QUANTIFYING HYDROLOGIC INTERACTIONS IN TUOLUMNE MEADOWS __________________ A University Thesis Presented to the Faculty of California State University, East Bay __________________ In Partial Fulfillment of the Requirements for the Degree Master of Science in Geology __________________ By Marcelino J. Vialpando III March, 2018 ABSTRACT High elevation meadows in the Sierra Nevada of California, USA represent mixing zones between surface water and groundwater. Quantifying exchanges between stream water and groundwater, and the residence time of water stored in meadow sediments allows for examination of a possible buffer effect groundwater has on meadows and streams during droughts and as climate change alters recharge conditions. Unraveling the complex hydrologic dynamics associated with these basins and quantifying input components is crucial for identifying sensitive influences on contributions to and from these alpine resources. This in turn has implications for the resilience of the ecosystems as well as the downstream communities that are dependent upon runoff for water supply. Using interdisciplinary methods, this study applied multiple tracers, geochemical signals, and isotopic signatures to investigate the age, source, and evolution of groundwater discharge within the meadow. Chloride concentrations, which were found to be distinct between late season surface water and groundwater, were used to identify end member mixing components. 3H and 35S data provided estimates of mean water residence times, which were generally found to be less than two years for meadow groundwater and much longer for the deep system hosted by fractured bedrock. Analyzing the high fidelity geochemical signal from deep bedrock sources, fractured flow contributions were calculated. The severe drought conditions in California at the time of sampling allowed for the quantification of deep fractured bedrock flow contribution, which was found to be a small percentage (<2%), and would otherwise be unlikely to have been calculated under normal hydrologic conditions. Radon analysis combined with ii stream gauge data were used to identify segments of the river where water was gained or lost, including groundwater inflow ‘hot spots’ that coincide with stream geomorphic features. Seasonal variations were noted by comparing results from samples collected in Fall 2014 and Summer 2015, and remarkably similar patterns suggest that stream morphology, rather than hydrologic conditions dictate surface water-groundwater exchange. The comprehensive examination of hydrologic properties involved in this study confirmed the high level of exchange between river water and groundwater taking place within the meadow. Using two component mixing analysis, >50% of the total flow exiting the meadow was revealed to be sourced from groundwater. Further, assessing the nature of the groundwater and surface water components indicated that very recent recharge dominates the groundwater and seasonal precipitation moves through the system at a rapid rate. iii iv ACKNOWLEDGMENTS I would like to express my deep gratitude and great appreciation to Dr. Jean Moran. I cannot express enough thanks for the seemingly endless patience she possessed during the journey of completing this thesis. Her invaluable technical support and advise, along with the supervisors and mentors at LLNL, allowed me to pursue this research and gain experience which otherwise would have been beyond my grasp. I received much generosity in the form of time, encouragement, and advise from Dr. Ate Visser and Dr. Brad Esser whose mentorships played an integral role in this research. I am particularly grateful for their assistance along with Dr. Stephanie Uriostegui; the extensive laboratory instruction, learning opportunities, and technical experience provided to me is irreplaceable. A special thanks goes out to Amanda Lee Deinhart along with the NSF RAPID program; the aid provided by both, though very different, were equally vital in supporting this study. I dedicate this thesis to my mother Loretta Vialpando, I am eternally grateful for your boundless love and emotional support. v TABLE OF CONTENTS ABSTRACT…………………………………………………………………....................ii ACKNOWLEDGEMENTS……………………………………………….........................v LIST OF FIGURES……………………………………………………….......................vii LIST OF TABLES………………………………………………………………...............x INTRODUCTION………………………………………………………………………...1 BACKGROUND………………………………………………….………......................10 Site description…….……………………………………………………..............10 History………….…………………………………………….…………..............13 Climate………….…………………………………………….………….............18 Hydrology……………………………………………….……………………….20 Water Quality and Diversions……………………………….…………………...24 Geology……………………………………………………....