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Elemental Cycling in a Flow-Through Lake in the Mcmurdo Dry Valleys, Antarctica

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Elemental Cycling in a Flow-Through Lake in the Mcmurdo Dry Valleys, Antarctica Elemental Cycling in a Flow-Through Lake in the McMurdo Dry Valleys, Antarctica: Lake Miers THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Alexandria Corinne Fair Graduate Program in Earth Sciences The Ohio State University 2014 Master’s Examination Committee: Dr. W. Berry Lyons, Advisor Dr. Anne E. Carey Dr. Yu-Ping Chin Copyright by Alexandria Corinne Fair 2014 ABSTRACT The ice-free area in Antarctica known as the McMurdo Dry Valleys has been monitored biologically, meteorologically, hydrologically, and geochemically continuously since the onset of the MCM-LTER in 1993. This area contains a functioning ecosystem living in an extremely delicate environment. Only a few degrees of difference in air temperature can effect on the hydrologic system, making it a prime area to study ongoing climate change. The unique hydrology of Lake Miers, i.e. its flow- through nature, makes it an ideal candidate to study the mass balance of a McMurdo Dry Valley lake because both input and output concentrations can be analyzed. This study seeks to understand the physical and geochemical hydrology of Lake Miers relative to other MCMDV lakes. Samples were collected from the two inflowing streams, the outflowing stream, and the lake itself at 11 depths to analyze a suite of major cations (Li+, + + + 2+ - - - 2- - - Na , K , Mg , Ca ), major anions (Cl , Br , F , SO4 , ΣCO2), nutrients (NO2 , NO3 , + 3- NH4 , PO4 , Si), trace elements (Mo, Rb, Sr, Ba, U, V, Cu, As), water isotopes (δD, δ18O), and dissolved organic carbon (DOC). The lake acts as a sink for all constituents + - 3- analyzed, but by amounts varying from ~10% (DOC, NH4 , and NO2 ) to PO4 at nearly 100%, indicating this lake may be P-limited. Cl-, a typically conservative element, was only 79% retained, which could be due to the late season sample collection, hyperheic zone influences, or other factors. The hyperheic zone’s role in lake and stream ii geochemistry was analyzed with a 24-hour sampling event. The positive relationships between stream flow and solute concentrations indicate that the delta in Miers Valley plays a role in controlling stream geochemistry and future work could help to explain this relationship. Lake depth profiles of trace elements U, V, Cu, and As decrease relative to Cl in the deepest part of the lake, while non-reducing trace elements show increases with 2- depth. SO4 and dissolved O2 lake depth profiles decrease from 53 μM and 22.3 mg/L to 18 μM and 1.8 mg/L, respectively, at depth, indicating that the lake bottom is under reducing and near anoxic conditions. Lake depth profiles show that, while the “biological pump” may be a factor controlling lake chemistry, it is masked by the stronger signal of diffusion from the lake bottom sediments and requires future work to understand fully. The “age” of Lake Miers was calculated with a diffusion model to be 84 years, which agrees with other estimates of 100-300 years. The diffusion of solutes from the lake bottom and the redox conditions at depth are two major processes controlling the geochemistry of Lake Miers, and future work can help determine their extent and relationship with other processes. iii ACKNOWLEDGMENTS I would like to thank a lot of people for their assistance in the completion of this document. The MCM-LTER Stream Team at University of Colorado, Boulder, including Devin Castendyk, Chris Jaros, and Adam Wlostowski, and the Limno group at Montana State University helped with sample collection and processing, and especially Chris Jaros and his help with stream discharge data. I would also like to thank Kelsey Bisson for staying up all night with me in the field, for analyzing DOCs and alkalinities, and for being a great support along the way. I am grateful to Holly Hughes at Kiowa Lab, UCB for running the nutrient samples. Dr. John Olesik, and especially Anthony Lutton, provided enormous help with analyzing my trace element samples. Thank you to Deb Leslie for her help with my isotope samples, and to Kelsey Dailey and Sue Welch for their help with my iron analysis. Thank you to Chris Gardner for your help with my computer-related questions. Thank you to Kathy Welch for your patience, advice, ion analysis, help with figures, answering all of my numerous questions, and for being someone who could always help with whatever problem I was facing. Thank you to my committee for you time and feedback. A huge thank you to my advisor, Dr. W. Berry Lyons, for being incredibly patient with me, and pushing me to get to this point. His knowledge and guidance have been critical to my graduate career. I would lastly like to thank the NSF grant ANT 1115245 for funding and PHI helicopters and ASC for logistical support during field work. iv VITA June 15, 1900 .................................................Born — Columbus, Ohio May 2012 .......................................................B.S. Anthropological Sciences and Chemistry, The Ohio State University August 2012 to present .................................Graduate Research and Teaching Associate, School of Earth Sciences, The Ohio State University Fields of Study Major Field: Earth Sciences. v Table of Contents ABSTRACT ........................................................................................................................ ii ACKNOWLEDGMENTS ................................................................................................. iv VITA ................................................................................................................................... v LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES ........................................................................................................... ix CHAPTER 1: INTRODUCTION ....................................................................................... 1 1.1 Rationale for Work ................................................................................................... 2 1.1.1 End-Member Example of MCM Lakes ............................................................. 2 1.1.2 Climate Change Impacts .................................................................................... 3 1.2 Flow-Through vs Closed-Basin ................................................................................ 4 1.2.1 Mass Balances .................................................................................................... 4 1.2.2 Test Bioreactor Hypothesis ................................................................................ 4 1.2.3 Future Scenarios for Closed-Basin Lakes .......................................................... 5 1.3 Objectives of Work ................................................................................................... 6 CHAPTER 2: STUDY AREA ............................................................................................ 7 2.1 Site Description ......................................................................................................... 7 2.1.1 Miers Valley....................................................................................................... 7 2.1.2 Summary of Previous Work on Lake Miers ...................................................... 8 CHAPTER 3: METHODS ................................................................................................ 14 3.1 Bottle Preparation ................................................................................................... 14 3.2 Sample Collection ................................................................................................... 15 3.2.1 Streams ............................................................................................................. 15 3.2.2 Lakes ................................................................................................................ 17 3.3 Methodology ........................................................................................................... 18 3.3.1 Major Ions and Alkalinity ................................................................................ 18 3.3.2 Nutrients and Silica .......................................................................................... 18 3.3.3 Trace Elements................................................................................................. 18 3.3.4 DOC ................................................................................................................. 19 3.3.5 Water Isotopes ................................................................................................. 20 vi 3.3.6 Precision and Accuracy.................................................................................... 20 3.4 Hydrologic Measurements ...................................................................................... 21 CHAPTER 4: RESULTS AND DISCUSSION ................................................................ 22 4.1 Streams .................................................................................................................... 22 4.1.1 Input ................................................................................................................. 23 4.1.2 Output .............................................................................................................. 24 4.1.3 Comparison to other MCM Streams ...............................................................
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