Soils Data Related to the 1999 FROSTFIRE Burn

By K.L. Manies, J.W. Harden, and R. Ottmar

Open-File Report 2011–1216

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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Suggested citation:

Manies, K.L., Harden, J.W., and Ottmar, R., 2011, Soils Data Related to the 1999 

FROSTFIRE Burn: U.S. Geological Survey Open-File Report 2011-1216, 8 p. and data 

tables, available at http://pubs.usgs.gov/of/2011/1216/. 

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endorsement by the U.S. Government. 

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copyright owners to reproduce any copyrighted material contained within this report.
iii

Contents

Abstract .............................................................................................................................................1

Introduction .......................................................................................................................................1

Site Descriptions ...............................................................................................................................2

Sample Collection & Processing .......................................................................................................3

Laboratory Methods ..........................................................................................................................4

 Total Carbon, Total Nitrogen, δ13C, δ15N .......................................................................................4

14C Analyses..................................................................................................................................5

Loss on Ignition, Elemental Analysis, and Mercury .......................................................................6

Sample Nomenclature.......................................................................................................................6

Dataset Descriptions.........................................................................................................................7

Acknowledgments.............................................................................................................................7

References Cited ..............................................................................................................................7

Figures

1. Landsat image of the area that burned during FROSTFIRE (red part of image) within the 

approximate boundary of the Caribou-Poker Creeks Research Watershed (CPCRW). The 

CPCRW is found within interior Alaska.......................................................................................2

2. A schematic showing the layout of the U.S. Forest Service (USFS) sites, which were used 

in this study by both USFS and U.S. Geological Survey (USGS) investigators for their preand post-burn sampling strategy. ...............................................................................................3

Tables

1. List of sites located within the FROSTFIRE watershed. .............................................................3

2. Organic soil horizon codes and descriptions, FROSTFIRE burn, Alaska. ..................................4

3. Statistics of analyses for working standards run on the IRMS from 2001 through 2008.............5
Soils Data Related to the 1999 FROSTFIRE Burn

By K.L. Manies, J.W. Harden, and R. Ottmar

Abstract

This report describes the sample collection and processing for U.S. Geological 

Survey efforts at FROSTFIRE, an experimental burn that occurred in Alaska in 1999. 

Data regarding carbon, water, and energy dynamics pre-fire, during, and post-fire were 

obtained in this landscape-scale prescribed burn. U.S. Geological Survey investigators 

measured changes in the stocks of carbon (C), nitrogen (N), mercury (Hg), and other 

components in pre- and post-burn soils of this watershed. 

Introduction

FROSTFIRE was a landscape-scale prescribed burn in Alaska, the goal of which 

was to study the large-scale consequences of fire on the C, water, and energy pools in 

boreal forests both during and after the fire. Of the 2,500 acres prescribed to burn, 

approximately 900 acres were consumed, the majority of which was black spruce (Picea 

mariana (Mill.) BSP) forest. More than 50 research teams studied a variety of topics, 

including the impacts of weather and vegetation on fire, the impacts of fire on CO2, CH4, 

and N2O fluxes, as well as the impacts of fire on stream chemistry. FROSTFIRE was

developed, in part, because boreal forests contain the majority of the world’s soil organic 

C (McGuire and others, 2009; Schuur and others, 2008; Tarnocai and others, 2009) and

play an important role in the global C cycle. Fire affects C storage of the boreal forest 

both directly (fire emissions, loss of vegetation) and indirectly. Indirect effects include 

altering the soil-temperature regime through changes in albedo and the loss of organic 

layers, which play an important role in soil insulation (O'Neill and others, 2002). 

Changes in soil temperature in turn affect decomposition rates (Wickland and others, 

2010) and vegetative regrowth (Johnstone and others, 2010). Therefore, a large-scale 

burn was needed to permit accurate analysis of the short- and long-term impact of fire on 

these ecosystems.

As a part of the FROSTFIRE project, U.S. Geological Survey (USGS) 

investigators measured changes in the stocks of C, nitrogen (N), mercury (Hg), and other 

components in pre- and post-burn soils. The data presented here represent the USGS 

sampling effort, as well as data from organic soils sampled by the U.S. Forest Service

(USFS) Fire and Environmental Research Applications (FERA) team that were shared 

with USGS. Results from this study were published in Harden and others (2004) and 

Turetsky and others (2006). 
2

Site Descriptions

The sites were located within the Caribou-Poker Creeks Research Watershed 

(CPCRW), which is ~45 km north of Fairbanks (fig. 1), Alaska, and managed by the 

Bonanza Creek Long-Term Ecological Research (LTER) program. CPCRW is 

comprised of birch and aspen stands on south-facing slopes and black-spruce dominated 

stands on north-facing slopes. The soils have a thin cap of loess over discontinuous 

permafrost. 

