Shore proximal sediment deposition in coastal marsh at the Grand Bay National Estuarine Research Reserve, Mississippi: net sedimentation tile and surface grab sediment physical properties datasets from October 2020 to January 2023

Between October 8-16, 2020, a special NST deployment occurred to collect data from the passing of Hurricane Delta. Each site (5-8) consisted of two plots located along a transect perpendicular to the marsh-estuary shoreline at 10 and 25 meters inland from the shoreline. At each distance, three unglazed NST were placed in randomly selected locations within a 1-m quadrat, referred to as the "NST plot". The unglazed NST was a 4.25-inch (in) square tile. Each NST was gently pushed down into the marsh surface until the NST was flush with the marsh surface. For more information on NST construction and deployment, refer to Terrano (2018). Immediately following the passing of Hurricane Delta, the NST were collected and brought back to the USGS SPCMSC for sedimentary analysis.

The post subtidal sill study consisted of Sites 5-9. Each site had of five NST plots located along a transect perpendicular to the marsh-estuary shoreline at 5-meter (m) increments (5, 10, 15, 20, and 25 m from the shoreline). To begin this study, three unglazed NST and three glazed NST were used in each plot to assess the NST design (glazed versus unglazed). Both designs used a 4.25-inch (in) square tile. At each distance, six NSTs were placed in randomly selected locations within the 1-m quadrat (NST plot). Each NST was gently pushed down into the marsh surface until the NST was flush with the marsh surface. For more information on NST construction and deployment, refer to Terrano (2018). The three glazed and three unglazed NST were deployed in each plot in August 2021 (30 per site or 120 total). In September 2021, all NST were collected and new NST were redeployed due to the passing of Hurricane Ida. After all the NST were collected, three new glazed and three new unglazed NST were then placed in the same locations. Following the deployment in September 2021, all 120 NST were collected and redeployed approximately every three months until August 2022. From August 2022 to January 2023, only three unglazed NST were deployed in each plot (60 total NST deployed) and were collected and redeployed every three months. During select trips, surface sediment samples were collected from the top one centimeter of the marsh or estuary surface. For marsh samples, a 4x4 inch sampling area was selected directly adjacent to each NST plot. For estuary samples, one sample was collected at each site using a petite Ponar grab sampler. Since the Ponar collected sediment from roughly the top ten centimeters, a 4x4 inch sampling area was selected. From within this box the top one centimeter of sediment was collected for analysis. All NST and surface samples were put into individual containers to prevent cross contamination. All sediment samples were brought back to the USGS-SPCMSC sedimentology laboratory and stored in a refrigerator until they were ready to be processed.

NSTs were processed in the USGS-SPCMSC sedimentology laboratory shortly after each sample collection trip. Wet volume was determined by packing the sediment into a syringe. The wet sediment was weighed and dried for 48 hours at 60 degrees Celsius (°C) to obtain a dry weight. Additional information about sediment processing can be found in Terrano (2018).

Organic matter 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 0.5-5 grams (g) of the dry sediment was placed into a pre-weighed porcelain crucible. The mass of the dried sediment was recorded. 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 absorbed 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 and held at this temperature until the sediments could be reweighed. The latter step prevents the absorption of moisture, which can affect the measurement. 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. Data are reported as a ratio of mass (g) of organic matter to mass (g) of dry sediment (post-110 °C drying). To be consistent with previous data releases, replicate analyses of loss on ignition was conducted for quality assurance and those values were averaged (Smith and others, 2020).

Sediment samples were collected from the top of NST or collected from the top 1 cm of sediment (surface samples). Prior to particle size analysis, sediment samples which appeared (by visual inspection) to consist of greater than 5 percent organic material had the organic matter chemically removed from the samples using approximately 8 milliliters (mL) of 30 percent hydrogen peroxide (H2O2) in 50 mL beakers overnight. The H2O2 was then evaporated through slow heating on a hot plate, and the sediment was washed and centrifuged twice with deionized water. Samples which appeared to consist of less than 5 percent organic material were dried at 60 degrees Celsius (°C). To prevent shell fragments from damaging the Beckman Coulter LS 13 320 particle size analyzer, particles greater than 1 millimeter (mm) in diameter were separated from all samples prior to analysis with a number 18 (1000 micrometer [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 deionized 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 LS 13 320 to break down aggregated particles. Two subsamples from each sample were processed through the Coulter LS 13 320 with a minimum of four runs apiece. The Coulter LS 13 320 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 specification for wire cloth and sieves for testing purposes. The raw grain-size data were then run through the free software program, GRADISTAT version 9.1, (Blott and Pye, 2001), which calculates the mean, median, 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 Friedman and Saunders (1978), a modified Wentworth (1922) size scale. 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 (7-8 runs per sample), and highlight runs that varied from the set average by more than ± 1.5 standard deviations. The highlighted runs were removed from the results, and the sample average was recalculated using the remaining runs. The raw, unaltered, individual run statistics measured by the LS 13 320 and class size distribution as produced by GRADISTAT (Blott and Pye, 2001), as well as the averaged run statistics and class size distributions, are available upon request. The averaged results for all samples, including the number of runs included and the standard deviation of the averaged results were summarized in an Excel workbook. The excel notebooks were compiled into a CSV file for NST samples and a CSV for surface sediment samples.