Fitzroy River Basin, Queensland, Australia. IV. Identification of flood sediment sources in the Fitzroy River
G. B. Douglas A F , P. W. Ford B , M. R. Palmer C , R. M. Noble D , R. J. Packett D and E. S. Krull EA CSIRO Land and Water, Centre for Environment and Life Sciences, Private Bag No. 5, Wembley, WA 6913, Australia.
B CSIRO Land and Water, Black Mountain Laboratories, GPO Box 1666, Canberra, ACT 2601, Australia.
C CSIRO Mathematical and Information Sciences, Centre for Environment and Life Sciences, Private Bag No. 5, Wembley, WA 6913, Australia.
D Queensland Department of Natural Resources and Water, Rockhampton, PO Box 1762, Rockhampton, Qld 4700, Australia.
E CSIRO Land and Water, PMB 2, Glen Osmond, SA 5064, Australia.
F Corresponding author. Email: grant.douglas@csiro.au
Environmental Chemistry 5(3) 243-257 https://doi.org/10.1071/EN07091
Submitted: 4 December 2007 Accepted: 9 May 2008 Published: 19 June 2008
Environmental context. During flood events, the Fitzroy River is a major contributor to the loads of suspended sediment and nutrients to the southern Great Barrier Reef. The present geochemical and modelling study provides for the first time a quantitative estimate of the temporal variation in sediment sources over an entire flood hydrograph. Basaltic soils are substantially enriched in this flood event relative to their catchment abundance.
Abstract. Suspended sediment collected over a complete flood hydrograph in the Fitzroy River provided an insight into the origin and transport of sediment in this system. Strong temporal trends are evident in the proportions of catchment soil types estimated using a Bayesian mixing model in the fine (<10 μm) fraction of the suspended sediment. These temporal trends were also manifested in changes in mineralogy, major and trace element and Nd–Sr and C–N isotope geochemistry. Tertiary Basaltic soils were the most abundant catchment soil type transported in the flood event studied here, constituting 39% of the <10-μm sediment fraction, but varied between an estimated 20 and 50% of the suspended solids over the course of the flood event. The techniques used here allow quantification and comparison between flow and suspended sediment sources and are widely applicable to other river systems.
Additional keywords: Bayesian model, geochemistry, suspended sediment.
Acknowledgements
We acknowledge helpful discussions and the provision of data by hydrologists from the Queensland Department of Natural Resources and Water – Rockhampton Branch, the FMBC for sampling access, and our colleagues in the Cooperative Research Centre for Coastal Zone, Estuary and Waterway Management (CRC CZEWM). The CRC CZEWM provided partial financial support for the present work. Two independent reviewers of the manuscript are acknowledged for their insight and assistance.
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