Water Quality of Lake Toya and of all the Lake's In- and Outflow Rivers

概要

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Lake Toya is situated near Mt. Usu, a volcano which erupted on August 7th, 1977, when ash fell on the lake surface and caused an abrupt increase of suspended matter in the lake water. No significant difference in the concentration of sodium, potassium, calcium, and magnesium ion was reported between the periods before and immediately after the activity of Mt. Usu. We investigated the water quality (pH, temperature, conductivity and concentration of each metal ion) in order to assess the long-term influence of the eruption of Mt. Usu and the changes on the standing water quality of Lake Toya. Sampling was carried out on December 8th and 9th, 1983, at the stations beside the basin of Lake Toya and on November 30th, 1983, at sampling points at all the lake's in- and outflow rivers. The pH values and concentrations of sodium and calcium ions were found to be higher than those measured immediately after the eruption. The conductivity and concentration of potassium ion were low as compared with the former data. A significantly positive correlation was detected between the depth from the lake surface and conductivity, while high negative correlations were observed between the depth and the pH and between the depth and water temperature. Nevertheless, the general features of the lake water were considered not to have changed.
北海道大学の論文
1985-07-31