Soils of the - Agriculture and Agri-Food Canada

COQUITLAM SOILS .
(CO)
Location and Extent : Coquitlam soils are only found near the south end of Coquitlam Lake and in the Statl u
Creek and Chehalis River valleys . There are about 330 ha of pure map units .
Topography and Elevation : The topography of Coquitlam soils is mostly moderately rolling to hilly wit h
slopes between 10 and 50 percent . Along gullies and escarpments, gradients may rise to over 60 percent .
Elevations lie between 150 and 300 m above sea level .
Parent Material and Texture : Coquitlam soils have developed from medium-textured, stone-free, usuall y
varved, glaciolacustrine deposits . There may be up to 25 cm of organic forest litter on the soil surface . Th e
texture of the surface and subsurface of the mineral soil is usually silty clay loam, varying sometimes to silt loam .
The subsoil is mostly silt loam and may contain thin, sandy lenses, especially near the boundary with Fellow s
soils .
Soil Moisture Characteristics : Coquitlam soils are moderately well drained . They have moderate to slo w
surface runoff (depending on steepness of slopes) and high water holding capacity . They are moderatel y
pervious in the surface and subsurface mineral soil layers, but this decreases to slowly pervious in the compac t
subsoil . A temporary, perched watertable develops over the compact subsoil (about 1 m from the surface )
during heavy, prolonged rains and telluric, lateral seepage occurs .
General Soil Description : Coquitlam soils have from 15 to 25 cm of dusky red to dark reddish brow n
organic forest litter on the soil surface which is mostly well-decomposed, matted and friable . This is abruptl y
underlain by 2 to 10 cm of leached, gray to brownish-gray, weakly structured, friable, silty material, which, i n
turn, is also abruptly underlain by a silty layer about 15 cm thick which is strong brown or dark reddish brown ,
moderately to strongly subangular blocky, friable to firm when moist, hard when dry, and contains from 10 to 1 5
percent organic matter. The variable colours are due to uneven organic matter distribution . This layer grades t o
about 20 cm of yellowish-brown or reddish-brown, moderately structured, friable to firm silty material . Under thi s
is a silty zone about 30 cm thick that is massive, firm, yellowish-brown to olive and contains reddish mottles .
Usually, a well-defined layer of concentrated roots is present in the lower part . This zone grades to very firm ,
varved, olive-gray, silty, unweathered parent material which contains a few yellowish to brownish mottles . Soi l
reaction is extremely acid in the upper 60 cm then gradually grades to strongly acid in the unweathered parent
material . Soil classification is Orthic Ferro-Humic Podzol .
Commonly Associated Soils : Fellows and Roach soils usually are closely associated with Coquitlam soils .
Fellows soils differ from Coquitlam soils by being sandy rather than silty in texture . Roach soils differ by bein g
gravelly and containing strongly cemented subsurface layers .
Vegetation : All areas are forested, mainly by second-growth coast Douglas-fir, western hemlock and wester n
red cedar with red alder, birch and vine maple . Rooting is unrestricted in the upper 100 cm of soil (from th e
surface) but is severely impeded below that by the dense, compact subsoil . A well-defined zone of roo t
concentration (root mat) is usually present immediately above the compact layers .
General Land Use Comments : (1) Steep, eroded topography generally limits use of Coquitlam soils fo r
agriculture although in the few, small areas where the topography is suitable, most crops not susceptible to
occasional, perched watertables can be produced . (2) Adverse topography, susceptibility to erosion and slow
subsoil permeability (which limits septic tank effluent disposal) generally make Coquitlam soils poorly suited fo r
urban use . (3) Coquitlam soils are well suited for forest growth . Annual wood production by coast Douglas-fi r
and western hemlock is estimated to be between 12 and 15 m 3/ha . During harvest (and other operations) care i s
required to prevent initiation or enhancement of erosion of the silty material . Operations should be limited to th e
dry summmer months . Rapid brush invasion is likely to be a problem during post-harvest management .
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