River Temperature Behaviour in Changing Environments: Trends, Patterns at Different Spatial and Temporal Scales and Role As a Stressor
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Erasmus Mundus Joint Doctorate School in Science for MAnagement of Rivers and their Tidal System Roshni Arora River temperature behaviour in changing environments: trends, patterns at different spatial and temporal scales and role as a stressor 2015 This thesis work was conducted during the period 1st October 2012 - 15th December 2015, under the supervision of Dr. Markus Venohr (Leibniz Institute of Freshwater Ecology and Inland Fisheries Berlin), Dr. Martin T. Pusch (Leibniz Institute of Freshwater Ecology and Inland Fisheries Berlin), Dr. Marco Toffolon (University of Trento, Italy) and Dr. Klement Tockner (Freie Universität Berlin) at Freie Universität Berlin, University of Trento, Italy and Leibniz Institute of Freshwater Ecology and Inland Fisheries Berlin. 1st Reviewer: Prof. Dr. Klement Tockner 2nd Reviewer: Prof. Dr. Gunnar Nützmann Date of defence: 15.02.2016 The SMART Joint Doctorate Programme Research for this thesis was conducted with the support of the Erasmus Mundus Programme1, within the framework of the Erasmus Mundus Joint Doctorate (EMJD) SMART (Science for MAnagement of Rivers and their Tidal systems). EMJDs aim to foster cooperation between higher education institutions and academic staff in Europe and third countries with a view to creating centres of excellence and providing a highly skilled 21st century workforce enabled to lead social, cultural and economic developments. All EMJDs involve mandatory mobility between the universities in the consortia and lead to the award of recognised joint, double or multiple degrees. The SMART programme represents a collaboration among the University of Trento, Queen Mary University of London, and Freie Universität Berlin. Each doctoral candidate within the SMART programme has conformed to the following during their 3 years of study: (i) Supervision by a minimum of two supervisors in two institutions (their primary and secondary institutions). (ii) Study for a minimum period of 6 months at their secondary institution (iii) Successful completion of a minimum of 30 ECTS of taught courses (iv) Collaboration with an associate partner to develop a particular component / application of their research that is of mutual interest. (v) Submission of a thesis within 3 years of commencing the programme. 1 This project has been funded with support from the European Commission. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein Table of Contents Table of Contents ................................................................................................. I Summary ............................................................................................................ IV Zusammenfassung ........................................................................................... VII Thesis outline ..................................................................................................... XI List of Tables .................................................................................................. XIV List of Figures ................................................................................................ XVII 1. General introduction ....................................................................................... 1 1.1 River temperature: importance in ecosystem functioning and research history .............................................................................................................. 1 1.2 Processes and controls determining river temperatures ......................... 3 1.3 Changing river temperatures in changing environments and its implications ..................................................................................................... 5 1.4 Research gaps, aims and structure of the thesis ..................................... 8 2. Changing river temperatures in Northern Germany: trends and drivers of change ................................................................................................ 11 2.1 Abstract ................................................................................................... 11 2.2 Introduction............................................................................................. 12 2.3 Materials and methods ........................................................................... 17 2.4 Results ..................................................................................................... 21 2.5 Discussion ............................................................................................... 29 2.6 Conclusion .............................................................................................. 35 3. Influence of landscape variables in inducing reach-scale thermal heterogeneity in a lowland river ...................................................................... 38 3.1 Abstract ................................................................................................... 38 3.2 Introduction............................................................................................. 38 I 3.3 Materials and methods ........................................................................... 41 3.4 Results ..................................................................................................... 53 3.5 Discussion ............................................................................................... 69 3.6 Conclusion .............................................................................................. 73 4. Interactions between effects of experimentally altered water temperature, flow and dissolved oxygen levels on aquatic invertebrates . 75 4.1 Abstract ................................................................................................... 75 4.2 Introduction............................................................................................. 76 4.3 Materials and methods ........................................................................... 83 4.4 Results ..................................................................................................... 86 4.5 Discussion ............................................................................................... 92 4.6 Conclusion .............................................................................................. 96 5. GENERAL DISCUSSION ........................................................................... 98 5.1 Rationale and research aims .................................................................. 98 5.2 Key research findings ............................................................................. 99 5.3 Synthesis ............................................................................................... 101 5.4 Implications for river ecosystem management ................................... 103 References ......................................................................................................... 107 Statement of academic integrity .................................................................... 123 Acknowledgements .......................................................................................... 124 APPENDIX A: Supplementary material for Chapter 2 ............................ 126 APPENDIX B: Supplementary material for Chapter 3 ............................ 133 APPENDIX C: Heat Flux Equations used in Chapter 3 ........................... 136 II III Summary Summary River/stream water temperature is one of the master water quality parameters as it controls several key biogeochemical, physical and ecological processes and river ecosystem functioning. Thermal regimes of several rivers have been substantially altered by climate change and other anthropogenic impacts resulting in deleterious impacts on river health. Given its importance, several studies have been conducted to understand the key processes defining water temperature, its controls and drivers of change. Temporal and spatial river temperature changes are a result of complex interactions between climate, hydrology and landscape/basin properties, making it difficult to identify and quantify the effect of individual controls. There is a need to further improve our understanding of the causes of spatiotemporal heterogeneity in river temperatures and the governing processes altering river temperatures. Furthermore, to assess the impacts of changing river temperatures on the river ecosystem, it is crucial to better understand the responses of freshwater biota to simultaneously acting stressors such as changing river temperatures, hydrology and river quality aspects (e.g. dissolved oxygen levels). So far, only a handful of studies have explored the impacts of multiple stressors, including changing river temperature, on river biota and, thus, are not well known. This thesis, thus, analysed the changes in river temperature behaviour at different scales and its effects on freshwater organisms. Firstly, at a regional scale, temporal changes in river temperature within long (25 years) and short time periods (10 years) were quantified and the roles of climatic, hydrological and landscape factors were identified for North German rivers. Secondly, at a reach scale, spatial temperature heterogeneity in a sixth-order lowland river (River Spree) was quantified and the role of landscape factors in inducing such heterogeneity was elucidated. Thirdly, at a site scale, short- term behavioural responses (namely drift)