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Response of Diatoms to Climate Change in Mountain Lakes in the Northern Calcareous Alps with Indications for the Future Development of the Lake Biota

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Response of Diatoms to Climate Change in Mountain Lakes in the Northern Calcareous Alps with Indications for the Future Development of the Lake Biota TECHNISCHE UNIVERSITÄT MÜNCHEN TUM School of Life Sciences Lehrstuhl für Aquatische Systembiologie Limnologische Station Iffeldorf Response of diatoms to climate change in mountain lakes in the Northern calcareous Alps with indications for the future development of the lake biota Wolfgang Küfner Vollständiger Abdruck der von der TUM School of Life Sciences der Technischen Universität München zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) genehmigten Dissertation. Vorsitzende*r: Prof. Dr. Rupert Seidl PrüferInnen der Dissertation: 1. Prof. Dr. Jürgen Geist 2. apl. Prof. Dr. Tanja Gschlößl 3. Prof. Dr. Reinhard Pienitz Die Dissertation wurde am 02.12.2020 bei der Technischen Universität München eingereicht und durch die TUM School of Life Sciences am 29.03.2021 angenommen. Preface Preface This dissertation aims to investigate the responses of the montane, subalpine and alpine mountain lake biota to climate warming by reconstructing the past development using sediment cores. The beginning of the thesis gives a fundamental definition of mountain lakes and introduces into their special features and enhanced vulnerabilities in times of climate change. The next two sections of the introduction further review the palaeolimnological methods for environmental reconstructions and lead to the diatoms as ideal bioindicators for the aims of this study. After the introduction closes with the main goals and objectives of this dissertation, chapter 2 presents an overview of investigated study sites and applied methods from on-site-measurements to sediment core separation until microscopical analyses. The subsequent chapters 3 to 5 base on published and autonomous research papers. Thereof, the chapters 3 and 4 elaborate a new method to reconstruct individual lake warming as a basis to better understand biotic developments in the lakes. Therefore, chapter 3 detected the significant correlation of a morphological trait of diatoms with lake temperatures. In chapter 4, this relationship was then set into a palaeolimnological context in terms of establishing a transfer- function, which can be applied to subfossil diatom assemblages of time series from sediment cores. With this method, individual lake warming could be calculated and contrasted to regional atmospheric warming. Based on this, chapter 5 then expands the scope to the entire diatom assemblage of all retrieved sediment cores to study the biotic lake developments. In this context, this chapter identifies the main lake characteristics and tipping points that modulate and determine the lake responses to global warming. The final chapter 6 provides the general discussion and focuses on three different topics. The first section evaluates the temporal development of the studied mountain lakes including predictions for future climate warming. The second section transfers the dissertation’s results derived from primary producers to a broader context in the food web of mountain lakes and generally discusses the developments of the aquatic fauna. The third section of the general discussion illustrates the global transferability of the findings of this dissertation and highlights their limits considering different climates and continents. Finally, this chapter closes with an outlook targeting a global understanding of biotic responses in mountain lakes to warming and their regional role for terrestrial wildlife to improve management and conservations strategies with future global change. Marginal note: In consideration of Emiliani (1952), this dissertation uses the term “planktic”, which is etymologically the actual adjective of “plankton”. ii Contents Contents Preface ............................................................................................................................................................................. ii Contents ......................................................................................................................................................................... iii List of Figures ............................................................................................................................................................... vi List of Tables ...............................................................................................................................................................viii Summary ......................................................................................................................................................................... 1 Zusammenfassung ......................................................................................................................................................... 2 1 Introduction .......................................................................................................................................................... 4 1.1 Mountain Lakes and Their Vulnerability in Times of Climate Warming ........................................... 4 1.2 Overview of Applied Palaeolimnology in Climate Change Research ................................................. 7 1.2.1 Physico- and Geochemical Methods in Palaeolimnology ................................................................ 8 1.2.2 Palaeobiological Methods in Palaeolimnology .................................................................................10 1.3 Biology and Bioindicator Characteristics of Diatoms .........................................................................14 1.4 Objectives ...................................................................................................................................................17 2 Materials and Methods.......................................................................................................................................18 2.1 Study Sites ..................................................................................................................................................18 2.2 Diatom Sampling and Sediment Coring ................................................................................................22 2.3 Sample Processing .....................................................................................................................................22 2.4 Diatom Counting ......................................................................................................................................23 3 The Silicification Value: A Novel Diatom-Based Indicator to Assess Climate Change in Freshwater Habitats ................................................................................................................................................................25 3.1 Abstract .......................................................................................................................................................25 3.2 Introduction ...............................................................................................................................................26 3.3 Methods ......................................................................................................................................................28 3.3.1 Study Site................................................................................................................................................28 3.3.2 Measurements and Analysis ................................................................................................................29 3.3.3 Diatom Sampling ..................................................................................................................................30 3.3.4 Diatom Analysis ....................................................................................................................................31 3.3.5 The Silicification Value ........................................................................................................................31 3.3.6 Valve Sizes .............................................................................................................................................33 3.3.7 Statistical analyses .................................................................................................................................33 3.4 Results .........................................................................................................................................................34 3.4.1 Diatom Analyses ...................................................................................................................................34 3.4.2 Environmental Variables .....................................................................................................................35 3.4.3 Silicification Value ................................................................................................................................35 3.5 Discussion ..................................................................................................................................................37 iii Contents 3.5.1 The Silicification Value and Size Effect ............................................................................................40 3.5.2 The Silicification Value and Alternatives ..........................................................................................41 3.6 Conclusions ................................................................................................................................................42
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