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Nitrification and denitrification processes in a well mixed tidal river in Japan are modeled, based on results of long term field observation on water quality and sediments in the river. Laboratory test results and values in references are used for the determination of parameters and coefficients in the model. In modeling of the processes, sediments, suspended solids, and overlying water are taken as elements and in computation a Lagrangian reference frame in terms of accumulated water volume is employed for reduction in numerical dispersion. Simulation results on ammonium and nitrate nitrogen, showing good agreement with long term field observation results, qualitatively explain well the processes in the river. The results indicate some countermeasures to reduce nitrate more such as the increase in the area of sediment surface. The simulation model is available for the estimation of water quality in well mixed tidal rivers and applicable for water quality control.

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ABSTRACT; Global environmental problems are attracting greater attention of the public. In spite of their consciousness about the environment, however, they still do not abandon their high consumption lifestyles. They waste energy and other resources and cause impact upon the environment. Saving of energy in our daily life is especially important in order to reduce the emission of CO2 which might cause the global warming and climatic changes. The problem here is the discrepancy between attitudes and actual behavior. It is needed to clarify what is the real substrate that promote or impede our environment friendly behaviors. From this viewpoint, a questionnaire study was conducted in Fukuoka and Kurume, with a view to analyzing the people's attitudes about environmental protection. Necessary conditions for encouraging people to conduct pro-environmental behaviors is discussed based on the data obtained. It is shown that a majority of the citizens are very conscious about the environmental problems, but relevant incentives to enhance their pro-environmental behaviors are not provided. Today's price of energy, for example, does not have enough incentive effects. Improved public education and information is essential to provide motivations for environmentally favorable attitudes and behaviors of the public.

Several field surveys were conducted to investigate changes of water quality with time in the tidal River Rokkaku, where a turbidity maximum exists. Suspended solids of the turbidity maximum reach more than 20 g/l in concentration. Based on the surveys, NH4-N, NO2-N, and NO3-N have peaks in concentration at certain salinities, located in order of NH4-N, NO2-N, and NO3-N toward the river mouth within 10 to 25 km from it. The salinities were 0.5, 1.7, and 3.0 %, respectively, and the maximum concentrations were about 3.0, 0.3, and 4.5 mg/l in winter time, respectively. Laboratory batch experiments were conducted, using suspended solids and sediments taken from the river, to study the effect of salinity on nitrification and to estimate kinetics parameters of it in the river. Suspended solids and sediments were sampled at a point in the middle stream. The sediments were collected from the aerobic layer of mud, less than 1 cm thick from the surface. Experimental results indicated much more inhibition of NO2 oxidation by salinity than that of NH4 oxidation. Nitrifying bacteria in sediments were less sensitive to salinity than those in suspended solids. The change of nitrogen concentration with time was clearly explained with the Monod growth model and the two kinetics parameters were obtained by the curve fitting method. Maximum specific growth rates of NH, oxdizing bacteria ranged from 0.015 to 0.029 (hour−1), which decreased markedly with more than 15 %. salinity. Those of NO2 oxidizing bacteria ranged from 0.015 to 0.025 (hour). Saturation constants of NH4 and NO2 oxidation were also dependent on salinity. Changes in NH4-N and NO2-N concentrations in the River Rokkaku with time were simulated well using a newly developed river model and the parameter values obtained in the laboratory tests. The mechanism of nitrification by suspended solids and sediments in the river is shown to depend on tidal effects.

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