An Assessment of Recent Changes in Catchment Sediment Sources and Sinks, Central Queensland
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An assessment of recent changes in catchment sediment sources and sinks, central Queensland, Australia Andrew Owen Hughes 2008 A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy School of Physical, Environmental and Mathematical Sciences (Geography) Australian Defence Force Academy University of New South Wales i ii ABSTRACT Spatial and temporal information on catchment sediment sources and sinks can provide an improved understanding of catchment response to human-induced disturbances. This is essential for the implementation of well-targeted catchment-management decisions. This thesis investigates the nature and timing of catchment response to human activities by examining changes in sediment sources and sinks in a dry-tropical subcatchment of the Great Barrier Reef (GBR) catchment area, in northeastern Australia. Changes in catchment sediment sources, both in terms of spatial provenance and erosion type, are determined using sediment tracing techniques. Results indicate that changes in sediment source contributions over the last 250 years can be linked directly to changes in catchment land use. Sheetwash and rill erosion from cultivated land (40–60%) and channel erosion from grazed areas (30-80%) currently contribute most sediment to the river system. Channel erosion, on a basin-wide scale, appears to be more important than previously considered in this region of Australia. Optically stimulated luminescence and 137Cs dating are used to determine pre-and post- European settlement (ca. 1850) alluvial sedimentation rates. The limitations of using 137Cs as a floodplain sediment dating tool in a low fallout environment, dominated by sediment derived from channel and cultivation sources, are identified. Low magnitude increases in post-disturbance floodplain sedimentation rates (3 to 4 times) are attributed to the naturally high sediment loads in the dry-tropics. These low increases suggest that previous predictions which reflect order of magnitude increases in post-disturbance sediment yields are likely to be overestimates. In-channel bench deposits, formed since European settlement, are common features that appear to be important stores of recently eroded material. i The spatially distributed erosion/sediment yield model SedNet is applied, both with generic input parameters and locally-derived data. Outputs are evaluated against available empirically-derived data. The results suggest that previous model estimates using generic input parameters overestimate post-disturbance and underestimate pre- disturbance sediment yields, exaggerating the impact of European catchment disturbance. This is likely to have important implications for both local-scale and catchment-wide management scenarios in the GBR region. Suggestions for future study and the collection of important empirical data to enable more accurate model performance are made. ii DECLARATION OF ORIGINALITY I hereby declare that this is my own work and to the best of my knowledge it contains no material previously published or written by another person, nor material which to a substantial extent has been accepted for the award of any other degree or diploma at UNSW or any other educational institutions, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual property of this thesis is the product of my own work, except to the extent that assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged. Signed Date 14 December 2008 iii ACKNOWLEDGEMENTS This research was completed with the financial support from the Australian Research Council (grant number: DP0449886), CSIRO Water for Healthy Countries Flagship, the Marine and Tropical Sciences Research Facility, and the Australian Rivers Institute. I would like to thank my supervisors Associate Professor Jacky Croke (UNSW@ADFA) and Professor Jon Olley (Griffith University) for their support. Jacky, thank you for allowing me to pursue my interests and for providing advice and feedback above and beyond the call of duty. Jon, thanks for your valuable input, particularly with the Monte Carlo mixing model and the 137Cs advection-diffusion modelling. Thanks also to Dr Ingrid Takken (UNSW@ADFA) for stepping into the breach and securing further funding at a crucial time. Lucy McKergow (NIWA) provided assistance with field and laboratory work and provided many constructive comments on aspects of this thesis. Tim Pietsch (CSIRO Land and Water) provided field work assistance, access to the CSIRO Land and Water OSL laboratory and help with single-grain OSL data interpretation. Ian Webster (CSIRO Land and Water) provided advice that ensured the 137Cs advection-diffusion modelling functioned correctly. Heiko Timmers (UNSW@ADFA) and Chris Leslie (CSIRO Land and Water) provided technical advice on gamma spectrometry. Ken McMillan (CSIRO Land and Water) prepared sediment samples for OSL analysis. Many thanks to Chris Thompson (UNSW@ADFA) whose unsurpassed field skills were critical to the completion of this research. Thanks also Eugene Wallensky (ANU) and David Purvis-Smith (formerly of UNSW@ADFA) for field work assistance. Maurice Conway (Queensland Department Primary Industries) generously provided the use of a vehicle-mounted soil coring rig. Cameron Dougall, George Bourne, Chris Carroll, and Bob Packett (all of the Queensland Department of Natural Resources and Water) provided spatial and hydrological data for Theresa Creek and comments on drafts. Thanks to the PEMS staff at UNSW@ADFA, especially Brian Lees, Peter Palmer, Ali Arezi and Ray Lawton. iv Thanks to Kathryn Amos (University of Adelaide), Rebecca Bartley (CSIRO Land and Water), Gary Caitcheon (CSIRO Land and Water), Peter Hairsine (CSIRO Land and Water), Gary Hancock (CSIRO Land and Water), Graham McBride (NIWA), Ian Prosser (CSIRO Water for Healthy Countries), and Peter Wallbrink (EWater) for constructive discussions and technical assistance. Thanks to the landowners within Theresa Creek. Special thanks to Robin Cross, David and Rose Staal, Jim Purvis, and Greg Purvis for property access and sharing their local knowledge. Thanks to my family and friends for love and support and for keeping me sane during the rollercoaster known as a PhD. Special thanks to Tanya, Geoff, Karen, Ian, Janelle and Hamish for housing me while in Canberra. Thanks to my son Cadel for his infectious smile and distracting me from my PhD worries. Finally, thanks to Lucy for your love, support, patience and strength, this thesis is dedicated to you v . vi “Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality.” Nikola Tesla (1856 – 1943) vii TABLE OF CONTENTS CHAPTER 1- Introduction...........................................................................................1 1.1. Introduction....................................................................................................2 1.2. Catchment sediment sources ........................................................................4 1.3. Catchment sediment sinks.............................................................................5 1.4. Human-induced catchment disturbance in Australia ......................................8 1.5. Research aims ............................................................................................12 1.6. Thesis structure...........................................................................................12 CHAPTER 2 - Sediment source changes over the last 250 years in a dry-tropical catchment, central Queensland, Australia..............................................................15 2.1. Introduction..................................................................................................16 2.2. Study site ....................................................................................................19 2.3. Methods ......................................................................................................23 2.3.1. Sediment sources................................................................................23 2.3.2. Temporal changes in sediment sources...............................................30 2.4. Results ........................................................................................................33 2.4.1. Geochemical differentiation of geological source areas .......................33 2.4.2. Fallout radionuclide differentiation of sediment sources .......................34 2.4.3. Sources of fine river bed sediment.......................................................37 2.4.4. Floodplain sediment ages and accretion rates .....................................41 2.4.5. The spatial provenance of floodplain deposits over the last 250 years.42 2.5. Discussion...................................................................................................44 2.6. Conclusions.................................................................................................50 CHAPTER 3 - Determining floodplain sedimentation rates using 137Cs in a low fallout environment dominated by channel- and cultivation-derived sediment inputs, central Queensland, Australia .....................................................................53 3.1. Introduction..................................................................................................54