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Comparing Hypotheses Proposed by Two Conceptual Models for Stream

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Comparing Hypotheses Proposed by Two Conceptual Models for Stream Comparing hypotheses proposed by two conceptual models for stream ecology by Sean Elliott Collins B.S. Marshall University M.S. Marshall University A dissertation submitted to the Graduate School of the University of Cincinnati in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Biological Sciences of the College of Arts and Sciences March 2014 Committee Chair: S. F. Matter, Ph.D. Abstract The broad goal of stream ecology is to understand and predict complex interactions between environmental factors and processes that occur within streams and rivers, such as biological community composition and their interactions, system metabolism (productivity and respiration), and nutrient sources and concentration. Multiple factors are thought to play important roles in these processes including regional environmental conditions (i.e., hydrology, geology, stream form/morphology) and longitudinal position within a stream network (defined by Strahler stream order). In the past, several theoretical concepts have been proposed to attempt to describe and explain how streams behave, and each concept uses various factors weighted differently to characterize streams and gain a better understanding of ecological processes and overall system functions. Here, two differing theories of stream ecology are compared – the River Continuum Concept (RCC) and the Riverine Ecosystem Synthesis (RES). Each of these theories has unique predictions based on either Strahler stream order (SSO; used by the RCC) or Functional Process Zone (FPZ; used by the RES) defined by hydrogeomorphic characteristics. Predictions from both theories were tested across sites representing multiple SSOs and FPZs within the Kanawha River Basin. Measures of environmental heterogeneity (an important concept for differentiating between FPZs) were also assessed. This project has shown that some predictions from both the RCC and the RES are valid. The physical character of the basin is variable; sampling of riverbed substratum at each site revealed that similarities within each FPZ in riverbed composition exist and that each FPZ is distinct. Hydrogeomorphic factors including underlying geology and valley floor width strongly influence the character of the riverbed substratum. The ratio of ii primary productivity to ecosystem respiration (i.e., a measure of metabolism) aligned with predictions from the RES where potential light availability and environmental heterogeneity were major drivers of this ratio. On the other hand, a “sliding scale” (i.e., one that changes with environmental variables) may be more appropriate for predictions from the RCC as the apparent trend toward higher rates of primary productivity was shifted from mid-order to larger streams. Neither the RCC nor the RES provide clear hypotheses for fluctuations in nutrient concentrations, and changes in these concentrations were not accurately explained by either SSO or FPZ. Finally, results from stable isotope analysis of carbon and nitrogen revealed that consumers in the Kanawha River Basin utilize a combination of aquatic and terrestrial organic carbon. While food web metrics and the proportional dependence upon in-stream and terrestrially derived carbon follow predictions of the RCC more closely, the mechanisms underlying these predictions are not always met. That is, there was no relationship between high measured rates of aquatic primary productivity and low dependence on terrestrial carbon sources. The RES also explains well the shift in organic carbon use from various sources by consumers. Perhaps the best model for understanding these processes is a combination of both concepts. Understanding the reasons for changes in processes and functions within streams and rivers is critical for developing a useful and successful model. It is through this process of model conceptualization, testing, and refining that true advancements in knowledge can take place. iii [This page intentionally left blank.] iv Acknowledgements This project would not be what it is without the help of many. I have had the privilege of working with some of the best mentors, fellow students, and colleagues that I could imagine. All the while, I have been supported by my friends and family. It is not without my deepest appreciation when I say thank you to you all. My gratitude goes out to various sources of funding including the University of Cincinnati, the University of New England, and the United States Environmental Protection Agency. I have been supported by the Graduate Assistant Scholarship, the Wieman Wendel Benedict Research Award, and the Choose Ohio First Scholarship, and I worked as a Teaching Assistant at the University of Cincinnati. I have also worked as a Student Services Contractor to the U.S. EPA under contract EP10D000363 and EP12D000302. Finally, I was awarded the International Graduate Student Assistance Scheme from the University of New England. Funds for travel to conferences and regional meetings were also provided by the Graduate School of the University of Cincinnati. I would also like to thank my lab mates Megan Lamkin, Natasha Urban, Matt Westbrook, Sasha Ramudit, and Hao Yuan Chen. You all have provided an excellent atmosphere for learning, sharing ideas, and developing as a scientist. I greatly appreciate the feedback you all have given on draft after draft of my grant proposals and manuscripts. I am sure that none of those would be the same without you. Thank you all, also, for your friendship during my time at the University of Cincinnati. During my time at UC, I have received assistance in the laboratory and the field from research scientists, other graduate students, and undergraduates. I would like to thank Madhav Machavaram for his patience and wisdom. Without him, the stable isotope portion v of this research would not have been completed. I would also like to thank Mark Mitchell, Kathleen Hurley, Kate Johnson, and Jeremy Alberts for their help with nutrient analyses. Brandon Armstrong, John Gorsuch, Brent Johnson, and Michael Moeykens also assisted me in the laboratory with organism identification and sample preparation. Brandon Armstrong, Michael Moeykens, Sheila North, and Aaron Stahl also provided much appreciated assistance with field work. I hope that the mountains and streams of West Virginia and Virginia were a reward for your work. My Research Advisory Committee consisted of Stephen Matter, Ishi Buffam, Joseph Flotemersch, Eric Maurer, Martin Thoms, and Amy Townsend-Small. Throughout my time at UC, each of you has contributed to my research project and my overall development as a scientist. You have all shared your knowledge and challenged me along the way. Steve has been an excellent advisor. He has given me enough freedom to develop my own ideas and project goals, and he has been readily available to help without hesitation. Manuscripts, grant proposals, and application documents have all passed over his desk, and each has benefited after his review. Ishi, I thank you passing on some of your knowledge of and expertise in freshwater systems. Nutrient analyses and dynamics are new concepts that I have added to my own repertoire. I would also like to thank Joe for his endless help in both the lab and field. I have learned so much from you. Thanks to Eric for challenging me and for providing valuable insight into my experimental design and implementation. Martin, I am truly grateful for the opportunity you afforded to me. Visiting the University of New England and spending time with you and other members of the Riverine Landscape Research Lab was incredibly rewarding. I would also like to extend my appreciation to Amy for teaching me both in and out of class. Your insight into stable isotope analysis and other vi aspects of my project have made this dissertation better than it could have been without you. Finally, I would like to thank my friends and family. I have had so much support from each of you, and I’ve been very fortunate to get to know so many wonderful people. To my family in-law, Jim, Nancy, and Jeremy, thank you so much for your kind words and support throughout my time at UC. Time spent with you has been relaxing and enjoyable. A wonderful relationship with you all is something special that I am so grateful to have. I would also like to thank my own family. To my brother, Seth, his wife, Tabitha, and their family, thank you for your support, encouragement, and understanding. Although our paths may be different, we will never grow apart. To my parents, Gene and Elaine, I appreciate everything you have done for me. You instilled in me a work ethic that has allowed me to succeed in whatever pursuits I may choose. Your guidance in my life has been beneficial, and you have given me an example that I hope to follow. To my wife, Kelly, you have given me so much in our life together. Thank you for your patience, assistance, and assurance. We make a great team, and I am sure that the next steps in our life will be as wonderful as our first steps together. vii Table of Contents Abstract ......................................................................................................................................................................... ii Acknowledgements .................................................................................................................................................. v List of Tables ............................................................................................................................................................
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