Limnological Investigations on Lake Ohama-ike of the Gassan Volcano, Northeast Japan

Lake Ohama-ike is northeast of Midagahara lava plateau of the Gassan Volcano. It was formed by landslide of talus deposits supplied from the high cliff at the lower edge of the lava plateau.The morphometrical data calculated from the bathymetric map of this lake are as follows:Surface area 1.62×104m2Length of shore line 578mMaximum depth 9.10mVolume 6.24×104m3Shore development 1.28.The results of authors' survey are summarized as follows:The bottom of this lake is covered with talus deposits through which the lake water easily permeate. The amount of seepage is about eight thousand tons per day in summer.In mid-summer, the distinct development of thermal and chemical stratification is observed in this lake.The water shows neutral reaction and poor dissolved minerals in which calcium bicarbonate is the main constituent.From the low photosynthetic productivity and the negative correlation between dissolved oxygen in the water and water temperature, it is inferred this lake is an oligotrophic lake.