Sedimentary Data from the Coastal Marshes Fringing the Lower Waccasassa River, Northwest Florida

A GPS base station, named WCB1, was erected at the NGS PID AC5947 site located southeast of the centerline of County Road 326 in Levy County, FL, within approximately 10 km of the furthest sample site. GPS receivers recorded the 12-channel full-carrier-phase positioning signals (L1/L2) from satellites via the Thales choke-ring antenna. This GPS instrument combination was duplicated on the rover GPS. The base receiver and the rover receiver record their positions concurrently at 1-second (s) recording intervals throughout the survey. Occupation times at the sample sites were a minimum of 30 minutes.

The coordinate values of the GPS base station (WCB1) are the time-weighted average of values obtained from OPUS. The base station coordinates were imported into GrafNav and GrafNet, version 8.6 (Waypoint Product Group) and the GPS data from the rover were post-processed to the concurrent GPS session data at the base station. The GPS data were processed and exported in the World Geodetic System of 1984 (WGS84) (G1150) geodetic datum.

Sample locations were transformed from the acquisition datum of WGS84 to NAD83, and NAVD88 orthometric elevation (geoid model of 2009, GEOID09) using NOAA VDatum version 3.4 transformation software (http://vdatum.noaa.gov/).

Sediments were collected in 50 cm intervals with an Eijkelkamp Peat Sampler with a 5.78 cm hemispherical barrel. Ten total cores were collected; cores WC04R, WC05R, WC20R, WC21R, WC22R, and WC23R at site A; WC01R at site B and WC10R, WC11R and WC12R at site C. At all sites, cores were pushed until refusal, resulting in occasional overlaps between the bottom two segments. Sediments were photographed in the field with a NIKON Coolpix AW100 camera while in the peat sampler. Sediments were then transferred to pre-cut PVC pipes, wrapped in plastic wrap, duct tape and labelled.

During the 2015 sampling trip, approximately 25 cubic centimeters (cc) of surface sediments were collected at 7 coring sites (WC10, WC11, WC12, WC20, WC21, WC22, and WC23) by scraping the top 1 cm of surface material into plastic test tubes, which were then capped and labelled in the field. These are the surface samples, designated with an “S” in the data files.

Rectangular sediment slabs with approximately 15 x 15 cm cross sections were collected with a 46 cm long AMS, Inc. “Montana Sharpshooter” shovel at sites WC04D, WC10D, WC11D, WC12D, WC20D, and WC21D. The slabs were photographed in the field with a NIKON AW100 camera, then placed on a transparent PVC board, wrapped in plastic wrap, duct tape and labelled. Core lengths ranged from 34-40 cm. At sites WC22 and WC23, an Eijkelkamp Peat Sampler was used to obtain two replicate hemispherical cores of the top 50 cm of sediments. The two hemispherical cores from each location were later combined in the lab and treated as a single short core, named WC22R-a-b, WC23R-a-b.

Long cores (WC01R, WC04R, WC05R, WC10R, WC11R, WC12R, WC20R, WC21R, WC22R, and WC23R) were transported to the Global Change and Coastal Paleoecology Laboratory of Louisiana State University, where they were opened and all cores subjected to X-ray fluorescence (XRF) analysis with an Innov-X Delta Premium DP-4000 handheld XRF unit at 2 cm resolution down the length of the core. The device analyzes each sample across three frequencies for 30 seconds per frequency producing elemental concentrations in parts per million (ppm) for the following elements: 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, Bi, Th, U and Pb. Elements that were below the limit of detection for all samples (Rh, Pd, Ag, Cd, Sn, Sb, Ba, Pt, Au, Hg, Bi, Th, U) were excluded from the dataset. The device was calibrated with certified standards NIST 2710a and 2711a. These lithologic data have not been independently verified for accuracy.

Following XRF analysis, the long cores (WC01R, WC04R, WC05R, WC10R, WC11R, WC20R, WC21R, and WC22R) were subjected to loss-on-ignition analysis using the methodology employed by the Global Change and Coastal Paleoecology Laboratory of Louisiana State University. Sediment was removed in approximately 1-cc volumes continuously down the center of each core at 1-cm intervals and placed in pre-weighed ceramic crucibles. The crucibles were then dried for 12 hours at 100 degrees Celsius (°C) and reweighed to determine percentage (wet weight) of water content. The crucibles were then placed in a muffle furnace and heated to 550°C for 2 1/2 hours and reweighed to determine percentage (dry weight) of organic matter, then placed in a muffle furnace at 1000°C for 2 hours and reweighed to determine percentage of carbonates (dry weight) and residuals (predominately clastics). These lithologic data have not been independently verified for accuracy.

Nineteen subsamples, each approximately 1 cc in volume, were extracted from core WC20R at the following depths (cm) 1, 5, 15, 20, 35, 55, 75, 95, 105, 115, 125, 135, 145, 165, 185, 199, 217, 230 and 245, packed in sterile plastic bags and sent to the USGS Pollen Lab in Reston, VA for palynological analysis. The nineteen samples were processed and counted following the procedures described in Bernhardt and Willard, 2015. These pollen data have not been independently verified for accuracy.

