Vertical profile of Chl-a concentration was measured on site with a fluorescent photometer at eleven stations in the Shichigashuku reservoir once a day during a period of phytoplankton bloom in late spring of 1996. The unsteady and unhomogeneous characteristics of the bloom was clarified as follows: (1) Asterionella, the dominant species, increases at the bottom of surface mixed layer where water column is gravitationally stable and temperature is around 15 °C which is suitable for them to breed and grow. Asterionella decays abruptly when the suitable layer moves down below compensation depth because of the deepening of thermocline at the beginning of summer. (2) Asterionella tends to concentrate in an area along the north boundary of the reservoir. This fact implies the existence of a mechanism for nutrient supply in the area.
A wind induced current under the thermal condition of late spring is numerically simulated by using 3-D k-ε model in order to investigate the mechanism of nutrient supply. The result shows that an upwelling flow takes place in the north area and transports materials from the bottom to the surface under the action of a northwest wind which is prevailing in the season of phytoplankton bloom.

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A study has been made of obtaining the gas phase photooxidative decomposition rate of trichloroethylene (TCE) which was extracted from contaminated soil by evacuation. A cylindrical reactor which was equipped with a low pressure mercury lamp at the center axis (reactor I) was divided into several spaces with barriers. Conversion of TCE increased with increasing the number of divided spaces in the reactor under low gas flow rate, however, the conversion of TCE decreased with increasing the number of the spaces under high gas flow rate. Moreover, the conversion increased with increasing the initial concentration of TCE under the condition of the same gas flow rate. The photooxidative decomposition rate of TCE was obtained by using graphical method under the assumption of that the complete mixing flow was formed and the average photo intensity in each spaces in the reactor was same. The maximum decomposition rate was obtained at the conversion of c.a. 0.8 and the rate was proportional to the 1.2th power of the concentration of TCE. The photooxidative decomposition rate of TCE in a reactor with larger diameter (reactor II) was in passable agreement with the value expected from the data obtained in the reactor I.

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Sessile animals' distribution and their water quality purification function in Tokyo inner bay were investigated. The following results were obtained.
1) In the coastal artificial structure which extends up to 192 km in the Tokyo inner bay, the number of species of sessile animals lies in the range of 43-46 throughout the year. A number of individuals show repetitive phenomena of increasing by the production of larva during spring and autumn which are their breeding period and decreasing during summer and winter when environmental conditions become worse.
2) The predominant four species mainly Mytilus edulis galloprovincialis and the rest Limnoperna fortunei kikuchii, Crassostrea gigas, Balanus spp., account for more than 90% of the biomass of sessile animals. It is presumed that an average of 9, 110t of sesile animals inhabited annually.
3) The sessile animals of Tokyo inner bay are presumed to possess the COD purification ability of 19t per day on the average in year and thus contribute immensely for purification of water environment of Tokyo inner bay.
4) The COD, N and P amounts which have been stored within the sessile animals' tissue are 2,292,127 and 16t per year respectively. These amounts recur to the water environment with sessile animals' longevity.

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Ozonation of nitrophenols and subsequent biodegradability were studied. Nitrophenols were easily decomposed by ozonation, but total organic carbon (TOC) could be reduced only to about 30-50% during an ozonation period of 120 minutes. The ozonated solution, after being mixed with activated sludge culture, was incubated for 4 days at 25°C, and biodegradability was then assessed by dissolved organic carbon (DOC) reduction. DOC of a non-ozonated solution was only slightly reduced even after 4 days incubation, indicating poor biodegradability. For the ozonated solution of nitrophenols, DOC removal more than 80% was achieved with a resulting DOC of less than 10 mg·l^-1. Ozonation thus greatly improves the biodegradability of refractory nitrophenols.

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A solution of Orange II, one of the typical azo dyestuffs was electrolyzed by Solid Polymer Electrolyte (SPE) electrolysis with two high oxygen overvoltage anodes, PbO₂ and SnO₂ without adding any electrolytes. The solution was decolorized completely by the 120 minutes electrolysis, using PbO₂ anode at current density of 0.2 A·:cm^-2. However, even after 180 minutes of electrolysis with PbO₂ anode at 0.3 A·cm^-2, 60% of total organic carbon (TOC) and 35% of chemical oxygen demand (COD) remained. Biodegradability of the electrolyzedobserved at high current density condition (about 0.5 A·cm^-2) and longterm electrolysis (about 200 hours). TOC reduction was higher for SnO₂ electrode doped with 1% Sb than for PbO₂. Although Sb doping reduced cell resistance, the electrolytical cell voltage for SnO₂ (8.5V) was much higher than that of PbO₂ (3.5V).

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The preserved or vegetated aquatic plant community offers refugia for large-bodied zooplankters from their visual predators. A field investigation was carried out to examine the horizontal distribution of zooplankton in an artificial pond with a preserved emergent macrophyte community (Typha angustifolia) zone and an artificial embankment. The results reveal that density of large bodied-crustaceans were higher in the vegetation area. However, this phenomena was changed by various factors, e.g. species character and annual transience of emergent macrophytes. Large-bodied and limnetic species cladocera were favoured when macrophytes were well emerged. Littoral species cladocera could inhabit constantly in the vegetation, and distribution of cyclopoida differed with the developmental stage. Copepodid stages preferred to inhabit the vegetated area than open water and nauplius stages distributed with no relation to the vegetation during their high biomass season. These phenomena may be related to size selective and visual predation by planktivorous fishes. Overall to our study, the ponds with preserved emergent macrophyte communities could stock higher density of large-bodied crustaceans than plain ones. It is suggested that these zooplankters graze phytoplanton intensively and improve the water quality.

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