Download Population Dynamics of Protozoa Associated with the Decay of

AMER. ZOOL., 13:149-160 (1973).
Population Dynamics of Protozoa Associated with the Decay of
Organic Materials in Fresh Water
HARTMUT BICK
Institute of Agricultural Zoology, University of Bonn, Bonn, West Germany
SYNOPSIS. The high intensity of decomposition in heavily polluted systems favors high
individual counts of certain species of cilate Protozoa, in spite of the lack of dissolved
oxygen and the presence of ammonia and other products of septic decay. Other species
grow best under the particular conditions of starting re-aeration or nitrification, respectively. In general, the whole range of the self-purification process may be divided
into zones which are characterized by particular associations of ciliates. The population
growth of these species is regulated by (1) availability of food, for example, bacteria;
(2) abiotic environmental factors, such as oxygen and products of septic decay; and
(3) competition and predator-prey relations.
tions of organisms—the so-called indicatororganisms-are assumed to indicate different stages of decomposition (or recovery).
Many of the indicator-organisms are arbitrarily selected, and there is a special urgent
requirement for fuller ecological data.
Within the last decade, investigations
have been undertaken by myself and coworkers dealing with the ecology of protozoa associated with the decay of organic
materials. Above all, we have investigated
the population dynamics of ciliates under
a variety of environmental conditions. The
present paper summarizes results of some
relevant studies. For detailed information
see: Bick (1964, 1967), Bick and Schmerenbeck (1971), Greiser (1971), Munch
(1970), Nusch (1970), and Wilbert (1969).
INTRODUCTION
Decomposition of organic materials originally built up by chlorophyll-bearing
plants is one of the fundamental processes
within any natural ecosystem. The complex
process of degradation controls the recycling of nutrients through mineralization of
dead organic matter. In aquatic ecosystems
we sometimes use the term "self-purification
process" instead of decomposers. The biotic
agents of decomposition are mainly heterotrophic microorganisms, the so-called saprotrophs or microconsumers, for example,
bacteria, actinomycetes, fungi, and protozoa. The role of protozoa is not understood
in full, but there is evidence that protozoa,
by feeding on bacteria, reduce bacterial
numbers and stimulate their further development (Javornicky and Prokesova, 1963).
METHODS
Furthermore, preying on bacteria may
speed the degradation process by energy
In order to avoid variations in environtransformation within the food chain.
mental conditions insofar as possible, exVery often protozoa are used as indi- perimental ecosystems were established in
cators for decomposition processes, for ex- 30-liter glass aquaria with artificial fresh
ample, in the well-known saprobity system water (Bick, 1967) and a natural inoculum
("Saprobien-system") of ecological classifi- of organisms from a wide variety of water
cation of water quality (Kolkwitz and bodies. Illumination with fluorescent lights
Marsson, 1908, 1909; Liebmann, 1962). was maintained on a 12-hr on-off cycle, inThis system is based on the assumption tensity 2,000 Lux measured at the upper
that, in the course of self-purification of level of aquaria. Temperature was 20 ±
rivers which had been polluted with pu- 1 C. Cellulose (1 g/liter) and peptone (0.25
trescible organic matter, distinct changes g/liter) were used as decomposing organic
in numbers and kinds of fauna and flora materials. The model systems containing
may be observed. The particular associa- cellulose had been enriched with inorganic
149
150
HARTMUT BICK
nitrogen (14 mg/liter NO3-N and 16 mg/
liter NH4-N) and phosphate compounds
(2.3 mg/liter PO 4 -P).
The following environmental factors
were investigated: dissolved oxygen, oxygen consumption, H2S, free CO2, pH, ammonia, nitrite, nitrate. Total counts of bacteria were achieved by means of direct
counts using Helber-counting cell and
phase contrast optics. Viable counts were
taken from plate counts (spread plates)
using Difco nutrient agar. Estimations of
individual numbers of cellulose decomposing bacteria and denitrifying microorganisms were established by appropriate selective media. Particular attention was paid
to the population dynamics of ciliated protozoa which were counted up to twice a
day using 0.5 ml plankton counting chambers or appropriate methods for periphyton
investigations: for methods, see Bick (1967)
and Bick and Schmerenbeck (1971). At
regular intervals organisms other than ciliates were counted.
