Below ground soil bulk density, carbon and nitrogen was measured at various depth increments in mineral and organic soil layers at three sites at and around the Anaktuvuk River Burn: severely burned, moderately burned and unburned. This data corresponds with the aboveground biomass and root biomass data files: 2011ARF_AbvgroundBiomassCN, 2011ARF_RootBiomassCN_byDepth, 2011ARF_RootBiomassCN_byQuad, 2011ARF_RootBiomassCN_byQuad.
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The Anaktuvuk River Fire occurred in 2007 on the North Slope of Alaska. In 2008, three eddy covariance towers were established at sites representing unburned tundra, moderately burned tundra, and severely burned tundra. The three sites (unburned, moderately burned and severely burned) were harvested for analysis of biomass, carbon concentration and nitrogen concentration during the summer of 2011.
Units: Tissue mass data are expressed in g/m2 , µg/m2 or percentages as indicated.Sampling description:
Two transects at each of three sites were harvested for aboveground biomass, where transects 108 and 109 are from the unburned control site, 101 and 114 are from the severely burned site and 103 and 104 are from the moderately burned site . Quadrats measuring 10 x 40 cm were harvested every 5 meters over 50 meter transects for a total of 20 quadrats per site. Aboveground biomass is considered "within" the quadrat if it is associated with a meristem that is within the quadrat. Briefly, harvest method were as follows: the rhizome-containing soil layer was harvested by cutting around each quadrat boundary with a serrated bread knife. All aboveground live vascular plant biomass, and all live rhizomes and belowground stems within the quadrat boundaries, were separated by species. Data for aboveground biomass and further methods are explained in 2011ARF_AbvgroundBiomassCN.
For every second quadrat in a transect, two contiguous 10 x 20 cm soil monoliths were excised from the side of the pit, extending from the surface of the green moss to the surface of the mineral soil (roughly 5-30 cm depth depending on location). In addition, two cores (2.42 cm in diameter) were taken through the mineral soil from the bottom of these monoliths to the ice surface at the bottom of the thawed layer. Monoliths and cores were wrapped in tinfoil to preserve structure, returned to the field station, and refrigerated prior to analyses. Within 24 hours of collection, one monolith and one core from each location were processed for determination of microbial biomass, bulk density, moisture, and carbon (C) and nitrogen (N) concentrations in both soluble pools and solid fractions. Coarse (> 2 mm) and fine roots (< 2 mm) were separated by hand from the other monolith and core respectively. Root data and method information is available in the file 2011ARF_RootBiomassCN_byDepth and 2011ARF_RootBiomassCN_byPlot.
Soil samples from monoliths and cores were separated into depth increments between 5 and 10 cm wide starting at the surface of the layer (mineral or organic). Samples were homogenized by hand and coarse organic materials (>2.5 cm twigs and roots) and rocks were removed. A subsample of 10 g (wet weight) homogenized soil was extracted with 2M KCl overnight, for determination of soluble DOC (dissolve organic carbon), DON (dissolved organic nitrogen), NH4+ and NO3- concentrations. A second 10 g subsample was fumigated with chloroform for 24 hours prior to extraction with 2M KCl as above, for determination of microbial biomass. Extracts were frozen prior to analysis for NH4+ and NO3- using an Astoria Pacific (Astoria, Oregon) colorimetric auto analyzer, and a Shimadzu TOC-L auto analyzer with a TN unit (Columbia, Missouri) for DOC and DON. Coarse and fine soil fractions were weighed wet, dried at 70° C for 48 hours to determine dry matter content, then ground on a Wiley mill with a 40 mm sieve. Dry matter content of fine mineral soil was also determined on subsamples dried at 105°C for 48 hours. For all samples dried at 70°C, C and N content was measured on the same Costech Elemental Analyzer as the roots. The volume of each organic monolith layer or mineral core was calculated as depth times area minus the volume of rocks. Bulk density, C and N pools for soil fractions, and C and N pools for extracted fractions, were calculated for both mineral and organic horizons.
Data summarized by quadrat area is shown in file 2011ARF_SoilCN_byQuad. This worksheet shows all data measurements for all depths taken in the mineral and organic soil layers.
For further information reference:
Bret-Harte, M.S., Mack, M.C., Shaver, G.R., Huebner, D.C., Johnston, M., Johica, C.A., Pizano, M.C., Reiskind, J.A. (2013) The response of arctic vegetation and soils following the Anaktuvuk River fire of 2007. Philosophical Transactions of the Royal Society: Biological Science, Submitted.
Notes:If no samples were present in the biomass data, zeros were used. Where calculations were not possible dots were used as place holders
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