Dissolved carbon and water quality data from a coastal Louisiana salt marsh

Discrete water-quality sensor data and dissolved carbon samples were collected at the USGS gage 292939089544400 (Wilkinson Bayou cutoff, north of Wilkinson Bay, LA). Field water-quality measurements were obtained using a YSI EXO2 water-quality sonde equipped with a data logger to measure water temperature, salinity, pH, fluorescent dissolved organic matter (fDOM), and dissolved oxygen (DO). Discrete samples of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and total alkalinity (TA) were collected at the tidal creek. For both DIC and TA, water samples were passed through a 0.45 µm glass-fiber syringe filter and collected without headspace into airtight 40 mL glass vials by filling from the bottom and allowing overflow of at least one vial volume to minimize atmospheric contamination. Samples were preserved with 20 µL of saturated mercuric chloride (HgCl₂) solution. For DOC analysis, creek water was filtered through 0.45 µm filters and stored in amber bottles without the addition of chemical preservatives (He and Xu, 2017). All water samples were transported to the laboratory on ice and stored at 5 °C until analysis. DIC was analyzed following the standard protocol for the semi-automated Apollo SciTech AS-C5 Dissolved Inorganic Carbon Analyzer (Newark, DE, USA). Total alkalinity was determined using the Gran titration method (Gran, 1952) with a semi-automated Apollo SciTech AS-ALK2 Total Alkalinity Titrator (Newark, DE, USA). Dissolved organic carbon was analyzed using a Shimadzu TOC-5000A analyzer with an ASI-5000A autosampler by converting all carbon to CO₂ via high-temperature combustion.