latter colony did not appear in the control system cultured in the PY nutrient
medium, these were judged to be OTC-resistant bacteria. The test lasted for
14 days after OTC was added to the system at concentrations ranging between
0.007 mg/L and 7 mg/L. No difference was recognized in the algal population,
which was evaluated from the total number of bacteria and the density of chlorophyll
a in comparison with the control system. Additionally, the population of Philodina
erythrophthalma, a metazoan, was not affected, the same as with algae. However, an
influence was observed in the populations of OTC-resistant bacteria, Cyclidium
glaucoma, Lecane sp., and Aeolosoma hemprichi, according to the OTC concentration over time.
The influences observed for 14 days after the addition of OTC were categorized
as acute (2–4 days later), subacute (7–10 days later), and chronic (14 days later) to
investigate changes in the microbial population in detail. It was determined that the
system was affected when a population increased or decreased beyond the range of
the control population. Because the population of Aeolosoma hemprichi exhibited an
acute decrease with the addition of 7 mg/L of OTC, the NOEC of Aeolosoma
hemprichi was estimated as less than 7 mg/L. Additionally, the NOEC for each
was judged to be under 0.007 mg/L because increases and decreases in the
populations of Cyclidium glaucoma and Lecane sp. were observed following the
addition of 0.007 mg/L of OTC. Additionally, the population of Cyclidium glaucoma increased with OTC addition, while the population of Lecane sp. decreased.
Because a common organism (bacteria) is assumed as the prey in this test, it is
thought that the observed population changes are an outcome of the competitive
interactions between organisms in the microcosm. Moreover, the NOEC of
OTC-resistant bacteria was estimated to be less than 0.07 mg/L because an increase
was observed in a number of bacteria with the addition of 0.07 mg/L of OTC. In this
way, it is possible to estimate the NOEC for subacute and chronic influences equally.
The effects of OTC on algae, all bacteria, and Philodina erythrophthalma were
minimal, and the NOEC of each organism was greater than 7 mg/L for acute,
subacute, and chronic influences. On the other hand, Cyclidium glaucoma and
Lecane sp. were susceptible to OTC, and the NOEC for these organisms was less
than 0.007 mg/L, except for the subacute influence (0.07 mg/L or less) of Lecane
sp. It became clear from the population changes observed in the microcosm that the
NOEC was less than 0.007 mg/L.
When high concentrations of OTC were added (7 mg/L and 0.7 mg/L), the
amounts of production (P) and respiration (R) decreased in comparison with the
control system (0 mg/L) over time, and the decrease in the amount of respiration was
particularly large (Fig. 7.22). It is unclear why the addition of OTC decreased the
amount of respiration, but it is likely that OTC binds to the intracellular ribosome,
decreasing metabolic activity. When low concentrations of OTC were added
(0.07 mg/L and 0.007 mg/L), a temporary increase in the amount of respiration
was observed in the system with 0.07 mg/L of OTC, but the amounts of production
and respiration both showed a tendency to decrease, the same as in the highconcentration systems. However, there were fewer decrements than in the highconcentration systems. The decrease in the amounts of production and respiration
7 Example Assessments of the Microcosm N-System
107
medium, these were judged to be OTC-resistant bacteria. The test lasted for
14 days after OTC was added to the system at concentrations ranging between
0.007 mg/L and 7 mg/L. No difference was recognized in the algal population,
which was evaluated from the total number of bacteria and the density of chlorophyll
a in comparison with the control system. Additionally, the population of Philodina
erythrophthalma, a metazoan, was not affected, the same as with algae. However, an
influence was observed in the populations of OTC-resistant bacteria, Cyclidium
glaucoma, Lecane sp., and Aeolosoma hemprichi, according to the OTC concentration over time.
The influences observed for 14 days after the addition of OTC were categorized
as acute (2–4 days later), subacute (7–10 days later), and chronic (14 days later) to
investigate changes in the microbial population in detail. It was determined that the
system was affected when a population increased or decreased beyond the range of
the control population. Because the population of Aeolosoma hemprichi exhibited an
acute decrease with the addition of 7 mg/L of OTC, the NOEC of Aeolosoma
hemprichi was estimated as less than 7 mg/L. Additionally, the NOEC for each
was judged to be under 0.007 mg/L because increases and decreases in the
populations of Cyclidium glaucoma and Lecane sp. were observed following the
addition of 0.007 mg/L of OTC. Additionally, the population of Cyclidium glaucoma increased with OTC addition, while the population of Lecane sp. decreased.
Because a common organism (bacteria) is assumed as the prey in this test, it is
thought that the observed population changes are an outcome of the competitive
interactions between organisms in the microcosm. Moreover, the NOEC of
OTC-resistant bacteria was estimated to be less than 0.07 mg/L because an increase
was observed in a number of bacteria with the addition of 0.07 mg/L of OTC. In this
way, it is possible to estimate the NOEC for subacute and chronic influences equally.
The effects of OTC on algae, all bacteria, and Philodina erythrophthalma were
minimal, and the NOEC of each organism was greater than 7 mg/L for acute,
subacute, and chronic influences. On the other hand, Cyclidium glaucoma and
Lecane sp. were susceptible to OTC, and the NOEC for these organisms was less
than 0.007 mg/L, except for the subacute influence (0.07 mg/L or less) of Lecane
sp. It became clear from the population changes observed in the microcosm that the
NOEC was less than 0.007 mg/L.
When high concentrations of OTC were added (7 mg/L and 0.7 mg/L), the
amounts of production (P) and respiration (R) decreased in comparison with the
control system (0 mg/L) over time, and the decrease in the amount of respiration was
particularly large (Fig. 7.22). It is unclear why the addition of OTC decreased the
amount of respiration, but it is likely that OTC binds to the intracellular ribosome,
decreasing metabolic activity. When low concentrations of OTC were added
(0.07 mg/L and 0.007 mg/L), a temporary increase in the amount of respiration
was observed in the system with 0.07 mg/L of OTC, but the amounts of production
and respiration both showed a tendency to decrease, the same as in the highconcentration systems. However, there were fewer decrements than in the highconcentration systems. The decrease in the amounts of production and respiration
7 Example Assessments of the Microcosm N-System
107