LONG TERM VARIABILITY OF WATER QUALITY AND SEDIMENT IN OSAKA BAY

In this study, a water quality - sediment coupled model built to consider the relationship between the long term variability of water quality and the sediment in Osaka Bay. Consequently, the water quality concentrations both T-N and T-P are maximum until around 1980, and turn to decrease afterwards. owever, the sediment concentrations do not change at the same period and tend to decline after 1990. The causes of such fluctuation characteristics of the water quality and sediment are as follows. The water quality immediately responds to reduction of nutrient load from the land and turns to a decreasing trend at an early stage. But in sediment, since it takes time until the decomposition and elution of the accumulated organic matter become larger than the accumulated amount, it is considered that the improvement takes time. In recent years, the concentration of T-N and T-P in sediment has tended to decrease, suggesting improvement of the sediment environment by sustained regulation of inflow load.