnema
Spirogyra

C2
Microcystis

 

Lyngbya

Volvox
Oedogonium

Spirogyra

D1
Microcystis
Lyngbya
Eudorina

 

Oedogonium

D2
Microcystis
Merismopedia

 

 

Plectonema
Eudorina
Oedogonium

Cosmarium
Closterium
Staurastrum
Pediastrum
Rhizoclonium
Ceratium

 

 

 

Cosmarium
Closterium
Staurastrum
Pediastrum
Ceratium

 

 

 

Cosmarium
Staurastrum
Pediastrum
Ceratium

 

 

Cosmarium
Staurastrum
Pediastrum
Ceratium

 

 

56

Figure 9. Photographs of pond section Cl showing filamentous
algae growing along the aeration hose. Bubbles on
the water surface indicate the aeration. The submerged
macrophyte is Potamogeton berchtoldii Fieber.

 

57

 

Figure 9e

 

Figure 9b

58

supply, and were not limiting algal growth, the aeration was evidently
contributing some factor to the pond which stimulated the growth of
filamentous algae. This factor was most likely carbon, in the form of
carbon dioxide. Although the air passing through the water column was
only 0.03% carbon dioxide, this gas is more soluble in water than is

oxygen and the CO content of the water would be expected to increase

2
slightly. Kerr et a1. (1972) reported that the nitrogen and phosphorus
stimulation of algal growth is an indirect one mediated by the increased
availability of C02. They found that algal growth was stimulated by

bubbling either air (0.03% C02) or 5% CO in air through the water

2
column. In another experiment these researchers found that more nitro-
gen and phosphorus were removed at night than during the day, which
they attributed to a greater abundance of bicarbonate and carbon
dioxide in the water at night.

The phosphorus - carbon controversy of which element is limiting
aquatic plant growth continues (Likens, 1972). In regard to the fil-
amentous algae in this study, a simplistic approach cannot be taken.
Pond D1 was enriched with nitrogen and was aerated but showed no
filamentous algae growth. Pond C2 was enriched with nitrogen and
phosphorus and was not aerated, and showed filamentous algae growth
several weeks after it appeared in pond Cl. In pond Cl phosphorus and
nitrogen were both present in adequate supply, and it appears that the
aeration system was providing enough carbon dioxide to stimulate the
growth of filamentous algae. Without the phosphorus in the system,

the filamentous algae did not grow, and without the aeration, its

growth was delayed.

Figure 10a.

Figure 10b.

59

Photograph of pond C on August 30, 1971. Section
Cl (aerated) is on the right of the divider,
section C2 (unaerated) on the left.

Photograph of pond C on September 6, 1971. Section
Cl (aerated) is on the right of the divider, section
C2 (unaerated) on the left.

 

60

 

Figure 108

a

1 wmv A mow;
I

as. ,

.5 . .
.m 1. .
. . r.

 

Figure 10b

Figure 11a.

Figure 11b.

61

Photograph of pond C on September 13, 1971. Section
Cl (aerated) is on the right of the divider, section
C2 (unaerated) on the left.

Photograph of pond C on September 20, 1971. Section
Cl (aerated) is on the right of the divider, section
C2 (unaerated) on the left.

62

;: (Xin’V-W‘ .'. I
T‘“

 

Figure 118

~- .
J C-Ix‘."
'2' we: "

.e
e.
'\

. . _
' .

e u .'
. .

h . .

n
I
’e

 

Figure 11b

63

Figures 10 and 11 show the changes which occurred in pond C
during the second phase of the project, when high nutrient concentra-
tions were maintained. The filamentous algae were seen first and
became most abundant in section C1. The photograph taken on September

20 shows filamentous algae mixed with dead Potamogeton berchtoldii

 

floating near the surface.

Periphyton

In shallow ponds, such as the ones used in this study, the peri-
phytic algae play a major role in the primary production of the system.
These algae may be found growing epilithically, epipelically and epi-
phytically. Epiphytic algae may interact with the host plant in ways
both beneficial and harmful to that plant. Included in these inter-
actions are competition for nutrients and shading of the host plant by
the epiphytes. These interactions are discussed in greater detail in
a later section.