RESULTS
Experiments with decomposition
of cellulose
As deduced earlier (Bick, 1964) from
some 50 experiments with decomposition
of cellulose, each proceeding for five weeks
after the inoculation of mixed populations
of organisms, the succession of organisms
proceeds in two sequential stages. First,
there is a heterotrophic stage characterized
by the prevalence of Zoomastigophora, bacteria, ciliates (mostly bacteria-eaters), and
amoebae. These organisms may be accompanied by diatoms and blue-green algae.
Because the rate of community respiration
exceeds primary production, this stage may
be called heterotrophic. Organisms flourishing during the following period of succession include autotrophic Phytomastigophora and green algae, which are accompanied by heterotrophic organisms. The latter group occupies the trophic level of
herbivores and carnivores. Metazoa are
dominating, and only relatively few protozoa are occurring. This second period
may be designated as the autotrophic phase.
The ecological conditions of the first period are characterized by high levels of
free carbon dioxide, with oxygen at low
level or even altogether absent in the deeper layers of the ecosystem. The second period, on the other hand, is characterized by
a lack of free carbon dioxide and high oxygen content.
Figures 1-4 illustrate the findings from
one individual experiment achieved in
fresh water enriched with inorganic nutrients and cellulose. Figure 1 shows the
changes in environmental conditions and
10
Bacteria
(plote counts)
°2
10
15 20 25 30 days
FIG. 1A
FIG. 1. Environmental conditions and succession
in tresh water aitifiually enriched with nitrogen
of organisms associated with the decay of cellulose
and phosphate compounds.
151
DYNAMICS OF PROTOZOA ASSOCIATED WITH DECAY
the succession of organisms. The two periods mentioned above are clearly distinguishable. It should be stressed that the
decomposition process started rather slowly;
total depletion of oxygen occurred in the
beginning of the second week. At the same
time, the nitrate content diminished. It
will be discussed later whether or not
denitrifying processes are involved in the
consumption of nitrate. The maximum of
free carbon dioxide coincided with the logphase of bacterial growth. The maximum
incidence of bacteria in this experiment
came after the ciliate peak. This observation is somewhat strange and will be discussed extensively later.
Euplotes pateUa
Suctorfa
Halteria grond:nello
Chilodonelto cucuUulu*
Coteps hirtus
I
Microthorax pusitlus
200 counts/ml
Litonotus lamella
Paramecium coudotum
Vorticetla
Stylonychio putrina
Colpidium compylum
Cyclidium a t full us
Glaucoma scinti'.tons
I
1000 counts/ml
Ankistrodesmus
Rototoria
(10:1)
Scenedesmus (1:10)
Amoebina
Chtlomonas
Euglena
Oiotomeae
Zoomastigophoro
(1:5)
CUiato
10
25
30 days
FIG. IB
5
10
15
20
25
30 days
FIG. 2. Succession of ciliates and growth curve of
bacteria. For environmental conditions, see Figure
1.
Figure 2 shows the succession of species
and numbers within the ciliates. The successive dominants proved to be: Glaucoma
scintillans, Cyclidium, Halteria, Colpidium, Coleps hirtus, Chilodonella cucullulus, Stylonychia putrina, Paramecium
caudatum, Litonotus lamella, Acineta, and
Microthorax. Most of these are bacteriophagous, the notable exceptions being Chilodonella, which feeds on diatoms, and
Litonotus and Acineta, which are carnivorous. The organisms of the first three weeks
belong to the heterotrophic stage mentioned above; in this stage both the number
of species of ciliates and the absolute number of individuals are very high. In the
later period of the experiment which shows
more autotrophic conditions, only a small
number of species of ciliates are present,
and the number of individuals is small.
Cyclidium, Halteria, and Euplotes patella,
and some other species are found at this
time too, the number of individuals being
low.