…………..............26 Topography………………………………………………….…………………...31 Seismicity and Faulting…………………………………………………………..34 METHODS………………………………………………………………………............35 Field Methods……………………………...…………………………….............35 Lab and Analysis Methods………………………...…………………….............41 SAMPLING LOCATIONS AND ID’S………………………………………………….49 RESULTS AND DISCUSSION…………………………………………………………54 Radon…………………………………………………………………………….54 Stable Isotopes…………………………………………………………………...59 Anions……………………………………………………………………………66 Mixing……………………………………………………………………………72 Contribution from Deep Fracture Flow………………...………………………..79 CONCLUSION…………………………………………………………………………..81 REFERENCES…………………………………………………………………………..83 vi LIST OF FIGURES Figure 1 Photo of Tuolumne River in Tuolumne Meadows…………..…….……...2 Figure 2 Yosemite Map……………………………………………….……...……..3 Figure 3 Hydrograph of Tuolumne River…………………………….……...……...6 Figure 4 Monitoring well locations…………………………………….…...………7 Figure 5 Tuolumne River tributaries within the meadow…………....…….......….11 Figure 6 Hetch Hetchy Project………………………………………………...…..12 Figure 7 Tuolumne Meadows cross section…………………………………....….13 Figure 8 Historic sheep grazing photo………………………………....……….....14 Figure 9 Vegetation of east Tuolumne Meadows....................................................16 Figure 10 Photo of channel widening………………………………………..……...18 Figure 11 Average monthly temperatures of Tuolumne Meadows…………..……..19 Figure 12 Average monthly precipitation of Tuolumne Meadows…………….…...19 Figure 13 Yearly hydrographs of Tuolumne River flow at Tuolumne Meadows a 2014………………………………………………………………………20 b 2015…………………………………………………………….………...21 c 2016……………………………………………………………....………21 d 2017……………………………………………………………….....…...22 Figure 14 Monitoring well transects in Tuolumne Meadows ...................................23 Figure 15 Tuolumne River water diversions…………………..……………………25 Figure 16 Tuolumne Intrusive Suite plutonic emplacement….…………….………27 Figure 17 Photo Cathedral Peak Granodiorite….…………………………………..28 vii Figure 18 Photo Johnson Granite Porphyry……………………….………………..29 Figure 19 Geologic map of Tuolumne Meadows………..………………………….30 Figure 20 Topography of Tuolumne Meadows……..………………………………32 Figure 21 Primary sample locations along Tuolumne River…………..……………36 Figure 22 River discharge measurement method………..………………………….39 Figure 23 Helium isotope sampling apparatus……......…………………………….41 Figure 24 Radon volatilization along a stream…………..………………………….43 Figure 25 Evolution of stable isotopes of water in precipitation……….…………..45 Figure 26 August 2013 sampling locations…………………………………………50 Figure 27 November 2013 sampling locations……………………………………...51 Figure 28 October 2014 sampling locations………………………………………...52 Figure 29 June 2015 sampling locations……………………………………………53 Figure 30 Graph of radon concentrations…………………………………………...54 Figure 31 Graph of 18O vs. distance………………………………………………...60 Figure 32 Graph of 2H vs. distance…………………………………...…………….61 Figure 33 Graph 18O vs. 2H for October 2014………..……………………………..63 Figure 34 Graph 18O vs. 2H for June 2015…………………………….……………64 Figure 35 Graph 18O vs. 2H for river samples October 2014………………….……65 Figure 36 Graph 18O vs. 2H for river samples June 2015………..………………….66 Figure 37 Graph Chloride by sample location ID……….………………………….69 Figure 38 Graph Chloride vs. Sulfate………………..……………………………...70 Figure 39 Graph Sulfate by sample location ID…………………..………………...72 viii Figure 40 Graph of percent groundwater influx along the Tuolumne River..............75 ix LIST OF TABLES Table 1 Sample location information, August and November 2013…...…………37 Table 2 Sample location information, October 2014 and June 2015…..…………38 Table 3 Radon concentrations (pCi/L)..…………………………………………..55 Table 4 Concentrations of stable isotopes of water (‰)………………...…..……62 Table 5 Chloride concentrations (mg/L)……………………………..………..….67 Table 6 Sulfate concentrations (mg/L)…………………………...……….………68 Table 7 Stream flow measurements (cfs)……………………...………...………..76 Table 8 35S concentrations (mBq/L)………………..……………………….……77 Table 9 Age calculation comparison using Tritium and 35S………………….…..77 Table 10 Tritium concentrations (pCi/L)…………………………………….…….78 x 1 INTRODUCTION The biological integrity of Tuolumne Meadows is sustained by the Tuolumne River [FIGURE 1] and, when combined with tributary areas of Dana Meadows and Lyell Fork, comprises one of the most extensive Sierra complexes of riparian habitats and subalpine meadows (Cooper et al., 2006; NPS, 2014; SFPUC, 2007; SFPUC, 2008). These meadows house a great diversity of species and highly productive plant life (Naiman, Bunn, Nilsson, Petts, Pinay & Thompson, 2002; Ratliff, 1985; Verner & Boss, 1980). This scientifically important refuge, being located in a designated wilderness [FIGURE 2], has some protection for the ecological