Sedimentary Data From Grand Bay, Alabama/Mississippi, 2014-2016

Three types of sediment cores were collected at five salt marsh sites along Grand Bay, Alabama/Mississippi. Push cores were collected with 10.2-centimeter (cm) diameter polycarbonate barrels, driven into the sediment until refusal. Measurements were taken on the inside and outside of the barrel to determine compaction or core shortening values. Upon retrieval, the push cores were capped, labeled, and inspected for integrity. Push core recovered lengths ranged between 37 and 72 cm. Two push cores were collected at site GB53, labeled as (A) and (B). A Russian peat auger was used to collected sediment cores in 5-cm diameter, 50-cm long segments. The peat auger was driven in successive 50-cm depth increments until refusal such that a continuous sediment record was obtained with occasional overlaps between the bottom two segments. Each core segment was photographed, transferred to a PVC core sleeve, and sealed in plastic wrap. A hand-dug core was also collected at each site. A block of marsh sediment was cut using an AMS Sharpshooter shovel with an 18-inch (in) (45.7 cm) long blade, each side of the block being the maximum width of the shovel blade (5-1/4 in, 5.7 cm). Sediment was excavated along one side of the sediment block. A thin board was placed along the exposed side and the cut block was carefully extracted from the surrounding sediment until it was laying horizontally on the board. The resulting shovel core was measured, photographed, and wrapped in plastic. The uppermost 1 cm of surficial sediment was collected at each core site for sediment characterization and microfossil analysis. A replicate surface sample was collected at site GB56 to investigate homogeneity of the sediments. Microfossil assemblages for the surface sediments and cores are available in Haller and others, 2018. Surficial water quality properties at each site were measured with an YSI Professional Plus multi-sensor meter. If there was not standing water at the marsh sites, the probe was inserted into a bore hole to measure the porewater. YSI measurements were not taken at sites GB38 and GB96. At GB38, a refractometer was used to obtain a salinity measurement. Core and surface sample identifiers consist of the USGS project ID (14CCT01) and a site-specific identifier (for example, GB30). An alphabetic identifier was appended to each site identifier to differentiate the collection method (M for push core, R for peat auger core, D for shovel cores, and S for surface sample). Site positioning and elevations were determined using an Ashtech differential GPS receiver. The site position was also recorded with a hand-held Garmin GPSMAP 62stc receiver. A GPS location was not recorded at site GB96, the site location was approximated from a reference map. Site locations, elevations, date of collection, core lengths and compaction, and YSI measurements are reported in an Excel spreadsheet. Comma-separated values data files containing the tabular data in plain text are included in the download files. Peat auger and shovel core field photographs including a reference scale bar are available in Portable Document Format (pdf) files.

At 19 sites within the marsh tidal channels and Grand Bay proper, estuarine bottom sediments were collected with a petite ponar grab sampler. The sediment recovered in the grab sampler was inspected for an undisturbed sediment-water interface. If the sediment was disturbed, the sediment was discarded and a new grab sample was collected. If the sediment surface was intact, the overlying water was gently removed, and the uppermost one centimeter of sediment was sampled for sediment characterization and microfossil analysis. A replicate surface sample was collected at site GB37 and GB62 to investigate homogeneity of the sediments. Microfossil assemblages for the estuarine surface sediments are available in Haller and others, 2018. Water quality properties at each site were measured with an YSI Professional Plus multi-sensor meter. At each site, 5 gallons of the tidal channel or bay water was filtered through manganese dioxide-coated acrylic fiber to extract radium radioisotopes. The radium radioisotopic analytical results are not presented in this publication. Surface and water sample identifiers consist of the USGS project ID (14CCT01) and a site-specific identifier (for example, GB30). An alphabetic identifier was appended to each site identifier to differentiate the collection method (B for Mn-fiber radium samples and G for bottom sediment grab samples). The site position was recorded with a hand-held Garmin GPSMAP 62stc receiver. Site locations, date of collection, and YSI measurements are reported in an Excel spreadsheet. Comma-separated values data files containing the tabular data in plain text are included in the download files.

DGPS Acquisition: The DGPS base station consisted of one Ashtech Z-Xtreme DGPS receiver, one DGPS Thales choke-ring antenna, and a tripod. To increase positional accuracy of the marsh core locations and surface sediment grab samples, a DGPS base station was erected within 8 kilometers from the sampling sites. The roving DGPS duplicated the base station setup but the tripod was replaced with stadia rod equipped with a pointed end and plate that sat flush with the marsh surface and the DGPS antenna attached to the top of the stadia rod sat above the marsh grasses providing a clear view of the sky. Both receivers, equipped with internal data cards, recorded the 12-channel full-carrier-phase positioning signals (L1/L2) from the satellites via the choke-ring antennae. The base receiver and the rover receiver recorded their positions concurrently at 1-second (s) recording intervals for a minimum of 30 minutes at each marsh site and a minimum of 300 s at each surface sediment grab sample site.

