A Geochemical Perspective
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ABSTRACT THOMPSON, CATHERINE E. Tracking Organic Matter from Source to Sink in the Waiapu River Watershed, New Zealand: A Geochemical Perspective. (Under the direction of Neal E. Blair and Elana L. Leithold). The significant contribution of small mountainous river systems, including the Waiapu River on New Zealand’s East Cape, to the global fluvial sediment supply motivates investigation into the processes that influence the character and composition of the organic carbon that they carry. Organic matter preserved in continental margin sediments originates from terrestrial sources such as kerogen, fresh and aged soil carbon, as well as marine sources. Due to the reactivity of marine carbon in the seabed, terrestrial sources of carbon are preferentially preserved unaltered. Therefore, identification of specific terrestrial sources of sediment from the watershed preserved on the continental margin can facilitate interpretation of the organic geochemical record and enable reconstruction of the watershed history. Carbon and nitrogen isotopic analyses and polycyclic aromatic hydrocarbons have been used to apportion terrestrial carbon sources preserved on the shelf, specifically to resolve aged soil contributions. Spatial geochemical patterns on the margin appear to be complicated by structural deformation of the shelf and its influence on marine sediment dynamics. Resolution of riverine sources suggests that gullying, bank failure, and sheetwash are the chronic geomorphic processes delivering most of the organic carbon to the Waiapu sedimentary system. The middle and outer Waiapu continental shelf buries an average of 59 Gg C/y. Relative to the 200 Gg C/y delivered by the Waiapu River to the ocean, approximately 23% of the riverine carbon is retained on the mid- to outer shelf, matching the sediment inventory. Radiocarbon analysis of DIC indicates that there is no apparent oxidation of kerogen in the seabed. Stable carbon isotopic signatures suggest minimal oxidation of modern terrestrial carbon, signifying that the 77% of the riverine carbon not accounted for has likely been retained and potentially oxidized on the inner shelf or escaped to the slope or beyond the established boundaries of the mid- to outer shelf. Tracking Organic Matter from Source to Sink in the Waiapu River Watershed, New Zealand: A Geochemical Perspective by Catherine E. Thompson A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Marine, Earth, and Atmospheric Sciences Raleigh, North Carolina May 2009 APPROVED BY: _____________________________ ____________________________ Dr. Neal E. Blair Dr. Elana L. Leithold Committee Chair Committee Co-chair _____________________________ _____________________________ Dr. Elizabeth G. Nichols Dr. David J. DeMaster _______________________________ Dr. J. Paul Liu DEDICATION For my Mom and Dad, whose love and support has sustained me through life’s challenges. And for my Aunt Vicki, who has always inspired and encouraged me. In his heart a man plans his course, but the Lord determines his steps. ~Proverbs 16:9~ “There are potholes on the road less traveled. Some deep, some not so deep, some you dig yourself. Most are filled with mud. Many contain rocks. Once in awhile, however, you’ll be walking along and step in one a bit more accommodating… shabby, green, and pulsing with life. It’ll tickle your feet, like clover.” Excerpt from Flabbergasted by Ray Blackston ii BIOGRAPHY Catherine Elizabeth Thompson graduated from Walter Hines Page High School in Greensboro, NC. She was a Libby Jones Scholar at the University of North Carolina at Greensboro, where she majored in chemistry. In her junior and senior years, Catherine was a Glaxo-Wellcome Women in Science Scholar, and conducted organic synthesis research with Dr. James Barborak. After her undergraduate studies, Catherine continued her chemistry research at the University of Michigan under Dr. Edwin Vedejs. She also focused on chemistry education as a Chemical Sciences at the Interface of Education fellow under Dr. Brian Coppola. After obtaining Ph.D. candidacy in organic chemistry, Catherine decided that her interests were better suited to environmental chemistry. She took a M.S. in organic chemistry, and joined Dr. Neal Blair and Dr. Lonnie Leithold at North Carolina State University for a Ph.D. in chemical oceanography, focusing on organic geochemistry. Her Ph.D. research has focused on the use of isotopic and molecular signatures of organic matter as tracers of sediment generation, transport, deposition, and burial in the Waiapu River watershed in New Zealand. iii ACKNOWLEDGMENTS I would like to first thank my advisors, Neal Blair and Lonnie Leithold, without whose guidance, this would not