Abstract
With the aim of elucidating the mechanism of the sulfides production by sulfate-reducing bacteria in the estuarine region of the river receiving industrial and municipal drainages which contain organic matter in high concentration, we observed the distribution of sulfate-reducing bac-teria, sulfides, sulfates, chlorinity, organic matter, etc. in the water and in the bottom mud in the Takano River, and subsequently studied the factors which participate in the sulfides production in such a region of the river. The Takano River receives a large amount of drainages from a pulp factory and Maizuru City, and discharges itself into Maizuru Bay.
Station where the present ecological observations were carried out are shown in Fig. 1.
Results obtained are as shown in Tables 1 and 2, and in Figs. 2, 3 and 4, and may be sum-marized as follows:
1) In the river water relatively small number of sulfate-reducing bacteria were sporadically distributed regardless of the distance from the mounth of the river. It is thought that the cells of these bacteria detected in the overlying river water were brought by the water movement from the bottom mud where was the proper inhabiting place of these bacteria.
2) In the bottom mud of the river, the distribution of sulfate-reducing bacteria, in the case of anyone of marine and fresh-water types, was influenced by the chlorinity of the bottom water (Figs. 2 and 3). However, the total counts of the sulfate-reducing bacteria including both types in the mud were hardly influenced by the chlorinity of the bottom water; total aulfate reducers were almost evenly distributed in high count in the mud throughout sea-water zone, brackish zone and fresh-water zone.
3) The distribution of total sulfate-reducing bacteria in the bottom mud was also hardly influe-nced by organic content of the mud or sulfate content of the river the growth or the counts of the total sulfate-reducing bacteria in the bottom mud was not limited by organic content of the mud or sulfate content of the bottom water, viz., in these bottom muds sulfate and organic matter were sufficiectly present for the growth of the sulfate-reducing bacteria (Figs. 2, 3, 4 and Table 2). It was generally found that organic matter contained in the bottom mud of this region of the river was higher in concentration and more easily decomposable than those contained in the bottom mud of the sea.
4) On the contrary, the production of sulfides in the bottom mud by the sulfate-reduc-ing bacteria was principally influenced by the sulfate content of the bottom water and the concentra-tion of available organic matter in the mud. In the fresh-water zone where the sulfate content of the bottom water was very small, the production of sulfides in the bottom mud was mainly suppressed by the low concentration of sulfate in the bottom water; in the sea-water zone where the sulfate content of the bottom water was sufficient, the production of sulfides in the mud was
