On the particulate materials collected at two stations in the central part of the Seto Inland Sea, Japan, at roughly monthly intervals from April 1972 to February 1974, particulate phosphorus (PP), particulate carbon (PC), particulate nitrogen (PN), sestonic chlorophyll α(chl. α) and dry weight of total particulate matter ("seston weight", SW) were determined.
PC was regarded as particulate organic carbon from the regression of PC to PN. The ratio PC/SW, i.e., the carbon content of the particulate material, was regarded as an index of organic feature of the particulate matter. The mean of this ratio was greater at the offshore station than at the inshore station, and was generally great during the high temperature season especially at 0 m layer.
The phosphorus content of the particulate material increased generally with the carbon content. The highest carbon contents were observed on the occasions of the red tide and also at 0 m layer of the offshore station, with phosphorus contents amounting to 0.32-0.45% of SW. Low phosphorus contents were observed mainly in the bottom layer or in the low temperature season.
The regression analysis of PC to chl.α indicates that living phytoplankton accounted for major portions of PC at the inshore station; in contrast, large proportions of PC were represented by detrital carbon at the offshore station.
SW was divided into the organic and the inorganic matter by calculation, and their contributions to PP was evaluated by multiple regression analysis. The multiple correlation of PP to these two variables was always significant, and this significant correlation derived chiefly from the positive contribution made by particulate organic matter. Therefore, it is concluded that the abundance of PP depended mostly on that of particulate organic matter in all layers of both stations.
PC was subdivided into the phytoplankton carbon and the non-phytoplankton carbon by calculation, and their contributions to PP was evaluated also by multiple regression analysis. The result shows that the abundance of PP depended on the abundance of phytoplankton carbon especially in the upper layers of both stations during the high temperature season. In the shallow inshore waters the dependence of PP upon phytoplankton carbon prevailed also in the low temperature season.
Recovered particulate materials were classified into four types on the basis of C, N and chlorophyll α contents. The occurrence of each type was discussed with regard to the season, station and depth.
A hexagonal diagram was devised to illustrate the chemical characteristics of individual particulate material.