ALGAL EFFECTS ON LITTORELLA UNIFLORA (L.) ASCHERSON IN SCOTTISH LOCHS A thesis submitted to the University of Glasgow for the degree of Doctor of Philosophy. Susar. J. Marrs © Susan J. Marrs ProQuest Number: 13818544 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13818544 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 GLASGOW UNIVERSITY LIBRARY I DECLARATION I hereby declare that this thesis is composed of work carried out by myself unless otherwise acknowledged and cited and that the thesis is of my own composition. The research carried out in the period October 1989 to September 1992. This dissertation in whole or in part has not been previously presented for any other degree. Susan J. Marrs II ACKNOWLEDGEMENTS This project was funded by the Science & Engineering Research Council in the United Kingdom and would have been impossible without the help of a large number of people. I would like to thank Professor R. Cogdell for allowing me to use the facilities of the Department of Botany, Glasgow University and for his continuous interest throughout the project. Thanks are also due to Professor M. Cowling for the use of computer facilities at Glasgow Marine Technology Centre to write the thesis, and for his encouragement and support in this task. The project was supervised by Dr Kevin Murphy to whom I am grateful for the freedom of being permitted follow my own ideas and his active promotion of my work at various scientific meetings throughout the tenure of my studentship. Physiological work was carried out under the supervision of Dr Peter Dominy and his input is appreciated. I would also like to thank Dr Steve Maberly from the Institute of Freshwater Ecology, Windermere, for several useful discussions throughout the course of this PhD. Dr James Currall provided statistical advice. Field work was aided by the owners of the following pairs of willing hands: Vicky Abemethy; Colin Adams; Magdi Ali; Colin Brown; Kevin Duffy; Jamie Graham; Jeremy Hills; Andy Johnson; Jim McGonagle; Rab McMath; Andrew Spink and Wee Mags. Especial thanks are given to Aileen Adams without whom the SCUBA component of the field work could not have been carried out and most certainly not have been so enjoyable. I am grateful to members of the Glasgow University Sub-Aqua Club for lending various items of equipment as my own fell into disrepair throughout the field season, namely: Al, Alan, Phil, Ruth & Sean. I am grateful to Dr Alan Barclay (Loch of Lowes Nature Reserve); Mr Naim (Loch End House, Lake of Menteith) and Dr F. Lees (Solway River Purification Board) for enabling me to gain access to the lochs and their continued interest throughout the project. Dr Tippett generously allowed access to Rowardennan field station on Loch Lomond and use of the following items of field and laboratory equipment are Ill gratefully acknowledged: Ekman grab; LICOR light metre; pHOX dissolved oxygen meter and inverted microscope. Thanks are also due Bob Cuthbertson for help in the design and construction of the circulatory system described in Chapter 5; Jim Muckersie for assembling the algae tanks used in Chapter 6 and Eion Robertson for his assistance with the Scanning Electron Microscope (Chapter 3). Lynda Handley from the Scottish Crop Research Institute, Invergowrie, provided advice and assistant in the measurement of A13C (Chapter 6). Anne Neville produced Figures 5.1 and 6.3. Alan Oakman produced Figure 6.1. Alan Bell photographed Figures 2.7, 3.8 & 3.9. My parents, Anne & David Marrs, have provided support in many ways for which I am appreciative. Thanks also to Jel for reading various drafts and providing innumerable cups of tea, and to Beatrice for helping me get away from it all when needed. Finally, I would like to thank the gentleman who gave Aileen and myself a lift to shore when our outboard broke down one breezy day on Loch Lomond in March 1991. IV Summary In order to investigate algal effects on submerged macrophytes, four lochs experiencing a range of algal loadings were studied over a two year period. Algal loading ranged from virtually no algal growth to extensive formation of filamentous algal mats and phytoplankton blooms During 1990 and 1991 SCUBA techniques were employed to regularly monitor the standing crop of aquatic macrophytes along the lm isobath. In 1990 phytoplankton density was estimated by measuring phytoplankton chlorophyll a. In 1991 measurements of filamentous algal biomass and cover estimates of epiphytes on the leaves of Littorella uniflora (L.) Ascherson were also carried out. Detrended Correspondence Analysis (DCA) of the macrophyte communities in the four lochs showed the lochs were examples of one community type. A total of 15 species were recorded, of these, the following were present in each of the four lochs: Isoetes lacustris L.: Myriophyllum alterniflorum