DEVELOPMENT OF RIVER ECOSYSTEM ASSESMENT BASED ON EXERGY EFFICIENCY

Abstract

A new ecosystem assessment method based on exergy efficiency is proposed to evaluate health of river ecosystem. The exergy takes into account of both energy quantity and energy quality. 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. This ecosystem assessment method is applied to natural riffle zone and riffle zone with bank protection in Genka River, Okinawa. The result shows that the exergy efficiency at the natural riffle zone is 0.84 and that at the riffle zone with bank protection is 0.13.