Ministry of Environment
2.4 The Soil Orders of British Columbia
K.W.G. Valentine and L.M. Lavkulich
The two previous sections have described the ways in which soils have formed and the method of classifying them in Canada. These discussions have been largely theoretical. It is now time to describe more specifically the types of environment, processes and properties that are associated with the nine major soil groupings - the soil orders - as they occur in British Columbia.
The Brunisolic Order
Soils of the Brunisolic order have undergone only moderate development from the original parent material. Physical, chemical and biological weathering has proceeded far enough to change the morphology of the parent material. There are no drastic translocations or transformations of the material that characterize many of the other orders.
There are a number of reasons for this sort of soil occurring in British Columbia. Firstly in many areas the climate has restricted the progression of soil weathering. Long winters and low temperatures restrict the rate of many of the transformations which constitute soil weathering. This is the reason why Brunisolic soils cover much of the high plateaus of northern British Columbia. Lack of soil moisture also limits transformations such as chemical weathering. Thus Brunisolic soils are also found in the subhumid to semiarid zones of the southern interior.
Secondly, some Brunisolic soils have developed on very coarse textured materials such as fluvioglacial sands and gravels in areas where the climate is not normally a limiting factor in soil development. Because clay-sized particles, the principal active fraction in chemical transformations, make up only a small volume of the total mineral soil, little weathering has taken place. Most of the soil is relatively inert gravel and quartz sand. Moreover the parent material has a low water-holding capacity, so that soil water content is low and thus chemical transformations are further restricted. The droughtiness of these soils means that the vegetation is often limited to open lodgepole pine and pinegrass. Therefore, organic matter additions to the topsoil are limited, and well-structured Ah horizons are thin or absent.
Thirdly, Brunisolic soils are found on very young geological sediments. In this case the time available for soil development since deposition has not been sufficient for anything more than a moderate amount of weathering to have taken place. Many of the soils on the Recent alluvium of the Fraser Valley fall into the Brunisolic order.
Soils of the Brunisolic order are often regarded as being in a transitional stage of development. We think that given time translocations of weathering products will begin within the soil to produce Podzols or possibly Luvisols. The Brunisolic soils on Fraser River alluvium are a probable example. However, there are many areas in British Columbia where Brunisolic soils occur on sediments that have been exposed to subaerial weathering since the ice melted about 11,000 years ago; for example the soils in the semiarid southern interior valleys. In other words it is necessary to decide whether transitional is to mean in the short or in the long term.
The main processes involved in the formation of Brunisolic soils are the removal by leaching of soluble salts and carbonates, the in situ weathering of the mineral fraction to form secondary minerals and hydrated iron and aluminum oxides, and the development of soil structure in the finer textured materials that is different from the original structure of the parent material. These are the processes that form the Bm horizon which is diagnostic of Brunisolic soils. In the field it is recognized by its browner or redder colour as compared with the parent material, by its structure and major accumulations of any materials translocated from the A horizon, such as clay. A common horizon sequence for these soils would be LFH, Bm, C or Ck.
The great groups of the Brunisolic order are separated on the basis of the presence or absence of an A horizon in which the mineral and organic fractions have been mixed together by soil fauna (an Ah horizon), and on the base status of the soils as shown by the pH. The Ah horizon indicates that there is a net addition of organic matter to the soil and that organic nutrients are available. A high base status shows that the soil can retain inorganic nutrients such as calcium and potassium, or that leaching is limited. The specific characteristics of the four great groups are as follows:
|Melanic Brunisol:||Thick Ah horizon + high base status (pH over 5.5)|
|Eutric Brunisol:||No or thin Ah horizon + high base status (pH over 5.5)|
|Sombric Brunisol:||Thick Ah horizon + low base status (pH less than 5.5)|
|Dystric Brunisol:||No or thin Ah horizon + low base status (pH less than 5.5)|
The Whipsaw soils are an example of a Eutric Brunisol. They have developed on coarse textured fluvioglacial deposits in the southern interior of British Columbia near Princeton. The following abbreviated description is from a profile on a southerly aspect at approximately 600 m elevation east of Wolfe Lake (49º 26'N, 120º 18'W).
|1 cm of moss, partially decomposed grass and pine needles.|
|5 cm of black sandy loam; granular structure; slightly stony.|
|20 cm of dark brown sandy loam; coarse granular structure; slightly stony.|
|15 cm of dark brown gravelly sandy loam; weak blocky structure; very stony.|
|loose sand and gravel.|
Photographs of a Brunisolic soil profile and landscape are included as Plates 2.4.1 and 2.4.2. Chemical and physical analyses from a Whipsaw profile are given in Table 2.4.1. The important points to note from the analyses are the approximately neutral pH all the way down the profile, the lack of clay or Fe + Al accumulation in the Bm horizon versus the Ah and the high percent base saturation dominated by calcium cations.
These data are taken from Green, A.J. and T.M. Lord. The soils of the Princeton area. B.C. Soil Survey Rpt. No. 14, Agriculture Canada, Queens Printer, Ottawa (in press).
The Chernozemic Order
Soils that belong to the Chernozemic order are associated with a grassland vegetation and a climate which ranges from subarid to subhumid. Some grasslands have shrubs and forbs, and in some areas the soils extend into the forest-grassland transition. The mean annual temperature is usually less than 5.5ºC and some part of the soil will be frozen for some time during the winter. However, the most important characteristics of the climate as a soil forming factor are low rainfall, high summer temperatures and high evapotranspiration rates. This inhibits tree growth, limits soil leaching and leads to the accumulation of the decomposition products of the grasses in the topsoil.
