Fine sediment budget on an inner-shelf coral-fringed island, Great Barrier Reef of Australia

A field study was undertaken to determine the deposition and removal budget of fine sediments on the windward and leeward sides of an inner-shelf coral-fringed island of the central Great Barrier Reef. Total sedimentation rates were about 2000 mg cm−2 yr−1 at all depths, with 30-60% imported from the reef-surrounding waters during calm periods, and the remaining material locally resuspended during storms. Storms resuspended fine sediment at depths less than ∼5.5 m on the leeward reef side and ∼12 m on the windward side. In these shallow waters there appeared to be a net annual sediment balance between import and export by resuspension events. Below these depths, there was no resuspension during storms; further there was a tenfold increase of the sedimentation rate during storms and most of this additional mud originated from resuspended material from shallower waters on the island slopes. The mud had accumulated on these deeper coral reefs to levels of about 9000 mg DW cm−2, equivalent to ∼4 years of sediment deposition that is presumably flushed out only during tropical cyclones. The data show that increased rates of advection of fine suspended sediments from soil erosion on land can result in increased sediment accumulation on inshore coral reefs below the depth of storm resuspension, with negative effects on the coral communities.