Estimates of periphytic primary production in this study were made
by measuring the amount of chlorophyll 3 found on artificial substrates
after a given time period. Wetzel (1963) observed that considerable
caution must be taken in interpreting estimates of primary production
from pigment measurements of this type. Variables such as light and
nutrient levels may affect the momentary concentrations of the pigments.
Wilhm and Long (1969) found that at high nutrient levels the periphyton
biomass and pigment concentration were high, but that net production

was no greater than in communities of intermediate nutrient levels.

64

It must be noted that the techniques used in this study resulted
in an estimate of the periphyton colonization rate and not an estimate
of the standing crop. The periphyton substrates were left in the pond
for either four or five days, and then were analyzed for periphyton
colonization. To obtain an estimate of standing crop, a series of
substrates would have had to be left in the pond for a considerable
time, periodically removing several substrates for analysis. _Although
a single exposure period would not provide a measure of the rate of
production of a well-established mat of periphyton (Kevern et al.,
1966), the values obtained would still be useful in making comparisons
within the same set of experiments. The colonization rates obtained
would be an underestimation of the actual standing crop in the pond.

As was expected, pond C showed much greater periphyton growth than
did pond D (significant at the 1% level, Analysis of Variance). Pond
D periphyton showed a very slow colonization rate, often yielding
amounts smaller than the sensitivity of the methods used. It was
noted that the highest values recorded for pond section Dl occurred
during the second week of August, following a large dieoff of the
macrophyte Najas. Pond section D2 also showed periphyton amounts
greater than had previously been observed. The periphyton colonization
rates of pond sections D1 and D2 were not found to be significantly
different at the 1% level.

The periphyton of pond C yielded some interesting data, with
section Cl having significantly greater (5% level) periphyton coloni-
zation rates than section C2. Figure 12 shows that the values from
C1 were greater than C2 throughout the project. Each data point in

Figure 12 is the mean of six samples. Since both pond sections

65

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.mucmEeusmmmE m HamcnonoHco an emcwEHmuoe
mm o econ nuwo mxmq now meow» cowumuwcofioo councnwuon

.NH mcsmcm

66

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67

received the same concentrations of fertilizer and other environmental
parameters were similar, it would seem that the aeration of section

Cl was stimulating periphytic growth. As was the case with the fil-
amentous algae, the most likely consequence of aeration was the increase
in available carbon.

It also can be seen from Figure 12 that the periphyton responded
quite rapidly to fertilization, with no seven day lag period as was
observed with the phytoplankton. The slopes of the lines in Figure
12 indicate the rate of colonization. This rate of colonization was
relatively fast at the end of July, following fertilization, and then
slowed down during August. Fertilization during the second phase of
the project resulted again in an increased rate of colonization.

A gradual change in the species composition of the periphyton in
pond C was observed over the summer. Whereas at the beginning of the
summer, the periphyton community included numerous diatoms, by the
end of the summer filamentous algae were most abundant, with the dia—
toms being more rare. Small filaments of Oedogonium including a
basal hold-fast cell were most common. Single celled Chlorophyta,

Scenedesmus, Pleodorina, Cosmarium, Closterium, and Staurastrum were

 

 

 

present throughout the summer.

Macrophytes

The macrophyte communities in the Lake City ponds were quite
extensive. Nearly all of the bottom area was covered with higher
aquatic plant growth, and it was obvious that their presence was a

major influence on the ecology of the ponds. Not only did these plants

68

provide cover for fish, zooplankton, and aquatic insects, but they also
contributed to the oxygen and carbon dioxide cycles of the pond. The
nitrogen, phosphorus, and carbon cycles are intricately tied with the
organic productivity of an aquatic system.