The principal areas of Chernozemic soils in Canada are found in the Prairie provinces. But there are also significant expanses of such soils in the valleys and some adjacent plateau areas of the south central interior of British Columbia. The distribution of Chernozemic soils is mainly a result of the climatic limitations to tree growth. These soils are therefore found on a wide variety of parent materials. In valleys they occur on fluvial deposits or terraced lake silts as in parts of the southern Okanagan valley. On plateaus they may occur on till as in the Chilcotin region, and in the very dry interior near Ashcroft they can be found on the colluvium of hill slopes. Local factors such as aspect that affect evapotranspiration are also important. In many areas Chernozemic soils occur on south- and west-facing slopes, with forested soils (usually either Brunisolic or Luvisolic) on north- and east-facing slopes.
The dominant process in the development of Chernozemic soils is the accumulation in the topsoil of organic matter derived from the decomposition of the leaves and roots of the grasses. The organic matter is intimately mixed with the mineral material by its repeated ingestion and excretion by soil fauna. This gives a dark colored surface Ah horizon with well-developed granular structure. The low rainfall means that there is only a limited movement of water down through the soil profile and very little leaching. This means that there will be little movement of clay down the profile and carbonates will tend to accumulate in the C and lower B horizons due to high soil evaporation rates. There will be weathering of primary to secondary minerals in the A and B horizons but there will be little translocation of the products within the soil. A typical but simplified sequence of horizons would therefore be Ah, Bm, Cca.
The four great groups within the Chernozemic order - Brown, Dark Brown, Black and Dark Gray - are differentiated on the color of the surface Ah horizon. This is associated with organic matter content which is itself a reflection of the aridity of the environment. In a study of a toposequence of Chernozemic soils near Kamloops (see van Ryswyk et al., 1966 in Further Reading) the Brown soils in a subarid environment with a big basin sagebrush plant community had an organic carbon content of 1.12% in the Ah horizon. The Dark Brown soils in a semiarid environment with a needle-and-thread grass - Sandberg's blue grass plant community had a carbon content of 1.75%, and the Black soils in a subhumid environment with a rough fescue plant community had 3.88% organic carbon in the Ah. Dark Gray soils are soils of the forest- grassland transition. They show some characteristics of forest soils such as the Luvisolics. The net accumulation of organic matter is less and there is some translocation of clay from the A horizon to the B.
The Black soils from the above mentioned study near Kamloops are taken as an example of soils from the Chernozemic order. They have developed on moderately coarse textured glacial till at about 950 m above sea level. An abbreviated profile description follows.
|25 cm of black sandy loam, which is friable with platy structure.|
|65 cm of dark brown gravelly sandy loam, friable with blocky structure.|
|30 cm of grayish brown gravelly sandy loam which is friable with blocky structure and contains carbonates.|
|Grayish brown gravelly sandy loam which is slightly friable with blocky structure but does not contain significant carbonates.|
Photographs of a Chernozemic soil profile and landscape are included as Plates 2.4.3 and 2.4.4. Some chemical and physical analyses of the Black soils near Kamloops are given in Table 2.4.2 (page 74). The significant features to note are the high pH throughout the profile, the high cation exchange capacity (C.E.C.), the high organic carbon content of the Ah horizon, and the low C:N ratio. This is a very fertile soil.
The Cryosolic Order
Cryosolic soils contain permafrost close to the surface. This is the feature that sets them apart from all other soil orders. Permafrost, or perennially frozen ground, is found where the temperature of the soil remains below 0ºC continuously for a number of years. Under these conditions soil water in the lower part of the profile will remain frozen throughout the summer months, but the upper part (the "active layer") will be thawed. For the purpose of soil classification Cryosolic soils either have permafrost within one metre from the surface or if they are cryoturbated (disrupted by frost heaving), they must have permafrost within two metres from the surface.
Plates 2.4.1 to 2.4.6
Profiles and Landscapes of Soils
From the Brunisolic, Chernozemic and Cryosolic Orders
|2.4.1||Profile of a Brunisolic soil developed in sandy loam over beach sands and gravels in the Nig Creek valley, northern Peace River area (photo A.J. Green).|
|2.4.2||Brunisolic landscape on a fluvioglacial terrace in the Wapiti River valley, northeastern British Columbia. The very coarse gravelly parent materials can be seen in the overturned tree stump. The vegetation is very open lodgepole pine and pine grass.|
|2.4.3||Profile of a Chernozemic soil developed on moderately fine glacial till near Douglas Lake, southern British Columbia (Photo A.J. Green).|
|2.4.4||Chernozemic soil landscape at the junction of the Fraser and Chilcotin Rivers, central British Columbia. Dark Brown soils are found on the terrace flats with a needle-and-thread grass community. Brown soils occur on the terrace slopes with bluebunch wheat grass and big basin sagebrush.|
|2.4.5||Profile of a Cryosol developed in deep organic matter on the flat very poorly drained Fort Nelson lowland of northeastern British Columbia. The soil was frozen below about 50 cm. Note the scale is in feet.|
|2.4.6||Cryosolic (Organic Cryosol) landscape in the Fort Nelson lowland. The vegetation cover of these very poorly drained bogs is sphagnum and hypnum mosses, common Labrador tea, bog glandular birch and occasional stunted black spruce and willows. This is the landscape of the profile shown in Plate 2.4.5.|
These data are taken from van Ryswyk et al., 1966 (see Further Reading).
