Tracing sediment across catchment to reef within the Burdekin region of the Great Barrier Reef lagoon

Zoe Bainbridge

The novel application of the SediPump® instrument to capture sufficient sediment mass from low concentration flood plume waters has enabled catchment source tracing of Great Barrier Reef (GBR) flood plume sediment for the first time. Geochemical tracing of sediment captured in Burdekin secondary water types up to 160 km north-east from the river mouth reveal two clear sediment source contributions from this catchment: the Upper Burdekin and Bowen sub-catchments. Our flood plume sediment samples show that colloidal, clay and fine silt grains (<20 μm) from these two key sources travel furthest in the GBR lagoon, and are almost exclusively derived from sub-soil erosion sources. These data extend the current sediment transport understanding and linkages beyond the freshwater zone, and through the Landholders Driving Change Project are also being traced to tributary sediment sources within the key Bowen-Broken-Bogie (BBB) area. This strong collaboration formed between our project, NQ Dry Tropics Landholders Driving Change and importantly landholders within the BBB has led to improved characterisation of sediments within this area and enhanced local understanding of catchment to reef water quality connections. The new data have also been extended to the GBR Dynamic SedNet modelling team to refine the BBB sediment budgets, and are informing targeted remediation efforts within the catchment.