Looking for the population dynamics of
the ciliates, we may state that the J-shaped
exponential type of population growth is
prevailing in the heterotrophic stage of
succession (e.g., Glaucoma, Cyclidium, Colpidium). After reaching the maximum in-
152
HARTMUT BICK
cidence, the population growth stopped
abruptly and encystment took place, thus
bringing the number of trophozoites down
to zero immediately. For these species there
is no equilibrium level, but the environmental resistance (competition, enemies)
and/or lack in nutrients becomes effective
rather suddenly. The J-shaped growth
curve is typical for species of rather small
size, which thus have a high capacity for
cell division.
S-shaped (sigmoid) forms of population
growth curve, and some variants, may be
observed in the second half of the experiS
10
15
doys
ment (e.g., Cyclidium, Halteria). In the
FIG. 3. Population growth curve of ciliates derived
case of Paramecium and Halteria, over- from Figure 1. Lower: numbers on arithmetic
shoots occurred due to the high amounts scale; Upper: numbers on semi-logarithmic scale.
of bacteria available for food in the second
and third week; later on, the population check the interrelations between bacteria
settled down to a rather low carrying ca- and bacteria-eating ciliates, the number of
pacity level, which depended on the slow bacteria was compared with the biomass
progress of decomposition of cellulose.
of ciliates; this was done by calculating the
In the course of the experiments, conju- volume of all the individuals of each spegation was often observed. As reported cies on each day. Figure 4 shows the reearlier (Bick, 1966), conjugation happened sults. The biomass curve shows two major
at the end of the exponential stage of pop- peaks. The first one corresponds to the
ulation growth or in the very beginning of maximum incidence in total counts of cilithe upper stabilization level. A maximum ates and the turning point of the growth
of 60% of all individuals of one species par- curve of bacteria. Colpidium is dominating
ticipated at the same time in conjugation in biomass at this moment. We may asprocesses; usually, however, the number of sume that the feeding activities of the ciliconjugants was less than 10% of the total ates have retarded the population growth
of bacteria at this moment. While the total
organisms counted.
Looking at the total counts of ciliates counts of ciliates decreased after the tenth
(Fig. 3) during the first weeks of the ex- day of experiment, the biomass reached a
periment, it may be seen very clearly that second peak. At this time Paramecium
the total numbers of all ciliates show ex- dominated in biomass; all the other species
ponential population growth. In Figure 3 showed only comparatively small amounts
numbers are plotted on an arithmetic scale of biomass. The maximum of the biomass
(lower), and a semi-logarithmic scale (up- of bacteria-eating ciliates corresponded to
per), respectively. The individual counts the peak of the bacteria-curve, and the demay be fitted to straight lines in the semi- cline in numbers of bacteria was followed
logarithmic scale, thus showing that in- by the decline in Paramecium. Therefore,
crease as well as decrease of the population it is evident that in this case also, predatormay be represented by an exponential equa- prey relationships were responsible for the
decline of the bacteria population. This
tion.
It has already been mentioned that the was not, however, apparent from the diagreatest incidence of bacteria was found to gram based on numerical calculations.
follow the numerical maximum of the ciliTn order to present further information
ates. This could possibly indicate that the on the subjects discussed here, Figure 5
bacteria were not able to develop before provides results from another experiment
the decline of their enemies. In order to with decomposition of cellulose. Total
153
DYNAMICS OF PROTOZOA ASSOCIATED WITH DECAY
Clliata / m l
volume
ro
ro
(total
counts)
A
A Ciliata (volume)
/ \
/ \
/ \
'/
\
/
\
/
\
/
\
/
\
/
\
/
\
'..•••'
V'-.. Bacteria
Ciliata
o
10 000,
E
:ten
ro
5 000-
ro
/ /
m
106
5-10 8 p 3
..-v
lr '
5
10
15
FIG. 4. Total counts and biomass (derived from
volume) of ciliates and viable counts of bacteria.
