Seasonal Flood Deposits in Hanalei Bay, Kaua'i, Hawaii—Implications of Fluvial Sedimentation for Coral-Reef Ecosystems

Sedimentary facies, short-lived isotopes 7Be and 137Cs, and magnetic properties of sediment cores were used to trace the thickness and distribution of terrestrial sediment in Hanalei Bay, Kaua'i, Hawaii, in order to assess spatial and temporal patterns of sediment deposition associated with seasonal flooding of the Hanalei River. Multiple flood deposits associated with high river discharge in spring and summer 2006 were apparent in sediment cores. The youngest and thickest terrigenous sediment is located on the east side of the bay: near the Hanalei River mouth and in a bathymetric depression known locally as the Black Hole that acts as a temporary sediment sink. Delivery and dispersal of flood-derived sediment in Hanalei Bay have important implications for the health of local coral reefs; sediment and dissolved substances from the Hanalei River have the potential to stress the reef ecosystem substantially. Increased turbidity and sedimentation on corals resulting from floods of the Hanalei River could affect the health and sustainability of coral reefs and their many associated species. This is a particular concern during summer months when wave energy is low and sediment is not readily remobilized and advected out of the bay.