General Introduction
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Modern and Recent Seafloor Environments (Sedimentary, Foraminiferal and Ostracode) of the Pitt Water Estuary, South-east Tasmania VOLUME 1 Dale Lewis A thesis submitted in total fulfilment of the requirements of the degree of Doctor of Philosophy May, 2006 School of Earth Sciences University of Tasmania Hobart DECLARATION This thesis contains no material which has been accepted for a degree or diploma by the university or any other institution, and to the best of the author’s knowledge and belief no material previously published or written by another person except where due reference is made in the text. ………………….. Dale Lewis May 2006 AUTHORITY OF ACCESS This thesis may be made available for loan and limited copying in accordance with the Copyright Act of 1968. ………………….. Dale Lewis May 2006 ii ABSTRACT The Pitt Water Estuary is a shallow, barrier estuary, with typically normal marine salinity, which has been subject to considerable anthropogenic modification. Modern seafloor environments were described using the distribution of sedimentary facies and foraminiferal and ostracod assemblages, examined from surficial sediment samples. Ten sedimentary facies were identified by grouping sediment samples using particle-size distribution data and lithic sand content. Faunal assemblages were identified by cluster analysis, with twelve sample, and eight species associations defined by foraminifera, and eight sample, and six species associations defined by Ostracoda. The distribution of sedimentary facies varies, firstly, with the upstream change in relative current energy (tidal versus fluvial) as reflected by the relative proportion of quartzose to lithic sand in sediment; and, secondly, with the water depth variation in current strength, as reflected by the sand grain size and mud content. The distribution and composition of foraminiferal and ostracod assemblages is determined mainly by average salinity and pH. The position of species along the axis of the estuary correlates with the altered salinity profile inferred to occur during floods, with tolerance to lowered salinity being greater further upstream. Low pH conditions are widely distributed (due to the anoxia of stagnant, nutrient-enriched waters), causing calcareous test dissolution which, in some areas, totally excludes calcareous foraminifera and ostracods. Illumination is also important in controlling ostracod distribution, being lowest in widespread turbid waters. Additional factors controlling foraminiferal and ostracod distribution include: substrate mobility, nutrients, seagrass distribution, tidal exposure, and tolerance to varying temperature. Recent seafloor environments were described using the distribution of sediments, foraminifera and ostracods in short cores and previous spatial surveys. They have changed considerably since the late 19th century, mainly as a result of human activities which continue to affect the estuary. During periods of increased agricultural activity (1920’s-1940s; 1960’s-present), greater land clearance, cultivation and fertiliser usage within the catchment area lead to increased sediment and nutrient loading of fluvial waters entering the estuary. This lead to increased sedimentation, mud accumulation, turbidity, and lowered dissolved oxygen and pH within the estuary, causing the demise of dense clam and oyster beds, reduced distribution of ostracods and calcareous foraminifera, increased distribution of agglutinated foraminifera, and increased faunal abundance within nutrient-enriched sediments. Dam construction and irrigation activities during the 20th century, reduced rainfall over the last thirty years, and iii causeway construction during the 1870’s, have all contributed to increased water stagnation, reduced flushing, and more upstream penetration of the estuary by marine waters. ACKNOWLEDGEMENTS There are a number of people I would like to thank for making this project possible. I would firstly like to thank my research supervisor, Associate Professor Pat Quilty, for his valuable guidance, advice, encouragment, and support since the project began. I would also like to thank my associate supervisors, Dr Ron Berry (2002-2005), and Dr Peter Haines (2000-2002) for their assistance, and Associate Professor Clive Burrett for getting me started in what was initially a Masters project. I would like to thank the Zoology Department (UTAS) and the Tasmanian Institute of Aquaculture and Fisheries (TAFI) for each providing a boat and field equipment during the fieldwork stage of the project. I would especially like to thank Iona Mitchell (TAFI, DPIWE) for her help in the field, as well as for valuable advice since then, and for providing the short cores, 210Pb dating, and other data. I also gratefully acknowledge the support of the Australian Institute of Nuclear Science and Engineering (AINSE) for the 210Pb dating. I would also like to thank Chris Lane (IASOS) for providing me with the Midway Bay core samples, and for allowing me to use some of his data. I am very grateful to Geoscience Australia, particularly Peter Harris, for the particle-size analysis of sediments, and to Andrew Heap (Geoscience Australia) for providing the Entropy software and instruction on its use. Many thanks to David Steele (Central Science Laboratory, UTAS) for his assistance in doing the SEM work. I would especially like to thank my friends and family for their support over the years this project took to complete. Most of all I would like to thank my fiancé Susie. This project was supported by a University of Tasmania scholarship in 2005. iv TABLE OF CONTENTS – VOLUME 1 DECLARATION ................................................................................................................II AUTHORITY OF ACCESS ..............................................................................................II ABSTRACT....................................................................................................................... III ACKNOWLEDGEMENTS ............................................................................................. IV TABLE OF CONTENTS – VOLUME 1 ..........................................................................V LIST OF FIGURES – VOLUME 1................................................................................. IX LIST OF TABLES – VOLUME 1................................................................................... XI CHAPTER 1. GENERAL INTRODUCTION ..................................................................1 1.1. WHAT ARE ESTUARIES? ........................................................................................................................... 1 1.2. OUR IMPACT UPON ESTUARIES ................................................................................................................. 1 1.3. ESTUARINE SEDIMENTATION AND BENTHIC FAUNA.................................................................................. 2 1.4. WHAT ARE FORAMINIFERA?..................................................................................................................... 2 1.5. WHAT ARE OSTRACODS?.......................................................................................................................... 3 1.6. AIMS OF THE PROJECT.............................................................................................................................. 3 1.7. PREVIOUS WORK ...................................................................................................................................... 4 1.7.1. On the study site............................................................................................................................... 4 1.7.2. Previous studies of estuarine sedimentation in Australia ................................................................ 5 1.7.3. Previous Australian studies of foraminifera .................................................................................... 7 1.7.4. Previous Australian studies of Ostracoda........................................................................................ 7 1.8. STRUCTURE OF THESIS ............................................................................................................................. 8 CHAPTER 2. THE PITT WATER CATCHMENT.........................................................9 2.1. INTRODUCTION ........................................................................................................................................ 9 2.2. CLIMATE................................................................................................................................................ 10 2.2.1. Temperature................................................................................................................................... 10 2.2.2. Rainfall and Winds......................................................................................................................... 10 2.2.3. Evaporation ................................................................................................................................... 11 2.3. GEOMORPHOLOGY ................................................................................................................................. 11 2.4. GEOLOGY/SOILS .................................................................................................................................... 12 2.5. CATCHMENT SUB-DIVISIONS AND DRAINAGE ........................................................................................