A SPATIO-TEMPORAL COMPARISON OF NUTRIENT DEFICIENCY INDICATORS IN LAKE ERIE A thesis submitted to Kent State University in partial fulfillment of the requirements for the degree of Master of Science By Leigh A. Martin May 2013 i Thesis written by Leigh A. Martin B.A., Skidmore College, 2007 M.S., Kent State University, 2013 Approved by: Dr. Darren Bade___________________________________, Advisor Dr. Laura Leff_____________________________________, Acting Chair, Department of Biological Sciences Dr. Raymond Craig_________________________________, Associate Dean, College of Arts and Sciences ii TABLE OF CONTENTS LIST OF FIGURES…………………………………………………………….…………v LIST OF TABLES………………………………………………………………….…….vi ACKNOWLEDGEMENTS……………………………………………………………...vii OBJECTIVES OF THE STUDY……………………………………….…………………1 CHAPTER 1: Introduction Study Background …….……………………………………………………………..……2 Study Site………………………………………………………………………………….7 Conclusions………………………………………………………………………………10 References………………………………………………………………………………..11 CHAPTER 2: A Nearshore-Offshore Comparison of Phosphorus Deficiency Indicators in Lake Erie Abstract…………………………………………………………………………………..14 Introduction...……………………………………………………………………………14 Methods………………………………………………………………………………….18 Results……………………………………………………………………………...…….22 Phosphorus Debt………………………………………………………………....22 Phosphorus Turnover Time……………………………………………………....24 Alkaline Phosphatase Activity…………………………………………………...27 Linear Regression Results………………………………………………………..30 Chl a, TP, and SRP………………………………………………………………31 Discussion………………………………………………………………………………..32 Conclusions………………………………………………………………………………37 Acknowledgements……………………………………………………………………....38 References………………………………………………………………………………..38 CHAPTER 3: Seasonal Shifts of Nutrient Deficiency in Lake Erie Abstract………………………………..…………………………………………………43 Introduction ……………………………………………………………………………...43 Methods…………………………………………………………………………………..46 Results……………………………………………………………………………………52 Phosphorus Debt…………………………………………………………………52 Phosphorus Turnover Time………………………………………………………54 Alkaline Phosphatase Activity…………………………………………………...56 Ammonium Enhancement Response………………………………………….…58 iii Nitrogen Debt ………………………………………………………………...…61 Chl a and Nutrient Concentrations………………………………………………64 Discussion………………………………………………………………………………..65 Considerations and Conclusions………………………………………………………....69 Acknowledgments……………………………………………………………………….71 References……………………………………………………………………………….72 APPENDICES…………………………………………………………………………..76 iv LIST OF FIGURES 1. Simplified diagram of phosphorus flow dynamics before and after the dreissenid mussel invasion, as asserted by the nearshore phosphorus shunt hypothesis…......6 2. Sample transect locations in Lake Erie………………………………………...….9 3. Phosphorus debt along Lake Erie transects in 2011 and 2012…………………...23 4. Phosphorus turnover times along Lake Erie transects in 2011 and 2012………..25 5. Alkaline phosphatase activity along Lake Erie transects in 2011 and 2012……..28 6. P debt values along transects in spring and fall of 2012…………………………53 7. Phosphorus turnover times along eight transects in Lake Erie in spring and fall of 2012………………………………………………………………………..……..55 8. Alkaline phosphatase concentrations along eight transects in Lake Erie in spring and fall of 2012…………………………………………………………………..57 9. Ammonium enhancement response ratios for Lake Erie transects in spring and fall of 2012…………………………………………………………………………...59 10. N debt values for Lake Erie transects in June and August 2012………………...62 v LIST OF TABLES 1. Algal phosphorus limitation values and deficiency thresholds…………………………19 2. Arithmetic mean Chl a and nutrient concentrations by season and basin……….32 3. Algal nutrient limitation values and deficiency thresholds…………………………..…48 vi ACKNOWLEDGEMENTS First and foremost I would like to thank my advisor, Dr. Darren Bade, whose insight and expertise on freshwater lake dynamics were invaluable when I was framing my research questions and ultimately when trying to make sense of my findings. Thanks are also owed to my committee members, Dr. Xiaozhen Mou and Dr. Ferenc de Szalay, for their feedback and encouragement. I am incredibly grateful to Heather Kirkpatrick Smith and Curtis Clevinger for showing me the ropes in the lab and for their assistance in processing samples during our impossibly busy sampling periods. Thanks are also in order for fellow graduate students Anna Ormiston, Margaret Gaglione, Ryan Schoeneman and Sumeda Madhuri for their help. Thanks also to Shunya Yagi and Cory Gargas, two dedicated undergraduate students whose assistance over the summer was instrumental to the success of the project. The scope of this project was honestly greater than I ever could have anticipated and I am proud to have played even a small part in it. Enough cannot be said for the