Abstract Number
B13B-0512
The Unified North American Soil Map and Its Implication on the Soil Organic Carbon Stock in North America
Shishi Liu*, Yaxing Wei, Wilfred M. Post, Robert B. Cook, Kevin Schaefer, and Michele M. Thornton
Shishi Liu: lius2@ornl.gov
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6290
AGU Fall Meeting, San Francisco, California, December 3-7, 2012
Introduction
Soil Properties
Soil characteristics, an important terrestrial ecosystem modeling input, affects the
photosynthesis, respiration, evapotranspiration, or other biosphere processes.
Unfortunately, a lack of comprehensive gridded information about North
American soil properties based on U.S. and Canadian soil datasets, has
impeded the understanding and improvement of modeling nutrients dynamics
in North America. Currently, North American carbon modeling relies on the
spatial subset of different world soil maps, such as digitized Food and Agriculture
Organization – United Nations Educational, Science and Cultural Organization
(FAO-UNESCO) soil map (Bouwman, et al. 1993; McGuire, et al. 1993),
a world dataset of derived soil properties by FAO-UNESCO soil unit for global
modeling (Batjes, 1997), the World Inventory of Soil Emission Potentials (WISE)
(Gijsman et al. 2007), and the Harmonized World Soil Database (HWSD).
We developed a two-layer gridded soil attributes dataset in North America for
use in biosphere and related modeling. The Unified North American Soil Map
(UNASM) is compared with the subset of HWSD 1.1 and the differences
between these two datasets are evaluated. We also analyzed the spatial
distribution of soil organic carbon and estimated the total soil organic carbon
stock in North America.
Methodology
Table 1 Soil depth, source code, and attributes of top soil layer (0-30 cm) and sub soil
layer (30-100 cm).
Soil Attribute
Maximum Soil Depth
Source Code
Topsoil Sand Fraction
Topsoil Silt Fraction
Topsoil Clay Fraction
Topsoil Gravel Fraction
Topsoil Organic Carbon
Topsoil pH (H2O)
Topsoil Bulk Density
Subsoil Sand Fraction
Subsoil Silt Fraction
Subsoil Clay Fraction
Subsoil Gravel Fraction
Subsoil Organic Carbon
Subsoil pH (H2O)
Subsoil Bulk Density
Abbreviation
Soil Depth
Source
tsand
tsilt
tclay
tgravel
toc
tph
tbd
ssand
ssilt
sclay
sgravel
soc
sph
sbd
Units
cm
na
% weight
% weight
% weight
% volume
% weight
-log(H+)
g/cm3
% weight
% weight
% weight
% volume
% weight
-log(H+)
g/cm3
The Comparison between UNASM and HWSD 1.1
Source Data
•
•
•
•
Spatial Distribution of Soil Organic Carbon Content (SOCC)
U.S. General Soil Map (STATSGO2)
Soil Landscapes of Canada (SLC) version 3.2 and 2.2
Harmonized World Soil Database (HWSD) Version 1.1
The Northern Circumpolar Soil Carbon Database (NCSCD) (for soil organic carbon
analysis only)
SOCC = OC × BD × T × (1-Gravel)
OC: soil organic carbon concentration
BD: soil bulk density
T: thickness
Gravel: gravel fraction
Figure 3 SOCC in the top 100 cm soil profile
(a) The NCSCD-modified UNASM
(b) HWSD1.1
Figure 4 The mean SOCC for major
vegetation types in the 0-30 cm and
the 0-100 cm soil profile.
Figure 2 The difference maps between UNASM and HWSD 1.1 for sand fraction and soil organic
carbon concentration.
Procedures
• Convert STATSGO2, SLCs, and HWSD 1.1 into 0.25 degree gridded format by selecting
the dominant soil type in each cell.
• Merged STATSGO2, SLCs and HWSD1.1 into a seamless map that can best represent
soil in North America.
• Harmonize the North American soil map developed in stage 2 into two standard layers, 030 cm and 30-100cm.
• Quality control.
STATSGO2 (U.S.)
SLC3.2&2.2 (Canada)
The Estimate of Soil Organic Carbon Mass (SOCM)
SOCM = SOCC × A
SOOC: soil organic carbon content
A: the area of each cell
Figure 5 The SOCM of the top 0-30
cm and the 0-100 cm soil profile in
North America derived from the
NCSCD-modified UNASM soil
organic carbon map and HWSD 1.1.
Harmonization
0-30cm
Filled
with
HWSD
……
UNASM
30-100cm
• Pronounced differences between the UNASM and HWSD 1.1, especially in
Alaska and southern Canada
• The difference in spatial distribution of soil texture would affect the hydrological
properties of soil, such as porosity and hydraulic conductivity.
• Gravel fraction is much higher in the western and northeastern U.S., some areas of
Alaska, and southwestern Canada in the UNASM.
• The UNASM has much higher soil organic carbon concentration in most area of Alaska,
and the lake area in the central Canada, but slightly lower values in the conterminous
U.S. for the top soil layer.
• The most significant differences of bulk density lie in Alaska, U.S. and northern Alberta
and southern Northwest Territories, Canada.
Figure 1 The procedures to develop UNASM.
ORNL is managed by the University of Tennessee-Battelle LLC under contract DE-AC05-00OR22725 with the U.S. Department of Energy
Discussion
• The UNASM provides more detailed and up-to-date soil information than the
HWSD 1.1, but the fixed spatial resolution (0.25 degree) limits the flexibility
for downscaling.
• The NCSCD-modified UNASM SOCC map can be used as a benchmark.
References
Liu, S., W. Post, Y. Wei, R. Cook, K. Schaefer, M. Thornton, 2012. The Unified North American Soil
Map and Its Implication on the Soil Organic Carbon Stock in North America. Biogeosciences
Discussion, 9, 15175-15211, doi:10.5194/bgd-9-15175-2012.
*Funded by NASA’s Terrestrial Ecology Program (TEP) for the Modeling and Synthesis Thematic Data Center (MAST-DC: project 09-TE09-26)