It was realized quite early in the study that the difference in
macrophyte communities between ponds C and D was great, and that com-
parisons between the two communities would be difficult. Whereas pond
C had a fairly diverse plant community, pond D was dominated by stands

of Potamogeton amplifolius. This is a large Potamogeton with both

 

 

submerged and floating leaves, and it occurred in stands which excluded

the growth of other macrophytes. Najas flexilis occurred in the shal-

 

lower water of pond D and Elodea canadensis was found in a very small

 

patch near the west shoreline. The major plants of pond C were N;

flexilis and Chara sp. occurring in the shallower water, and Potamogeton

 

berchtoldii Fieber being found in the deeper water (0.7-1.5 meters

 

deep). Water lilies, Nymphaea odorata, occurred at the north and

 

southeast sides of the pond. Table 5 records the major aquatic plant
species observed in the two ponds.

The aquatic environment places numerous limitations on plant
growth. Depth of the water, for example, is known to be a key variable
in determining the plant species present (Swindale and Curtis, 1957).
Light limitation in deep water may be the major factor limiting macro-
phyte growth. Depth also places a limit on the plant biomass of sub-
merged species. Submerged macrophytes are well adapted to the aquatic
environment, but cannot extend much beyond the air-water interface.

Numerous problems were encountered in regard to sampling the

macrophyte community. The periphyton attached to the leaves and stems

69

Table 5. The major aquatic plants observed in the Lake City ponds
during the summer of 1971.

 

 

 

 

 

Pond C Pond D
Chara sp. Potamogeton amplifolius
Potamogeton natans Najas flexilis
P. berchtoldii Fieber Elodea canadensis

 

 

E: praelongus

P; zosteriformis
Najzs flexilis
Elodea canadensis
Nymphaea odorata
Myriophyllum Sp

 

 

 

 

 

 

 

70

of the macrophytes required a great deal of time to remove. As the
summer progressed and filamentous algae became more abundant, the
problem increased. The great variability between samples (range of
0 to 3.85 gm dry wt./de) was also a problem in that it required a
greater number of samples to be taken than time allowed. The dieoff
of several species of plants towards the end of the summer increased
this variability.

As a result of the above problems, the conclusions that can be
drawn from my data are limited. It was interesting, however, that
on September 7, section C2 had a significantly larger biomass of macro-
phytes than did section C1. One possible reason for this may have

been due to a dieoff of Potamogeton berchtoldii Fieber, which occurred

 

in section Cl before it occurred in C2. The greater amount of fil-
amentous algae in C1 may have been responsible for this earlier dieoff.
Both sections of pond D showed an interesting occurrence during

the second week of August, when the Najas flexilis population was

 

found dead or dying. Plants were floating on the surface, and the
bottom areas were becoming barren. Since the Najas of the other ponds
were in good condition, it is logical to assume that this dieoff was
in response to the fertilization with nitrate. The plants themselves
appeared intact and as if they had been cut off at the mud-water inter-
face. If the bacterial activity of the sediments was increased by the
fertilization, then perhaps this could account for the dieoff. It is
not known why a similar response was not observed in pond C.
Observations made of the quadrats set up in the ponds showed some
very interesting trends. As a means of comparison, a relative abundance

term was used. This term was obtained by multiplying the average of

71

the recorded heights for each species, times the percentage of the 16
units per quadrat where the species was tallest. This was therefore

a three-dimensional term obtained by multiplying a percent of area
times height. Figure 13 shows the observed trends when relative abun-
dance was plotted against time.

Whether or not the observed trends are a response to fertilization
and/or aeration or to natural seasonal changes is not known. In both
sections of pond C.QEE£E was observed to decline in relative abundance
throughout the summer. Forsberg (1964) reports that a high concentra-
tion of phosphorus in the water inhibits the growth of Chara, and
that this sensitivity to phosphorus would explain the absence of Chara
in very eutrophic waters. Since Chara is often observed under the ice
during the winter and is present throughout the year, the decline in
abundance to zero would appear to be more of a response to the high
phosphorus levels than to a seasonal change.

