Louisiana State University LSU Digital Commons LSU Master's Theses Graduate School 2007 Environmental factors affecting the distribution of native and invasive aquatic plants in the Atchafalaya River Basin, Louisiana, U.S.A. Rachel Cathleen Walley Louisiana State University and Agricultural and Mechanical College, [email protected] Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_theses Part of the Environmental Sciences Commons Recommended Citation Walley, Rachel Cathleen, "Environmental factors affecting the distribution of native and invasive aquatic plants in the Atchafalaya River Basin, Louisiana, U.S.A." (2007). LSU Master's Theses. 2931. https://digitalcommons.lsu.edu/gradschool_theses/2931 This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master's Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected]. ENVIRONMENTAL FACTORS AFFECTING THE DISTRIBUTION OF NATIVE AND INVASIVE AQUATIC PLANTS IN THE ATCHAFALAYA RIVER BASIN, LOUISIANA, U.S.A. A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in The School of Renewable Natural Resources by Rachel C. Walley B.S., Louisiana State University, 2004 December 2007 ACKNOWLEDGEMENTS First of all, I thank my major professor, Dr. William E. Kelso for giving me this opportunity. I also thank Drs. D. Allen Rutherford and Megan LaPeyre for serving on my committee. I would also like to thank Jerry Lang, Adam Piehler, and Brian Heiman for all the sweaty field work they did for me. I thank the following persons who saved me from countless hours of grueling laboratory work: Lauren Hart, Robyn Sellers, Jenny Bodin, Alison Martin, and Rachel Smith. For their advice, I thank Jonathan Fisher, Thorpe Halloran, Aaron Podey, Jonathan West, and Jesse Bahm. I would also like to thank Dr. Robert Gambrell for all of his assistance and the use of his laboratory. Very special thanks to Dr. Michael D. Kaller for all of the encouragement and help with statistical analysis. And another special thanks to Deb Kelly for all the support, lunch breaks, and laboratory help. I would also like to thank Jefe, Gypsy, Guano, and Toulouse for never judging me and keeping a smile on my face through graduate school. Finally, I wish to thank my husband, Walley for all of his committed support, without him this would not have been possible, and the rest of my family for being there for me. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS .................................................................................................ii LIST OF TABLES ..............................................................................................................iv LIST OF FIGURES .............................................................................................................v ABSTRACT........................................................................................................................vi INTRODUCTION ...............................................................................................................1 METHODS Study Site .................................................................................................................8 Sampling and Laboratory Methods..........................................................................8 Statistical Methods.................................................................................................12 RESULTS Plant Collections ....................................................................................................15 Biomass Accumulation of Invasive Versus Native Macrophytes..........................21 Physicochemical Characteristics of Sampling Locations ......................................23 Physicochemical Associations with Native Macrophytes .....................................23 Physicochemical Associations with Invasive Macrophytes ..................................24 Macrophyte Associations .......................................................................................25 Differences between Vegetated and Non-vegetated Locations within Years........26 Year-to-year Changes in Plant Communities within a Location...........................27 DISCUSSION....................................................................................................................32 LITERATURE CITED......................................................................................................39 APPENDIX A: WATER QUALITY DATA.....................................................................47 APPENDIX B: SOIL QUALITY DATA ..........................................................................63 APPENDIX C: PERCENT PLANT COVERAGE DATA ...............................................69 APPENDIX D: DRY WEIGHTS OF SAMPLED PLANTS ..........................................102 VITA ................................................................................................................................106 iii LIST OF TABLES 1. Percent coverage of macrophytes for the four habitat types of the Atchafalaya River Basin in 2005 and 2006. .......................................................................................17 2. Linear equations used to estimate dry weight of plants (g) from percent coverage. ....19 3. Mean biomass of macrophytes for the four habitat types of the Atchafalaya River Basin in 2005 and 2006..........................................................................................20 4. Principal component analysis of aquatic macrophyte groups within quadrats sampled in 2005....................................................................................................................26 5. Principal component analysis of aquatic macrophyte groups within quadrats sampled in 2006....................................................................................................................27 iv LIST OF FIGURES 1. The Atchafalaya River Basin, Louisiana and study sites................................................9 2. Digital photograph of aquatic macrophytes taken within a 0.25 m2 floating PVC quadrat....................................................................................................................12 3. Atchafalaya River stages for 2005 and 2006 ................................................................13 4. Areal coverage – dry weight regressions (with 95% confidence intervals) for exotic Hydrilla verticillata and native Ceratophyllum demersum ...................................21 5. Areal coverage – dry weight regressions (with 95% confidence intervals) for exotic Eichhornia crassipes and native Limnobium spongia ...........................................22 6. Areal coverage – dry weight regressions (with 95% confidence intervals) for exotic Salvinia minima and native Lemna spp. ................................................................22 7. Canonical discriminant function analysis of the plant community data for each location in 2005 and 2006......................................................................................29 8. Canonical discriminant function analysis of the plant community with the 22 out of 103 locations sampled that had a distance greater than two units along the CDFA axis .........................................................................................................................30 9. Canonical discriminant function analysis of the physicochemical data for the 22 locations from the reduced model..........................................................................31 v ABSTRACT Over the last century, the aquatic macrophyte community of the Atchafalaya River Basin (ARB) has become increasingly dominated by invasive species. I used digital photography and GIS software to determine ARB macrophyte community composition by measuring percent cover of each plant species within five 0.25-m2 quadrats sampled from 108 sites in 2005 and 103 sites in 2006. Macrophyte community data and measurements of soil and water physicochemistry at each site were used to investigate environmental associations of the macrophytes inhabiting bayou, lake, excavated canal, and swamp habitats. Analyses indicated substantial differences in physicochemical conditions among habitats, but none of the 20 macrophyte species collected during the study exhibited consistent preferences for specific habitat types. Percent coverage of invasive plants was greater than native plants across all habitat types in both years, with invasive plant richness increasing in 2006 with the arrival of giant salvinia (Salvinia molesta). Common salvinia (Salvinia minima) appeared to have the greatest impact on the native plants, exhibiting inverse abundance relationships with six of fourteen species (43%). Comparisons of slopes from areal coverage – dry weight regressions based on macrophytes that were photographed, collected, and dried from quadrats sampled at 26 sites in 2006 suggested that invasive species accumulated more biomass per unit area than ecologically similar native taxa. In both years, terrestrial plants were observed in association with floating mats of other macrophyte species, apparently taking advantage of the mats as “terrestrial” substrate. Submerged plants exhibited few significant differences in abundance among the four habitats,