The Sludge Bioindicator is a simple tool to understand the treatment condition by making the use of characteristic of microfauna which is fluctuated according to the environmental change. Although the Sludge Bioindicator has been introduced in many wastewater treatment plants which adopt conventional treatment method, recently it has been reported that this Sludge Bioindicator is not accommodated to the advanced treatment. Dissolved oxygen （DO） concentration is suggested to be the reason for the difference in microfauna, though there are very few quantitatively studies on the effect of DO concentration on microfauna. In this study, to enhance the reliability of Sludge Bioindicator, relation between concentration of DO （7.2～0.2 mg/L, 8 phases） and micro fauna in activated sludge was examined.
As a result, it was cleared that microfauna varied with concentration of DO, instead the dissolved organic carbon removal ratio has not been changed. Mastigophora and Amoebozoa increased their cell densities in lower DO phase （2.4～0.2 mg/L） than higher DO phase （7.2～3.6 mg/L）. Although Metazoa preferred a more aerobic condition, Ciliophora appeared in wide range of DO. However, the aptitude for the low DO environment differed within the same taxonomic group.
The relation between the ratio of surface area to volume （S/V ratio） of microorganisms and DO level was also surveyed. It was cleared that microorganisms with higher S/V ratio （such as Mastigophora and Amoebozoa） tend to increase their cell density in the lower DO environment （R2 = 0.5434）. However, not all microorganisms showed this tendency, it is supposed that there are other factors will affect to the aptitude for the lower DO environment.
In this research work, the medium- and long-term mass balance in the multi-stage constructed wetland （MS－CW） treating milking parlor wastewater was estimated and the effect of vegetation on the sediment formation and mass balances for carbon, nitrogen and phosphorus were elucidated. The sediment formation for BOD removed at 1st filtration bed where the raw wastewater received was 1069 cm3/kg－BOD, while the sediment formation for SS removed was 1430 cm3/kg－SS. The increment of the sediment formation by the vegetation for the BOD was negligible and for the SS was around 20%. The residual organic matter per BOD removed in the MS－CW was 0.057 kg－VSS/kg－BOD and its increment due to vegetation was 40%. The loss ratio of nitrogen removed in the MS－CW was approximately 75%, resulting in 25% of nitrogen retention and its increment by the vegetation reached 55%. On the other hand, the phosphorus retention ratio in the MS－CW was approximately 50% and it was not affected by the vegetation. The estimated discharge load increased 20% considering transpiration and precipitation amount, however, the removal efficiency and residual ratio almost did not vary because of much higher removal load compared to discharge load.
Research on the diurnal vertical migration of cyanobacteria in shallow shore areas, where water bodies are easily mixed by wind and waves, is limited. In addition, the relationships between these migrations and cyanobacterial colony sizes and environmental nutrient concentrations are unclear. We therefore investigated whether cyanobacteria show diurnal vertical migration patterns in the extremely shallow area of Lake Hachiro in Akita, Japan （ca.60cm） and assessed the further influence of colony size and environmental nutrient concentrations. The water body was well mixed, leading to the uniform vertical distribution of water temperature and dissolved oxygen. Microcystis and Oscillatoria spp. were the dominant cyanobacterial genera detected during the sampling period; colonies of Microcystis spp. exhibited diurnal vertical migration patterns that were more pronounced in larger colonies, whereas Oscillatoria spp. did not show diurnal vertical migration patterns. A significant negative relationship between the number of Oscillatoria spp. and NO3－N concentrations was detected. It was suggested that utilization of NO3－N by Oscillatoria spp. was reflected to the NO3－N concentrations of the water column because this cyanobacteria species was moving with the water flow. Moreover, the vertical distribution of the Microcystis spp. colonies and nutrient concentrations varied drastically over time, indicating that this variation must be accounted for when sampling from shallow water areas.