Multi-scale effects of hydrological and landscape variables on macrophyte richness and composition in British lakes Junyao Sun August 2016 Submitted to Biological and Environmental Sciences School of Natural Sciences University of Stirling UK For the degree of Doctor of Philosophy Supervisors: Dr. Peter Hunter, Prof. Andrew Tyler & Prof. Nigel Willby STATEMENT OF ORIGINALITY I hereby confirm that this PhD thesis is an original piece of work conducted independently by the undersigned and all work contained herein has not been submitted for any other degree. All research material has been duly acknowledged and cited. Signature of Candidate: Junyao Sun Date: 31st of August 2016 ii GENERAL ABSTRACT Macrophytes are an integral component of lake littoral zones and play an irreplaceable role in maintaining the ecological balance of wetlands. Recent research has highlighted the role of lake-scale environmental factors (or “filters”) and catchment- and/or landscape-scale processes in explaining variation in macrophyte communities across different scales. In this work, the effects of land-use and connectivity on macrophyte communities were explored at two contrasting spatial scales (i.e. local catchment scale and topographic catchment scale). At the local catchment scale, the results revealed strong scale-dependency. The effects of land use on macrophyte richness were most apparent at fine spatial scales (within 0.5 to 1 km) and significantly outweighed the importance of hydrology. In terms of growth form composition, the effects of hydrological connectivity were stronger than those of land use, with the greatest effect observed at an intermediate distance (~ 5 km) from the lake. The study on the hydrologically-connected lake pairs indicated that environmental filters were more influential in explaining species turnover than lake connectivity. Interestingly, geographical connectivity explained more of the variability in species turnover than hydrological connectivity. Moreover, the relative importance of environmental filters and lake connectivity to species turnover was very sensitive to the degree of human disturbance. The multi-scale interaction analyses indicated the effect of lake alkalinity on macrophyte composition is strongly influenced by catchment scale variables including hydrological features and land use intensity. The turnover in macrophyte composition in response to variability in alkalinity was stronger in catchments with low lake and stream density and weaker in catchments with a more highly developed hydrological network. Lake abiotic variables were found to have more influence on macrophyte composition in lowland catchments with a higher intensity of human disturbance. Moreover, the catchment-scale factors promoting the establishment of different communities were found to vary between catchments depending on lake type, the degree of environmental heterogeneity and hydrological connectivity. iii ACKNOWLEDGMENTS First and foremost, I would like to express my thanks and respects to my primary supervisor Peter Hunter, for contributing his time, patience and ideas to give me a rewarding experience to be an independent researcher, for training me to form a rigorous attitude in scientific works. I extent this thanks to my additional supervisors Andrew Tyler and Nigel Willby. They both kindly offered me a large amount of valuable and professional supervisions in my Ph.D. work, as well as assisted me to improve my academic writing and presentation skills. I thank both Laurence Carvalho (Center for Ecology & Hydrology) and Luc Bussiere (University of Stirling) for spending large amount of time to read and examine my thesis. The amendments they proposed on statistics and discussion improved the quality of whole thesis. I would like to thank Phil Bartie (University of Stirling) for giving me some useful suggestions on GIS and Kendra Cheruveili (Michigan State University) for promoting me to generate some new ideas and offering me some helps on R statistic analyses. Thanks to Li wei and Liu fan (Wuhan botany Garden, China academy of science) for helping me to develop the ideas about my analyses. Thanks to University of Stirling for funding my trip to the Macrophyte Symposium in Wuhan, China. And Thanks to the British Ecological Society for providing the funding to allow me to attend the World lake conference in Perugia, Italy. John McArthur, Scott Jackson very kindly offered me some GIS and IT supports, which I would like to express my huge of thanks. Thanks to my officemates Angela McClumpha, Cerian Tatchley and Adam Varley, as well as my dear friend Jennifer Sjölund, who offered me a lot of concerns and helps on my study and life in my first year. And in no particular order I thank these people who offered me many helps on my works and assistants on my writing: Alan Law, Christopher Sneddon, Amani Becker, Anna Doeser, Zarah Pattison, Alex Seeney, Pauline Pantoja. Finally, to my parents, who funded my whole Ph.D. and always inspired me to move on and support me, which I am very grateful. This thesis is dedicated to my grandparents Wang Houyu and Guan Lin (1930 - 2016) who left too suddenly. iv TABLE OF CONTENTS STATEMENT OF ORIGINALITY ·········································································· ii GENERAL ABSTRACT ························································································ iii ACKNOWLEDGMENTS ······················································································ iv TABLE OF CONTENTS ························································································ v LIST OF FIGURES ···························································································· viii LIST OF TABLES ································································································ xi KEY CONCEPTS ······························································································· xiii Chapter 1 – General Introduction ····································································· 1 1.1 General background ·························································································································· 1 1.2 Scientific background and objectives ································································································· 3 1.2.1 Catchment Ecology (or Watershed Ecology) ·············································································· 3 1.2.2 Human disturbance on catchment ecology ··············································································· 3 1.2.3 Research objectives ···················································································································· 4 1.3 Study sites ·········································································································································· 4 1.4 Research results introduction ············································································································ 5 Chapter 2 – Scale-dependency and multi-scale interaction of lake aquatic vegetation: A review ························································································· 7 2.1 Abstract ············································································································································· 7 2.2 Introduction ······································································································································· 8 2.3 Background review ···························································································································· 8 2.4 Factors controlling macrophytes in lakes at multi-scale ································································· 10 2.4.1 Local catchment (Aquatic-terrestrial ecotones) ······································································· 13 2.4.2 Topographic catchment ··········································································································· 13 2.4.3 Freshwater ecoregion ·············································································································· 14 2.5 Discussion ········································································································································ 17 2.5.1 Contribution of environmental filtering and broad-scale processes to structuring of macrophyte assemblages ·················································································································· 17 2.5.2 Multi-scale dynamics in freshwater ecosystem ······································································· 18 Chapter 3 – A buffer analysis of hydrology and land use influences on macrophyte richness in lakes – the role of catchment versus landscape ······ 21 3.1 Abstract ··········································································································································· 21 3.2 Introduction ····································································································································· 21 v 3.3 Methods ··········································································································································· 24 3.3.1 Study sites ································································································································ 24 3.3.2 Lake and macrophyte sampling ·······························································································