Dataset: 2018 sediment properties: Anahuac and Aransas

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.