EFFECT OF FRESHWATER INFLOW ON MACROBENTHOS PRODUCTIVITY AND NITROGEN LOSSES IN TEXAS ESTUARIES Paul A. Montagna, Principal Investigator TWDB Contract No. 2000-483-323 Technical Report Number TR/00-03 November 2000 FINAL REPORT EFFECT OF FRESHWATER INFLOW ON MACROBENT-HOS PRODUCTIVITY AND NITROGEN LOSSES IN TEXAS ESTUARIES by Paul A. Montagna, Principal Investigator from University of Texas at Austin Marine Science Institute 750 Channelview Drive Port Aransas, Texas 78373 to Texas Water Development Board P.O. Box 13231, Capital Station 1700 N. Congress Ave., Rm. 462 Austin, TX 78711-3231 Interagency Cooperative Contract TWDB Contract No. 2000-483-323 The University of Texas Marine Science Institute Technical Report Number TR/00-03 November 2000 TABLE OF CONTENTS LIST OF FIGURES . n LIST OF TABLES ............................................................ iv PREFACE ................................................................... v ACKNOWLEDGMENTS ...................................................... vi INTRODUCTION ............................................................. 1 METHODS .................................................................. 2 Study Design and Area .................................................... 2 Hydrographic Measurements ............................................... 3 Geological Measurements ................................................. 4 Biological Measurements .................................................. 4 Sediment Nitrogen Measurements ........................................... 4 RESULTS ................................................................... 6 Hydrographic Data ....................................................... 6 Macrofauna! Abundance and Biomass ...................................... 21 Macrofauna! Community Structure ......................................... 31 Nitrogen Losses in East Matagorda Bay ..................................... 64 DISCUSSION ............................................................... 71 CONCLUSION .............................................................. 73 REFERENCES .............................................................. 74 REVIEW LETTER FROM TWDB ............................................... 75 LIST OF FIGURES Figure I. Map of the Guadalupe and Lavaca-Colorado Estuaries ........................ 3 Figure 2. Mixing diagram of nutrient concentrations along the salinity gradient for stations in Guadalupe Estuary ....................................................... 8 Figure 3. Mixing diagram of nutrient concentrations along the salinity gradient foNtations in Lavaca-Colorado Estuary .................................................. 9 Figure 4. Salinity at stations in the Guadalupe Estuary over time ....................... 13 Figure 5. Salinity at stations in the Lavaca-Colorado Estuary over time ................... 14 Figure 6. Dissolved Oxygen at stations in the Guadalupe Estuary over time ............... 15 Figure 7. Dissolved Oxygen at stations in the Lavaca-Colorado Estuary over time .......... 16 Figure 8. Long-term salinity change in the Lavaca-Colorado and Guadalupe Estuaries ...... 17 Figure 9. Long-term DO change in the Lavaca-Colorado and Guadalupe Estuaries ......... 18 Figure 10. Long-term DIN and salinity change in the Guadalupe Estuary ................. 19 Figure 11. Long-term DIN and salinity change in the Lavaca-Colorado Estuary ............ 20 Figure 12. Abundance over time at stations in the Guadalupe Estuary ................... 22 Figure 13. Biomass over time at stations in the Guadalupe Estuary ...................... 23 Figure 14. Abundance over time at stations in the Lavaca-Colorado Estuary .............. 24 Figure 15. Biomass over time at stations in the Lavaca-Colorado Estuary ................ 25 Figure 16. Long-term trend in abundance, biomass and salinity in the Guadalupe Estuary .... 26 Figure 17. Long-term trend in abundance, biomass and salinity in the Lavaca-Colorado Estuary ..................................................................... 27 Figure 18. Salinity and organismal relationships in the Guadalupe Estuary (data from Fig. 16) ..................................................................... 28 Figure 19. Salinity and organismal relationships in Lavaca-Colorado Estuary (data from Fig. 17) ..................................................................... 29 Figure 20. Comparison of estuarine-wide abundance and biomass over the long term ....... 30 Figure 21. Loading vectors from a principal components analysis of dominant species in the Guadalupe Estuary ...................................................... 58 Figure 22A. Scores for dates and stations from a principal components analysis of dominant species in the Guadalupe Estuary ........................................... 