Abstract
To examine the behavior of DO from the viewpoint of formation and the break of density stratification, we continuously measured the water quality and micrometeorology of Lake Koyama at its deepest point of about 6 m from June to November in 2003. DO and EC in the surface and bottom layers, the vertical profile of the water temperature, the wind velocity and insolation were observed. As a result, DO in the bottom layer was lacking due to the formation of the thermal stratification in summer, and due to the saline stratification in a non-irrigation period after a large amount of sea water had flowed into Lake Koyama. The results also revealed a negative correlation between DO in the bottom layer and Wedderburn number W. Further analysis of the relationship between them indicated that anoxic water was generated due to the repression of the DO supply below surface layer under the stratification conditions of W>4.5, and that the anoxic state in the bottom layer could be eliminated by the generation of vertical circulation when the wind velocity of W<4.5, more than 4.0 m/s in summer and more than 10.0 m/s in the non-irrigation period, operated on the water area.
