Holocene and Modern Sediment Budgets and Trapping Efficiency of the Subtropical Macrotidal Ftizroy River Estuary, Southeast Queensland, Australia  

Authors / CoAuthors

Bostock, H. | Ryan, D.A. | Brooke, B. | Hancock, G. | Pietsch, T.

Abstract

There is growing global concern for the impact of increased fluvial sediment loads on tropical coral reefs and seagrass ecosystems. The Fitzroy River is a macrotidal, tide-dominated estuary in the dry tropics of central Queensland and is a major contributor of sediment to the southern Great Barrier Reef (GBR) lagoon. The estuary currently receives most of its sediment during large episodic flood events commonly associated with cyclonic depressions. The sediment dynamics of macrotidal estuaries and especially of wet-dry tropical systems, with intermittent flows and sediment discharge are poorly understood. Average annual sediment budgets for such a system are also difficult to estimate due to the sporadic nature of flood discharge events. Therefore we have estimated a long-term sediment accumulation rate of catchment-derived sediment trapped in the estuary using the Holocene stratigraphic sequence, determined from a series of sediment cores, dated with radiocarbon and optically stimulated luminescence (OSL), and integrated with industry borehole data. We estimate that 17,400 million tonnes (Mt) of river sediment has accumulated in the estuary during the last 8000 years. This suggests a minimum mean annual bulk sediment discharge of the Fitzroy River of 2000 kt yr-1. This estimated 2175 kilotonnes per year (kt yr-1) of bulk sediment is equivalent to 25% of the estimated average annual modern bulk sediment discharge of the Fitzroy River of 8800 kt yr-1, (Kelly and Wong, 1996) suggesting that the sediment trapping efficiency of the Fitzroy estuary during the Holocene has been approximately 25%. This implies that 75% of the river sediment has been exported from the estuary into Keppel Bay and the adjacent GBR lagoon during the Holocene. With minimal accommodation space left in the floodplain, modern sediment accumulation appears to be focussed around the mangroves and tidal creeks, which cover an area of 130 km2. Cores from the tidal creeks were dated using 137Cs, excess 210Pb, and OSL and display sedimentation rates of approximately 1.5 cm yr-1 for the last 45-120 years, or 1700 kt yr-1, and suggest a modern sediment trapping efficiency for the estuary of around 19%. These results provide useful insights into the long-term sedimentation and quantification of the sediment trapping efficiency of a subtropical macro-tidal estuary with episodic floods, where sediment trapping will vary seasonally and inter-annually.

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nonGeographicDataset

eCat Id

64888

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Keywords

• External PublicationScientific Journal Paper

( Theme )

• stratigraphy

( Theme )

• coasts

( Theme )

• sedimentology

( Theme )

• marine

• AU-QLD

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

Publication Date

2006-08-31T00:00:00

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Australian Government Security ClassificationSystem    

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Creative Commons Attribution 4.0 International Licence    

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geoscientificInformation

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[-24.0, -23.0, 150.5, 151.0]

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