20
25
30 days
Basic data provided by Figure 2.
counts and biomass (volume) of ciliates
are plotted against total counts of bacteria,
The bacteria showed four maximum incidences, the ciliates (total counts) achieved
two obvious peaks and a smaller one between them. The decrease of bacteria
counts corresponded with the increase in
ciliate counts. The biomass of ciliates
Ciliata/ml
Ciliata volume/ml
—
Bacteria/ml
1
Ciliata
•2-10 9 p 3
(volume)
E
m
/
b"
E
20 000- .2
• 109JJ3
CD
10 000-
/
Citiata
(total counts)
51
\
/
/
1
2 000
1
2
./,-' \...B"'-.'::. v
3
FfG. 5. Total counts and biomass (derived from
volume) of ciliates and viable counts of bacteria.
4
5
6
Ciliata /
108 ^u 3 volume'
,
/ml
weeks
Experimental set with decomposition of cellulose
in brackish water (salinity 10.5%c).
154
HARTMUT BICK
showed three strong peaks: the first one peak at the tenth day (Fig. 6) which is cor(Paramecium) corresponded to the small related with the maximum intensity of oxypeak in total counts mentioned above, thus gen consumption (BOD). (3) Numbers of
demonstrating that the decrease in bacteria cellulose-decomposing bacteria were estabpopulation in the fourth week, in fact, de- lished by a selective media. The growth
pended on the feeding capacity of ciliates. curve shows three peaks and resembles the
The second peak in biomass was built up population dynamics of bacteria counts
by Paramecium, too, and the third one achieved by plate counts. (4) Denitrifying
which corresponded to the maximum in bacteria achieved by means of an apprototal counts included Vorticella (bacteria- priate selective media showed the highest
feeders) and the carnivorous Acineta. The counts in the period of decreasing nitrate
initial population growth of ciliates in the content, thus supporting the assumption
second week started with Uronema; the that denitrifying processes are the main
biomass of this species is very low, and the reason for nitrate depletion.
total biomass showed only a very small inIf we try to find out interrelationships
crease.
between the growth curves of ciliates and
In order to get fuller information on the bacteria, it is necessary to take into conrelationship of ciliated protozoa and bac- sideration the particular species of ciliates
teria, detailed studies have been performed (Fig. 7). The main bacteria-feeders are
on microbial activities during the decomposition process. The results discussed now
7 000
are based on experiments undertaken in
6 0005 000
cooperation with H. P. Miiller; the techtooo
niques employed will be published else3000
where.
2 000 Figure 6 shows environmental conditions
1000
and population dynamics of bacteria dur10'
ing three weeks of decomposition of cel10
lulose in fresh water enriched with inor10
ganic nitrogen and phosphate compounds.
£
to'
The changes in environmental conditions
to
correspond to those presented in Figure
g
1. The bacteria are subdivided into four
io'
5,00groups. (1) Bacterial numbers achieved by
locter.o
iM •
direct counts using phase optics; the peak
10
(plate counts)
300 of the curve coincides with the exponential
200 growth phase of the ciliates, and the total
too •
Pi
depletion of dissolved oxygen. (2) Bacterial
counts taken from spread plates using nutrient agar (colony counts, viable counts,
Bacteria
to
(direct counts)
saprotrophs). The viable counts showed a
fast increase in the very beginning of the
experiment and a rather slow but steady
increase up to the sixth day. Due to
lack in dissolved oxygen and increase in
bacteria-eating ciliates the number of bacteria decreased for some time. At the
moment it is impossible to decide whether
lack in oxygen or increase in predators is
responsible for the depression of bacteria FIG. 6. Environmental conditions and population
counts. The maximum of bacterial activity dynamics of bacteria and ciliates associated with
decomposition of cellulose. No artificial aeration.
derived from viable counts is marked by a Counts per milliliter.
