Abstract
The purpose of this study is to clarify the relationship amongst tidal range, distribution of Chlorophyll a and phosphorus flux around the mouth of the Arakawa River. We observed the phytoplankton bloom occurred around the density front during the spring tide when a moderately mixed estuary appeared. Conversely, the phytoplankton bloom occurred thinly under the halocline during the neap tide when a fully stratified estuary appeared. A three-dimensional hydrostatic model was used to better understand the mechanism of the change in Chlorophyll a distribution and phosphorus flux due to tidal range. Additionally, the phosphorus flux around the mouth of the river during the neap tide was found to be twice as large as during the spring tide. Therefore, it appears that the mouth of the river where the stratification strength changes with tidal range has a role of buffer against the phosphorus load.