Thirteen sediment intervals were subsampled to obtain radiocarbon dates. Samples were collected from depths of 123 cm in WC01R, 112 cm in WC05R, 96 cm in WC10R, 85 and 186 cm in WC11R, 22, 90, 132,174, and 212 cm in WC20R, 92 cm in WC21R, and 71 and 190 cm in WC22R. Sample selection depths were based on stratigraphic changes. Small (approximately 1-2 cc) volumes of material were removed from interior sections of the sediment cores and were 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 de-ionized water. The selected organic fragments were then placed in sterilized glass vials containing de-ionized 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 radiocarbon date for the plant material was calibrated to calendar years using Calib 7.0 and the INTCAL 13 curve, based on the dataset from Reimer and others (2013). The Calib 7.0 program provides a median probability date for each sample, calculated from the probability distribution.

The LOI and XRF results for the overlapping segments of cores WC01R, WC04R, WC05R, WC10R, WC11R, WC20R, WC21R, and WC22R, were used to create a single dataset for each core, with the depth of segment transition accurately determined with a resolution of transition of approximately 1 cm. Visual logs were created using Canvas 15 software to display core photos. A separate photo log was created for each peat borer core (WC01R, WC04R, WC05R, WC10R, WC11R, WC12R, WC20R, WC21R, WC22R, and WC23R) by aligning the separate 50-cm segments on scale bars. The overlap (when applicable) is marked by non-horizontal alignment of the photos. All segment intervals were analyzed for LOI and XRF. Specifying which data were used to create a single dataset, for each core, was determined by carefully matching the two overlapping segments and choosing the precise depth (1-cm resolution) for the transition. XRF and LOI data are presented using the consolidated dataset for each core. Photo logs were also created for shovel cores WC01R, WC04D, WC05D, WC10D, WC11D, WC12D, WC20D, WC21D, and the short peat borer cores WC22Ra-b, and WC23Ra-b.

Bulk density analysis was conducted, at the USGS SPCMSC, on the sediment samples (surface samples, shovel cores WC04D, WC10D, WC11D, WC12D, WC20D, WC21D and the replicate hemispherical surface cores WC22Ra-b, and WC23Ra-b) that were not transported to the Global Change and Coastal Paleoecology Laboratory of Louisiana State University. The subsamples were homogenized in the sample bag and a subsample of each 1 or 2 cm interval was processed for basic sediment characteristics. Water content and dry bulk density were determined using water mass lost during drying. A known volume (15-60 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 was recorded. The wet sediment and tray were placed in a drying oven for approximately 48 hours at 60°C. Water content was determined as the mass of water (in other words, mass lost when dried) relative to the initial wet mass. Replicate analyses of bulk density are reported for quality assurance.

Organic matter content analysis was also conducted, at the USGS SPCMSC, on the samples listed in the previous processing step. The dry sediment created as a result of the bulk density analysis described above was homogenized using a porcelain mortar and pestle. Approximately 5 g of the dry sediment was placed into a pre-weighed porcelain crucible. The mass of the dried sediment was recorded with an analytic balance to a precision of 0.01 g. The samples were then placed into a laboratory muffle furnace with stabilizing temperature control. The furnace was ramped to 550°C over a 30-minute interval and then held 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. Samples were reweighed using the same analytic balance and to a precision of 0.01 g. The mass lost during the 6-hour baking period, relative to the initial dry mass, is used as a metric of organic matter content. Replicate analyses of loss on ignition are reported for quality assurance.

Prior to particle size analysis, organic material was chemically removed from subsamples of cores WC04D, WC10D, WC20D, and WC21D, by treatment with 30% hydrogen peroxide (H2O2). Wet sediment from the marsh samples were dissolved in H2O2 overnight. The H2O2 was then evaporated and the sediment washed and centrifuged twice with deionized water. Grain-size analyses were performed using a Coulter LS 200 (https://www.beckmancoulter.com/) particle-size analyzer, 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). In order to prevent shell fragments from damaging the LS 200, 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 LS 200 a minimum of four runs each. The LS 200 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; https://doi.org/10.1002/esp.261), which calculates the mean, sorting, skewness, and kurtosis of each sample geometrically in metric units and logarithmically in phi units method. 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 (four 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 an of Excel workbook with each core on its own tab.

Dried sediment (15-30 g) from core WC20D were sealed in airtight polypropylene containers. The sample weights and the geometry of the counting container were matched to pre-made calibration standards. The sealed samples were allowed to sit for a minimum of 3 weeks 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 48-72 hours on a planar-style, low energy, high purity germanium, gamma-ray spectrometer. Sample count rates were corrected for detector efficiency (referenced to the IAEA RGU-1 standard), standard photo peak intensity, and self-absorption corrections using a U-238 sealed source. Activities are decay-corrected to the date of field collection. The radioisotopic activities reported in the Excel spreadsheet include the counting error for all samples. The critical level is reported for the sample set.

Total Pb-210 (via granddaughter polonium-210 [Po-210]) was determined by alpha spectroscopy for core WC10D. Five grams of sediment was spiked with 0.5 mL of Po-209 of known activity (12 decays per minute per milliliter). Sediments were leached with a combination of concentrated nitric and hydrochloric acid with the addition of 30% hydrogen peroxide (H2O2) to remove organics. Sediments were taken to dryness and re-saturated three times with hydrochloric acid until all nitric acid was removed. Po-209 and Po-210 were electroplated onto silver planchets and counted on an alpha spectrometer. Count rate efficiencies for Po-209 were determined and applied to Po-210 counts. Total Pb-210 is then assumed to be in secular equilibrium with Po-210 in the down-core sediment. The radioisotopic activities reported in the Microsoft Excel spreadsheet include the counting error for all samples. A subset of samples were analyzed in duplicate for quality assurance.

Added keywords section with USGS persistent identifier as theme keyword.