The principal areas of Cryosolic soils in Canada are in the far north. British Columbia has two types of landscapes which contain them: firstly the drier peatlands in the extreme northeast within the "discontinuous zone" of permafrost, and secondly the high mountains.
The northeastern corner of British Columbia lies on the southern fringe of the discontinuous permafrost zone. The -1ºC mean annual air isotherm is approximately the southern limit of this zone. Permafrost in this area occurs as small isolated patches, usually in peat bogs. The peat moss acts as an insulation and keeps the lower layers frozen in the summer. Permafrost can also occur on north facing slopes and in heavily shaded areas. The peatlands must not be too wet since water effectively melts permafrost.
The occurrence of permafrost in the mountains of British Columbia south of the discontinuous permafrost zone is far less predictable. The principal control is still climatic, but aspect, exposure, vegetation, soil or rock type and the extent of snow cover are also important. The distribution of permafrost is therefore very patchy, but is most common on high north facing slopes which have little or no snow cover. In the mountains and plateaus of northern British Columbia the lower limit is about 1200 m whereas at the 49th parallel it is at about 2000 m above sea level. In the mountains permafrost will be found in mineral as well as in organic soils.
Cryosolic soils have very cold subarctic or cold cryoboreal soil temperature regimes. Under such cold environments the rates of chemical and microbiological reactions are slow and transformations within the soils are limited. Mineral soils often have deep organic surface horizons because the low soil temperatures inhibit microbial decomposition of organic matter rather than plant growth. Organic soils are raw and poorly decomposed but transformations and translocations due to physical weathering are prevalent. This is especially true in the active layer above the permafrost where freezing and thawing occurs. As water freezes in cracks it expands. Therefore rock fragments and individual minerals can be broken apart. Also particles are moved within a soil by frost heaving, and in extreme cases horizons can be disrupted and churned.
There are three great groups in the Cryosolic order. They are separated on the degree of disruption of the profile and the type of parent material as follows:
|Turbic Cryosol:||mineral soils with disrupted horizons and displaced material, due to cryoturbation.|
|Static Cryosol:||mineral soils with no disruption of horizons.|
|Organic Cryosol:||organic soils with no disruption of horizons.|
Cryosolic soils in mountainous areas of British Columbia will be mainly Turbic Cryosols with a few Organic Cryosols in the depressions. Little is known about these soils in British Columbia but a description of a soil on a north facing slope at an elevation of 2350 m just north of Banff, Alberta taken in September showed 15 cm of fibric (Of) organic matter and fine humus (Oh) over 25 cm of unfrozen loose fine colluvial rubble over large colluvial fragments which were frozen together (see Ogilvie and Baptie, 1967, in Further Reading).
The Cryosolic soils within the zone of discontinuous permafrost in British Columbia will be principally Organic Cryosols in the peatlands. One of the soils from the Klua complex east of Fort Nelson is taken as an example. It was described and sampled on an exposed road cut north of Clarke Lake (58º 44'N, 122º 29'W). In the bog away from the road cut permafrost was at about 50 cm in late July. An abbreviated description follows:
|Ofl||30 cm of yellowish brown partially decomposed sphagnum and hypnum moss remains.|
|Om||55 cm of dark brown semidecomposed moss and leaf remains.|
|Of2||65 cm of dark brown partially decomposed moss and sedge remains.|
|Ofz||frozen, partially decomposed moss and sedge remains.|
Photographs of the profile and soil landscape are included as Plates 2.4.5 and 2.4.6. Some chemical and physical analyses are given in Table 2.4.3. Points to note are the very low pH values, the high organic carbon contents and low bulk densities.
Chemical and Physical Analyses of an Organic Cryosol
These data are taken from Valentine, K.W.G., 1971. Soils of the Fort Nelson area of British Columbia. B.C. Soil Survey Rpt. No. 12, Canada Dept. Agric., Ottawa.
The Gleysolic Order
Soils of the Gleysolic order are saturated with water for long periods of the year and their profiles show evidence of reducing conditions. Reduction in the chemical sense is caused by a lack of oxygen. The water excludes air from the pore spaces, and the microorganisms rapidly use up any oxygen in the water, causing anaerobic reducing conditions. The transformations of the mineral fraction by chemical oxidation and the decomposition of the organic fraction by aerobic microorganisms are severely curtailed. For the rest of the year Gleysolic soils may be well aerated and aerobic weathering proceeds. Only in the extreme cases of almost permanent saturation are the soils raw and relatively unweathered with deep accumulations of organic matter on their surfaces.
