Abstract
We studied trends in the annual variations of the items related to turbidity in the water in Ariake Bay and Isahaya Bay, and analyzed the relationships between these variations and decrease in tidal current velocity caused by the mean sea level rise and other influences.
Transparency observed at the center and mouth of Ariake Bay increased because of a decrease in turbidity, which was caused by a decrease in tidal currents. The decrease in tidal currents was caused by the increase in mean sea level; this has occurred since the 1980s in the whole Kyushu area, including Ariake Bay. We found that the contribution of the changes in turbidity caused by the mean sea level rise was larger than that of the changes caused by the setting of the net during the Nori cultivation period at the head and center of the Bay. We also noted that the changes in turbidity observed at the center and mouth of Isahaya Bay were similar to the ones measured at the head and center of Ariake Bay and that the mean sea level rise in Ariake Bay was the main contributor to these changing trends. Moreover, it was suggested that in addition to the mean sea level rise, the changes in turbidity observed at the head of Isahaya Bay were influenced by the construction of the Isahaya sea-dyke in 1997.
