Abstract
Dammed up lake Ono is located in the northeast part of Ube-shi, Yamaguchi Prefecture. Since limestone comprises part of drainage basin of rivers flowing into the lake, the Ca concentration of the lake water is comparatively high (20-25 mg⋅l-1), though still beneath the level of hard water.
Although a high saturation index of CaCO3 (calcite) was confirmed in the epilim-nion of the lake, no precipitation was detected.
A laboratory test, however, demonstrated that addition of a few seed crystals of calcite (8-9 μm in diameter) to the lake water adjusted the temperature and pH to summer conditions (25°C, pH 9.12). This warming, together with addition of NaOH induced precipitation of CaCO3 along with phosphate, thus eliminating about 20% of Ca ions in the lake water. This phenomenon was not observed when pH was adjusted by decarbonization.