Four USFS sites were used to characterize the pre- and post-burn organic soils 

(table 1). Within each site, eighteen plots were positioned 20.1 m (2 chains) apart along 

two transects established perpendicular to the slope. Sixteen depth-of-burn or 

consumption rods were systematically positioned around each plot to mark the surface of 

the organic soils (fig. 2). These pins were remeasured following the fire to determine 

organic soil-depth reduction. Pre-burn soil samples were located randomly along these 

transects. The burning of FROSTFIRE occurred July 8–15, 1999. Initial post-burn soil 

sampling occurred once the watershed was open to scientists at locations adjacent to the 

severity pins. Additional post-burn sampling of the lower black spruce (LBS) site 

occurred in May of 2000. 

Figure 1. Landsat image of the area that burned during FROSTFIRE (red part of image) within 

the approximate boundary of the Caribou-Poker Creeks Research Watershed (CPCRW). The 

CPCRW is found within interior Alaska.
3

Table 1. List of sites located within the FROSTFIRE watershed.

USFS Code USFS name General location

FFS2 Lower black spruce (LBS) Located at the base of the watershed along Poker 

Creek

FFS3 Birch #2 (BIR) Located on a south facing hillslope above Poker 

Creek

FFS4 Sloped black spruce (SLBS) Located along a north facing hillslope below FFS5

FFS5 Upper black spruce (UPBS) Located at the top of the hillslope near Helmer’s 

Ridge

[USFS, U.S. Forest Service

Figure 2. A schematic showing the layout of the U.S. Forest Service (USFS) sites, which were 

used in this study by both USFS and U.S. Geological Survey (USGS) investigators for their 

pre- and post-burn sampling strategy.

Sample Collection & Processing

Pre-burn soil samples collected by USGS personnel were characterized by 

describing the individual horizons, or layers, to the depth at which the soil was frozen. 

(Since these sites were initially sampled in May, frozen soil was encountered before 

mineral soil was reached.) Bulk soil (or combined horizons) was then sampled

volumetrically to a depth greater than that which the fire was predicted to burn. Each of 

these samples was divided into two subsamples: a moisture sample and a bulkdensity/analytical sample. Post-burn samples collected in 1999 and 2000 were obtained

by cutting blocks of organic soil of known dimensions from the forest floor and 

subdividing these blocks into distinct soil horizons. The entire sample was used for 

moisture, bulk density, and analytical purposes for the 1999 post-burn samples. In 2000, 

Moisture Plug

Depth Plug

Depth Plug

Depth Plug

Depth Plug

Consumption Rods

(Welding rod)

Welding Rod

Litter 

Upper Duff

Lower Duff

Mineral Soil

Side view: pre-burn

Litter

Upper Duff

Lower Duff

Mineral Soil

Side view: post-burn
4

these samples were only used for bulk density and analytical purposes and a separate 

moisture subsample was taken adjacent to the initial sampling location. 

Regardless of sampling method, all samples were air dried to a constant mass. 

Next, a split of the sample or the moisture subsample was oven dried at 65°C. The 

analytical subsample/split was not oven dried, but these data can be converted to an ovendry basis using gravimetric moisture content in the air dried sample. Analytical splits 

were weighed and roots wider than 1 cm in diameter were removed, weighed, and saved 

separately. The remaining sample was then milled in an Udy Corp. Cyclone mill (Fort 

Collins, Colorado) to pass through a 0.5-mm screen. The milled sample was thoroughly 

mixed and a representative sample was placed in a labeled, glass sample bottle for 

chemical analysis. Archive fractions of most of the samples are available by contacting 

J.W. Harden at the USGS Menlo Park, California office. 

Table 2. Organic soil horizon codes and descriptions, FROSTFIRE burn, Alaska. 

Horizon code General description

LM Live moss: green moss layers, leaf and needle litter.

DM Dead moss: undecomposed or very slightly decomposed moss. Few roots.

UD Upper duff: fibric layers in which roots are more abundant than recognizable moss 

parts. They would be classified at fibric layers (Canadian system) or Oi layers (U.S. 

system).

LD Lower duff: well decomposed organics with no or little recognizable plant parts. They 

would be mesic or humic layers (Canadian system) or Oa layers (U.S. system).

LT Litter: hardwood leaf and twig litter.

LDF Combined horizon of live moss, dead moss, and upper duff.

LTF Combined horizon of litter, dead moss, and upper duff.

L Live moss, generally green. May contain leaf and needle litter.

D Dead moss. Not decomposed or slightly decomposed. Few, if any, roots.

F Fibric organics, with roots often more abundant than plant parts. 

M Mesic, or moderately decomposed, organics. Amorphous material present.

H Humic, or highly decomposed, organics. Smears upon squeezing.

