Abstract
Properties of estuary sediment change dramatically by repetition of flushing events under management of the river flow. The dynamics of fine sediments in the Tonegawa river estuary were studied from analyses of physicochemical properties and bacterial community structure of sediments throughout flushing, static and transitional periods. In flushed period, coarse sand occupied the estuary sediment in place of fine sediment flushing out to the sea with flood. In static period, fine sediment dominated in almost all points and sedimentation of labile organic matter (LOM) and amorphous iron (Feo) gradually spread from river mouth towards upstream in connection with the intrusion of saline wedge and the estuary circulation. The following explanation for chemical dynamics of estuary environment in the Tonegawa river was lead from the evidence obtained by bacterial community structure. The rapid decomposition of LOM by sulfate and/or sulfide reducing bacteria generated anaerobic condition with produce of hydrogen sulfide and release of reductive Fe(II), which reacted to dominate precipitation of iron sulfide. The chemical properties of estuary sediment were strongly influenced by the river flow and the dynamics of saline wedge.