GPS Post-Processing: The base station coordinates were established using OPUS. Every base station session was processed using OPUS and a solution in International GNSS (Global Navigation Satellite System) Service reference frame of 2008 (IGS08) was received and logged into a spreadsheet. The position from each OPUS solution was then converted from the IGS08 into the WGS84 (G1150) which is equivalent to the International Terrestrial Reference System of 2000 (ITRF2000) for consistency with other datasets. This conversion was accomplished using the NGS’ Horizontal Time-Dependent Positioning (HTDP) utility version 3.2.3. The weighted average of the base station positions was calculated and any elevations greater than three standard deviations were excluded from the average. All DGPS rover static sessions 30 minutes or longer were processed using Novatel Waypoint Consulting Group’s GrafNet version 8.5 software program. All DGPS stop and go roving sessions that were five minutes or longer were processed in GrafNav version 8.5. For all DGPS sessions, the antenna height, antenna model and DGPS session type (rover or base) was accounted for and then processed. The processed marsh core and the surface sediment grab sample coordinates were then converted into The North American Datum of 1983 (NAD83, (CORS96)) for the horizontal component and the North American Vertical Datum 1988 referenced to GEOID12A for the vertical component using the National Oceanic and Atmospheric Administration’s (NOAA) VDatum tool version 3.3.

The peat auger cores, shovel cores, and surficial sediment samples were transported to the Global Change and Coastal Paleoecology Laboratory of Louisiana State University. X-ray fluorescence (XRF) analyses were performed on all cores and surficial sediment samples with an Innov-X Delta Premium DP-4000 handheld XRF unit. Two readings of each surface sample were taken through the plastic wrap covering the sediments. Cores were analyzed at 2-cm resolution down the length of the core. The XRF device analyzes each sample across three frequencies for 30 seconds per frequency producing elemental concentrations in parts per million (ppm) for the following elements: P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Zr, Mo, Rh, Pd, Ag, Cd, Sn, Sb, Ba, Pt, Au, Hg, and Pb. The device was calibrated with certified standards NIST 2710a and 2711a. Elemental concentrations and corresponding standard deviations are reported in an Excel spreadsheet with each core on its own tab. Comma-separated values data files containing the tabular data in plain text are included in the download files.

At the SPCMSC, five push cores [excluding GB53M(A)] were x-rayed vertically onto an iCRco 11 x 14-inch cassette using an Ecotron EPX-F2800 x-ray unit. The cassette was inserted into and scanned using an iCR3600+ cassette scanner and processed using iCRco QPC XSCAN32 version 2.10 software. Images were then exported as tagged image file format (.tiff) files and edited in Adobe Photoshop, using grayscale color inversion. The color-inverted x-ray images including a reference scale bar are available in Portable Document Format (PDF) files.

At the SPCMSC, the six push cores were vertically extruded and sectioned into 1-cm intervals. The outer circumference of each interval was removed to avoid use of sediment that was in contact with the polycarbonate barrel. The shovel cores were also sectioned into 1-cm depth intervals by laboratory staff. Each sediment interval was bagged and homogenized. The bagged intervals were refrigerated until processing.

In the SPCMSC laboratory, a subsample of each 1-cm interval from the six push cores, five shovel cores, and the surficial sediment grab samples (G & S samples) was processed for basic sediment characteristics (dry bulk density and porosity). Water content, porosity and dry bulk density were determined using water mass lost during drying. For each 1-cm interval, 9–91 milliliters (mL) of each wet subsample was packed into a graduated syringe with 0.5 mL resolution. The wet sediment was then extracted into a pre-weighed aluminum tray and the weight of the wet sediment and the volume was recorded. The wet sediment and tray were placed in a drying oven for a minimum of 48 hours at 60 degrees Celsius (°C). Water content (θ) was determined as the mass of water (mass lost when dried) relative to the initial wet sediment mass. Dry bulk density was determined by ratio of dry sediment to the known volume of sediment packed into the syringe. Porosity (φ) was calculated from the equation φ = θ / [θ+(1-θ)/ρs] where ρs is grain density assumed to be 2.5 grams per cubic centimeter (g/cm^3). Salt-mass contributions were removed based on the salinity measured at the time of sample collection or estimated to be 25 if a field measurement was not recorded. Water content, porosity and dry bulk density are reported in the Excel spreadsheet. A comma-separated values data file containing the tabular data in plain text is included in the download file.

