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Limnological Studies of Dystrophic Waters

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Limnological Studies of Dystrophic Waters LIMNOLOGICAL STUDIES OF DYSTROPHIC WATERS by Lee Clifford Bowling, B.Sc. Hons ( ) in the Department of Botany Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy University of Tasmania January, 1988 DECLARATION This thesis contains no material which has been accepted for the award of any other higher degree or graduate diploma in any tertiary institution and that , to the best of the candidate 's knowledge and belief, this thesis contains no material previously published or written by another person, except when due reference is made in the text of the thesis. Lee C. Bowling ABSTRACT A number of aspects of the limnology of dystrophic lentic freshwaters are covered in this thesis . Initially, studies covering a wide range of heterogeneous lakes and reservoirs from several different areas are reported , to give an overall perspective of many of the roles dissolved humic substances play in various limnological processes . More detailed case studies of a number of dystrophic lakes and reservoirs are then outlined , to demonstrate how dissolved humic substances actively influence the limnology of these individual waters . Investigations of the underwater ligh t cl imates of fifty lakes and reservoirs from Tasmania, thirty-seven from north-east New South Wales , and of twenty-six coastal dune lakes in south-east Queensland showed that dissolved humic substances were the maj or attenuators of light in all three areas . Increasing gilvin concentrat ions led to the rapid extinction of light at shallow depths, and to changes in its underwater spectral distribution from green-yellow in the clearest waters, to red in the most humic . Turbidity and phytoplankton were important contributors to attenuation in only a few of the waters studied . Results from Tasmania allowed the construction of a predictive model for use in estimating the underwater light climates of the many remote lakes of the island wh ere in situ measurements are impossible, from simple laboratory measurements of small water samples . The rapid attenuation of light in humic waters also strongly affects thermal stratification, leading to strong thermal gradients , shallow thermoclines , and lengthy periods of stratification. Chemical aspects were also examined. Strong negative correlations were found between the concentration of dissolved humic substances and pH in coastal dune lake waters from south-east Queensland , King and Flinders Islands, and western and south-west Tasmania. In contrast , there was no correlation between these two parameters in north-east New South Wales waters, probably due to lower humic concentrations and buffering by higher bicarbonate levels. Calcium and bicarbonate levels were also sometimes low in acidic , dystrophic lakes . A wide range of photosynthetic organisms were present in the sites investigated from New South Wales , Queensland , and coastal lakes of south-west Tasmania. Phytoplankton came both from the Chlorophyceae and from other algal divisions , and desmids and dinoflagellates were especially common . Proportions of green algae decreased relative to those with accessory photosynthetic pigments, as humic concentration increased, in the highly humic western and south-west Tasmanian lagoons, but this was not apparent in the less dystrophic waters of the other two areas . However , high humic concentrations reduced the number of phytoplankton genera present from all groups. Chrysophytes dominated the phytoplankton communities of polyhumic Lake Chisholm. Studies of Lake Chisholm , the reservoirs of the Pieman River Power Development, and the meronictic lakes of the lower Gordon Riv er , all in Tasmania, showed humic materials played an important role in their limnology. The rapid attenuation of light , and subsequent strong thermal stratification for much of the year lead to sluggish circulation, allowing near-mero�ictic conditions in Lake Chisholm , and the protection and resultant slowing of the demise of ectogenic meromixis in the Gordon River lakes . These features, along with enhancing the sol��9ility of iron and manganese in the reducing , sulphide laden bottom waters of the Pieman River reservoirs , enabled their chemical stratification . However , other factors , such as basin morphometry and shelter , are also of importance in the limnology of these lakes and reservoirs . ACKNOWLEDGEMENTS I wish to thank my supervisor, Dr P A Tyler , for his valuable assistance and encouragement throughout the project . I also thank Dr M A Brock for her encouragement during the final stages of this work, and for her constructive comm ents on the initial drafts of this thesis. I am grateful also for the interest and assistance of the staf f and postgraduate studentsof the Dep artment of Botany , University of Tasmania during the earlier stages