Whereas the Najas flexilis of pond D died off during early August,

 

the population in pond C first increased and then gradually declined

to zero by the end of the summer. The abundance of Potamogeton

 

berchtoldii Fieber increased through most of the project and was then

 

observed to dieoff first in pond section C1. The population in section
C2 was also beginning to decline by the last sampling date as is shown

by Figure 13. A small quantity of Potamogeton praelongus in section

 

C2 appeared quite constant throughout the project. The percent of
barren bottom area did not increase considerably until the last sam-
pling date. The percent of algae covered bottom area increased in
section Cl during the first week of September, whereas that of CZ

did not increase until the last sampling date.

72

Figure 13a. The observed relative abundance of macrophytes in
Lake City pond section C1 during the summer of 1971.
( Najas flexilis, ---- Potamogeton berchtoldii
Fieber, -°-- Chara sp.)

 

 

 

Figure 13b. The observed relative abundance of macrophytes in
Lake City pond section C2 during the summer of 1971.
( Najas flexilis, ---- Potamogeton berchtoldii
Fieber, ---- Chara sp., -°-- Potamogeton praelongus)

 

 

 

 

RELATIVE ABUNDANCE

RELATIVE ABUNDANCE

500 1
450 1
400 4
350 l
300 ~
250 5

200 1

100 ‘

50 ‘

 

400 a

350 1

250 i

200 ‘

50 ‘

 

0’
o ’
IL._
"1|\.
7123 8/6
'*'- - ---.;«¢:EL
O I
.......... £!"
A ..........
7,23 8,6

73

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I \
\
\
\
\
\
\
\
\
\
\
\
\
\
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1 Figure 13a
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W‘P’ ''''''' .\ \
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\-
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308 9/2 9/i6

74

The uptake of nutrients by higher aquatic plants is an important
aspect of the eutrophication problem. Where phytoplankton must obtain
all of their nutrients from the water, macrophytes may get their
nutrients from either the sediments or the water. Some macrophytes
have better developed root systems than others and are more efficient
at taking nutrients from the sediments.

Several interesting studies have been made in regard to the uptake
of phosphorus by aquatic plants. Bristow and Whitcombe (1971), for

example, found that in Myriophyllum brasiliense, M; spicatum and Elodea

 

£2233 most of the phosphorus present in the upper shoot had been absorb-
ed by the root systems. In these plants the concentration of phosphorus
in the water was relatively unimportant in relation to the growth of

the plants and their uptake of phosphorus through the roots. These

researchers found that Myriophyllum brasiliense grew equally well in

 

nutrient rich or distilled water if the water exposed to the root
section was a nutrient solution.

Other researchers have found similar results to those presented
above. Martin, Bradford, and Kennedy (1970) showed that Najag sp.
absorbed most of its phosphorus from the sediments. Nuphar sp. is
also thought to take phosphorus up through its roots (Coffin et al.,

1949). Elodea canadensis, Potamogeton sp., Myriophyllum sp., and

 

 

Ludwigia palustris have been found to take up phosphorus through the

 

root system and transport it to the stem and leaves (personal un-
published data).

Also of interest in the discussion of phosphorus and aquatic macro-
phytes is the adsorption of phosphorus onto surfaces. In a nutrient

rich pond with abundant plant growth, such as pond C, this adsorption

75

phenomenon may be considerable. It would seem to be of major importance
to the periphytic algae. Some epiphyte-macrophyte interactions are

discussed in the next section.

Macrophyte - Algal Interactions

There are numerous paths of interaction between macrophytes and
the periphytic and planktonic algae. It has not been until fairly
recently, however, that some of these interactions were actually iden-
tified. Hasler and Jones (1949) were one of the first to show that
dense growths of macrophytes had a significant inhibiting effect on
phytoplankton. The mechanism of this inhibiting effect has been the
subject of much interesting research (Fitzgerald, 1969; Brandl et al.,
1970; and others).

