Spatial and Temporal Variance of River Discharge on Okinawa (Japan): Inferring the Temporal Impact on Adjacent Coral Reefs

摘要

Land-use changes and associated river discharges in coastal tropical regions present a global threat to coral reef environments. This study investigated the temporal variation in biological oxygen demand (BOD_5) and sus- pended particulate matter (SPM) at the mouths of seven rivers on Okinawa Island (Japan) over 20 years. We re- port strong positive relationships between human popula- tion densities within river catchment areas and both average BOD_5 concentration (r~2=0.968; p<0.001) and SPM (r~2=0.659; p<0.003) at the mouths of the rivers. At the reef adjacent to one river (Hija River, 50.2 km~2 Catchment area) we applied moving window analysis to Assess an optimal sampling strategy for elucidating tran- Stional boundaries in coral composition from the river Mouth to a point where the effect of river discharge was Minimal.