Analysis of Agricultural Nonpoint Source Runoff to Baffin Bay and Its Possible Effect on the Brown Tide Phytoplankton Bloom
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Analysis of Agricultural Nonpoint Source Runoff to Baffin Bay and its Possible Effect on the Brown Tide Phytoplankton Bloom CCBNEP Publication August 1999 Prepared by Edward J. Buskey, Ph.D., Dr. Kenneth H. Dunton, Ph.D., Dr. Paul A. Montagna, Ph.D. The University of Texas at Austin Marine Science Institute Dr. Dean A. Stockwell, Ph.D. The University of Alaska Institute of Marine Science Terry E. Whitledge, Ph.D. The University of Alaska Institute of Marine Science Submitted to: Coastal Bend Bays & Estuaries Program 1305 N. Shoreline Blvd. Ste 205 Corpus Christi, Texas 78401 The views expressed herein are those of the authors and do not necessarily reflect the views of CBBEP or other organizations that may have provided funding for this project. Analysis of Agricultural Nonpoint Source Runoff to Baffin Bay and its Possible Effect on the Brown Tide Phytoplankton Bloom TNRCC Interagency Cooperation Contract Contract Number: 62-000000-39 prepared by: University of Texas Marine Science Institute Analysis of Agricultural Nonpoint Source Runoff to Baffin Bay and its Possible Effect on the Brown Tide Phytoplankton Bloom Edited by: Paul A. Montagna Principal Investigators: (In Alphabetical Order) Edward J. Buskey, Ph.D. The University of Texas at Austin Marine Science Institute Dr. Kenneth H. Dunton, Ph.D. The University of Texas at Austin Marine Science Institute Dr. Paul A. Montagna, Ph.D. The University of Texas at Austin Marine Science Institute Dr. Dean A. Stockwell, Ph.D. The University of Alaska Institute of Marine Science Terry E. Whitledge, Ph.D. The University of Alaska Institute of Marine Science Publication CCBNEP- August 1999 TABLE OF CONTENTS LIST OF TABLES .......................................................... xiii LIST OF FIGURES .......................................................... xiv ACKNOWLEDGMENTS ..................................................... xv EXECUTIVE SUMMARY ......................................................1 1. INTRODUCTION ...........................................................5 1.1. Background .........................................................5 1.2. Objectives ..........................................................5 1.3. Approach...........................................................6 2. MATERIALS AND METHODS................................................8 2.1. Project Organization ..................................................8 2.2. Mesocosm Experiment on Agricultural Runoff . 8 2.2.1. Study Site...................................................8 2.2.2. Timing of Study and Collection of Agricultural Runoff Water . 9 2.2.3. Mesocosm Experimental Setup ..................................9 2.2.4. Analytical Measurements In Mesocosms . 11 2.3. Tracing Agricultual Runoff in Bay ......................................15 2.3.1. Collection Sites .............................................15 2.3.2. Stable Carbon and Nitrogen Measurements . 15 3. RESULTS ................................................................15 3.1. Mescosom Experiment ...............................................15 3.1.1. Hydrography................................................16 3.1.2. Nutrients...................................................17 3.1.3. Phytoplankton ..............................................18 3.1.4. Brown Tide ................................................42 3.1.5. Zooplankton ................................................42 3.1.6. Benthos ...................................................47 3.2. Tracers in Bay ......................................................55 4. DISCUSSION .............................................................59 4.1. Mesocosm Experiment ...............................................59 4.1.1. Plankton Processes...........................................59 4.1.2. Nutrient Amendment Studies...................................60 4.1.3. Benthic Processes............................................60 4.2. Tracers in Bay ......................................................62 4.3. Analysis of Effects of Cropland and Nonpoint Runoff on the Brown Tide Phytoplankton Bloom in Baffin Bay ..................................63 xi 5. CONCLUSIONS AND MANAGEMENT RECOMMENDATIONS . 64 6. REFERENCES ............................................................66 xii LIST OF TABLES Table 1. Setup of the runoff experiment in mesocosms. 11 Table 2. Macrofauna biomass (g m-2) and density (n m-2) . 48 Table 3. Macrofauna diversity ..................................................49 Table 4. Macrofauna species list.................................................49 Table 5. Meiofauna density (n core-1) .............................................49 Table 6. Meiofauna density differences among log transformed treatment means . 