Geoscience Reference
In-Depth Information
3.3.2
Chemical Analyses
Key chemical properties that are analyzed include pH (in water or a dilute salt
suspension), organic C, total N, extractable P (Mehlich-1 is used for ornithogenic
soils), total P, exchangeable bases (Ca, Mg, K, and Na), exchangeable acidity,
extractable Al, cation-exchange capacity (CEC; pH 7 and/or 8.2), extractable Fe
and Al (Na-pyrophosphate yields organic-bound forms; acid NH
4
-oxalate yields
organic and amorphous forms; and citrate-dithionite yields all “free” forms), and
the optical density of the oxalate extract (ODOE). Effective (ECEC) represents the
CEC from the sum of base cations and Al extracted with KCl. Salt-bearing soils
should be analyzed for electrical conductivity, CaCO
3
, and gypsum. Total elemental
analysis is useful for evaluating the magnitude of weathering.
3.3.3
Mineralogical Analyses
Common mineralogical analyses include the use of optical techniques for the coarse
silt (20-50
ʼ
m) and coarser fractions and X-ray diffraction for fi ne silt (5-2
ʼ
m),
and clay (<2
ʼ
m) fractions.
3.3.4
Micromorphological Analyses
As with non-permafrost-affected soils (Bullock et al.
1985
), microscopic examina-
tion of soils is important for evaluating soil-forming processes, particularly those
related to cryogenesis. When viewed in thin sections, cryosols contain a variety of
fabrics resulting from compaction (desiccation), displacement due to alignment,
rotation, sorting, and inclusions, and pore formation (planar voids, cracks, vesicles)
(see Chap.
5
)
(Fig .
3.7
).
3.4
Summary
In addition to the usual properties described in low-latitude soils, properties that are
unique to cryosols that should be described include patterned ground, cryoturbation
features, the depth to the top and bottom of each horizon (for broken horizons),
cryostructures, and the depth to and nature of permafrost. Sketches or fi eld-ready
photographs are recommended for diagramming soil horizons, cryoturbation, and
other features. There are no universally accepted guidelines for delineating soil
horizons; Table
3.2
compares horizon symbols used in the US, Russian, Canadian,
and WRB systems.
