Wetland Paleoecological Study of Coastal Louisiana: X-radiographs

Cores were collected at Rockefeller Wildlife Refuge (RWR) using an airboat. RWR is state-owned refuge that is managed primarily for waterfowl and fishery habitat with a primary mission to promote 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 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 10-cm diameter, clear acrylic tubes into the marsh. The barrel edge was sharpened and vegetation was sliced around the perimeter of the tube to reduce compaction during tube insertion. Compaction was estimated by measuring the difference in the marsh elevation between the inside and outside of the top of the barrel prior to extraction. The tube was capped and extracted from the sediment using a handle constructed from 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a narrow plastic tube to a depth of 10 cm and using suction, supplied by an attached syringe, a sample of water was withdrawn. The water sample was placed in a cup and salinity measured using a handheld probe.
The cores were sealed and transported to the lab. The cores remained cold and vertical during transport by placing them in an insulated and lined 50-gallon plastic barrel with ice. Upon arrival at the lab, the cores were x-radiographed (58-64 kV, 2.0 mAs) using 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 and recorded on core description sheets.

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