Assessing the Biological Condition of Florida Lakes: Development of the Lake Vegetation Index (LVI) Final Report Prepared for: Florida Department of Environmental Protection Twin Towers Office Building 2600 Blair Stone Road Tallahassee, FL 32399-2400 Leska S. Fore*, Russel Frydenborg**, Nijole Wellendorf**, Julie Espy**, Tom Frick**, David Whiting**, Joy Jackson**, and Jessica Patronis** * Statistical Design 136 NW 40th St. Seattle, WA 98107 ** Florida Department of Environmental Protection 2600 Blair Stone Rd. Tallahassee, FL 32399-2400 December, 2007 This project and the preparation of this report was funded by a Section 319 Nonpoint Source Management Program Implementation grant from the U.S. Environmental Protection Agency through an agreement with the Nonpoint Source Management Section of the Florida Department of Environmental Protection. The cost of the project was $54,600, which was provided entirely by the U.S. Environmental Protection Agency. ii TABLE OF CONTENTS Table of Contents.......................................................................................................................iii List of Tables .............................................................................................................................. v List of Figures............................................................................................................................ iv List of Appendices ..................................................................................................................... vi Acknowledgments..................................................................................................................... vii Foreword..................................................................................................................................viii Abstract....................................................................................................................................... 1 Introduction................................................................................................................................. 3 Methods....................................................................................................................................... 5 Study area................................................................................................................................ 5 Lake sampling......................................................................................................................... 6 Quantifying human disturbance.............................................................................................. 8 Metric development and testing............................................................................................ 11 Sensitive and tolerant taxa evaluation................................................................................... 14 Lake Vegetation Index (LVI) development and testing ....................................................... 15 Expectations for statistical correlation.................................................................................. 18 Results....................................................................................................................................... 20 Human disturbance gradient ................................................................................................. 20 Metric selection..................................................................................................................... 21 Sensitive and tolerant taxa .................................................................................................... 31 Evaluation of the Lake Vegetation Index (LVI)................................................................... 33 Correlation of LVI with human disturbance and natural features ................................... 34 Variability analysis of alternative lake sampling protocols ............................................. 35 Metric scoring for the LVI ................................................................................................ 40 Validation of the LVI with independent data .................................................................... 41 Description of outliers ...................................................................................................... 42 iii Comparison of spring and summer LVI values................................................................. 44 Discussion................................................................................................................................. 46 Human disturbance gradient ................................................................................................. 46 Biological indicators ............................................................................................................. 47 Statistical precision of the Lake Vegetation Index (LVI)..................................................... 48 Recommendations..................................................................................................................... 50 Conclusions............................................................................................................................... 53 References................................................................................................................................. 54 iv LIST OF TABLES Table 1. Scoring rules for HDG.....................................................................................................10 Table 2. Examples of LDI coefficient values ................................................................................11 Table 3. Coefficient of conservatism (CC) scoring criteria ..........................................................13 Table 4. Correlation for HDG and its component measures..........................................................20 Table 5. Comparison of water chemistry measures for porous and non-porous soils ...................21 Table 6. Candidate plant metrics and their correlation with HDG, WQ index, LDI, and habitat index...............................................................................................................................................23 Table 7. Plant taxa most frequently identified as dominant ..........................................................25 Table 8. Plant taxa that were significantly associated with low or high HDG ..............................32 Table 9. Correlation between LVI, measures of disturbance, and natural features.......................34 Table 10. Coefficients from multiple regression for LVI and its component metrics...................35 Table 11. Cumulative number of taxa for 12 lake sections ...........................................................36 Table 12. Variance estimates and number of detectable categories for LVI.................................37 Table 13. Correlation between LVI, its component metrics and HDG for different sampling methods..........................................................................................................................................39 Table 14. Correlation between LVI and measures of disturbance for different numbers of replicate LVI samples ....................................................................................................................40 Table 15. Metric scoring rules for LVI..........................................................................................41 Table 16. Correlation between LVI and measures of disturbance for the validation data set .......42 Table 17. Lakes with higher or lower LVI values than predicted by HDG...................................43 v LIST OF FIGURES Figure 1. Diagram showing 12 lake sampling sections ...................................................................7 Figure 2. Detail of lake section sampling methods..........................................................................8 Figure 3. LVI plant metrics plotted against HDG..........................................................................27 Figure 4. LVI plant metrics plotted against the WQ index............................................................28 Figure 5. LVI plant metrics plotted against the habitat index........................................................29 Figure 6. LVI plant metrics plotted against LDI............................................................................30 Figure 7. Plant CC value plotted against the average HDG for lakes in which taxon was found .33 Figure 8. Species accumulation curve for lake sections ................................................................36 Figure 9. Number of categories that LVI could detect for different sampling protocols ..............38 Figure 10. Distribution of LVI values............................................................................................39 Figure 11. LVI plotted against HDG for the validation data set....................................................42 Figure 12. LVI plotted against HDG with outliers indicated.........................................................43 Figure 13. LVI for repeat visits during spring and summer for 15 lake sites................................45 Figure 14. Diagram showing recommended lake sampling for LVI .............................................50 LIST OF APPENDICES Appendix 1. Aquatic plant attributes Appendix 2. EPA’s wetland plant attributes Appendix 3. Results of testing for tolerance and sensitivity