抄録
Since August, 1941, three limnological observations have been made on four lakes in the Koikuchi lake group, i. e. Ao-ike, Wakitsubo-no-ike, Koikuchi-no-ike, and Hakkei-no-ike. The present paper deals with the nutrient salts which are said to have close bearing upon the production of the phytoplankton, being such as soluble silicate, soluble phosphate, and nitrogenous compounds (ammonia-, nitrite-, and nitrate nitrogen).
From the results obtained the following comments can be given;
1) The surface water of the former two lakes are very rich in nitrate nitrogen and soluble phosphate.
2) In the hypolimnion of the latter two lakes ammonia nitrogen, soluble phosphate and silicate showed a marked stratification during the period of summer stagnation, while nitrite- and nitrate nitrogen showed no such stratification.
3) In the middle of December when the water temperature showed an equal vertical distribution this chemical stratification still remained, though in Hakkei-no-ike it had already disappeared.