hard work of the Great Lakes Restoration Initiative and our collaborative partners from Buffalo State College, Case Western University, the University of Toledo, and Heidelberg University. Thanks also to Dr. Jacques Finlay from the University of Minnesota for his assistance with refining our nitrogen debt protocol. vii I would also like to thank Donna Warner in the Department of Biological Sciences office and Robin Wise and Jennifer Kipp in the stockroom, who have always been incredibly patient in answering my multitude of questions. Last, but certainly not least, I would like to thank my husband Michael for his ongoing encouragement and understanding during this endeavor. Thank you for believing in me. viii 1 OBJECTIVES OF THE STUDY The main objective of this study was to obtain a better understanding of the nutrient dynamics affecting algal growth in Lake Erie’s photic zone. To achieve this goal, a series of physiological nutrient deficiency bioassays was conducted on water samples from Lake Erie during the growing seasons of 2011 and 2012. The study has been organized into three chapters, which are described briefly below. CHAPTER 1: Introduction. Because Chapters 2 and 3 will be written in the format of articles to be submitted for publication, this chapter will serve to provide background information for the two nutrient deficiency studies conducted during the 2011 and 2012 growing seasons in Lake Erie, as well as present a summary of our conclusions. CHAPTER 2: A Nearshore-Offshore Comparison of Phosphorus Deficiency Indicators in Lake Erie. This chapter describes the data obtained from our two years of P deficiency research in Lake Erie and how they relate to the hypothesis that limitation by P should increase with depth as a result of the dreissenid mussel invasion. CHAPTER 3: Seasonal Shifts of Nutrient Deficiency in Lake Erie. In continuance of Chapter 2, this chapter further explores nutrient deficiency in Lake Erie with the addition of bioassays in 2012 that determined whether or not nitrogen deficiency is a contributing factor to restricting primary productivity in the lake. 1 2 CHAPTER ONE: INTRODUCTION Study Background When nutrients accumulate in excess in an aquatic system, phytoplankton are released from their usual growth constraints and experience an increase in primary productivity. This process of eutrophication has long been an issue of concern throughout the Laurentian Great Lakes, particularly in Lake Erie. While eutrophication occurs naturally through sedimentation over time, it can be significantly accelerated by an influx of nutrients stemming from anthropogenic sources, such as agricultural and wastewater runoff. Lake Erie, the shallowest of the Great Lakes, is largely surrounded by agricultural and urban development. The impacts of eutrophication on the Lake Erie ecosystem have been substantial, and include the loss of vascular plants and periphytic phytoplankton, fish kills resulting from anoxic conditions, and potential health risks to humans from toxins produced by harmful algae blooms (Correll 1998, de Jonge et al. 2002; Smith and Schindler 2007). It is believed that degradation of the Lake Erie’s water quality began as early as the 1830s when the construction of the Erie Canal was completed. Population growth and the sudden increase in agricultural and industrial usage in the watershed supplied the lake with an excess of nutrients, which gradually accumulated and increased primary productivity. The issue started to receive national attention in the 1960s when algal blooms began appearing regularly in the lake and massive fish kills began to threaten the lake’s fisheries (Mortimer 1987; Lu et al. 2010). In response to public concerns, the 2 3 Great Lakes Water Quality Agreement between the United States and Canada established annual target loads for total phosphorus (TP) in each of the lakes beginning in 1972 (Schindler 1974; Robertson and Saad 2011; Schwab et al. 2009). The management scheme defined in Great Lakes Water Quality Control Agreement was based largely on data obtained from the Experimental Lakes Area (ELA) in Canada. The ELA served as the location for whole ecosystem experiments that tested hypotheses concerning eutrophication management in freshwater lakes (Schindler 1990). The ELA’s whole ecosystem manipulations held what was arguably a distinct advantage over bottle assays in that the experiments were subject to the same nutrient cycling and natural processes as the ecosystems they were theoretically mimicking (Wang and Wang 2009). Prior to the research conducted in the ELA there had been little consensus in limnology about which nutrients were limiting to algal growth in eutrophic lakes, although commercial interests were actively promoting the idea of carbon (C)