2
6
2
2
2
155
DYNAMICS OF PROTOZOA ASSOCIATED WITH DECAY
£inetochitum marg
Loxocephatus
Vorticellidae
Halteria grandinella
Urotricha farcta
Litonotus lamella
Paramecium bursaria
Cyctidium citrutlus
Spirostomum teres
Stylonychia putrina
Par. caudatum
5
10
15
Par. trichium
Leptopharynx sphag
Chilodonella uncinata
Suptotes patella
Colpoda steini
Glaucoma scintillans
days
high content of dissolved oxygen and. the
very low oxygen demand (BOD). The total
counts of ciliates proved to be relatively
low according to the low rate of BOD. The
first maximum incidence of ciliates occurred earlier than in anaerated ecosystems of the same series. The maximum
was built up by Colpoda, while Glaucoma
showed only very few counts (Fig. 9). The
main maximum of ciliate counts coincided
with a marked decrease of bacteria; the
bacteria-feeding Leptopharynx sphagnetorum and Cyclidium dominated and were
preyed on by Litonotus. Paramecium and
Urotricha occurred only in small numbers.
Figure 10 shows the succession of further
groups of organisms, such as Zoomastigo
phora, Amoebina, Ochromonas, Oscillatoria, and others. The high counts of Ochromonas are very similar to those achieved in
anaerated systems and suggest the idea that
FIG. 7. Succession of ciliates associated with decomposition of cellulose (continuation o£ Figure 6).
Glaucoma, Cyclidium, Paramecium, and
vorticellids. Urotricha fed on Ochromonas;
the latter showed mass development between the fifth and fifteenth day. The carnivorous Litonotus preyed on Cyclidium.
The maximum incidence of Glaucoma coincided with peaks of all physiological
groups of bacteria. This observation supports the idea that Glaucoma grows well
only in periods of high bacterial activities. The highest counts of Cyclidium, Paramecium, and Vorticellidae coincided with
the more or less obvious decrease of all
bacterial populations. On the other hand,
the bacteria counts increased after decrease
of ciliates. It is assumed that predator-prey
relations are responsible for this observation.
Figure 8 presents results achieved in an
experiment with decomposition of cellulose
and artificial re-aeration. Techniques of
graphs are the same as in Figure 6. The
peculiarities of this experiment are the
nitrate reducing
Bacteria
5
10
15
days
FFG. 8. Environmental conditions and population
dynamics of bacteria and ciliates associated with
decomposition of cellulose. With artificial re-acration. Counts per milliliter.
HARTMUT BICK
156
Cinetochilum morg
Loxocephalus
Vorticellidoe
Litonotus lamella
Kalterio grandmella
Urotricha
farctc
Paramecium bursana
Cyclidium citrullus
Spirostomum teres
Stylonychio putrina
Paramecium caudotum
Paramecium tnchium
A model ecosystem set up for decomposition studies on cellulose was heated to
50 C, thus killing most of the protozoa.
Only cysts of Chilodonella uncinata, Colpoda steini, and Platyophrya vorax survived. The decomposition process was very
slow, apparently some groups of bacteria
were damaged, too. The level of dissolved
oxygen was nearly as high as in artificial
re-aerated ecosystems. Under these particular conditions Colpoda showed high individual counts (up to 900/ml) on the fourth
day. The population was maintained for
about 10 days, and later was replaced by
Leptophorynx sphag
Euplotes
patella
Colpoda steini
Chilodonella uncinata
Scenedesmus
Rototoria
Glaucoma scintillons
15
days
FIG. 9. Succession of ciliates (continuation of Figure 8) .
Oscillatoria
(1-5)
lack in nutrients should not be the reason
for the small numbers of herbivorous
Entosiphon
Urotricha. With decreasing numbers of
cellulose-decomposing bacteria, that means
with decreasing intensity of decay, the
Amoebina
number of autotrophic Oscillatoria and
Scenedesmus is increasing. This marks the
beginning of the autotrophic phase of succession mentioned above in connection
with Figure 1. Differences between anDiotomeoe
aerated and aerated systems were as follows: The anaerated system showed a
period of increase in number of diatoms
in the second week; Actinophrys sol ocChlamydomonas
curred only in the artificial re-aerated system.
