Edith Cowan University Research Online Theses: Doctorates and Masters Theses 2013 Inorganic hydrogeochemical responses to fires in wetland sediments on the Swan Coastal Plain, Western Australia David Blake Edith Cowan University Follow this and additional works at: https://ro.ecu.edu.au/theses Part of the Environmental Health and Protection Commons, Natural Resources and Conservation Commons, and the Water Resource Management Commons Recommended Citation Blake, D. (2013). Inorganic hydrogeochemical responses to fires in wetland sediments on the Swan Coastal Plain, Western Australia. https://ro.ecu.edu.au/theses/689 This Thesis is posted at Research Online. https://ro.ecu.edu.au/theses/689 Edith Cowan University Research Online Theses: Doctorates and Masters Theses 2013 Inorganic hydrogeochemical responses to fires in wetland sediments on the Swan Coastal Plain, Western Australia David Blake Edith Cowan University Recommended Citation Blake, D. (2013). Inorganic hydrogeochemical responses to fires in wetland sediments on the Swan Coastal Plain, Western Australia. Retrieved from http://ro.ecu.edu.au/theses/689 This Thesis is posted at Research Online. http://ro.ecu.edu.au/theses/689 Edith Cowan University Copyright Warning You may print or download ONE copy of this document for the purpose of your own research or study. The University does not authorize you to copy, communicate or otherwise make available electronically to any other person any copyright material contained on this site. You are reminded of the following: Copyright owners are entitled to take legal action against persons who infringe their copyright. A reproduction of material that is protected by copyright may be a copyright infringement. 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INORGANIC HYDROGEOCHEMICAL RESPONSES TO FIRES IN WETLAND SEDIMENTS ON THE SWAN COASTAL PLAIN, WESTERN AUSTRALIA David Blake Bachelor of Science (Environmental Management) HONS This thesis is presented in fulfilment of the requirements for the Degree of Doctor of Philosophy Faculty of Computing Health and Science Edith Cowan University June 2013 USE OF THESIS The Use of Thesis statement is not included in this version of the thesis. ABSTRACT In the past decade the wetlands of the Swan Coastal Plain (SCP) region of Western Australia have been subject to increasing fire frequency and intensity. Whilst wetland sediment fires (also known as peat fires) on the SCP are not new phenomena, the increased frequency, duration and extent of combustion have been concomitant with an increase in urbanisation and reduction in average annual rainfall for the region. This has led to a decrease in ground- and surface-water levels which, in turn, has increased the susceptibility of the wetland sediments to ignition and combustion events. Increased wetland fire severity has resulted in the loss of large pools of organic matter as well as numerous geochemical changes in wetland sediments. The physical and chemical modifications of wetland sediments have implications for the water quality of these wetlands, particularly on the SCP where an intimate link between water quality and the underlying geomorphology can be demonstrated. Previous wetland sediment disturbance events, such as drought and dewatering, have led to the oxidation of sediments, which has resulted in the acidification, base cation leaching and metal contamination of both ground- and surface-waters. The buffering capacity is strongly linked to the underlying geomorphology. Wetlands on the highly-leached, poorly-buffered Bassendean dune geomorphic unit tend to acidify readily, whereas wetlands on the well-buffered, Spearwood dune geomorphic unit, generally tend to be less acidic and have the capacity to recover (i.e. return to near- neutral conditions). In recent times, some of the wetlands on the Spearwood dune system have remained acidic. This suggests that the buffering capacity of this system is finite and may be linked to the severity of the oxidation event. The physical, temporal and chemical nature of water quality response from dried, heated and combusted wetland sediments are not well understood nor are the processes that drive them. The aim of this research, therefore, was to identify and characterise the inorganic water quality responses to the combustion of organic-rich wetland sediments. The study examined post-fire sediment pore-water and downstream ground-water quality, and the short and long term temporal characteristics of these responses. A laboratory microcosm experiment was conducted to investigate the role of temperature and sediment heterogeneity on observed water quality responses. ii The porewater of burnt sediments differed greatly from that of unburnt sediments and was indicative of pyrite oxidation. There were also temporal changes associated with seasonal rainfall events and groundwater fluxes. Results of the long-term temporal analysis indicated the exhaustion of the in-situ buffering capacity of the wetland sediments, which resulted in the permanent acidification of the groundwater downstream of the burnt sediments. These patterns were partly obscured by transient buffering supplied by the ash created from the combustion of vegetative organic material and the influx of carbonate-rich groundwater. Laboratory microcosm analyses confirmed the inorganic hydrochemical signals, and the significance of sediment type; including parent geomorphology, in influencing the water quality response. The increased frequency, duration and extent of drying, heating and combustion of wetland sediments suggest an erosion of buffering, and thereby a loss of resilience for these wetlands, threatening their ecological integrity. This research enhances our understanding of the environmental impacts of wetland sediment fires and increases the potential for pre-emptive, rather than reactive management services. iii DECLARATION I certify that this thesis does not, to the best of my knowledge and belief: i.) incorporate without my knowledge any material previously submitted for a degree or diploma in any institution of higher education; ii.) contain any material previously published or written by another person except where due reference is made in the text; or iii.) contain any defamatory material. I also grant permission for the Library at Edith Cowan University to make duplicate copies of my thesis as required. Signature: Date: 13/11/2013 iv ACKNOWLEDGEMENTS I am forever grateful to my principal supervisor, Professor Pierre Horwitz. Your guidance, compassion and mentoring have been influential in my development as a scientist and shaping my views on the environment. Thank you also for your continued enthusiasm, even after reading countless drafts of individual chapters. I would also like to thank my associate supervisors, Professor Will Stock, whose guidance and knowledge on statistics and fire ecology were immeasurable. To Dr Mary Boyce, a big thanks for all your help with all things chemistry and for tolerating my ignorance during our chats about the environmental geochemistry. Finally, thank you to Dr Ian Lau, your knowledge and guidance on remote sensing and interpretation of spectral data was immensely beneficial, as was your assistance with x-ray diffraction. I would like to acknowledge the generous financial and technical contribution of the Department of Fire and Emergency Services (DFES). In particular, I would like to acknowledge Ralph Smith who made this research possible. The significant funding allowed this project to have such a broad scope, and by extension, provide solutions to the management problems your agency has been dealing with. I would also like to acknowledge DFES staff, particularly those stationed at the Perth – North Coastal Office who were always willing to accommodate requests for access to sites, personnel and information. A number of people assisted with data collection and field trips throughout the life of this research. In particular, I would like to thank Brad Reynolds, Jareth Howard, Lisa Edwards, Niall Somesan, Kylie Mckay and my father George Blake. Your enthusiasm, humour, commitment and professionalism made this period of the research bearable and in some instances, almost enjoyable. I would also like to thank Coral Newman for your editorial skills in reviewing each chapter. It would not have been possible for me to undertake this research were it not for the generous funding from the Centre for Ecosystem Management (CEM), Edith Cowan University Postgraduate Research Scholarship (ECUPRS), and top-up funding from the Department of Fire and Emergency Services. v To my beautiful wife Tracy, and my three wonderful sons Matthew, Nathan and Callum, thank you for allowing me this opportunity, and for putting up with me, particularly when I was sooooo grumpy! vi Table of Contents USE OF THESIS i ABSTRACT ii DECLARATION iv ACKNOWLEDGEMENTS v CHAPTER 1: INTRODUCTION 1 1.1. Burning wetlands: a paradox? .........................................................................