50 Table 7. Nematoda feeding groups ...............................................50 Table 8. *15N and *15C values of fauna collected in Baffin Bay in April 1996 and 1997 . 56 xiii LIST OF FIGURES Figure 1. Study area in Baffin Bay region...........................................7 Figure 2. Photographs of mesocosms .............................................10 Figure 3. Mixing model of nutrients in mesocosms at startup . 20 Figure 4. Salinity in mesocosms .................................................21 Figure 5. Temperature in mesocosms .............................................22 Figure 6. Dissolved oxygen in mesocosms.........................................23 Figure 7. pH in mesocosms.....................................................24 Figure 8. Secchi depth mesocosms ...............................................25 Figure 9. Nitrate in mesocosms..................................................26 Figure 10. Nitrite in mesocosms .................................................27 Figure 11. Ammonium in mesocosms ............................................28 Figure 12. DIN in mesocosms...................................................29 Figure 13. Silicate in mesocosms ................................................30 Figure 14. Phosphate in mesocosms ..............................................31 Figure 15. Chlorophyll in mesocosms ............................................32 Figure 16. Primary production in mesocosms.......................................33 Figure 17. Nutrient amendments 10 April 1997 . 36 Figure 18. Nutrient amendments 10 April time series . 37 Figure 19. Nutrient amendments 18 April 1997 . 38 Figure 20. Nutrient amendments 18 April 1997 time series . 39 Figure 21. Nutrient amendments 23 April 1997 . 40 Figure 22. Nutirent amendments 23 April 1997 time series . 41 Figure 23. Salinity, temperature, brown tide, and ciliate density in mesocosm 3 (24% dilution). .....................................................................43 Figure 24. Salinity, temperature, brown tide, and ciliate density in mesocosm 5 (46% dilution) .....................................................................44 Figure 25. Salinity, temperature, brown tide, and ciliate density in mesocosm 6 (46% dilution) .....................................................................45 Figure 26. Salinity, temperature, brown tide, and ciliate density outside of mesocosms . 46 Figure 27. Principal components analysis of macrofauna species data showing relationships among treatments .......................................................51 Figure 28. Principal components analysis of macrofauna species data showing relationships among species .........................................................52 Figure 29. Principal components analysis of meiofauna taxa data showing relationships among treatments.............................................................53 Figure 30. Principal components analysis of meiofauna taxa data showing relationships among taxa..................................................................54 Figure 31. Nitrogen isotope values (*15N) for taxa in Baffin Bay based on samples collected at all sites under dry conditions (April 1966) . 57 Figure 32. Comparison of nitrogen isotope(*15N) values for trophic groups during an extended dry period (April 1996) and following a runoff event (April 1997) . 58 xiv ACKNOWLEDGMENTS Many people played critical roles in helping to successfully complete this project. Dr. Bobby Eddleman, Texas A&M Agricultural Experiment Station, helped determine sampling locations and generally gave us advice on working on King Ranch. Hudson DeYoe, University of Texas- Pan American, was research program coordinator for the Corpus Christi Bay National Estuary Program and was instrumental in make this project a reality. The mesocosm experiment was set up with the help of Lynn Tinnin, Brian Wysor and Christopher Collumb. Hydrographic and nutrient studies were aided by Lynn Tinnin, who performed sampling and nutrient analyses in the laboratory. Zooplankton studies were performed by Brian Wysor and Christopher Collumb. The benthic studies were aided by several people. Rick Kalke performed the benthic sampling in the field and performed the macrofauna benthic laboratory analyses. Steve Jarvis analyzed meiofaunal samples. Jyotsna Sharma, University of Texas-San Antonio, identified the nematode feeding groups. Carrol Simanek organized and managaed benthic data. The final report was completed with help from many people. Susan Schonberg created the map of the study area. Carrol Simanek reformatted and prepared most of the figures in the report. xv EXECUTIVE SUMMARY There is a strong theoretical basis to predict that non-point agricultural runoff has a stimulating affect on phytoplankton