Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • Problem Description
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Field sampling

Galveston Bay is a semi-enclosed microtidal estuary located in the nwGOM [42]. With an average water depth of 3 m and surface area covering 1554 km2, Galveston Bay is the seventh largest estuary in the U.S. and the second largest estuary on the Texas coast [35, 43, 44]. Galveston Bay receives freshwater from the Trinity River, San Jacinto River, Clear Creek, and smaller bayous and creeks, with the Trinity River providing 70% of the freshwater entering the Bay [35, 45, 43, 44]. The Bolivar Peninsula and Galveston Island separate Galveston Bay from the GOM, with exchange of water between the Bay and the GOM occurring through Bolivar Roads, i.e., the mouth of the Bay [46, 43]. 

Monthly cruises were conducted between October 2017 and September 2018 on board the R/V Trident. Timing of the study allowed for examination of the factors regulating CO2 flux over the course of a year following Hurricane Harvey in late August of 2017. Although the study began more than 45 days (the residence time of the Bay) after Harvey, salinity recovery of the Bay was likely still ongoing in the inner and middle sections of the Bay [47, 48]. 

During each monthly survey, a transect was run between five water sampling stations, extending northwest from the Bay mouth (Station 1) opening to the Five Mile Marker on the Houston Ship Channel (Station 5). One offshore cruise in the nwGOM outside Galveston Bay was conducted in October of 2018. 

Pigments 

Chlorophyll-a concentrations were analyzed from surface water samples collected at each station in the Bay as in [65]. Surface waters were filtered through GF/F filters, which were frozen immediately in liquid nitrogen and later stored in the freezer at -80 ⁰C until analysis. Extraction of pigments from filters followed procedures from [66, 67], whereby filters were extracted in acetone in polypropylene centrifuge tubes, which were sonicated for 15 min in a sonicator (Model FS 60, Fisher Scientific). Acetone extract was filtered through a syringe filter (0–2 μm Nylon filter). Procedures were repeated for sample filters, and the two extracts (total 6 mL) were combined and blown with nitrogen gas under ice to dryness [68], and acetone (0.5 mL) was added to dissolve the residue before the high-performance liquid chromatography (HPLC) analysis [65].

Pigments were analyzed using a Shimadzu HPLC system with a reverse phase column (Agilent Eclipse XDB-C8, 3.5 μm particle size, 150 mm length x 4.6 mm diameter), with photodiode array (PDA) detector set as 450 nm. The mobile phases included A (70:30 v/v methanol: 28 mM tetrabutyl ammonium acetate; pH 6.5) and B methanol (100%). After sample injection (400 μL, mixing 0.5 mL acetone extract and 1.25 mL 28 mM tetrabutylammonium acetate), a gradient program (1.0 mL/min) began with 5% B and increased to 95% B in 22 min, then to 95% B isocratically over 30 min. All chromatographic separations were performed in a column oven set at 60 ⁰C. Pigments were identified by comparing retention times with authentic standards purchased from DHI (Denmark) or Sigma-Aldritch (USA). Peak areas were converted to concentrations based on response factors calculated from authentic standards. Duplicate analyses of the same extract generally agreed within 20%. 

Monthly and spatial trends in chlorophyll-a  were examined graphically and on maps created  using R, Excel, and MATLAB  in comparison with carbonate chemistry measurements (separate dataset).

NSF Award Abstract:
Hurricane Harvey made landfall Friday 25 August 2017 about 30 miles northeast of Corpus Christi, Texas as a Category 4 hurricane with winds up to 130 mph. This is the strongest hurricane to hit the middle Texas coast since Carla in 1961. After the wind storm and storm surge, coastal flooding occurred due to the storm lingering over Texas for four more days, dumping as much as 50 inches of rain near Houston. This will produce one of the largest floods ever to hit the Texas coast, and it is estimated that the flood will be a one in a thousand year event. The Texas coast is characterized by lagoons behind barrier islands, and their ecology and biogeochemistry are strongly influenced by coastal hydrology. Because this coastline is dominated by open water systems and productivity is driven by the amount of freshwater inflow, Hurricane Harvey represents a massive inflow event that will likely cause tremendous changes to the coastal environments. Therefore, questions arise regarding how biogeochemical cycles of carbon, nutrients, and oxygen will be altered, whether massive phytoplankton blooms will occur, whether estuarine species will die when these systems turn into lakes, and how long recovery will take? The investigators are uniquely situated to mount this study not only because of their location, just south of the path of the storm, but most importantly because the lead investigator has conducted sampling of these bays regularly for the past thirty years, providing a tremendous context in which to interpret the new data gathered. The knowledge gained from this study will provide a broader understanding of the effects of similar high intensity rainfall events, which are expected to increase in frequency and/or intensity in the future.

The primary research hypothesis is that: Increased inflows to estuaries will cause increased loads of inorganic and organic matter, which will in turn drive primary production and biological responses, and at the same time significantly enhance respiration of coastal blue carbon. A secondary hypothesis is that: The large change in salinity and dissolved oxygen deficits will kill or stress many estuarine and marine organisms. To test these hypotheses it is necessary to measure the temporal change in key indicators of biogeochemical processes, and biodiversity shifts. Thus, changes to the carbon, nitrogen and oxygen cycles, and the diversity of benthic organisms will be measured and compared to existing baselines. The PIs propose to sample the Lavaca-Colorado, Guadalupe, Nueces, and Laguna Madre estuaries as follows: 1) continuous sampling (via autonomous instruments) of salinity, temperature, pH, dissolved oxygen, and depth (i.e. tidal elevation); 2) bi-weekly to monthly sampling for dissolved and total organic carbon and organic nitrogen, carbonate system parameters, nutrients, and phytoplankton community composition; 3) quarterly measurements of sediment characteristics and benthic infauna. The project will support two graduate students. The PIs will communicate results to the public and to state agencies through existing collaborations.