Table of Contents

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

Three sediment cores were collected for analytical analyses from each site for a total of six cores. Sediments were extracted using a polycarbonate push core (7 cm ID x 50 cm L) with beveled edges pushed into the marsh surface. Cores were sectioned into 1-cm intervals on site on the day of collection and stored cold until laboratory analysis at the University of North Carolina, Chapel Hill, NC. All sediment samples were weighed damp, placed into a drying oven at 60°C for at least 48 hours for evaporation of water content and re-weighed dry. Bulk plant material, such as root mats and rhizomes, was manually removed with tweezers after the samples dried. Dried sediment samples were then homogenized using a mortar and pestle.

One 2014 pre-storm core from both sites, AR2 and AN2 (sediment collected in a previous study), and one 2018 post-storm core from Aransas, B, and two 2018 post-storm cores from Anahuac, D and E, were selected for bulk radiocarbon analyses. Samples were paired, one sample from the pre-storm core and one sample from the post-storm core, based on deposition age determined by 210Pb geochronology. Four pairs of samples were selected from each study site to be analyzed for bulk 14C age. In addition, one sediment surface sample from each site from the 2018 post-storm cores was selected for bulk 14C age analyses, for a total of 18 samples.

Aliquots of approximately 300 mg of dried and homogenized sample were placed into acid cleaned and pre-baked glass tubes with 3 mL of a 10 % hydrochloric acid solution, with the sediment slightly agitated to ensure full saturation, and left to soak overnight to thoroughly remove inorganic carbon. After sediments settled the acid was carefully removed via pipette as to not resuspend or extract fine sediments. Samples were then rinsed five times with 5 mL of Milli-Q water over the course of 48 hours, with at least 4 hours between rinses to allow sediment to settle, to raise the pH of the samples back to neutral, and then placed in a 60 °C oven until dry. About 1 mg of OC, based on % TOC results, was weighed into tin capsules, sealed, and analyzed for bulk Δ14C at the National Ocean Sciences Accelerator Mass Spectrometry facility at the Woods Hole Oceanographic Institution, Woods Hole, MA (NOSAMS).

A slow thermal ramp of 5 °C min-1 was performed on only three pairs of acid rinsed aliquots of pre- and post-storm samples and the post-storm surface sample from Aransas, for a total of seven sediment samples, in order to collect fractions of evolved CO2 as temperatures increased (i.e. fraction 1 is lower temperatures and 4 are higher). Detailed RPO experimental set-up and methods are available in Rosenheim et al. (2008) and Hemingway et al. (2017b). Detailed CO2 to graphite conversion methods are provided in Pearson et al. (1998) and Shah Walter et al. (2015). Graphite was analyzed for 14C on a Continuous Flow Accelerator Mass Spectrometer at NOSAMS. Samples were normalized to OX-I (Olsson, I.U., 1970) and radiocarbon-free acetanilide (J.T. Baker, A068-03) was used for blank correction. Standards from multiple international radiocarbon intercalibration comparisons and from International Atomic Energy Agency were used for secondary standards. δ13C was analyzed from gas samples on an Optima or Prism stable isotope mass spectrometer.

Analysis of raw RPO data, described in detail in Hemingway et al. (2017a) and Hemingway (2016), was performed using the Python® package rampedpyrox.

BCO-DMO Processing Notes:
- data submitted in Excel file "Radiocarbon.xlsx" extracted to csv
- extracted site, station, lat, and lon data into a separate stations .csv file
- created new columns for station and sample by splitting the Sample_ID column for use as a join key to the stations file
- joined the stations file to the radiocarbon file so lat, lon, and site are included in the final table
- added conventional header with dataset name, PI name, version date
- renamed columns to conform with BCO-DMO naming conventions (removed units and special characters)

NSF Award Abstract:
Coastal wetlands store more than 20% of global carbon, and salt marshes are estimated to have the highest carbon burial rates of all coastal wetlands. Disturbances, like large storms, have the potential to reduce the storage of carbon in salt marshes and lower their overall impact on the global carbon cycle. Previous studies have shown that large quantities of sediment were deposited on salt marshes in Louisiana after Hurricanes Katrina and Rita in 2005, but little was known about the state of the marshes before these impacts. Consequently, we can only speculate about the true impact of those storms on sediment carbon storage. Comparing pre-storm carbon storage to post-storm storage immediately (weeks to months) following landfall allows us to quantify the storm impacts and capture critical data before inventory signals are lost to the next event. This project will take advantage of the fact that the investigators have recently (2014) sampled salt marshes near both of the locations where Hurricane Harvey made landfall in August, 2017. They will collect new salt marsh sediment samples and compare their data to 2014 data in order to study the impact of storm passage on these important systems.

Hurricane Harvey made landfall as a Category 4 storm at Rockport, TX, on 25 Aug 2017, moved inland, circled back, and made a second landfall as a tropical storm east of Port Arthur, TX, on 30 Aug 2017. These two major storm landfalls coincide with locations of salt marsh carbon burial studies performed in 2014 by this research group at the Aransas National Wildlife Refuge (NWR) and the Anahuac NWR. These data provide a baseline against which to assess the impacts of recent major storm landfalls on marsh accretion and carbon burial. It is imperative to return to these study sites as soon as possible to ensure that the perishable data resulting from the impacts of this storm on these marshes are not altered by other meteorological events or human disturbances. The investigators hypothesize hurricanes redistributed sediments from offshore and within the fringing salt marsh onto the marsh platform, increasing the elevation of the marsh and burying organic matter as stored carbon. The objectives of this research are 1) to quantify the impact of extratropical storm sediment accretion on carbon storage in two salt marshes at the local scale using 2014 baseline data; and 2) to extend these local storm-induced carbon changes to the landscape scale using pre- and post-storm LiDAR and satellite imagery. To address these objectives and preserve the perishable data, field work will take place at the Aransas and Anahuac NWRs during the week of 16 Oct 2017. Four 50 cm cores, two from each site, will be collected and sectioned based on stratigraphic changes. Sediment will be analyzed for total organic carbon, carbon-14, lead-210, and sediment physical properties (Obj. 1). Ground-truth measurements across the marsh will be obtained using a Macaulay auger and used to validate post- hurricane LiDAR measurements, which will be compared to pre-hurricane measurements from 2014 (Obj. 1 & 2). Freely available archived and new satellite imagery and LiDAR will be used to measure changes in marsh height and area (Obj. 2). The project will form part of the doctoral research of a graduate student, and will also support a senior undergraduate student.