These soils occur throughout the province wherever water is retained in the soil profile for long periods. They are associated with a wide variety of other soils and there is a continuous gradation from the Gleysolics to the well drained soils with which they are associated. The principal reason for their occurrence is restricted drainage due to topography. Wherever water is added to the soil faster than it drains away Gleysolic soils develop. This may be in depressions, on very flat plains or at the foot of slopes. For example, many depressions in the hummocky topography of the Cariboo plateau contain Gleysolic soils. There are also large flat plains in northern British Columbia that are covered with Gleysolic soils, and in mountain regions these soils tend to occur on the lower sections of many slopes in what is known as the receiving position. Other factors also contribute to their development. Fine textured parent materials will restrict soil drainage. For example, much of the northeastern plains is underlain by very fine marine shales which further restrict soil water movement on this flat landscape. In many of the large river floodplains in British Columbia saturation from a prolonged high groundwater table causes Gleysolic soils to develop. Heavy rainfall especially in the coastal region produces Gleysolic soils even on gentle slopes that elsewhere in the province would be better drained. Frozen layers or impermeable soil horizons can also lead to saturated soil conditions.
The lower portion of the profile of a Gleysolic soil is saturated for most of the time. Consequently the lower B and C horizons often have a dull gray colour derived from reduced ferrous iron compounds. Above this the soil is seasonally aerated and patches of bright reddish brown mottling occur where ferrous compounds have been oxidized to ferric iron. The surface horizons often have an accumulation of poorly decomposed organic matter because the action of microorganisms is restricted by the low temperature and lack of aeration.
A typical Gleysolic soil profile has LFH, Bg, Cg or LFH, Ah, Bg, and Cg horizons. Under conditions of prolonged saturation the drier organic LFH surface horizons of leaves, twigs and grasses will be replaced by an 0 horizon of mosses and sedges derived from wetland vegetation.
The great groups of the Gleysolic order are separated upon the basis of the presence or absence of an Ah horizon with organic matter accumulation, or upon the presence or absence of a Bt horizon with clay accumulation. The names of the great groups and the details of their properties are as follows:
|Humic Gleysol:||thick Ah and no Bt horizon.|
|Gleysol:||thin or no Ah and no Bt horizon.|
|Luvic Gleysol:||Btg horizon.|
The Cowichan soils from southern Vancouver Island are an example of soils from the Gleysolic order. They have developed on fine textured marine deposits in the depressions of a gently undulating landscape. They are poorly drained and the marine clay is only very slowly permeable. The following is an abbreviated description of a Cowichan soil.
|L||3 cm of undecomposed grass, leaves and needles.|
|H||3 cm of dark brown well decomposed organic matter.|
|Ah||20 cm of very dark brown clay loam with granular structure.|
|Ae||15 cm of brown silt loam, with faint mottling and blocky structure.|
|Btg||25 cm of pale brown, hard, prominently mottled silty clay.|
|Cg||pale brown silty clay, prominently mottled with a blocky structure.|
The Cowichan soils are Luvic Gleysols because they have a Btg horizon with clay accumulation (see Table 2.4.4). Other features to be noted are the high organic carbon content of the Ah horizon and the presence of the Ae horizon from which clay and bases have evidently been translocated. A Gleysolic soil profile and landscape are illustrated in Plates 2.4.7 and 2.4.8.
The Luvisolic Order
Soils that belong to the Luvisolic order are formed under deciduous, mixed deciduous-coniferous, boreal forest or under mixed forest in the forest grassland transition zone. Their parent materials are generally neutral to slightly alkaline and they usually occur in areas having more effective precipitation than do the Chernozemic or Brunisolic soils. In other words they are found in areas which either have higher rainfall or lower temperatures with less evapotranspiration. Therefore leaching of soil constituents and weathering are more intense than they are in Chernozemic or Brunisolic soils.
Luvisolic soils cover a large portion of the province. They are found over much of the south and central interior in areas of humid or subhumid soil moisture regime. This region is in the lee of the perhumid coast mountains with their Podzolic soils, and is further north or at higher elevations than the semiarid or subarid areas of the Chernozemic and Brunisolic soils. Another large area of Luvisolic soils occurs east of the Rocky Mountains in the northeast of the province. They are formed on a wide variety of fine to medium textured sediments, but not often on coarse textured materials.
Chemical and Physical Analyses of a Luvic Gleysol
These data are taken from Day, J.H., L. Farstad, and D.G. Laird, 1959. Soil Survey of Southeast Vancouver Island and Gulf Islands, British Columbia. B.C. Soil Survey Rpt. No. 6, Canada Dept. of Agric., Ottawa.
The dominant process in Luvisolic soils is the translocation of clay-sized mineral particles in suspension from the A to the B horizon. These form thin shiny layers of clay on crack faces and down pores. They are called clay skins and it is this Bt horizon which distinguishes Luvisolic soils from the soils of other orders. It can be an important horizon in the soil since the clay can accumulate so much that root and water penetration is restricted. These soils can be very wet in the spring. Other processes are the addition of organic matter to form LFH horizons on the mineral soil surface, the weathering of the mineral fraction in the A and B horizon and the leaching of soluble salts and calcium carbonate into the C horizon. This gives an accumulation in the C horizon which may be detected in the field by applying a few drops of hydrochloric acid and observing the effervescence. A common horizon sequence for these soils would be LFH, Ae, Bt, Cca, Ck.
There are two great groups within the order; the Gray Brown Luvisol and the Gray Luvisol. The Gray Luvisol is the one most common in British Columbia. There is little or no incorporation of organic matter into the top of the mineral soil so that it does not have an Ah horizon. It occurs in cool subhumid climates. The Gray Brown Luvisol has so far been recognized only in parts of the lower Fraser Valley. It has an Ah horizon and is most commonly found in the mild, humid climate of the St. Lawrence Lowlands in eastern Canada.
