Abstract
A new ecosystem assessment method based on exergy efficiency is employed to evaluate the health of fluvial ecosystems. The exergy takes into account both energy quantity and energy quality. In this method, the ecological exergy efficiency, which is calculated as the ratio of organism exergy produced in a system to exergy supplied from outside the system (photosynthetically active radiation exergy and organic exergy supplied by flood) , is defined as an indicator of the health of a fluvial ecosystem. This ecosystem assessment method is applied to three small rivers on the main island of Okinawa, Japan. The results show that the exergy efficiency of the fluvial ecosystems takes different values among the three rivers and can clarify the difference in the health between the natural zone and the artificial zone with bank protection of the Genga River, which is difficult to identify by means of the evaluation using water quality and biological environment.
