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An experimental study was conducted to establish the control strategy of an anoxic-oxic sequencing batch reactor system (AOSBR) using a specific feature of N2O generated during the anoxic and oxic phases. Since NH4+-N, NO2--N and gaseous N2O (GN2O) were found to disappear simultaneously in the oxic phase, the end point of nitrification may be detected from the GN2O profile. It was suggested that the stagflation of nitrification and denitrification could be detected by abnormal GN2O emission in the oxic and anoxic phases. Compared with the conventional indexes of AOSBR, GN2O has several advantages. First, the regulation of GN2O emission could be conducted directly, and second maintenance is easier than conventional indexes because the GN2O monitoring system is more durable than the monitoring system for water quality.

The terrestrial plant Luffa cylindrica was applied to a surface-flow-constructed wetland (SFCW) to treat effluent from rice fields. To control the excessive growth of weeds that interfere with the maintenance of SFCWs, SFCWs with and without shading were constructed and the effect of shading was investigated. The average removal efficiencies of T-N and T-P for 135 day operation of the SFCW with shading were 57 and 53%, respectively, while in the case of those without shading were 44 and 41%, respectively. This result indicates that the nutrient removal efficiency was stimulated by shading. Although L. cylindrica completely dominated the SFCW with shading, the total plant biomass production including weeds was higher without shading. The total length of the roots in the SFCW with shading was, however, 2.2-fold that without shading. Consequently, it was suggested that the longer root length observed in SFCW with shading promoted the sedimentation of nutrients, resulting in a nutrient removal efficiency higher than that in the case without shading. These results demonstrate that shading is effective not only to control the growth of weeds but also to enhance the growth of roots in SFCWs, resulting in easier maintenance and a higher nutrient removal efficiency.

Field observations were carried out in Banzu intertidal flat in Tokyo Bay throughout two days in the summer of 2000, in order to clarify the spatiotemporal fluctuatuions of water quality during a tidal cycle. Concentrations of DO, ON (TN-DIN) or OP (TP-PO4-P) at the offshore station were higher than those at the onshore station, whereas DIN and PO4-P had an inverse trend, during submergence. During flood tides, an abrupt increase in the concentrations of DIN and PO4-P was observed around a shoreline.We constructed a box model, incorporating both the release flux of inorganic nutrients from sediment and the nutrient uptake rate by overlaying water, that were experimentally obtained in situ at each tide. The observed fluctuation of nutrients during ebb tide was well reproduced by the model. However, agreement was poor during flood tide. These results strongly indicate that the increase in nutrient concentrations during flood tide was attributed to the temporally increased effluxes of nutrients from the sediment and/or the physical resuspension of sediments at the shoreline.The mass balance of TP during a tidal cycle showed that the tidal flat acted as a sink of TP (1μmol·m-2·h-1) during daytime, in turn, source of TP (30μmol·m-2·h-1) during nighttime. The influx of organic N and organic P to the tidal flat and the efflux of inorganic nutrients from the tidal flat were commonly dominant processes when evaluated through a tidal cycle. Possibility that the light intensity during exposure affect the sediment-water flux of nutrients was indicated.

The purpose of this study was to evaluate the influence of pollutant from Coho Salmon cultivation on water quality through analyzing the data of weather and water quality for several years, and to estimate the adequate loading amount into the Shizugawa Bay locating at Miyagi Prefecture.As a result, it was recognized that COD in the bay was improved from 0.94 mg·l-1 to 0.57 mg·l-1, the delta DO in the bay was improved from 0.86 mg·l-1 to 0.55 mg·l-1, maximum COD in the salmon area changed from 1.13 mg·l-1 to 0.68 mg·l-1 and δDO in the salmon area changed from 1.28 mg·l-1 to 0.69 mg·l-1, respectively, at the end of the cultivation time compared with the large cultivation period.From the results of multiple regression analysis, it was showed that the factors affecting the COD in the salmon area were input loading, temperature and duration of sunshine, whereas the factors affecting δDO in the salmon area were input loading, temperature, duration of sunshine and rainfall, respectively. In particular, it was found that both items were great influenced by the salmon cultivation. In addition, through evaluating the prediction equation for the bottom DO in the salmon area, it was suggested that the annual cultivation amount should be restricted by 4,000 ton·y-1 to prevent the bottom water from the deficient water.