The Tyee soils are an example of a Gray Luvisol. They have developed on loam to clay loam glacial till on the Cariboo plateau near Williams Lake. The following abbreviated description is from a profile near Williams Lake airport at about 920 m above sea level (52º 13'N, 122º 3'W).
|LFH||3 cm of partially and well decomposed grass, needles and roots.|
|Ae||15 cm of light gray sandy loam with weak granular structure.|
|Bt||38 cm of brown loam with strong blocky structure and clay skins on peds.|
|BC||25 cm of pale brown gravelly loam with weak blocky structure.|
|Ck||greyish brown gravelly loam with calcium carbonate.|
Photographs of a Luvisolic soil profile and landscape are included as Plates 2.4.9 and 2.4.10. Table 2.4.5 contains chemical and physical analyses of the above profile. The points to note from the analyses are the moderately acid pH of the A and B horizons and the alkaline pH of the Ck horizon, the low organic carbon content, the low clay content of the Ae and the build up of fine clay in the Bt horizon.
The Organic Order
Soils in the Organic order are composed mainly of organic matter. Most of them have developed under highly saturated conditions. They are different from mineral soils because they develop by being built up through the progressive accumulation of organic material as plants die and are succeeded by others. Under these saturated conditions the action of the microorganisms and macro soil fauna that chew up organic matter and help in the production of humus is severely restricted. This results from low temperatures and a lack of oxygen. Once again we have an example of a particular soil formed by a particular balance of processes. Organic soils occur where dead vegetation accumulates faster than it is decomposed. Where the soil is saturated for only part of the year organic soils will grade into mineral Gleysolic soils with only a thin surface accumulation of organic matter.
Chemical and Physical Analyses of a Gray Luvisol
* For the details of the analytical methods used see
McKeague, 1976, in Further Reading.
These data are from the unpublished soil survey of National Topographic Sheet 93 B SE by W. Scott.
The most common type of organic soil throughout British Columbia is one that has developed in depressions in the landscape. Water drains into these depressions and the soil is saturated for most of the year. In most cases these hollows in the landscape were lakes immediately after the ice melted. They have gradually filled in with vegetation and their surfaces have built up. The characteristics of organic soils are controlled by the hydrology of the area (the amount and quality of the water) and the vegetation that is or has been growing on them. Over much of the central interior the surrounding mineral subsoil is highly calcareous. Water in the depressions is thus neutral to alkaline. The organic soils are relatively nutrient-rich and the vegetation is mainly sedges, willows and bog glandular birch. The organic material is moderately well decomposed.
On the coast the mineral materials are more acid and there is a higher rainfall. The organic soils are also acid; they are poorly decomposed and consist mainly of moss peat.
Another form of raw acid peat is found on the plains of northeastern British Columbia. The flat topography and fine textured parent materials lead to saturated surface conditions. The cold climate produces subarctic or cryoboreal soil temperatures and a very slow rate of decomposition of organic matter. Much of the soil water is from snow melt and few nutrients drain from the surrounding mineral soil. Hence there are vast areas of poorly decomposed acid sphagnum peat or muskeg. Black spruce, tamarack and soopolallie also grow on these soils.
Plates 2.4.7 to 2.4.12
Profiles and Landscapes of Soils From the Gleysolic,
Luvisolic and Organic Orders
|2.4.7||Profile of a Gleysolic soil developed on clay loam glacial till in the Nig Creek valley in the northern Peace River area of British Columbia (photo A.J. Green).|
|2.4.8||Gleysolic landscape in the Bridge River valley near 100 Mile House, central British Columbia. The Gleysolic soils occur on the imperfectly drained floodplain below the terrace. Sedges, sea-side arrowgrass and willows grow on them.|
|2.4.9||Profile of a Luvisolic soil developed on clay loam glacial till near Fort Nelson, northeastern British Columbia (photo J.H. Day).|
|2.4.10||Luvisolic landscape west of Quesnel, central British Columbia. Douglas-fir and lodgepole pine form a relatively open tree cover. Soopolallie and pine grass form the groundcover. White spruce is regenerating under the main tree canopy (photo T.M. Lord).|
|2.4.11||Profile of an Organic soil developed on a deep accumulation of organic matter in a depressional meadow south of 100 Mile House, central British Columbia.|
|2.4.12||Organic soil landscape on the Cariboo plateau south of 100 Mile House, central British Columbia. These organic meadows develop in the very poorly drained depressions of the hummocky plateau surface. Sedges, sea-side arrow-grass and mosses are the main plants growing on them. This is the landscape of the profile shown in Plate 2.4.11.|
Finally, a rather different form of organic soil is found on the west coast mountains under the dense forests. In this case an enormous amount of needles, twigs, wood and bark accumulates over the very thin soils or directly on bedrock. This material is not quickly broken down and forms a thick spongy organic surface. These organic soils are different from the others because they are not saturated, they can occur on slopes and ridge crests and are composed of forest debris, not bog debris.
