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.

抄録全体を表示

Cercarial contamination (being suspected as a gasterostome trematode, Bucephalidae: Digenea) in the Yodo River was studied by the water monitoring using experimental fishes. The fishes including Pseudorasbora parva and Squalidus chankaensis subsp. were exposed in the river and the cercariae that penetrated tail fin of the fishes were observed with a stereoscopic microscope. The monitoring was carried out three times from December 2000 to January 2001 in the Yodo River. Over 80% of the fishes were infected by the cercariae (average numbers of metacercariae in an infected fish ranged from 5.2 to 18.1) during 4 to 10 days of the exposure. The numbers of cercariae in the river water were estimated to be 0.12 to 1.72·m^-3.

抄録全体を表示

Dissolved fulvic acid extracted from the stream water was characterized. The stream named Omoshironbetsu River runs through Kushiro Bog, eastward of Hokkaido Prefecture, Japan. The surface water of this stream showed yellow color, and it implied dissolution of humic substances derived from marsh plants. However, we attributed the fulvic acid to the woody tissues rather than the marsh plants by the analyses of stable carbon isotope and lignin-phenol compounds. And the contribution of the fulvic acids in DOC of this stream water was about 30% regardless of the season.

抄録全体を表示

The effects of various positions of aeration in Multi-Soil-Layering (MSL) method of bio-genic waste water treatment were investigated. Porous aeration pipes were installed in upper, middle, and lower positions in model MSL systems. Each model MSL packed in 10X50X60cm sized acrylic box. Air was supplied at the rate of 48000 l·m^-3·d^-1 through the porous pipes installed at various positions. Loading rate of waste water was 288 l·m^-2·d^-1. In the upper position of aeration, clogging was prevented and nitrogen removal was efficient. But efficiency of aeration was low for high level of removal of COD·BOD and T-P, because air leaked from surface of the system. In the middle position of aeration, the efficiency of T-P removal and decomposition of organic matter were high because of the efficient aeration to create relatively large aerobic parts in the MSL. But nitrogen removal was low. Because of nitrate was leaching. It was thought that anaerobic parts were too small to efficient denitrification. In the lower position of aeration, clogging was happened at the early stages of treatments. Fe(II) and Mn(II) were oxidized efficiently to prevent the solubilization. COD·BOD of final effluent water was also low. Based on this study, if only one aeration position has to be selected, the appropriate aeration position was considered to be the position between the first and second of soil layers of MSL. This aeration position may prevent clogging effectively. Large aerobic condition may contribute to efficient phosphorus and organic matter removals. Nitrogen removal may also be enhanced because of nitrification of the upper position and denitrification of the lower position.
However, since each upper, middle, and lower position showed different efficiency characteristics on treatments, the positioning of aeration and the operational condition should be selected depending on the given target of the treatment, including the combinations of the two positions, upper/lower, upper/middle, and middle/lower.

抄録全体を表示