The Soils of The Regional Municipality of Ottawa=Carleton

Mapped Soil Combinations Sixty percent of all Rideau association
soils were mapped in combination with either soils of
other associations or with miscellaneous land units . Approximately,
1,800 ha were mapped as the dominant component in
complex map units, and 2,500 ha were mapped as the significant
component . When mapped as the dominant component,
theRideau-Bearbrook combination is by farthe mostextensive
accounting for approximately 1,200 ha of all Rideau soils .
When mapped as the significant component, Bearbrook-
Rideau and Dalhousie-Rideau combinations are the most
extensive and account for 1,300 ha and 1,000 ha respectively of
all Rideau soils mapped .
Large areas of Rideau-Bearbrook and Bearbrook-Rideau
combinations were mapped in the northern part of Cumberland
Township, and these areas account for the majority of
Rideau soils mapped with soils of the Bearbrook association .
Several smaller but significant areas of these combinations
were also mapped in March and West Carleton townships .
Combinations of Dalhousie-Rideau occur on level to nearly
level landscapes in which individual separation was extremely
difficult at the scale of mapping . The similarity of each association
in physical characteristics, especially clay content, also
warranted this combination at the scale ofmapping .
General Land Use Rideau association soils support a wide
range of agricultural land uses including corn, cereal grain,
and hayproduction . These crops are often grown on a rotation
basis, the frequency of which depends upon the type of farming
operation . Rideau soils are also utilized for permanent pasture,
and a significant proportion remain forested .
Correlation to Ottawa Urban Fringe Rideau soils in the survey
area for the most part are similar to those mapped in the
Ottawa Urban Fringe. Both have developed on grayish colored
heavy clay parent material of similar origin . Rideau soils of
this area, however, are somewhat more variable with some
deposits possessing considerable layers ofclay and silty clay.
ST.THOMAS (ST)
Location and Extent Soils of the St . Thomas association
occur mainly in Cumberland and West Carleton townships,
with a small area also occurring in Rideau Township. In Cumberland
Township, they are found on the relatively recent flood
plains ofthe Ottawa River, and inthe channel floors andonthe
ancient flood plains of the ancestral Ottawa River. In West
Carleton Township, they are mainly found on what was once
the channel floor of the present Ottawa River, or on recent
floodplains associated with it . In Rideau Township, they are
found on the recent flood plain of the Rideau River in the
southern part of the township . Approximately 8,000 ha of St .
Thomas soils were mapped, of which 900 ha were mapped in
combination with either soils of other associations or the
Rockland miscellaneous land unit . Approximately 76% of all
St . Thomas soils mapped occur in Cumberland Township . A
further 18 01o occur in West Carleton Township .-
Landform and Topography St . Thomas soils have developed
in a blanket of coarse textured fluvial or eolian material which
is generally 2 m deep or more. Although most often underlain
by clayey marine material, the underlying material was not differentiated
and may be quite variable . The topography of St .
Thomas soils ranges from level to gently sloping or undulating .
Slopes range from 0to 9% .
Soil Material St . Thomas soils have parent materials consisting
of noncalcareous fine sand which ranges from light yellowish
brown to olive gray in color. Soil reaction of the parent
material is medium to strongly acid . Weathered subsoil overlying
the parent material also has fine sand textures, and grades
from dark brown to strong brown in color nearest the surface,
to dark yellowish brown to light olive brown in color at depth .
Soil reaction tends to be more acidic than the parent material,
ranging from strongly to very strongly acidic . Horizons
enriched with iron and aluminum combined with organic matter
(Bfand Bfj horizons) commonly occur in the upper portion
of the weathered subsoil . A thin eluvial horizon (Ae or Aej
horizon), less than 5 cm thick, quite often overlies the weathered
B horizons . These horizons have fine sand or loamy fine
sand textures, and arebrown to light gray incolor. Iron, aluminum,
and organic matter have been removed from these horizons
and transported downward in the profile . Eluvial
horizons are not always present, and when they occur are usually
not continuous across the landscape.
Under non-forested conditions, a dark yellowish brown to
black surface Ahorizon occurs which isusually less than 10cm
thick. Texturally it may be either fine sand, loamy fine sand, or
fine sandy loam . Soil reaction is quite variable, ranging from
slightly to extremely acid . Under forested conditions, a layer of
accumulated organic matter (LFH horizon) overlies the A
horizon at the surface. It is usually less than 5 cm thick, and is
very dark brown to black in color. Slightly decomposed leaves
and twigs mainly constitute this surface layer.
Soil materials of the association are well sorted, with the
sand content of the parent material ranging from 84 to 99% .
Mean sand content is 94% . Of the total sand content, the fine
sand fraction ranges from 37 to 93 %, with the mean fine sand
content being 70% . Gravel size particles greater than 2 mm in
size are almost non-existent in St . Thomas soils .
Soil Moisture Characteristics St . Thomas soils are excessive
to well-drained onthe crests and upper slopes of sand ridges or
knolls which are common in many landscapes . Imperfectly
drained soils are found on the lower slopes of sand ridges or
knolls, in depressional areas between well-drained soils, or on
the slightly elevated areas in very gently undulating topography.
Poorly drained soils occur on level to nearly level topography,
or depressional areas between better drained soils .
Due to the coarse nature ofthe materials, St . Thomas soils
are rapidly permeable and have a low moisture holding capacity.
Periodic droughty conditions are common in the excessive
towell-drained soils . Surface runoff is slow.
Soil Landscape Units Eight units were identified in the St .
Thomas association . They are described as follows :
Recognized Recognized
Subgroups Series
STl : Dominantly exces- Orthic Humo- St . Thomas
sive to well-drained ferric
soils found on very Podzols
gently to gently Orthic Dystric Limoges
sloping or undulating Brunisols
topography. Slopes
range from 2 to 9% .