The great groups within the Organic order are separated on the degree of decomposition and the kind of plant material, and the degree of saturation, as follows:
|Fibrisols:||saturated, poorly decomposed. These soils are found in the northeast and on the coast.|
|Mesisols:||saturated, moderately decomposed. These soils are found in the central interior.|
|Humisols:||saturated, well decomposed. These soils are occasionally found in the central interior and on the coast.|
|Folisols:||rarely saturated, forest debris over thin mineral layers or rock. These soils are found in the coast mountains.|
The frozen soil from the Klua complex described under the Cryosolic order is made up of fibric organic matter. The upper horizons would be typical of the unfrozen Fibrisols of northeastern British Columbia.
The Rail soils are a Mesisol from the central interior. They have formed from the gradual infilling of lakes that occupied the depressions in the hummocky surface of the plateau. The following is an abbreviated description of such a soil taken in a meadow just south of 100 Mile House (51º 33'N, 121º 18'W). The vegetation is principally sedges and sea-side arrowgrass with some moss. The meadow had been partially drained and the water table was at about 40 cm in July.
|Of||3 cm of poorly decomposed moss and sedge remains.|
|Oml||76 cm of brown fairly well decomposed sedge and moss remains.|
|Cm||3 cm of light gray volcanic ash.|
|Om2||55 cm of dark brown moderately well decomposed sedge and moss remains.|
Photographs of the profile and the meadow forming the organic soil landscape are included as Plates 2.4.11 and 2.4.12. Some chemical and physical analyses are given in Table 2.4.6. Note the lower fibre content and higher pH values and higher total nitrogen values than the Klua soils. The Rail soils will be more productive.
Chemical and Physical Analyses of a Mesisol
These data are taken from Sneddon, J.I. and H.A. Luttmerding, 1967. Organic Soils Tour, British Columbia section, mimeo rpt. 48 pp.
The Podzolic Order
Soils of the Podzolic order have been formed under subarctic to cryoboreal and perhumid to humid soil climates. Their parent materials are mostly coarse textured and well drained. They contain much silica and few bases such as calcium or magnesium carbonate. The vegetation growing on them is usually coniferous forest, but some Podzolic soils develop under heather.
Under these conditions there is an abundance of water moving through the soil during the year. Chemical and biological transformations are intense in the upper horizons. Organic matter is decomposed and primary minerals are broken down releasing iron and aluminum in the non-calcareous soil environment. These three weathering products are readily moved out of the A horizon and into the B in the porous parent materials. It is the accumulation, in various combinations, of organic matter, iron and aluminum in the B horizon that is the distinguishing characteristic of Podzolic soils.
Podzolic soils have a striking appearance. There is a black LFH organic litter layer on the surface under which the top of the mineral soil is light gray. This is the Ae horizon from which bases, organic matter, iron and aluminum have been translocated. There is little left apart from silica silt and sand. The B horizon is in sharp contrast: a reddish brown layer enriched with organic matter, iron and aluminum, the colour becoming more yellow with depth. A typical horizon sequence would therefore be LFH, Ae, Bhf, BC, C.
There are some variations of this classic podzol profile in British Columbia. In many areas of coastal forest there is no bleached Ae horizon in the profile. The addition of organic matter to, and the weathering of iron and aluminum in, the upper mineral horizon is so great that despite the heavy leaching there is no net depletion to form an Ae horizon. In other areas the organic matter simply masks the Ae horizon under moist field conditions.
Many of the Podzolic soils of the west coast mountains have compacted horizons in the subsoil. These may be at various depths, have varying thickness and contain different cementing agents. They are given different names - ortstein, placic, duric or fragic - according to their morphology and mode of origin. They have the common effect of restricting root penetration and permeability.
Over much of southern British Columbia, especially in the mountains, volcanic ash makes up a significant proportion of the topsoil. As it weathers the ash releases large amounts of iron and especially of aluminum. When the iron and aluminum are translocated into the B horizon a Podzolic soil profile is produced. This can happen in areas that do not have a typically high rainfall, nor dense conifers nor a generally acid bedrock. The profile has been formed because the parent material was able to supply large quantities of moveable iron and aluminum. The result is an example of comparable soils being formed in two different environments where the lack of one factor is compensated for by the excess of another.
There are three great groups in the Podzolic order. They differ according to the relative amounts of organic matter and iron plus aluminum that have accumulated in the upper B horizon as follows:
|Humic Podzol:||accumulation of organic matter and little Fe to give a Bh horizon. These soils occur in wet environments such as the coastal forests or at high elevations inland.|
|Ferro-Humic Podzol:||accumulation of organic matter and Fe plus Al to give a Bhf horizon. These soils occur under humid coniferous forest conditions on the west coast where there is often a thick ground cover of moss.|
|Humo-Ferric Podzol:||accumulation of Fe plus Al and little organic matter to give a Bf horizon. These soils occur in less humid or cooler areas than the other two great groups such as the eastern side of Vancouver Island or the subalpine forests of the interior.|
The following soils from the east side of Vancouver Island are used as an example of a Humo-Ferric Podzol. They have developed from glacial moraine derived from granodiorite bedrock. The vegetation cover is Douglas-fir, western hemlock and western red cedar with a dense ground cover of salal. The following abbreviated description is of a well drained soil on a 20% slope at an elevation of 730 m above sea level in the Dunsmuir Creek valley (49- 02'N, 124- 16'W).
|LFH||8 cm of reddish black semidecomposed needles, leaves and roots.|
|Ae||10 cm of brownish gray sandy loam, very friable with no structure.|
|Bfcc||15 cm of yellowish red sandy loam with blocky structure and small concretions.|
|Bm||40 cm of yellowish brown sandy loam with blocky structure and faint mottling.|
|C||Olive gray sandy loam, massive and hard.|
Table 2.4.7 contains chemical and physical analyses of the above profile. The points to note are the low pH and base saturation values and the differences in Fe plus Al content of the Ae and Bf horizons. Plates 2.4.13 and 2.4.14 show a Humo-Ferric podzol and a Podzolic soil landscape respectively.
