Phosphorus Release from Sediments in a Riparian Phragmites australis Community at the Estuary of the Chikugogawa River, Western Japan

In order to determine the contribution of aquatic macrophyte communities on nutrition to sustain the high primary productivity of an estuary aquatic community, we analyzed the process of phosphorus release from sediments in aquatic macrophyte community in the estuary of the Chikugogawa River, South-Western Japan. Vertical profile of 4 PO  concentration and redox potential (Eh) of pore water in sediments were investigated within and outside the Phragmites australis community. Sediment horizon lower than 23 cm layer from the surface showed anaerobic (Eh < −200 mV) in the P. australis community, whereas sediment was constantly oxic (Eh > 0 mV) up to 50 cm depth outside the P. australis community without organic matter accumulation. Non-vegetated sediment with organic matter accumulation showed anoxic profile as vegetated site. concentration in anaerobic parts of sediment showed higher than oxic parts, and higher concentration in sediment pore water corresponded to sulfur deposition in sediment. Sulfate ion supplied from the sea water is reduced under the anoxic condition and S reacts with water-insoluble phosphorus salts e.g. Fe3(PO4)2 or AlPO4 and Fe2S3 or Al2S3 precipitates. Thus 3 4 PO 