Wetland Paleoecological Study of Coastal Louisiana: Sediment Cores and Diatom Samples Dataset

Cores were collected at Rockefeller Wildlife Refuge (RWR) aboard an airboat. RWR is state-owned refuge that is managed primarily for waterfowl and fishery habitat with a primary mission of promoting scientific research. Five core sites were located along a transect perpendicular to the Gulf of Mexico coastline, ranging from 0.5 to 5.75 km distant from the shoreline. To examine small-scale variation, two additional sites were located 100 meters to the east and west of site 09WCC01_04 and parallel to the shore. Two additional sites were located to the west and east of the transect.
Sediment was extracted by pushing a clear acrylic tube, 10-cm in diameter into the marsh. The barrel edge was sharpened and vegetation around the extraction point's perimeter was sliced to reduce compaction during tube insertion. Compaction was estimated by measuring the difference in the marsh elevation between the inside and outside of the barrel top prior to extraction. The tube was capped and extracted from the sediment with a handle constructed of PVC. Geographic position, time of day, water depth, and surface water salinity were measured at each site. Porewater salinity was measured by driving a narrow plastic tube to a depth of 10 cm and using suction supplied by an attached syringe, to withdraw a water sample. The water sample was placed in a cup and salinity was measured with a handheld YSI conductivity probe.
The cores were sealed and transported to the lab. The cores remained cold and vertical during transport in an insulated and lined 50-gallon barrel containing ice. Upon arrival at the lab, the cores were x-radiographed (58-64 kV, 2.0 mAs) with a Torrex 120 portable X-ray unit and a ScanX CR2500 imaging system (exposure setting 58/2.0), producing bitmap files at 4457 x 5500-6000 pixels, 8-bit depth and approximate 23-25MB each. After imaging, cores were extruded and sliced at 2-cm intervals. Compaction from core transport and sampling (extrusion) were estimated by the difference between the measured lengths of the core before and after each procedure. Sedimentary characteristics; sediment texture, physical characteristics, presence of roots/shells/burrow, and stratification type; were described in detail during the sampling process.
Field data was hand-entered into Microsoft Excel 2010, double-checked for accuracy, and exported into a comma-delimited text file.

Laboratory procedure: All sediment core samples were analyzed for bulk density, organic carbon, and lead-dating. A 30-mL sediment sample was weighed wet, dried in an oven at 60 °C, and weighed again to calculate bulk density (dry mass divided by volume). Loss-on-ignition (LOI) was determined by grinding the dried sample into a fine powder and combusting a subsample at 650 °C for four hours. Lead-210 was determined by measuring the activity of Po-210 using alpha-spectrometry. Polonium-210 is assumed to be in secular equilibrium with its parent Pb-210. The fired sample from LOI analysis was transferred to a glass beaker and Po-210 was acid leached from the sediment. A known quantity of the tracer Po-209 was added to the solution prior to auto-plating and counted on low-level alpha spectrometer coupled to a pulse-height analyzer. Reported errors are the statistical counting errors at the 95 percent confidence interval. At least five samples per core were processed in duplicate in order to calculate relative standard deviation for an estimate of between sample errors. Select core samples were identified for gamma-ray spectrometry (Cs-137) by examining Pb-210 profile data, isolating the depth where the detectable limit where excess Pb-210 reaches zero (provides a rough estimate 100 years before present), and estimating where Cs-137 activity would likely be detected (1950 to 1984). Approximately 15 g of dried, ground sample was sealed in a plastic jar and stored for at least 3 weeks to allow activity to reach equilibrium. Samples were counted using a germanium detector for low-energy gamma rays and a multi-channel analyzer was used for data collection. Samples were counted for at least 24 hours or until counting errors were less than 5 percent. In addition, select core samples were processed for grain size by examining x-ray images and bulk density data to identify possible changes in sedimentary layers. Data was hand entered into Microsoft Excel, double-checked for accuracy, and exported into a comma-delimited text file.

Microfossil analyses: Approximately 0.5 mL of sediment was digested in a 100-mL beaker using hydrogen peroxide and potassium dichromate. Samples were rinsed twice with deionized (DI) water (the beaker was filled with DI water; sample was allowed to settle overnight, decanted to 500-mL mark, and refilled, etc.). Since samples contained a significant fraction of fine-grained sediment (silt and clay), a 7 percent sodium hexametaphosphate solution was added to deflocculate fine-grained sediments. Each sample was continually rinsed until decant was clear. A known volume (5 or 10 mL depending on the density of diatoms and sand grains) of diatom solution was added to settling trays containing four cover slips and allowed to dry (Battarbee, 1973). Cover slips were sealed to microscope slides using Zrax diatom mountant (refractive index ~ 1.7+). A minimum of 300 diatoms were identified to species and counted using a Nikon Optiphot light microscope at 1000x magnification (Plan 100x / 1.25 oil DIC objective). The identification of species and autecology, including general salinity preferences, was determined from taxonomic literature. Each species identified was given a code, composed of the genus and species name, and checked with surface sediment samples of the same area for differences. Any species missing from the regional assessment were added. Data was hand-entered into Excel, double-checked for accuracy, and exported as a comma-delimited text file.

Keywords section of metadata optimized by correcting variations of theme keyword thesauri and updating/adding keywords.

Added keywords section with USGS persistent identifier as theme keyword.