Role of Freshwater Inflows and Nutrients on Phytoplankton Community Composition in a Subtropical Estuary: Insights from a Decade Long Study

Jamie L Steichen, Jamie L Steichen, Galveston, TX, United States, Rachel Windham, Houston-Galveston Area Council, Houston, TX, United States, Tyra Booe, (formerly) Texas A&M University at Galveston, Marine Biology, Galveston, United States, Lucchese Allyson, (formerly) Texas A&M University, Oceanography, College Station, TX, United States, Alicia Williams, University of New England, Marine Sciences, Biddeford, ME, United States, Amelia McAmis, Environmental Chemistry Inc, Houston, TX, United States, Hannah Lee, Massachusetts Water Resources Authority, Charlestown, MA, United States, McInnes Skinner Allison, Queensland Institute of Medical Research, Brisbane, QLD, Australia, Samuel Dorado, (formerly) Texas A&M University at Galveston, Marine Biology, Galveston, TX, United States and Antonietta Quigg, Texas A&M University at Galveston, Marine Biology, Galveston, United States
Abstract:
The Dallas/Fort Worth and Houston metroplexes (combined pop. ~9 million) are located within the watershed of Galveston Bay, TX (USA) which is an economically and ecologically important estuary along the Gulf of Mexico. Changing freshwater inflow quality and quantity due to extreme weather and anthropogenic forcing can impact the phytoplankton ecology of the Bay. At discrete stations, surface water quality parameters (temperature, salinity, dissolved oxygen and water clarity) were recorded and water samples were collected monthly from 2008-2018 for nutrient and phytoplankton pigment analyses from sites across the Bay. Phytoplankton community dynamics can be indicative of ecological responses to changes in water quality including those incurred during weather events such as prolonged droughts and floods. Our findings show that ratios of Bacillariophyta and Dinophyta (estuarine/marine phytoplankton) compared to Chlorophyta and Cyanophyta (freshwater phytoplankton) are influenced by the magnitude and duration of freshwater inflows. Drought periods were dominated by Bacillariophyta and Dinophyta bay wide with a transition to freshwater phytoplankton (Chlorophyta and Cyanophyta) during flooding events (2015, 2016 and 2017). Following Hurricane Harvey in 2017, the phytoplankton community transitioned from a freshwater community immediately following the flooding event towards an estuarine/marine community within a month after the storm. The consequences of these shifts in community composition to the overall productivity within the Bay food web is yet to be determined. In addition to periods of flooding and droughts, compounding factors affecting the phytoplankton community may include but are not limited to introductions of phytoplankton via ballast water discharges and productivity loss due to petrochemical spills and other pollutants into the Bay including the Texas City Y spill (2014), reformate spill (2019) and Deer Park Fire runoff (2019). Algal blooms (some being harmful) occur periodically within the Bay, although most blooms have not been linked to fish kills. This decade long study highlights the value of the phytoplankton community as an effective means of monitoring the ecological response within the Bay following a variety of perturbations.
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