抄録
On the middle of October 1932 the limnological observations were made at eight ponds situated in the Etigo district and water temperature, oxygen content, hydrogen ion concentration, free carbon dioxide, chlorine, soluble organic matter, silicate, phosphate nitrate and nitrite were determined. At Asahi-ike the temperature. O2-, CO2-content and pH were observed at 14 stations and the figure of their horizontal distribution show that the values of O2 and pH are higher in the littoral region than that in the middle part of the pond, due to the photosynthetic reaction of the bottom flora.
Phytoplankton especially Synedra pulchella is extraodinarily predominated in the water of Utibori, counting 98, 000 per 10 c. c. The relation between the quantity of plankton and the amount of the nutrient salts as above mentioned was examined. As far as the present observation is concerned, the limiting factor controlling the production of the ponds seems to be nitrite or phosphate.
