The balance of supply, transport and retention of FPOM(fine particulate organic matter) plays a key role as energy resources to river ecosystem. This study aims to show the relations of channel morphology to FPOM dynamics using the lake originated plankters as FPOM tracers. We estimated a transport distance of suspended FPOM by calculation of the decreasing ratio of the lake originated plankters with channel distance. Hydraulic radius was adopted as an index of channel morphologic complexity and its influence on FPOM transport distance was analyzed. Study sites were established in two artificial canals from lake Biwa and two natural rivers with different channel morphology below dam reservoir.

Results showed that the lake originated plankters were suitable for quantitative FPOM tracers in streams below dam reservoir. The FPOM transport distance in each stream decreased exponentially with channel distance, but the decreasing ratio had a negative correlation with the hydraulic radius. This result indicates increasing complexity of channel morphology will increase the FPOM retention efficiency.