X Unknown

Ash Ash

A Mineral soil with less than 20% organic matter, as judged in the field.

bX A lower case b before a horizon code indicates that the layer has been burned.

fX A lower case f before a horizon code indicates that the layer was frozen when sampled.

[These descriptions are modified from Canadian (Committee, 1998) and U.S. Department of AgricultureNatural Resources Conservation Service (USDA-NRCS; Staff, 1998) methodologies.] 

The week before the fire USFS personnel also collected pre-burn samples for 

determining water content. Some of these samples were obtained volumetrically by 

inserting a square metal box of a known volume into the forest floor. Different soil 

horizons (table 2) within the profile were separated and described. Horizons thicker than 

5 cm were also divided. These samples were oven dried at 65°C and then sent to the 

USGS to be processed for chemistry in the same manner as the USGS pre-burn samples. 

Laboratory Methods

Total Carbon, Total Nitrogen, δ13C, δ15N 

A Carlo Erba NA1500 elemental analyzer coupled to a Micromass Optima 

isotope ratio mass spectrometer (IRMS) in continuous flow mode was used to determine 

total C, total N, δ13C, and δ15N. Because carbonates are rare in this area and mineral-soil 
5

pH values from a previous study were <7.0 (Rieger and others, 1972), nearly all of this C 

can be considered organic. Samples were combusted in the presence of excess oxygen. 

The resulting sample gasses were swept in a continuous flow of helium through an 

oxidation furnace, followed by a reduction furnace, to yield CO2, N2, and water vapor. 

Water was removed by a chemical trap, and CO2 and N2 were chromatographically 

separated before entering the Micromass Optima IRMS for the measurement of C, N, 

δ13C and δ15N. Carbon and N were determined by integrating the major ion peaks (mass 

44 for CO2, and mass 28 for N2). For reliable quantification of δ15N, 15 to 30 μg N 

generally are needed, and few samples met this criterion. Thus, the δ15N data are not 

reported here; these data are available from the authors by request. The δ13C data are 

reported as deviations in parts per thousand (‰) relative to a standard, here Vienna Pee 

Dee Belemnite (V-PDB). δ13C was calculated as:

δ13C ‰ = (((13C sample/12C sample) / (13C standard/12C standard)) – 1) * 1000. (1)

Table 3. Statistics of analyses for working standards run on the IRMS from 2001 through 2008.

%C %N 13C

Standard Avg. Stdev. N Avg. Stdev. N Avg. Stdev. N

MESS-1 3.02 0.15 49 0.18 0.01 49 -25.64 0.14 49

NBS16455.21 0.39 53 0.09 0.01 55 -22.29 0.27 53

[Certified values: MESS-1 = 2.99 percent C; NBS-1645 = 0.08 percent.]

All samples were compared to a main working standard, ethylenediamine tetraacetic acid (EDTA). The chemical formula for this compound corresponds to a C content 

of 41.09 percent and a N content of 9.59 percent. Two working standards were analyzed 

as samples in all runs to check consistency and overall precision: a marine sediment 

standard (MESS-1), issued by the Chemistry Division of the Canadian National Research 

Council, and a river sediment standard (NBS 1645), issued 

by the National Bureau of Standards, now the National Institute of Standards and 

Technology (NIST). Certified values were obtained from Govindaraju (1989). Measured 

values of these working standards for runs including FROSTFIRE and other samples can 

be found in table 3. 

14C Analyses

A subset of samples were run for 14C activity. Most of these samples were chosen 

to aid in modeling soil turnover and(or) to partition carbon into more labile versus stabile 

pools. The 14C content of ground, untreated soil was measured by vacuum sealing a 

homogenized sample containing ~1 mg C with cupric oxide and elemental silver in a 

quartz tube. The sample was then combusted at 850°C, and the resulting CO2 was 

purified cryogenically and reduced to graphite using a modified reduction method with 

titanium hydride, zinc, and cobalt catalyst (Vogel, 1992). The graphite target was 

measured The graphite target was measured directly for 14C at W. M. Keck C Cycle 

Accelerator Mass Spectrometer (AMS) Laboratory at UC Irvine. 

The 14C data are expressed in Delta notation (∆14C), which, similar to δ13C, 

expresses the deviation in the 14C/C in parts per thousand (‰) as compared to the 

standard NIST Oxalic Acid I (C2H2O4), with additional correction for fractionation, based 

on generalized 13C values (see Stuiver, 1980; Stuiver and Polach, 1977). ∆14C values 

also are presented as Fraction Modern (FM) values, calculated using the following 

equation: 
6

FM = [(S – B) / (M – B)], (2)

where B, S, and M represent the 14C/12C rations of the blank, the sample, and the modern 

reference, respectively. The modern reference is defined at 95 percent of the radiocarbon 

concentration (in AD 1950) of NBS Oxalic Acid I normalized to δ13CVPDB = -19 ‰ 

(Olsson, 1970). 

