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To characterise indirect effects of ionising radiation on aquatic microbial communities, effects of acute gamma-irradiation were investigated in a microcosm consisting of populations of green algae (Chlorella sp. and Scenedesmus sp.) and a blue-green alga (Tolypothrix sp.) as producer; a ciliate protozoan (Cyclidium glaucoma), rotifers (Lecane sp. and Philodina sp.) and an oligochaete (Aeolosoma hemprichi) as consumer; and more than four species of bacteria as decomposers. Population changes in the constituent organisms were observed over 160 days after irradiation. Prokaryotic community structure was also examined by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA. Principle response curve analysis revealed that the populations of the microcosm as a whole were not significantly affected at 100 Gy while they were adversely affected at 500-5000 Gy in a dose-dependent manner. However, some effects on each population, including each bacterial population detected by DGGE, did not depend on radiation doses, and some populations in the irradiated microcosm were larger than those of the control. These unexpected results are regarded as indirect effects through interspecies interactions, and possible mechanisms are proposed originating from population changes in other organisms co-existing in the microcosm. For example, some indirect effects on consumers and decomposers likely arose from interspecies competition within each trophic level. It is also likely that prey-predator relationships between producers and consumers caused some indirect effects on producers.

Ecosystems consist of various organisms, and there are complex interactions among these organisms. Indirect effects through interspecies interactions should be considered as well as direct effects of ionising radiation when environmental effects are evaluated. We therefore began to investigate radiation effects on experimental model ecosystems, i.e., microcosms mimicking aquatic microbial communities. The microcosm used in this study consisted of green algae (Chlorella sp. and Scenedesmus sp.) and blue-green alga (Tolypothrix sp.) as producers; oligochaete (Aeolosoma hemprichi), rotifers (Lecane sp. and Philodina sp.) and ciliate protozoa (Cyclidium glaucoma) as consumers; and four or more species of bacteria as decomposers. The steady-state microcosm was acutely irradiated with 60Co gamma-rays at 100, 500, 1000 and 5000 Gy, and population changes were observed for 25 days. In the control microcosm, population densities of the constituent organisms were almost constant during the experiment. At 100 Gy, significant effects were not observed for any organisms. At 500 Gy, A. hemprichi died out. Green algae and bacteria were not affected until day 15, but were decreased on day 25. C. glaucoma was temporarily decreased just after irradiation, but the cell density was recovered to a control level on day 7. Tolypothrix sp. was not affected until day 15, but was increased on day 25. Rotifers were not affected. At 1000 Gy, A. hemprichi died out. Bacteria were decreased just after irradiation, and the cell density remained slightly lower than controls during the experiment. Chlorella sp. and Scenedesmus sp. were not affected until day 15 and 10, respectively, but were decreased thereafter. C. glaucoma was temporarily decreased just after irradiation, but the cell density was recovered to a control level on day 10. Tolypothrix sp. was not affected until day 15, but was increased on day 25. Rotifers were not affected. At 5000 Gy, A. hemprichi, Lecane sp., and C. glaucoma died out. Bacteria were decreased just after irradiation, and the cell density remained significantly lower than controls during the experiment. Green algae were not affected until day 10, but were decreased thereafter. Tolypothrix sp. was not affected until day 15, but was increased on day 25. Philodina sp. was not affected. Most of observed effects were adverse, and were generally depended on radiation doses. But Tolypothrix sp. was increased at 500 Gy or higher doses. It is thought that this unexpected result arose from indirect effects. In the irradiated microcosm, decrease in green algae might provide Tolypothrix sp. with an advantage in the competition for light and inorganic nutrients. Breakdown products such as CO2 and inorganic nutrients originated from dead organisms might also contribute to increase in Tolypothrix sp. Equi-dosimetric analysis will be carried out between gamma-rays and some chemicals. That is, effective radiation doses evaluated in this study will be quantitatively compared with effective concentrations of herbicides (simazine and thiobencarb), surfactants (LAS and soap) and copper, which had been evaluated in other studies., International Conference on Radioecology and Enviornmental Radioactivity

In order to remove high-strength nitrogen and organics in landfill leachate simultaneously, the modified RBC which was combined with the standard RBC and the anaerobic biofilter was proposed. The treatability for actual landfill leachate of the standard RBC and the modified RBC was evaluated. The capability of COD removal in the modified RBC is much greater than that in the standard RBC, although both RBCs showed a BOD removal rate of more than 95%. This suggested that the combination method of aerobic and anaerobic treatment was effective in reducing refractory organic compounds. The nitrogen removal in the modified RBC was about 90% compared to 50% in Che standard RBC. The modified RBC had the advantage of nitrogen removal because nitrification and denitrification proceeded efficiently, even if a carbon source was not added. The performance of the modified RBC was superior to that of the standard RBC in both BOD surface loading and BOD volumetric loading.

Study was made on the use of hydroponic bio-filter method (HBFM) for eutrophic surface water. Results show that HBFM can remove 16.8% of TN and 30.8% of TP at the hydraulic loading rate (HLR) of 3.0 m3/(m2 x d). The removal loading rate of TN and TP can accordingly reach 1.0 and 0.1 g/(m2 x d) respectively. The sedimentation of particulate nitrogen and particulate phosphorus plays a major role in nitrogen and phosphorus removal, and its contribution is 62.2% and 75.9% respectively. The optimal HLR of HBFM ranges from 3.0 to 4.0 m3/(m x d). The intension of secateur for Nasturtium officinale has some effect on its uptake rate, thus the length of cut when harvesting should be less than 10 cm. The harvesting frequency of once a month for Nasturtium officinale has no effect on nitrogen and phosphorus removal of HBFM.