Physical and bacterial processes affecting suspended particulate matter in a tidal river

In order to clarify the origin and behavior of suspended particulate matter (SPM)in a tidal river, variation of SPM in a tidal river was investigated with regard to its size and constituents. SPM was separated into three groups according to size. Change of contents of titanium and organic substances of each group of SPM was examined. SPM which was discharged by run-off was transported with decomposition and sedimentation in a tidal river. Concentration of SPM with a particle size greater than 0.45 mu m increased due to resuspension in a tidal river. Origin of SPM with a size of less than 0.45 mu m at upstream areas was from natural soil and most of such SPM which had been transported settled near a river mouth. It was determined from examination of the CN ratio and the ratio of the number of attached bacteria to free bacteria that SPM with a size greater than 1.0 mu m at upstream areas was decomposing intensively. At the downstream areas, SPM with a size of less than 0.45 mu m came from the sea. SPM with particle size greater than 1.0 mu m consisted of plankton and substances which were decomposed sufficiently while flowing. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.