University of New Mexico UNM Digital Repository Earth and Planetary Sciences ETDs Electronic Theses and Dissertations 12-1-2014 Continental-scale isotope hydrology Scott aJ sechko Follow this and additional works at: https://digitalrepository.unm.edu/eps_etds Recommended Citation Jasechko, Scott. C" ontinental-scale isotope hydrology." (2014). https://digitalrepository.unm.edu/eps_etds/40 This Dissertation is brought to you for free and open access by the Electronic Theses and Dissertations at UNM Digital Repository. It has been accepted for inclusion in Earth and Planetary Sciences ETDs by an authorized administrator of UNM Digital Repository. For more information, please contact [email protected]. Scott Jasechko Candidate Earth and Planetary Sciences Department This dissertation is approved, and it is acceptable in quality and form for publication: Approved by the Dissertation Committee: Dr. Zachary D. Sharp , Co-chairperson Dr. Peter J. Fawcett , Co-chairperson Dr. Joseph Galewsky Dr. Juske Horita CONTINENTAL-SCALE ISOTOPE HYDROLOGY by SCOTT ALLAN JASECHKO B.Sc., University of Victoria, 2009 M.Sc. University of Waterloo, 2011 DISSERTATION Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Earth and Planetary Sciences The University of New Mexico Albuquerque, New Mexico December, 2014 DEDICATION To Jennifer, Gordon, Glenn and Edith – for your love and your encouragement. iii ACKNOWLEDGMENTS I am grateful to Zachary Sharp, Peter Fawcett and Joseph Galewsky for supporting, challenging and guiding me throughout my Ph.D. education. I am thankful for my friends and mentors who continue to grant me the joy of belonging in a community. iv CONTINENTAL-SCALE ISOTOPE HYDROLOGY By Scott Jasechko B.Sc., Physical Geography and Earth and Ocean Sciences, University of Victoria, 2009 M.Sc., Earth and Environmental Sciences, University of Waterloo, 2011 Ph.D., Earth and Planetary Sciences, University of New Mexico, 2014 ABSTRACT Providing sustainable sources of fresh water for a growing population of 7 billion people is one of the grand challenges of the 21st century. This dissertation outlines several applications of isotope hydrology to address four previously unknown questions involving surface- and ground-water resources at regional- to continental-spatial scales over contemporary- to millennial-temporal scales. The four chapters in this dissertation investigate (1) the rate of plant transpiration, (2) the seasonality of groundwater recharge, (3) the climate of the last ice age, and (4) the chemistry of Ugandan waters. (1) Chapter one presents a new global compilation of lake water isotopic data, river isotopic data, stand-level transpiration rates, and water use efficiency measurements, and analyzes the newly synthesized data to show that plant transpiration is the largest water flux from Earth’s continents, exceeding both physical evaporation and continental runoff. (2) Chapter two presents a new global synthesis of rain, snow and groundwater isotopic compositions, and analyzes the paired v precipitation-groundwater dataset to show that the percentage of precipitation that recharges aquifers is at a maximum during the winter (extra-tropics) and wet (tropics) seasons. (3) Chapter three presents a new global compilation of groundwater radiocarbon, tritium, and stable O and H isotopic data, and maps the isotopic shift of meteoric waters since the last ice age. The analysis shows that the majority (~90%) of precipitation during the last ice age had lower 18O/16O and 2H/1H ratios than the modern day, except in some exclusively coastal locations. We also show that current isotope-enabled general circulation models capture some, but not all, spatial variability in ice-age-to-late-Holocene 18O/16O and 2H/1H shifts, providing a new calibration tool that can be used to improve our understanding of glacial climate dynamics. (4) Chapter four presents isotopic and chemical analyses of Ugandan lake, river, rain, and ground water collected during a field expedition led in July of 2013. Analysis of this new dataset reveals new estimates of lake water balances across Uganda. vi TABLE OF CONTENTS DEDICATION .................................................................................................................................................. iii ACKNOWLEDGMENTS ............................................................................................................................... iv ABSTRACT .......................................................................................................................................................... v TABLE OF CONTENTS ............................................................................................................................... vii PREFACE............................................................................................................................................................. 1 CHAPTER 1 — GLOBAL PLANT TRANSPIRATION FLUXES ........................................................ 9 1.1 Abstract ...................................................................................................................................................... 9 1.2 Introduction ............................................................................................................................................... 9 1.3 Dataset and methods .............................................................................................................................. 32 1.4 Results ....................................................................................................................................................... 54 1.5 Discussion ................................................................................................................................................ 61 1.6 References ................................................................................................................................................ 63 CHAPTER 2 — THE SEASONALITY OF GLOBAL GROUNDWATER RECHARGE ............ 83 2.1 Abstract .................................................................................................................................................... 83 2.2 Introduction ............................................................................................................................................. 83 2.3 Dataset and methods .............................................................................................................................. 88 2.4 Results ..................................................................................................................................................... 101 2.5 Discussion .............................................................................................................................................. 106 2.6 References .............................................................................................................................................. 121 CHAPTER 3 — THE ISOTOPIC COMPOSITION OF ICE AGE GROUNDWATERS ........... 142 3.1 Abstract .................................................................................................................................................. 142 3.2 Introduction ........................................................................................................................................... 143 3.3 Dataset and Methods............................................................................................................................ 148 3.4 Results ..................................................................................................................................................... 151 3.5 Discussion .............................................................................................................................................. 164 3.6 References .............................................................................................................................................. 188 CHAPTER 4 — THE ISOTOPE HYDROLOGY OF UGANDA ..................................................... 212 4.1 Abstract .................................................................................................................................................. 212 4.2 Introduction ........................................................................................................................................... 212 4.3 Dataset and methods ............................................................................................................................ 214 4.4 Results ..................................................................................................................................................... 217 4.5 Discussion .............................................................................................................................................. 231 4.6 References .............................................................................................................................................. 241 vii List of Figures 1-1. Schematic of fresh water fluxes ............................................................................................................... 10 1-2. Schematic of plant transpiration .............................................................................................................. 12 1-3. Water yields before and after the clearing of vegetation