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The Relative Importance of Eutrophication and Connectivity in Structuring Biological Communities of the Upper Lough Erne System, Northern Ireland

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The Relative Importance of Eutrophication and Connectivity in Structuring Biological Communities of the Upper Lough Erne System, Northern Ireland THE RELATIVE IMPORTANCE OF EUTROPHICATION AND CONNECTIVITY IN STRUCTURING BIOLOGICAL COMMUNITIES OF THE UPPER LOUGH ERNE SYSTEM, NORTHERN IRELAND Thesis submitted for the degree of Doctor of Philosophy University College London by JORGE SALGADO Department of Geography University College London and Department of Zoology Natural History Museum December 2011 1 2 Abstract This study investigates the relative importance of eutrophication and connectivity (dispersal) in structuring macrophyte and invertebrate lake assemblages across spatial and temporal scales in the Upper Lough Erne (ULE) system, Northern Ireland. Riverine systems and their associated flood-plains and lakes comprise dynamic diverse landscapes in which water flow plays a key role in affecting connectivity. However, as for many other freshwater systems, their ecological integrity is threatened by eutrophication and hydrological alteration. Eutrophication results in a shift from primarily benthic to primarily pelagic primary production and reductions in species diversity, while flow regulation often reduces water level fluctuation and hydrological connectivity in linked riverine systems. Low water levels promote isolation between areas and increases the importance of local driving forces (e.g. eutrophication). Conversely, enhanced water flow and flooding events promote connectivity in systems thus potentially increasing local diversity and homogenising habitats through the exchange of species. Therefore, connectivity may help to override the local effects of eutrophication. Attempts at testing the above ideas are rare and typically involve the examination of current community patterns using space for time substitution. However, biological community responses to eutrophication and changes in hydrological connectivity may involve lags, historical contingency, and may be manifested over intergenerational timescales (10s -100s of years), rendering modern studies less than satisfactory for building an understanding of processes that drive community structure and effect change. By combining contemporary and palaeolimnological data this study demonstrates that the ULE system is far from its pre-disturbance state as an oligotrophic-mesotrophic system. Furthermore, contemporary and palaeo-data suggest there has been a strong interaction between eutrophication and hydrological change, which influences the distributions and abundances of representative taxa in the ULE system. Thus, while eutrophication has promoted a decrease in compositional heterogeneity of organisms and has exerted a homogenising effect over time, connectivity has buffered the effects of eutrophication helping to maintain local diversity via re-introductions. 3 Acknowledgements I would like to thank my supervisors who have brought different qualities to the task of supervision. These included, Beth Okamura, Carl Sayer, Steve Brooks and Thomas Davidson. Thanks to Rick Battarbee and Helen Bennion for stepping in with words of wisdom and encouragement when called for. Thanks, in no particular order, for your guidance, enthusiasm, patience, tolerance, friendship and advice. I would like to give a special thank to Phil Rainbow and the Department of Zoology of the Natural history Museum for funding this work and giving me the opportunity of developing and testing my ideas at the Museum. I would like to thanks also to the Freshwater Biological Association for funding my fieldwork and the Central Research Fund of University of London for funding the radiometric laboratory analyses. This study is also a contribution to the EU FP7 Project Biofresh (Biodiversity of Freshwater Ecosystems: Status, Trends, Pressures, and Conservation Priorities) Contract No. 226874”. I would like to thank the various landowners in Fermanagh County, Northern Ireland, for site access and generous hospitality. Thanks to Tony Waterman and Gareth Greer for valuable information. I am indebted to all the staff at the Natural History Museum for all their help and friendship. I would really like to thank Peter, Patrik, Laura, Charlotte and the mighty full metal Ian for all your help, thoughts, patience and support in the field. Sorry for the long-days and make you spend hours sampling green stuff, bubbly stuff and mud. Without you guys I would not be able to collect as many data as we did together. Many thanks to Gavin Simpson for the patience, guidance on numerical techniques and vital assistance with R during some of the most confusing but in the end helpful hours of the PhD. I would like to thank everyone at the ECRC who has helped through advice, discussion, assistance in the field and most importantly invaluable entertainment and friendship at the JB and John Russel. Thanks to Ben Goldsmith, Simon Patrick, and all the Water Monitoring Network team for all your help, generosity and specially for giving me the opportunity of visiting some of the most wonderful pubs, B&Bs and landscapes in the UK. Finally I would like to give a big thank to Claudia, Vale, my family and friends for all the support you provided me during this time. 4 Table of contents ABSTRACT ............................................................................................................................................ 3 TABLE OF CONTENTS ....................................................................................................................... 5 LIST OF TABLES .................................................................................................................................. 7 1 CHAPTER 1 – INTRODUCTION ............................................................................................... 13 1.1 BACKGROUND ........................................................................................................................... 13 1.2 RIVERINE SYSTEMS ................................................................................................................... 16 1.2.1 Eutrophication .................................................................................................................. 17 1.2.2 Hydrological alteration ..................................................................................................... 18 1.2.3 Riverscapes and metacommunities.................................................................................... 18 1.2.4 Long-term records and metacommunity ........................................................................... 19 1.3 OVERALL AIM AND SPECIFIC RESEARCH QUESTIONS.................................................................. 20 1.4 STUDY SITE ............................................................................................................................... 21 1.4.1 A history of eutrophication and connectivity .................................................................... 22 1.5 STRUCTURE AND OUTLINE OF THESIS ........................................................................................ 25 1.5.1 Spatial contemporary dynamics: ....................................................................................... 25 1.5.2 Spatial-temporal dynamics ................................................................................................ 25 1.6 GLOSSARY OF TERMS ................................................................................................................ 27 2 CHAPTER 2 – THE RELATIVE IMPORTANCE OF LOCAL AND REGIONAL PROCESSES IN STRUCTURING SHALLOW LAKE METACOMMUNITIES ......................... 29 2.1 ABSTRACT ................................................................................................................................. 29 2.2 INTRODUCTION.......................................................................................................................... 30 2.3 STUDY SITE ............................................................................................................................... 32 2.4 MATERIALS AND METHODS ....................................................................................................... 34 2.4.1 Data analysis .................................................................................................................... 39 2.5 RESULTS ................................................................................................................................... 44 2.5.1 Relative contributions of spatial and environmental variables ......................................... 45 2.5.2 Community similarity along environmental and spatial gradients ................................... 50 2.6 DISCUSSION .............................................................................................................................. 52 2.6.1 Environmental variables and assemblage variation ......................................................... 52 2.6.2 Spatial variables and assemblage variation ..................................................................... 54 2.6.3 Metacommunity perspectives ............................................................................................ 57 2.6.4 Community similarity along environmental and spatial gradients ................................... 58 2.7 CONCLUSIONS ........................................................................................................................... 59 3 CHAPTER 3 – ENVIRONMENTAL AND SPATIAL PROCESSES DETERMINE LAKE MACROPHYTE DIVERSITY AND COMPOSITIONAL HETEROGENEITY IN A METACOMMUNITY LANDSCAPE. ..............................................................................................
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