An ecosystem assessment method based on exergy efficiency is applied to Saba River. In this method, ecological exergy efficiency, which is calculated by the ratio of organism exergy produced in system to exergy supplied from outside of system (photosynthetically active radiation exergy and organic exergy supplied by flood) is defined as an indicator of health of river ecosystem. Field observations of water quality, river sediment and amount of detritus, attached algae and benthic animal were conducted at 8 points in Saba River. The temporal variations of exergy efficiency at 4 points of Saba River were estimated by these observation results and the prediction model of attached algae and benthic animal. The result shows that the exergy efficiency can clarify the difference of the soundness of river ecosystem between the 4 points of Saba River, where no significant difference was observed in terms of water quality and river sediment.
