Surface sediment physical parameters data collected in August 2015 from Dauphin Island and the surrounding areas

At each sample location, the top 1 cm of the recovered, undisturbed surface material was subsampled for sediment characterization, placed in individual storage bags, and stored on ice. The surface samples were transported to the USGS SPCMSC.

In the laboratory, samples were homogenized. The sediment parameters subsample from each sample location was processed for basic sediment characteristics: dry bulk density and porosity. Water content, porosity, and dry bulk density were calculated by determining water mass lost during drying. Known volumes of each wet subsample, usually 30 – 60 mL, were packed into a graduated syringe with 0.5 cm-3 (cubic centimeter) resolution. The wet sediment was then extracted into a pre-weighed aluminum tray and the wet sediment's weight was recorded. The wet sediment and tray were placed in a drying oven for 48 hours at 60 °C. Water content was determined as the mass of water (lost when dried) relative to the initial wet sediment mass. Porosity was estimated using the equation provided in the report associated with with metadata record (http://pubs.usgs.gov/ds/1046/ds1046_methods.html). Salt-mass contributions were removed based on the salinity measured at the time of sample collection. If salinity was not measured in the field, pore water salinity was estimated to be 30.75 for G sites (grab samples) and 25.89 for S sites (land surface samples), the average salinity values from this trip for the site type. Dry bulk density was calculated from the report equation in the document (http://pubs.usgs.gov/of/2015/1219/ofr2015-1219_methods.html).

Organic matter (OM) content was determined with a mass loss technique, referred to as loss on ignition (LOI). The dry sediment from the previous process was homogenized with a porcelain mortar and pestle. Approximately 5 grams of the dry sediment was placed into a pre-weighed porcelain crucible. The mass of the dried sediment was recorded with a precision of 0.01 g on an analytical balance. The sample was then placed inside a laboratory muffle furnace with stabilizing temperature control. The furnace was heated to 110 °C for a minimum of 6 hours to remove hygroscopic water adsorbed onto the sediment particles. The furnace temperature was then lowered to 60 °C, at which point the sediments could be reweighed. The dried sediment was returned to the muffle furnace. The furnace was heated to 550 °C over 30 minutes and kept at 550 °C for 6 hours. The furnace temperature was then lowered to 60 °C, at which point the sediments could be reweighed. The mass lost during the 6-hour baking period relative to the 110 °C-dried mass is used as a metric of organic matter content.

Added keywords section with USGS persistent identifier as theme keyword.