University of Wollongong Research Online Faculty of Science, Medicine & Health - Honours Theses University of Wollongong Thesis Collections 2017 Mangrove Establishment and its Effect on the Natural Processes of Southern Lake Illawarra Robert Dixon Follow this and additional works at: https://ro.uow.edu.au/thsci University of Wollongong 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 authorise 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: This work is copyright. Apart from any use permitted under the Copyright Act 1968, no part of this work may be reproduced by any process, nor may any other exclusive right be exercised, without the permission of the author. Copyright owners are entitled to take legal action against persons who infringe their copyright. 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For further information contact the UOW Library: [email protected] Mangrove Establishment and its Effect on the Natural Processes of Southern Lake Illawarra Abstract Mangrove and saltmarsh contribute extensively to health of estuarine systems. Their extent and distribution is dependent on hydrological regime, in particular, tidal inundation. The hydrological regime of Intermittently Closed and Opened Lakes and Lagoons (ICOLLs) usually limit mangrove growth, primarily during entrance closure when anoxic shock occurs from the prolonged inundation of pneumatophores. Saltmarsh however, can be extensive in these systems. Entrance training alters the hydrological regime of ICOLLs by preventing closure, which ensures a constant, and increasing tidal exchange promoting mangrove expansion. This has occurred at Lake Illawarra, particularly on the southern shoreline following recent (2007) entrance training. Increasing mangrove coverage could lead to declines in saltmarsh which is classified as an endangered ecological community following significant losses elsewhere in southeast Australia. This study aimed to investigate mangrove dynamics in Lake Illawarra, focusing on the response to entrance training. Mangrove response was defined on the basis of the ecological niche that it occupies, which was quantified using spatial and field based techniques. The term accommodation space was used to conceptualise mangroves niche and was defined as portion of the intertidal zone where the majority of post-entrance training recruitment occurred. Saltmarsh accommodation space was assigned above mangrove to the tidal limit. The current accommodation space, as well as its future extent under increased sea-levels and tidal amplitude at 2050 was also quantified. The majority of mangrove increase between 1977 and 2016 occurred post-entrance training. Growth was concentrated in entrance back channel (Zone 1). The intertidal zone between Mean High Water (MHW) level and slightly below Mean Sea Level (MSL) supported the greatest proportion mangrove establishment and was defined as the accommodation space. If mangrove could occupy all of the current accommodation space, considerable areas of saltmarsh could be lost. The areas at 2050 suitable for mangrove and saltmarsh were found to be dependent on local topography, with retreat possible in some areas and exclusion in others. This research suggests that entrance training allows for mangrove expansion which has the potential to impact on saltmarsh. As increased mangrove coverage may have a range of ecological benefits, it is recommended that management strategies be applied that focus on saltmarsh preservation rather than removing mangrove. Strategies could include, allowing for managed retreat under sea-level rise and controlling for other factors which favour mangrove expansion in saltmarsh areas. Degree Type Thesis Degree Name BEnviSc Hons Department School of Earth & Environmental Science Advisor(s) Kerrylee Rogers Keywords Mangroves, Saltmarsh This thesis is available at Research Online: https://ro.uow.edu.au/thsci/150 1 Environmental Science Program School of Earth and Environmental Sciences Faculty of Science, Medicine and Health The University of Wollongong Mangrove Establishment and its Effect on the Natural Processes of Southern Lake Illawarra Robert Dixon A thesis submitted in part fulfilment of the requirements of the Bachelor of Environmental Science in the School of Earth and Environmental Sciences, Faculty of Science, Medicine and Health, University of Wollongong 2017. November 2017 2 The information in this thesis is entirely the result of investigations conducted by the author, unless otherwise acknowledged, and has not been submitted in part, or otherwise, for any other degree or qualification. Robert Dixon 5th November 2017 3 Acknowledgements I would like to express my sincere gratitude to my two supervisors, Kerrylee Rogers and Ben Gooden for their ongoing support, encouragement and feedback throughout the duration of the project. This gratitude extends to Tuesday Heather from Shellharbour City Council for sponsoring the project and providing resources, direction and advice. I would also like to thank, Heidi Brown, Rafaela, Danny Weicek, Alex Pescud, Kristian Kmbre, my family, house mates, friends and everyone else who helped or supported me throughout the year 4 Abstract Mangrove and saltmarsh contribute extensively to health of estuarine systems. Their extent and distribution is dependent on hydrological regime, in particular, tidal inundation. The lack of tidal inundation of Intermittently Closed and Opened Lakes and Lagoons (ICOLLs) usually limits mangrove growth, primarily during entrance closure when prolonged inundation of pneumatophores occurs. Saltmarsh however, can be extensive in these systems. Entrance training alters the inundation regime of ICOLLs by preventing closure, which ensures a constant, and increasing tidal exchange promoting mangrove expansion. This has occurred at Lake Illawarra, particularly on the southern shoreline following entrance training in 2007. Favourable conditions for mangrove growth could lead to exclusion and declines in saltmarsh which is classified as an endangered ecological community following significant losses elsewhere in southeast Australia. This study aimed to investigate mangrove dynamics in Lake Illawarra, focusing on the response to entrance training. Mangrove response was defined on the basis of the ecological niche that it occupies, which was quantified using spatial and field based techniques. The term accommodation space was used to conceptualise this niche and was defined as the portion of the intertidal zone where most of post-entrance training recruitment occurred. Saltmarsh accommodation space was assigned above mangrove to the tidal limit. The current accommodation space as well as its future extent 2050 with increased sea-levels and tidal amplitude was projected using spatial analysis. The majority of mangrove increase between 1977 and 2016 occurred post-entrance training. Growth was concentrated in the entrance back channel (Zone 1). The intertidal zone between Mean High Water (MHW) level and slightly below Mean Sea Level (MSL) supported the greatest proportion mangrove establishment and was defined as the accommodation space. On the basis of mangrove occupying all of the current accommodation space, considerable areas of saltmarsh were projected to be lost. The areas at 2050 suitable for mangrove and saltmarsh were found to be dependent on local topography, with retreat possible in some areas and exclusion in others. This research suggests that entrance training allows for mangrove expansion which has the potential to encroach upon saltmarsh. As increased mangrove coverage may have a range of ecological benefits, it is recommended that management strategies be applied that focus on saltmarsh preservation rather than removing mangrove. Strategies could include, allowing for managed retreat under sea-level rise and controlling for other factors which favour mangrove expansion in saltmarsh areas. 5 Table of contents 1 Introduction ........................................................................................................................ 16 1.1 Background ............................................................................................................................. 16 1.2 Aims and Objectives ............................................................................................................. 18 2 Literature Review ............................................................................................................. 19 2.1 Mangroves composition and distribution