The occurrence of either phytoplankton or macrophyte communities
at different nutrient levels in sewage ponds suggests that a nutri-
tional interaction may exist. Competition for nutrients between species
of algae has been observed (Fitzgerald, 1969). Mulligan and Baranowski
(1969) report that submersed vascular aquatics have lower nutrient
requirements than filamentous or planktonic algae. However, if the
macrophytes are obtaining most of their nutrients from the sediments,
then they are not competing with the algae for these same nutrients.
Competition for carbon, however, may be of considerable importance and

has been observed in stands of Elodea canadensis, where a decreased

 

phytoplankton production was partly due to the decrease in C02 in the

water due to its utilization by macrophytes (Brandl et al., 1970).

76

Competition for light and the shading of phytoplankton by macro-
phytes has also been reported. Straskraba and Pieczynska (1970)
found light to be the dominant factor limiting photosynthesis of algae

among stands of Phragmites, an emergent macrophyte. Similar results

 

have been found in regard to submerged macrophytes. Brandl et al.,
(1970) did some very interesting research dealing with macrophyte -
algal interactions and found a decrease in primary production of phyto-
plankton among stands of submerged macrophytes was caused by shading.
Possible substances excreted by macrophytes inhibiting the growth of
phytoplankton were not found by these researchers. Phytoplankton
samples collected from the macrophyte stands and exposed to light
increased in primary production.

Whereas Hasler and Jones (1949) found a lower abundance of phyto-
plankton among stands of macrophytes, Brandl et a1. (1970) found a
slight increase in abundance, but a very significant decrease in
production rate when compared with open water phytoplankton. In an
isolated marsh area Sloey (1969) found a decrease in phytoplankton
abundance when compared to the open water algae. From the work of
Brandl et a1. (1970), it would appear that the decreased primary pro-
duction may lead to a decrease in phytoplankton abundance when a macro-
phyte stand is isolated.

The shading of macrophytes by phytoplankton is also of importance
to the overall production of ponds. A bloom of phytoplankton would
severely limit light penetration and could result in the elimination
of macrophytes. The depth of water in which macrophytes can grow is

limited by the degree of light penetration.

77

A bloom of filamentous algae also would create unfavorable con-
ditions for aquatic macrophytes. Not only could the algae limit the
light penetration of the water, but they could accumulate epiphytically
on the macrophytes in such amounts as to restrict other life processes
of the plant. The filamentous algae of Lake City pond C were present
in bloom proportions and were attached to macrophytes in such amounts
as to completely cover them. When filamentous algae break loose from
the bottom and form mats on the water surface, even macrophytes with
floating leaves may become shaded.

Periphyton also interact with macrophytes in several ways. For
example, the increased surface area created by the macrophytes is of
critical importance to the epiphytic algae. Edwards and Owens (1965)
found that in four shallow streams the surface area was increased 30
times by the presence of macrophytes. This increased surface area is
also of importance to the epiphytic bacterial populations.

Fitzgerald (1969) found that when macrophytes were placed in nutri-
ent rich water in the lab, the epiphytic algae increased tremendously,
often obscurring any nutritional response of the macrophytes. He

then observed that cultures of Myriophyllum sp., Ceratophyllum sp.,

 

 

Lemna minor, Cladophora, and Pithophora oedogonium will remain relative-

 

 

ly free of epiphytes or competing phytoplankton if the cultures were
nitrogen-limited. A phosphorus-limited medium with abundant nitrogen
still resulted in epiphyte growth. This latter finding appears in
conflict with the periphyton results from Lake City pond D, where
abundant growth was not observed, although nitrate levels were high.
As Fitzgerald points out, however, some type of bacterial interaction

also may be involved in limiting algal growth.

78

Certain kinds of bacteria in the water may act as inhibitors to
the growth of certain species of algae. Bacteria found in sewage

effluent, for example, inhibited the growth of Microcystis; and Chlorella

 

was unable to grow in aquaria where Pithophora was present (Fitzgerald,

 

1969). It was hypothesized by Fitzgerald that perhaps the filamentous
green algae support a characteristic bacterial flora that inhibit the
growth of epiphytes only when the filamentous algae are growing under
nitrogen-limited conditions.