Chemical and Physical Analyses of a Humo-Ferric Podzol
These data are from an unpublished Ph.D. thesis - personal communication, D. Moon, Dept. of Soil Science, University of British Columbia
The Regosolic Order
Soils of the Regosolic order do not have a B horizon and may lack even an A horizon. They occur in all parts of the province, but rarely, except in the high mountains, do they extend over large areas.
Regosolic soils are very weakly developed for a variety of reasons. They may have developed on very young geological materials such as river alluvium or coastal beaches. They may be found in unstable situations such as constantly eroding slopes or shifting sand dunes. But probably their most common occurrence, and the one about which we know least, is in the mountains. In the very cold and sometimes relatively dry regions above the well-vegetated alpine meadows but below the snowline there are large expanses of rock debris. Little vegetation grows here and frost action continually disrupts the surface materials. There is little chance for strong soil horizons to develop and Regosols abound.
Two great groups are recognized in the Regosolic order according to whether or not there is an accumulation of organic matter at the surface to form an Ah horizon.
|Regosol:||little or no organic matter, only a C horizon.|
|Humic Regosol:||significant accumulation of organic matter to give Ah, C horizon sequence.|
The Chemainus soils on Vancouver Island are an example of a Humic Regosol. They have developed on very young fluvial deposits in the floodplains of river valleys. Their texture and drainage vary according to their position on the floodplain. These floodplains were the first areas to be logged so the vegetation is mixed, with western hemlock and western red cedar in some areas and second growth maple, red alder, western sword fern and willows in others. The following is an abbreviated description of a Chemainus soil:
|H||3 cm of very dark brown well decomposed leaf litter.|
|Ah||10 cm of black silt loam with granular structure.|
|C||50 cm of grayish brown stratified silt loam.|
|IIC||stratified sands and gravels.|
Some chemical and physical analyses for the Chemainus soils are given in Table 2.4.8. These analyses are typical of a young, fertile, floodplain soil but must not be regarded as typical for Regosolic soils as a whole. Since these soils can develop in a wide variety of environments, their chemical and physical characteristics may also vary widely. Their diagnostic feature is a lack of profile development, rather than a particular combination of chemical and physical characteristics.
A profile of a Humic Regosol from the San Juan River valley on Vancouver Island is shown in Plate 2.4.15. This is on a gravel bar associated with the Chemainus soils. A Regosolic landscape in the valley of the Fraser River is shown in Plate 2.4.16.
Chemical and Physical Analyses of a Humic Regosol
These data are taken from Day, J.H., L. Farstad, and D.G. Laird, 1959. Soil Survey of Southeast Vancouver Island and Gulf Islands, British Columbia. B. C. Soil Survey Rpt. No. 6, Canada Dept. of Agric., Ottawa.
The Solenetzic Order
These soils contain a high proportion of exchangeable sodium or sodium and magnesium salts in their B horizon. This distinguishes them from all the other orders, gives their profile a particular appearance, often limits vegetation to the most salt tolerant plants only and restricts their use considerably.
Solonetzic soils are found in two separate areas of British Columbia for two different reasons. In the southern part of the province they occur in semiarid to subarid areas where there is high evaporation and restricted drainage in the depressions of rolling topography. This situation is usually found in valleys for instance near Merritt and Kamloops or on the lower parts of the plateaus such as around 70 Mile House. Soil water drains into these depressions from the surrounding country bringing with it calcium, sodium and magnesium salts in solution. The water evaporates instead of draining away into the groundwater, leaving an accumulation of these salts in the soil. In the northern part of the province is an area of saline soils in the Peace River region. Here the salts result not from the interaction of climate and topography but from residual salinity in the parent materials. Many of the shales, siltstones and mudstones that form the bedrock were originally laid down in a sea and consequently have retained a high salt content. The vegetation cover is usually restricted to salt tolerant grasses and forbs. Trees sometimes grow on marginally saline soils which are beginning to lose their salts through leaching.
The dominant process then is the accumulation of sodium and magnesium salts in the B horizon. It must be emphasized that in most saline soils calcium is still the predominant cation in the soil but the increase of sodium and magnesium from negligible to moderate amounts causes them to affect the soil morphology. When the soil gets wet the sodium causes the soil aggregates to break down into individual particles. The clods are not stable and there are no structural cracks down which water can move. The soil, especially the B horizon, becomes an impermeable sticky mass. On drying the B horizon becomes extremely hard and columnar structural blocks develop. The production of these distinctive columns is probably also enhanced by the expansion of water in the cracks when it freezes in the winter. In most Solonetzic soils there is also a translocation of salts, and to some extent, organic matter from the A to the B horizon. The A horizon therefore becomes less saline and more acidic with time and dark clay and organic matter coatings are deposited on the outside of the structural columns in the B horizon.
