uptake of the radioactive substrate was monitored. The population densities of
Chlorella vulgaris and Cyclidium glaucoma increased, as the initial phosphorus
concentration increased, while that of Pseudomonas putida remained constant. The
photosynthetic activity of Chlorella vulgaris also increased as the initial phosphorus
concentration increased. In the microcosm, Pseudomonas putida uses the metabolites produced by Chlorella vulgaris and is preyed on by Cyclidium glaucoma.
Therefore, the growth activity of Pseudomonas putida increased as the photosynthetic activity of Chlorella vulgaris increased, but predation pressure by Cyclidium
glaucoma also increased. Consequently, the population of Pseudomonas putida
remained constant. These findings led to the conclusion that the phosphorus concentration strongly affects microbial population dynamics and the material flux in
the microbial loop of the aquatic ecosystem. However, the mass balance of each
organism should remain in a steady state in environments where the population of
predators, such as protozoans, invertebrates, and fish, are suitable.
11.5 Metal Addition
The complexity (e.g., species diversity) of the system required for environmental
impact assessment using the microcosm is an important problem. It becomes difficult
to maintain the plasticity of the experiment while the accuracy of the provided
toxicity data increases, and it is generally assumed that the cost increases because
it more closely approximates the complexity of real (natural) ecosystems. Conversely, in the flask-sized aquatic microcosm, constant toxicity data were provided
regardless of the species diversity. Here, Cu, Mn, and Al were loaded on a microcosm subsystem comprised of Escherichia coli as a decomposer, Euglena gracilis as
a producer, and Tetrahymena thermophila as a consumer, and their influence on
production and respiration rates and the P/R ratio (functional parameter) was compared with the result from the more complicated microcosm N-system, and the
superiority was inspected.
In the control group, an irregular daily change in DO, such as increased respiration, was observed until the fifth day after cultivation began, suggesting that the
system changed into one that was different from the original microcosm. Such a
phenomenon was not observed in the microcosm N-system. Because a pure culture
was used for the constituent species of the microcosm subsystem, in contrast to that
used in the microcosm N-system that was derived from nature, the subsystem lacked
any natural resistance to invasion. This is thought to result in the defeat of various
germs in the naturally derived microcosm N-system and the spread of germs, which
attached to oxygen electrodes, in the subsystem.
No significant influence was observed with respect to the cell count, whereas the
influence on production and respiration rates increased relative to the control system
and was observed at ~0.64 mg/L of Cu. Only a slight influence was recognized in the
198
Y. Inamori et al.
Chlorella vulgaris and Cyclidium glaucoma increased, as the initial phosphorus
concentration increased, while that of Pseudomonas putida remained constant. The
photosynthetic activity of Chlorella vulgaris also increased as the initial phosphorus
concentration increased. In the microcosm, Pseudomonas putida uses the metabolites produced by Chlorella vulgaris and is preyed on by Cyclidium glaucoma.
Therefore, the growth activity of Pseudomonas putida increased as the photosynthetic activity of Chlorella vulgaris increased, but predation pressure by Cyclidium
glaucoma also increased. Consequently, the population of Pseudomonas putida
remained constant. These findings led to the conclusion that the phosphorus concentration strongly affects microbial population dynamics and the material flux in
the microbial loop of the aquatic ecosystem. However, the mass balance of each
organism should remain in a steady state in environments where the population of
predators, such as protozoans, invertebrates, and fish, are suitable.
11.5 Metal Addition
The complexity (e.g., species diversity) of the system required for environmental
impact assessment using the microcosm is an important problem. It becomes difficult
to maintain the plasticity of the experiment while the accuracy of the provided
toxicity data increases, and it is generally assumed that the cost increases because
it more closely approximates the complexity of real (natural) ecosystems. Conversely, in the flask-sized aquatic microcosm, constant toxicity data were provided
regardless of the species diversity. Here, Cu, Mn, and Al were loaded on a microcosm subsystem comprised of Escherichia coli as a decomposer, Euglena gracilis as
a producer, and Tetrahymena thermophila as a consumer, and their influence on
production and respiration rates and the P/R ratio (functional parameter) was compared with the result from the more complicated microcosm N-system, and the
superiority was inspected.
In the control group, an irregular daily change in DO, such as increased respiration, was observed until the fifth day after cultivation began, suggesting that the
system changed into one that was different from the original microcosm. Such a
phenomenon was not observed in the microcosm N-system. Because a pure culture
was used for the constituent species of the microcosm subsystem, in contrast to that
used in the microcosm N-system that was derived from nature, the subsystem lacked
any natural resistance to invasion. This is thought to result in the defeat of various
germs in the naturally derived microcosm N-system and the spread of germs, which
attached to oxygen electrodes, in the subsystem.
No significant influence was observed with respect to the cell count, whereas the
influence on production and respiration rates increased relative to the control system
and was observed at ~0.64 mg/L of Cu. Only a slight influence was recognized in the
198
Y. Inamori et al.