Assessment of Groundwater Input and Water Quality Changes Impacting Natural Vegetation in the Loxahatchee River and Floodplain Ecosystem, Florida By William H. Orem, Peter W. Swarzenski, Benjamin F. McPherson, Marion Hedgepath, Harry E. Lerch, Christopher Reich, Arturo E. Torres, Margo D. Corum, and Richard E. Roberts Open-File Report 2007-1304 U.S. Department of the Interior U.S. Geological Survey 1 U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia 20192 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Suggested citation: Orem, W., and others, 2007, Assessment of Groundwater Input and Water Quality Changes Impacting Natural Vegetation in the Loxahatchee River and Floodplain Ecosystem, Florida: U.S. Geological Survey Open-File Report 2007-1304. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. 2 Table of Contents Page List of Figures ..................................................................................................................................... 5 List of Tables...................................................................................................................................... 7 Conversion Factors ............................................................................................................................. 8 Abbreviations...................................................................................................................................... 9 Summary............................................................................................................................................. 10 I. Introduction ..................................................................................................................................... 12 I.A. Background.......................................................................................................................... 12 I.B. Objectives............................................................................................................................. 17 II. Retrospective.................................................................................................................................. 19 II.A. General................................................................................................................................ 19 II.B. Influence of Saltwater Intrusion on Freshwater Vegetation............................................... 19 II.C. Long-Term Patterns in Groundwater Levels and Rainfall................................................. 20 II.D. Long-term Patterns in Floodplain Vegetation.................................................................... 26 III. Study Area and Sampling............................................................................................................. 26 III.A. General Description........................................................................................................... 26 III.B. Loxahatchee River and Estuarine Sites............................................................................. 28 III.C. Loxahatchee River Floodplain Sites.................................................................................. 30 IV. Methods........................................................................................................................................ 41 IV.A. Groundwater Flux Measurements..................................................................................... 41 IV.B. Groundwater Flux Calculations........................................................................................ 42 IV.C. Analytical Methods for Chemical Species........................................................................ 43 IV.C.1. River and estuarine water column samples............................................................ 43 IV.C.2. Floodplain surface and pore water samples........................................................... 43 IV.C.3. Floodplain sediment samples................................................................................. 44 IV.D. Vegetation Analysis.................................................................................................. 46 V. Results............................................................................................................................................ 50 V.A. Loxahatchee River Water Column Chemical Measurements............................................ 50 V.A.1. General.................................................................................................................... 50 V.A.2. Trace elements and DOC......................................................................................... 54 V.A.3. Surface water Radium and Radon isotopes............................................................. 54 V.B. Loxahatchee River Floodplain Water Quality Measurements........................................... 59 V.B.1. General..................................................................................................................... 59 3 V.B.2. pH, alkalinity, and redox......................................................................................... 59 V.B.3. Conductivity, salinity, and total dissolved solids.................................................... 60 V.B.4. Chloride, fluoride, and bromide............................................................................... 62 V.B.5. Sulfate and sulfide....................................................................................................63 V.B.6. Nitrate, ammonium, and phosphate......................................................................... 66 V.B.7. Sodium, potassium, magnesium, and calcium......................................................... 68 V.C. Loxahatchee River Floodplain Sediment Chemistry.......................................................... 70 V.D. Floodplain Vegetation Communities.................................................................................. 71 VI. Discussion..................................................................................................................................... 79 VI.A. Loxahatchee River Geochemistry..................................................................................... 79 VI.A.1. General................................................................................................................... 79 VI.A.2. Biogeochemical estuarine trace element transport................................................. 79 VI.B. Groundwater Flux in Loxahatchee River.......................................................................... 84 VI.B.1. Ra-derived estuarine water mass ages.................................................................... 82 VI.B.2. Ra-derived submarine groundwater discharge models.......................................... 85 VI.B.3. Groundwater recharge estimates............................................................................ 87 VI.B.4. Electromagnetic seepage meter measurements...................................................... 88 VI.B.5. Surface water Rn-222 activities............................................................................. 88 VI.B.6. Subsurface streaming resistivity profiling measurements...................................... 89 VI.B.7. Groundwater-derived nutrient fluxes..................................................................... 89 VI.C. Water Chemistry – Loxahatchee River Floodplain........................................................... 92 VI.D. Sediment Geochemistry – Floodplain............................................................................... 94 VI.E. Water Quality and Vegetation Change in Floodplain....................................................... 94 VII. Conclusions................................................................................................................................. 97 VII.A. Groundwater and Chemical Flux..................................................................................... 97 VII.B. Floodplain Water Quality and Vegetation Change.......................................................... 97 Acknowledgments............................................................................................................................... 99 References Cited................................................................................................................................. 99 Appendix A – Loxahatchee River Floodplain Water Chemistry Tables Appendix B - Loxahatchee River Floodplain Water Chemistry Figures Appendix C – Loxahatchee River Floodplain Soil/Sediment Tables Appendix D - Loxahatchee River Floodplain Soil/Sediment Chemistry Figures Appendix E - Loxahatchee River Floodplain Forest Types 4 List of Figures in Text Fig. 1. Map showing the location of the Loxahatchee River in south Florida (top), and satellite image of the Loxahatchee River, its tributaries, and the