Abstract
In connection with these lakes, the writer studied the pH, O2, and CO2 on three occasions, namely, in the middle of Aug., 1933, in the beginning of July, 1934, and the end of July 1934, having been assisted by Messesrs. K. Koba, N. Obara, I. Nagatu, N. Andô, and K. Sibata. The data obtained are given in Table 1-3, 6-9, and 13-16.
From the viewpoint of chemical stratifications during summer, the Tugaru Zyûniko Lake Group consists of two different kinds of lakes.
The first kind is a spring pond, such as Lake Aoike, which receives a large supply of cold spring water. The chemical stratifications are not well established. Although the water in every layer contains sufficient free carbon dioxide, it is undersaturated in dissolved oxygen. It reacts either weakly acidic or almost neutral.
The other kind is a deep lake with but little spring water, such as Lakes Kosigutinoike and Ooike. In these lakes, chemical stratifications are very well developed. The surface water is saturated or supersaturated in oxygen and is poor in carbon dioxide. It reacts neutral or weakly alkaline. In most of lakes of this type, oxygen is suddenly reduced in the metalimnion, and the bottom water contains no oxygen. The bottom water contains much free carbon dioxide, and reacts weakly acidic.
Two kinds of stratification are met with in lake of this class. The one characterized by marked maximum in the middle layer where oxygen is dissolved in supersaturation. It is due to the assimilation of diatoms. The water reacts strongly alkaine.
The other stratification is recognized either in rather shallow and clear lakes or in deep and turbid lakes. Owing to the shallowness of the compensation depth or to the great turbulences in these lakes, no metalimnion maximum is established.
Most Japanese lakes with anaerobic strata have dichotomous stratification of pH. Due to the strong buffer action of the water, except L. Yabureike, the lakes of the Tugaru Zyûniko have no such stratification.
The lakes in the neighbourhood of Mt. Kuzureyama (east of the district) contain large amounts of hydrocarbonate CO2, and react neutral, while those in the western part are poor in HCO3-CO2, and react weakly acidic.
