ABSTRACT Understanding Key Factors Influencing Habitat Quality for the Endangered Fountain Darter (Etheostoma fonticola) in the Comal River Kelsey S. Biles, M.S. Mentor: Robert D. Doyle, Ph.D. The research in this thesis was divided into 3 main studies that took place in Landa Lake: water column, sediment, and plant nutrient analyses, an herbivory and soil fertility experiment, and a spatial study of diel dissolved oxygen dynamics. Nutrient data were collected via water samples, nutrient diffusing substrata (NDS), sediment cores, and plant samples. The water samples and NDS results indicated a severe phosphorus limitation in the water column and some macrophyte species may be limited by phosphorus as well. Herbivory in Landa Lake, particularly by crayfish, appears to be much more severe than previously thought and increased soil fertility exacerbates the issue in Ludwigia repens. Diel dissolved oxygen varied across the lake, largely correlated with flow conditions. During drought, there may be several areas of the lake where DO is low enough to threaten fountain darter survival, but there is little cause for concern under current conditions. Understanding Key Factors Influencing Habitat Quality for the Endangered Fountain Darter (Etheostoma fonticola) in the Comal River by Kelsey S. Biles, B.S. A Thesis Approved by the Department of Biology Dwayne D. Simmons, Ph.D., Chairperson Submitted to the Graduate Faculty of Baylor University in Partial Fulfillment of the Requirements for the Degree of Master of Science Approved by the Thesis Committee Robert D. Doyle, Ph.D., Chairperson Darrell S. Vodopich, Ph.D. Joe C. Yelderman, Ph.D. Accepted by the Graduate School May 2017 J. Larry Lyon, Ph.D., Dean Page bearing signatures is kept on file in the Graduate School. Copyright © 2017 by Kelsey S. Biles All rights reserved TABLE OF CONTENTS LIST OF FIGURES ........................................................................................................... vi LIST OF TABLES ........................................................................................................... viii ACKNOWLEDGMENTS ................................................................................................. ix CHAPTER ONE ................................................................................................................. 1 Introduction ..................................................................................................................... 1 Comal River ................................................................................................................. 1 Importance of Macrophytes to Fountain Darters ................................................... 3 Crayfish and Fountain Darters ............................................................................... 7 Dissolved Oxygen Dynamics ................................................................................... 9 Restoration of River Systems ..................................................................................... 11 Herbivory and Soil Fertility .................................................................................. 15 Proposed Experiments ............................................................................................... 20 CHAPTER TWO .............................................................................................................. 22 Nutrient Assessment in Landa Lake.............................................................................. 22 Nutrients in the Water Column .................................................................................. 22 Methods ................................................................................................................. 23 Results ................................................................................................................... 28 Discussion ............................................................................................................. 35 Sediment and Macrophyte Tissues Nutrient Survey in Landa Lake .......................... 39 Methods ................................................................................................................. 39 Results ................................................................................................................... 42 Discussion ............................................................................................................. 46 CHAPTER THREE .......................................................................................................... 50 Herbivory by Fertility Interaction in situ ...................................................................... 50 Methods ................................................................................................................. 51 Results ................................................................................................................... 58 Discussion ............................................................................................................. 65 iv CHAPTER FOUR ............................................................................................................. 71 Dissolved Oxygen Dynamics of Landa Lake ................................................................ 71 Methods ................................................................................................................. 72 Results ................................................................................................................... 80 Discussion ............................................................................................................. 89 CHAPTER FIVE .............................................................................................................. 94 Research Summary ........................................................................................................ 94 APPENDIX A ................................................................................................................. 100 Additional Nutrient Diffusing Substrata Figures ........................................................ 100 APPENDIX B ................................................................................................................. 101 Additional Herbivory by Fertility Experiment Figures ............................................... 101 APPENDIX C ................................................................................................................. 105 Additional Dissolved Oxygen Figures ........................................................................ 105 References ....................................................................................................................... 109 v LIST OF FIGURES Figure 1. Density of fountain darters collected by vegetation type .....................................5 Figure 2. Map of NDS deployment locations in Landa Lake and Upper Spring Run .......25 Figure 3. Relative Chl-a at each location in the first NDS experiment ............................30 Figure 4. Mean relative Chl-a from each treatment in the first NDS experiment .............31 Figure 5. Micrograms of Chl-a per centimeter squared on the fritted disk for the second NDS deployment for all 5 treatments and both deployment types ..................33 Figure 6. Mean relative Chl-a from each treatment in the second NDS experiment .........33 Figure 7. Mean micrograms of Chl-a per centimeter squared from each treatment in the second NDS experiment.........................................................................................34 Figure 8. Mean micrograms of Chl-a per centimeter squared from each NDS location and deployment type in the second NDS experiment ..................................................34 Figure 9. Location of the vegetation and sediment core samples from June 8, 2016 ........40 Figure 10. Visual representation of variation in N:P ratios across and within species ......45 Figure 11. Two-by-two factorial design used in the herbivory by fertility experiment ....51 Figure 12. Depiction of exclosure cages used in the herbivory by fertility experiment ....53 Figure 13. Mean biomass of the total plant tissue of the 20 “reject” plants ......................58 Figure 14. Mean biomass of the total plant tissue of the 12 “initials” plants ....................60 Figure 15. Mean ratio of above-ground plant tissue biomass to below-ground of the 12 “initials” plants.............................................................................................................61 Figure 16. Percent survival by day of the plants in the H+ treatment ...............................61 Figure 17. Mean biomass of the total plant tissue of the 16 experimental plants ..............64 Figure 18. Mean ratio of above-ground plant tissue biomass to below-ground of the 16 experimental plants ......................................................................................................64 vi Figure 19. Locations of the 14 MiniDOT sensors during the initial short-term study ......74 Figure 20. Long-term deployment locations of MiniDOT sensors....................................79 Figure 21. Maximum and minimum dissolved oxygen results from the 14 MiniDOT sensors used during the short-term spatial evaluation study ........................................81 Figure 22. Maximum and minimum dissolved oxygen levels from MiniDOT sensors during long-term deployment at 13 locations ..............................................................83