The variation between and within sites in the Peace River highlighted the role of landscape features and management in soil heterogeneity.  While parent material is of similar origins throughout the region, differences in depositional processes could be observed between sites.  Site specific topography and parent material interacted with the regional climate to influence local biota and produce four unique soils.

The presence of coarse fragments in the Bt horizon was a unique feature of the first site.  These appeared to be from two separate sources.  The site’s location appears to be on the edge of the furthest reaches of the Cordilleran ice sheet described by Matthews (1980) in (Lord, Green et al. 1986) We found rounded subangular fragments that appeared to be granitic, indicating a glacial origin from the Cordilleran ice from the west.  However, in the horizon below, platy slate like gravel was found.  While that material is consistent with underlying Cretaceous sedimentary bedrock (Valentine 1978) the varying textures between horizons is indicative of glacial-fluvial deposits from the Keewatin till originating from the northeast.  These contrasting origins highlight the unique history of the region.  While the granitic gravels break down into coarse textured acidic materials with limited nutrients, the slate produces nutrient rich fine textured soil.  The sloping landscape appeared to have moderate drainage, though mottling was present in depressions and downslope locations.  The texture of all of the pits became progressively more clayey with depth.  However, due to the slight incline, gleying was not present upslope and was minimally visible midslope, while it was quite apparent at the downslope pit.  Likewise, clay films were common and of medium thickness downslope, while they were not detected upslope.  The vegetation at the site was a managed forest plantation.  Rooting depth was limited by the massive illuviated horizons beginning at 23cm deep.  The soil was classified as an Orthic Gray Luvisol based on the <8 degrees Celsius mean annual temperature (Soil Classification Working Group, 1998).  The site is located in the Alcan-Donnelly map unit; these soils tend to be loamy and clayey.  While Alcan soils are derived from morainal till, the Donnelly soils originate from lacustrotill.  Since the soil was classified as an Orthic Gray Luvisol and not a Solonetzic Gray Luvisol, the soil an Alcan rather than a Donnelly soil.  Alcan soils can contain accumulations of lime, gypsum and salts below 180cm; we were not able to dig deeper than 42cm due to the accumulation of clay in the Bt₂ horizon and so did not observe this occurrence.  Drainage on these soils is described as moderate, the soils are also moderately pervious, which generally agrees with our observations.  The mixed alpine/spruce vegetation at the site is in accordance with the history of frequent fires.  The presence of white spruce suggests that the site has been free of fire for a long period of time (Lord, Green et al. 1986).  At two of the pits on this site, there was evidence of past burns in the form of thin, discontinuous layers of charcoal.

At site two, the silty texture was indicative of a flood plain origin, which is supported by the geographical location in the lowlands.  The fine textured parent material appears to have produced a fertile soil and created the necessary conditions for a grassland ecosystem to develop.  Organic matter was more thoroughly incorporated into the mineral horizons and to a slightly deeper depth than site one due to the gradual decomposition of fine grass roots.  However, the accumulation of clay in the lower horizons in combination with abundant base cations appeared to have produced a saline environment with columnar structure, which could impede site productivity.  The combination of fine texture and salinity make this site particularly vulnerable to degradation through compaction. The dark dry colouration (10YR 3/2) placed the soil within the Black Chernozemic group (Soil Classification Working Group 1998).  The presence of a Bnj horizon suggests a Solonetzic Black Chernozem, while the slickenside found in the Ckss horizon suggest a Vertic Black Chenerozem.  The salinization appears to be more strongly developed than the vertic processes, so this soil was classified as a Solonetzic Black Chernozem (Soil Classification Working Group 1998).  This is in agreement with the existing soil maps of the area.  The site occurs on Falher soils that have undulating clayey glaciolacustrine parent material that tends to be somewhat calcareous and saline.  These soils are moderately well drained but slowly pervious, creating the risk of sheet erosion in heavy precipitation events or during rapid spring runoff.  Thus, the site is well suited to the perennial forage that is grown there; the roots of the grass help bind the soil and prevent erosion (Gliessman, Engles et al. 2007).  In addition, only minimal tillage is needed every three years to ensure even distribution of grass.  While the pit we examined appeared to be part of the original prairie, pits dug in the managed area of the field had weaker structure and lacked slickensides.  While (Lord, Green et al. 1986) suggest that agricultural soils would require irrigation to reach full productivity, this site is non-irrigated and did not appear to suffer from drought.  Moreover, an irrigation system on this site would require installation of drainage in order to prevent further salinization of the soil (Brady, Weil 2008).

