Nutrient Sources, Fate, Transport, and Effects Study of Galveston Bay, Texas Rachel Windham, Department of Marine Biology Texas A&M University at Galveston 2 Acknowledgements: Dr. Antonietta Quigg Members of the Phytoplankton Dynamics Laboratory Dr. Jamie Tyra Rachel Allyson Steichen Booe Windham Lucchese Dr. Allison Sam Hannah Alicia McInnes Dorado Preischel Shepard 3 Galveston Bay • Galveston Bay is an estuary located on the Texas coast (northwest Gulf of Mexico) • 600 square miles (1,500 square kilometers) of open water • Largest estuary in Texas and 7th largest in the nation • Freshwater sources: Trinity River and San Jacinto River • Supports multi-billion dollar fisheries industry (crab, shrimp, oyster) • Highly productive; source of 1/3 of the state’s commercial fisheries revenue Introduction Methods Results & Analysis Other Projects Future Efforts 4 Watershed • Watershed spans area of 24,000 square miles (62,000 square kilometers) • Trinity River and San Jacinto River have origins in highly-urbanized Dallas- Fort Worth metroplex and Houston area respectively • Freshwater inflows (FWI) maintain salinity gradients, nutrient loads, and sediment inputs contributing to the health of Galveston Bay • Nutrient loading can positively impact the ecosystem in appropriate quantities; however, in excessive amounts, nutrients can contribute to harmful algal blooms which further impact the system by contributing to hypoxia and fish kills Introduction Methods Results & Analysis Other Projects Future Efforts 5 Urbanization • Houston and Dallas populations expected to double by 2050 • Recent changes in land use and development could affect nutrient influx via freshwater inflows into Galveston Bay especially considering increased flow from Houston (wastewater) • Important to monitor current nutrient loads and assess impacts on the ecosystem Legend Legend Red Red Developed Land Developed Land Other Colors Other Colors Crop and Crop and Natural Land Natural Land Introduction Methods Results & Analysis Other Projects Future Efforts 6 Objectives • Support continued research to understand nutrient fluxes in Galveston Bay • Determine nutrient budget for ecosystem • Examine the effect of nutrient loading associated with freshwater inflows on the phytoplankton community • Particular focus on freshwater inflows from the Trinity River and to a lesser degree, those associated with the San Jacinto River • Perform intensive resource limitation assays (RLAs) across six locations in the Trinity-San Jacinto Estuary during March and July (representative of “high-flow” and “low-flow” periods) • Use the resulting data and conclusions to develop the next generation of predictive models relating freshwater inflows to bay health Introduction Methods Results & Analysis Other Projects Future Efforts 7 Nutrient and sediment loading • Assessment of phytoplankton response to nutrient loading through resource limitation assays in concert with assessment of water quality • Treat seawater with nutrient additions and incubate for one week in ambient conditions • Analyze phytoplankton community health by observing parameters such as chlorophyll-a concentration, pigment composition and fluorescence response Introduction Methods Results & Analysis Other Projects Future Efforts 8 Project Evolution • 2008-2009: Early RLA studies in Galveston Bay involved monthly analyses of two stations in Galveston Bay (north: freshwater influence, south: marine influence) • Included nutrient addition treatments of nitrogen, phosphorous, and a combination of nitrogen and phosphorous • Yielded three notable insights: • Phytoplankton response to nutrient additions higher in periods of low-flow • Different responses in scale and species composition of phytoplankton communities at different stations • Phytoplankton frequently co-limited by nutrients, typically nitrogen and phosphorous Introduction Methods Results & Analysis Other Projects Future Efforts 9 More Intensive Study • 2010-2012: Examined phytoplankton community response to nutrient additions on a finer spatial scale • Investigated response to different nitrogen sources (nitrate vs. ammonium) • Nitrate, ammonium, phosphate, nitrate & phosphate, nitrate & ammonium, silicate, “all” • Note that 2011 was among the warmest and driest years on record for Texas since the record’s origin in 1871 (one of the top five driest years on record for the watershed) • Extreme conditions in 2011 presented opportunity to observe seasonal responses with freshwater inflow influence “turned off” • Comparing 2011 data to higher flow years (2010 and 2012) could inform system function in “normal,” “drought,” and “recovery” stages Introduction Methods Results & Analysis Other Projects Future Efforts 10 FWI During Study Period * ) s f c ( e g r a h c s i D 2010 2011 2012 ) t f ( t h g i e H e g a G 2010 2011 2012 Introduction Methods Results & Analysis Other Projects Future Efforts