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An Investigation of Hydrological Separation

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An Investigation of Hydrological Separation Water cycling on cultivated land: an investigation of hydrological separation in the vadose zone Thesis Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Devin Foster Smith Graduate Program in Earth Sciences The Ohio State University 2019 Thesis Committee Anne E. Carey Thomas H. Darrah Michael T. Durand Rattan Lal 1 Copyrighted by Devin Foster Smith 2019 2 Abstract There is a need to improve our understanding of water cycling in the soil-plant- atmosphere-continuum and the degree of hydrological separation in the vadose zone. Stable water isotopes, oxygen-18 and hydrogen-2, are natural tracers that effectively delineate water flow paths. Isotopic fingerprinting methods can be used to track hydrologic flow through a system after the water is extracted from the sample. However, the ecohydrologic community lacks a universally accepted method of water extraction from soils and plants. This study incorporated methods development, field work, and modeling to delineate water flow and determine the degree of hydrological separation in a Crosby silt loam field planted with Zea mays L. (maize) at the Waterman Agricultural and Natural Resources Laboratory on The Ohio State University campus from May to September 2018. Stable water isotopes were used as natural tracers to delineate flow throughout the soil profile. Soil water samples were extracted via cryogenic vacuum distillation and analyzed for δ18O and δD using cavity ring-down spectroscopy. Field results showed vertically dominated flow regimes and low variation in soil water isotopic composition, which indicated limited mixing between precipitation event water and pre- existing soil water. The expected relationship between maize xylem tissue and soil water content was modeled using IsoSource. ii Acknowledgments I would like to thank my advisor, Anne Carey, for acting as my mentor and providing support throughout this project. She has been a phenomenal female role model in the Earth Sciences. I would also like to thank my committee members for providing me with guidance throughout the research process. In addition to providing intellectual guidance, Thomas Darrah contributed funding for field equipment and lab space. Rattan Lal provided lab space and equipment as well. I greatly appreciate both contributions. Additionally, I would like to thank Nall Moonihall for assisting with field samples and my peers in my lab group. I also like to acknowledge Sue Welch and Berry Lyons for providing guidance and assistance with my research over the past two years. Finally, I extend a loving thank you to my family and friends who have always supported me and encouraged me to pursue my passion. Thank you to everyone who made this possible along the way. I feel incredibly lucky to have had this opportunity. iii Vita May 2013 New Trier High School May 2017 B.S. Environmental Science, B.A. Geography, Villanova University August 2017 – Graduate Fellow, August 2018 School of Earth Sciences, The Ohio State University August 2018 – Graduate Teaching Assistant, Present The Ohio State University Fields of Study Major Field: Earth Sciences iv Table of Contents Abstract ............................................................................................................................... ii Acknowledgments.............................................................................................................. iii Vita ..................................................................................................................................... iv List of Tables .................................................................................................................... vii List of Figures .................................................................................................................. viii Chapter 1. Introduction ....................................................................................................... 1 1.1 Stable Water Isotopes ............................................................................................... 2 1.2 Global and Local Meteoric Water Lines ................................................................... 4 1.3 The two water world hypothesis ............................................................................... 6 1.4 Transition into “n water worlds”............................................................................... 9 1.5 Hydrological Separation in Agriculture .................................................................. 11 1.6 Soil Moisture Characteristics .................................................................................. 12 1.7 Mass Balance Mixing Models ................................................................................ 16 1.8 Objectives and Hypothesis ...................................................................................... 19 Chapter 2. Methods ........................................................................................................... 21 2.1 Overview ................................................................................................................. 21 2.2 Site Location ........................................................................................................... 21 2.3 EC-5 Soil Moisture Sensor Calibration .................................................................. 23 2.4 Field Placement of Sensors ..................................................................................... 24 2.5 Soil Moisture Content Determination at Field Capacity and Permanent Wilting Point .............................................................................................................................. 25 2.6 Local Meteoric Water Line (LMWL) ..................................................................... 25 2.7 Field Sampling Overview ....................................................................................... 26 2.8 Soil Sampling .......................................................................................................... 26 2.9 Field Water Sampling ............................................................................................. 26 v 2.10 Zea mays L. (Maize) Sampling ............................................................................. 27 2.11 Sample Water Analysis ......................................................................................... 27 2.12 Cryogenic Vacuum Distillation: Literature Review ............................................. 28 2.13 Cryogenic Vacuum Distillation Methods ............................................................. 33 Chapter 3. Results ............................................................................................................. 39 3.1 Establishing Cryogenic Vacuum Distillation Methods........................................... 39 3.2 Extraction Results of Standard Soil Samples.......................................................... 40 3.3 Climate Conditions in Ohio 2018 ........................................................................... 41 3.4 Soil Physical Properties .......................................................................................... 42 3.5 Soil Water Characteristics....................................................................................... 43 3.6 Analysis of Sample Contamination: ChemCorrectTM ............................................. 48 3.7 Soil Water and Precipitation Water Isotopic Composition ..................................... 51 3.8 Xylem Isotopic Compositions and Modeling Soil Water Proportion with IsoSource ....................................................................................................................................... 56 Chapter 4. Discussion ....................................................................................................... 64 4.1 Cryogenic Vacuum Distillation Methods Development ......................................... 64 4.2 Cryogenic Vacuum Distillation: Sample Water Extraction .................................... 66 4.3 Soil Water Characteristics in the Soil Profile ......................................................... 67 4.4 Insight from the Composition of Groundwater, Tile Water and Stream Water ...... 70 4.5 Soil Water Isotopic Composition ............................................................................ 71 4.6 Modeled Xylem Isotopic Compositions and Expected Outcomes ......................... 75 4.7 Soil Water Source Proportion Scenarios................................................................. 77 Chapter 5. Future Work .................................................................................................... 79 Chapter 6. Conclusion ....................................................................................................... 81 Work Cited ........................................................................................................................ 83 Appendix A. Soil Water Source Proportion Scenarios ..................................................... 90 Appendix B. Cryogenic Vacuum Distillation Standards .................................................. 94 vi List of Tables Table 1. 2018 Ohio Climate Conditions: Monthly precipitation totals, percent of annual precipitation, temperature and relative humidity for 2018. Mean monthly precipitation totals for 2014-2018. ........................................................................................................
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