The parent materials at site three appeared to be of fluvial origin.  The repeated bands of coarse sand found within the profile indicate changes in streamflow rates.  The coarser texture resulted in better drainage than site two; it also produced less capillary action, resulting in a drier surface horizon and lower accumulations of organic matter potentially indicative of decreased site productivity.  However, the lack of capillarity may also have a positive effect on site productivity by not drawing up and depositing soluble salts within the root zone, evidenced by calcarious concretions that were limited to the C horizon.  Despite the low quantities of organic matter, the site is reported to have good productivity.  The integration of perennial legumes and grasses with occasional grazing appears to result in adequate soil nutrition.  What is particularly interesting about this soil is that it does not match with the corresponding map unit.  The site falls within the Sloane-Coldstream map unit, which contains Organic soils, Gleysols, and Luvisols (Lord, Green et al. 1986).  While Sloane soils tend to be well drained, Coldstream soils are characterized by poor drainage.  Both are developed from glacial lake basins.  The clay deposits that underlay the sandy alluvium create numerous management challenges for both forestry and agriculture.  However, the climate tends to be relatively warm which enhances site productivity.  Since the site is quite close to the river, it’s possible that this soil developed close to the mouth of a glacial lake; fine sand dominated the profile while bands of coarser materials suggest glacio-fluvial rather than lacustrine activity.  While the pH and depth of Ape suggest a Melanic Brunisol, the colour value of the Ape was only recorded while dry, and is greater than the specified value of 4.  However, the presence of eluviation and a Bfj horizon otherwise match the description of an Eluviated Melanic Brunisol, and so this appears to be the best choice (Soil Classification Working Group 1998).  Inadequate moisture appears to be the limiting factor in both soil formation and plant growth at this site; the area receives approximately 250mm of precipitation during the growing season (Lord, Green et al. 1986).

The fine textured poorly drained soil of site four is characteristic of an ancient lake bed; the presence of varves suggests the lake was glacial.  The lack of drainage supported a peat ecosystem, producing acidic and slow to decompose organic matter.  Despite the low pH of the organic matter, the soil became increasingly alkaline with depth.  Translocation of clays within the soil profile produced unique structural characteristics at this site.  The illuviated lower horizon had platy structure, impeding root growth and limiting biological activity.  The heavy clay deposits below were massive, further impeding root growth and slowing percolation.  This is a site that, should temperatures rise and precipitation decrease with climate change, has the potential to become a source of carbon dioxide into the atmosphere as microbial activity increased and began to decompose the large stores of organic matter.  Despite the surficial layer of litter, this soil was classified as an Orthic Luvic Gleysol as it lacked an Ah horizon thicker than 10cm.  Presence of an Aeg and Btg confirmed this classification.  The site falls within the Fellers map unit whose soils are described as being derived from loamy and clayey morainal materials that are well drained but slowly pervious.  The dominant subgroup is Brunisolic Gray Luvisols; orthic and gleyed subgroups with lithic phases are common (Lord, Green et al. 1986).  While the parent material we observed differs from what is suggested by the soil survey, the soil forming processes are similar.  We observed that gleying was the dominant soil forming process within 50cm of the soil surface, based on the strong contrast between the colour of mottles and the soil matrix.   While the per-humid moisture regime supplies adequate water, temperature is a limiting factor on soil formation and site productivity (Lord, Green et al. 1986).

The four sites described in this report display both the richness and limitations of the Peace River region.  The soils reflect the unique history of the landscape: ancient glacial lakes, river outflows, and intersecting glaciers are all represented.  While Luvisols may be the most common soil in the region, we observed Chernozems, Brunisols, and Gleysols all within a radius of about thirty kilometers from the town of Dawson Creek.  Most of the soils we found matched up with the existing soil descriptions, but there were some surprises and some exceptions.  This conflict between anticipated conditions and what was actually observed highlights the importance of conducting on site surveys when considering the sustainability of different land uses.  For example, site two exists on the Sloane-Coldstream map unit where we would have expected fine textured soils with potentially poor drainage and moderate to slow percolation.  The sandy Brunisol we observed did not match this description, and had much more potential for agricultural productivity with less management challenges associated with drainage.  It is also possible that as soil mapping technology improves, and maps are digitized, pinpointing a location will become more precise.  One of the challenges in producing this report has been finding and utilizing appropriate resources.  The soils of British Columbia have been studied, categorized, and mapped, yet accessing this information often involves sifting through outdated databases or squinting at poor resolution maps.  I found that the best option was to seek out original paper copies of maps, on which I would then try to pinpoint the latitude and longitude of the different sites visited.  This was moderately effective, but time consuming.  Land management can be improved with better understanding of soils, and the ability to access accurate information for a site is an important challenge to overcome.  Describing and classifying soils is an important skill for many kinds of professionals, not just soil scientists.  While experience in the field is perhaps the most effective and enjoyable way to build and maintain this knowledge, there is a recent trend towards the development of online learning resources.  Overall, this field experience reminded me of both the large amount of work that has already gone into understanding BC’s soils, and also of the vast possibilities for refining and communicating that knowledge further.

References:

BRADY, N.C. and WEIL, R.R., 2008. The nature and properties of soils. International , 14th edn. Upper Saddle River, N.J.: Pearson Prentice Hall.

GLIESSMAN, S.R., ENGLES, E. and KRIEGER, R., 2007. Agroecology: the ecology of sustainable food systems. 2 edn. Boca Raton: Taylor and Francis.

LORD, T.M., GREEN, A.J. and  CANADA. AGRICULTURE CANADA.RESEARCH BRANCH, 1986. Soils of the Fort St. John – Dawson Creek area, British Columbia. no. 42. Ottawa: Research Branch, Agriculture Canada.

SOIL CLASSIFICATION WORKING GROUP, 1998. The Canadian system of soil classification. Ottawa, Ont: NRC Research Press.

VALENTINE, K.W.G., 1978. The soil landscapes of British Columbia. Victoria, B.C: Resource Analysis Branch, Ministry of the Environment.

SOIL CLASSIFICATION WORKING GROUP. 1998. The Canadian System of Soil Classification. 3rd ed. Agriculture and Agri-Food Canada Publication 1646, 187 pp