Impacts of Droughts and Low Flows on Estuarine Health and Productivity Paul A. Montagna, Ph.D. Terry Palmer, M.S. Texas A&M University – Corpus Christi Harte Research Institute for Gulf of Mexico Studies 6300 Ocean Drive, Unit 5869 Corpus Christi, Texas 78412 Interagency Contract 1100011150 Report Submitted to the Texas Water Development Board Austin, Texas October 2012 Cite as: Montagna, P.A. and T. Palmer. 2012. Impacts of Droughts and Low Flows on Estuarine Health and Productivity. Final Report to the Texas Water Development Board, Project for Interagency Agreement 1100011150. Harte Research Institute, Texas A&M University-Corpus Christi, Corpus Christi, Texas. 142 pp. TABLE OF CONTENTS TABLE OF CONTENTS ................................................................................................................. i LIST OF TABLES ......................................................................................................................... iii LIST OF FIGURES ........................................................................................................................ v ABSTRACT ................................................................................................................................... ix INTRODUCTION .......................................................................................................................... 1 STUDY AREA ............................................................................................................................... 2 ESTUARINE DATA ACQUISITION ........................................................................................... 2 METHODS - ANALYSIS ONE - HYDROLOGY ........................................................................ 3 Defining Droughts ....................................................................................................................... 3 Changes in Estuarine Water Quality ........................................................................................... 4 Changes in Macrofauna Communities ........................................................................................ 4 Identification of Vulnerable Species ........................................................................................... 5 Presence / Absence of Marine Species ........................................................................................ 5 Changes in Epifaunal (Trawl-Collected) Communities .............................................................. 5 METHODS - ANALYSIS TWO - SALINITY .............................................................................. 6 Defining Droughts ....................................................................................................................... 6 Changes in Estuarine Water Quality ........................................................................................... 6 Changes in Macrofauna Communities ........................................................................................ 6 Identification of Vulnerable Species ........................................................................................... 7 Presence / Absence of Marine Species ........................................................................................ 7 Changes in Epifaunal (Trawl-Collected) Communities .............................................................. 7 METHODS - VERIFICATION OF DROUGHT DEFINITIONS ................................................. 8 RESULTS – ANALYSIS ONE - HYDROLOGY.......................................................................... 9 Macroinfauna .............................................................................................................................. 9 Epifauna .................................................................................................................................... 13 RESULTS – ANALYSIS TWO - SALINITY.............................................................................. 15 Drought Definition .................................................................................................................... 15 Changes in Estuarine Water Quality ......................................................................................... 15 i Changes in Macrofauna Communities ...................................................................................... 18 Identification of Vulnerable Species ......................................................................................... 19 Presence / Absence of Marine Species ...................................................................................... 19 Changes in Epifaunal (Trawl-Collected) Communities ............................................................ 20 RESULTS - VERIFICATION OF DROUGHT DEFINITIONs .................................................. 22 Method One ............................................................................................................................... 23 Method Two .............................................................................................................................. 23 DISCUSSION ............................................................................................................................... 24 Comparison of the Two Drought Definitions ........................................................................... 24 Changes in Estuarine Water Quality ......................................................................................... 24 Changes in Macrofauna Communities ...................................................................................... 26 Identification of Vulnerable Species ......................................................................................... 27 Presence / Absence of Marine Species ...................................................................................... 27 Changes in Epifauna Communities ........................................................................................... 28 CONCLUSION ............................................................................................................................. 29 REFERENCES ............................................................................................................................. 30 TABLES ....................................................................................................................................... 34 FIGURES ...................................................................................................................................... 75 ii LIST OF TABLES Table 1. Water and macrofauna samples taken by HRI (before 2010). ........................................ 34 Table 2. Nueces Estuary droughts (Method One). ........................................................................ 35 Table 3. Guadalupe Estuary droughts (Method One). .................................................................. 36 Table 4. Lavaca-Colorado Estuary droughts (Method One). ........................................................ 37 Table 5. Palmer Drought Severity Index Classes (from Palmer 1965). ....................................... 38 Table 6. Mean Palmer Drought Severity Index value for drought and wet periods in each estuary (Method 1). ................................................................................................................................... 39 Table 7. Means and significance of differences for water quality between drought and wet periods in each estuary (Method One, data is from TPWD). ........................................................ 40 Table 8. Means and significance of differences for nutrients between drought and wet periods in each bay (Method One). ................................................................................................................ 41 Table 9. Mean abundance, biomass and N1 diversity for drought and wet periods (Method One). ....................................................................................................................................................... 42 Table 10. Thirty most abundant macrofauna species in Rincon Bayou during drought and wet periods (Method One). .................................................................................................................. 43 Table 11. Forty most abundant macrofauna species in Nueces and Corpus Christi Bays (n m-2) during drought and wet periods (Method One). ............................................................................ 44 Table 12. Forty most abundant macrofauna species in the Guadalupe Estuary (n m-2) during drought and wet periods (Method One). ....................................................................................... 45 Table 13. Forty most abundant macrofauna species in the Lavaca-Colorado Estuary (n m-2) during drought and wet periods (Method One). ............................................................................ 46 Table 14. Similarity percentages - species (SIMPER) in Rincon Bayou in drought and wet periods (Method One). .................................................................................................................. 47 Table 15. Similarity percentages – macrofauna species (SIMPER) in the upper Guadalupe Estuary in drought and wet periods (Method One). ...................................................................... 48 Table 16. Similarity percentages – macrofauna species (SIMPER) in the lower Guadalupe Estuary in drought and wet