Holocene and modern sediment storage in the subtropical macrotidal Fitzroy River estuary, Southeast Queensland, Australia

Over the past 100 years, sediment accumulation has been focused around mangrove and tidal creek environments, which cover an area of 130 km2. Cores from the tidal creeks, dated using 137Cs, 210Pb, and OSL, provide sedimentation rates of approximately 15 mm yr− 1 for the past 45-120 years, or sediment mass accumulation of 1700 kt yr− 1, which includes a component that is reworked into the estuary by tidal currents. Combined with the small amount of sediment that accumulates on the floodplain during floods (∼ 1 mm yr− 1, 640 kt yr− 1), we estimate that approximately 2350 kt yr− 1 of sediment is trapped in the modern lower floodplain and estuary. This estimate of sediment storage suggests that greater than 50% of the modern mean annual sediment discharge of the Fitzroy River, 4162 kt yr− 1, may be retained in the lower floodplain and estuary. These results provide useful insights into the spatial pattern of sedimentation, long-term rates of accumulation and estimates of sediment trapping in a tropical, macrotidal sedimentary system.