Calamagrostis canadensis
National Institutes of Health
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......................................................................................................................................... ii Preface ........................................................................................................................................... iv Table of Contents ...........................................................................................................................v List of Tables .................................................................................................................................. x List of Figures .............................................................................................................................. xii List of Abbreviations ................................................................................................................... xv Acknowledgements .................................................................................................................... xvi Chapter 1: Introduction ................................................................................................................1 1.1 Overview ............................................................................................................................ 1 1.2 Literature review ................................................................................................................ 2 1.2.1 The Arctic ecosystem .................................................................................................. 2 1.2.2 Permafrost & Arctic ecosystem fluxes ....................................................................... 3 1.2.2.1 Permafrost thaw implications .............................................................................. 3 1.2.2.2 Net ecosystem exchange ...................................................................................... 4 1.2.3 Disturbance ecology .................................................................................................... 5 1.2.4 Thermokarst disturbances ........................................................................................... 7 1.2.4.1 Active layer detachment slides (ALDS) .............................................................. 8 1.2.4.2 Retrogressive thaw slumps (RTS) ..................................................................... 10 1.2.5 Climate impacts of ALDS and RTS .......................................................................... 13 1.3 Research objectives .......................................................................................................... 15 1.4 Structure of the thesis ....................................................................................................... 17 vi 1.5 Introduction to the study area .......................................................................................... 18 1.5.1 Previous research at the study location ..................................................................... 19 Chapter 2: Vegetation succession after permafrost disturbance on the Fosheim Peninsula, Ellesmere Island ...........................................................................................................................21 2.1 Overview .......................................................................................................................... 21 2.2 Introduction ...................................................................................................................... 22 2.3 Methods............................................................................................................................ 24 2.3.1 Study site ................................................................................................................... 24 2.3.2 Vegetation sampling (1994 and 2012) ...................................................................... 28 2.3.2.1 Active layer detachment slides .......................................................................... 28 2.3.2.2 Retrogressive thaw slumps ................................................................................ 29 2.3.3 Comprehensive site characterization (2012) ............................................................. 30 2.3.3.1 Soil moisture and active layer depth .................................................................. 30 2.3.3.2 Soil nutrient availability ..................................................................................... 30 2.3.3.3 Soil temperature ................................................................................................. 30 2.3.4 Statistical analysis ..................................................................................................... 31 2.3.4.1 Time comparison ............................................................................................... 31 2.3.4.2 Vegetation composition and cover ..................................................................... 31 2.3.4.3 Soil moisture and active layer depth .................................................................. 32 2.3.4.4 Soil temperature ................................................................................................. 33 2.4 Results .............................................................................................................................. 33 2.4.1 Comparison of historical and modern data ............................................................... 33 2.4.1.1 Vegetation community composition and cover ................................................. 33 vii 2.4.2 Comparison of plant communities in disturbances sampled in 2012 ....................... 36 2.4.3 Retrogressive thaw slump vegetation analysis ......................................................... 40 2.4.4 Site characteristics of disturbances sampled in 2012 ................................................ 42 2.4.4.1 Soil moisture ...................................................................................................... 42 2.4.4.2 Active layer depth .............................................................................................. 43 2.4.4.3 Soil temperature ................................................................................................. 45 2.4.4.4 Soil nutrients ...................................................................................................... 47 2.5 Discussion ........................................................................................................................ 50 2.5.1 Successional response ............................................................................................... 50 2.5.2 Soil characteristics .................................................................................................... 54 2.5.3 Permafrost thaw implications ................................................................................... 55 2.6 Conclusion ....................................................................................................................... 56 Chapter 3: Variability of the impacts of active retrogressive thaw slumps on net ecosystem exchange in the Canadian High Arctic ......................................................................................58 3.1 Overview .......................................................................................................................... 58 3.2 Introduction ...................................................................................................................... 59 3.3 Materials and methods ..................................................................................................... 62 3.3.1 Study area .................................................................................................................. 62 3.3.2 Site selection ............................................................................................................. 63 3.3.3 Vegetation sampling ................................................................................................. 66 3.3.4 Soil characteristics .................................................................................................... 67 3.3.5 Portable CO2 efflux chamber system ........................................................................ 68 3.3.6 Eddy covariance measurement of NEE .................................................................... 70 viii 3.3.7 Flux data processing ................................................................................................. 71 3.3.8 Statistical analysis ..................................................................................................... 72 3.4 Results .............................................................................................................................. 73 3.4.1 Micrometeorological conditions ............................................................................... 73 3.4.2 Vegetation ................................................................................................................. 75 3.4.3 Thermal regime ......................................................................................................... 77 3.4.4 Moisture regime ........................................................................................................ 79 3.4.5 Nutrient availability .................................................................................................. 81 3.4.6 Ecosystem respiration ............................................................................................... 82 3.4.7 Net ecosystem exchange (NEE) ................................................................................ 83 3.5 Discussion ........................................................................................................................ 85 3.6 Conclusions .......................................................................
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