The role of submerged macrophytes in seasonally-flowing agricultural streams Robyn L. Paice B.Sc. (Honours), B.Sc. (Environmental Science, Biology) Supervised by Dr Jane M. Chambers and Assoc Prof Belinda J. Robson Environment and Conservation Sciences Murdoch University This thesis is presented for the degree of Doctor of Philosophy 2016 Cover photo Clockwise from top left: Cycnogeton huegelii growing in the Carbunup River, exclosure for macrophyte transplants in the lower Vasse River, a tributary of Mary Brook flowing through farmland, a reach of the Buayanyup River with remnant riparian vegetation (R. Paice). Dedication I dedicate this thesis to two unforgettable men who have inspired me in different ways on the same path. To my father, A. David Paice, and to Dr. Luke J. Pen. Declaration I declare that this thesis is my own account of my research and contains as its main content work which has not previously been submitted for a degree at any tertiary education institution. Robyn L. Paice Date Statement of Contribution of Others Chapters 3, 4 and 5 of this thesis have been published in scientific journals, and the supervisors of Robyn L. Paice are included as co-authors for these papers. As first author, Robyn L. Paice has completed this research and prepared these manuscripts, and co-authors have had intellectual input through conceptual guidance, experimental design, data analysis and review. Robyn L. Paice Date Jane M. Chambers Date Belinda J. Robson Date Permits Lower Vasse River sampling: Licence to take fauna for scientific purposes, licence number SF008312, Department of Environment and Conservation, Western Australia; Murdoch University Ethics Permit No RW247912. Catchment sampling: Licence to take fauna for scientific purposes, licence number SF010065, Department of Environment and Conservation, Western Australia; Fish Resources Management Act 1994 exemption number 2121, Department of Fisheries Western Australia; Murdoch University Ethics Permit No. RW252912. i ii Contents Declaration ................................................................................................................. i Statement of Contribution of Others....................................................................... i Permits ....................................................................................................................... i List of Tables .......................................................................................................... vii List of Figures ........................................................................................................ viii Acknowledgements .................................................................................................. xi Thesis Abstract ......................................................................................................... 1 Chapter 1. General Introduction ............................................................................ 1 Research aim .......................................................................................................................... 3 Theoretical Context ................................................................................................................ 4 Consequences of anthropogenic change for the distribution of submerged macrophytes in seasonally-flowing streams .................................................................. 5 Ecological role of submerged macrophytes in seasonally-flowing streams .................. 8 Potential for restoration outcomes using submerged macrophytes ............................... 9 Thesis structure .................................................................................................................... 11 Chapter 3. Native submerged macrophyte distribution in seasonally-flowing, south- western Australian streams in relation to stream condition......................................... 11 Chapter 4. Potential of aquatic macrophytes to support food webs in lowland agricultural streams. .................................................................................................... 11 Chapter 5. Outcomes of submerged macrophyte restoration in a shallow impounded, eutrophic river. ............................................................................................................ 12 References ............................................................................................................................ 14 Chapter 2. Study Area ........................................................................................... 23 Location ............................................................................................................................... 23 Climate and hydrology ......................................................................................................... 25 Natural environment ............................................................................................................ 28 Land use change and impacts............................................................................................... 29 References ............................................................................................................................ 34 iii Chapter 3. Native submerged macrophyte distribution in seasonally-flowing, south-western Australian streams in relation to stream condition .................... 37 Abstract ................................................................................................................................ 38 Introduction .......................................................................................................................... 39 Methods ................................................................................................................................ 42 Study area .................................................................................................................... 42 Sampling design and field methods ............................................................................. 44 Data analysis ................................................................................................................ 46 Results .................................................................................................................................. 48 Spatial variation in environmental characteristics ....................................................... 48 Native macrophyte assemblages .................................................................................. 48 Invertebrates ................................................................................................................ 54 Discussion ............................................................................................................................ 57 Native macrophyte occurrence .................................................................................... 57 Macrophyte assemblage response to riparian condition .............................................. 59 Macroinvertebrates ...................................................................................................... 61 Management implications ............................................................................................ 63 References ............................................................................................................................ 64 Chapter 4. Potential of submerged macrophytes to support food webs in lowland agricultural streams ................................................................................. 73 Abstract ................................................................................................................................ 74 Introduction .......................................................................................................................... 75 Methods ................................................................................................................................ 77 Study area .................................................................................................................... 77 Study design ................................................................................................................ 80 Sample collection and preparation............................................................................... 81 Stable isotope analysis ................................................................................................. 82 Fish stomach contents .................................................................................................. 83 Data analysis ................................................................................................................ 83 Results .................................................................................................................................. 86 Consumer occurrence .................................................................................................. 86 Fish diet ....................................................................................................................... 86 iv Basal Resources........................................................................................................... 86 Mixing model outputs ................................................................................................. 91 Discussion ...........................................................................................................................