EFFECTS OF FLOW ALTERATION ON THE AQUATIC MACROPHYTE PODOSTEMUM CERATOPHYLLUM (RIVERWEED); LOCAL RECOVERY POTENTIAL AND REGIONAL MONITORING STRATEGY by JENNIFER P. PAHL (Under the Direction of C. Ronald Carroll) ABSTRACT A survey of Podostemum ceratophyllum Michx. biomass and recovery rates was conducted in the Middle Oconee River, Athens, GA over a one-year time period under altered hydrology and severe drought. Biomass was found to be an order of magnitude lower than reported by previous studies conducted in non-drought years. An information-theoretic (AIC) modeling approach found variation in biomass within the study site to be related in part to variation in duration of low flow events. Recovery rates in the Middle Oconee River as well as Hunnicutt Creek, a tributary, were similar among sites and under varying hydrologic regimes. Re-colonization from vegetative growth seemed most prominent, and little support was found for seed dispersal as a major mechanism or recovery. Regionally, P. ceratophyllum range is likely expansive, and the impact of hydrologic alteration may be equally as widespread. Future monitoring could be accomplished through existing programs, focusing in basins where P. ceratophyllum is present and flow modification is prevalent. INDEX WORDS: Podostemum ceratophyllum, hydrologic alteration, drought, Middle Oconee River, re-colonization, monitoring EFFECTS OF FLOW ALTERATION ON THE AQUATIC MACROPHYTE PODOSTEMUM CERATOPHYLLUM (RIVERWEED); LOCAL RECOVERY POTENTIAL AND REGIONAL MONITORING STRATEGY by JENNIFER P. PAHL B.S., The University of Vermont, 2005 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GA 2009 © 2009 Jennifer Plourde Pahl All Rights Reserved EFFECTS OF FLOW ALTERATION ON THE AQUATIC MACROPHYTE PODOSTEMUM CERATOPHYLLUM; LOCAL RECOVERY POTENTIAL AND REGIONAL MONITORING STRATEGY by JENNIFER P. PAHL Major Professor: C. Ronald Carroll Committee: Mary Freeman Catherine Pringle Amy Rosemond Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia May 2009 ACKNOWLEDGEMENTS First I would like to thank my major advisor, Dr. Ron Carroll for his endless support. While I struggled to find my footing amidst an infinitely large field of study, Ron was always there to ground me in the tangible but remind me to think big picture. I would also like to thank my committee members, Dr. Amy Rosemond and Dr. Catherine Pringle for their encouragement and expertise in field and lab methods. The work they have done has served as a foundation for my education in the field of stream ecology. I want to specially thank my fourth committee member, Dr. Mary Freeman. Mary’s dedication to this work was immeasurable and her approach profoundly shaped my view of scientific research. Thank you Mary! Of course, none of this work would have been possible without the collaboration of Rachel Katz. Rachel is a wonderful friend and colleague; this partnership enabled me to achieve and learn more than possible on my own. I thank her for pushing me to perform better science and immerse myself in the professional world. I would like to acknowledge the financial support of the Upper Altamaha Grant (# 271 GRAM 63B/ 1031RE271419) as well as Dr. Mary Freeman of the U.S. Geological Survey. Mr. Jeff Knight (Athens-Clarke County), Kevin Williams (Bear Creek Reservoir) and Brian McCallum (USGS) provided valuable hydrologic data. Thank you to Christina Baker, Nicole Pontzer, Tyler Kartzinel and Mathew Carroll of the University of Georgia, James Plourde of Purdue University, and Ryan Pahl for providing field assistance. Thanks also to the River Basin Center for fostering an environment of learning and camaraderie. Finally, I would like to extend a special thank you to my family; my husband Ryan, my parents Daniel and Joanne Plourde, my brother James and my grandparents Ken and Ellie Wall and Fern and Rita Plourde; your support, patience and encouragement has been amazing! iv TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ......................................................................................................................... iv LIST OF TABLES ...................................................................................................................................... vii LIST OF FIGURES ................................................................................................................................... viii LIST OF IMAGES ....................................................................................................................................... ix CHAPTER 1. INTRODUCTION ................................................................................................................................... 1 2. HIGH RESOLUTION ASSESSMENT OF ENVIRONMENTAL FACTORS THAT INFLUENCE BIOMASS OF PODOSTEMUM CERATOPHYLLUM (RIVERWEED) IN A SIXTH-ORDER PIEDMONT RIVER ..................................................................................................................................... 6 ABSTRACT ......................................................................................................................................... 6 INTRODUCTION ................................................................................................................................ 7 METHODS .......................................................................................................................................... 9 RESULTS .......................................................................................................................................... 17 DISCUSSION .................................................................................................................................... 19 3. RECOVERY AND RE-COLONIZATION POTENTIAL FOR PODOSTEMUM CERATOPHYLLUM (RIVERWEED) IN A SOUTHEASTERN PIEDMONT RIVER .......................... 23 ABSTRACT ....................................................................................................................................... 23 INTRODUCTION .............................................................................................................................. 24 METHODS ........................................................................................................................................ 26 RESULTS .......................................................................................................................................... 33 DISCUSSION .................................................................................................................................... 36 v 4. MONITORING PRIORITY FOR PODOSTEMUM CERATOPHYLLUM, (RIVERWEED), IN MAJOR BASINS ABOVE THE FALL LINE IN GEORGIA, USA ......................................................... 39 ABSTRACT ....................................................................................................................................... 39 INTRODUCTION .............................................................................................................................. 40 METHODS ........................................................................................................................................ 41 RESULTS .......................................................................................................................................... 43 DISCUSSION .................................................................................................................................... 44 5. CONCLUSIONS .................................................................................................................................... 48 REFERENCES ........................................................................................................................................... 50 APPENDIX A: RAW DATA: RIVERWEED BIOMASS AND OTHER VARIABLES ........................ 119 vi LIST OF TABLES Page Table 2.1: Characteristic sections of the cross-sectional transect. .............................................................. 56 Table 2.2: Comparison of annual mean P. ceratophyllum biomass between three decades. ...................... 57 Table 2.3: AIC analysis of the top five of 32 covariate models. ................................................................. 58 Table 2.4: AIC analysis of 25 models. ........................................................................................................ 58 Table 2.5: A comparison of the total weight of relative support for each parameter. ................................. 60 Table 2.6: Top AIC model parameter estimates. ........................................................................................ 61 Table 2.7: Hydrology effect scenarios. ...................................................................................................... 62 Table 3.1: Middle Oconee River block annual comparisons. ..................................................................... 63 Table 3.2: Middle Oconee River and Hunnicutt Creek comparisons. ........................................................ 64 Table 3.3: Middle Oconee River growing season block comparisons. ....................................................... 65 Table 3.4: Middle Oconee River and Hunnicutt Creek growing season comparisons. .............................. 66 Table 4.1: Hydrologic alteration by major Georgia river basin. ................................................................