IN SITU OPTICAL SENSORS FOR MEASURING NITRATE IN FLORIDA WATERS By ALEXANDRA GUIBORD ROZIN UNIVERSITY OF FLORIDA 2014 © 2014 Alexandra Guibord Rozin ACKNOWLEDGMENTS I would like to thank the many colleagues who made this work possible. The Clark Lab group has been influential in providing feedback and talking me through decisions. Thank you to my advisor, Dr. Clark, for being supportive in all of my endeavors. My committee members, Drs. Ramesh Reddy, Matt Cohen, and Paul Monaghan, have each helped me understand concepts and provided support. Many thanks to the Analytical Research Laboratory at the University of Florida for teaching me about analyzing nitrate in the lab and answering my endless questions. The operators at the GRU Main Street Wastewater Treatment Plant had a large role in making this work possible – allowing me to use their laboratory space and instruments, helping me troubleshoot mechanical failures, and asking me great questions that kept me on my toes. Finally, I thank RJ Sindelar, for his willingness to act as field assistant even when I insist on pre-dawn departures, his guidance in the lab with procedures and instrumentation, and his tireless advice as someone who has been through all this before. 3 TABLE OF CONTENTS ACKNOWLEDGMENTS ................................................................................................... 3   LIST OF TABLES ............................................................................................................. 6   LIST OF FIGURES ........................................................................................................... 7   LIST OF ABBREVIATIONS .............................................................................................. 8   CHAPTER 1 BACKGROUND AND OBJECTIVES ......................................................................... 9   Nitrate in the environment .......................................................................................... 9   Optical nitrate sensors ............................................................................................. 10 Objectives and hypotheses ...................................................................................... 12   2 COMPARISION OF WET CHEMICAL LABORATORY AND IN SITU OPTICAL METHODOLOGY FOR THE MEASUREMENT OF NITRATE ................................ 17   Introduction .............................................................................................................. 17   Materials and methods ............................................................................................. 19 Study sites ............................................................................................................ 19   Field analyses ....................................................................................................... 20   Laboratory analyses ............................................................................................. 22   Statistical analyses ............................................................................................... 22   Results and discussion ............................................................................................ 22 First experiment .................................................................................................... 23   Second experiment ............................................................................................... 25   Conclusions ............................................................................................................. 26 3 EFFECT OF PATH LENGTH LENGTH ON OPTICAL INTERFERENCE ............... 34   Introduction .............................................................................................................. 34   Materials and methods ............................................................................................. 36 Turbidity ................................................................................................................ 36   Colored dissolved organic matter ......................................................................... 36   Nitrate spikes ........................................................................................................ 37   Results and discussion ............................................................................................ 37   Conclusions ............................................................................................................. 39   4 CONCLUSIONS AND RECOMMENDATIONS ........................................................ 47   APPENDIX 4 A CHAPTER 3 SUPPLEMENTARY TABLES ............................................................. 49   LIST OF REFERENCES ................................................................................................ 76   BIOGRAPHICAL SKETCH ............................................................................................. 78   5 LIST OF TABLES Table 1-1 SUNA Specifications for a 10mm path length instrument 16 2-1 Experiment 1 p-Values for paired method comparisons 31 2-2 Experiment 2 p-Values for paired method comparisons 32 2-3 Statistical significance of methods using Tukey test 33 3-1 Experimental design of interfering constituents and nitrate spikes 40 3-2 Summary statistics for interference from turbidity 41 3-3 Summary statistics for interference from natural organic matter 42 6 LIST OF FIGURES Figure 1-1 Conceptual diagram of attenuation in an optical nitrate sensor 14 1-2 Submersible Ultraviolet Nitrate Analyzer (SUNA) by Satlantic, Inc. 15 2-1 Study sites in North Central Florida 28 2-2 Comparison of method accuracy for Experiment 1 29 2-3 Comparison of method accuracy for Experiment 2 30 3-1 Distribution of error for 5mm path length SUNA measuring turbidity 43 interference from suspended kaolinite 3-2 Distribution of error for 10mm path length SUNA measuring turbidity 44 interference from suspended kaolinite 3-3 Distribution of error for 5mm path length SUNA measuring 45 Suwannee River Natural Organic Matter interference 3-4 Distribution of error for 10mm path length SUNA measuring 46 Suwannee River Natural Organic Matter interference 7 LIST OF ABBREVIATIONS ARL Analytical Research Laboratory CDOM Colored dissolved organic matter EPA Environmental Protection Agency N Nitrogen SUNA Submersible Ultraviolet Nitrate Analyzer SUNA V2 Submersible Ultraviolet Nitrate Analyzer Version 2 UV Ultraviolet WBL Wetland Biogeochemistry Laboratory 8 CHAPTER 1 BACKGROUND AND OBJECTIVES Nitrate in the environment Similar to all systems on earth, the health of aquatic systems depend on a delicate balance between available energy and elements. The concept of ecological stoichiometry is defined by the specific ratio of essential elements in ecological systems (Frost et al., 2005). All systems operate with a specific ratio of carbon-to-nitrogen-to- phosphorus when in balance; when the stoichiometric ratio changes, the system becomes unbalanced. A critical concern in aquatic systems is changes in nutrient stoichiometry causing nutrient limitation or nutrient enrichment. A nutrient (predominately nitrogen and phosphorus) is limiting in a system when the amount of that nutrient limits primary productivity (Liebig, 1855), leading to direct and indirect effects on ecosystem health and stability. Nutrient enrichment of the limiting element increases productivity, upsetting the balance between biological and chemical components and shifting ecosystem structure and function. The resulting eutrophication of aquatic systems can have drastic and long- lasting impacts on water quality, biogeochemical cycling, and community composition (Smith et al., 1999; Smith and Schindler, 2009). Eutrophication of surface waters can cause increased growth of algal biomass, decreased water clarity, decreased macrophyte vegetation, reduced species diversity, and depletion of dissolved oxygen (Smith, 2003). These visible effects of nutrient enrichment can abruptly and catastrophically shift species composition and ecosystem function (Smith and Schindler, 2009). Growing concerns about the declining health of aquatic systems have prompted 9 the development of novel methods for water quality analysis. Improved methods are needed for the detection and prediction of nutrient impairment before there are long- term effects. Instead of analyzing the stoichiometry of a single spatial and / or temporal point as traditional water sampling methods are designed, scientists are looking to increase the spatial and temporal resolution when monitoring nutrients to obtain an ecosystem scale perspective. Finding the solution to complex environmental problems is reliant on understanding time-dependent dynamics of nutrients in aquatic systems. By monitoring nutrient loads at a fixed temporal scale, discrete sampling methods are potentially missing short-term event or seasonal trends in biogeochemical transformations and nutrient export. Flow from storm events totaling less than 20% of the time is estimated to be responsible for 80% of nutrient export from certain watersheds (Dalzell et al., 2007). To understand nitrate dynamics at the same temporal scale in which environmental conditions change, more sophisticated instruments are needed to report data at a rate equal to or greater than the rate of change. Higher resolution data can lead to improved interpretations about short-term processes affecting aquatic systems and improved management decisions to stimulate ecosystem health. Optical nitrate sensors Used for decades in wastewater monitoring (Rieger et al., 2008) and oceanographic applications (Johnson and Coletti, 2002), optical nitrate sensors have only recently been developed for use in freshwater aquatic systems (Pellerin et al., 2013). This current generation of optical nitrate sensors for freshwater systems arose from the initial design of Dr. Kenneth Johnson and Mr. Luke Coletti at the Monterey Bay 10