Hydric Soil Identification Techniques - Wetland Techniques - page 246

the material feels greasy, it may be either mucky mineral or organic soil material. If
after additional rubbing (2-3 ) the sample feels gritty or plastic, it is considered

mucky mineral soil material; if it still feels greasy, it is organic soil material.
Accumulation of silt residue on fingers after rubbing indicates that the sample is
likely mineral or mucky mineral.
Another method is to take equal amounts of known mineral soil and the horizon
in question. An organic soil material will be much lighter than equal amounts of
mineral material. Mucky mineral would be slightly lighter than equal amounts of
mineral material. The reason for the difference in weight is due to the greater bulk
density of mineral material compared to organic matter. If the material is organic
soil material, a further division should be made to identify the type of organic soil
material. Organic soil materials are classified as sapric, hemic, or fibric which
correspond to the organic texture classes muck, mucky peat, and peat, respectively.
Organic texture class can be determined by rubbing a soil sample about ten times and
then visually estimating the proportion of the sample comprised of fibers (excluding
live roots). After rubbing, sapric material or muck will have less than 1/6 visible
fibers; fibric material or peat will have more than 3/4 fibers; and hemic material
or mucky peat will have between 1/6 and 3/4 fibers (Soil Survey Staff 1999 ).

4.9 Formation of Hydric Soils

Hydric soils are soils that developed under conditions of saturation close to the soil
surface. Under saturated conditions, plant roots and microorganisms use O 2 faster
than it can be replenished by diffusion from the atmosphere resulting in first
anaerobic conditions and then reducing conditions. The change from aerobic
conditions to anaerobic conditions causes a shift in the direction or rate of a number
of biogeochemical processes, especially those that impact the accumulation or loss
of Fe, Mn, sulfur (S), or C compounds. This results in distinct soil morphological
characteristics that serve as the basis for the Field Indicators. For more information
on this subject refer to Chap. 7 on Wetland Biogeochemistry Techniques .

4.9.1 Processes

4.9.1.1 Soil Saturation

A horizon is considered saturated when the soil water pressure is zero or positive
(at or above atmospheric pressure). At these pressures, water will flow from the soil
matrix into unlined auger holes. Three types or patterns of saturation are defined:

1. Endosaturation-ground water table. Soil is saturated in all horizons below the
water table to a depth of 2 m.
2. Episaturation-perched water table. Soil is saturated in a horizon that overlies an
unsaturated horizon, and the unsaturated horizon lies within a depth of 2 m from
the surface.