Abstract
Sayama-ike which is utilized as an irrigation reservoir covers an, area of 38.6 ha. and has a pondage of 1, 799, 000 m3. Consecutive investi-gations numbered 59 were made by the writer from March, 1954 to De-cember, 1956, and the findings are as follows:
(1) Circulation takes place from November to March, and the condition of the water is even in every respect during this period. The amount of dissolved oxygen increases gradually according to the falling of temperature of the water, and gradually approaches the saturation point. Sayama-ike has never been frozen.
(2) During the summer, non dissolved oxygen layer and pH dicho-tomous stratification are noticeable and a remarkable increase of hydrogen sulfide appears in the hypoliminion. Carbon dioxide assimilation takes place vigorously from the surface of the water down to the 2m-layer. It was found out that the saturation point of oxygen is 150% and pH 9.6. Conpensation depth exists between the 2m and 3-m layers. It is sometimes between the 3m and 4m-layers.
(3) During the stagnant period bicarbonate, free carbon dioxide, ammonia-nitrogen, organic nitrogen, phosphate, iron, manganese, and sulfide stratificulate conspicuously in the hypoliminion.
(4) The vertical stratification of sulphate and calcium are irregular-ly noticed. Chloride shows non stratification throughout the year.