Turning once more to Figure 9, it should
be stressed that Colpoda steini showed
I
500 counts/mt
comparatively high individual counts (see
Fig. 7). From earlier experiments (Bick,
1964), it has been concluded that Colpoda
is able to build up high population den0:5)
sities under extreme environmental condiZoomastigophora
tions which exclude predators and com<20/jm
petitors (Maguire, 1963) in the very beginOchromonas
ning of die heterotrophic stage of suc(1:20)
15
days
cession as well as in later periods. In order
to get more information on this subject, FIG. 10. Succession of organisms (continuation of
the following experiments were performed: Figure 8).
DYNAMICS OF PROTOZOA ASSOCIATED WITH DECAY
Chilodonelta and Platyophrya.
Experiments with decomposition of peptone
In experiments using peptone as a resource for decomposers, the number of
species of ciliates decreased with increasing
amounts of peptone added to the individual system. The initial stage of decomposition showed rather bad environmental
conditions, for example, total lack in dissolved oxygen, high amounts of ammonia,
and hydrogen sulfide. Under these particular conditions, numbers of individuals of
the remaining species very often increased
to high levels of population growth. Successions of protozoa associated with the decomposition of peptone have been reported
in full by Bick (1967), Bick and Schmerenbeck (1971), and Munch (1970). In the
present paper only the general aspects will
be discussed. Figure 11 provides data from
an experiment with decomposition of pep-
. «"ks
1
2
3
4
Wochen
FIG. 11. Environmental conditions and succession
of bacteria and ciliates in a laboratory ecosystem.
Initial heterotrophic stage only. The broken line
under D.O. marks the saturation concentration.
157
tone (250 mg/liter). Only the initial heterotrophic succession has been pictured. The
autotrophic stage started in the second
week and brought the oxygen level to
about 120% of theoretical saturation point.
Ammonia has been completely oxidized to
nitrite and nitrate; the correlated changes
in oxygen contents and level of pH are
clearly to be seen. During the initial
heterotrophic stage of succession, Vorticella microstoma and Glaucoma scintillans
dominated.
By increasing the organic load to 1.5 g/
liter peptone, a rather long lag-phase of
population growth occurred and Colpoda
steini dominated (not figured). This is another evidence of the capacity of Colpoda
to colonize habitats with extreme environmental conditions.
In further experiments, I tried to get information on the reaction of populations
of ciliates to changing environmental conditions within the initial stage of succession. Figure 12 provides data on dissolved
oxygen content and other environmental
factors from an ecosystem receiving 250
mg/liter peptone once a week for a period
of five weeks. Since the dissolved oxygen
content is rather low, no oxidation of ammonia takes place. The re-aeration by absorption of atmospheric oxygen and oxygen production by algae is rather ineffective, as compared with the high uptake
of oxygen by the activities of bacteria. The
population of Vorticella microstoma is
showing obvious response to each addition
of peptone; only in the third week population growth of Vorticella is hampered by
the occurrence of the carnivorous Diliptus.
In the fifth week the population of Vorticella decreased, owing to the strong increase in ammonia. We may derive from
this figure that certain species of ciliates
which feed on bacteria are able to utilize
the high amounts of nutrients even under
conditions of septic decay. The decreasing
numbers of species in habitats poor in dissolved oxygen and rich in products of septic decay cause a reduction in competition
for food; therefore, the remaining species
may achieve high individual counts without further increase in food. The species
158
HARTMUT BICK
tion should be paid to the fact that the organisms show reactions upon pollution,
even when the level of dissolved oxygen
does not alter at all. The rather slight or
even lacking response of Chilodonella,
Glaucoma, and Colpoda to additional pollution may be explained by the occurrence
of carnivorous ciliates, such as Dileptus
and Gastrostyla.
In summary, it may be derived from
Figures 12 and 13 that the population dynamics of ciliates showed obvious reactions
to any change in the intensity of decomposition or—speaking in terms of a saprobiologist—to changing saprobity. The peculiar reproductive activity enables the protozoa to react very quickly to changes in
environmental conditions.
