Effects of wildfire on mercury, organic matter, and sulfur in soils and sediments By Jackson Paul Webster B.S., University of Nevada, 2008 M.S., University of Nevada, 2010 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Civil, Environmental, and Architectural Engineering 2015 This thesis entitled: Effects of wildfire on mercury, organic matter, and sulfur in soils and sediments written by Jackson Paul Webster has been approved for the Department of Civil, Environmental, and Architectural Engineering Joseph N. Ryan, committee chair George R. Aiken Diane M. McKnight Fernando L. Rosario-Ortiz Jeffrey H. Writer Date The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. Abstract Webster, Jackson P. (Ph.D., Civil, Environmental, and Architectural Engineering) Effects of wildfire on mercury, organic matter, and sulfur in soils and sediments Thesis directed by Joseph N. Ryan The transport and deposition of mercury from natural and anthropogenic sources has led to its enrichment in surficial soils on a global scale. In arid climates, such as the western United States, the common occurrence of wildfire mobilizes accumulated mercury. In addition to atmospheric re- emission, wildfire enhances the transport of mercury from forest soils to the sediments of lakes and reservoirs through increased watershed runoff and soil destabilization. Little information is reported on the fate mercury in waters affected by wildfire. To address the knowledge deficit, multiple studies were conducted throughout forested watersheds of Colorado, United States, subjected to historical and recent wildfire to characterize mercury, organic matter, and sulfur oxidation state in soils and sediment. Simulated wildfire heating of soil was conducted using a muffle furnace to observe the influence of heat on sulfur oxidation. Batch experiments were conducted on soils to assess aqueous mercury release from burned, unburned, and laboratory heated soils. To examine the sulfur speciation and mercury behavior following ash-laden sediment deposition in a reservoir, reservoir cores containing these sediments were obtained and analyzed. Additionally, redox transitions occurring during sediment deposition were simulated using microcosms. To measure how oxidizing (heating) and reducing (reservoir deposition) conditions influence sulfur speciation, X-ray absorbance near-edge structure (XANES) spectroscopy was employed. Changes in mercury binding capacity were quantified using a competitive ligand exchange method. In Mesa Verde National Park, it was found that soils affected by historical wildfires contained about 50 % less organic matter and mercury than unburned soils collected adjacent to the burned samples, which corresponded to mercury release of 19 ± 8.2 g ha-1. In aqueous release experiments from historically burned soils, there was half the amount of carbon and mercury as unburned soils. In contrast, laboratory heating increased the release of organic matter and major ions from soils. Mercury release was linked to organic matter release, though losses from volatilization during heating reduced the total release into solution. Soil subjected to heating contained more oxidized sulfur species and concomitant losses of intermediate oxidation state species, while sulfur oxidation states in ash-laden sediments shifted toward reduced forms following deposition in a reservoir. Laboratory experiments simulating each of these shifts resulted in increased mercury binding capacity. Following heating a 1.5-fold increase in strong mercury binding sites was measured. Following simulated reservoir deposition, there was a 10-fold increase in the number of strong binding sites in the ash-laden sediments. Overall, this study characterizes the underlying processes influencing mercury behavior in soils and sediments following wildfire. iii Acknowledgements First and foremost, I would like to thank Joseph Ryan and George Aiken. It has been a pleasure to have been advised by both and I am very thankful for the inspiration, advice, and support they have given me in this process. I greatly appreciate the participation of my committee members; Diane McKnight, Fernando Rosario-Ortiz, and Jeffrey Writer, all of whom have contributed to this effort and my experience at University of Colorado, Boulder beyond this committee as well. There are many co-authors in these chapters and I thank all of them for their contributions and help: Kathryn Nagy, Alain Manceau, Erika Callagon, Brett Poulin, Chris Peltz, Benjamin Kamark, Genevieve Nano, David Vine, and Tyler Kane. I would like to thank Kenna Butler for her leadership in the Aiken lab. Many people have contributed there professional expertise and time to various aspects of this project and I would like to acknowledge Deborah Martin with the U.S. Geological Survey, Jill Oropeza with City of Fort Collin’s Utilities, John McCutchan with City of Greeley Utilities, George San Miguel with Mesa Verde National Park, and Marcie Bidwell with Mountain Studies Institute. I thank all of the current and former Joe Ryan Lab Group: Jessica Dehart Rogers, Chase Gerbig, Sanjay Mohanty, Tim Dietrich, and Alison Craven for their contributions to my experience. I would like to also thank all of the undergrads who have helped over the years: Doug Winter, Crystal Kelly, Chelsea Ottendfeldt, Michelle Hummel, Steven Walton, and Tyler Doughty. I would like to thank my girlfriend Dorey Chaffee for being loving, patient, and supportive throughout this process. Finally, I would like to thank my parents Sue Jackson and Jim Webster, who are always my best teachers and advisors. Thank you both for your love and support. This dissertation was partially funded by the Department of Civil, Environmental, and Architectural Engineering of the University of Colorado Boulder through the Dissertation Completion Fellowship. iv Table of Contents Chapter 1: An Introduction to the Potential Influence of Wildfire on the Fate and Transport of Mercury…………………………………………………………………………………………………………………………………..…1 Chapter 2: Effect of Fire on the Mercury in Soils in Pinion-Juniper Woodland of Mesa Verde National Park Abstract ..................................................................................................................................... 13 Introduction............................................................................................................................... 14 Methods .................................................................................................................................... 16 Results ....................................................................................................................................... 22 Discussion .................................................................................................................................. 31 Chapter 3: Simulated Wildfire Heating of Forest Soil Increases Mercury Affinity and Alters Sulfur Speciation Abstract ..................................................................................................................................... 37 Introduction............................................................................................................................... 38 Methods .................................................................................................................................... 40 Results ....................................................................................................................................... 48 Discussion .................................................................................................................................. 59 Chapter 4: Characterization of Mercury, Sulfur, and Organic Matter in Ash-Laden Stream Bank and Reservoir Sediments Abstract ..................................................................................................................................... 66 Introduction............................................................................................................................... 67 Methods .................................................................................................................................... 70 Results ....................................................................................................................................... 77 Discussion………………………………………………………………………………………………………………………………………….85 v Chapter 5: Mercury Affinity for Ash-Laden Sediment Increases Following Simulated Reservoir Deposition Abstract ..................................................................................................................................... 92 Introduction............................................................................................................................... 93 Methods ................................................................................................................................... .96 Results ..................................................................................................................................... 102 Discussion ................................................................................................................................ 108 Chapter 6: Summary