of this project . In the same vein , I acknowledge the encouragement and assistance of the staff and postgraduate students of the Department of Botany , University of New England , during the later period of the work , and for allowing me to continue with the project after my move there . I thank the Internal Resear ch Grants Comm ittee , University of New England , for research money which allowed the collection of data from nortfreast New South Wales and south-east Queensland , and the Tasmanian National Parks and Wildlife Service for a research grant and logistical support to enable sampling of remote coastal lagoons in western and south-west Tasmania. The remainder of the work reported in this thesis was carried out using various research grants made to my supervisor . I am particularly indebted to the many people who freely made time available to assist with field work. Of particular note ar e J M Ferris , who also advised on use of the LIMNO computer program, 0 Bourke for her assistance on Fraser Island , and R L Croome , with whom data from the Gordon River has been jointly collected and shared. R. D. King also made his original field note-books available so I could use data from 1977 and 1978 for the computation of stabilities , heat budgets, and other similar parameters. The cheerful help of Mrs Rosemaree Wickham throughout the project is al so acknowledged . Mrs J Hanlan is thanked for her typ ing . I thank R J Ban�ns for assistance with the nutrient analyses of waters from north-east New South Wales , south-east Queensland , and western and south-west Tasmania. Finally , I wish to thank my wife, Regie , and children for their support and forbearance during the course of the proj ect , especially during my many absences from home ; and my parents for their encouragement , and for funding the production costs of this thesis . I therefore dedicate this thesis to my family, without whose help it would never have eventuated . TABLE OF CONTENTS CHAPTER 1: INTRODUCTION TO THE STUDY 1 1.1 Aims and Significance 1 1.2 The Scop e of this Thesis 2 CHAPTER 2: A REVIEW OF LITERATURE RELEVANT TO THIS STUDY 5 Part One : Descrip tion of Study Areas 5 2.1 A Limnological Background to Tasmania 5 2 .1.1 The Western Limnological Prov ince 5 2.1. 2 The Eastern Limnological Prov ince 8 2.1.3 The Coastal Limnological Province 9 2.1.4 Additional Limnological Studies in Tasmania 10 2.2 A Limnological Background to North-east New South Wales 10 2.3 A Limnological Background to Studies on Coastal Lakes 11 2. 3.1 The Nature of Australian Coastal Dune Lakes 11 2.3.2 Studies of Coastal Lakes of the Australian Mainland 13 Part Two : A Theoretical Background to the Studies 18 2.4 The Nature of Humic Substances in Aquatic Systems 18 2.4.1 The Chemistry, Origin , and Distribution of Dissolved Humic Substances 18 2.4.2 Humic Substances and Colour 19 2.4.3 Humic Substances and pH 20 2.4.4 Humic Substances and Metal Ions 20 2.4.5 The Ecological Significance of Humic Substances 21 2.4.6 Limnological Features of Humic Lakes - Examples from Finland 23 2.5 Factors Determining the Underwater Light Climates of Lakes 27 2.5. 1 The Fate of Light in Water 27 2.5.2 Components of the Aquatic Medium Causing Ab sorption and Scattering 27 2.5.3 The Op tical Properties of the Water Column 29 2.5.4 The Attenuation of P.A.R. with Depth 31 2.5.5 Studies of Light At tenuation in Australian and New Zealand Inland Waters 31 2.6 A Background to Chemical Stratification and Meromixis 34 2.6.1 The Nature of Chemical Stratification 34 2.6.2 Meromixis in Impoundments 35 2.6.3 Causes of Biogenic Meromixis in Impoundments 36 CHAPTER 3: STUDIES OF THE u�ERWATER LIGHT CLIMATES OF LENTIC FRESHWATERS FROM TASMANIA, NORTH-EAST NEW SOUTH WALES, AND SOUTH-EAST QUEENSLAND 37 3.1 Introduct ion 37 3.1.1 The Aims and Scope of the Study 37 3.1.2 The Study Sites 38 3.2 Methods 41 3.2.1 Sources of Data 41 3.2.2 Collection and Analysis of Samples , and Computation of the Data 3.3 Results 46 Part A: Tasmania 46 3.3.1 Colour , Turbidity, and Chlorophyll a 46 3.3.2 Attenuation of Total P.A.R. 46 3.3 .3 Reflectance and Scattering Coefficients 49 3.3.4 Spectral Distribution of Underwater P.A.R. 52 3.3.5 Secchi Disc Transparency 61 3. 3.6 Regression Analysis 61 Part B: North-east New South Wales 64 3.3.7 Surface Temperature , pH, and Conductivity 64 3.3.8 Total Nitrogen and Total Phosphorus 64 3.3.9 Turbidity, Colour , and Chlorophyll a 64 3.3.10 The Attenuation of P.A.R. 66 3. 3.11 Reflectance and the Scattering Coefficient 68 3. 3.12 The Spectral Distribution of Underwater P.A.R. 68 3.3.13 Secchi Disc Transparency 74 3.3.14 Regression and Correlation Analyses 74 3.3.15 Phytoplankton 76 Part C: South-east Queensland 79 3.3.16 Temper ature, pH, and Conductivity at 18°C (K18) 79 3.3.17 Total Nitrogen and Total Phosphorus 79 3.3.18 Turbidity, Colour , and Chlorophyll a 81 3.3.19 The Attenuation , Reflectance, and Scattering of P.A.R.
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