In the surrounding area of Nabekoshi Pass, many lakes and swamps are distributed here and there. In spite of abundance of lakes, this district has ever been ignored by the limnologists. The author has had cherished desire to explore these lakes from the standpoint of regional limnology. In the snmmer of1965, he had a chance to carry out the survey of Lake Nabekoshi-numa, arepresentative one of these lakes. The results of the investigation are summarized as follows:
(1)The morphometrical data calculated from the bathymetric map(Fig.2) are shown in the next table.
Surface area 5.69×104m2
Length of shore line 1, 650m
Maximum depth 19.20m
Shore development 1.95
Volume 3.66×105m3
From the geomorphological point of view, this lake is considered to be a dammedlake formed by landslide.
(2)In summer stagnation period, this lake exhibits a thermal stratificationcommon to temperate lakes. As for many dissolved materials, the development of stratification is also observed.
(3)The chemical analyses reveal that the surface water shows neutral reaction and the main dissolved substance is sodium chloride derived from the atmospheric salt which is transported by the melt water.
(4)Judging from the low photosynthetic productivity and the poor content of dissolved materials, this lake is deduced to be an oligotrophic lake.