have been possible. Under their tutelage, I have transitioned from an organic chemist to an organic geochemist. They taught me to “think outside of the beaker”, putting chemistry in an environmental context. I will always be grateful for all they have done. I would also like to thank the other members of my committee, Elizabeth Nichols, Dave DeMaster, and Paul Liu, who have supported my education at NCSU. Dr. Elizabeth Nichols has provided me immeasurable support over the last five years. In addition to serving on my committee, she has supported my research both with her time and funding. She has always been available to talk about science, school, and life in general. Without her support, my graduate school experience would have been vastly different; there simply are not words to express my gratitude. Dr. Alan Palmer at Massey University in Palmerston North, New Zealand supported my field research in 2007. He taught me a great deal about soil science and the geology of New Zealand. Alan was also so kind as to open his home to me throughout my tenure in New Zealand. Dr. Chris Osburn, my supervisor in the IRMS Lab, has provided many insights towards my research. I am very appreciative for his time and efforts on my behalf. iv I am greatly appreciative of my various funding sources throughout the years. The departments of Marine, Earth and Atmospheric Sciences and Forest and Environmental Resources at NCSU supported me through teaching assistantships and as an instrument technician. Grants from the National Science Foundation and the Environmental Protection Agency/North Carolina Department of Environmental and Natural Resources/Division of Water Quality have provided funding for me as a research assistant for Neal Blair, Lonnie Leithold, and Elizabeth Nichols. An EAPSI fellowship through NSF and the Royal Society of New Zealand supported my soil science research in New Zealand in 2007. Previous and current lab members have contributed technical support. Specifically, I want to thank Kristen Lloyd and Laurel Childress, the lab monkeys, who have not just been lab mates, but also very good friends. They have been supportive through the good times and bad. My office mates Anita McCulloch and Linda Waters were with me at NCSU since day one, quickly becoming two of my closest friends and my support system. We studied together, worked all hours of the night in the office, provided new perspectives on research ideas, and found every possible coffee shop, bookstore, and restaurant in the greater Triangle area with available power outlets and free internet connections. Their contribution to my graduate education and life in general is beyond measure and deserves infinite gratitude and thanks. Other friends, both at NCSU and at the University of Michigan deserve acknowledgement. Special thanks are extended to Jane Griffiths, Yiyi Wong, Tara v Conser Hagena, Mark Bielaska, Tim and Beth DeVries, Andrew Callender, Robyn Gdula, Nancy Santagata, Beth Rueschhoff, Pete Lazaro, Rachel Cook, and Thorne Gregory. Special thanks also go to Jason Smulik, who pushed and antagonized me to be the best scientist possible. My father and mother, Rich and Janice Thompson, have been the foundation of my support structure. They have been there for me regardless of the need. Without their love, encouragement, and all of forms of support, I would not have been able to survive the graduate school process. My brother and sister-in- law, Tim and Traci Thompson, have been very supportive of me. My niece Annika and my nephew Dane have been the joy in my life over these last few years. They constantly remind me that life should be approached with curiosity. My aunt, Janet Register, has supported me as if I were one of her own daughters. My grandparents, Richard and Lois Gainer, have supported me with constant prayer, love, and financial gifts for which I am overwhelmingly thankful. My aunt and uncle, Vicki and John Winterton have taught me that both work and fun should be approached with same diligence and fervor; that all things should be done to the best degree possible. Finally, I lost my beloved dog, Gracie, during my tenure at NCSU. Her presence added some normalcy to my life, ensuring that I went home at regular hours and had a life outside of work. She taught me many lessons in patience and devotion. Her love was unconditional; she was always there with a smile and a bark. vi TABLE OF CONTENTS List of Tables............................................................................................................ xiii List of Figures ...........................................................................................................xv Chapter 1. Introduction .............................................................................................