Three sediment pushcores were collected manually from the White Oak River, Station H. Cores were transported to the Institute of Marine Sciences in Morehead City, NC, and sectioned at 3 cm intervals. Porewater was preserved for methane, sulfate, DIC, and cell count measurements as described in Lloyd et al (2011) Environmental Microbiology 13(9) 2548-2564.
Briefly, for cell counts: sediments were fixed with 3% formaldehyde for 4-5 hours at 2 degrees C, washed twice with PBS and stored at -20 degrees C in 1:1 PBS:ethanol for approximately two weeks before counting. For sulfate, 15-ml tubes filled with sediment were centrifuged. The resulting porewater was filtered at 0.2 um, acidified with 10% HCl, and sulfate was measured by ion chromatograph. For methane measurements, 3 ml of sediment was sampled immediately after sectioning using a cutoff syringe into the side of the core, and quickly added to 60 ml serum vials which had been preloaded with 1 ml 0.1 M KOH. These were immediately stoppered and crimp-sealed with butyl rubber stoppers and then shaken vigorously to equilibrate methane into the headspace. Headspace methane was then measured by gas chromatography. Porewater for DIC was preserved in sealed glass vials and measured by ion chromatography.
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