The population (structural parameter) of phytoplankton decreased over time after
the addition of dimethoate, and only Tolypothrix sp. maintained its population at all
addition concentrations. The abundance of Cyclidium glaucoma decreased sharply at
concentrations of 0.5 mg/L or more during the subacute period, and extinction was
observed at a concentration of 1 mg/L during the acute period. A remarkable
difference was observed in the abundance of phytoplankton and zooplankton from
B 16–30 (days 16–30). As for the phytoplankton, Scenedesmus quadricauda and
Tolypothrix sp. tended to increase in abundance, relative to the control system, at
concentrations of more than 1 mg/L, but Chlorella sp. did not. All species of
zooplankton decreased in abundance, as compared with the control system, at
concentrations of more than 0.2 mg/L. It is thought that differences might occur
among the influences on species due to the mechanisms of the insecticide used for
pest extermination. As a functional parameter, a difference in the DO concentration
was not recognized between dimethoate addition systems with concentrations
between 0.05 mg/L and 0.2 mg/L and the control system, but the activity rose
with 0.5 mg/L of added dimethoate. Additionally, activity became uniform at
concentrations ranging from 0.5 mg/L to 1 mg/L, and an active decline was observed
at a concentration of 2 mg/L. However, it is necessary to examine systems with
concentrations of more than 2 mg/L because there is not a system to decrease than
control system on DO level. As for P/R ratio, activity also rose using test additions
ranging from 0.2 mg/L to 1.0 mg/L of dimethoate, but it began to decrease when
more than 1.0 mg/L and up to 2.0 mg/L was used (Fig. 7.19).
The m-NOEC of the structural parameter was estimated to be less than 1 mg/L
because of the extinction of Cyclidium glaucoma, and m-NOEC of the functional
parameter was in the range of 1 mg/L to 2 mg/L. Because the abundance of
phytoplankton and the amount of production decreased over time, it is thought
that there is no influence on the function per individual phytoplankton. On the
other hand, it is thought that the function per individual decreased in zooplankton
a) 0.2mg/l
b) 1mg/l
c) 2mg/l
1
2
3 4 5
6
7
8
9
10
11
12
13
14
1
2
3
4
5
6
7
8
9
10
1
2 3 4
5
6
7
8
9
10
11 12
13
14
Respiration(mg O 2 /L)
Respiration(mg O 2 /L)
Respiration(mg O 2 /L)
Production(mg O
2 /L)
Production(mg O
2 /L)
Production(mg O
2 /L)
0
2
4
6
8
10
0
2
4
6
8
10
0
2
4
6
8
10
0 2 4 6 8 10
0 2 4 6 8 10
0 2 4 6 8 10
Fig. 7.19 Time course of P/R ratio in Dimethoate-added microcosm N-system. (a) 0.2 mg/L. (b)
1 mg/L. (c) 2 mg/L
100
K. Murakami et al.
the addition of dimethoate, and only Tolypothrix sp. maintained its population at all
addition concentrations. The abundance of Cyclidium glaucoma decreased sharply at
concentrations of 0.5 mg/L or more during the subacute period, and extinction was
observed at a concentration of 1 mg/L during the acute period. A remarkable
difference was observed in the abundance of phytoplankton and zooplankton from
B 16–30 (days 16–30). As for the phytoplankton, Scenedesmus quadricauda and
Tolypothrix sp. tended to increase in abundance, relative to the control system, at
concentrations of more than 1 mg/L, but Chlorella sp. did not. All species of
zooplankton decreased in abundance, as compared with the control system, at
concentrations of more than 0.2 mg/L. It is thought that differences might occur
among the influences on species due to the mechanisms of the insecticide used for
pest extermination. As a functional parameter, a difference in the DO concentration
was not recognized between dimethoate addition systems with concentrations
between 0.05 mg/L and 0.2 mg/L and the control system, but the activity rose
with 0.5 mg/L of added dimethoate. Additionally, activity became uniform at
concentrations ranging from 0.5 mg/L to 1 mg/L, and an active decline was observed
at a concentration of 2 mg/L. However, it is necessary to examine systems with
concentrations of more than 2 mg/L because there is not a system to decrease than
control system on DO level. As for P/R ratio, activity also rose using test additions
ranging from 0.2 mg/L to 1.0 mg/L of dimethoate, but it began to decrease when
more than 1.0 mg/L and up to 2.0 mg/L was used (Fig. 7.19).
The m-NOEC of the structural parameter was estimated to be less than 1 mg/L
because of the extinction of Cyclidium glaucoma, and m-NOEC of the functional
parameter was in the range of 1 mg/L to 2 mg/L. Because the abundance of
phytoplankton and the amount of production decreased over time, it is thought
that there is no influence on the function per individual phytoplankton. On the
other hand, it is thought that the function per individual decreased in zooplankton
a) 0.2mg/l
b) 1mg/l
c) 2mg/l
1
2
3 4 5
6
7
8
9
10
11
12
13
14
1
2
3
4
5
6
7
8
9
10
1
2 3 4
5
6
7
8
9
10
11 12
13
14
Respiration(mg O 2 /L)
Respiration(mg O 2 /L)
Respiration(mg O 2 /L)
Production(mg O
2 /L)
Production(mg O
2 /L)
Production(mg O
2 /L)
0
2
4
6
8
10
0
2
4
6
8
10
0
2
4
6
8
10
0 2 4 6 8 10
0 2 4 6 8 10
0 2 4 6 8 10
Fig. 7.19 Time course of P/R ratio in Dimethoate-added microcosm N-system. (a) 0.2 mg/L. (b)
1 mg/L. (c) 2 mg/L
100
K. Murakami et al.