The determination of suspended-sediment loads in the southern Great Barrier Reef: field techniques

A mechanical system for collecting samples of suspended sediment in the water column at various stages of a tidal cycle, together with measurement of tidal current velocities, has provided quantitative data on suspended-sediment load transport in a modern coral reef environment. This is the first time that an experiment of this nature has been conducted in such an environment. Suspension load in the water column was monitored over One Tree Reef in the southern Great Barrier Reef by erecting sampling towers at various sites. Suspension loads were collected by siphon action at selected levels of the flooding tide and by a float-activated siphon system at selected levels of the falling tide. Suspended calcium carbonate in the samples was determined by complexometric titration. Water movement was monitored by fluorescein dye casts and arrays of bidirectional current meters. The results show large suspension-load fluxes, which fluctuate with the tidal cycle. Suspended-sediment transport into lagoons and over leeward margins is an important sedimentological process.