Abstract

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Dataset Citation

Lydia Vaughn, Mark Conrad, Margaret Torn, Markus Bill, Bryan Curtis, Oriana Chafe. 2015. CO2 and CH4 Surface Flux, Soil Profile Concentrations, and Stable Isotope Composition, Utqiagvik (Barrow), Alaska, 2012-2013. Next Generation Ecosystem Experiments Arctic Data Collection, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, USA. Dataset accessed on [INSERT_DATE] at https://doi.org/10.5440/1227684.

Dates

2012-08-01 - 2013-11-20

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Methodology

Fluxes of CO2 and CH4 were measured using opaque or transparent static chambers (25 cm diameter, 15-20 cm height). Chambers were tall enough to enclose vegetation and were vented according to Xu et al., (2006) to minimize pressure excursions due to the Venturi effect. In inundated plots, a floating chamber was used whose base extended 4 cm below the water surface. In all other plots, chambers were seated on PVC bases extending ~15 cm below the soil surface. To minimize disturbance, bases were installed at the beginning of the sampling season and left in place throughout the remainder of the season season. For each flux measurement, the chamber was seated in a 3 cm-deep, water-filled trench in the base's top rim to create an airtight seal. A Los Gatos Research, Inc. (LGR) portable Greenhouse Gas Analyzer was used to record CO2 and CH4 concentrations within the chamber over 4-8 minutes, and the flux rate of each gas was calculated from the slope of the linear portion of the concentration vs. time curve. Volumetric water content was measured with a MiniTrase TDR (Soilmoisture Equipment Corp). Soil temperature was measured with a thermistor or thermocouple probe, as indicated. As vegetation and inundation status varied between plots, depths of moisture and temperature measurements were determined from the top of the moss layer, bare soil, or water surface. Soil pore gas for trace gas stable isotope and concentration analyses was collected through 0.25 in diameter stainless steel probes into 60 mL syringes using a peristaltic pump. Water samples were filtered in the field through 0.1 um syringe filters and injected directly into evacuated glass vials sealed with 14 mm-thick chlorobutyl septa (Bellco Glass, Inc). Gas samples were injected directly into vials. In cases where syringes contained a mixture of water and gas, both sample types were collected and analyzed separately All isotope and concentration analyses were conducted at the Center for Isotope Geochemistry (CIG) at Lawrence Berkeley National Laboratory, Berkeley, CA. We report isotope ratios using the conventional delta notation. Carbon isotope ratios are reported relative to Vienna Peedee Belemnite (VPDB), and hydrogen isotope ratios are reported relative to Vienna Standard Mean Ocean Water (VSMOW). We measured carbon isotope ratios of dissolved inorganic carbon (DIC) in water samples and CO2 in gas samples using a variation on the technique outlined in Torn et al. (2003). The carbon isotope ratios of DIC or CO2 are accurate to +/- 0.33 permil (1sd) based upon repeated analyses of the laboratory standards. Carbon isotope ratios of CH4 were measured using a Trace Gas Ultra system interfaced to a Delta V Plus mass spectrometer (Thermo Fisher Scientific, Bremen, Germany). CH4 was chromatographically separated from other gases in the Trace Gas Ultra using an HP-molesieve fused silica capillary column (30 m x 0.320 mm). The CH4 was then combusted to CO2 at 1000C in a capillary ceramic tube loaded with Ni, Cu, and Pt wires, dried and transferred to the IRMS for the carbon isotope measurements. The reproducibility of measured carbon isotope ratios of CH4 is estimated to be +/- 0.16 permil (1sd) based on repeated analyses of an in-house laboratory standard Concentrations of CH4, CO2, and N2O in gas samples were determined using a 2014 Shimadzu GC. 4.5 mL of gas headspace from sample vials were flushed through a 1 mL stainless steel loop. The gases were then isolated on a HayeSep-D packed column (4 m x 1/8 in), then quantified with a flame ionization detector. For water samples, we used Henry's law with measured headspace pressures and water volumes to convert headspace CH4 and N2O concentrations to dissolved gas concentrations. DIC concentrations were calculated from IRMS results, using known sample aliquot volumes and calibrated mass 44 (CO2) peak areas.

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