Textural description of surface sediment samples collected in March/April 2014 and October 2014 from Chincoteague Bay, Virginia and Maryland (U.S. Geological Survey Field Activity Numbers 14CTB01, and 14CTB22).

99 surface sediment samples were collected with a Ponar grab from Chincoteague Bay and Tom’s Cove in March/April and October 2014 (USGS Field Activity Numbers 14CTB01, and 14CTB02). Samples were transported to the USGS St. Petersburg, FL Coastal and Marine Science Center (SPCMSC) for analysis.Prior to particle size analysis, organic material was chemically removed from the samples using approximately 8 mL of 30 percent hydrogen peroxide (H2O2) overnight. The H2O2 was then evaporated through slow heating on a hot plate, and the sediment was washed and centrifuged twice with deionized water. Grain-size analyses on the surface samples were performed using a Coulter LS200 (https://www.beckmancoulter.com) particle size analyzer, which uses laser diffraction to measure the size distribution of sediments ranging in size from clay (0.4 microns [µm]) to very coarse-grained sand (2 millimeters [mm]). A total of 99 surface samples were analyzed. To prevent shell fragments from damaging the Coulter LS200, particles greater than 1 mm in diameter were separated from all samples prior to analysis with a number 18 (1000 µm) U.S. standard sieve, which meets the American Society for Testing and Materials (ASTM) E11 standard specifications for determining particle size with woven-wire test sieves. The samples were washed through the sieve with filtered St. Petersburg, FL municipal water and a few milliliters of sodium hexametaphosphate solution to act as a deflocculant. The sediment slurry was sonicated with a wand sonicator for 30 – 60 seconds before being introduced into the Coulter LS200 to break down aggregated particles. Two subsamples from each sample were processed through the Coulter LS200 with a minimum of three runs apiece. The Coulter LS200 measures the particle-size distribution of each sample by passing sediment suspended in solution between two narrow panes of glass in front of a laser. The particles scatter light into characteristic refraction patterns that are measured by an array of photodetectors as intensity per unit area and recorded as relative volume for 92 size-classification channels, or bins. The size-classification boundaries for each bin were based on the ATSM E11 standard.

The raw grain-size data were then run through the free software program GRADISTAT (Blott and Pye, 2001; http://www.kpal.co.uk/gradistat.html), which calculates the mean, sorting, skewness, and kurtosis of each sample geometrically in metric units and logarithmically in phi units (Krumbein, 1934) using the Folk and Ward (1957) method. GRADISTAT also calculates the fraction of sediment from each sample by size category (for example, clay, coarse silt, fine sand) based on a modified Wentworth (1922) size scale. Entire list of references may be found at http://pubs.usgs.gov/of/2015/1219/ofr2015-1219_references.html. A macro function in Microsoft Excel, developed by the USGS SPCMSC, was applied to the data to calculate the average and standard deviation for each sample set (6 runs per sample), and highlight runs that varied from the set average by more than 1.5 standard deviations. Excessive deviations from the mean are likely the result of equipment error or extraneous organic material in the sample and are not considered representative of the sample. The highlighted runs were removed from the results and the sample average was recalculated using the remaining runs.

The averaged results for all samples, including the number of runs included and the standard deviation of the averaged results were summarized in a series of Excel workbooks for each sampling trip.

Added keywords section with USGS persistent identifier as theme keyword.