Finally, I should like to discuss the question of whether or not the different stages
/\_^
FIG. 12. Environmental conditions and population
dynamics o£ bacteria and ciliates in a laboratory
system receiving 250 mg/liter peptone weekly
(I-V) .
involved here are euryecious; their mass
development indicates high amounts of
available nutrients. High amounts of bacteria mean high intensity of decomposition ("high saprobity" or polysaprobic
conditions). Therefore, species like Glaucoma, Colpoda, or Vorticella microstoma
may be used as polysaprobic indicator organisms in the saprobity system. But, due
to the euryecious character, only occurrence in high abundance presents valid
results.
Figure 13 deals with an artificially
aerated ecosystem receiving peptone weekly
for a period of five weeks. Oxygen consumption by decomposition and re-aeration is more or less in balance. Nitrification
starts several times, but completion of the
process is stopped by further pollution
(^addition of peptone). The most remarkable result concerns the correlation
between the addition of organic subs'ance
and the population dynamics of ciliates,
above all those of the peritrichs. Atten-
Rotatoria
•50
' 25
FIG. 13. Environmental conditions and population
dynamics of bacteria and ciliates in a laboratory
ecosystem with artificial re-aeration. Addition of
250 mg/liter peptone once a week like in Figure
12. The broken line under D.O. marks the saturation concentration.
DYNAMICS OF PROTOZOA ASSOCIATED WITH DECAY
of die self-purification process are characterized in fact by particular associations of
ciliates. In the case of decomposition of
cellulose, I have already mentioned two
main stages in protozoan colonization. The
population dynamics of ciliates under the
conditions of peptone decomposition were
recently investigated by Greiser (1971), using seven laboratory ecosystems put in
series by connecting tubes. Ecosystem No.
1 received peptone in aqueous solution
(50 mg/liter) continuously, used as a model
for sewage pollution. The load of artificial
sewage required about a fortnight to pass
through the whole system. The experimental set was maintained for a period of
two months. The individual ecosystems reflect different stages of decreasing pollution
or increasing self-purification. Figure 14
summarizes the experimental results of a
period of 10 days. Population counts of
ciliates were achieved on glass slides which
were exposed in each system at the beginning of the 10-day period of investigation.
The periphyton communities in question
no. of system
159
proved to be a reliable indicator of the respective self-purification stages. The diagrams in Figure 14 show quite well the increasing levels of dissolved oxygen, the decreasing amount of ammonia, and the
progress in nitrification. All the environmental factors mentioned mark the progress in mineralization. We may assume
that the highest bacterial activities are in
systems without dissolved oxygen, while
decreasing microbial decomposition renders an increase in dissolved oxygen. The
ciliates show remarkable differences in
population dynamics, diversity, and abundance which correspond to the alterations
in environmental conditions. For instance,
Glaucoma and Colpidium occurred only
in systems Nos. 1 and 2; Paramecium,
mainly in Nos. 2 and 3; Cyclidium, in No.
3; Aspidisca, in Nos. 3-6, which means in
all systems with nitrification processes. It
should be stressed that Figure 14 contains
only species which are listed as indicators
of water pollution levels up to now. The
total list of ciliates achieved by Greiser
includes several other species. Most of
them showed preference for certain stages
of the self-purification process. For details,
see Greiser (1971).
REFERENCES
A
FIG. 14. Environmental conditions in seven ecosystems put in series by connecting tubes. System No.
1 received artificial sewage twice a day. Individual
counts of periphyton ciliates during primary succession on glass slides exposed at the beginning of
the 10-day period oE investigation. Data provided
by Greiser (1971).
Bick, H. 1964. Die Sukzession der Organismen bei
der Selbstreinigung von organisch verunreinigtem
Wasser inner verschiedenen Milieubedingungen.
Dusseldorf.
Bick, H. 1966. Populationsokologische Beobachtungen iiber das Auftreten sexueller Prozesse bei
Siibwasserpolypen und Ciliaten. Zool. Anz. 176:
183-192.
Bick, H. 1967. Vergleichende Untersuchung der
Ciliatensukzession beim Abbau von Pepton und
Cellulose (Modellversuche) . Hydrobiologia 30:
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