control system after the 7th day. The populations of Cyclidium glaucoma,
Aeolosoma hemprichi, Philodina erythrophthalma, and Lecane sp. were affected,
and the fluctuations grew large with increasing addition concentrations of AE.
The functional parameter (i.e., the P/R ratio) remained constant as production and
respiration remained the same in the control system throughout the measurement
period; approximately the same behavior was observed even at an AE concentration
of 2 mg/L (Fig. 7.2). Production and respiration volumes increased just after the
addition of 10 mg/L of AE, and a change was observed in comparison with the control
system. However, the behavior of the 10 mg/L AE load system was similar to that of
the control system after the 2nd day (i.e., the system was only disturbed temporarily,
and it recovered afterward). Production and respiration volumes suddenly increased
just after the addition of 25 mg/L of AE, and a remarkable change was observed; the
P/R ratio remained less than 1 for 7 days after the addition of AE. This continuous state
of a P/R < 1 meant the reduction of food resources by overconsumption, and it was
thought that a load of 25 mg/L of AE heightened the risk of ecosystem collapse in the
microcosm because a risk for future ecosystem collapse was expressed by the constituent microorganisms. A system with a 25 mg/L load of AE exhibited strong disturbance and risked collapse, but its behavior was similar to that of the control system
after the 12th day. There was also an observed difference in the influence of the culture
period, and it was suggested that the pattern of influence was similar to that of the
10 mg/L AE load. The importance to strengthen including degree and periods from
influence by the chemical substance addition to recovery was suggested.
The results of the P/R ratio and the behavior of the population were consistent.
However, a change might occur in the behavior of the P/R ratio even if the
population is maintained at the same level as in the control system, and it is thought
that the behavior of the P/R ratio broadly reflects changes in the population. The
utility of the risk evaluation using the P/R ratio as an evaluation index was also
demonstrated. No influence was observed in either the P/R ratio or the population
densities at an AE concentration of 2 mg/L, which was estimated as the m-NOEC as
a result of this experiment. However, it was thought that there was a need for
endpoint setting that considered resistance to change, the analysis of patterns of
resiliency, and relaxation of the influence of an autoregulatory function for ecosystem disturbance in natural environments modeled by the microcosm.
7.1.3 Sodium Dodecyl Sulfate (SDS)
The addition concentration of sodium dodecyl sulfate (SDS) was adjusted to 4, 8,
and 16 mg/L and was added on the 16th day of the stable state into the microcosm.
The endpoints were abundance (structural parameter) and the concentration of DO
(functional parameter), and the population was measured using an optical microscope and counted from the start of culturing on days 0, 2, 4, 7, 14, 16, 18, 20,
23, and 30. It was evaluated from the results of B 16–30 (days 16–30), which was the
ratio of abundance and the population density (N 30 ) on the 30th day.
7 Example Assessments of the Microcosm N-System
73
Aeolosoma hemprichi, Philodina erythrophthalma, and Lecane sp. were affected,
and the fluctuations grew large with increasing addition concentrations of AE.
The functional parameter (i.e., the P/R ratio) remained constant as production and
respiration remained the same in the control system throughout the measurement
period; approximately the same behavior was observed even at an AE concentration
of 2 mg/L (Fig. 7.2). Production and respiration volumes increased just after the
addition of 10 mg/L of AE, and a change was observed in comparison with the control
system. However, the behavior of the 10 mg/L AE load system was similar to that of
the control system after the 2nd day (i.e., the system was only disturbed temporarily,
and it recovered afterward). Production and respiration volumes suddenly increased
just after the addition of 25 mg/L of AE, and a remarkable change was observed; the
P/R ratio remained less than 1 for 7 days after the addition of AE. This continuous state
of a P/R < 1 meant the reduction of food resources by overconsumption, and it was
thought that a load of 25 mg/L of AE heightened the risk of ecosystem collapse in the
microcosm because a risk for future ecosystem collapse was expressed by the constituent microorganisms. A system with a 25 mg/L load of AE exhibited strong disturbance and risked collapse, but its behavior was similar to that of the control system
after the 12th day. There was also an observed difference in the influence of the culture
period, and it was suggested that the pattern of influence was similar to that of the
10 mg/L AE load. The importance to strengthen including degree and periods from
influence by the chemical substance addition to recovery was suggested.
The results of the P/R ratio and the behavior of the population were consistent.
However, a change might occur in the behavior of the P/R ratio even if the
population is maintained at the same level as in the control system, and it is thought
that the behavior of the P/R ratio broadly reflects changes in the population. The
utility of the risk evaluation using the P/R ratio as an evaluation index was also
demonstrated. No influence was observed in either the P/R ratio or the population
densities at an AE concentration of 2 mg/L, which was estimated as the m-NOEC as
a result of this experiment. However, it was thought that there was a need for
endpoint setting that considered resistance to change, the analysis of patterns of
resiliency, and relaxation of the influence of an autoregulatory function for ecosystem disturbance in natural environments modeled by the microcosm.
7.1.3 Sodium Dodecyl Sulfate (SDS)
The addition concentration of sodium dodecyl sulfate (SDS) was adjusted to 4, 8,
and 16 mg/L and was added on the 16th day of the stable state into the microcosm.
The endpoints were abundance (structural parameter) and the concentration of DO
(functional parameter), and the population was measured using an optical microscope and counted from the start of culturing on days 0, 2, 4, 7, 14, 16, 18, 20,
23, and 30. It was evaluated from the results of B 16–30 (days 16–30), which was the
ratio of abundance and the population density (N 30 ) on the 30th day.
7 Example Assessments of the Microcosm N-System
73