In this study, we assessed the impact of discharged water from a 1 MW-class Ocean Thermal Energy Conversion (OTEC) plant on marine ecosystems (corals) in Kume Island, Okinawa. Based on field survey data, including detailed topographic data, numerical simulations were conducted using a physical model (MEC model) and an ecosystem model (NPZD model). Through the simulation with different discharge water qualities and discharge locations, the extent of the discharge water’s impact was compared. The results suggested that while the cooling effect of the discharge water could expand the area suitable for coral habitats, the increase in nutrient concentrations might have a negative impact on corals. It was also found that this negative effect could be reduced by discharging the water separately after secondary use. Furthermore, the diffusion range of the discharge water was influenced not only by the depth of discharge, but also by the surrounding topography. Sensitivity analyses of tidal currents and diffusion coefficients confirmed that their impact on the spread of discharged water was limited.
Kotani et al. (Wed,) studied this question.