Abstract
Oxygen deficit water near the bottom of Lake Suwa has often been measured during the summer since the 1990’s. This report is based on field measurements at one point and intermittently with a cycle of two weeks. In this study, continuous field measurements of dissolved oxygen near the bottom at several points were conducted in order to understand the temporal and spatial characteristics of the oxygen deficit water in detail. The main results indicated that: 1) Rainfall and strong winds often put an end to the oxygen deficit state, but the variation in air temperature and water temperature of the inflow from rivers after these phenomena play an important role in the regeneration of the oxygen deficit state. 2) At night on some fine weather days, strong water cooling to the surface water by cold air supplied oxygen to the bottom water due to the disappearance of daily stratification. The spatial distribution is not uniform and this phenomenon was often measured at the north-west part in a lake especially.
