Mg to the end of cultivation (B 16–30 ). The regular succession pattern is similar. After
cultivation began, bacteria grew rapidly using a polypeptone in the basal medium,
and after that the protozoan Cyclidium glaucoma predated these bacteria and
increased its abundance. The chlorophyceans, Chlorella sp. and Scenedesmus
quadricauda, grew via photosynthesis under artificial light. After that, the other
microorganisms increased their numbers through microbial interactions, such as
prey-predator interactions, and the succession of microbiota into the stationary
phase 14 days after cultivation began. The succession pattern of the P/R ratio in
the period from the day of Mg addition to the final day of microcosm cultivation was
compared with the control system. The results showed that the respiration rate
(R rate) was greatly affected in the case of a 10.0 mg/L concentration of Mg injection
in comparison with the production rate (P rate) (i.e., the respiration rate increased
from 0.9 mg/day on the 16th day to 4.3 mg/day on the 18th day (maximum) and
recovered to ~1.1 mg/day by the 24th day). Similarly, the production rate increased
from 1.2 mg/day on the 16th day to 2.2 mg/day on the 18th day (maximum) and
recovered to ~1.1 mg/day by the 24th day. The P/R ratio temporarily decreased from
1 to 0.5, and, after that, the P/R ratio recovered to ~1. Based on the results from
statistical analyses, there was a significant difference between the system with
10.0 mg/L of Mg added and the control ( p < 0.05) regarding the R rate in the period
between the 16th day and the 24th day and the P/R ratio during the period between
the 16th day and the 21st day. Conversely, there was no significant influence on the
P/R ratio observed at a Mg concentration of 5.0 mg/L ( p < 0.05). From this, the
10.0 mg/L concentration of Mg was considered toxic, although not chronic (but
temporary), with respect to the P/R ratio as the functional parameter.
From an evaluation of the succession pattern of microorganisms as the structural
parameter, the protozoan, Cyclidium glaucoma, and oligochaete, Aeolosoma
hemprichi, were greatly influenced by the addition of 10.0 mg/L of Mg, and these
two species decreased in their abundance in the 10.0 mg/L addition system. Other
microanimals, such as the rotifers, Lecane sp. and Philodina erythrophthalma, also
decreased in comparison with the control system. Thus, the influence of Mg differed
for different species under coexisting culture conditions, such as those in the
microcosm. Conversely, there was no significant difference observed in the abundance of organisms, when compared with the control system, at Mg concentrations
of under 5.0 mg/L. As for the water quality, the pH rose with the addition of Mg, but
the value of the pH was approximately 8.5–9.5 in all experiments. From an estimation of N 30 at a concentration of 10.0 mg/L of Mg, the microorganisms were divided
into two groups, those with increasing abundance and those with decreasing abundance. The former group contained algae as the producers (Chlorella sp.,
Scenedesmus quadricauda, and Tolypothrix sp.) and bacteria as the decomposers
(Pseudomonas putida, Acinetobacter sp., Bacillus cereus, coryneform bacteria, etc.),
and the latter group contained protozoans and metazoans as the consumers
(Cyclidium glaucoma, Lecane sp., Philodina erythrophthalma, and Aeolosoma
hemprichi). From an estimation of B 16–30 , the microorganisms were divided into
two groups, the increasing abundance and the decreasing abundance groups, the
same as for N 30 . The m-NOEC of Mg was estimated to be more than 10.0 mg/L.
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K. Murakami et al.
cultivation began, bacteria grew rapidly using a polypeptone in the basal medium,
and after that the protozoan Cyclidium glaucoma predated these bacteria and
increased its abundance. The chlorophyceans, Chlorella sp. and Scenedesmus
quadricauda, grew via photosynthesis under artificial light. After that, the other
microorganisms increased their numbers through microbial interactions, such as
prey-predator interactions, and the succession of microbiota into the stationary
phase 14 days after cultivation began. The succession pattern of the P/R ratio in
the period from the day of Mg addition to the final day of microcosm cultivation was
compared with the control system. The results showed that the respiration rate
(R rate) was greatly affected in the case of a 10.0 mg/L concentration of Mg injection
in comparison with the production rate (P rate) (i.e., the respiration rate increased
from 0.9 mg/day on the 16th day to 4.3 mg/day on the 18th day (maximum) and
recovered to ~1.1 mg/day by the 24th day). Similarly, the production rate increased
from 1.2 mg/day on the 16th day to 2.2 mg/day on the 18th day (maximum) and
recovered to ~1.1 mg/day by the 24th day. The P/R ratio temporarily decreased from
1 to 0.5, and, after that, the P/R ratio recovered to ~1. Based on the results from
statistical analyses, there was a significant difference between the system with
10.0 mg/L of Mg added and the control ( p < 0.05) regarding the R rate in the period
between the 16th day and the 24th day and the P/R ratio during the period between
the 16th day and the 21st day. Conversely, there was no significant influence on the
P/R ratio observed at a Mg concentration of 5.0 mg/L ( p < 0.05). From this, the
10.0 mg/L concentration of Mg was considered toxic, although not chronic (but
temporary), with respect to the P/R ratio as the functional parameter.
From an evaluation of the succession pattern of microorganisms as the structural
parameter, the protozoan, Cyclidium glaucoma, and oligochaete, Aeolosoma
hemprichi, were greatly influenced by the addition of 10.0 mg/L of Mg, and these
two species decreased in their abundance in the 10.0 mg/L addition system. Other
microanimals, such as the rotifers, Lecane sp. and Philodina erythrophthalma, also
decreased in comparison with the control system. Thus, the influence of Mg differed
for different species under coexisting culture conditions, such as those in the
microcosm. Conversely, there was no significant difference observed in the abundance of organisms, when compared with the control system, at Mg concentrations
of under 5.0 mg/L. As for the water quality, the pH rose with the addition of Mg, but
the value of the pH was approximately 8.5–9.5 in all experiments. From an estimation of N 30 at a concentration of 10.0 mg/L of Mg, the microorganisms were divided
into two groups, those with increasing abundance and those with decreasing abundance. The former group contained algae as the producers (Chlorella sp.,
Scenedesmus quadricauda, and Tolypothrix sp.) and bacteria as the decomposers
(Pseudomonas putida, Acinetobacter sp., Bacillus cereus, coryneform bacteria, etc.),
and the latter group contained protozoans and metazoans as the consumers
(Cyclidium glaucoma, Lecane sp., Philodina erythrophthalma, and Aeolosoma
hemprichi). From an estimation of B 16–30 , the microorganisms were divided into
two groups, the increasing abundance and the decreasing abundance groups, the
same as for N 30 . The m-NOEC of Mg was estimated to be more than 10.0 mg/L.
118
K. Murakami et al.