DC: Lobelia dortmanna L.: Littorella uniflora. Conditions in the four lochs ranged from acidic Loch Dee, to the oligotrophic mid-basin of Loch Lomond, through to mesotrophic/eutrophic Lake of Menteith and eutrophic Loch of Lowes. Morphological and some physiological attributes of Littorella field populations, measured over the two year period, were related to algal loading and measured \ abiotic parameters using stepwise linear multiple regression. Variation in morphology of Littorella, explained by the selected variables was generally low: this was attributed to a lack of morphological plasticity in this species. In contrast, physiological attributes, such as chlorophyll content and shoot nitrogen, had a far higher percentage variation that could be explained by the selected variables. The abiotic variables most commonly selected, to explain variations in Littorella attributes, were sediment organic content and exposure rating. Sites that were more exposed to wind/wave action tended to have fewer, smaller Littorella plants. Sites with a high sediment organic content tended to have a greater total macrophyte and Littorella biomass. V Filamentous algal biomass was the most important variable that explained the variation in Littorella field measurements. Littorella plants under filamentous algal mats had a higher total leaf chlorophyll and nitrogen content and a lower chlorophyll a:b , indicating a possible shade response. In the presence of filamentous algal mats, Littorella also tended to have fewer leaves and a greater number of stolons per plant. In the absence of filamentous algal biomass data, phytoplankton chlorophyll a was more commonly selected to explain variation in Littorella field measurements. It is suggested that in situations where filamentous algae are present, but not quantified, the effects of phytoplankton on aquatic macrophytes may be overestimated. Epiphyte percentage cover was not selected to explain any of the variation in measured field attributes of Littorella. In a greenhouse experiment, Littorella showed a quadratic response to sediment organic content with maximal biomass accrual occurring at a sediment organic matter concentration of 75%. After six weeks under shade conditions in the greenhouse, Littorella plants were significantly smaller than unshaded controls. After the removal of shading Littorella plants grew rapidly, until 17 weeks after the removal of shading there was no significant difference in the biomass of previously shaded plants when compared with unshaded controls. In comparison with unshaded controls, \ plants that had been previously subjected to shading, tended to produce fewer shorter leaves and a greater number of new plants. Significant increases in the total chlorophyll concentration of leaves were observed 9 days after the application of shading. A decrease in chlorophyll a:b was only observed in experiments where shading was applied for between 3 and 6 weeks. Photosynthetic light response curves, measured using a gas phase oxygen electrode were determined in further greenhouse experiments. These data showed shade adapted Littorella to have a lower maximum photosynthetic rate and higher photosynthetic efficiency at low irradiances, when compared with VI unshaded controls. There were no differences between the dark respiration rates of shaded and unshaded Littorella. Shaded Littorella plants showed a higher A13C in comparison with unshaded controls, indicating a reduction in CAM at low irradiance. A model of population maintenance of Littorella in Scottish lochs is proposed. It is suggested that Littorella can withstand periods of algal shading by adapting physiologically with little or no loss in biomass, and the population is maintained by winter and spring growth. Loss of a population could occur under one of two sets of conditions: 1: Due to the seasonal presence of filamentous algal mats, the population becomes weakened by successive shading experiences and gradually declines. 2: The population may be able to be maintained under conditions of algal loading; however in the event of a catastrophic destruction of part or all of the population, recolonisation is not possible. Tabic of Contents Declaration I Acknowledgements II Summary IV Table of Contents VII Chapter la The Impact of Acidification and Eutrophication on Aquatic Macrophytes in Freshwater Lentic Systems 1 Section 1 Introduction 1 Section 2 Physical Properties of Water and Effects on Macrophyte Distribution 1 Section 3 Photosynthesis in the Aquatic Environment 3 3.1 Light in Lakes 3 3.2 Carbon Dioxide 5 3.3 Oxygen 6 Section 4 Anthropogenic Effects 4.1 Eutrophication 8 4.2 Acidification 11 Section 5 Macrophyte Species Studied 13 Chapter lb The Ecology and Physiology of Littorella urtiflora (L.) Ascherson 14 Chapter lc Aims & Approaches 19 Chapter 2.