Abstract
Osaka Bay has two openings. Osaka Bay is a highly enclosed sea area where various large and small rivers such as the Yodo River, Yamato River, and Inagawa River flow into the bay. As for the topography of the sea area, the eastern sea area is shallow and flat with a depth of less than 20m, while the western sea area is deeper toward the strait, reaching a maximum depth of 100m. In the past, during the high economic growth period, Osaka Bay became eutrophic due to nutrients such as nitrate and phosphorus supplied from factories and household wastewater, and red tides were frequently observed. After that, nutrients gradually decreased due to legal regulations, and in recent years, it has become oligotrophic. Regarding the chemical composition of Osaka Bay, there is many information on nutrients such as nitrate and phosphorus from the viewpoint of eutrophication, but there is few information on bioactive trace elements which essential for phytoplankton growth. The purpose of this study is to clarify the vertical distribution of Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb and Se, which are classified as bioactive trace elements, and elucidate the factors that govern its distribution.