There are three great groups in the Solonetzic order. They differ according to the degree of leaching of salts and clay from the A to the B horizon as follows:
|Solonetz:||very little leaching, clear boundary between the Ah and Bn horizons.|
|Solodized Solonetz:||leaching of salts and clay has produced an Ae horizon between the Ah and Bnt.|
|Solod:||leaching is very advanced. There is a loss of salts from the B as well as the A horizon so that the columnar structure is breaking up, and the Bnt reverts to a Bt horizon.|
Most saline soils in British Columbia have undergone a considerable amount of leaching and are Solodized Solonetz or Solods. The Murdale soils in the Peace River area are an example. They are classified as a Solod developed on saline and calcareous clayey glacial moraine. The vegetation cover is trembling aspen, willow, rose, saskatoon and grasses. The following abbreviated description is from a soil 13 km north of Fort St. John (56º 21'N, 120º 49'W).
|LFH||4 cm of partially and well decomposed organic matter.|
|Ah||7 cm of very dark brown gravelly clay loam with granular structure, very friable.|
|Ahe||5 cm of dark gray gravelly clay loam with granular structure, friable.|
|Ae||7 cm of pale brown gravelly loam with platy structure.|
|AB and BA||16 cm of transition horizons of pale brown gravelly clay with blocky structure.|
|Bt||25 cm of very dark gray gravelly clay with coarse blocky structure that breaks down into very hard smaller blocks. 24 cm of a transition horizon of dark gray gravelly clay.|
|BC||24 cm of a transition horizon of dark gravelly clay.|
|Csk||dark gray gravelly saline clay with carbonate accumulation and gypsum concretions.|
Chemical and physical analyses of this profile are included in Table 2.4.9. There are a number of features of this soil that mark it off from any of the other soils listed in this section. In the Csk horizons the pH value, sodium and magnesium content and electrical conductivity are all high. The magnesium content remains high throughout the profile. The sodium content of the B horizons is high but it is low in the A horizons and the pH and electrical conductivity drop markedly in the B and A horizons. Plates 2.4.17 and 2.4.18 show a Solod profile and a Solonetzic soil landscape respectively.
Plates 2.4.13 to 2.4.18
Profiles and Landscapes of Soils From the Podzolic,
Regosolic and Solenetzic Orders
|2.4.13||Profile of a Podzolic soil developed on glacial till in the West Kootenay area of southeastern British Columbia (photo J. Jungen).|
|2.4.14||Podzolic soil landscape in the Nanaimo Lake area of eastern Vancouver Island. The main trees are western hemlock, Douglas-fir and western red cedar. Salal and vaccinium form the main shrub cover (photo J. Jungen).|
|2.4.15||Profile of a Regosolic soil developed on fluvial sands and gravels in the floodplain of the San Juan River valley on Vancouver Island, British Columbia.|
|2.4.16||Two examples of a Regosolic landscape in the Fraser River valley near Dog Creek, central British Columbia. There are Regosolic soils on the steep banks in the middle distance (1) because erosion constantly strips away surface horizons as they develop. The gravel bar in the centre of the photograph (2) contains Regosolic soils, because the materials are very young. They have only just been laid down by the river.|
|2.4.17||Profile of a Solonetzic soil developed in silty lacustrine deposits in the Bridge Creek valley near 100 Mile House central British Columbia.|
|2.4.18||Solonetzic soil landscape in a depression of hummocky glacial till near Osoyoos, southern British Columbia. The centre of the depression is so saline that no vegetation grows and a white salt crust accumulates (1). Desert salt grass grows round the edges of the depression (2) (photo R.K. Jones).|
Chemical and Physical Analyses of a Solod
* For the details of the analytical methods used see McKeague, 1976, in Further Reading.
These data are derived from a profile sampled and described for Soil Tours Nos. 7 and 15 (Peace River Region) 11th Congress, International Soil Science Society, Edmonton, 1978 - personal communication, T.M. Lord, Soil Research Institute, Vancouver.
- Brown, R.J.E., 1967. Permafrost in Canada. Map 1246A, Geol. Surv.
This map shows the distribution of continuous and discontinuous permafrost in Canada, and discusses its causes.
- Canada Soil Survey Committee, 1978. The Canadian System of Soil
Classification. Agric. Canada, Queen's Printer, Ottawa.
There are introductory descriptions of the environment and genetic concepts associated with each order in this classification.
- McKeague, J.A., 1976. Manual on Soil Sampling and methods of analysis.
Soil Research Institute, Agric. Canada, Ottawa, mimeo, 212 pp.
This gives details of the methods of laboratory analyses.
- Ogilvie, R.T. and B. Baptie, 1967. A Permafrost Profile in the
Rocky Mountains of Alberta. Can. J. Earth Sci. 4, 744-745.
This is a short note describing a colluvial soil profile with a frozen layer at 2350 m in Banff National Park.
- Ryswyk, A.L. van., McLean, Alistair, and L.S. Marchand, 1966. The
climate, native vegetation and soils of some grasslands at different
elevations in British Columbia. Can. J. Soil Sci., 46, 35-50.
An elevational transect through Brown, Dark Brown and Black Chernozemic soils near Kamloops.
- Part 1: The Environmental Factors
- Part 2: The Major Soils and Soil Processes of BC
- Part 3: The Soils Landscapes of BC
- Part 4: The Development and Use of Soil and Terrain Surveys in BC