Environmental Condition as Limiting Factors in Primary Productivity in Disposed Coastal Area

In order to clarify the primary productivity in disposed coastal area, we measured primary production of phytoplankton by simulated in situ deck incubations in southern part of Kashima-Nada every season from 1995 to 2002. Productivity was high in spring and when river water overflowed in summer. The mean value of the primary production in a site with a bottom depth of 40 m in winter, spring, summer and autumn was estimated at 362, 932, 440, 210 mg-C/m2/day respectively. Production was limited by lack of nutrients (DIN: <1 μM, silicate: <5 μM) or solar radiation (<17.5 MJ/m2/day). Spring bloom occurred from March to May when both nutrients and light condition were good.