The Stability of Temperate Lakes Under the Changing Climate

Western University Scholarship@Western Electronic Thesis and Dissertation Repository 9-27-2019 10:30 AM The Stability of Temperate Lakes Under the Changing Climate Aleksey Paltsev The University of Western Ontario Supervisor Creed, Irina The University of Western Ontario Trick, Charles The University of Western Ontario Graduate Program in Biology A thesis submitted in partial fulfillment of the equirr ements for the degree in Doctor of Philosophy © Aleksey Paltsev 2019 Follow this and additional works at: https://ir.lib.uwo.ca/etd Part of the Biogeochemistry Commons, Biology Commons, Climate Commons, Environmental Sciences Commons, Fresh Water Studies Commons, Other Ecology and Evolutionary Biology Commons, Other Oceanography and Atmospheric Sciences and Meteorology Commons, and the Terrestrial and Aquatic Ecology Commons Recommended Citation Paltsev, Aleksey, "The Stability of Temperate Lakes Under the Changing Climate" (2019). Electronic Thesis and Dissertation Repository. 6658. https://ir.lib.uwo.ca/etd/6658 This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. Abstract There is a collective prediction among ecologists that climate change will enhance phytoplankton biomass in temperate lakes. Yet there is noteworthy variation in the structure and regulating functions of lakes to make this statement challengeable and, perhaps, inaccurate. To generate a common understanding on the trophic transition of lakes, I examined the interactive effects of climate change and landscape properties on phytoplankton biomass in 12,644 lakes located in relatively intact forested landscapes. Chlorophyll-a (Chl-a) concentration was used as a proxy for phytoplankton biomass. Chl- a concentration was obtained via analyzing Landsat satellite imagery data over a 28-year period (1984-2011) and using regression modelling. The most common lake trophic state was oligotrophic (median Chl-a < 2.6 μg L-1), while the least common was hyper- eutrophic (median Chl-a > 56 μg L-1). Lake volume was the most important factor in determining the present trophic state of the lakes. The majority of the lakes (91.6%) did not show a change in trophic state over an almost 3-decade long sampling period; only 4.0% of the lakes became more eutrophic, and 4.4% of the lakes became more oligotrophic. Lakes with smaller volumes were further responsive to temperature (warmer lakes were more eutrophic), while lakes with larger volumes were more responsive to precipitation (wetter lakes were more oligotrophic). Early warning indicators of change in trophic state were examined in the patterns of the residuals of the time series of Chl-a once non-stationary and stationary trends were removed. Remarkably, the majority (56.5%) of the lakes showed patterns in the residuals that were not defined by a single trophic metric but fluctuated among different trophic states. There was an unexpected instability among some lakes as they switched between oligotrophic and eutrophic states (12.5%) or were transitioning from eutrophic towards oligotrophic states (23.4%), or from oligotrophic towards eutrophic states (20.6%). The complex responses of phytoplankton biomass to climate change suggests that our ability to predict the future trophic state of lakes will be limited but enhanced if we recognize that lakes and their catchments will be both impacted by climate change. ii Keywords Lake, phytoplankton, chlorophyll-a, trophic state, stable states, instability, oligotrophication, eutrophication, climate change. iii Summary for Lay Audience The impact that climate change will have on Canadian temperate lakes remains poorly understood. There are several reasons for our lack of confidence in describing the effect of climate change. First, many lakes that are near human populations are also impacted by the anthropogenic pressures – direct or indirect use of surface waters for consumption and the use of lakes for the intended or unintended deposits of wastes. Second, our ability to predict the changes in lake ecology is hampered by our slow observance of changes that are currently taking place. It appears that lakes may be changing from clear water states to turbid productive water states with an increased incidence of potentially harmful algal blooms. Although undesirable, these changes can be either gradual (i.e., linear), or small and non-linear, and the latter is much harder to identify. Finally, since lakes are of many shapes and sizes (i.e., they have different morphometry), they will not be impacted by climate change equally. Thus, reports on climate change about the functioning of lakes might be too general. This thesis attempts to avoid these problems by studying over 12,000 lakes in the temperate forest region of Canada. Using satellite records of lake chlorophyll-a (a proxy measure of algal biomass in lakes) over 28 years, I have determined that climate change affects ~44 % of the lakes, with ~21 % of the lakes becoming more productive and ~23 % of the lakes becoming less productive. The remaining lakes either do not respond to the changing climate or oscillate between low and high productivity. The trends documented in this thesis indicate how the lakes might look like in the future (as climate change continues) and if they can be used as a healthy water supply for the next generations. iv Co-Authorship Statement The PhD thesis contains three manuscripts. In each of these manuscripts, Aleksey Paltsev will be first author, as he conducted pre-processing of Landsat products (Chapter 2) and statistical analysis; he contributed to design of the research, interpretation of the research results and writing of the manuscripts. In each of these manuscripts, Dr. Irena Creed will be second author, as she contributed to the definition of the research problem, interpretation of results, synthesis of ideas and editing of the manuscripts. The PhD thesis is extension of Aleksey Paltsev’s Master of Science research: “Exploration of spatial and temporal changes in trophic status of lakes in the Northern Temperate Forest Biome using remote sensing” published as a Master’s thesis in 2015. Although in this PhD thesis, Aleksey Paltsev adopted research approach and some ideas initially developed in his Master’s research, all pre-processing steps of Landsat products and statistical analyses (including the development of the regression model) were substantially modified, which resulted in a different set of modelled data. Furthermore, more in-depth analyses were performed, for example the space-time kriging and the Mann-Kendall test. The Master’s thesis is cited throughout the PhD thesis where it is appropriate. This PhD thesis was funded by Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants awarded to Dr. Irena Creed. v Acknowledgments I cannot express the level of gratitude and appreciation I have for my amazing supervisor, Dr. Irena Creed. The past years have been some of the most challenging and inspirational years of my life. Your passion for knowledge and advancing science is second to none, and I am grateful for your dedication to my personal development. We have done amazing and rewarding work together and through this, I have learned a lot. You have helped me advance my passion for knowledge and nature and have always pushed me to do more. I am grateful to my co-supervisor, Dr. Charles Trick. Your wisdom and extremely valuable comments during my presentations and talks continually kept me afloat. I would like to thank my PhD advisory committee, Dr. Adam Yates and Dr. Ben Rubin. I am grateful for our time together and your continued dedication to the development and completion of my degree. Your insight and guidance throughout the years has enabled me to be successful. A very special thank you to Mr. David Aldred. I am extremely grateful for all your help– from making maps and figures pretty to your guidance in analyzing and processing GIS data and beyond. For sure, without your help this thesis would take me more than these several years to complete. vi Table of Contents Abstract ............................................................................................................................... ii Summary for Lay Audience ............................................................................................... iv Co-Authorship Statement.................................................................................................... v Acknowledgments.............................................................................................................. vi Table of Contents .............................................................................................................. vii List of Tables ..................................................................................................................... xi List of Figures .................................................................................................................. xiii List of Appendices .......................................................................................................... xvii List of Abbreviations ..................................................................................................... xviii 1 Introduction ...................................................................................................................

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