A Study on the Cause of Long-term Variations in Water Exchange and Water Quality in a Semi-enclosed Bay

摘要

Hamana Lake has very high closeness, chronic eutrophication and bottom hypoxia during summer. The causes of long-term variations in water exchange and water quality are discussed using the long-term data such as topographic and bathymetric changes, measurement and meteorological change over the recent 50 years. The construction of the outside jetties at the inlet led to the higher water exchange rate, which made the bottom water environment better. Since 1980, the water temperature rise associated with meteorological changes such as air temperature rise and the increase of phosphorus release flux are responsible for the deterioration of water quality.