Development of Nutrient Response Model for Dominant phytoplankton in Ariake Bay Considering Dissolved Silicate

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A survey was conducted on dissolved silicon (Dsi) and other nutrient salt concentrations and plankton in the northeastern area of the Ariake Sea to examine the effects of Dsi on the coastal ecosystem. The Dsi concentration in the area decreased twice a year. A significant decrease in Dsi was particularly noted in February and March, and dissolved inorganic phosphorus (DIP) also reduced. The decreases are presumably due to the proliferation of large diatoms, including Eucampia spp. Significant decreases in nutrient salt ratios were also noted: the Dsi/DIN ratio was 1 or lower and the Dsi/DIP ratio was 10 or lower. The spatial distribution of the nutrient salt concentration didn’t make the differences of the species of phytoplankton during this period. However, Dsi was identified as a limited factor for diatom growth within about 2 months.