The cell count (CFU) of bacteria at 10 Gy/day (low dose of irradiation system)
decreased more than in the control condition after irradiation began on the 19th day,
but no influence was observed in other species. At 23 Gy/day (high dose of
irradiation system), the abundance of Tolypothrix sp. increased to more than that
of the control system after the 28th day. The bacteria decreased after the 4th day, and
Lecane sp. decreased on the 45th day, but no influence was observed in other
microorganisms. Culturing of the microcosm was conducted under a light and
dark period for 12 h each, but, as for DO (functional parameter), the value of the
P/R ratio was stable at approximately 1 under both control and irradiation conditions
during the experimental period; no remarkable influence of gamma beam irradiation
was recognized, and the behavior of DO was very stable (Fig. 7.33).
The structural parameter of the microcosm system was affected when the
populations of certain microorganisms decreased or increased, but the functional
parameter that assumed the P/R ratio by consecutive irradiation of the gamma beam
did not come under influence. Mechanistically, even if a population increases or
decreases, the metabolic activity of the population was not affected, and accordingly
the possibility that the metabolic activity of an individual changed was suggested.
For example, it is thought that the metabolic activity of an individual that survived
rose when a population declined. Additionally, when the population of a certain
organism increased or decreased, and the metabolic activity of the population
changed, the metabolic activity of organisms with similar ecological functions
changed accordingly, and the possibility that the metabolic activity of the population
was not affected is considered. In other words, it is thought that when the population
of an organism decreased, and its metabolic activity decreased, other organisms’
populations rose using a surplus of resources. By either mechanism, the results
obtained suggest the ability of the microcosm to be maintained functionally at the
population or community level, even in the case in which the microcosm has been
structurally affected (Fuma et al. 2010).
It is thought that the possibility that a real ecosystem will be bombed at equivalent
dose rates to these experiments (i.e., 10 Gy/day and 23 Gy/day radiation) is
extremely low. Serious atomic energy accidents do occur, and the inappropriate
disposal of high-level atomic waste has been practiced, but most of the associated
dose rates are less than the values used in this experiment. For example, in the
Chernobyl nuclear power plant accident, which occurred in the former Soviet Union
(present-day Ukraine) in 1986 and was said to be the worst nuclear disaster ever, the
maximum dose rate that a fish received was only 0.03 Gy/day. Additionally, in the
Mayak nuclear compound, also in the former Soviet Union (present-day Russia) and
south of the Ural region, it is thought that an individual fish received a maximum
dose of radiation equal to 0.6 Gy/day due to the inappropriate disposal of radioactive
waste into the Techa River from 1950 to 1951, and a maximum of 0.1 Gy/day was
provided in the Kyshtym accident due to malfunctioning of the cooling facilities,
which occurred in 1957. The only example of a natural environment being bombed
with dose rates greater than those examined in this experiment is due to the
inappropriate disposal of large quantities of radioactive waste to Lake Karachay in
the southern Ural Mountains from 1951 through 1952, when the dose rate was
7 Example Assessments of the Microcosm N-System
131
decreased more than in the control condition after irradiation began on the 19th day,
but no influence was observed in other species. At 23 Gy/day (high dose of
irradiation system), the abundance of Tolypothrix sp. increased to more than that
of the control system after the 28th day. The bacteria decreased after the 4th day, and
Lecane sp. decreased on the 45th day, but no influence was observed in other
microorganisms. Culturing of the microcosm was conducted under a light and
dark period for 12 h each, but, as for DO (functional parameter), the value of the
P/R ratio was stable at approximately 1 under both control and irradiation conditions
during the experimental period; no remarkable influence of gamma beam irradiation
was recognized, and the behavior of DO was very stable (Fig. 7.33).
The structural parameter of the microcosm system was affected when the
populations of certain microorganisms decreased or increased, but the functional
parameter that assumed the P/R ratio by consecutive irradiation of the gamma beam
did not come under influence. Mechanistically, even if a population increases or
decreases, the metabolic activity of the population was not affected, and accordingly
the possibility that the metabolic activity of an individual changed was suggested.
For example, it is thought that the metabolic activity of an individual that survived
rose when a population declined. Additionally, when the population of a certain
organism increased or decreased, and the metabolic activity of the population
changed, the metabolic activity of organisms with similar ecological functions
changed accordingly, and the possibility that the metabolic activity of the population
was not affected is considered. In other words, it is thought that when the population
of an organism decreased, and its metabolic activity decreased, other organisms’
populations rose using a surplus of resources. By either mechanism, the results
obtained suggest the ability of the microcosm to be maintained functionally at the
population or community level, even in the case in which the microcosm has been
structurally affected (Fuma et al. 2010).
It is thought that the possibility that a real ecosystem will be bombed at equivalent
dose rates to these experiments (i.e., 10 Gy/day and 23 Gy/day radiation) is
extremely low. Serious atomic energy accidents do occur, and the inappropriate
disposal of high-level atomic waste has been practiced, but most of the associated
dose rates are less than the values used in this experiment. For example, in the
Chernobyl nuclear power plant accident, which occurred in the former Soviet Union
(present-day Ukraine) in 1986 and was said to be the worst nuclear disaster ever, the
maximum dose rate that a fish received was only 0.03 Gy/day. Additionally, in the
Mayak nuclear compound, also in the former Soviet Union (present-day Russia) and
south of the Ural region, it is thought that an individual fish received a maximum
dose of radiation equal to 0.6 Gy/day due to the inappropriate disposal of radioactive
waste into the Techa River from 1950 to 1951, and a maximum of 0.1 Gy/day was
provided in the Kyshtym accident due to malfunctioning of the cooling facilities,
which occurred in 1957. The only example of a natural environment being bombed
with dose rates greater than those examined in this experiment is due to the
inappropriate disposal of large quantities of radioactive waste to Lake Karachay in
the southern Ural Mountains from 1951 through 1952, when the dose rate was
7 Example Assessments of the Microcosm N-System
131