Distribution of Oxygen-Deficient Water and Estimation of Its Area in Lake Kitaura

Detailed distributions of oxygen-deficient water were observed using a high-resolution tow-yo instrument, YODA Profiler, in Lake Kitaura to investigate the formation of oxygen-deficient water. The results of observations showed that oxygen-deficient water widely appeared at a depth of deeper than 4 m, and the dissolved oxygen （ DO ） concentration in deep areas was particularly low. Furthermore, it was suggested that high phosphorus （ PO 4 -P ） concentrations were eluted from sediments in areas of oxygen-deficient water. The DO concentration at 10 cm above the lake bottom tended to be lower than that at 50 cm above the lake bottom. The oxygen-deficient water in Lake Kitaura is greatly affected by the water depth, which implies that the ratio of the area of oxygen-deficient water can be inferred by lake bathymetry and observed DO profiles. The area of oxygen-deficient water reached 55.9 ％ at 50 cm above the bottom and 63.2 ％ at 10 cm above the bottom of the total area of Lake Kitaura.