Loss on Ignition, Elemental Analysis, and Mercury

Loss on Ignition (LOI) was measured by the USGS for the majority of samples. 

Air-dried, ground samples were heated at 550°C in a muffle furnace for five hours. The 

change in weight pre- and post-heating was used to calculate LOI. For 28 samples, LOI 

was measured by XRAL Laboratories (SGS Group, Toronto, Canada). 

Elemental concentrations were analyzed using inductively coupled plasma (ICP) 

procedures at XRAL Laboratories. Samples analyzed for LOI at the USGS were

submitted to XRAL as ash. These samples were analyzed using the 95 element ICP 

method (also known as ICP-95 and WR ICP). The remaining samples were submitted as 

ground soil and analyzed using the 40 element ICP (ICP-40) method. The two ICP 

procedures differ in that the ICP-95 method uses a lithium metaborate fusion followed by 

dissolution, while the ICP-40 method uses an acid dissolution. Therefore, if samples 

contain refractory minerals impervious to strong acid, the ICP-40 data will be lower than 

the ICP-95 data. We do not expect there to be a large difference between the two 

processes for our samples. Phosphorus data from the ICP-40 procedure were reported as 

percent P, while the ICP-95 data were reported as percent P2O5. Therefore, the percent P 

data was converted to percent P2O5 data by multiplying percent P values by 2.2912. 

More information regarding the ICP-40 procedure, calibration techniques, and its 

detection limits can be found in Briggs (2002). More information regarding the ICP-95 

procedure can be found in Marabini and others (1992). 

Hg was analyzed by XRAL Laboratories. Samples were digested with mixtures 

of H2SO4, HNO3 , HCL, KMnO4 (5 percent), and K2S2O8 (5 percent). Excess KMnO4

was reduced using a hydroxylamine sulfate solution, and the resulting Hg (II) was

reduced by a solution of SnCL2. The Hg vapor was then separated and measured using a 

LEEMAN PS200 Automated Mercury Analyzer (H. De Souza, XRAL Laboratories, oral

commun.). 

Sample Nomenclature

All samples are labeled with a code describing the site and location from which 

the samples were obtained. Pre-burn USGS samples have the site represented by the site 

code (table 1) followed by a “U”, indicating that the sample is unburned. A space 

separates the site information from further information. This space is followed by the 

USFS plot number nearest to the sample location. The number after the decimal point 

represents the basal depth (cm) of the sample. Pre-burn USFS samples have the site 

represented by the site name (table 1) followed by a space. This space is followed by the 

USFS sample number (based on the number of samples taken that day). The number 

after the decimal point is the basal depth (cm) of the sample.

Post-burn samples from 1999 were all taken at site FFS5 (also referred to as

UPBS). This notation was shortened to FS5. The letter “A” after the site name indicates 

the sample was obtained post-burn. This information is followed by a space. The 

number after the space represents the plot number from which the sample was taken. 
7

Within each plot were sixteen fire-severity pins. The number in the parentheses 

represents the pin number next to which the sample was taken. The number after the 

decimal point is the basal depth (cm) of the sample. The letter “R” after the sample 

means this sample is a duplicate taken post-rain. This extra sampling effort occurred 

because it rained lightly during the night between the two days of post-burn sampling. 

Some upper-surface profiles were resampled post-rain to test whether significant mixing 

or leaching of ash occurred during the rain.

Dataset Descriptions

Four separate downloadable files contain the soil data collected from the sites 

described in this report. The first file, 1_FROSTFIRE_File_Descriptions, which is a PDF, 

describes in detail the data within the following three workbook files (in several file 

formats). of2011-1216_FROSTFIRE_megaPhysical contains physical descriptions of the 

samples, such as volumetric field moisture, bulk density, and height above mineral soil. 

of2011-1216_FROSTFIRE_megaChemistry contains elemental C, N, δ13C, 14C, elements 

from ICP analysis, and Hg for samples on which these analyses were run. The last file, 

of2011-1216_FROSTFIRE_Transects, contains field descriptions for individual horizons 

that make up the pre-burn USGS soil profiles. 

Acknowledgments

We thank Terry Fries for overseeing sample analysis for much of the data, Sue 

Trumbore and her lab at U.C. Irvine for the preparation and the processing of 14C 

samples, and XRAL for discussions of methodologies. Many people associated with the 

University of Alaska, Fairbanks, helped guide our involvement in this opportunity. 

Thanks in particular to Terry Chapin, A. Dave McGuire, and Larry Hinzman. This work 

was supported by the Bonanza Creek Long-Term Ecological Research program (funded 

jointly by NSF Grant DEB-0423442 and USDA Forest Service, Pacific Northwest 

Research Grant PNW01-JV11261952-231) and by the USGS Earth Surface Dynamics 

Program. 

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