Table of Contents

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

Field Sampling

Galveston Bay is a semi-enclosed microtidal estuary located in the NWGOM (Montagna et al., 2013). With an average water depth of 3 m and a surface area covering 1,554 km², Galveston Bay is the seventh-largest estuary in the U.S. and the second-largest estuary on the Texas coast (Bass et al., 2018; Morse et al., 1993; Solis & Powell, 1999). 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 (Bass et al., 2018; Dellapenna et al., 2020; Morse et al., 1993; Solis & Powell, 1999). The Bolivar Peninsula and Galveston Island separate Galveston Bay from the GOM, with the exchange of water between the Bay and the GOM occurring through Bolivar Roads, i.e., the mouth of the Bay (Glass et al., 2008; Morse et al., 1993).

Monthly cruises were conducted between October 2017 and September 2018 onboard the R/V Trident. Timing of the study allowed for the examination of the factors regulating CO₂ flux over the course of a year following Hurricane Harvey in late August 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 (Du & Park, 2019; Du et al., 2019).

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 2018. At each station, surface (~0.5 m below water surface) and bottom water (~0.5 m above the sediment) samples for carbonate analyses were collected. A van Dorn sampler was used to collect unfiltered surface and bottom water into 250 mL borosilicate glass bottles for total alkalinity (TA), dissolved inorganic carbon (DIC), and pH analyses. A total of 100 μL saturated HgCl₂ was added to each water sample to cease biological activity, and bottle stoppers were replaced following the application of Apiezon® grease and secured with rubber bands and hose clamps. The samples were stored at 4 °C in the dark until analyses, usually within 2–3 weeks of sample collection. Surface and bottom unpreserved water samples were collected in 125 mL polypropylene bottles for Ca²⁺ analysis.

Discrete Sample Analyses

Water samples collected at the surface and bottom at each station were analyzed for DIC, TA, pH, and salinity (Dickson et al., 2003; Bass et al., 2018). DIC was analyzed by acidifying 0.5 mL water samples with 0.5 mL 10% H₃PO₄ using a 2.5 mL syringe pump on an AS-C3 DIC analyzer (Apollo SciTech Inc.) with a precision of ±0.1%. TA was analyzed at 22.0 ± 0.1 °C using Gran titration of a 25 mL water sample with 0.1 M HCl solution (in 0.5 M NaCl) on an AS-Alk2 alkalinity titrator (Apollo SciTech Inc.), with a precision of ±0.1%. Precisions were estimated based on randomly collected duplicate samples. Reference Material (RM) produced in the lab of Andrew Dickson at Scripps was used in both TA and DIC analysis to ensure data quality (Dickson et al., 2003).

A spectrophotometric method with a precision of ±0.0004 and purified m-cresol purple (mCP) obtained from Dr. Robert Byrne’s lab (University of South Florida) (Liu et al., 2011) was used for pH (on the total scale) analysis (Carter et al., 2013). Prior to each sample analysis, a calibrated Orion™ Ross™ glass electrode was used to adjust the indicator to pH 7.92 ± 0.01. A 10 cm water-jacketed absorbance cell for pH measurements (Carter et al., 2013) was kept at 25 ± 0.01 °C. Consecutive runs were done for each sample whereby two volumes (30 μL and 60 μL) of mCP were added to correct the dye effect (Clayton & Byrne, 1993). Equations from Liu et al. (2011) were used when salinity was greater than 20 for the entirety of a sampling trip, and equations from Douglas and Byrne (2017), which allow for a wider salinity range (0–40 vs. 20–40) (Douglas & Byrne, 2017), were used when salinity was less than 20 for an entire sampling trip for pH calculations. Calculated pH values (on the total scale) were converted to in situ temperature using the program CO2SYS with DIC as the other input parameter.

Salinity was measured with a benchtop salinometer (Orion Star™ A12, Thermo Scientific), which was calibrated using Milli-Q water and known salinity CRM seawater before each sample analysis. Calcium ([Ca²⁺]) concentration was measured using automatic potentiometric titration with ethylene glycol tetraacetic acid (EGTA), with a precision of ±0.2% (Kanamori & Ikegami, 1980). A Metrohm® Titrando calcium-selective electrode on a titration system (Metrohm Titrando 888) was used to detect the endpoint.

Meteorological Data

United States Geological Survey (USGS, 2021) streamgages for the Trinity River (gage #08066500) and San Jacinto River, east fork (SJE; gage #08070200) and west fork (SJW; gage #08068000), were used to obtain freshwater discharge. These stations were identified as the closest gages to the mouths of the rivers having complete discharge data for the study period. Discharges of less than or equal to 45 days (residence time of the Bay) prior to flux estimates were utilized (Morse et al., 1993; Solis & Powell, 1999). The Texas Commission on Environmental Quality (TCEQ, 2022) performs routine water quality monitoring, and TCEQ water sampling stations were used for river endmember values from the San Jacinto (average of west fork station #11243 and east fork station #11238) and Trinity (station #10896) rivers. River endmember DIC was calculated from TA and pH measurements using K₁ and K₂ constants from Millero (2010) and pH values on the NBS scale. Seasonally weighted averages were calculated by summing the TA or DIC concentration multiplied by daily discharge values for all river measurements of that season and dividing by the sum of all discharge values for all river measurements of that season (using meteorological seasons).

Carbonate Speciation and Saturation State Calculations

Carbonate speciation was calculated under field conditions (temperature and pressure) using the Excel® version of the CO2SYS program (Lewis & Wallace, 1998) based on DIC and lab-measured pH (at 25 °C) from discrete samples. Carbonic acid dissociation constants (K1, K2) from Millero (2010), the bisulfate dissociation constant from Dickson (1990), the dissociation constant of HF (KF) from Dickson and Riley (1979), and total boron concentration from Uppström (1974) were used.

The CO2SYS output for carbonate saturation state with respect to aragonite (ΩAr, CO2SYS) was corrected using the measured Ca²⁺ concentration, which exhibited a near-linear relationship with salinity (R² = 0.96). This correction was necessary for the estuary due to the non-zero calcium concentration of the riverine endmember. The corrected aragonite saturation state (ΩAr) was calculated as:

Corrected ΩAr = (ΩAr, CO2SYS) × ([Ca²⁺ measured] / [Ca²⁺ theoretical])

Where:

• [Ca²⁺ measured] is the calcium concentration measured directly.
• [Ca²⁺ theoretical] is the theoretical calcium concentration based on salinity as calculated in the CO2SYS program.

- Units and special characters removed from parameter names
- Spaces in parameter names replaced with underscores ("_")
- The original submitted primary data file was an Excel file containing a "Metadata" tab and "Data" tab; the "Data" tab is served in this dataset as the primary data table and the content from the "Metadata" tab informs the parameter details of this 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.