59 Figure 22B. Scores for seasons and period types from a principal components analysis of dominant species in the Guadalupe Estuary ................................... 60 Figure 23. Loading vectors from a principal components analysis of dominant species in the Lavaca-Colorado Estuary ................................................. 61 Figure 24A. Scores for dates and stations from a principal components analysis of dominant species in the Lavaca-Colorado Estuary ..................................... 62 11 Figure 24B. Scores for seasons and period types from a principal components analysis of dominant species in the Lavaca-Colorado Estuary ............................. 63 Figure 25. Nitrogen content of East Matagorda Bay sediments ......................... 67 Figure 26. Carbon content of East Matagorda Bay sediments .......................... 68 Figure 27. Average nitrogen and carbon content in East Matagorda Bay sediments ......... 69 Figure 28. Profile of nitrogen (o 15 N) isotope values in East Matagorda Bay sediments ...... 70 Figure 29. Profile of carbon (o 13C) isotope values in East Matagorda Bay sediments ....... 71 Figure 30. Average of nitrogen (o 15N)and carbon (o 13C)isotope values in East Matagorda Bay sediments ............................................................. 72 Ill LIST OF TABLES Table 1. Locations are given in degrees and decimal seconds format. Readings were made with a GPS unit ............................................................... 5 Table 2. Hydrographic characteristics at stations in two estuaries. Average over all dates and depths, except depth which is bottom ...............................,., ......... 7 Table 3. Hydrographic characteristics in two estuaries. Average over all dates, stations, and depths, except depth which is bottom ....................................... 10 Table 4. Monthly average salinity (psu), temperature CC), and dissolved oxygen (DO) (mg/1) for bottom water over entire data set ........................................... 12 Table 6. Guadalupe Estuary macrofauna species list ................................. 32 Table 7. Guadalupe Estuary macrofauna dominance list .............................. 39 Table 8. Lavaca-Colorado Estuary macrofauna species list ............................ 43 2 Table 9. Lavaca-Colorado Estuary macrofauna dominance list. Average abundance (n m ) and percent composition over all samples ....................................... 52 Table 10. Codes for Figures 22 and 24 ............................................ 64 IV PREFACE The current contract is a continuation of a long-term study with the goal to determine the importance of freshwater inflow in maintaining benthic productivity in two Texas estuaries. Previous work has been performed with support, or partial support, by the Texas Water Development Board, Water Research Planning Fund, authorized under the Texas Wftter Code sections 15.402 and 16.058(e). This support was administered by the Board under interagency cooperative contract numbers: (1986-87) 0757, 8-483-607, 9-483-705,90-483-706,91-483-787, 92-483-300,93-483-352,94-483-003,95-483-068,96-483-132,97-483-199,98-483-233,99- 483-267, and most recently 2000-483-323. This is a final interpretive report. Data is added to the time series based on previous reports, and the whole time series is reported so that year-to-year comparisons can be made. The report has two main sections: a synthesis of data collected over the entire study period, and appendices with data on biological, hydrographical, and sediment data on nitrogen losses compiled over the entire study period. v ACKNOWLEDGMENTS I must acknowledge the significant contributions of Mr. Rick Kalke. Rick began the first sampling study of Lavaca Bay in 1984. He is an outstanding field person and taxonomist. The work reported on in this study could not have been performed without him. Carrol Simanek also provided significant help in data management. We obviously are collecting and processing a large amount of data. Input, proof-reading and maintenance of this large data set is a daunting task that Carrol handles very well. Dr. Steve Jarvis, Mr. Robert Burgess, Mr. Chris Kalke aided in field collections. This work has also benefitted by discussions with colleagues at the Texas Water Development Board (TWDB), e.g., William Longley (who retired), David Brock, and Gary Powell who have provided much help and guidance. The Texas estuarine research reported here has been supplemented by many other projects. The most interesting trend is that we have moved from monitoring and evaluating freshwater inflows to using diverted, restored, or returned inflows to enhance and restore wetland areas of estuaries. Two such projects are currently under