Table of Contents

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

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. 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. Porosity of samples was calculated using the difference between the wet and dry weight multiplied by the assumed density of water to estimate the volume of the void space. The void space volume was then divided by the total volume to calculate porosity. The dry bulk densities were calculated by dividing the mass of the dry sediment by the known volume of the sample. 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. Percent organic matter (OM) was determined on an aliquot of the homogenized sediments via loss on ignition. Between 1.0 and 3.0 g of sediment was distributed into pre-weighed porcelain crucibles and ignited in a Lindberg Blue M1100 muffle furnace at 550°C for 4 hours and reweighed to obtain percent OM content.

An additional aliquot, between 15 and 60 mg, of the original homogenized sediment underwent one of two acid treatments depending on the amount of inorganic carbon determined by LOI. For low inorganic carbon content samples (< 10 % IC) treatment consisted of weighing sediment into silver capsules, vapor acidifying with 12N trace metal grade hydrochloric acid overnight, and then dried at 80°C for one hour before being sealed. For high inorganic carbon content samples (> 10 % IC) treatment consisted of rinsing sediments with 3 mL of a 10% 12N trace metal grade hydrochloric acid solution. Sediments underwent three rinses of 5 mL of deionized water, approximately 4 hours apart to allow sediments to settle, to bring the samples back to a neutral pH. Samples were then dried for 48 hours at 60 °C, weighed into silver capsules, and sealed. Samples were analyzed for TOC, TN, delta13C, and delta15N by the Stable Isotope Facility at the University of California, Davis, CA.

Aliquots of the dried homogenized sediment samples, ranging from 12 to 20 g, were prepared for 210Pb analysis by gamma spectrometry. Sediment was packed into plastic petri dishes (50 mm x 9 mm), sealed with tape, and stored for at least 4 weeks for equilibration of 226Ra with 222Rn. Samples were counted for 24 hours on one of two planar germanium detectors for 210Pb, 137Cs, and 226Ra (as 214Pb and 214Bi) (25% relative efficiency). Germanium detectors were corrected for background activity and calibrated using IAEA-300 Baltic Sea marine sediment standards. The activity of 226Ra was subtracted from the total 210Pb activity and decay corrected to the time of collection to calculate unsupported 210Pb (210Pbex).

Data were analyzed using Excel and R.

Carbon and nitrogen were below detection for station F. Data listed as nd.

BCO-DMO Processing Notes:
- data submitted in Excel file "Anahuac 2018 Sediment properties.xlsx" and "Aransas 2018 Sediment.xlsx" extracted to csv
- extracted station, lat, and lon data into a separate stations .csv file
- removed empty rows and duplicate header rows from Anahuac and Aransas files
- concatenated tables from Anahuac and Aransas into a single table
- created new columns for station and sample by splitting the Sample_ID column for use as a join key to the stations file
- rounded values C13 and N15 to 1 digit to match the bulk of data in those columns
- 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.