Grain size, bulk density, and carbon content of sediment collected from Whale's Tail South marsh and adjacent bay floor, South San Francisco Bay, California, 2021-2022

SEDIMENT COLLECTION. Sediment samples were collected from a small vessel near pre-established USGS instrument moorings using a Gomex box corer that was subsampled with three push cores (37 mm in diameter) per Gomex core when sufficient sample was recovered. At MEV the push cores were collected on foot by pressing the push core directly into the sediment. Six subsamples were collected from the top 5 centimeters (cm) of each push core, a few push cores included longer sections with a maximum of the top 19 cm. The top two subsamples were each 0.5 cm thick, and all following subsamples were each 1 cm thick. Subsamples were placed into pre-weighed Whirl-pak bags.

SEDIMENT COLLECTION. Additional samples were collected using a variety of grab samplers to collect surface sediment, where a small surficial layer was sampled and processed for grain size. Sediment deposited upon ceramic tiles placed on the marsh top was collected and processed for grain size. Large rip-up clasts deposited on the marsh surface were sampled for bulk density.

GRAIN-SIZE ANALYSIS: Grain-size analysis was conducted by the USGS Pacific Coastal and Marine Science Center (PCMSC) sediment lab using a Beckman Coulter LS 13 320 particle size analyzer with an aqueous liquid module attachment. PCMSC procedures are modified from those described in Carver (1971) and Folk (1974, 1980). 5-50 grams of sediment was sub-sampled and at least 10 milliliters of 30 percent hydrogen peroxide were added to oxidize overnight to remove organics. The samples were then heated to 250 degrees Celsius to drive off excess hydrogen peroxide. Next, samples were placed in an ultrasonic bath to help disperse silt and clay (mud) from sand and larger-sized particles. Samples were then rinsed twice in deionized water with centrifugation to remove soluble ions. Subsequently, the samples were wet sieved with 1 millimeter and 0.063 millimeter sieves to segregate the combined gravel and coarse sand fraction (greater than 1 millimeter), sand (1 millimeter to 0.063 millimeter), and mud (less than 0.063 millimeter). The coarse sand + gravel fractions were then dried, dry sieved at 1/4phi intervals and weighed (Carver, 1971). The sand fraction was dried and weighed. The mud fraction was collected in a 1 liter graduated cylinder, 5 milliliters of at least 10 percent sodium hexametaphosphate (dispersant) were added, and deionized water was added to bring the total the volume to 1 liter. The mud + dispersant solution sat overnight to ensure complete dispersion and to observe if flocculation occurred. Subsequently, a 20 milliliter aliquot was extracted from the graduated cylinder and dried to obtain the mud fraction weight normalized to a 1-liter basis. The mud and sand fractions were analyzed separately via the Beckman Coulter LS 13 320 with the aqueous liquid module attachment. All size fraction data were compiled and converted by the PCMSC sediment lab pcSDSZ program (Penscil, 2015) to a grain-size distribution at 1/4phi size intervals on a weight percent basis. pcSDSZ also calculated interpolated sizes and graphical statistics on a percent coarser basis (Folk and Ward, 1957; Folk, 1966; Folk, 1974, 1980; Inman, 1952; Trask, 1930, 1932) and moment measures (Collias and others, 1963; Jaquet and Vernet, 1976; Folk, 1980).

INTERPOLATED SIZES: Grain sizes at select cumulative percentage values (D) were calculated by the PCMSC Sediment Lab software pcSDSZ version 1.71 on a percent coarser basis, which summed from coarse to fine bins. D values were interpolated between phi bins bracketing the specified D value. Grain sizes were converted into units of millimeters (mm) using the formula mm=reciprocal of 2(exponent)phi or (phi=-log2(mm)). Interpolated grain sizes at D5, D10, D16, D25, D50, D75, D84, D90, and D95 are reported in phi and millimeter units.

The bulk density reported here was calculated with the formula: bulk density = (dry sediment mass + water mass) /((dry sediment mass/sediment density) + (water mass/water density)), where water density is 1 g/cm3 and sediment density is 2.65 g/cm3. Local salinity readings were used to calculate salt mass, which was removed from dry sediment mass prior to this calculation. Measurements were made in the USGS Pacific Coastal and Marine Science Center sediment lab.

CARBON ANALYSIS: Carbon analysis was performed by the PCMSC carbon lab employing a coulometric titration technique described in Engleman and others (1985) and UIC operating manuals for the UIC CM5200 autosampler furnace, the UIC CM5230 acidification module, and the UIC CM5017 coulometer. Total carbon (TC), total inorganic carbon (TIC), total organic carbon (TOC) and percent calcium carbonate (CaCO3) are reported as percent dry weight. Approximately 5 grams of sediment were dried in an 80 degrees Celsius oven. Samples were then pulverized, redried, and placed in a desiccator. For TC analysis, approximately 20 milligrams of the pulverized sample were weighed and wrapped in an aluminum capsule then combusted at 950 degrees Celsius in an UIC CM5200 autosampler furnace attached to an UIC CM5017 coulometer. The carbon dioxide (CO2) produced by combusting the sample was then converted to TC by the UIC CM5017 coulometer. For TIC, approximately 20 milligrams of sample were weighed and loaded into an UIC CM5230 acidification module attached to an UIC CM5017 coulometer. The samples were then digested in a perchloric acid solution, and the CO2 generated was measured and converted to TIC. Two analyses per sample were run and the results were averaged. TOC was calculated by subtracting TIC from TC. The TIC value was then multiplied by 8.333 (the molar stochiometric ratio of CaCO3 to C) to convert TIC to percent CaCO3.