陸水学雑誌

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During the period 1965 to 1968, determinations were made of salinity, temperature and velocity in the Kitakami River.
The salinity concentration of bottom layer is much higher than the surface layer at the lower end of the river. Consequently, the water of surface layer is fresh water and that of the bottom layer is salt water (Fig. 2).
The salt wedge type of the Kitakami River shows fine negligible mixing. This phenomenon is rare, because in the rivers empting into the Pacific Ocean, it is generally moderate mixing. The salt wedge type is caused by the level difference between the low water and the high water, but it is also caused by discharge, too (Fig. 3).
The salt wedge length affected by an influence of discharge. When discharge decreases into about 70m³/sec, the salt water intrudes into upper stream, about 8 km point from river mouth. But, when discharge increases into about 400 m³/sec, the salt water is restricted to the vicinity river mouth (Fig. 6).

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Lake Saizuchi-numa, situated on the boundary of Mogami and Kitamurayama districts in Yamagata Prefecture, is considered to be a type of the tectonic lakes from the geological point of view.
At the summer stagnation period, thermal as well as chemical distinguished stratifications are observed and this anaerobic layer developes near the bottom.
The annual observation reveals that the main constituent of the dissolved substances is sodium chloride which is transported by snow from Japan Sea in winter time. Throughout this season, the sea-breezed salt by monsoon is accumulated in fallen snow which will melt and furnish this lake.
This lake belongs to the dystrophic lake.

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