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). Replicate analyses of loss on ignition for a representative subset of the core intervals are reported for quality assurance in the Excel spreadsheet. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Down-core particle size analysis was performed on each 1-cm depth interval for 4 push cores (GB36M, GB53M(A), GB60M, and GB64M), one shovel core (GB60D), and the surficial sediment (G & S) samples. All intervals from the push cores were analyzed to a depth of 40 cm in the core. Select intervals spanning the entire length the shovel were chosen for analysis. All surficial sediments (G & S) samples were analyzed. A total of 219 samples were analyzed for particle size. Prior to particle size analysis, organic material was chemically removed for the samples using 30% hydrogen peroxide (H2O2). Wet sediment was dissolved in H2O2 overnight. The H2O2 was then evaporated by gentle heating and the sediment washed and centrifuged twice with deionized water. Grain size analyses on the sediment cores were performed using a Coulter LS 200 or LS 13 320 (https://www.beckmancoulter.com/) particle-size analyzer (PSA), which uses laser diffraction to measure the size distribution of sediments ranging in size from 0.4 microns to 2 millimeters (mm) (clay to very coarse-grained sand). To prevent shell fragments from damaging the Coulter instrument, particles greater than 1 mm in diameter were separated from all samples prior to analysis using a number 18 (1000 microns or 1 mm) U.S. standard sieve, which meets the American Society for Testing and Materials (ASTM) E11 standard specifications for determining particle size using woven-wire test sieves. Two subsamples from each depth interval were processed through the instrument a minimum of three runs each. The sediment slurry made from the digested sample and deionized water was sonicated with a wand sonicator for 1 minute before being introduced into the Coulter PSA to breakdown aggregated particles. The Coulter PSA 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. Light is scattered by the particles into characteristic refraction patterns measured by an array of photodetectors as intensity per unit area and recorded as relative volume for 92 size-related channels (bins). The size-classification boundaries for each bin were specified based on the ASTM 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), which calculates the mean, sorting, skewness, and kurtosis of each sample geometrically in metric units and logarithmically in phi units. GRADISTAT also calculates the fraction of sediment from each sample by size category (for example, clay, coarse silt, fine sand). A macro function in Microsoft Excel, developed by the USGS SPCMSC, was applied to the data to calculate average and standard deviation for each sample set (6-8 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 averaged runs and the standard deviation of the averaged results were summarized in an Excel workbook with each core on its own tab. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Dried ground sediment from the 1-cm depth intervals of the 6 push cores and 1 shovel core (GB53D) were analyzed for the detection of radionuclides by standard gamma-ray spectrometry (Cutshall and Larsen, 1986) at the USGS SPCMSC radioisotope lab. Most intervals from the uppermost 20-25 cm were analyzed from each core with selected intervals analyzed at lower depths in the cores. A total of 209 depth intervals were analyzed for radioisotopic activities. The sediments (4-50 g) were sealed in airtight polypropylene containers. The sample weights and counting container geometries were matched to pre-determined calibration standards. The sealed samples were stored for a minimum of 3 weeks prior to analysis to allow Ra-226 to come into secular equilibrium with its daughter isotopes Pb-214 and Bi-214. The sealed samples were then counted for 24-72 hours on a 50-millimeter diameter planar-style, low energy, high-purity germanium, gamma-ray spectrometer. The suite of naturally-occurring and anthropogenic radioisotopes measured along with their corresponding photopeak energies in kiloelectron volts (keV) are Pb-210 (46.5 keV), Th-234 (63.3 keV), Pb-214 (295.7 and 352.5 keV; proxies for Ra-226), Bi-214 (609.3 keV; proxy for Ra-226), Cs-137 (661.6 keV), and K-40 (1640.8 keV). Sample count rates were corrected for detector efficiency determined with International Atomic Energy Agency RGU-1 reference material, standard photopeak intensity, and self-absorption using a U-238 sealed source (Cutshall and others, 1983). All activities, with the exception of short-lived Pb-214 and Bi-214, were decay-corrected to the date of field collection. The radioisotopic activities reported in the Excel spreadsheet include the counting error for all samples, results from each core are on its own tab. The critical level is reported for each core. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Total Pb-210 activity was measured by alpha spectroscopy for 13 estuarine bottom sediment grab samples. The Pb-210 (half-life = 22.3 years) activity is determined by directly measuring the activity of its granddaughter Po-210 (half-life = 138 days) via alpha particle decay. Po-210 is assumed to be in secular equilibrium with its parent. The analytical method exploits the ability of polonium to self­plate onto silver planchets, which facilitates the alpha counting (Flynn, 1968). The laboratory method used at the USGS SPSMSC for chemical separation of Po-210 from sediments was developed by Martin and Rice (1981). Po-210 was acid leached from 5 grams of dried, ground sediment with concentrated nitric acid and a known activity of the tracer Po-209 was added to the solution. The solution digested overnight and then was dried on a hotplate, followed by several washings with 30% hydrogen peroxide and 8N hydrochloric acid. The final acidic solution was brought to 70 mL with deionized water. Several buffering solutions were added to reduce interference from other cations and oxidants present during the plating process. The pH was adjusted to between 1.8-1.9 with ammonium hydroxide. The Po-210 was autoplated onto 1.9-cm diameter sterling silver planchets while stirring and heating the solution. After 2 hours, the planchets were removed from solution, rinsed and dried. The planchets were counted for 24 hours in low-level alpha spectrometers coupled to a pulse-height analyzer. The radioisotopic activities reported in the Excel spreadsheet include the counting error for all samples. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Dried ground sediment from the 5 surficial marsh sediment samples (GB33S, GB49S, GB53S, GB60S, and GB68S) and 3 estuarine bottom sediment samples (GB46G, GB52G, and GB58G) were submitted for inductively coupled plasma-atomic emission spectrometer (ICP-AES) element concentration analysis to the USGS Central Mineral and Environmental Resources Science Center (CMERSC). Between 0.98 and 1.46 g of material was sent in 25 mL glass scintillation vials for a 42-element analysis of concentrations (Taggart, 2002). At CMERSC, samples were digested using hydrochloric, nitric, perchloric, and hydrofluoric acids and then aspirated into the ICP-AES and inductively coupled plasma-mass spectrometer (ICP-MS). The ICP-AES was calibrated using digested rock reference materials as well as a series of multi-element solution standards. The ICP-MS was calibrated with aqueous standards. To account for internal drifts and matrix effects, internal standards were used. The elemental concentrations are reported in the Excel spreadsheet. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Sediment samples from the surficial marsh sediments and estuarine bottom sediments were submitted to the Yale Analytical and Stable Isotope Center (YASIC, http://earth.yale.edu/yasic-yale-analytical-and-stable-isotope-center) for nitrogen-15 and carbon-13 stable isotope analysis. Dried, homogenized sediment was placed in 8 x 5-millimeter (mm) silver capsules, wet with 50 microliters (µL) of deionized water, and fumigated in a desiccator with 100 mL of concentrated hydrochloric acid for 6 hours to remove inorganic carbon (Harris and others, 2001). Samples were then dried at 60 °C overnight, and double encapsulated in tin for combustion purposes. For quality assurance, ten percent of the fumigated samples were submitted in duplicate. Dried, homogenized sediment from the same set of samples were also submitted for the identical analysis without fumigation, which may potentially alter the nitrogen values, prior to encapsulation in a single tin capsule . All samples were analyzed using a Costech ESC 4010 Elemental Analyzer with Conflo III Interfaced connected to a Thermo Finnigan DELTAplus Advantage isotope ratio mass spectrometer. Values are relative to international standards: the VPDB (Vienna Pee Dee Belemnite) for carbon, and atmospheric air for nitrogen. The stable isotopic ratios reported in the Excel spreadsheet include the replicate sample analyses and laboratory-reported reference sample results for quality assurance and quality control. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Seven sediment depth intervals from select peat auger cores were subsampled to obtain radiocarbon dates. Sample selection depths were based on stratigraphic changes. Small (approximately 1 cc) volumes of material were removed from interior sections of the sediment cores and passed through a 63-micron sieve to remove silt and clay. Plant fragments were selected from the remaining material under a dissecting microscope after being washed in deionized water. The selected organic fragments were then placed in sterilized glass vials containing deionized water. When sufficient material was collected, each vial was placed in an oven at 60 °C until all moisture was removed (variable time, but usually 1-4 days). This material was sent to the National Ocean Sciences accelerator mass spectrometry (NOSAMS) laboratory at Woods Hole Oceanographic Institution (Woods Hole, MA, USA), where accelerator mass spectrometry (AMS) radiocarbon dating was performed by means of a 500 kV compact pelletron accelerator. The NOSAMS facility is supported by National Science Foundation Cooperative Agreement number, OCE-1239667. The radiocarbon analytical results are reported in the Excel spreadsheet. A comma-separated values data file containing the tabular data in plain text is included in the download file.

Added keywords section with USGS persistent identifier as theme keyword.