Allen (1971) has studied the nutritional interactions of the epiphy-
tic bacteria and algae on macrophytes. He reports that dissolved or-
ganic matter released by macrophytes is rapidly taken up by the plant's
epiphytic algae and bacteria. These algae and bacteria interact by
each releasing respired CO2 and excreted dissolved organic matter to
the other. The epiphytic bacteria are also thought to release various
growth factors and vitamins to the algae and to the surrounding water.
Allen (1971) also mentions that well-developed macrophyte stands,
with their nutritionally associated epiphytes are probably capable
of using up a large portion of the dissolved organic materials present
in some lakes. This event would deprive phytoplankton of these materials
and most likely limit their abundance.

It is evident from the above discussion that the macrophyte -
algal interaction question is considerably complex. The physical
aspect of shading and the more complex nutritional relations both
play major roles in determining the presence of certain forms of plant

life. This subject continues to be an active area of research.

SUMMARY

Two farm ponds were fertilized, one (Pond C) with both phosphates
and nitrates to approximate a secondary sewage effluent, and the other
(Pond D) only with nitrates. Half of each pond was then aerated to
determine if this would result in less chance of oxygen depletion in
the aerated section. The responses of phytoplankton, periphyton,
macrophytes, and zooplankton were measured.

The project was divided into two sections, the first being that
the ponds were fertilized once and continuously aerated and the chemical
and biotic changes monitored. During the second phase, the ponds were
fertilized every four days to maintain high nutrient levels. Again
aeration was continued and the various chemical and biotic changes
observed.

In all cases the phosphate and nitrate concentrations in the water
were observed to decline very rapidly. It is thought that the rapid
decline in nitrate concentrations may have been due to bacterial
activity. The rapid decline of phosphate concentrations was most
likely due to a combination of factors including adsorption by the
sediments, uptake by plants and precipitation with Ca++. The concen-
trations of both nitrates and phosphates were consistently lower in
aerated Cl than in unaerated C2, presumably because of the larger
amount of plant growth in section C1 and the resulting greater uptake

of nutrients.

79

80

The standing crop of phytoplankton was observed to increase slightly
and then decline again during the first phase of the project. At
continued high nutrient levels, the phytoplankton levels were observed
to increase and remain at a relatively higher level. These increases
in phytoplankton standing crop were noted to occur in both sections
of both ponds C and D. In both phases of the project the increase in
phytoplankton was delayed by approximately seven days. This occurrence
was thought possibly to be due to bacterial activity.

The colonization rates of periphyton were observed to increase
in response to fertilization with nitrogen and phosphorus, but not in
response to an added nitrogen supply alone. The periphyton production
of aerated section C1 was greater than that of unaerated section C2.
This was thought to be due to the aeration system, which was acting
as an additional source of carbon by bringing CO2 into the water.

Filamentous algae became very abundant in pond C by the end of
the summer. Its first appearance was along the aeration hose of section
Cl. This was attributed to the carbon dioxide being brought into the
pond by aeration. Since filamentous algae were not observed in aerated
section D1, it appears that the algae were phosphorus limited in
pond D.

The macrophyte communities proved to be very difficult to accurate-
ly measure. A system of periodically recording the growth of plants
in quadrats set up in the ponds showed that the different species of
macrophytes behaved differently over the summer period. Whether the
responses were due to the fertilization or to normal seasonal changes

could not be determined.

81

The ecological interactions between macrophytes and algae have
proved to be quite complex. The shading of macrophytes by algae or
of algae by macrophytes can result in a dominance of one plant community
or another. Nutritional interactions, some involving bacteria, have
also been recorded. It is evident that some if not all of these inter-
actions were operating in the Lake City ponds.

It would appear from the work reported here that aeration of
shallow nutrient rich ponds may result in complex problems with algal
growth. With a more powerful aeration system and conditions of oxygen
deficiency in the ponds, it is possible that other factors may become
important. Further research will hopefully answer some of these

questions.

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